Rachel Ferebee

Transparent and High Refractive Index Thermoplastic Polymer Glasses Using Evaporative Ligand Exchange of Hybrid Particle Fillers

Development of high refractive index glasses on the basis of commodity polymer thermoplastics presents an important requisite to further advancement of technologies ranging from energy efficient lighting to cost efficient photonics. This contribution presents a novel particle dispersion strategy that enables uniform dispersion of zinc oxide (ZnO) particles in a poly(methyl methacrylate) (PMMA) matrix to facilitate hybrid glasses with inorganic content exceeding 25% by weight, optical transparency in excess of 0.8/mm, and a refractive index greater than 1.64 in the visible wavelength range. The method is based on the application of evaporative ligand exchange to synthesize poly(styrene-r-acrylonitrile) (PSAN)-tethered zinc oxide (ZnO) particle fillers. Favorable filler-matrix interactions are shown to enable the synthesis of isomorphous blends with high molecular PMMA that exhibit improved thermomechanical stability compared to that of the pristine PMMA matrix. The concurrent realization of high refractive index and optical transparency in polymer glasses by modification of a thermoplastic commodity polymer could present a viable alternative to expensive specialty polymers in applications where high costs or demands for thermomechanical stability and/or UV resistance prohibit the application of specialty polymer solutions.

Biocatalytic Stimuli-Responsive Asymmetric Triblock Terpolymer Membranes for Localized Permeability Gating.

The functionalization with phosphotriesterase of poly(isoprene-b-styrene-b-4-vinylpyridine)-based nanoporous membranes fabricated by self-assembly and nonsolvent induced phase separation (SNIPS) is shown to enable dynamically responsive membranes capable of substrate-specific and localized gating response. Integration of the SNIPS process with macroporous nylon support layers yields mechanically robust textile-type films with high moisture vapor transport rates that display rapid and local order-of-magnitude modulation of permeability. The simplicity of the fabrication process that is compatible with large-area fabrication along with the versatility and efficacy of enzyme reactivity offers intriguing opportunities for engineered biomimetic materials that are tailored to respond to a complex range of external parameters, providing sensing, protection, and remediation capabilities.

Light Scattering Analysis of Mono- and Multi-PEGylated Bovine Serum Albumin in Solution: Role of Composition on Structure and Interactions

The effect of polymer conjugation on the interactions between proteins in solution is evaluated by systematic analysis of the second virial coefficient (A2) for the particular example of single- and double-PEGylated bovine serum albumin (PEG-BSA) in dilute PBS solution. The effect of PEGylation on A2 is found to sensitively depend on both the composition and the distribution of PEG segments within the conjugate. Most importantly, at a given PEG volume fraction, A2 significantly increases with the degree of polymerization of tethered chains. Hence, a lesser number of long chains is more effective in solubilizing BSA than a correspondingly larger number of short chains. Analysis of the hydrodynamic radii of protein-PEG conjugates suggests that the increased solubility is concurrent with a structural transition in the case of high molecular PEG grafts that results in compact core-shell-type structures. The results reveal a link between the composition, structure, and solubility of polymer conjugates that might benefit the understanding of their biochemical characteristics and their design for functional material applications.

Photocatalytic Active Nanoporous Carbon/ZnO Hybrid Materials from Block Copolymer Tethered ZnO Nanocrystals

Severe water pollution issues present an important contemporary challenge that drives the development and advancement of efficient and environmentally benign photocatalysts that enable the degradation of pollutants upon visible light irradiation. One example is zinc oxide/carbon (ZnO/C) hybrid materials that have been shown to be effective photocatalysts. To maximize the effectiveness of ZnO/C hybrids, materials with high accessible surface area of ZnO are required. Here, a novel strategy is presented to enable the synthesis of fine dispersions of ZnO nanoparticles within a porous carbon matrix. The synthesis entails the grafting of ZnO nanparticles with polystyrene-b-poly(styrene-co-acrylonitrile) (PS-b-PSAN) block copolymer and subsequent pyrolysis of the material under inert gas (N2) atmosphere. During the pyrolysis process, the PS block effectively prevents agglomeration of ZnO particles, thus resulting in a fine dispersion of ZnO nanocrystals within a prorous C matrix. Materials are found to exhibit a dye adsorption capacity of 125 mg g-1 (from a methylene blue aqueous solution with a concentration of 305 mg L-1) and dye degradation rate constant of 0.021 min-1. The significant increase of effective surface area and degradation efficacy (as compared to ZnO/C synthesized by the pyrolysis of binary PSAN/ZnO blends) is rationalized as a consequence of the increased porosity that promotes dye adsorption and transport within the hybrid material.

Interpretation of small-angle scattering of block copolymer/nanoparticle blends using random phase approximation

The scattering characteristics of block copolymer (BCP)/nanoparticle (NP) blend systems are analyzed in the weak segregation limit using random phase approximation (RPA). The scattering function is established and shown to adequately capture reported data of small-angle neutron scattering in poly(norbornene-b -d-norbornene dicarboxylic acid)/ Fe3O4 nanoparticle blend systems over the entire small-angle range for a variety of BCP and NP compositions. Besides predicting the relevant length scales of microstructure formation, the RPA analysis reveals the increase of segregation in the BCP system upon NP addition. The insight into the thermodynamics of microstructure formation in BCP/NP blend systems that is provided by the RPA analysis should be a valuable asset for the design of BCP-based microstructured hybrid materials with predetermined structure and properties.Graphical abstract