Researcher: Songqing Weng

Semicrystalline polymers are arguably the most important polymeric materials from application point of view. Inspite of the extensive research that has been devoted to studying polymer crystallization, many issues still remain unclear. Our research in this field includes exploring structures of novel polymeric materials as well as finding new horizons for polymer crystallization applications. The latter is closely related to the fast developing nanotechnology.

As a consequence of their extraordinary physical properties and large application potential, carbon nanotubes (CNTs) have attracted the interest of scientists and engineers since their discovery in 1991. However, in order to effectively explore the remarkable properties and manipulate CNT, one essential step involves their functionalization. Our study of functionalization of CNTs via controlled polymer crystallization method has resulted in “nano hybrid shish-kebab” (NHSK), which is CNT periodically decorated with polymer lamellar crystals. The degree of functionalization can be directly visualized by microscope techniques and controlled by tuning experimental parameters such as concentration of polymers and CNT, crystallization. This research opens the gate to periodical patterning on individual 1D nanostructures.

Related publications:

Lingyu Li, Yao Yang, Guoliang Yang, Xuming Chen, Benjamin S. Hsiao, Benjamin Chu, Jonathan E. Spanier, and Christopher Y. Li, "Patterning Polyethylene Oligomers on Carbon Nanotubes Using Physical Vapor Deposition", Nanoletters, 2006, 6 (5), 1007-1012.

L. Li, C. Y. Li*, C. Ni, “Polymer Crystallization-driven, periodic patterning on carbon nanotubes”, J. Am. Chem. Soc., 2006, 128, 1692-1699.

C. Y. Li*, L. Li, W. Cai, S. L. Kodjie and K. K. Tenneti, “Nano-Hybrid Shish-kebab: Polymer decorated carbon Nanotubes”, Adv. Mater. 2005, 17, 1198-1202.

Researcher : Kishore Tenneti

The aim of this research is to study the phase behavior of rod-coil block copolymers (RCBCPs). Block copolymers (BCPs) are macromolecules made of chemically distinct species that are combined using a chemical bond. They undergo phase separation and form ordered structures whose dimensions are comparable to the size of the polymers. Traditionally, four types of equilibrium ordered structures are known; they are spheres, hexagonally packed cylinders, gyroid and lamellae. However, non-equilibrium phase structures are also possible. If one of the combining blocks has a rigid conformation (such as a liquid crystal (LC)), the resultant block copolymers are called RCBCPs. Due to the extreme nature of the combining blocks, complex phase structures are possible. Liquid crystals and block copolymer morphology are two very interesting and huge fields of research by themselves and the incorporation of them into a single phase system to study mutual interactions and their effect on the overall behavior of the system is very exciting. In order to get a complete understanding of the RCBCP system, we “tamper” with a lot of variables of the system such as the volume fractions of the combining blocks, molecular weights, shape of the liquid crystals etc. To start with, we characterized the simplest of phase structures (lamellar) and studied the hierarchical phase behavior of RCBCPs where BCP phase separation and LC ordering compete with each other to result in structures that range from a few nanometers to tens of nanometers. Currently, the research is focused on the effect of changing the shape of the LC molecule on the final phase structures and also effect of incorporating nanoparticles into the BCP system.

Related publications:

X. Chen, K. K. Tenneti, C. Y. Li*, Y. Bai, R. Zhou, X. Wan, X. Fan, Q-F Zhou,* “Design, synthesis and characterization of bent-core mesogen-jacketed liquid crystalline polymers”, Macromolecules 2006, 39, 517-527.

K. K. Tenneti, X. F. Chen, C. Y. Li*, X. Wan, Q-F Zhou,* I. Sics, and B. Hsiao “Perforated structures in rod-coil liquid crystalline block copolymers”. J. Am. Chem. Soc., 2005, 127, 15481-15490.

Researcher : Michael Birnkrant

Fabricating structures with length scales spanning from nanometer to micron regime is challenging. There is often a gap between top-down and bottom-up nanomanufacturing techniques. To bridge this gap, we combine the top-down and bottom-up methods in one system: using the top-down technique to create long-range, large scale (~100 nm) features within which self-assembly is employed to create tailored fine scale (1 to 100 nm) architectures. In particular, we explore the feasibility of this methodology by combining holographic polymerization (H-P, top-down technique) and block copolymer (BCP) self assembly (bottom-up) to create active, tunable hierarchical nanostructures.

Related publications:

C. Y. Li*, M. J. Birnkrant, L. V. Natarajan, V. P. Tondiglia, P. F. Lloyd, R. L. Sutherland, T. J. Bunning,* “Holographically patterned, thermally switchable Bragg reflectors”, Soft Matter, 2005, 1, 238-242.

Researcher : Rebecca Chen

Our research in this field is two-fold: 1) self-assembly of synthetic polypeptides such as poly(g-benzyl-L-glutamate), polylysine in solution and 1-D confined space. 2) novel polymer/inorganic hybrid materials for biomedical applications. Both self-assembly and electro-spinning (collaborating with Prof. Frank Ko, Drexel University).

Related publications:

W. Cai, C. Y. Li*, L. Li, B. Lotz, M. Keating and D. Marks, “Sub-micro tube/scroll polymer single crystal from Nylon 6,6”, Adv. Mater. 2004, 16, 600-605.

Researcher: Matthew Hood

Polyurethane is a block copolymer that has been widely used commercially for nearly a century. Polyurethane's complex composition allows it to possess a myriad of properties that can be controlled during synthesis and processing. Due to the tailorability of polyurethane we find this versatile product being used in foam insulation, chemical adhesives, protective transparent coatings and many other applications. We are interested in controlling the structure of polyurethane from the initial design of the polymer to the addition of nano-sized materials such nanoparticles and carbon nanotubes. It is our goal to control the structure of polyurethane at every level in order to produce highly tailorable transparent structural coatings.

Researcher: Bing Li

Nanoparticles (NPs), especially nanocrystals, are of particular interest because of the impressive electronic, optical and mechanical properties. NP assembling is a crucial step towards fabrication of advanced electronic and optical devices, which exploit those fascinating properties. There are generally two ways to assemble NPs, self-assembly and templated self-assembly. My project is focused on the second approach using microscale polymer single crystals as templates to assemble NPs into a variety of nanostructures. What's more interesting is that as the NP/polymer hybrids are dissolved, asymmetrically functionalized NPs are obtained in solution because of the geometry confinement of the planar polymer single crystals. By designing the experimental procedure and introducing other functional groups, the asymmetrically functionalized NPs may link up with each other forming NP chains, which are able to combine the special properties of various types of NPs together.

Researcher: Bing-Bing Wang

1. Asymmetrically functionalized Metal Nanoparticles with Polymers: We are currently exploring 2 methods to selectively functionalize metal nanoparticles. The first method uses PEO single crystals as 'living-substrates'. Gold nanoparticles can then be asymmetrically modifed with different ligands on the surface, in a 'grafting-to' technique. The second methods uses the ATRP method to grow polymer chains from the asymmetrically functionalized gold nanoparticles, which could be described as a 'grafting from' technique.

2. Multiple-dimensional Nanometer-scaled Structures Based on Electrospinning Technology: One-dimensional nanofibers, which were obtained by electrospinning, were used as substrates to form 2-D even 3-D nano-structures by polymer crystallization.