(2fs) Controlling Self-Assembled Block Copolymer Morphologies for Tailored Performance

Block copolymers (BCPs) are an extremely versatile class of self-assembling material which are used as commodity thermoplastics and extensively studied as advanced functional materials. Advances in synthetic chemistry have allowed the tailoring of block chemistries and architectures for a given application. However, the grand challenge remains in understanding the rules governing the self-assembly process and correlating the nanoscale structure to macroscale properties. My PhD work has focused on understanding the thermodynamics and kinetics of self-assembly process in different block-copolymer systems with the goal of designing materials with tailored performance. Two of the projects are outlined here:

Structure-property relationships of block copolymer elastomers with interaction tuned additives:

In this work a systematic interrogation was conducted on how enthalpic and entropic interactions of polymeric additives impacts specific mechanical properties such as modulus, creep behavior and toughness of poly(styrene-b-ethylene butylene-b-styrene) (SEBS), a widely studied BCP elastomer. The additives are linear poly(methyl methacrylate-co-cyclohexyl methacrylate) (PrC) and linear polystyrene (PS). PrC is enthalpically compatible with the glassy polystyrene domain of SEBS over a range of copolymer composition, while PS is an athermal additive. Entropic effects that contribute to miscibility was controlled by varying the molecular weight of the additives. The structure and phase behavior of blends studied using Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM) revealed that the attractive PS/PrC interaction as well as the molecular weight of additives have a huge impact on the additive distribution in the glassy domain, morphology, and phase behavior of the blend which in turn impacts the mechanical properties of the blend. In-situ SAXS experiments during tensile deformation was used to study how the self-assembled structure of unoriented lamellar domains changes under applied strain. This study provides an insight on designing polymeric additives for tailoring structure and mechanical properties of BCP elastomers.

Process dependent ordering of sulfonated block copolymer domains:

Solution-cast films of ionic block copolymers are investigated for applications as membranes for water purification, gas separations, and fuel cells. The morphology and ordering of block domains tailors the transport pathways in these membranes. A major challenge with solvent processing is understanding how process variables during casting will influence the final film morphology. In this work the effect of solvent quality and casting method on the structure of the casting solution and final dry film of a sulfonated block copolymer was investigated. SAXS and TEM analysis were used to identify the process parameters that determine the kinetics of self-assembly in solution and film structure formed after drying. Grazing transmission SAXS studies were used to identify how structural anisotropy is formed in solvent processed films, which would greatly impact directional transport properties.

Research Interests:

My research interest broadly lies in understanding molecular level physics of polymer systems and developing characterization techniques to elucidate structure-processing-property relationships. My areas of experience and interests include self-assembly in soft materials, process based structures in polymeric systems, X-ray scattering and reflectivity techniques, complex-fluid rheology, thermodynamics of polymer blends, mechanics of elastomers, ion-transport in polymers, polymer crystal structures and crystallization kinetics.