An attempt was made to arrange polystyrene latex particles (2, 5, and 10 microm in diameter) dispersed in aqueous media making use of their dielectrophoresis and electrophoresis with a hyperbolic quadruple electrode system. Application of a high-frequency ac field enabled the particles to arrange themselves between the electrodes forming a particle monolayer due to the negative dielectrophoretic force. Simultaneous application of high-frequency ac and dc fields caused the particles to gather in the region surrounded by the electrodes to form particle multilayers. Appropriate choice of the way of applying an electric field thus allowed the reversible control of particle arrangements (monolayer, multilayer, dispersion). Reapplication of an ac field to the particle layers produced highly dense particle multilayers.

We attempted to align a large number of silica particles dispersed in aqueous solution by controlling the alternating electric field between the two electrodes (400 microm apart). Relatively large particles (9.9 microm) were found to align forming strings in the direction parallel to the electric field while relatively small particles (2.0 and 4.9 microm) were observed to align making stripes in the direction perpendicular to the field. The number of stripes formed by particles between the electrodes increased with increasing frequency of the alternating field. This peculiar perpendicular particle alignment appeared when the contribution to particle alignment of electroosmotic flow exceeded that of dielectric polarization and the osmotic flow was found to be stronger around the particles than in the vicinity of the electrode surface.

No abstract

Unsaturated fatty acids play an important role in vivo not only as energy sources but also as main components of biomembranes (1-3). It is well known that fluidity of biomembrane is affected by its characteristic dynamic structure and is dependent on the unsaturated fatty acid, oleic acid (4-8). Oleic acid, which has a double bond at C9 position in its molecule and freely-rotating, adjacent methylene groups, is one of the representative cismonoene unsaturated fatty acids which are able to bend comparatively freely. Until recently the purity of available oleic acid is low, and there has been restriction in its study for basic physical properties as well as its application for a speciality chemical field such as pharmaceuticals, cosmetics and biosciences. In recent years however, a product where purity is 99% or greater is constantly available and there have been many reports on the analysis of its basic physical properties (9-13) as well as the basic physical properties of nonionic surfactants which are its derivatives (14-16) and its use as an enhancer of drug penetration through the skin (17-20). These studies have shown that oleic acid has a big space-filling volume (21,22) based on cis-type double 325 JOS

used in many applications such as cosmetics, agriculture, and the food industry owing to their biodegradability and low toxicity compared to chemical surfactants 8−10) . In addition to these benefits, biosurfactants have properties that are suitable for cosmetic applications, such as compatibility with human skin and skin surface moisturizing 10) .Furthermore, consumers pay more attention to natural products when considering environmental sustainability 11) . Therefore, biosurfactants have scope to be further deployed in the cosmetic industry. For instance, in addition to their potential skin benefits, the eco-friendly characteristics of biosurfactants have attracted attention for cleaning applications and their potential applications in haircare 12) .Sophorolipids are biosurfactants that possess both capacities for the disruption 13−16) and removal 17) of biofilms. Owing to the high complexity of biofilms, it is challenging to understand which of their components should be target-Abstract: Biofilms are communities of microorganisms that have been widely studied because they can cause hospital-acquired infections and skin disorders. Polysaccharides secreted by microorganisms are constituents of biofilms, contributing to their adhesion and mechanical stability. Sophorolipids are biosurfactants with the ability to disrupt and remove biofilms. Biosurfactants have been targeted as potential substitutes for classical petrochemical-based surfactants in cosmetics. In this study, we fabricate a β-glucan film as a model biofilm, and quartz crystal microbalance with dissipation monitoring (QCM-D) measurements are used to assess the biofilm removal. The viscoelasticity of the β-glucan films is monitored while sophorolipid solutions are introduced into the system, and we found that the film removal performance increases with the sophorolipid concentration. In addition, Δf (change in frequency)-ΔD (change in energy dissipation) plot analyses reveal that two processes are involved in the removal mechanism. The first process involves the adsorption of water (hydration) on the β-glucan film. The second process involves the removal of the β-glucan film from the sensor surface. Furthermore, it is suggested that sophorolipids interfere with the hydration of the β-glucan film and suppress increases in its viscosity. This is expected to be an essential factor for the removal of the β-glucan film. Sophorolipids, therefore, show potential for use in cosmetics as an eco-friendly agent for biofilm removal.