Composition Dependence of the Flory-Huggins Interaction Parameter in Polymer Blends: Structural and Thermodynamic Calculations
Date of Award
Doctor of Philosophy
Bamin Khomami, Robert Counce, Dibyendu Mukherjee
Flory-Huggins Theory has been the basis for understanding polymer solvent and blended polymer thermodynamics for much of the last 60 years. Within this theory, a parameter (χ) [chi] was included to quantify the enthalpic energy of dispersion between distinct components. Thin film self-assembly of polymer melts and block copolymers depends critically on this parameter, and in application, χ has generally been assumed to be independent of the concentrations of the individual components of the system. However, Small-Angle Neutron Scattering data on isotopic polymer blends, such as polyethylene and deuterated polyethylene, have shown a roughly parabolic concentration dependency for χ. Therefore, an investigation of this concentration dependency was undertaken from both thermodynamic (χT) [chi T] and structural (χS) [chi S] theories. Thermodynamic information was obtained through thermodynamic integration with χT defined using the original Flory-Huggins theory, and structural calculations for χS were based on the Random Phase Approximation of de Gennes. Comparison of the two theories revealed that χT and χS possess unique composition dependencies; however, via an expression developed within the Random Phase Approximation involving the second derivative of the Gibbs free energy function with respect to composition, χT can be transformed into χS while sacrificing some information related to system specificity.
Having investigated the composition dependencies of χT and χS, simulations were then performed to address the effects of wavenumber selection and chain length on the observed composition dependencies of χT and χS. Lastly, simulations on a polymer melt and its corresponding diblock copolymer were completed to investigate the differences in the characteristics of their interaction parameter composition dependencies. This study was inspired due to a desire to extend the original Flory-Huggins Theory to include a composition dependency for χ, thereby producing more accurate morphological data for polymeric systems, and develop more precise methods for calculation of the interaction parameter in polymer systems.
Russell, Travis H., "Composition Dependence of the Flory-Huggins Interaction Parameter in Polymer Blends: Structural and Thermodynamic Calculations. " PhD diss., University of Tennessee, 2014.
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