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Computational optimization of synthetic water channels

Rempe, Susan; Rogers, David M.

Membranes for liquid and gas separations and ion transport are critical to water purification, osmotic energy generation, fuel cells, batteries, supercapacitors, and catalysis. Often these membranes lack pore uniformity and robustness under operating conditions, which can lead to a decrease in performance. The lack of uniformity means that many pores are non-functional. Traditional membranes overcome these limitations by using thick membrane materials that impede transport and selectivity, which results in decreased performance and increased operating costs. For example, limitations in membrane performance demand high applied pressures to deionize water using reverse osmosis. In contrast, cellular membranes combine high flux and selective transport using membrane-bound protein channels operating at small pressure differences. Pore size and chemistry in the cellular channels is defined uniformly and with sub-nanometer precision through protein folding. The thickness of these cellular membranes is limited to that of the cellular membrane bilayer, about 4 nm thick, which enhances transport. Pores in the cellular membranes are robust under operating conditions in the body. Recent efforts to mimic cellular water channels for efficient water deionization produced a significant advance in membrane function. The novel biomimetic design achieved a 10-fold increase in membrane permeability to water flow compared to commercial membranes and still maintained high salt rejection. Despite this success, there is a lack of understanding about why this membrane performs so well. To address this lack of knowledge, we used highperformance computing to interrogate the structural and chemical environments experienced by water and electrolytes in the newly created biomimetic membranes. We also compared the solvation environments between the biomimetic membrane and cellular water channels. These results will help inform future efforts to optimize and tune the performance of synthetic biomimetic membranes for applications in water purification, energy, and catalysis.

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TYPE SAND Report YEAR 2012
DOIOSTI

Irreversible thermodynamics

Journal of Physics: Conference Series

Rogers, David M.; Rempe, Susan

We present a maximum-entropy theory of mesoscopic kinetics. The theory gives fully nonlinear nonequilibrium thermodynamic relationships and has no explicit requirement for either microscopic bath variables, an equilibrium energy, or an equilibrium partition function. The entropy maximization process is instead carried out over transition probability distributions with constraints on particle position and velocity updates. The Lagrange multipliers for these constraints express the instantaneous temperature and pressure of external (or microscopic) thermostatic driving systems, with which the distinguished system may or may not eventually reach equilibrium. We show that the analogues of the Gibbs-Maxwell relations and free energy perturbation techniques carry over to fluctuation-dissipation theorems and nonequilibrium ensemble reweighting techniques as should be expected. The result is a fully time-dependent, non-local description of a nonequilibrium ensemble coupled to reservoirs at possibly time-varying thermostatic or mechanical states. We also show that the thermodynamic entropy production extends the generalized fluctuation theorem through the addition of an instantaneous information entropy term for the end-points, leading to a concise statement of the second law of thermodynamics. © Published under licence by IOP Publishing Ltd.

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TYPE Conference YEAR 2012
OSTIScopus
Results 126–150 of 189
Results 126–150 of 189