Lee Kyoungmun, Choi Siyoung Q
Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Korea.
Soft Matter. 2020 Dec 7;16(45):10326-10333. doi: 10.1039/d0sm01504k. Epub 2020 Oct 14.
In drying liquid films of polymer-colloid mixtures, stratification in which polymers are placed on top of larger colloids is studied. It is often presumed that the formation of segregated polymer-colloid layers is solely due to the proportion in size at fast evaporation as in binary colloid mixtures. By comparing experiments with a theoretical model, we found that the transition in viscosity near the drying interface was another important parameter for controlling the formation of stratified layers in polymer-colloid mixtures. At high evaporation rates, increased polymer concentrations near the surface lead to a phase transition from a semidilute to concentrated regime, in which colloidal particles are kinetically arrested. Stratification only occurs if the formation of a stratified layer precedes the evolution to the concentrated regime near the drying interfaces. Otherwise, the colloids will be trapped by the polymers in the concentrated regime before forming a segregated layer. Also, no stratification is observed if the initial polymer concentration is too low to form a sufficiently high polymer concentration gradient within a short period of time. Our findings are relevant for developing solution-cast polymer composites for painting, antifouling and antireflective coatings.
在聚合物 - 胶体混合物的液膜干燥过程中，研究了聚合物位于较大胶体之上的分层现象。人们通常认为，与二元胶体混合物一样，在快速蒸发时，聚合物 - 胶体层的分离形成仅仅是由于尺寸比例。通过将实验与理论模型进行比较，我们发现干燥界面附近粘度的转变是控制聚合物 - 胶体混合物中分层形成的另一个重要参数。在高蒸发速率下，表面附近聚合物浓度的增加导致从半稀溶液到浓溶液状态的相变，其中胶体颗粒在动力学上被捕获。只有当分层层的形成先于干燥界面附近向浓溶液状态的演化时，分层才会发生。否则，胶体将在形成分离层之前被浓溶液状态下的聚合物捕获。此外，如果初始聚合物浓度过低，无法在短时间内形成足够高的聚合物浓度梯度，则不会观察到分层现象。我们的研究结果对于开发用于涂料、防污和抗反射涂层的溶液浇铸聚合物复合材料具有重要意义。
