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Fall 2016 Seminars

August 22, 2016
August 29, 2016Developing a fluctuating lattice Boltzman method for the diffusion equationKyle Strand
September 5, 2016<Labour Day>
September 12, 2016
September 19, 2016Analytical and numerical approach to cyclic diffusion Aaron Feickert

September 26, 2016

Lattice Boltzmann with collision operator derived from Molecular DynamicReza Parsa
October 3, 2016TBAAlan Denton
October 10, 2016TBA Guilherme Volpe Bossa
October 17, 2016TBAKent Ridl
October 24, 2016TBADayton Jon Vogel
October 31, 2016TBADeyan Mihaylov
November 7, 2016TBASylvio May
November 14, 2016
November 21, 2016

November 28, 2016

December 5, 2016
December 12, 2016<Exam Week!>



Role of ion hydration for the differential capacitance of an electric double layer

Guilherme Bossa

Graduate Student,
Department of Physics,
North Dakota State University,


Monday October 10, 3:00-4:00pm.

221 South Engineering,

In this talk we use Monte Carlo simulations and various Mean-Field models to investigate the influence of soft, hydration-mediated ion-ion and ion-surface interactions on the differential capacitance of an electric double layer. We focus on a planar electrode surface at physiological concentration of monovalent ions in a uniform dielectric background. Hydration-mediated interactions are modeled on the basis of Yukawa potentials that add to the Coulomb and excluded volume interactions between ions. We present a mean-field model that includes hydration-mediated anion-anion, anion-cation, and cation-cation interactions of arbitrary strengths. In addition, finite ion sizes are accounted for through excluded volume interactions, described either on the basis of the Carnahan-Starling equation of state or using a lattice gas model. Both our Monte Carlo simulations and mean-field approaches predict a characteristic double-peak (the so-called camel shape) of the differential capacitance; its decrease reflects the packing of the counterions near the electrode surface. The presence of hydration-mediated ion-surface repulsion causes a thin charge-depleted region close to the surface, which is reminiscent of a Stern layer. We analyze the interplay between excluded volume and hydration-mediated interactions on the differential capacitance and demonstrate that for small surface charge density our mean-field model based on the Carnahan-Starling equation is able to capture the Monte Carlo simulation results. In contrast, for large surface charge density the mean-field approach based on the lattice gas model is preferable.

Thermal and Structural Properties of Microgel Suspensions

Alan Denton

Associate Professor,
Department of Physics,
North Dakota State University,


Monday October 3, 3:00-4:00pm.

221 South Engineering,

Microgels are microscopic gel particles that become swollen when dispersed in a solvent.  The equilibrium size of a microgel is governed by a balance of osmotic pressures, which can be tuned by varying single-particle properties and externally controlled conditions, such as temperature, pH, ionic strength, and concentration.  Because of their tunable size and ability to encapsulate dye or drug molecules, these soft colloidal particles have practical relevance for biosensing, drug delivery, carbon capture, and filtration.  Combining theory and simulation for a model of elastic, compressible particles, we demonstrate that, with increasing concentration, ionic microgels can deswell due to a redistribution of counterions, while nonionic microgels deswell due to steric interparticle interactions.  We further explore consequences of size polydispersity for the structure and thermodynamic phase behavior of microgel suspensions.

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Last Updated: Monday, October 10, 2016 2:00:11 PM
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