Pair diffusion, hydrodynamic interactions, and available volume in dense fluids

Mittal, Jeetain; Hummer, Gerhard

doi:10.1063/1.4732515

Cited by 20 publications

(24 citation statements)

References 32 publications

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“…In particular, recent work has highlighted the importance of including the solvent coordinate, N, in describing the kinetics of hydrophobically driven collapse and assembly (49)(50)(51)59). Our results show that water density fluctuations stabilize nonclassical pathways, which reduce the barriers along the N coordinate, and should therefore enhance the kinetics of dewetting-mediated biophysical phenomena.…”

Section: Discussion and Outlookmentioning

confidence: 99%

Pathways to dewetting in hydrophobic confinement

Remsing

Vembanur

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

107

136

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Liquid water can become metastable with respect to its vapor in hydrophobic confinement. The resulting dewetting transitions are often impeded by large kinetic barriers. According to macroscopic theory, such barriers arise from the free energy required to nucleate a critical vapor tube that spans the region between two hydrophobic surfaces-tubes with smaller radii collapse, whereas larger ones grow to dry the entire confined region. Using extensive molecular simulations of water between two nanoscopic hydrophobic surfaces, in conjunction with advanced sampling techniques, here we show that for intersurface separations that thermodynamically favor dewetting, the barrier to dewetting does not correspond to the formation of a (classical) critical vapor tube. Instead, it corresponds to an abrupt transition from an isolated cavity adjacent to one of the confining surfaces to a gap-spanning vapor tube that is already larger than the critical vapor tube anticipated by macroscopic theory. Correspondingly, the barrier to dewetting is also smaller than the classical expectation. We show that the peculiar nature of water density fluctuations adjacent to extended hydrophobic surfacesnamely, the enhanced likelihood of observing low-density fluctuations relative to Gaussian statistics-facilitates this nonclassical behavior. By stabilizing isolated cavities relative to vapor tubes, enhanced water density fluctuations thus stabilize novel pathways, which circumvent the classical barriers and offer diminished resistance to dewetting. Our results thus suggest a key role for fluctuations in speeding up the kinetics of numerous phenomena ranging from Cassie-Wenzel transitions on superhydrophobic surfaces, to hydrophobically driven biomolecular folding and assembly.capillary evaporation | fluctuations | kinetic barriers | assembly T he favorable interactions between two extended hydrophobic surfaces drive numerous biomolecular and colloidal assemblies (1-5), and have been the subject of several theoretical, computational, and experimental inquiries (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22). Examples include the association of small proteins to form multimeric protein complexes, of amphiphlic block copolymers, dendrimers, or proteins to form vesicular suprastructures, and of patchy colloidal particles into complex crystalline lattices (23-27). When two such hydrophobic surfaces approach each other, water between them becomes metastable with respect to its vapor at a critical separation, d c , that can be quite large (8,9,(28)(29)(30). For nanometer-sized surfaces at ambient conditions, d c is proportional to the characteristic size of the hydrophobic object, whereas for micron-sized and larger surfaces, d c ∼ 1 μm (29, 30). However, due to the presence of large kinetic barriers separating the metastable wet and the stable dry states, the system persists in the wet state, and a dewetting transition is triggered only at much smaller separations (∼ 1 nm) (13,22,28,30).To uncover the mechanism of dewetting, a numbe...

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Section: Discussion and Outlookmentioning

confidence: 99%

Pathways to dewetting in hydrophobic confinement

Remsing

Vembanur

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

107

136

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“…17,30,31 BI analysis follows a method that was reported previously for a system with dynamical behavior captured adequately by a single order parameter, which was clearly physically justified. 30,32,33 Although Smoluchowski-equation coefficients can also be obtained via linear fits to short time slopes of the average and variance of order parameter displacements, 22 this approach is not viable when short time linear regions do not exist in displacement data. 30 BI does not suffer from these shortcomings and is used in the present work.…”

Section: Two-dimensional Master Equation and Bayesian Inference Analysismentioning

confidence: 99%

Colloidal cluster crystallization dynamics

Beltran-Villegas

Sehgal

Maroudas

et al. 2012

The Journal of Chemical Physics

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The crystallization dynamics of a colloidal cluster is modeled using a low-dimensional Smoluchowski equation. Diffusion mapping shows that two order parameters are required to describe the dynamics. Using order parameters as metrics for condensation and crystallinity, free energy, and diffusivity landscapes are extracted from brownian dynamics simulations using bayesian inference. Free energy landscapes are validated against Monte Carlo simulations, and mean first-passage times are validated against dynamic simulations. The resulting model enables a low-dimensional description of colloidal crystallization dynamics.

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“…The long-range nature of hydrodynamic interactions makes them difficult to be dealt with but also extraordinarily interesting. Many efforts have been made in measuring concentration dependence of the hydrodynamic interaction by its influence on the diffusion coefficient [15,16]. For dilute suspensions, the hydrodynamic interaction decays fast with particle distances.…”

Section: Introductionmentioning

confidence: 99%

Two dimensional colloidal crystals formed by particle self-assembly due to hydrodynamic interaction

Huo

Zhang

2015

Colloid Polym Sci

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Aggregation and crystallization of colloidal particles deposited from suspensions on glass surfaces were studied. Trajectories of individual particles are tracked and recorded. Statistics over large amount of particles were made to measure the mean square displacement (MSD), , as functions of time, t. Isolated particles diffuse normally along the solid surface in a two dimensional random manner. A power law of ~t α is obeyed both by short and long time scale MSDs of particles with neighbors. However, the exponent values are quite different. When the particle area fraction f≤ 80 %, the particles diffuse normally at the short time scale with a retarded diffusion coefficient. While at the long time scale, a superdiffusive behavior of the particles is detected due to collective motion of particles. When f>80 %, a spatial confinement effect shows in addition. The retarded particle dynamics and the collective particle movements both originate from the many-body hydrodynamic interaction enhanced by the quasitwo dimensional geometric conditions due to the existence of the substrate and the neighbor particles. If the substrate surface condition is favorable and the hydrodynamic interaction dominates, the long-range hydrodynamic interaction can lead particles in dense particle aggregations to self-assemble into long particle chains. This chaining behavior finally results in a phase transition taking place gradually over a large range of the particle area fraction.

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Pair diffusion, hydrodynamic interactions, and available volume in dense fluids

Cited by 20 publications

References 32 publications

Pathways to dewetting in hydrophobic confinement

Pathways to dewetting in hydrophobic confinement

Colloidal cluster crystallization dynamics

Two dimensional colloidal crystals formed by particle self-assembly due to hydrodynamic interaction

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