Actuating thermo- and photo-responsive tubes from liquid crystalline elastomers
Actuating thermo- and photo-responsive tubes from liquid crystalline elastomers
复制标题
DOI：
10.1039/c8tc02873g
复制
发表时间：
2018-09-14
影响因子：
6.4
通讯作者：
Zentel, Rudolf
中科院分区：
文献类型：
--
作者：
Braun, Lukas B.;Hessberger, Tristan;Zentel, Rudolf
来自液晶（LC）-弹性体的大（许多mm长）封闭管可以在微流体设置中通过LC-单体混合物的光聚合来制备。在这些管中，LC相的指向矢平行于它们的长轴取向，如通过X射线测量所证明的，从而导致在向各向同性相转变时缩短，而它们的壁同时变得更厚。管制备的过程依赖于在微流体设置中适当选择3个不混溶相（连续相、LC-单体相和内相）以及它们的界面张力。水可用作内相，与选择性洗涤剂（来自PNIPAM和LC-聚合物的两亲嵌段共聚物）组合以降低LC/水表面张力。通过这种方式，可以用热致液晶弹性体或含偶氮液晶弹性体制备长致动（高达50%）管，后者既具有热响应性又具有光响应性。通过用白色（trans-cis）或红光（cis-transs）照射由偶氮体系组成的单个管，可以实现高达29%的致动。因此，管的收缩（缩短）需要约10秒，而光化学再异构化需要约230秒。这为管的光化学致动设置了时间范围。
Large (many mm long) closed tubes from liquid crystalline (LC)-elastomers can be prepared in a microfluidic setup by photopolymerization of an LC-monomer mixture. In these tubes, the director of the LC-phase is oriented parallel to their long axes as proven by X-ray measurements, thus leading to shortening at the transition to the isotropic phase while their walls become thicker simultaneously. The process of tube preparation relies on an appropriate choice of 3 immiscible phases in the microfluidic setup (continuous, LC-monomer and inner phase) as well as their interfacial tensions. Water can be used as the inner phase in combination with a selective detergent (an amphiphilic block copolymer from PNIPAM and the LC-polymer) to reduce the LC/water surface tension. In this way, long actuating (up to 50%) tubes can be prepared either from a thermotropic LC-elastomer or from an azo-containing LC-elastomer with the latter being both thermo- and photo-responsive. By irradiation of individual tubes consisting of the azo-system with white (trans-cis) or red light (cis-trans), actuations of up to 29% can be achieved. The contraction (shortening) of the tubes thereby requires about 10 seconds, while the photochemical reisomerization needs about 230 seconds. This sets the time frame for the tubes' photochemical actuation.