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.
Dark-field microscopy, DFM, is widely used to optically image and spectroscopically analyze nanoscale objects. In a typical DFM configuration, a sample is illuminated at oblique angles and an objective lens collects light scattered by the sample at a range of lower angles. As demonstrated in an article published as the cover of ACS Photonics, researchers in the Cahoon Group have developed waveguide scattering microscopy, WSM, as an alternative technique to image and analyze photonic nanostructures. WSM uses an incoherent white-light source coupled to a dielectric slab waveguide to generate an evanescent field that illuminates objects located within several hundred nanometers of the waveguide surface.
Using standard microscope slides or coverslips as the waveguide, the group demonstrate high-contrast dark-field imaging of nanophotonic and plasmonic structures such as Si nanowires, Au nanorods, and Ag nanoholes. Scattering spectra collected in the WSM configuration show excellent signal-to-noise with minimal background signal compared to conventional DFM. In addition, the polarization of the incident field is controlled by the direction of the propagating wave, providing a straightforward route to excite specific optical modes in anisotropic nanostructures by selecting the appropriate input wavevector. Considering the facile integration of WSM with standard microscopy equipment, the Cahoon Group scientists anticipate it will become a versatile tool for characterizing photonic nanostructures.
Researchers in the Ashby and Sheiko groups have fabricated textured surfaces capable of reversibly changing in response to a thermal stimulus. These surfaces are fabricated with PRINT© molds provided by the DeSimone Lab, and could find use in applications requiring modular surface wetting or roughness. Reversibly switching topography on micrometer length scales greatly expands the functionality of stimuli-responsive substrates.
In an article published in ACS Applied Materials & Interfaces the groups report the first usage of reversible shape memory for the actuation of two-way transitions between microscopically patterned substrates, resulting in corresponding modulations of the wetting properties. Reversible switching of the surface topography is achieved through partial melting and recrystallization of a semi-crystalline polyester embossed with microscopic features. This behavior is monitored with atomic force microscopy, AFM, and contact angle measurements. The groups demonstrate that the magnitude of the contact angle variations depends on the embossment pattern.
Hopping Diffusion of Nanoparticles in Polymer Matrices. Li-Heng Cai Sergey Panyukov, and Michael Rubinstein. Macromolecules, 2015, 48 (3), pp 847–862.
Doubling Absorption in Nanowire Solar Cells with Dielectric Shell Optical Antennas. Kim, Sun-Kyung; Zhang, Xing; Hill, David J.; Song, Kyung-Deok; Park, Jin-Sung; Park, Hong-Gyu; Cahoon, James F.. NANO LETTERS, 15 (1):753-758; 10.1021/nl504462e JAN 2015.
Continuous Liquid Interface Production of 3D Objects. John R. Tumbleston, David Shirvanyants, Nikita Ermoshkin, Rima Janusziewicz, Ashley R. Johnson, David Kelly, Kai Chen, Robert Pinschmidt, Jason P. Rolland, Alexander Ermoshkin, Edward T. Samulski, Joseph M. DeSimone. Science 20 March 2015, Vol. 347 no. 6228 pp. 1349-1352.
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.