Uchiyama Hiroaki, Matsui Tadayuki, Kozuka Hiromitsu
Department of Chemistry and Materials Engineering, Kansai University , 3-3-35 Yamate-cho, Suita, Osaka 564-8680, Japan.
Langmuir. 2015 Nov 17;31(45):12497-504. doi: 10.1021/acs.langmuir.5b02929. Epub 2015 Nov 5.
Evaporation-driven surface tension gradient in the liquid layer often causes the convective flow, i.e., Bénard-Marangoni convection, resulting in the formation of cell-like patterns on the surface. Here, we prepared sol-gel-derived titania films from Ti(OC3H7(i))4 solutions by dip coating and discussed the effect of the addition of co-solvents with a high surface tension and low volatility on the spontaneous pattern formation induced by Bénard-Marangoni convection. Propylene glycol (PG, with a surface tension of 38.6 mN m(-1)) and dipropylene glycol (DPG, with a surface tension of 33.9 mN m(-1)) were added to the coating solutions containing 2-propanol (2-Pr, with a surface tension of 22.9 mN m(-1)) for controlling the evaporation-driven surface tension gradient in the coating layer on a substrate. During dip coating at a substrate withdrawal speed of 50 cm min(-1) in a thermostatic oven at 60 °C, linearly arranged cell-like patterns on a micrometer scale were spontaneously formed on the titania gel films, irrespective of the composition of coating solutions. Such surface patterns remained even after the heat treatment at 200 and 600 °C, where the densification and crystallization of the titania films progressed. The width and height of the cell-like patterns increased with increasing PG and DPG contents in the coating solutions, where the addition of PG resulted in the formation of cells with a larger height than DPG.
液层中由蒸发驱动的表面张力梯度通常会引起对流，即贝纳德-马兰戈尼对流，从而导致在表面形成细胞状图案。在此，我们通过浸涂法从四异丙醇钛（Ti(OC3H7(i))4）溶液制备了溶胶-凝胶衍生的二氧化钛薄膜，并讨论了添加具有高表面张力和低挥发性的共溶剂对贝纳德-马兰戈尼对流诱导的自发图案形成的影响。将丙二醇（PG，表面张力为38.6 mN m(-1)）和二丙二醇（DPG，表面张力为33.9 mN m(-1)）添加到含有2-丙醇（2-Pr，表面张力为22.9 mN m(-1)）的涂层溶液中，以控制基材上涂层中由蒸发驱动的表面张力梯度。在60℃的恒温烘箱中以50 cm min(-1)的基材提拉速度进行浸涂时，二氧化钛凝胶薄膜上自发形成了微米级的线性排列的细胞状图案，与涂层溶液的组成无关。即使在200℃和600℃进行热处理后，这种表面图案仍然存在，此时二氧化钛薄膜发生了致密化和结晶。细胞状图案的宽度和高度随着涂层溶液中PG和DPG含量的增加而增加，其中添加PG导致形成的细胞高度比DPG形成的细胞大。
