Spatial inhomogeneities in emulsion polymerizations: Repulsive wall calculations

The extent of the spatially inhomogeneous distribution of polymer particles in a latex formed by emulsion polymerization, dictated by thermodynamic considerations, is investigated computationally. Polymer chains suffer a loss of freedom near the particle surface, causing an entropic repulsion away from the surface and so favoring enhanced monomer concentration near the surface and thus polymerization by encapsulation. Thermodynamic calculations of the equilibrium polymer segment density distribution within a swollen latex particle show that while substantial entropic repulsions do occur, these are countered at higher polymer concentrations by polymer crowding effects. These calculations are performed using the iterative convolution technique to evaluate the segment-segment and segment-boundary correlations, corroborated where practicable with Monte Carlo calculations. This technique represents an advance over previous work which neglected polymer excluded-volume effects. Although the calculations were for low polymer fraction, trends from the results show that repulsive wall effects are highly unlikely to give rise to any significant inhomogeneities in latex particles formed from emulsion homopolymerization in conventional systems