Jian Qin

All Publications

• Efficient Electronic Tunneling Governs Transport in Conducting Polymer-Insulator Blends. Journal of the American Chemical Society Keene, S. T., Michaels, W., Melianas, A., Quill, T. J., Fuller, E. J., Giovannitti, A., McCulloch, I., Talin, A. A., Tassone, C. J., Qin, J., Troisi, A., Salleo, A. 2022

  Abstract

  Electronic transport models for conducting polymers (CPs) and blends focus on the arrangement of conjugated chains, while the contributions of the nominally insulating components to transport are largely ignored. In this work, an archetypal CP blend is used to demonstrate that the chemical structure of the non-conductive component has a substantial effect on charge carrier mobility. Upon diluting a CP with excess insulator, blends with as high as 97.4 wt % insulator can display carrier mobilities comparable to some pure CPs such as polyaniline and low regioregularity P3HT. In this work, we develop a single, multiscale transport model based on the microstructure of the CP blends, which describes the transport properties for all dilutions tested. The results show that the high carrier mobility of primarily insulator blends results from the inclusion of aromatic rings, which facilitate long-range tunneling (up to ca. 3 nm) between isolated CP chains. This tunneling mechanism calls into question the current paradigm used to design CPs, where the solubilizing or ionically conducting component is considered electronically inert. Indeed, optimizing the participation of the nominally insulating component in electronic transport may lead to enhanced electronic mobility and overall better performance in CPs.

  View details for DOI 10.1021/jacs.2c02139

  View details for PubMedID 35658455

• Liquid electrolyte: The nexus of practical lithium metal batteries JOULE Wang, H., Yu, Z., Kong, X., Kim, S., Boyle, D. T., Qin, J., Bao, Z., Cui, Y. 2022; 6 (3): 588-616

  View details for DOI 10.1016/j.joule.2021.12.018

  View details for Web of Science ID 000773205200008

• Suspension electrolyte with modified Li+ solvation environment for lithium metal batteries. Nature materials Kim, M. S., Zhang, Z., Rudnicki, P. E., Yu, Z., Wang, J., Wang, H., Oyakhire, S. T., Chen, Y., Kim, S. C., Zhang, W., Boyle, D. T., Kong, X., Xu, R., Huang, Z., Huang, W., Bent, S. F., Wang, L., Qin, J., Bao, Z., Cui, Y. 1800

  Abstract

  Designing a stable solid-electrolyte interphase on a Li anode is imperative to developing reliable Li metal batteries. Herein, we report a suspension electrolyte design that modifies the Li+ solvation environment in liquid electrolytes and creates inorganic-rich solid-electrolyte interphases on Li. Li2O nanoparticles suspended in liquid electrolytes were investigated as a proof of concept. Through theoretical and empirical analyses of Li2O suspension electrolytes, the roles played by Li2O in the liquid electrolyte and solid-electrolyte interphases of the Li anode are elucidated. Also, the suspension electrolyte design is applied in conventional and state-of-the-art high-performance electrolytes to demonstrate its applicability. Based on electrochemical analyses, improved Coulombic efficiency (up to ~99.7%), reduced Li nucleation overpotential, stabilized Li interphases and prolonged cycle life of anode-free cells (~70 cycles at 80% of initial capacity) were achieved with the suspension electrolytes. We expect this design principle and our findings to be expanded into developing electrolytes and solid-electrolyte interphases for Li metal batteries.

  View details for DOI 10.1038/s41563-021-01172-3

  View details for PubMedID 35039645

• Rational solvent molecule tuning for high-performance lithium metal battery electrolytes NATURE ENERGY Yu, Z., Rudnicki, P. E., Zhang, Z., Huang, Z., Celik, H., Oyakhire, S. T., Chen, Y., Kong, X., Kim, S., Xiao, X., Wang, H., Zheng, Y., Kamat, G. A., Kim, M., Bent, S. F., Qin, J., Cui, Y., Bao, Z. 2022

  View details for DOI 10.1038/s41560-021-00962-y

  View details for Web of Science ID 000742253900001

• Distribution cutoff for clusters near the gel point ACS Polymers Au Li, D. T., Rudnicki, P. E., Qin, J. 2022

  View details for DOI 10.1021/acspolymersau.2c00020

• Early-career investigator special issue JOURNAL OF POLYMER SCIENCE Lynd, N. A., Qin, J. 2021; 59 (21): 2364

  View details for DOI 10.1002/pol.20210769

  View details for Web of Science ID 000713466500004

• Steric Effect Tuned Ion Solvation Enabling Stable Cycling of High-Voltage Lithium Metal Battery. Journal of the American Chemical Society Chen, Y., Yu, Z., Rudnicki, P., Gong, H., Huang, Z., Kim, S. C., Lai, J., Kong, X., Qin, J., Cui, Y., Bao, Z. 2021

  Abstract

  1,2-Dimethoxyethane (DME) is a common electrolyte solvent for lithium metal batteries. Various DME-based electrolyte designs have improved long-term cyclability of high-voltage full cells. However, insufficient Coulombic efficiency at the Li anode and poor high-voltage stability remain a challenge for DME electrolytes. Here, we report a molecular design principle that utilizes a steric hindrance effect to tune the solvation structures of Li+ ions. We hypothesized that by substituting the methoxy groups on DME with larger-sized ethoxy groups, the resulting 1,2-diethoxyethane (DEE) should have a weaker solvation ability and consequently more anion-rich inner solvation shells, both of which enhance interfacial stability at the cathode and anode. Experimental and computational evidence indicates such steric-effect-based design leads to an appreciable improvement in electrochemical stability of lithium bis(fluorosulfonyl)imide (LiFSI)/DEE electrolytes. Under stringent full-cell conditions of 4.8 mAh cm-2 NMC811, 50 mum thin Li, and high cutoff voltage at 4.4 V, 4 M LiFSI/DEE enabled 182 cycles until 80% capacity retention while 4 M LiFSI/DME only achieved 94 cycles. This work points out a promising path toward the molecular design of non-fluorinated ether-based electrolyte solvents for practical high-voltage Li metal batteries.

  View details for DOI 10.1021/jacs.1c09006

  View details for PubMedID 34709034

• Predictably Engineering the Viscoelastic Behavior of Dynamic Hydrogels via Correlation with Molecular Parameters. Advanced materials (Deerfield Beach, Fla.) Lou, J., Friedowitz, S., Will, K., Qin, J., Xia, Y. 2021: e2104460

  Abstract

  Rational design of dynamic hydrogels with desirable viscoelastic behaviors relies on an in-depth understanding of the principles correlating molecular parameters and macroscopic properties. To quantitatively elucidate such principles, a series of dynamic covalent hydrogels crosslinked via hydrazone bonds is designed. The exchange rate of the hydrazone bond is tuned by varying the concentration of an organic catalyst, while maintaining the crosslinking density unchanged. This strategy of independently tuning exchange dynamics of crosslinks and crosslinking density allows unambiguous analysis of the viscoelastic response of the dynamic hydrogels as a function of their network parameters. It is found that the terminal relaxation time of the dynamic hydrogels is primarily determined by two factors: the exchange rate of crosslinks and the number of effective crosslinks per polymer chain, and is independent of the network architecture. Furthermore, a universal correlation is identified between the terminal relaxation time determined from stress relaxation and the exchange rate determined via reaction kinetics, which can be generalized to any viscoelastic hydrogel network, in principle. This quantitative correlation facilitates the development of dynamic hydrogels with a variable desired viscoelastic response based on molecular design.

  View details for DOI 10.1002/adma.202104460

  View details for PubMedID 34636090

• A molecular design approach towards elastic and multifunctional polymer electronics. Nature communications Zheng, Y., Yu, Z., Zhang, S., Kong, X., Michaels, W., Wang, W., Chen, G., Liu, D., Lai, J., Prine, N., Zhang, W., Nikzad, S., Cooper, C. B., Zhong, D., Mun, J., Zhang, Z., Kang, J., Tok, J. B., McCulloch, I., Qin, J., Gu, X., Bao, Z. 2021; 12 (1): 5701

  Abstract

  Next-generation wearable electronics require enhanced mechanical robustness and device complexity. Besides previously reported softness and stretchability, desired merits for practical use include elasticity, solvent resistance, facilepatternability and high charge carrier mobility. Here, we show a molecular design concept that simultaneously achieves all these targeted properties in both polymeric semiconductors and dielectrics, without compromising electrical performance. This is enabled by covalently-embedded in-situ rubber matrix (iRUM) formation through good mixing of iRUM precursors with polymer electronic materials, and finely-controlled composite film morphology built on azide crosslinking chemistry which leverages different reactivities with C-H and C=C bonds. The high covalent crosslinking density results in both superior elasticity and solvent resistance. When applied in stretchable transistors, the iRUM-semiconductor film retained its mobility after stretching to 100% strain, and exhibited record-high mobility retention of 1 cm2 V-1 s-1 after 1000 stretching-releasing cycles at 50% strain. The cycling life was stably extended to 5000 cycles, five times longer than all reported semiconductors. Furthermore, we fabricated elastic transistors via consecutively photo-patterning of the dielectric and semiconducting layers, demonstrating the potential of solution-processed multilayer device manufacturing. The iRUM represents a molecule-level design approach towards robust skin-inspired electronics.

  View details for DOI 10.1038/s41467-021-25719-9

  View details for PubMedID 34588448

• Reversible ion binding for polyelectrolytes with adaptive conformations AICHE JOURNAL Friedowitz, S., Qin, J. 2021

  View details for DOI 10.1002/aic.17426

  View details for Web of Science ID 000695335100001

• Potentiometric Measurement to Probe Solvation Energy and Its Correlation to Lithium Battery Cyclability. Journal of the American Chemical Society Kim, S. C., Kong, X., Vila, R. A., Huang, W., Chen, Y., Boyle, D. T., Yu, Z., Wang, H., Bao, Z., Qin, J., Cui, Y. 2021

  Abstract

  The electrolyte plays a critical role in lithium-ion batteries, as it impacts almost every facet of a battery's performance. However, our understanding of the electrolyte, especially solvation of Li+, lags behind its significance. In this work, we introduce a potentiometric technique to probe the relative solvation energy of Li+ in battery electrolytes. By measuring open circuit potential in a cell with symmetric electrodes and asymmetric electrolytes, we quantitatively characterize the effects of concentration, anions, and solvents on solvation energy across varied electrolytes. Using the technique, we establish a correlation between cell potential (Ecell) and cyclability of high-performance electrolytes for lithium metal anodes, where we find that solvents with more negative cell potentials and positive solvation energies-those weakly binding to Li+-lead to improved cycling stability. Cryogenic electron microscopy reveals that weaker solvation leads to an anion-derived solid-electrolyte interphase that stabilizes cycling. Using the potentiometric measurement for characterizing electrolytes, we establish a correlation that can guide the engineering of effective electrolytes for the lithium metal anode.

  View details for DOI 10.1021/jacs.1c03868

  View details for PubMedID 34184873

• Atomistic Modeling of PEDOT:PSS Complexes II: Force Field Parameterization MACROMOLECULES Michaels, W., Zhao, Y., Qin, J. 2021; 54 (12): 5354-5365

  View details for DOI 10.1021/acs.macromol.1c00860

  View details for Web of Science ID 000665741600006

• Weakening of Solvation-Induced Ordering by Composition Fluctuation in Salt-Doped Block Polymers ACS MACRO LETTERS Kong, X., Hou, K., Qin, J. 2021; 10 (5): 545-550

  View details for DOI 10.1021/acsmacrolett.1c00107

  View details for Web of Science ID 000654292600006

• Dual-Solvent Li-Ion Solvation Enables High-Performance Li-Metal Batteries ADVANCED MATERIALS Wang, H., Yu, Z., Kong, X., Huang, W., Zhang, Z., Mackanic, D. G., Huang, X., Qin, J., Bao, Z., Cui, Y. 2021: e2008619

  Abstract

  Novel electrolyte designs to further enhance the lithium (Li) metal battery cyclability are highly desirable. Here, fluorinated 1,6-dimethoxyhexane (FDMH) is designed and synthesized as the solvent molecule to promote electrolyte stability with its prolonged -CF2 - backbone. Meanwhile, 1,2-dimethoxyethane is used as a co-solvent to enable higher ionic conductivity and much reduced interfacial resistance. Combining the dual-solvent system with 1 m lithium bis(fluorosulfonyl)imide (LiFSI), high Li-metal Coulombic efficiency (99.5%) and oxidative stability (6 V) are achieved. Using this electrolyte, 20 µm Li||NMC batteries are able to retain ≈80% capacity after 250 cycles and Cu||NMC anode-free pouch cells last 120 cycles with 75% capacity retention under ≈2.1 µL mAh-1 lean electrolyte conditions. Such high performances are attributed to the anion-derived solid-electrolyte interphase, originating from the coordination of Li-ions to the highly stable FDMH and multiple anions in their solvation environments. This work demonstrates a new electrolyte design strategy that enables high-performance Li-metal batteries with multisolvent Li-ion solvation with rationally optimized molecular structure and ratio.

  View details for DOI 10.1002/adma.202008619

  View details for Web of Science ID 000648495100001

  View details for PubMedID 33969571

• Atomistic Modeling of PEDOT:PSS Complexes I: DFT Benchmarking MACROMOLECULES Michaels, W., Zhao, Y., Qin, J. 2021; 54 (8): 3634-3646

  View details for DOI 10.1021/acs.macromol.1c00351

  View details for Web of Science ID 000645430100005

• Physical networks from entropy-driven non-covalent interactions. Nature communications Yu, A. C., Lian, H., Kong, X., Lopez Hernandez, H., Qin, J., Appel, E. A. 2021; 12 (1): 746

  Abstract

  Physical networks typically employ enthalpy-dominated crosslinking interactions that become more dynamic at elevated temperatures, leading to network softening. Moreover, standard mathematical frameworks such as time-temperature superposition assume network softening and faster dynamics at elevated temperatures. Yet, deriving a mathematical framework connecting the crosslinking thermodynamics to the temperature-dependent viscoelasticity of physical networks suggests the possibility for entropy-driven crosslinking interactions to provide alternative temperature dependencies. This framework illustrates that temperature negligibly affects crosslink density in reported systems, but drastically influences crosslink dynamics. While the dissociation rate of enthalpy-driven crosslinks is accelerated at elevated temperatures, the dissociation rate of entropy-driven crosslinks is negligibly affected or even slowed under these conditions. Here we report an entropy-driven physical network based on polymer-nanoparticle interactions that exhibits mechanical properties that are invariant with temperature. These studies provide a foundation for designing and characterizing entropy-driven physical crosslinking motifs and demonstrate how these physical networks access thermal properties that are not observed in current physical networks.

  View details for DOI 10.1038/s41467-021-21024-7

  View details for PubMedID 33531475

• Phase segregation mechanisms of small molecule-polymer blends unraveled by varying polymer chain architecture SmartMat Chen, J., Das, S., Shao, M., Li, G., Lian, H., Qin, J., Browning, J., Keum, J., Uhrig, D., Gu, G., Xiao, K. 2021; 2

  View details for DOI 10.1002/smm2.1036

• Looping-in complexation and ion partitioning in nonstoichiometric polyelectrolyte mixtures Science Advances Friedowitz, S., Lou, J., Barker, K. P., Will, K., Xia, Y., Qin, J. 2021; 7 (31)

  View details for DOI 10.1126/sciadv.abg86

• Molecular design for electrolyte solvents enabling energy-dense and long-cycling lithium metal batteries NATURE ENERGY Yu, Z., Wang, H., Kong, X., Huang, W., Tsao, Y., Mackanic, D. G., Wang, K., Wang, X., Huang, W., Choudhury, S., Zheng, Y., Amanchukwu, C., Hung, S. T., Ma, Y., Lomeli, E. G., Qin, J., Cui, Y., Bao, Z. 2020

  View details for DOI 10.1038/s41560-020-0634-5

  View details for Web of Science ID 000542060100001

• Comparing Experimental Phase Behavior of Ion-Doped Block Copolymers with Theoretical Predictions Based on Selective Ion Solvation MACROMOLECULES Hou, K. J., Loo, W. S., Balsara, N. P., Qin, J. 2020; 53 (10): 3956–66

  View details for DOI 10.1021/acs.macromol.0c00559

  View details for Web of Science ID 000537677300034

• A New Class of Ionically Conducting Fluorinated Ether Electrolytes with High Electrochemical Stability. Journal of the American Chemical Society Amanchukwu, C. V., Yu, Z., Kong, X., Qin, J., Cui, Y., Bao, Z. 2020

  Abstract

  Increasing battery energy density is greatly desired for applications such as portable electronics and transportation. However, many next-generation batteries are limited by electrolyte selection because high ionic conductivity and poor electrochemical stability are typically observed in most electrolytes. For example, ether-based electrolytes have high ionic conductivity but are oxidatively unstable above 4 V, which prevents the use of high-voltage cathodes that promise higher energy densities. In contrast, hydrofluoroethers (HFEs) have high oxidative stability but do not dissolve lithium salt. In this work, we synthesize a new class of fluorinated ether electrolytes that combine the oxidative stability of HFEs with the ionic conductivity of ethers in a single compound. We show that conductivities of up to 2.7 * 10-4 S/cm (at 30 °C) can be obtained with oxidative stability up to 5.6 V. The compounds also show higher lithium transference numbers compared to typical ethers. Furthermore, we use nuclear magnetic resonance (NMR) and molecular dynamics (MD) to study their ionic transport behavior and ion solvation environment, respectively. Finally, we demonstrate that this new class of electrolytes can be used with a Ni-rich layered cathode (NMC 811) to obtain over 100 cycles at a C/5 rate. The design of new molecules with high ionic conductivity and high electrochemical stability is a novel approach for the rational design of next-generation batteries.

  View details for DOI 10.1021/jacs.9b11056

  View details for PubMedID 32233433

• Dendrite Suppression by a Polymer Coating: A Coarse-Grained Molecular Study ADVANCED FUNCTIONAL MATERIALS Kong, X., Rudnicki, P. E., Choudhury, S., Bao, Z., Qin, J. 2020

  View details for DOI 10.1002/adfm.201910138

  View details for Web of Science ID 000513653700001

• Electrochemical generation of liquid and solid sulfur on two-dimensional layered materials with distinct areal capacities Nature Nanotechnology Yang, A., Zhou, G., et al 2020

  View details for DOI 10.1038/s41565-019-0624-6

• Transient Voltammetry with Ultramicroelectrodes Reveals the Electron Transfer Kinetics of Lithium Metal Anodes Adv. Energy Lett. Boyle, D., Kong, X., Pei, A., Rudnicki, P., Shi, F., Huang, W., Bao, Z., Qin, J., Cui, Y. 2020; 5: 701-709

  View details for DOI 10.1021/acsenergylett.0c00031

• 'Chromatic' neuronal jamming in a primitive brain Nature Physics Khariton, M., Kong, X., Qin, J., Wang, B. 2020

  View details for DOI 10.1038/s41567-020-0809-9

• Reversible Gelation of Entangled Ionomers MACROMOLECULES Cao, X., Yu, X., Qin, J., Chen, Q. 2019; 52 (22): 8771–80

  View details for DOI 10.1021/acs.macromol.9b01116

  View details for Web of Science ID 000500039300026

• Impact of Liquid-Crystalline Chain Alignment on Charge Transport in Conducting Polymers MACROMOLECULES Rudnicki, P. E., MacPherson, Q., Balhorn, L., Feng, B., Qin, J., Salleo, A., Spakowitz, A. J. 2019; 52 (22): 8932–39

  View details for DOI 10.1021/acs.macromol.9b01729

  View details for Web of Science ID 000500039300040

• A Dynamic, Electrolyte-Blocking, and Single-Ion-Conductive Network for Stable Lithium-Metal Anodes JOULE Yu, Z., Mackanic, D. G., Michaels, W., Lee, M., Pei, A., Feng, D., Zhang, Q., Tsao, Y., Amanchukwu, C., Yan, X., Wang, H., Chen, S., Liu, K., Kang, J., Qin, J., Cui, Y., Bao, Z. 2019; 3 (11): 2761–76

  View details for DOI 10.1016/j.joule.2019.07.025

  View details for Web of Science ID 000497987900018

• Molecular Architecture Directs Linear-Bottlebrush-Linear Triblock Copolymers to Self-Assemble to Soft Reprocessable Elastomers ACS MACRO LETTERS Nian, S., Lian, H., Gong, Z., Zhernenkov, M., Qin, J., Cai, L. 2019; 8 (11): 1528–34

  View details for DOI 10.1021/acsmacrolett.9b00721

  View details for Web of Science ID 000498285200022

• Mechanically resolved imaging of bacteria using expansion microscopy. PLoS biology Lim, Y., Shiver, A. L., Khariton, M., Lane, K. M., Ng, K. M., Bray, S. R., Qin, J., Huang, K. C., Wang, B. 2019; 17 (10): e3000268

  Abstract

  Imaging dense and diverse microbial communities has broad applications in basic microbiology and medicine, but remains a grand challenge due to the fact that many species adopt similar morphologies. While prior studies have relied on techniques involving spectral labeling, we have developed an expansion microscopy method (muExM) in which bacterial cells are physically expanded prior to imaging. We find that expansion patterns depend on the structural and mechanical properties of the cell wall, which vary across species and conditions. We use this phenomenon as a quantitative and sensitive phenotypic imaging contrast orthogonal to spectral separation to resolve bacterial cells of different species or in distinct physiological states. Focusing on host-microbe interactions that are difficult to quantify through fluorescence alone, we demonstrate the ability of muExM to distinguish species through an in vitro defined community of human gut commensals and in vivo imaging of a model gut microbiota, and to sensitively detect cell-envelope damage caused by antibiotics or previously unrecognized cell-to-cell phenotypic heterogeneity among pathogenic bacteria as they infect macrophages.

  View details for DOI 10.1371/journal.pbio.3000268

  View details for PubMedID 31622337

• Nonpolar Alkanes Modify Lithium-Ion Solvation for Improved Lithium Deposition and Stripping ADVANCED ENERGY MATERIALS Amanchukwu, C., Kong, X., Qin, J., Cui, Y., Bao, Z. 2019

  View details for DOI 10.1002/aenm.201902116

  View details for Web of Science ID 000487515200001

• TCR-pMHC bond conformation controls TCR ligand discrimination. Cellular & molecular immunology Sasmal, D. K., Feng, W., Roy, S., Leung, P., He, Y., Cai, C., Cao, G., Lian, H., Qin, J., Hui, E., Schreiber, H., Adams, E. J., Huang, J. 2019

  Abstract

  A major unanswered question is how a TCR discriminates between foreign and self-peptides presented on the APC surface. Here, we used in situ fluorescence resonance energy transfer (FRET) to measure the distances of single TCR-pMHC bonds and the conformations of individual TCR-CD3zeta receptors at the membranes of live primaryT cells. We found that a TCR discriminates between closely related peptides by forming single TCR-pMHC bonds with different conformations, and the most potent pMHC forms the shortest bond. The bond conformation is an intrinsic property that is independent of the binding affinityandkinetics, TCR microcluster formation, and CD4 binding. The bond conformation dictates the degree of CD3zeta dissociation from the inner leaflet of the plasma membrane via a positive calcium signaling feedback loop to precisely control the accessibility of CD3zeta ITAMs for phosphorylation. Our data revealed the mechanism by which a TCR deciphers the structural differences among peptides via the TCR-pMHC bond conformation.

  View details for DOI 10.1038/s41423-019-0273-6

  View details for PubMedID 31530899

• Ultrathin, flexible, solid polymer composite electrolyte enabled with aligned nanoporous host for lithium batteries. Nature nanotechnology Wan, J., Xie, J., Kong, X., Liu, Z., Liu, K., Shi, F., Pei, A., Chen, H., Chen, W., Chen, J., Zhang, X., Zong, L., Wang, J., Chen, L., Qin, J., Cui, Y. 2019

  Abstract

  The urgent need for safer batteries is leading research to all-solid-state lithium-based cells. To achieve energy density comparable to liquid electrolyte-based cells, ultrathin and lightweight solid electrolytes with high ionic conductivity are desired. However, solid electrolytes with comparable thicknesses to commercial polymer electrolyte separators (~10mum) used in liquid electrolytes remain challenging to make because of the increased risk of short-circuiting the battery. Here, we report on a polymer-polymer solid-state electrolyte design, demonstrated with an 8.6-mum-thick nanoporous polyimide (PI) film filled with polyethylene oxide/lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI) that can be used as a safe solid polymer electrolyte. The PI film is nonflammable and mechanically strong, preventing batteries from short-circuiting even after more than 1,000h of cycling, and the vertical channels enhance the ionic conductivity (2.3*10-4Scm-1 at 30°C) of the infused polymer electrolyte. All-solid-state lithium-ion batteries fabricated with PI/PEO/LiTFSI solid electrolyte show good cycling performance (200 cycles at C/2 rate) at 60°C and withstand abuse tests such as bending, cutting and nail penetration.

  View details for DOI 10.1038/s41565-019-0465-3

  View details for PubMedID 31133663

• Tunable Coacervation of Well-Defined Homologous Polyanions and Polycations by Local Polarity ACS CENTRAL SCIENCE Lou, J., Friedowitz, S., Qin, J., Xia, Y. 2019; 5 (3): 549–57

  Abstract

  The ionic complexation of polyelectrolytes is an important mechanism underlying many important biological processes and technical applications. The main driving force for complexation is electrostatic, which is known to be affected by the local polarity near charge centers, but the impact of which on the complexation of polyelectrolytes remains poorly explored. We developed a homologous series of well-defined polyelectrolytes with identical backbone structures, controlled molecular weights, and tunable local polarity to modulate the solvation environment near charged groups. A multitude of systematic, accurate phase diagrams were obtained by spectroscopic measurements of polymer concentrations via fluorescent labeling of polycations. These phase diagrams unambiguously revealed that the liquidlike coacervation is more stable against salt addition at reduced local polarity over a wide range of molecular weights. These trends were quantitatively captured by a theory of complexation that incorporates the effects of dispersion interactions, charge connectivity, and reversible ion-binding, providing the microscopic design rules for tuning molecular parameters and local polarity.

  View details for PubMedID 30937382

  View details for PubMedCentralID PMC6439447

• Charge polarization near dielectric interfaces and the multiple-scattering formalism SOFT MATTER Qin, J. 2019; 15 (10): 2125–34

  Abstract

  Interfacial charge polarization is ubiquitous in systems with sharp dielectric contrast. Fully resolving the interfacial charges often relies on demanding numerical algorithms to solve the boundary value problem. The recent development of an analytical multiple-scattering formalism to solve the interfacial charge polarization problem for particles carrying monopolar, dipolar, and multipolar charges is reviewed. Every term produced in this formalism has a simple interpretation, and terms for spherical particles can be rapidly evaluated using an image-line construction. Several practical applications of this formalism are illustrated. A dielectric virial expansion for polarizable particles based on this formalism is also described. The origins of singular polarization charges for particles in close contact are explained and evaluated for both dielectric and conducting spheres.

  View details for DOI 10.1039/c8sm02196a

  View details for Web of Science ID 000460596900002

  View details for PubMedID 30762054

• Self-healing of electrical damage in polymers using superparamagnetic nanoparticles NATURE NANOTECHNOLOGY Yang, Y., He, J., Li, Q., Gao, L., Hu, J., Zeng, R., Qin, J., Wang, S. X., Wang, Q. 2019; 14 (2): 151-+

  View details for DOI 10.1038/s41565-018-0327-4

  View details for Web of Science ID 000457765800017

• Ion distribution in microphase-separated copolymers with periodic dielectric permittivity Macromolecules Chu, W., Qin, J., de Pablo, J. 2018; 51: 1986

  View details for DOI 10.1021/acs.macromol.7b02508

• Solvation and entropic regimes in ion-containing block copolymers Macromolecules Hou, K. J., Qin, J. 2018; 51: 7463
• Dielectric virial expansion of polarizable dipolar spheres Journal of Chemical Physics Lian, H., Qin, J., Freed, K. 2018; 149: 163332
• Crosslinked poly(tetrahydrofuran) as a loosely-coordinating solid polymer electrolyte Advanced Energy Materials Mackanic, D., Michaels, W., Lee, M., Feng, D., Lopez, J., Qin, J., Cui, Y., Bao, Z. 2018
• Polarization energy of two charged dielectric spheres in close contact Molecular Systems Design & Engineering Lian, H., Qin, J. 2018; 3: 197

  View details for DOI 10.1039/C7ME00105C

• Role of electrostatic correlations in polyelectrolyte charge association Journal of Chemical Physics Friedowitz, S., Salehi, A., Larson, R., Qin, J. 2018; 149: 163335
• Tuning precursor reactivity towards nanometer-size control in palladium nanoparticles studied by in-situ small angle X-ray scattering Chemistry of Materials Wu, L., Lian, H., Willis, J., Goodman, E., McKay, I., Qin, J., Tassone, C., Cargnello, M. 2018; 30: 1127

  View details for DOI 10.1021/acs.chemmater.7b05186

• Field-theoretic simulations of random copolymers with structural rigidity Soft Matter Mao, S., MacPherson, Q., Qin, J., Spakowitz, A. J. 2017; 13: 2760

  View details for DOI 10.1039/C7SM00164A

• Image method for electrostatic energy of polarizable dipolar spheres J. Chem. Phys. Gustafson, K., Xu, G., Freed, K., Qin, J. 2017; 147 (064908)

  View details for DOI 10.1063/1.4997620

• High-temperature crystallization of nanocrystals into three-dimensional superlattices Nature Wu, L., Willis, J. J., McKay, I. S., Diroll, B. T., Qin, J., Cargnello, M., Tassone, C. J. 2017; 548 (197)

  View details for DOI 10.1038/nature23308

• Singular electrostatic energy of nanoparticle clusters PHYSICAL REVIEW E Qin, J., Krapf, N. W., Witten, T. A. 2016; 93 (2)

  Abstract

  The binding of clusters of metal nanoparticles is partly electrostatic. We address difficulties in calculating the electrostatic energy when high charging energies limit the total charge to a single quantum, entailing unequal potentials on the particles. We show that the energy at small separation h has a singular logarithmic dependence on h. We derive a general form for this energy in terms of the singular capacitance of two spheres in near contact c(h), together with nonsingular geometric features of the cluster. Using this form, we determine the energies of various clusters, finding that more compact clusters are more stable. These energies are proposed to be significant for metal-semiconductor binary nanoparticle lattices found experimentally. We sketch how these effects should dictate the relative abundances of metal nanoparticle clusters in nonpolar solvents.

  View details for DOI 10.1103/PhysRevE.93.022603

  View details for Web of Science ID 000369735300005

• Criticality and connectivity in macromolecular charge complexation Macromolecules Qin, J., de Pablo, J. 2016; 49 (8789)

  View details for DOI 10.1021/acs.macromol.6b02113

• A Hybrid Human-computer Approach to the Extraction of Scientific Facts from the Literature Procedia Computer Science Tchoua, R. B., Chard, K., Audus, D., Qin, J., de Pablo, J. J., Foster, I. 2016; 80: 386

  View details for DOI 10.1016/j.procs.2016.05.338

• Image method for induced surface charge from many-body system of dielectric spheres Journal of Chemical Physics Qin, J., de Pablo, J. J., Freed, K. F. 2016; 145 (124903)

  View details for DOI 10.1063/1.4962832

• An O(N) and parallel approach to integral problems by a kernel-independent fast multipole method: Application to polarization and magnetization of interacting particles Journal of Chemical Physics Jiang, X., Li, J., Zhao, X., Qin, J., Karpeev, D., Hernandez-Ortiz, J., de Pablo, J. J., Hernonen, O. 2016; 145 (064307)

  View details for DOI 10.1063/1.4960436

• Broadly accessible self-consistent field theory for block polymer materials discovery Macromolecules Arora, A., Qin, J., Morse, D. C., Delaney, K. T., Fredrickson, G. H., Bates, F. S., Dorfman, K. D. 2016

  View details for DOI 10.1021/acs.macromol.6b00107

• Ordering transition in salt-doped diblock copolymers Macromolecules Qin, J., de Pablo, J. J. 2016; 49: 3630-3638

  View details for DOI 10.1021/acs.macromol.5b02643

• Tube dynamics works for randomly entangled rings PHYSICAL REVIEW LETTERS Qin, J., Milner, S. T. 2016; 116: 068307

  View details for DOI 10.1103/PhysRevLett.116.068307

• A theory of interactions between polarizable dielectric spheres JOURNAL OF COLLOID & INTERFACE SCIENCE Qin, J., Li, J., Lee, V., Jaeger, H., de Pablo, J. J., Freed, K. F. 2016; 469: 237

  View details for DOI 10.1016/j.jcis.2016.02.033

• Blending education and polymer science: semiautomated creation of a thermodynamic property database Journal of Chemical Education Tchoua, R. B., Qin, J., Audus, D. J., Chard, K., Foster, I. T., de Pablo, J. J. 2016; 93 (1561)

  View details for DOI 10.1021/acs.jchemed.5b01032

• Sculpting bespoke mountains: Determining free energies with basis expansions JOURNAL OF CHEMICAL PHYSICS Whitmer, J. K., Fluitt, A. M., Antony, L., Qin, J., McGovern, M., de Pablo, J. J. 2015; 143 (4)

  Abstract

  The intriguing behavior of a wide variety of physical systems, ranging from amorphous solids or glasses to proteins, is a direct manifestation of underlying free energy landscapes riddled with local minima separated by large barriers. Exploring such landscapes has arguably become one of statistical physics's great challenges. A new method is proposed here for uniform sampling of rugged free energy surfaces. The method, which relies on special Green's functions to approximate the Dirac delta function, improves significantly on existing simulation techniques by providing a boundary-agnostic approach that is capable of mapping complex features in multidimensional free energy surfaces. The usefulness of the proposed approach is established in the context of a simple model glass former and model proteins, demonstrating improved convergence and accuracy over existing methods.

  View details for DOI 10.1063/1.4927147

  View details for Web of Science ID 000358929100007

  View details for PubMedID 26233101

• Finding Entanglement Points in Simulated Polymer Melts MACROMOLECULES Cao, J., Qin, J., Milner, S. T. 2015; 48 (1): 99-110

  View details for DOI 10.1021/ma5010315

  View details for Web of Science ID 000348085600012

• Chirality-selected phase behaviour in ionic polypeptide complexes NATURE COMMUNICATIONS Perry, S. L., Leon, L., Hoffmann, K. Q., Kade, M. J., Priftis, D., Black, K. A., Wong, D., Klein, R. A., Pierce, C. F., Margossian, K. O., Whitmer, J. K., Qin, J., de Pablo, J. J., Tirrell, M. 2015; 6

  Abstract

  Polyelectrolyte complexes present new opportunities for self-assembled soft matter. Factors determining whether the phase of the complex is solid or liquid remain unclear. Ionic polypeptides enable examination of the effects of stereochemistry on complex formation. Here we demonstrate that chirality determines the state of polyelectrolyte complexes, formed from mixing dilute solutions of oppositely charged polypeptides, via a combination of electrostatic and hydrogen-bonding interactions. Fluid complexes occur when at least one of the polypeptides in the mixture is racemic, which disrupts backbone hydrogen-bonding networks. Pairs of purely chiral polypeptides, of any sense, form compact, fibrillar solids with a β-sheet structure. Analogous behaviour occurs in micelles formed from polypeptide block copolymers with polyethylene oxide, where assembly into aggregates with either solid or fluid cores, and eventually into ordered phases at high concentrations, is possible. Chirality is an exploitable tool for manipulating material properties in polyelectrolyte complexation.

  View details for DOI 10.1038/ncomms7052

  View details for Web of Science ID 000348830100006

  View details for PubMedID 25586861

• Tubes, Topology, and Polymer Entanglement MACROMOLECULES Qin, J., Milner, S. T. 2014; 47 (17): 6077-6085

  View details for DOI 10.1021/ma500755p

  View details for Web of Science ID 000341542900023

• Evolutionary Optimization of Directed Self-Assembly of Triblock Copolymers on Chemically Patterned Substrates ACS MACRO LETTERS Khaira, G. S., Qin, J., Garner, G. P., Xiong, S., Wan, L., Ruiz, R., Jaeger, H. M., Nealey, P. F., de Pablo, J. J. 2014; 3 (8): 747-752

  View details for DOI 10.1021/mz5002349

  View details for Web of Science ID 000340701900011

• Interfacial Tension of Polyelectrolyte Complex Coacervate Phases ACS MACRO LETTERS Qin, J., Priftis, D., Farina, R., Perry, S. L., Leon, L., Whitmer, J., Hoffmann, K., Tirrell, M., de Pablo, J. J. 2014; 3 (6): 565-568

  View details for DOI 10.1021/mz500190w

  View details for Web of Science ID 000337644500015

• Simulating Constraint Release by Watching a Ring Cross Itself MACROMOLECULES Cao, J., Qin, J., Milner, S. T. 2014; 47 (7): 2479-2486

  View details for DOI 10.1021/ma500325z

  View details for Web of Science ID 000338807300034

• Ternary, tunable polyelectrolyte complexes driven by complex coacervation 247th National Spring Meeting of the American-Chemical-Society (ACS) Priftis, D., Xia, X., Margossian, K., Perry, S. L., Leon, L., Qin, J., de Pablo, J., Tirrell, M. AMER CHEMICAL SOC. 2014

  View details for Web of Science ID 000348457604250

• Collective and Single-Chain Correlations in Disordered Melts of Symmetric Diblock Copolymers: Quantitative Comparison of Simulations and Theory MACROMOLECULES Glaser, J., Qin, J., Medapuram, P., Morse, D. C. 2014; 47 (2): 851-869

  View details for DOI 10.1021/ma401694u

  View details for Web of Science ID 000330543500043

• Tube Diameter of Oriented and Stretched Polymer Melts MACROMOLECULES Qin, J., Milner, S. T. 2013; 46 (4): 1659-1672

  View details for DOI 10.1021/ma302095k

  View details for Web of Science ID 000315618800046

• Evolutionary pattern design for copolymer directed self-assembly SOFT MATTER Qin, J., Khaira, G. S., Su, Y., Garner, G. P., Miskin, M., Jaeger, H. M., de Pablo, J. J. 2013; 9 (48): 11467-11472

  View details for DOI 10.1039/c3sm51971f

  View details for Web of Science ID 000327500200005

• Tube Diameter of Stretched and Compressed Permanently Entangled Polymers MACROMOLECULES Qin, J., So, J., Milner, S. T. 2012; 45 (24): 9816-9822

  View details for DOI 10.1021/ma301830w

  View details for Web of Science ID 000312563900028

• Effects of tube persistence length on dynamics of mildly entangled polymers JOURNAL OF RHEOLOGY Qin, J., Milner, S. T., Stephanou, P. S., Mavrantzas, V. G. 2012; 56 (4): 707-723

  View details for DOI 10.1122/1.4708594

  View details for Web of Science ID 000304305700004

• Fluctuations in Symmetric Diblock Copolymers: Testing Theories Old and New PHYSICAL REVIEW LETTERS Qin, J., Morse, D. C. 2012; 108 (23)

  Abstract

  Computer simulations are used to study composition fluctuations in disordered diblock copolymer melts over a range of values of the chain length N, and test several theories for the structure factor S(q). Specifically, we test the random-phase approximation (RPA), which is based on a self-consistent field treatment of fluctuations, the Fredrickson-Helfand theory, which was designed to describe fluctuations near the order-disorder transition, and the relatively new renormalized one-loop (ROL) theory. The results confirm claims that the RPA is exact in the limit N→∞ and that the ROL theory yields the dominant corrections to the RPA within a systematic expansion in powers of N(-1/2), and show that the ROL theory is much more accurate than either older theory.

  View details for DOI 10.1103/PhysRevLett.108.238301

  View details for Web of Science ID 000304855900012

  View details for PubMedID 23003999

• Test of a scaling hypothesis for the structure factor of disordered diblock copolymer melts SOFT MATTER Glaser, J., Qin, J., Medapuram, P., Mueller, M., Morse, D. C. 2012; 8 (44): 11310-11317

  View details for DOI 10.1039/c2sm26536b

  View details for Web of Science ID 000310829600013

• Finding the Tube with Isoconfigurational Averaging MACROMOLECULES Bisbee, W., Qin, J., Milner, S. T. 2011; 44 (22): 8972-8980

  View details for DOI 10.1021/ma2012333

  View details for Web of Science ID 000296893400032

• Renormalized one-loop theory of correlations in disordered diblock copolymers JOURNAL OF CHEMICAL PHYSICS Qin, J., Grzywacz, P., Morse, D. C. 2011; 135 (8)

  Abstract

  A renormalized one-loop (ROL) theory developed in previous work [P. Grzywacz, J. Qin, and D. C. Morse, Phys. Rev E. 76, 061802 (2007)] is used to calculate corrections to the random phase approximation (RPA) for the structure factor S(q) in disordered diblock copolymer melts. Predictions are given for the peak intensity S(q∗), peak position q∗, and single-chain statistics for symmetric and asymmetric copolymers as functions of χ(e)N, where χ(e) is an effective Flory-Huggins interaction parameter and N is the degree of polymerization. The ROL and Fredrickson-Helfand (FH) theories are found to yield asymptotically equivalent results for the dependence of the peak intensity S(q∗) upon χ(e)N for symmetric diblock copolymers in the limit of strong scattering, or large χ(e)N, but to yield qualitatively different predictions for symmetric copolymers far from the ODT and for asymmetric copolymers. The ROL theory predicts a suppression of S(q∗) and a decrease of q∗ for large values of χ(e)N, relative to the RPA predictions, but an enhancement of S(q∗) and an increase in q∗ for small χ(e)N. The decrease in q∗ near the ODT is shown to be unrelated to any change in single-chain statistics, and to be a result of inter-molecular correlations. Conversely, the predicted increase in q∗ at small values of χ(e)N is a direct result of non-Gaussian single-chain statistics.

  View details for DOI 10.1063/1.3609758

  View details for Web of Science ID 000294484700072

  View details for PubMedID 21895217

• Relationships among coarse-grained field theories of fluctuations in polymer liquids JOURNAL OF CHEMICAL PHYSICS Morse, D. C., Qin, J. 2011; 134 (8)

  Abstract

  Two closely related field-theoretic approaches have been used in previous work to construct coarse-grained theories of corrections to the random phase approximation for correlations in block copolymer melts and miscible polymer blends. The "auxiliary field" (AF) approach is based on a rigorous expression for the partition function Z of a coarse-grained model as a functional integral of an auxiliary chemical potential field. The "effective Hamiltonian" (EH) approach is instead based on an expression for Z as a functional integral of an observable order parameter field. The exact effective Hamiltonian H(eff) in the EH approach is defined as the free energy of a system with a constrained order parameter field. In practice, however, H(eff) has often been approximated by a mean-field free energy functional, yielding what we call a mean-field effective Hamiltonian (MFEH) approximation. This approximation was the starting point of both the Fredrickson-Helfand analysis of fluctuation effects in diblock copolymers and earlier work on the Ginzburg criterion in polymer blends. A more rigorous EH approach by Holyst and Vilgis used an auxiliary field representation of the exact H(eff) and allowed for Gaussian fluctuations of this field. All applications of both AF and EH approaches have thus far relied upon some form of Gaussian, or "one-loop" approximation for fluctuations of a chemical potential and/or order parameter field about a mean-field saddle-point. The one-loop EH approximation of Holyst and Vilgis and the one-loop AF theory are equivalent to one another, but not to the one-loop MFEH theory. The one-loop AF and MFEH theories are shown to yield predictions for the inverse structure factor S(-1)(q) that (in the absence of further approximations to either theory) differ by a function that is independent of the Flory-Huggins interaction parameter χ. As a result, these theories yield predictions for the peak scattering intensity that exhibit a similar χ-dependence near a spinodal. The Fredrickson-Helfand theory for the structure factor in disordered diblock copolymer melts is an asymptotic approximation to the MFEH one-loop theory that captures the dominant asymptotic behavior of very long, symmetric copolymers very near the order-disorder transition.

  View details for DOI 10.1063/1.3548888

  View details for Web of Science ID 000287811300037

  View details for PubMedID 21361554

• Counting polymer knots to find the entanglement length SOFT MATTER Qin, J., Milner, S. T. 2011; 7 (22): 10676-10693

  View details for DOI 10.1039/c1sm05972f

  View details for Web of Science ID 000296388300025

• Phase Behavior of Nonfrustrated ABC Triblock Copolymers: Weak and Intermediate Segregation MACROMOLECULES Qin, J., Bates, F. S., Morse, D. C. 2010; 43 (11): 5128-5136

  View details for DOI 10.1021/ma100400q

  View details for Web of Science ID 000278109700037

• Polydispersity effects in poly(isoprene-b-styrene-b-ethylene oxide) triblock terpolymers JOURNAL OF CHEMICAL PHYSICS Meuler, A. J., Ellison, C. J., Qin, J., Evans, C. M., Hillmyer, M. A., Bates, F. S. 2009; 130 (23)

  Abstract

  Four hydroxyl-terminated poly(isoprene-b-styrene) diblock copolymers with comparable molecular weights and compositions (equivalent volume fractions of polyisoprene and polystyrene) but different polystyrene block polydispersity indices (M(w)/M(n)=1.06,1.16,1.31,1.44) were synthesized by anionic polymerization using either sec-butyllithium or the functional organolithium 3-triisopropylsilyloxy-1-propyllithium. Poly(ethylene oxide) (PEO) blocks were grown from the end of each of these parent diblocks to yield four series of poly(isoprene-b-styrene-b-ethylene oxide) (ISO) triblock terpolymers that were used to interrogate the effects of varying the polydispersity of the middle bridged polystyrene block. In addition to the neat triblock samples, 13 multicomponent blends were prepared at four different compositions from the ISO materials containing a polystyrene segment with M(w)/M(n)=1.06; these blends were used to probe the effects of increasing the polydispersity of the terminal PEO block. The melt-phase behavior of all samples was characterized using small-angle X-ray scattering and dynamic mechanical spectroscopy. Numerous polydispersity-driven morphological transitions are reported, including transitions from lamellae to core-shell gyroid, from core-shell gyroid to hexagonally packed cylinders, and from network morphologies [either O(70) (the orthorhombic Fddd network) or core-shell gyroid] to lamellae. Domain periodicities and order-disorder transition temperatures also vary with block polydispersities. Self-consistent field theory calculations were performed to supplement the experimental investigations and help elucidate the molecular factors underlying the polydispersity effects. The consequences of varying the polydispersity of the terminal PEO block are comparable to the polydispersity effects previously reported in AB diblock copolymers. Namely, domain periodicities increase with increasing polydispersity and domain interfaces tend to curve toward polydisperse blocks. The changes in phase behavior that are associated with variations in the polydispersity of the middle bridged polystyrene block, however, are not analogous to those reported in AB diblock copolymers, as increases in this middle block polydispersity are not always accompanied by (i) increased domain periodicities and (ii) a tendency for domain interfaces to curve toward the polydisperse domain. These results highlight the utility of polydispersity as a tool to tune the phase behavior of ABC block terpolymers.

  View details for DOI 10.1063/1.3140205

  View details for Web of Science ID 000267166200053

  View details for PubMedID 19548752

• Renormalized one-loop theory of correlations in polymer blends JOURNAL OF CHEMICAL PHYSICS Qin, J., Morsea, D. C. 2009; 130 (22)

  Abstract

  The renormalized one-loop theory is a coarse-grained theory of corrections to the random phase approximation (RPA) theory of composition fluctuations. We present predictions of corrections to the RPA for the structure function S(k) and to the random walk model of single-chain statics in binary homopolymer blends. We consider an apparent interaction parameter chi(a) that is defined by applying the RPA to the small k limit of S(k). The predicted deviation of chi(a) from its long chain limit is proportional to N(-1/2), where N is the chain length. This deviation is positive (i.e., destabilizing) for weakly nonideal mixtures, with chi(a)N less than or approximately 1, but negative (stabilizing) near the critical point. The positive correction to chi(a) for low values of chi(a)N is a result of the fact that monomers in mixtures of shorter chains are slightly less strongly shielded from intermolecular contacts. The predicted depression in chi(a) near the critical point is a result of long-wavelength composition fluctuations. The one-loop theory predicts a shift in the critical temperature of O(N(-1/2)), which is much greater than the predicted O(N(-1)) width of the Ginzburg region. Chain dimensions are found to deviate slightly from those of a random walk even in a one-component melt and contract slightly as thermodynamic repulsion is increased. Predictions for S(k) and single-chain properties are compared to published lattice Monte Carlo simulations.

  View details for DOI 10.1063/1.3124799

  View details for Web of Science ID 000266968800031

  View details for PubMedID 19530784

• Bicontinuous Polymeric Microemulsions from Polydisperse Diblock Copolymers JOURNAL OF PHYSICAL CHEMISTRY B Ellison, C. J., Meuler, A. J., Qin, J., Evans, C. M., Wolf, L. M., Bates, F. S. 2009; 113 (12): 3726-3737

  Abstract

  Polymeric bicontinuous microemulsions are thermodynamically stable structures typically formed by ternary blends of immiscible A and B homopolymers and a macromolecular surfactant such as an AB diblock copolymer. Investigations of these bicontinuous morphologies have largely focused on model systems in which all components have narrow molecular weight distributions. Here we probe the effects of AB diblock polydispersity in ternary blends of polystyrene (PS), polyisoprene (PI), and poly(styrene-b-isoprene) (PS-PI). Three series of blends were prepared using the same PS and PI homopolymers; two of them contain nearly monodisperse components while the third includes a polydisperse PS-PI diblock. The PS and PI homopolymers and two of the PS-PI diblocks were prepared by anionic polymerization using sec-butyllithium and have narrow molecular weight distributions. The polydisperse PS-PI diblock was prepared by anionic polymerization using the functional organolithium 3-tert-butyldimethylsilyloxy-1-propyllithium; this diblock has a polydisperse PS block (Mw/Mn = 1.57) and a nearly monodisperse PI block (Mw/Mn < 1.1). The phase behavior of the three series of blends was probed using a combination of dynamic mechanical spectroscopy, small-angle X-ray scattering, and cloud point measurements, and a bicontinuous microemulsion channel was identified in each system. These results prove that monodisperse components are not required to form bicontinuous microemulsions and highlight the utility of polydispersity as a tool to tune polymer blend phase behavior. The random-phase approximation, originally advanced by de Gennes, and self-consistent field theory are used to provide a theoretical supplement to the experimental work. These theories are able to predict the directions of the polydispersity-driven shifts in domain spacing, order-disorder transition temperatures, and the location of the microemulsion channel. Self-consistent field theory is also used in conjunction with the experimental data from a series of nearly monodisperse blends to probe the variations of chi with temperature. A single linear relation of the form chi = alpha/T + beta does not describe chi at all blend compositions. Rather, two separate relations describe chi as a function of temperature; one is obtained from data on the diblock-rich side of the bicontinuous microemulsion channel while the other is obtained from data on the homopolymer-rich side of the channel. The blend morphology, rather than the composition (homopolymer fraction), apparently dictates whether the system is in the "diblock chi" or "homopolymer chi" regime. These results reinforce the notion that a true understanding of chi still eludes the polymer science community.

  View details for DOI 10.1021/jp807343b

  View details for Web of Science ID 000264348900017

  View details for PubMedID 19673066

• Linear response and stability of ordered phases of block copolymer melts MACROMOLECULES Ranjan, A., Qin, J., Morse, D. C. 2008; 41 (3): 942-954

  View details for DOI 10.1021/ma0714316

  View details for Web of Science ID 000252944900062

• Renormalization of the one-loop theory of fluctuations in polymer blends and diblock copolymer melts PHYSICAL REVIEW E Grzywacz, P., Qin, J., Morse, D. C. 2007; 76 (6)

  Abstract

  Attempts to use coarse-grained molecular theories to calculate corrections to the random-phase approximation (RPA) for correlations in polymer mixtures have been plagued by an unwanted sensitivity to the value of an arbitrary cutoff length, i.e., by an ultraviolet (UV) divergence. We analyze the UV divergence of the inverse structure factor S(-1)(k) predicted by a "one-loop" approximation similar to that used in several previous studies. We consider both miscible homopolymer blends and disordered diblock copolymer melts. We show, in both cases, that all UV divergent contributions can be absorbed into a renormalization of the values of the phenomenological parameters of a generalized self-consistent field theory (SCFT). This observation allows the construction of an UV convergent theory of corrections to SCFT phenomenology. The UV-divergent one-loop contribution to S(-1)(k) is shown to be the sum of (i) a k -independent contribution that arises from a renormalization of the effective chi parameter, (ii) a k-dependent contribution that arises from a renormalization of monomer statistical segment lengths, (iii) a contribution proportional to k(2) that arises from a square-gradient contribution to the one-loop fluctuation free energy, and (iv) a k-dependent contribution that is inversely proportional to the degree of polymerization, which arises from local perturbations in fluid structure near chain ends and near junctions between blocks in block copolymers.

  View details for DOI 10.1103/PhysRevE.76.061802

  View details for Web of Science ID 000251985600060

  View details for PubMedID 18233860

• SCFT study of nonfrustrated ABC triblock copolymer melts MACROMOLECULES Tyler, C. A., Qin, J., Bates, F. S., Morse, D. C. 2007; 40 (13): 4654-4668

  View details for DOI 10.1021/ma062778w

  View details for Web of Science ID 000247340700040

• Calculation of resistivity of the insulating layer in tunneling-magnetoresistive head by fast Green function method Chinese Physics Letters Wei, D., Piao, K., Qin, J., Dong, Z. 2005; 22: 2063-2065
• Thermodynamic behavior of a nano-sized magnetic grain near the superparamagnetic limit IEICE Trans. Elec. Qin, J., Wei, D. 2003; E86-C: 1825-1829