Surface Polaron Effect on the Ion Transfer across the Interface of Two Immiscible Electrolytes

An ion disposed near the interface of two immiscible liquids creates a protrusion of one solvent into the other, subject to hydrophobic or hydrophilic interaction with these solvents. Due to a finite relaxation time the protrusion may not be able to spontaneously follow the ion when it moves across the interface. This, as well as any improper thermal fluctuation of the protrusion, will cause slowdown of the ion transfer. Here we present the results of theoretical analysis in which the stochastic motions of the ion and protrusion are coupled and considered on the same footing. We show that if the equilibrium electrochemical potential for the ion has no barrier, the ion transport is purely diffusional with D _eff = k _B T/{6[r + (4/3)(h _max/)² L]} being the effective diffusion coefficient. Here, is the average viscosity of the liquids, r is the Stokes radius of an ion, L and h _max are the average lateral size and the maximal height of the protrusion, and is the half-width of the function h _eq(z) which characterizes the equilibrium ion-interface coupling [h _eq(z) is the height of the protrusion for a given distance of the ion to the unperturbed interface, if the ion had been infinitely slowly moving]. This function could be obtained from model calculations or molecular dynamic simulations. The second term in the denominator is the one that causes the slowdown of ion transfer across the interface. This expression can easily rationalize an order of magnitude slowdown, but hardly much more than that. This is not inconsistent with recent more careful claims on the true scale of the observed effect. Otherwise, one should invoke models that rest on the existence of the barrier in the electrochemical potential.     

Stabilizing stick-slip friction

Even the most regular stick-slip frictional sliding is always stochastic, with irregularity in both the intervals between slip events and the sizes of the associated stress drops. Applying small-amplitude oscillations to the shear force, we show, experimentally and theoretically, that the stick-slip periods synchronize. We further show that this phase locking is related to the inhibition of slow rupture modes which forces a transition to fast rupture, providing a possible mechanism for observed remote triggering of earthquakes. Such manipulation of collective modes may be generally relevant to extended nonlinear systems driven near to criticality.     

Quantum theory of adsorption of isolated adatoms

Various trends in the development of modern quantum-mechanical theory of absorption of isolated adatoms on the surface of crystals are considered. Particular attention is given to the generalization of Anderson's adsorption model and to the studies concerned with its substantiation with the use of the equations of the Lippman-Schwinger type.It is shown that different equilibrium and nonequilibrium processes arising due to adsorption can be described by means of a finite number of microscopic parameters.The applications of the theory to the thermodynamics of adsorption and its dynamic manifestations in field-emission, modulation spectroscopy and some other processes are discussed.     

Investigation of thermal plasma generator of technological function

Experimental results on energy characteristics of electric-arc plasma generator for heating technical nitrogen with the power of up to 500 kW are presented. The features of arc discharge glow, thermal efficiency, and service life of the electrodes were determined under the regime of melting the metallurgical raw material in the test plasma electric furnace.     

The escape of a particle from a driven harmonic potential to an attractive surface

We investigate theoretically the dynamics of a colloidal particle, trapped by optical tweezers, which gradually approaches an attractive surface with a constant velocity until it escapes the trap and jumps to the surface. We find that the height of the energy barrier in such a colloid-surface system follows the scaling DeltaE proportional, variant(z(0)(t)-const)(32) when the trap approaches the surface, z(0)(t) being the trap surface distance. Using this scaling we derive equations for the probability density function of the jump lengths, for the velocity dependence of its mean and most probable values, and for the variance. These can be used to extract the parameters of the particle-surface interaction from experimental data.     

Friction through dynamical formation and rupture of molecular bonds

We introduce a model for friction in a system of two rigid plates connected by bonds (springs) and experiencing an external drive. The macroscopic frictional properties of the system are shown to be directly related to the rupture and formation dynamics of the microscopic bonds. Different regimes of motion are characterized by different rates of rupture and formation relative to the driving velocity. In particular, the stick-slip regime is shown to correspond to a cooperative rupture of the bonds. Moreover, the notion of static friction is shown to be dependent on the experimental conditions and time scales. The overall behavior can be described in terms of two Deborah numbers.     

Slow cracklike dynamics at the onset of frictional sliding

We propose a friction model which incorporates interfacial elasticity and whose steady state sliding relation is characterized by a generic nonmonotonic behavior, including both velocity weakening and strengthening branches. In 1D and upon the application of sideway loading, we demonstrate the existence of transient cracklike fronts whose velocity is independent of sound speed, which we propose to be analogous to the recently discovered slow interfacial rupture fronts. Most importantly, the properties of these transient inhomogeneously loaded fronts are determined by steady state front solutions at the minimum of the sliding friction law, implying the existence of a new velocity scale and a "forbidden gap" of rupture velocities. We highlight the role played by interfacial elasticity and supplement our analysis with 2D scaling arguments.