Many challenging problems in the modern science and technology are related to preparation, properties, and utilization of novel functional materials. The polymer chemistry and the chemical microelectronics programs represent parts of the multidisciplinary effort in this field. The many-pronged approach includes: synthesis and molecular characterization of well-defined block and graft copolymers; preparation of new engineering thermoplastics and liquid crystalline materials; synthesis, modification and processing of polymers in super-critical carbon dioxide; chemical design of hybrid polymers for catalysis and photoredox activity, polymers for microelectronics applications including 193 nm and 157 nm photoresists and low-k dielectrics, and defined microstructures.
Chemical microelectronics is focused on preparation of organic and inorganic electronic materials; microscopic patterning of thin films using novel techniques, plasma, ion beam, laser beam, etc.; kinetics of etching and film formation; characterization of mechanical, electronic, and optical properties; spatially resolved chemical analysis of surfaces, interfaces, and thin films and microstructures. A broad variety of expertise includes visualization and probing of submicrometer surface structures by scanning probe microscopy, characterization of polymer dynamics by NMR techniques and light scattering, measurement of molecular conductivity, and analytical as well as computational and numerical methods in polymers.
To further improve the physical strength and biomedical applicability of bioceramics built on hydroxyapatite-gelatin, HAp-Gel, and siloxane sol-gel reactions, the You group incorporated mussel adhesive inspired polydopamine, PD, into the original composite based on HAp-Gel cross-linked with siloxane, discovered by Dr. Ching-Chang Ko at the UNC Dental School.
Surprisingly, with the addition of PD, the team of You/Ko observed that the processing conditions and temperatures play important roles in the structure and performance of these materials. A systematic study to investigate this temperature dependence behavior discloses that the rate of crosslinking of silane during the sol–gel process is significantly influenced by the temperature, whereas the polymerization of the dopamine only shows minor temperature dependence. With this discovery, reported in the Journal of Materials Chemistry B, the team report an innovative thermal process for the design and application of these biocomposites..
Published in Macromolecules, Professor Michael Rubinstein, in collaboration with Ekaterina Zhulina with the Institute of Macromolecular Compounds, Russian Academy of Sciences in Saint Petersburg, describe the development of a scaling model relating the friction forces between two polyelectrolyte brushes sliding over each other to the separation between grafted surfaces, number of monomers and charges per chain, grafting density of chains, and solvent quality. They demonstrate that the lateral force between brushes increases upon compression, but to a lesser extent than the normal force.
The shear stress at larger separations is due to solvent slip layer friction. The thickness of this slip layer sharply decreases at distances on the order of undeformed brush thickness. The corresponding effective viscosity of the layer sharply increases from the solvent viscosity to a much higher value, but this increase is smaller than the jump of the normal force resulting in the drop of the friction coefficient. At stronger compression the group members predict the second sharp increase of the shear stress corresponding to interpenetration of the chains from the opposite brushes. In this regime the velocity-dependent friction coefficient between two partially interpenetrating polyelectrolyte brushes does not depend on the distance between substrates because both normal and shear forces are reciprocally proportional to the plate separation. Although lateral forces between polyelectrolyte brushes are larger than between bare surfaces, the enhancement of normal forces between opposing polyelectrolyte brushes with respect to normal forces between bare charged surfaces is much stronger resulting in lower friction coefficient. The model quantitatively demonstrates how polyelectrolyte brushes provide more effective lubrication than bare charged surfaces or neutral brushes.
The Role of Temperature in Forming Sol–Gel Biocomposites Containing Polydopamine. Jason Christopher Dyke, Huamin Hu, Dong Joon Lee, Ching-Chang Ko, and Wei You. J. Mater. Chem. B, 2014,2, 7704-7711.
Lubrication by Polyelectrolyte Brushes. Ekaterina B. Zhulina and Michael Rubinstein. Macromolecules, 2014, 47 (16), pp 5825–5838.
Shapeshifting: Reversible Shape Memory in Semicrystalline Elastomers. Jing Zhou, Sara A. Turner, Sarah M. Brosnan, Qiaoxi Li, Jan-Michael Y. Carrillo, Dmytro Nykypanchuk, Oleg Gang, Valerie S. Ashby, Andrey V. Dobrynin, and Sergei S. Sheiko. Nature Methods 11, 959–965 (2014).
Waveguide Scattering Microscopy for Dark-Field Imaging and Spectroscopy of Photonic Nanostructures. David J. Hill , Christopher W. Pinion , Joseph D. Christesen , and James F. Cahoon. ACS Photonics, 2014, 1 (8), pp 725–731.
Switchable Micropatterned Surface Topographies Mediated by Reversible Shape Memory. Sara A. Turner, Jing Zhou, Sergei S. Sheiko, and Valerie Sheares Ashby. ACS Appl. Mater. Interfaces, 2014, 6 (11), pp 8017–8021.
Particle Replication in Nonwetting Templates Nanoparticles with Tumor Selective Alkyl Silyl Ether Docetaxel Prodrug Reduces Toxicity. Kevin S. Chu, Mathew C. Finniss, Allison N. Schorzman, Jennifer L. Kuijer, J. Christopher Luft, Charles J. Bowerman, Mary E. Napier, Zishan A. Haroon, William C. Zamboni. Nano Lett., 2014, 14 (3), pp 1472–1476.
Controlling Molecular Weight of a High Efficiency Donor-Acceptor Conjugated Polymer and Understanding Its Significant Impact on Photovoltaic Properties. Wentao Li, Liqiang Yang, John R. Tumbleston, Liang Yan, Harald Ade, and Wei You. Adv. Mat., First published online, 14 MAR 2014, DOI: 10.1002/adma.201305251.
The Influence of Molecular Orientation on Organic Bulk Heterojunction Solar Cells. John R. Tumbleston, Brian A. Collins, Eliot Gann, Wei Ma and Harald Ade, Liqiang Yang, Andrew C. Stuart and Wei You. Nature Photonics (2014) doi:10.1038/nphoton.2014.55.
Copolymerization of Metal Nanoparticles: A Route to Colloidal Plasmonic Copolymers. Kun Liu, Ariella Lukach, Kouta Sugikawa, Siyon Chung, Jemma Vickery, Heloise Therien-Aubin, Bai Yang, Michael Rubinstein, and Eugenia Kumacheva. Angewandte Chemie International Edition, Volume 53, Issue 10, pages 2648–2653, March 3, 2014.
Storage of Electrical Information in Metalâ€“Organic-Framework Memristors. Seok Min Yoon, Scott C. Warren, and Bartosz A. Grzybowski. Article first published online: 14 MAR 2014, DOI: 10.1002/anie.201309642.