Film dynamics and lubricant depletion by droplets moving on lubricated surfaces

Lubricated surfaces have shown promise in numerous applications where impinging foreign droplets must be removed easily; however, before they can be widely adopted, the problem of lubricant depletion, which eventually leads to decreased performance, must be solved. Despite recent progress, a quantitative mechanistic explanation for lubricant depletion is still lacking. Here, we first explained the shape of a droplet on a lubricated surface by balancing the Laplace pressures across interfaces. We then showed that the lubricant film thicknesses beneath, behind, and wrapping around a moving droplet change dynamically with droplet's speed---analogous to the classical Landau-Levich-Derjaguin problem. The interconnected lubricant dynamics results in the growth of the wetting ridge around the droplet, which is the dominant source of lubricant depletion. We then developed an analytic expression for the maximum amount of lubricant that can be depleted by a single droplet. Counter-intuitively, faster moving droplets subjected to higher driving forces deplete less lubricant than their slower moving counterparts. The insights developed in this work will inform future work and the design of longer-lasting lubricated surfaces

Magnetic nanocomposites at microwave frequencies

Most conventional magnetic materials used in the electronic devices are ferrites, which are composed of micrometer-size grains. But ferrites have small saturation magnetization, therefore the performance at GHz frequencies is rather poor. That is why functionalized nanocomposites comprising magnetic nanoparticles (e.g. Fe, Co) with dimensions ranging from a few nm to 100 nm, and embedded in dielectric matrices (e.g. silicon oxide, aluminium oxide) have a significant potential for the electronics industry. When the size of the nanoparticles is smaller than the critical size for multidomain formation, these nanocomposites can be regarded as an ensemble of particles in single-domain states and the losses (due for example to eddy currents) are expected to be relatively small. Here we review the theory of magnetism in such materials, and we present a novel measurement method used for the characterization of the electromagnetic properties of composites with nanomagnetic insertions. We also present a few experimental results obtained on composites consisting of iron nanoparticles in a dielectric matrix.Comment: 20 pages, 10 figures, 5 table

Europe’s Care Regimes and the Role of Migrant Care Workers Within Them

This paper is an examination of the recent restructuring and subsequent convergence of European long-term care models. This paper also aims to highlight the increased role of migrant care workers and the need for great social and governmental recognition for all care providers. The provision of long term care is complex, divided between state, market and family providers; the state alone could not and does not act as the sole provider of care (Banks 1998). The extent to which different sectors are relied upon is largely dependent on the ideology of the country's welfare state (Timonen and Doyle 2007)

A Coarse-grained Model for Aqueous Two-phase Systems: Application to Ferrofluids

Aqueous two-phase systems (ATPSs), that is, phase-separating solutions of water soluble but mutually immiscible molecular species, offer fascinating prospects for selective partitioning, purification, and extraction. Here, we formulate a general Brownian dynamics based coarse-grained simulation model for a polymeric ATPS comprising two water soluble but mutually immiscible polymer species. A third solute species, representing, e.g., nanoparticles (NPs), additional macromolecular species, or impurities can readily be incorporated into the model. We demonstrate that the model captures satisfactorily the phase separation, partitioning, and interfacial properties of a model ATPS composed of a polymer mixture of dextran and polyethylene glycol (PEG) in which magnetic NPs selectively partition into one of the two polymeric phases. The NP partitioning is characterized both via the computational model and experimentally under different conditions. The simulation model captures the trends observed in the experiments and quantitatively links the partitioning behavior to the component species interactions. Finally, the response of the simulation model to external magnetic field, with the magnetic NPs as the additional partitioned component, shows that the ATPS interface fluctuations can be controlled by the magnetic field at length scales much smaller than those probed experimentally to date