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T D Blake

Publications and source records attributed to T D Blake.

7 recordsLinked to original sources
PubMed2005

Dynamics of imbibition into a pore with a heterogeneous surface.

We use large-scale molecular dynamics simulations to study the dynamics of liquid penetration into a cylindrical pore having a randomly heterogeneous surface comprising areas of differing wettability. Our results confirm that the equilibrium contact angle in the heterogeneous pore is well described by Cassie's law. As in the case of the uniform pore studied previously, the dynamics of penetration can be described by the Lucas-Washburn equation corrected to include the effect of a dynamic contact angle. The dissipation at the three-phase line, which gives rise to the dynamic contact angle, may be characterized in terms of a friction coefficient. Interestingly, the wetting-line friction on the heterogeneous surface also turns out to be a linear function of the fractional concentration of the areas of different wettability, analogous to Cassie's law. These results can be interpreted in terms of an independent random walk mechanism.

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PubMed2005

Spreading dynamics of chain-like monolayers: a molecular dynamics study.

Using large-scale molecular dynamics simulations, we have shown previously that the spreading dynamics of sessile drops on solid surfaces can be described in detail using the molecular-kinetic theory of dynamic wetting. Here we present our first steps in extending this approach to investigate the spreading dynamics of Langmuir-Blodgett monolayers. We make use of a monolayer model originally developed by Karaborni and Toxvaerd, but somewhat simplified to facilitate large-scale simulations. Our preliminary results are in good agreement with recent experimental observations and also support a molecular-kinetic interpretation in which the driving force for spreading is the lateral pressure in the monolayer. Away from equilibrium, initial spreading rates are constant and logarithmically dependent on pressure. However, near equilibrium, spreading is pseudo-diffusive and follows the square root of time. In both regimes the controlling factor is the equilibrium frequency of molecular displacements within the monolayer.

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PubMed2004

The possibility of different time scales in the dynamics of pore imbibition.

To model the imbibition of liquids into porous solids, use is often made of the Lucas-Washburn equation, which relates the distance of penetration of a liquid at a given time to the pore radius, the viscosity and surface tension of the liquid, and the effective contact angle between the liquid and the solid. In this paper, we extend previous large-scale molecular dynamics simulations to show how this tool can be used to study the details of liquid imbibition, including the impact of the contact angle on the dynamics of penetration and the evolution of the internal flow field. In particular, we show that the asymptotic behavior of the contact angle versus time for a completely wetting liquid is given by approximately t(-1/4).

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PubMed2003

Influence of the dynamic contact angle on the characterization of porous media.

It has been shown recently that the classical Lucas-Washburn equation, often used to model the dynamics of liquid penetration into porous media, should be modified to take account of the dynamic contact angle between the liquid and the pore. Here we show how neglect of this effect can lead to significant errors in estimation of the effective pore radius.

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PubMed2002

Dynamic wetting by liquids of different viscosity.

The velocity-dependence of the dynamic contact angle is studied experimentally for a series of water-glycerol solutions having viscosities ranging from 1.5 to 672 mPa s. The results are interpreted through a theory of dynamic wetting as an interface disappearance-formation process, with the goal to analyse the dominant microscopic mechanism by which the interface formation occurs. As is shown, an assumption that this mechanism is diffusive in nature allows one to adequately describe the whole set of experimental data. Some estimates for the phenomenological parameters of the model are obtained.

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PubMed2002

The influence of solid-liquid interactions on dynamic wetting.

The molecular-kinetic theory of dynamic wetting has been extended to take specific account of solid-liquid interactions. By equating the work of adhesion with the surface component of the specific activation free energy of wetting, equations have been derived which show the way in which solid-liquid interactions modify both the driving force and the resistance to wetting. For a liquid meniscus advancing across the surface of a solid, these two effects have opposing consequences. Thus, strong interactions increase both the driving force and the resistance, while weak interactions decrease the driving force and the resistance. Because of the form of the relationships, the two effects do not simply cancel out. As a result, the maximum rate at which a liquid can wet a solid may exhibit its own maximum at some intermediate level of interaction. Data taken from both experimental and molecular-dynamics simulations are shown to support these findings, which have significant implications for any process where wetting dynamics are important, such as coating.

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