A Simulation Approach to Thermodynamics in Interfacial Phenomena



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Industrial applications such as production of high performance polymer-nanocomposites, semiconductor fabrication, and catalysis involve molecular level phenomena governed by interfacial interactions. Precise control of these interactions will leverage the performance of materials in these applications. However, the ability to tailor the molecular characteristics is hindered by incomplete understanding of the controlling factors. This dissertation is broadly divided in three parts discussing the development and application of modern computational methods to elucidate such characteristics.

In the first part, detailed atomistic simulations of polymer-nanoparticle systems are performed by coupling preferential sampling techniques with connectivity-altering Monte Carlo algorithms to address the challenges in modeling polymer melts in proximity to a solid. The results reveal that polymer architecture holds a prominent role in systems with nanoscopic particles. Furthermore, a scheme for developing coarse-grained models of polymers with specific chemistry in contact with the solid surface is presented and quantitatively evaluated. These models are necessary to address the larger length scales required for study of polymer-particle mixtures.

Interfaces and substrate interactions play an important role for increasingly thinner polymer films employed in the semiconductor industry. There is a clear need to develop predictive models capable of describing reaction-diffusion phenomena in chemically-amplified resists and analyze their performance as a function of film thickness. In this dissertation, using mesoscopic models it is found that a central aspect governing reactions is the anomalous diffusion of the photogenerated acid. The anomalous diffusion coupled with a simple second-order acid annihilation scheme quantitatively captures experimental data for all practical conditions - with only two adjustable parameters. The need to combine the developed scheme with substrate interactions is demonstrated.

Finally, the mechanism of zeolite crystal growth in solutions in the presence of growth modifiers is probed by employing atomistic simulations. It is hypothesized that molecules preferentially bind to specific crystal surfaces, which alters the crystal morphology. Using free energy calculations, the affinity of these molecules to interact with model zeolite surfaces is estimated. Distinct free energy minima and orientations of the inhibitor molecule in these minima are characterized and quantified providing a unique molecular understanding of the phenomena.



Polymers at interfaces, Interfacial phenomena, Molecular modeling, Stochastic simulations