Deuteration Effects on Micellization, Crystallization and Melting of Styrene-block-Butadiene Copolymers in Dilute Near-Critical Solutions

University Of Wyoming, Laramie WY

Investigators

Abstract

NSF/CTS/Radosz CTS-0625338 Project Abstract /Summary Deuteration Effects on Micellization, Crystallization and Melting of Styrene-block- Butadiene Copolymers in Dilute Near-Critical Solutions University of Wyoming The goal of this one-year nano-related project is to explore the phase behavior of deuterated styrene-block-diene copolymers in dilute near-critical solutions, where the solvent is a compressed fluid used either below or above its critical temperature. The micellar order-disorder (ODT) transitions of blocky polymers in such near-critical solutions can be induced not only by increasing temperature, which leads to critical micelle temperature, but also by increasing pressure, which leads to critical micelle pressure. All such pressure-induced transitions in dilute near-critical solutions, including micellization, crystallization, melting, and fluid-liquid transitions (cloud points), are fast, reproducible, and easy to detect accurately, often in contrast to the sluggish transitions induced by heating and cooling in concentrated solutions, melts and blends. This is because polymer solutions in near-critical solvents have low viscosity and high diffusion rates. Therefore, such solutions offer a robust and efficient approach to characterizing micellization and crystallization of deuterated polymer samples used for neutron scattering studies, where deuteration is needed to enhance the contrast. The experimental aspect of this work is to characterize cloud-point separation, crystallization, melting, and micellization of deuterated and non-deuterated pairs of otherwise identical styreneblock- diene samples, such as polystyrene-b-polybutadiene (PS-b-PBD), with variable 1,2/1,4 addition and variable crystallizability (obtained by complete or partial hydrogenation of the 1,4-rich samples only). These phase and micellar transitions in supercritical propane and propylene will be determined from high-pressure dynamic light scattering in the Soft Materials Laboratory at the University of Wyoming. The copolymer samples will be synthesized via living anionic polymerization in the Center for Nanophase Materials Sciences at Oak Ridge National Laboratory. The intellectual merit of the proposed work lies in unique experimental results that will help understand differences in micellization, crystallization, and melting caused by deuteration. Broader Impact. This project will educate students in characterizing self assembling molecules that lead to nanostructured materials. These students will not only be exposed to the experimental characterization methods in the PI's lab, but also to the synthesis and neutron scattering facilities at the Oak Ridge National Laboratory. Furthermore, the high-pressure dynamic light scattering method of characterizing micellar solutions of blocky polymers will be incorporated in the graduate and undergraduate thermodynamics and polymer science classes. This project will also indirectly contribute to the micelle-based nanoparticle recovery technology, such as freeze-dry recovery, for example, by providing basic understanding how to recover dry micelles from near-critical solvents without having to freeze the solvent, which is relevant to manufacturing drug and gene delivery nanoparticles.