Keiko Gotoh

Wettability of ultraviolet excimer-exposed PE, PI and PTFE films determined by the contact angle measurements

Effects of the exposure of ultraviolet (UV) excimer light on the physicochemical surface properties of polymer films were investigated by contact angle measurements and X-ray photoelectron spectroscopy (XPS). The UV light at wavelength of 172 nm was exposed to polyethylene (PE), polyimide (PI), and polytetrafluoroethylene (PTFE) films in ambient air. The advancing and receding contact angles of water on the unexposed and UV-exposed films were determined by the sessile drop and the Wilhelmy methods as a measure of the wettability. For the PE and PI films, remarkable decrease in the water contact angle was accomplished by the UV exposure of several or several 10 s. The XPS data showed that such increase in the wettability was attributed to the increased atomic oxygen concentration at the film surfaces. The wettability of the PTFE film did not change due to the UV exposure. When the UV-exposed PE and PI films were stored in ambient air, the increase in the water contact angle, i.e. the hydrophobic recovery, was observed over a time scale of several days. It was suggested that the gasification of the low-molecular weight oxidized materials as well as the reorientation and the migration of polymer chains in the oxidized surface layer was responsible for the hydrophobic recovery in air. The UV exposure was also attempted to the PI film being covered with a metal mesh to prepare the film having both non-exposed and UV-exposed surface regions. The differences in the advancing and receding contact angles between the both regions were observed on the continuous weight recording at constant interfacial moving velocity by the Wilhelmy method. The Wilhelmy method in combination with the UV lithography technique enabled the simultaneous evaluation of the wettabilities of the treated and untreated surfaces.

Estimation of surface free energies and hamaker constants for fibrous solids by wetting force measurements

Wetting force at three-phase line was measured by the Wilhelmy technique using fibrous solids/liquid/liquid systems. Advancing and receding contact angles were calculated from the wetting forces during fiber immersion and emersion. The obtained results showed that contact angle hysteresis was due to the heterogeneity of the fiber surfaces. The dispersive and polar components of surface free energies of the fibers were determined from the advancing and receding contact angles, respectively. The Hamaker constants of the fibers were estimated from the dispersive components of their surface free energies.

Surface modification of PET films by atmospheric pressure plasma exposure with three reactive gas sources

The surface modification of poly (ethylene terephthalate) (PET) film was carried out using an atmospheric pressure plasma (APP) jet device with three reactive gases: air, N2, and Ar. The water contact angles on the PET film were found to decrease considerably after the APP exposure. The changes in the advancing and receding contact angles of water on the APP-exposed PET film with aging time were examined by the wetting force measurements employing the Wilhelmy method. The hydrophobic recovery due to the rinsing with water as well as the aging in air was observed only for the advancing angle, which was probably caused by the dissolution of low molecular weight oxidized materials into water, the loss of volatile oxidized species to the atmosphere and the reorientation and the migration of polymer chains. The wettability and the surface free energy of the APP-exposed PET film after diminishing hydrophobic recovery was sufficiently large compared with the untreated film. X-ray photoelectron spectroscopy confirmed that the PET film surface was oxidized due to the APP exposure. When N2 gas was used for the APP exposure, the surface nitrogen concentration was found to increase with decreasing D. The surface oxygen concentration on the APP-exposed PET film was reduced by rinsing with water, in accordance with the hydrophobic recovery behavior. From atomic force microscopy, surface topographical change due to the APP exposure was observed. The changes in the PET surface properties due to the APP exposure as mentioned above were remarkable for using N2 gas.

Local deviation in contact angles on heterogeneous fibrous solids

Wetting force measurements in solid/water/n-alkane systems were carried out using carbon fibers, boron fiber, fibrous quartz, and polymeric fibers by the Wilhelmy technique. Contact angles of water were independent of the velocity of the moving three-phase boundary on repyrolyzed PAN-based carbon fibers which did not show any contact angle hysteresis. Hysteresis in contact angles due to surface heterogeneity began to appear after irradiation with atomic oxygen which oxidized the carbon fibers. On atomic oxygen exposed carbon fibers, advancing contact angles increased and receding ones decreased with increasing velocity, and there was a region where both angles were constant. The range of deviations in contact angles due to surface heterogeneity was determined from local deviations in weight traces at the velocity of three-phase boundary of 0.3 mm min-1 where both angles were independent of the velocity. Deviations in contact angles, Δ, were larger in advancing than in receding for hydrophilic solids (e.g....

Adhesion of nylon particles to a quartz plate in an aqueous solution and their removal by electro-osmosis

Particle removal by electro-osmotic flow was investigated by comparison with the removal by ordinary flow of water without electrokmetic effect. The relationship between adhesion and removal of particles in terms of force acting on the particle was also discussed. Experiments were carried out in an aqueous solution using nylon particles and a quartz plate. The adhesive force,F′T, for the particles which adhered to the quartz plate in secondary minima in the total potential energy of interaction versus separation distance curves was calculated. Particle removal experiments were carried out applying electro-osmotic and Poiseuille flows. The hydrodynamic force,Fd, which was required to remove particles from the plate was estimated using flow velocities. The effectiveness of electro-osmotic flow on particle removal was larger than that of Poiseuille flow. In the particle removal by electro-osmotic flow, the minimum of the ratioFd/F′t for particle removal was found to be 50 and the ratio for removal efficiency of 0.5 was about 140.

The detachment of nylon particles from quartz plate by electro-osmotic flow

The direct application of electrokinetic phenomena to detergency was investigated. Experiments were carried out to remove particles from substrate by electro-osmosis. A model system which consisted of spherical nylon particles of 5Μm in mean diameter, a quartz plate, and wash liquid were used in analyzing the kinetic process of particle removal from substrate. When an electric field was applied to the system, electro-osmotic flow took place, and hence the particles were removed from the quartz surface. The ζ-potentials of nylon particles and quartz plate were measured by electrophoresis. The rate constants of removal,κ, were obtained from the changes with time in the ratio of particle residue by applying the first-order reaction scheme. The value ofκ increased with increasing electric field and with increasing concentration of surfactant. The total force of interaction between particle and plate was calculated on the basis of heterocoagulation theory of colloid stability.It was found from results thus obtained that the hydrodynamic force due to the electro-osmotic flow worked effectively as a mechanical force on the removal process and the adhesion force of particle to substrate reduced by adding surfactant.

Application of ultrasound to textiles washing in aqueous solutions.

The ultrasound was applied to textile washing as a mechanical action for soil removal. The polyester fabric was soiled with carbon black or oleic acid as a model contaminant, and washed with the original fabric in aqueous solutions without and with alkali or surfactant by applying ultrasound, shaking or stirring action. The detergency and soil redeposition were evaluated from the change in the surface reflectance of artificially soiled fabrics and the original fabric due to washing. In comparison with shaking and stirring actions, ultrasound was found to remove the particulate and oily soils efficiently in a short time and at low bath ratio. With increasing ultrasound power, the detergency of both soils increased and exceeded that obtained with Wascator, a horizontal axis drum type washer. Using three standard fabrics for determining mechanical action during washing, it was shown that ultrasound washing caused little mechanical damage to the fabric. However, the soil redeposition was frequently observed for ultrasonic washing, especially at low bath ratio.

Atmospheric Pressure Plasma Modification of Polyester Fabric for Improvement of Textile-Specific Properties

Polyester fabrics were treated by atmospheric pressure plasma (APP) to enhance hydrophilic behavior of the fiber surfaces. Damage of the fabric due to the APP exposure was not significantly observed. It was found that the APP exposure increased the wettability, oxygen concentration and roughness of the polyester fiber surface. As a result, the water wicking and antistatic property were successfully enhanced. Moreover, the detergency and the dyeability were found to be enhanced. It was found that the exposure of polyester fabrics to APP may help to improve its functional properties.

Water Contact Angles on Poly(ethylene terephthalate) Film Exposed to Atmospheric Pressure Plasma

The poly(ethylene terephthalate), PET, film was exposed to atmospheric pressure plasma under various plasma processing parameters. The wettability of the PET film immediately after the exposure and after storage in air, which was determined by the sessile drop method, was strongly dependent on the plasma processing parameters. The contact angle hysteresis on the plasma-exposed PET film was examined by the Wilhelmy method. It was found that the hydrophobic recovery of the PET surface on storage after the plasma exposure was observed only for the advancing contact angle and that the receding angle remained almost the same. These experimental findings were explained on the basis of the calculation by Johnson and Dettre for the advancing and receding contact angles on model heterogeneous surfaces.

Detachment behavior of Langmuir–Blodgett films of arachidic acid from a gold surface studied by the quartz crystal microbalance method

Abstract The detachment process of an oily contaminant from a gold surface was investigated using a model system constructed by the application of the quartz crystal microbalance (QCM) method and the Langmuir–Blodgett (LB) technique. Long-chain fatty acid, arachidic acid, was used as a model oily contaminant. The solid-condensed monolayers of arachidic acid on water were transferred onto the QCM by the vertical dipping method. The frequency change of the QCM at each immersion–withdrawal cycle indicated that the monolayers were successfully deposited on the gold surface of the QCM as Y-type multilayers. The QCM having the LB films of arachidic acid was cleaned in aqueous solutions containing sodium chloride, sodium hydroxide, surfactants and/or ethanol by applying ultrasonic waves. Surfactants used were sodium dodecyl sulfate (SDS) and n -octyl β- d -glucopyranoside (OGP). The detachment efficiency of the LB films from the gold surface was evaluated from the frequency change of the QCM due to the detachment. The efficiency increased with time and showed saturation at 20–30 min. The detachment was found to increase with increasing concentrations of sodium hydroxide, SDS, OGP, and ethanol. At the critical micelle concentrations of SDS and OGP or at ca. 50 vol.% of ethanol, the LB films were perfectly removed from the gold surface. The detachment efficiencies obtained in all systems were correlated with the free energy change due to liquid penetration between the LB films and the gold surface, which was calculated from the experimentally determined contact angles and surface free energies. The saponification of arrachidic acid by alkali as well as the liquid penetration was found to contribute to the detachment of the LB films. The exposure of the 172 nm ultraviolet excimer light prior to the ultrasonic washing was effective for the removal of the LB films.