Abstract
We use molecular dynamics simulations in order to investigate the time evolution of the effect of adsorbed polymer coatings on the electro-osmotic flow (EOF) in a capillary. Weakly adsorbed coatings show no time-dependent performance, but they do not strongly reduce the EOF. On the other hand, strongly adsorbed coatings made of longer polymer chains are often quenched in non-equilibrium conformations that can strongly reduce the EOF over extremely long periods of time. For intermediate adsorption strengths, we observe that the EOF increases as a function of time due to the relaxation of the coating layer. The concentration of polymers in solution and the length of the polymer chains also affect the time-dependence of the EOF. These results show that the quality of electrophoretic separations can depend on the waiting time between the formation of the coating and the beginning of the separation. We conclude by suggesting experimental tests of our predictions.
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Acknowledgments
We would like to thank Christian Holm for helpful discussion. This work was supported by the National Science and Engineering Research Council through Discovery Grants to GWS and JLH. OAH would also like to acknowledge funding from a University of Ottawa Entrance Scholarship and National Science and Engineering Research Council through the Canada Graduate Scholarship program. Sharcnet provided computational resources for this work.
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Hickey, O.A., Harden, J.L. & Slater, G.W. Computer simulations of time-dependent suppression of EOF by polymer coatings. Microfluid Nanofluid 13, 91–97 (2012). https://doi.org/10.1007/s10404-012-0944-4
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DOI: https://doi.org/10.1007/s10404-012-0944-4