Huang Hao, Su Yechao, Xu Jianhong, Wang Xiaogong
Department of Chemical Engineering, Laboratory of Advanced Materials (MOE) , Tsinghua University , Beijing 100084 , People's Republic of China.
Department of Chemical Engineering, The State Key Lab of Chemical Engineering , Tsinghua University , Beijing 100084 , People's Republic of China.
Langmuir. 2019 Nov 26;35(47):15295-15305. doi: 10.1021/acs.langmuir.9b02882. Epub 2019 Nov 11.
In this work, photoinduced asymmetric morphology transformation of a type of azo molecular glass microspheres was thoroughly investigated to understand the effects of controlling factors on the process, related mechanism and unique functions. The monodispersed microspheres with their sizes over ten microns were fabricated from an isosorbide-based azo compound (IAC-4) by microfluidics. Under irradiation with linearly polarized light, the ten-micron-scale microspheres were transformed into three-dimensional (3D) asymmetric particles through directional mass transfer. Microscopic observations and optics simulation were employed to investigate the morphology transformations. The results show that the penetration depth of light at different wavelengths plays an extremely important role to affect the asymmetric deformation behavior of the IAC-4 microspheres, which determines deformation region, deformation degree and final shapes of the particles. The light intensity (50-200 mW/cm) is a less important factor, while the deformation rate of the light-penetrated part linearly increases with the intensity. When the light intensity varies in this range, the deformation degree and the final asymmetric morphology are determined by exposure energy (light intensity × irradiation time). The IAC-4 microspheres with different sizes show distinct morphology transformation behavior and the deformed particles possess different shapes, caused by the variation of volume fraction of the light-penetrated part in the microspheres. The increase in the ratio of the light-penetrated part to the total volume of the microspheres results in larger scale deformations. Based on the above understanding, asymmetric particles with various morphologies can be fabricated through a precisely controllable way. The asymmetric particles loaded on various surfaces show ability to render remarkable wetting anisotropy of water droplets on the substrates.
在本工作中，对一种偶氮分子玻璃微球的光致不对称形态转变进行了深入研究，以了解控制因素对该过程、相关机理及独特功能的影响。通过微流控技术，由基于异山梨醇的偶氮化合物（IAC-4）制备出尺寸超过十微米的单分散微球。在线偏振光照射下，十微米尺度的微球通过定向质量传递转变为三维（3D）不对称颗粒。采用显微镜观察和光学模拟来研究形态转变。结果表明，不同波长光的穿透深度对影响IAC-4微球的不对称变形行为起着极其重要的作用，这决定了颗粒的变形区域、变形程度和最终形状。光强（50 - 200 mW/cm）是一个不太重要的因素，而光穿透部分的变形速率随光强呈线性增加。当光强在该范围内变化时，变形程度和最终的不对称形态由曝光能量（光强×照射时间）决定。不同尺寸的IAC-4微球表现出不同的形态转变行为，且变形颗粒具有不同形状，这是由微球中光穿透部分的体积分数变化引起的。微球中光穿透部分与总体积之比的增加导致更大尺度的变形。基于上述认识，可通过精确可控的方式制备出具有各种形态的不对称颗粒。负载在各种表面上的不对称颗粒表现出能使基底上的水滴呈现出显著的润湿性各向异性的能力。
