With the rapid development of microsystems in the last few decades, there is a
requirement for high precision tools for micromanipulation and transportation of micro-objects, such as microgrippers, for applications in microassembly, microrobotics, life
sciences and biomedicine. Polymer based microgrippers and microrobots executing
various tasks have been of significant interest as an alternative to the traditional silicon
and metal based counterparts due to the advantages of low cost fabrication, low
actuation temperature, biocompatibility, and sensitivity to various stimuli. The
exceptional actuation properties of liquid crystal elastomers (LCE) have made these
materials highly attractive for various emerging applications in the last two decades.
Large programmable deformations and the benefits offered by the elastic, thermal and
optical properties of LCEs are suitable for implementing stimuli-responsive
microgrippers as well as various biomimetic motion in soft robots.
In this thesis, a method and the associated processes for fabrication and molecular
alignment in LCE were developed, which enabled new functionality and improved
performance of the LCE based microactuators and microgrippers, providing controlled
response by thermal and remote photothermal actuation, and allowing easy integration
of the LCE end-effectors into robotic systems for automated operation. Lateral bending
actuation has been demonstrated in LCE microbeams of 900 µm of length and 40 µm of
thickness, owing to the new monolithic micromolding technique using vertical patterned
walls for alignment. The effects of parameters such as the beam width, the size of the
microgrooves, and the surface treatment method on the behavior of the microactuators
were studied; the internal alignment pattern of liquid crystals in the structure was
investigated by different microscopy methods. An efficient method for finite element
modeling of the bending LCE actuators was developed and experimentally verified,
based on the gradient of equivalent thermal expansion in the multi-layer structure,
which was able to predict the bending behavior of the actuators in a large range of
thicknesses as well as rolling behavior of the actuators of tapered thickness. The novel
LCE microgripper with in-plane operation showed efficient thermal and photothermal
actuation, achieving the gripping stroke of 64 µm under the light intensity of 239
mW/cm2
for the gripper length of 900 µm, which is more efficient than the typical SU-8
polymer based microgrippers of the same dimensions. The LCE gripper was
successfully demonstrated for the application in manipulation of the objects of tens to
hundreds of micrometers in size. Therefore, the novel LCE microgripper bridges the gap in the LCE-based gripper technologies for typical object size in applications for
systems microassembly, biological and cell micromanipulation. The lateral bending
functionality enabled by the proposed method expands design opportunities for thermal
and photothermal LCE microactuators, providing an effective route toward realization
of new modes of gripping, locomotion, and cargo transportation in soft microrobotics
and micromanipulation
