Preparation of Highly Water-repellent Surface by Spontaneous Formation of Double Scale Roughness Pattern

Abstract

Hydrophobic organic-inorganic hybrid composite suspensions were prepared by mixing hydrophobic octylsilyl titanium dioxide particles having average diameter of 35 nm with drying oil or moisture cure room temperature vulcanization silicone gum in volatile silicone. They were spread on a glass plate by using a linear motor coater and an applicator. Spatially periodic stripe patterns parallel to the direction of dragging the applicator were usually generated. The phenomenon is called directional viscous fingering, i.e. spontaneous pattern formation by the growth of fluctuation in morphology of mobile interface during the dragging coat. The pattern spontaneously formed on the surface became double scale when stored samples were coated. In this case, the large scale spatially periodic pattern was formed by the directional viscous fingering and the small ragged random pattern may be due to the giant molecules formed by cross-linking of silicone gum. Double scale roughness patterns were also generated by double dragging coat. The large and small scale pattern was formed by the first and second dragging coat, respectively. The formation of double scale roughness enhanced the water-repellent property of the hydrophobic surface. In some cases, water contact angle increased by 20˚ to realize super water-repellent surface with a value exceeding 150˚.

Problems on the Evaluation of the Critical Wavelength of Sunscreens for “Broad Spectrum” Approval Brought on by Viscous Fingering During Sunscreen Application

“…The linear motor coater used in our previous studies was used for the application of the pseudosunscreen solutions. To analyze the pure influence of the geometric factor generated by the viscous fingering on the UV transmission, no roughened PMMA plate for the current in vitro measurements was used, but a flat square quartz plate of 10 cm × 10 cm and a thickness of 3.1 mm was employed as a substrate.…”

“…Viscous fingering patterns are generated at the moving interface when it becomes unstable to morphological fluctuations . Spatially periodic stripe patterns are spontaneously formed when two pieces of adhesive tape that are stuck together are peeled and a viscous fluid is applied on a solid substrate . Intensity of transmitted UV light passing through the sunscreen layer are varied by the surface shape generated by the viscous fingering, even though the amount of the sunscreens applied per unit area on the substrate is identical.…”

Problems of in vitro SPF Measurements Brought about by Viscous Fingering Generated during Sunscreen Applications

“…The linear motor coater used in our previous study [24,25] was used for the application of the pseudo-sunscreen composite onto a flat square quartz plate with a side length of 10 cm and a thickness of 3.1 mm. In current in vitro measurements [26,27,28], the use of rough polymethylmethacrylate (PMMA) plate is stipulated.…”

“…The characteristic length of the spatial periodicity corresponds to the wavelength of the fastest growing fluctuation. We found that the stripe pattern was spontaneously formed by the directional viscous fingering during the application of viscous fluid on a glass plate, and we analyzed the influence of the coating condition on the geometry of the surface [24,25]. …”

Coexistence effect of UVA absorbers to increase their solubility and stability of supersaturation

“…They were applied onto a quartz plate and iso-propanol was evaporated. To prevent the pattern formation by the viscous fingering during the application [19][20][21], four-sided applicator was used [22,23]. The gap between the quartz plate and the face of the applicator was 35-45 lm, and the coating velocity was 10 mm s À1 .…”