Switching wetting morphologies in triangular grooves

Static wetting morphologies in grooves with triangular cross section are studied here. Using the electrowetting effect, we can switch between different equilibrium morphologies and transport liquid along prefabricated grooves. The particular filling and drainage behavior in triangular grooves is discussed in terms of the groove geometry.     

Surface plasmon enhanced transient thermoreflectance

It is shown that optically excited surface plasmons can be used for measurements of the surface temperature of a metal with nanosecond time resolution. This method is closely related to transient thermoreflectance, but its sensitivity is considerably higher. We give a survey on the mechanisms involved, briefly discussing the dependence on the sample properties. Experimental confirmation of the proposed sensitivity enhancement as well as the time resolution is presented.     

Dynamics of wet granular matter

Recent advances in understanding model systems of wet granular materials are presented, with particular emphasis on statistical concepts, dynamics, and phase transitions. It is demonstrated that although wet granular systems are quite complex, their main features may be understood on the basis of rather simple concepts. The significance of these systems for investigating fundamental problems of non-equilibrium dynamics are shortly discussed.     

Wetting, spreading, and adsorption on randomly rough surfaces

The wetting properties of solid substrates with customary (i.e., macroscopic) random roughness are considered as a function of the microscopic contact angle of the wetting liquid and its partial pressure in the surrounding gas phase. Analytic expressions are derived which allow for any given lateral correlation function and height distribution of the roughness to calculate the wetting phase diagram, the adsorption isotherms, and to locate the percolation transition in the adsorbed liquid film. Most features turn out to depend only on a few key parameters of the roughness, which can be clearly identified. It is shown that a first-order transition in the adsorbed film thickness, which we term "Wenzel prewetting", occurs generically on typical roughness topographies, but is absent on purely Gaussian roughness. It is thereby shown that even subtle deviations from Gaussian roughness characteristics may be essential for correctly predicting even qualitative aspects of wetting.     

Free cooling of the one-dimensional wet granular gas

The free cooling behavior of a wet granular gas is studied in one dimension. We employ a particularly simple model system in which the interaction of wet grains is characterized by a fixed energy loss assigned to each collision. Macroscopic laws of energy dissipation and cluster formation are studied on the basis of numerical simulations and mean-field analytical calculations. We find a number of remarkable scaling properties which may shed light on earlier unexplained results for related systems.     

Dissipation mechanisms in ionic liquids

The spreading of ionic liquids on molecularly smooth solid surfaces has been little studied in the past. We show that the spreading behaviors of the two ionic liquids, [EMIM] ethyl sulfate and ECOENG™ 500, are well described by the combined molecular kinetic and hydrodynamic model of de Ruijter, de Coninck, and Oshanin [M.J. de Ruijter, J. de Coninck, G. Oshanin, Langmuir 15 (1999) 2209] with reasonable values for the molecular friction coefficient ζ, molecular displacement λ, and frequency K₀ associated with contact line motion, as well as reasonable values for the microscopic cutoff a associated with hydrodynamic dissipation.     

Universal and non-universal aspects of wet granular matter under vertical vibrations

The phase diagram of vertically vibrated wet granular matter is investigated by both experiments and molecular dynamics type simulations, with a focus on the coexistence regime of the fluid and gas phases. Phase diagrams measured at various parameters including the rupture energy of liquid bridges, are presented. While for elastic grains, the transition from the fluid to the fluid-gas coexistence phase is found to be determined only by the rupture energy of liquid bridges [Fingerle et al. New J. Phys. 10, 053020 (2008)], inelasticity is found to introduce non-universal features into the phase diagram, which are also affected by the grain size.