We present molecular dynamics simulations of rhodamine B diffusion in various aqueous polyelectrolyte solutions. We have studied both sodium poly(styrene sulfonate) (PSS) solutions and poly(diallyldimethyl ammonium) chloride (PDDA) solutions, each with varying salt concentrations and types of salt. These simulations were undertaken to help elucidate the anomalous diffusion found experimentally in our group for these systems. These single molecule diffusion measurements using fluorescence correlation spectroscopy (FCS) indicated a complex process that could be fit only to a multi-component diffusion analysis or a stretched exponential fit. It was suspected that long-term interactions of the charged or zwitterionic dye molecule with the charged polymer chains was causing the anomalous diffusion, and the simulations presented here corroborate that. In particular, 1 microsecond simulation trajectories provide adequate reproductions of the anomalous dye diffusion and measures of the on and off rates (association and dissociation) of dye-polyelectrolyte interactions. The zwitterionic, cationic, and anionic forms of rhodamine B are studied.

Molecular dynamics simulations of small molecule diffusion in polyelectrolyte solutions

254th National Meeting (2017)

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