Laboratory of Process Technology, Department of Microsystems Engineering (IMTEK), University of Freiburg, 79110 Freiburg im Breisgau, Germany.
Freiburg Materials Research Center (FMF), University of Freiburg, 79104 Freiburg im Breisgau, Germany.
ACS Appl Mater Interfaces. 2023 Jun 7;15(22):27234-27242. doi: 10.1021/acsami.2c22979. Epub 2023 May 22.
Softness plays a key role in the deformation of soft elastic substrates at the three-phase contact line, and the acting forces lead to the formation of a wetting ridge due to elastocapillarity. The change in wetting ridge and surface profiles at different softness has a great impact on the droplet behavior in different phenomena. Commonly used materials to study soft wetting are swollen polymeric gels or polymer brushes. These materials offer no possibility to change the softness on demand. Therefore, adjustable surfaces with tunable softness are highly sought-after to achieve on-demand transition between wetting states on soft surfaces. Here, we present a photorheological physical soft gel with adjustable stiffness based on the spiropyran photoswitch that shows the formation of wetting ridges upon droplet deposition. The presented photoswitchable gels allow the creation of reversibly switchable softness patterns with microscale resolution using UV light-switching of the spiropyran molecule. Gels with varying softness are analyzed, showing a decrease in the wetting ridge height at higher gel stiffness. Furthermore, wetting ridges before and after photoswitching are visualized using confocal microscopy, showing the transition in the wetting properties from soft wetting to liquid/liquid wetting.
柔软度在三相接触线处软弹性基底的变形中起着关键作用，作用于基底的力会导致由于弹性毛细作用而形成润湿脊。不同柔软度下润湿脊和表面轮廓的变化对不同现象中液滴的行为有很大的影响。常用于研究软润湿的材料是溶胀聚合物凝胶或聚合物刷。这些材料无法按需改变柔软度。因此，人们迫切需要具有可调柔软度的可调谐表面，以实现软表面上润湿状态的按需转变。在这里，我们提出了一种基于螺吡喃光致变色的光流变物理软凝胶，该凝胶具有可调硬度，在液滴沉积时会形成润湿脊。所提出的光致变色凝胶允许使用紫外线光开关螺吡喃分子来创建具有微尺度分辨率的可重复切换的柔软度图案。对具有不同柔软度的凝胶进行了分析，结果表明在较高的凝胶硬度下，润湿脊的高度降低。此外，使用共聚焦显微镜可视化了光致变色前后的润湿脊，显示了润湿性质从软润湿到液/液润湿的转变。
