Akemi Yasukawa

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....

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.

Contact angle hysteresis in carbon fibers studied by wetting force measurements

The surface free energy of polyacrylonitrile carbon fibers was investigated by using the Wilhelmy technique. The difference in surface free energy between immersion and emersion was observed for the carbon fiber pyrolyzed at 2500 °C.In contrast, the hysteresis disappeared with repyrolyzation of the carbon fibers at 3000 °C. Auger electron spectroscopic analysis indicated that the surface of the latter carbon fiber (repyrolyzed at 3000 °C) consisted of the basal planes of graphite. Rough surface topography of the carbon fiber repyrolyzed at 3000 °C, as observed by scanning electron microscope, did not affect the hysteresis. Therefore, the contact angle hysteresis was attributed to the chemical adsorbants on the activation sites of the fiber surfaces, as detected by Auger electron spectroscopy.

Surface Characterization of Carbon Fibers Exposed to 5 eV Energetic Atomic Oxygen Beam Studied by Wetting Force Measurements

Changes in contact angle hysteresis and surface free energy of carbon fibers due to the irradiation of 5 eV energetic atomic oxygen beam were investigated. Atomic oxygen with kinetic energy of 5 eV was used in order to simulate the low earth orbit. Contact angle hysteresis in carbon fibers became larger with respect to the fluence of atomic oxygen. Auger electron spectroscopic analysis shows that the hysteresis of the contact angle is proportional to surface oxygen concentration as well as the polar component of surface free energy. Since adsorbed oxygen or the surface functional group plays an important role in the hysteresis, it is clear that the carbon fiber surface was destroyed due to the attack of atomic oxygen.

Ultraviolet shielding properties of cotton fabric supported by cerium-calcium hydroxyapatite solid solution particles

Cotton fabric was supported by three types of cerium-calcium hydroxyapatite (CeCaHap) solid solution particles and the properties were compared. The three types of CeCaHap were prepared using different wet methods. The crystallinity and morphology of the particles were altered depending on the preparation conditions. Because all the CeCaHap particles exhibited a strong ultraviolet (UV) absorption under 400 nm on the ultraviolet-visible spectra, they were supported on cotton fabric by immersing the fabric into the dispersion containing the particles. The treated fabric showed UV shielding properties and fine particles especially showed stronger UV screening properties than large and long particles. With increasing the concentration of the particles in the dispersion, the amount of particles that was supported on the fabric increased and UV screening properties of the fabric were enhanced. The UV shielding ability of the fabric was sufficiently maintained after washing using water or a sodium dodecyl sulfate solution.

Dyeing silk and cotton fabrics using natural blackcurrants

Silk and cotton fabrics were dyed using the extract from blackcurrants, and the properties of the dyed fabrics were investigated. The natural dyes present in the blackcurrants were identified as four types of anthocyanins, i.e. delphinidin-3-glucoside, delphinidin-3-rutinoside, cyanidin-3-glucoside, and cyanidin-3-rutinoside. The colors of the fabrics dyed with and without five types of mordants, including Mg2+, Ca2+, Al3+, Fe3+, and Cu2+, were measured and expressed according to the CIELAB color system, ΔE* value, and K/S value. The affinity of the extracted dye for the silk fabric was higher compared with that for the cotton fabric. The crystallinity of silk was lower than that of cotton. The fabrics dyed with blackcurrants had UV shielding ability, especially at 330–400 nm, and antibacterial properties. Although color fastness to light and washing (color change) was not sufficient, treatment with Mg2+, Fe3+, and Cu2+ mordants could enhance the color fastness.