Lateral Structuring and Stability Phenomena Induced by Block Copolymers and Core-Shell Nanogel Particles at Immiscible Polymer/Polymer Interfaces

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Title: Lateral Structuring and Stability Phenomena Induced by Block Copolymers and Core-Shell Nanogel Particles at Immiscible Polymer/Polymer Interfaces
Author: Gozen, Arif Omer
Advisors: Jan Genzer, Committee Co-Chair
Richard J. Spontak, Committee Co-Chair
Orlin Velev, Committee Member
Peter Kilpatrick, Committee Member
Abstract: We have investigated the parameters such as copolymer/nanoparticle concentration, architecture and molecular weight combined with film thickness, time and temperature in order to develop a molecular-level insight on how lateral interfacial structuring occurs at immiscible polymer/polymer interfaces. In order to develop a molecular-level understanding of how these ‘smart’ self-assembling materials and core-shell nanogel particles interact both intra- and inter-molecularly and form ordered structures in bulk, as well as at immiscible interfaces, we first focused on the response of core-shell polymer nanoparticles, designated CSNGs, composed of a cross-linked divinylbenzene core and poly(methyl methacrylate) (PMMA) arms as they segregate from PMMA homopolymer. We have demonstrated that these nanogel particles exhibit autophobic character when dispersed in high molecular weight homopolymer matrices and segregate to the interface with another fluid. We have further explored the migration of these new-generation nanogel particles (CSNG-Rs) segregating from PS homopolymer to PS/PMMA interfaces. Unlike the instability patterns observed with the CSNGs, which exhibit classical nucleation and growth mechanism with circular hole formation, we have observed an intriguing dewetting pattern and CSNG-Rs forming lateral aggregates and tentacle-like structures at the interface. In parallel with our core-shell particle studies, we have also explored the structuring of copolymer molecules that are far from equilibrium in bulk and complex laminate of polymer thin films. Our early triblock copolymer studies have proven that molecular asymmetry has a profound effect on order-disorder transition temperature. We focused primarily on the effect of the copolymer chemical composition (i.e., block sizes) on the dewetting behavior of PS/SM thin films on PMMA. We elucidate the interfacial segregation and concurrent micellization of diblock copolymers in a dynamically evolving environment with changing boundary conditions as spherical holes develop. These studies reveal that in-plane interfacial nanostructures produced by block copolymers may not always provide stabilization of the bilayer; this behavior has been attributed to the interplay between copolymer micellization and copolymer segregation at the immiscible polymer interface. Lastly, we have investigated the dewetting behavior of PS/PMMA assemblies containing compositionally varied mixtures of mirrored copolymers, such as PS50-b-PMMA10 / PS10-b-PMMA50 and PS50-b-PMMA20 / PS20-b-PMMA50. The dewetting rates of systems composed of copolymer mixtures lie between those of systems modified with the neat copolymers. This observation suggests that the dewetting behavior of the double layer with a copolymer mixture may be approximated satisfactorily by a linear rule of mixtures.
Date: 2010-03-08
Degree: PhD
Discipline: Chemical Engineering

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