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  • 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)

    Abstract

    A wide variety of intracellular membraneless compartments are formed via liquid-liquid phase separation of charged proteins and nucleic acids. Understanding the stability of these compartments, while accounting for the compositional heterogeneity intrinsic to cellular environments, poses a daunting challenge. We combined experimental and theoretical efforts to study the effects of nonstoichiometric mixing on coacervation behavior and accurately measured the concentrations of polyelectrolytes and small ions in the coacervate and supernatant phases. For synthetic polyacrylamides and polypeptides/DNA, with unequal mixing stoichiometry, we report a general "looping-in" phenomenon found around physiological salt concentrations, where the polymer concentrations in the coacervate initially increase with salt addition before subsequently decreasing. This looping-in behavior is captured by a molecular model that considers reversible ion binding and electrostatic interactions. Further analysis in the low-salt regime shows that the looping-in phenomenon originates from the translational entropy of counterions that are needed to neutralize nonstoichiometric coacervates.

    View details for DOI 10.1126/sciadv.abg8654

    View details for PubMedID 34330707

  • Enhancing Mechanical and Combustion Performance of Boron/Polymer Composites via Boron Particle Functionalization. ACS applied materials & interfaces Jiang, Y., Dincer Yilmaz, N. E., Barker, K. P., Baek, J., Xia, Y., Zheng, X. 2021

    Abstract

    High-speed air-breathing propulsion systems, such as solid fuel ramjets (SFRJ), are important for space exploration and national security. The development of SFRJ requires high-performance solid fuels with excellent mechanical and combustion properties. One of the current solid fuel candidates is composed of high-energy particles (e.g., boron (B)) and polymeric binder (e.g., hydroxyl-terminated polybutadiene (HTPB)). However, the opposite polarities of the boron surface and HTPB lead to poor B particle dispersion and distribution within HTPB. Herein, we demonstrate that the surface functionalization of B particles with nonpolar oleoyl chloride greatly improves the dispersion and distribution of B particles within HTPB. The improved particle dispersion is quantitatively visualized through X-ray computed tomography imaging, and the particle/matrix interaction is evaluated by dynamic mechanical analysis. The surface-functionalized B particles can be uniformly dispersed up to 40 wt % in HTPB, the highest mass loading reported to date. The surface-functionalized B (40 wt %)/HTPB composite exhibits a 63.3% higher Young's modulus, 87.5% higher tensile strength, 16.2% higher toughness, and 16.8% higher heat of combustion than pristine B (40 wt %)/HTPB. The surface functionalization of B particles provides an effective strategy for improving the efficacy and safety of B/HTPB solid fuels for future high-speed air-breathing vehicles.

    View details for DOI 10.1021/acsami.1c06727

    View details for PubMedID 34110148

  • Dinaphthobenzo[1,2:4,5]dicyclobutadiene: Antiaromatic and Orthogonally Tunable Electronics and Packing ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Jin, Z., Yao, Z., Barker, K. P., Pei, J., Xia, Y. 2019; 58 (7): 2034–39

    View details for DOI 10.1002/anie.201812581

    View details for Web of Science ID 000458828000026

  • Dinaphthobenzo[1,2:4,5]dicyclobutadiene with Strong Antiaromaticity and Orthogonally Tunable Electronics and Packing. Angewandte Chemie (International ed. in English) Jin, Z., Yao, Z., Barker, K. P., Pei, J., Xia, Y. 2018

    Abstract

    Polycyclic conjugated hydrocarbons containing antiaromatic four-membered cyclobutadienoids are of great fundamental and technical interest. However, their challenging synthesis has hampered the exploration and understanding of such systems. We report herein a modular and efficient synthesis of novel CBD-containing acene analogues, dinaphthobenzo[1,2:4,5]dicyclobutadiene (DNBDCs) with orthogonally tunable electronic properties and molecular packing. Our design also features strong antiaromaticity of CBD units, as revealed by nucleus-independent chemical shift and anisotropy of the induced current density calculations as well as X-ray crystallography. Tuning the size of silyl substituents resulted in the most favorable "brick-layer" packing for triisobutylsilyl-DNBDC and a charge mobility of up to 0.52 cm2 V-1 s-1 in field-effect transistors.

    View details for PubMedID 30565363