Title: Photocontrolled Liquid Transportation in Microtubes by Manipulating Mesogen Orientations in Liquid Crystal Polymers

Author: Quan Liu, Yuyun Liu, Jiu-an Lv, Erqiang Chen, Yanlei Yu*

Journal: Adv. Intell. Syst., 2019, 1(6), 1900060

Abstract:

Tubular microactuators (TMAs) fabricated by photodeformable liquid crystal polymers (LCPs) pave a significant way for smart microfluidic applications with contactless, spatial, and precise manipulation of liquids. To realize liquid transportation in these TMAs, LCPs should have excellent photodeformation property and suitable mechanical properties. Herein, linear liquid crystal polymers (LLCPs) with different mesogen orientations are used to prepare TMAs to study their liquid transportation behaviors. The mesogen orientation in each LLCP is formed spontaneously and varies with the spacer length, leading to different deformations of LLCP films. It is found that only LLCPs with mesogens oriented out-of-plane realize self-support of the TMAs, whereas the TMAs with mesogens oriented in-plane are so weak that they collapse in the radial direction, indicating the importance of mesogen orientation in fabricating three-dimensional structures. Upon attenuated 470 nm light irradiation, the TMAs deform to an asymmetric conical structure, leading to the motion of liquid slug toward the narrow side. The liquid motion is accelerated in the TMA with longer spacer, showing the control of liquid speed by the mesogen orientation. These photocontrolled TMAs are expected to be applied in biological applications, such as whole blood analysis and flow cytometry, for precise liquid manipulation.

Fulltext Link: https://onlinelibrary.wiley.com/doi/pdf/10.1002/aisy.201900060

In this work, we use ROMP to synthesize three azobenzene-containing photodeformable linear liquid crystal polymers (LLCP) with different spacer lengths, namely PC-AB6, PC3AB6, and PC7AB6. The PC-AB6 mesogens spontaneously form in-plane orientation, and the mesogens of PC3AB6 and PC7AB6 are out-of-plane orientation. The Young's modulus of LLCP TMAs parallel to the mesogen orientation direction is about twice as large as that for the perpendicular one. Therefore, PC-AB6 TMA collapses in the radial direction, whereas PCnAB6 TMAs is well self-supported, which demonstrates that out-of-plane orientations in the LCPs is essential to afford enough mechanical robustness in fabricating 3D tubular structures.