Electrical charging of parallel plates confining a model ionic liquid down to nanoscale distances yields a variety of charge-induced changes in the structural features of the confined film. That includes even-odd switching of the structural layering and charging-induced solidification and melting, with important changes of local ordering between and within layers, and of squeezout behavior. By means of molecular dynamics simulations, we explore this variety of phenomena in the simplest charged Lennard-Jones coarse-grained model including or excluding the effect a neutral tail giving an anisotropic shape to one of the model ions. Using these models and open conditions permitting the flow of ions in and out of the interplate gap, we simulate the liquid squeezout to obtain the distance dependent structure and forces between the plates during their adiabatic approach under load. Simulations at fixed applied force illustrate an effective electrical pumping of the ionic liquid, from a thick nearly solid film that withstands the interplate pressure for high plate charge to complete squeezout following melting near zero charge. Effective enthalpy curves obtained by integration of interplate forces versus distance show the local minima that correspond to layering and predict the switching between one minimum and another under squeezing and charging.

Mechanical vibrations are known to affect frictional sliding and the associated stick-slip patterns causing sometimes a drastic reduction of the friction force. This issue is relevant for applications in nanotribology and to understand earthquake triggering by small dynamic perturbations . We study the dynamics of repulsive particles confined between a horizontally driven top plate and a vertically oscillating bottom plate. Our numerical results show a suppression of the high dissipative stick-slip regime in a well defined range of frequencies that depends on the vibrating amplitude, the normal applied load, the system inertia and the damping constant. We propose a theoretical explanation of the numerical results and derive a phase diagram indicating the region of parameter space where friction is suppressed. Our results allow to define better strategies for the mechanical control of friction.PACS numbers: 81.40. Pq, 46.55.+d, 68.35.Af, Natural or artificially induced manipulations by small mechanical vibrations, when applied at suitable frequency and amplitude ranges, may help in driving a contacting sliding interface out of its potential energy minima, thus increasing considerably surface mobility and diffusion, and reducing friction. This has been shown experimentally for sliding of nanoscale contacts through, e.g., the atomic force microscope [1,2,3], and in computer simulations via extended molecular dynamics [4] and simple modeling approaches [5,6,7]. On a larger scale, it has been observed that in sheared granular media experiments the stick slip behavior is significantly perturbed by tiny transverse vibrations [8,9]. Since geological faults are often filled with a granular gouge, these results might be relevant to understand earthquake triggering by low amplitude seismic waves [10]. Despite these promising numerical and experimental contributions, a quantitative theory accounting for the friction dependence on vibrations is still lacking.In this letter, we study the frictional properties of a two dimensional set of repulsive particles confined between two rigid plates (see Fig.1) [11,12]. The top plate is attached to a spring that is pulled at constant velocity, while the bottom FIG. 1: Sketch of the system, with the rigid top and bottom plates indicated in black and the confined particles in red. The top is dragged through a spring of elastic constant K moving at constant velocity Vext, while the bottom vibrates vertically with frequency ω0 and amplitude A plate is vibrated vertically. Without vibration, the top plate would slide exhibiting a characteristic stick-slip behavior. Vibrations induce a drastic reduction of the friction coefficient and a suppression of the stick-slip behavior, but only in a well defined frequency range. We propose a theoretical argument to explain this behavior and construct a phase diagram indicating the parameter region for which friction is suppressed. The theoretical results are in excellent quantitative agreement with numerical simulations. Finally, we investigate the fr...

Electroporation of in-vitro cultured cells is widely used in biological and medical areas to deliver molecules of interest inside cells. Since very high electric fields are required to electroporate the plasma membrane, depending on the geometry of the electrodes the required voltages can be very high and often critical to cell viability. Furthermore, in traditional electroporation configuration based on planar electrodes there is no a priori certain feedback about which cell has been targeted and delivered and the addition of fluorophores may be needed to gain this information. In this study we present a nanofabricated platform able to perform intracellular delivery of membrane-impermeable molecules by opening transient nanopores into the lipid membrane of adherent cells with high spatial precision and with the application of low voltages (1.5–2 V). This result is obtained by exploiting the tight seal that the cells present with 3D fluidic hollow gold-coated nanostructures that act as nanochannels and nanoelectrodes at the same time. The final soft-electroporation platform provides an accessible approach for controlled and selective drug delivery on ordered arrangements of cells.

The onset of frictional motion for elastic sliders with extended rough surfaces is governed by the rupture dynamics of the interfacial contacts. In these systems significant variations of static friction coefficient have been found for the same materials. Here we propose a model for understanding how and why the values of static friction coefficient can vary within wide limits. We establish a relationship between measured values of static friction and preslip stress profiles at the frictional interface and predict how the range of variation of the static friction depends on material properties and on the size of the slider.