Kovalchuk Nina M, Sagisaka Masanobu, Komiyama Hinata, Simmons Mark J H
School of Chemical Engineering, University of Birmingham, B15 2TT, UK.
Graduate School of Science and Technology, Hirosaki University, 036-8561, Japan.
J Colloid Interface Sci. 2024 May;661:1046-1059. doi: 10.1016/j.jcis.2024.02.031. Epub 2024 Feb 6.
The question of why aqueous solutions of some surfactants demonstrate a rapid spreading (superspreading) over hydrophobic solid substrates, while solutions of other similar surfactants do not, has no definitive explanation despite numerous previous studies. The suggested hypothesis for this study assumes that once the spreading coefficient of surfactant is positive, there is a concentration range for solutions of any surfactant which demonstrates rapid spreading. As it is impossible to calculate spreading coefficients for solid substrates, we compare the spreading performance of known superspreaders and non-superspreaders on liquid (oil) substrate.
The kinetics of spreading of aqueous solutions of a series of branched ionic surfactants and non-ionic trisiloxane surfactants on two liquid substrates was studied and compared with the spreading of a surfactant-free liquid, silicone oil. Both dynamic and equilibrium spreading coefficients were calculated using measured surface and interfacial tensions.
There is no difference in spreading rate on liquid substrate between solutions of surfactants proven as superspreaders (while spreading on solid substrate) or non-superspreaders. A rapid spreading (superspreading) with the characteristic rate of spreading O(10-10) mm/s occurs if the dynamic spreading coefficients exceeds the positive threshold value. If the dynamic spreading coefficient is negative or slightly positive, complete wetting still occurs, but the spreading is slow with the spreading rate is O(1) mm/s. Spreading exponents for surfactant solutions in the rapid spreading regime are considerably larger than for the surfactant-free liquid. A number of spreading and dewetting patterns were observed depending on the surfactant type, its concentration and substrate.
尽管此前已有大量研究，但对于为何某些表面活性剂的水溶液能在疏水固体基质上迅速铺展（超铺展），而其他类似表面活性剂的溶液却不能，尚无定论。本研究提出的假设是，一旦表面活性剂的铺展系数为正，那么任何表面活性剂溶液都存在一个能表现出快速铺展的浓度范围。由于无法计算固体基质的铺展系数，我们比较了已知的超铺展剂和非超铺展剂在液体（油）基质上的铺展性能。
研究了一系列支链离子型表面活性剂和非离子型三硅氧烷表面活性剂的水溶液在两种液体基质上的铺展动力学，并与无表面活性剂的液体硅油的铺展情况进行了比较。利用测得的表面张力和界面张力计算了动态和平衡铺展系数。
在液体基质上，被证明为超铺展剂（在固体基质上铺展时）的表面活性剂溶液和非超铺展剂溶液的铺展速率没有差异。如果动态铺展系数超过正阈值，则会以特征铺展速率O(10 - 10)毫米/秒发生快速铺展（超铺展）。如果动态铺展系数为负或略为正，则仍会发生完全润湿，但铺展速度较慢，铺展速率为O(1)毫米/秒。在快速铺展状态下，表面活性剂溶液的铺展指数比无表面活性剂的液体大得多。根据表面活性剂类型、其浓度和基质的不同，观察到了多种铺展和去湿模式。
