All Publications


  • High Energy Density Shape Memory Polymers Using Strain-Induced Supramolecular Nanostructures. ACS central science Cooper, C. B., Nikzad, S., Yan, H., Ochiai, Y., Lai, J., Yu, Z., Chen, G., Kang, J., Bao, Z. 2021; 7 (10): 1657-1667

    Abstract

    Shape memory polymers are promising materials in many emerging applications due to their large extensibility and excellent shape recovery. However, practical application of these polymers is limited by their poor energy densities (up to 1 MJ/m3). Here, we report an approach to achieve a high energy density, one-way shape memory polymer based on the formation of strain-induced supramolecular nanostructures. As polymer chains align during strain, strong directional dynamic bonds form, creating stable supramolecular nanostructures and trapping stretched chains in a highly elongated state. Upon heating, the dynamic bonds break, and stretched chains contract to their initial disordered state. This mechanism stores large amounts of entropic energy (as high as 19.6 MJ/m3 or 17.9 J/g), almost six times higher than the best previously reported shape memory polymers while maintaining near 100% shape recovery and fixity. The reported phenomenon of strain-induced supramolecular structures offers a new approach toward achieving high energy density shape memory polymers.

    View details for DOI 10.1021/acscentsci.1c00829

    View details for PubMedID 34729409

  • Modular Synthesis of Fully Degradable Imine-Based Semiconducting p-Type and n-Type Polymers CHEMISTRY OF MATERIALS Tran, H., Nikzad, S., Chiong, J. A., Schuster, N. J., Pena-Alcantara, A. E., Feig, V. R., Zheng, Y., Bao, Z. 2021; 33 (18): 7465-7474
  • Influence of solution-state aggregation on conjugated polymer crystallization in thin films and microwire crystals GIANT Zheng, Y., Yao, Z., Dou, J., Wang, Y., Ma, W., Zou, L., Nikzad, S., Li, Q., Sun, Z., Yu, Z., Zhang, W., Wang, J., Pei, J. 2021; 7
  • A Design Strategy for Intrinsically Stretchable High-Performance Polymer Semiconductors: Incorporating Conjugated Rigid Fused-Rings with Bulky Side Groups. Journal of the American Chemical Society Liu, D., Mun, J., Chen, G., Schuster, N. J., Wang, W., Zheng, Y., Nikzad, S., Lai, J., Wu, Y., Zhong, D., Lin, Y., Lei, Y., Chen, Y., Gam, S., Chung, J. W., Yun, Y., Tok, J. B., Bao, Z. 2021

    Abstract

    Strategies to improve stretchability of polymer semiconductors, such as introducing flexible conjugation-breakers or adding flexible blocks, usually result in degraded electrical properties. In this work, we propose a concept to address this limitation, by introducing conjugated rigid fused-rings with optimized bulky side groups and maintaining a conjugated polymer backbone. Specifically, we investigated two classes of rigid fused-ring systems, namely, benzene-substituted dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene (Ph-DBTTT) and indacenodithiophene (IDT) systems, and identified molecules displaying optimized electrical and mechanical properties. In the IDT system, the polymer PIDT-3T-OC12-10% showed promising electrical and mechanical properties. In fully stretchable transistors, the polymer PIDT-3T-OC12-10% showed a mobility of 0.27 cm2 V-1 s-1 at 75% strain and maintained its mobility after being subjected to hundreds of stretching-releasing cycles at 25% strain. Our results underscore the intimate correlation between chemical structures, mechanical properties, and charge carrier mobility for polymer semiconductors. Our described molecular design approach will help to expedite the next generation of intrinsically stretchable high-performance polymer semiconductors.

    View details for DOI 10.1021/jacs.1c04984

    View details for PubMedID 34284578

  • Metal-Ligand Based Mechanophores Enhance Both Mechanical Robustness and Electronic Performance of Polymer Semiconductors ADVANCED FUNCTIONAL MATERIALS Wu, H., Lissel, F., Wang, G., Koshy, D. M., Nikzad, S., Yan, H., Xu, J., Luo, S., Matsuhisa, N., Cheng, Y., Wang, F., Ji, B., Li, D., Chen, W., Xue, G., Bao, Z. 2021
  • Monolithic optical microlithography of high-density elastic circuits. Science (New York, N.Y.) Zheng, Y. Q., Liu, Y., Zhong, D., Nikzad, S., Liu, S., Yu, Z., Liu, D., Wu, H. C., Zhu, C., Li, J., Tran, H., Tok, J. B., Bao, Z. 2021; 373 (6550): 88-94

    Abstract

    Polymeric electronic materials have enabled soft and stretchable electronics. However, the lack of a universal micro/nanofabrication method for skin-like and elastic circuits results in low device density and limited parallel signal recording and processing ability relative to silicon-based devices. We present a monolithic optical microlithographic process that directly micropatterns a set of elastic electronic materials by sequential ultraviolet light-triggered solubility modulation. We fabricated transistors with channel lengths of 2 micrometers at a density of 42,000 transistors per square centimeter. We fabricated elastic circuits including an XOR gate and a half adder, both of which are essential components for an arithmetic logic unit. Our process offers a route to realize wafer-level fabrication of complex, high-density, and multilayered elastic circuits with performance rivaling that of their rigid counterparts.

    View details for DOI 10.1126/science.abh3551

    View details for PubMedID 34210882

  • Tuning Conjugated Polymer Chain Packing for Stretchable Semiconductors. Advanced materials (Deerfield Beach, Fla.) Xu, J., Wu, H. C., Mun, J., Ning, R., Wang, W., Wang, G. N., Nikzad, S., Yan, H., Gu, X., Luo, S., Zhou, D., Tok, J. B., Bao, Z. 2021: e2104747

    Abstract

    In order to apply polymer semiconductors to stretchable electronics, they need to be easily deformed under strain without being damaged. A small number of conjugated polymers, typically with semicrystalline packing structures, have been reported to exhibit mechanical stretchability. Herein, a method is reported to modify polymer semiconductor packing-structure using a molecular additive, dioctyl phthalate (DOP), which is found to act as a molecular spacer, to be inserted between the amorphous chain networks and disrupt the crystalline packing. As a result, large-crystal growth is suppressed while short-range aggregations of conjugated polymers are promoted, which leads to an improved mechanical stretchability without affecting charge-carrier transport. Due to the reduced conjugated polymer intermolecular interactions, strain-induced chain alignment and crystallization are observed. By adding DOP to a well-known conjugated polymer, poly[2,5-bis(4-decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4-(2H,5H)-dione-(E)-1,2-di(2,2'-bithiophen-5-yl)ethene] (DPPTVT), stretchable transistors are obtained with anisotropic charge-carrier mobilities under strain, and stable current output under strain up to 100%.

    View details for DOI 10.1002/adma.202104747

    View details for PubMedID 34558121

  • Tuning the Mechanical Properties of a Polymer Semiconductor by Modulating Hydrogen Bonding Interactions CHEMISTRY OF MATERIALS Zheng, Y., Ashizawa, M., Zhang, S., Kang, J., Nikzad, S., Yu, Z., Ochiai, Y., Wu, H., Tran, H., Mun, J., Zheng, Y., Tok, J., Gu, X., Bao, Z. 2020; 32 (13): 5700–5714
  • Inducing Molecular Aggregation of Polymer Semiconductors in a Secondary Insulating Polymer Matrix to Enhance Charge Transport CHEMISTRY OF MATERIALS Nikzad, S., Wu, H., Kim, J., Mahoney, C. M., Matthews, J. R., Niu, W., Li, Y., Wang, H., Chen, W., Toney, M. F., He, M., Bao, Z. 2020; 32 (2): 897–905
  • Multivalent Assembly of Flexible Polymer Chains into Supramolecular Nanofibers. Journal of the American Chemical Society Cooper, C. B., Kang, J. n., Yin, Y. n., Yu, Z. n., Wu, H. C., Nikzad, S. n., Ochiai, Y. n., Yan, H. n., Cai, W. n., Bao, Z. n. 2020

    Abstract

    Polymeric materials in nature regularly employ ordered, hierarchical structures in order to perform unique and precise functions. Importantly, these structures are often formed and stabilized by the cooperative summation of many weak interactions as opposed to the independent association of a few strong bonds. Here, we show that synthetic, flexible polymer chains with periodically placed and directional dynamic bonds collectively assemble into supramolecular nanofibers when the overall molecular weight is below the polymer's critical entanglement molecular weight. This causes bulk films of long polymer chains to have faster dynamics than films of shorter polymer chains of identical chemical composition. The formation of nanofibers increases the bulk film modulus by over an order of magnitude and delays the onset of terminal flow by more than 100 °C, while still remaining solution processable. Systematic investigation of different polymer chain architectures and dynamic bonding moieties along with coarse-grained molecular dynamics simulations illuminate governing structure-function relationships that determine a polymer's capacity to form supramolecular nanofibers. This report of the cooperative assembly of multivalent polymer chains into hierarchical, supramolecular structures contributes to our fundamental understanding of designing biomimetic functional materials.

    View details for DOI 10.1021/jacs.0c07651

    View details for PubMedID 32901473

  • Effect of Extensional Flow on the Evaporative Assembly of a Donor-Acceptor Semiconducting Polymer ACS APPLIED ELECTRONIC MATERIALS Nikzad, S., Wu, H., Wang, G., Yan, H., Schneider, S. A., Toney, M. F., Bao, Z. 2019; 1 (11): 2445–54