[Applications for Photo-actuated Bi-Layered Liquid Crystal Polymer strips]

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ACKNOWLEDGEMENT

I would like to thank my supervisor for supporting me throughout my project and giving his valuable suggestions. Finally thanks to all my friends and family for their utmost support and inspiration.

DECLARATION

I, (), would like to declare that all contents included in this dissertation stand for my individual work without any aid, & this dissertation has not been submitted for any examination at academic as well as professional level previously. It also represents my own views & not essentially the ones associated with university.

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ACKNOWLEDGEMENT2

DECLARATION3

ABSTRACT5

CHAPTER 1: INTRODUCTION6

CHAPTER 2: LITERATURE REVIEW9

Introduction9

In Vitro Microelectrode Arrays10

From In Vitro to In Vivo23

Electrode Arrays For In Vivo Electrophysiology25

Design and Fabrication Aspects26

Pdms as a Soft and Flexible Substrate Material34

Flexible, Polymer-Based Electrode Materials34

Electrode Functionalization and Post-Processing Strategies36

Performance of Polymea Devices38

Interconnection Technologies41

Shielding42

CHAPTER 3: PHOTOISOMERIZATION AND GRADIENT STRAINS INDUCED BY LIGHT44

Dynamics of photoisomerization of azobenzene44

Light induced strain45

Decay of light due to absorption and the gradient strain47

CHAPTER 4: MODEL DEVELOPMENT50

Beam bending model of crosslinked chromatic LCP strips under light illumination50

Small-deflection Euler-Bernoulli LCP beam50

Large-deflection Euler-Bernoulli LCP beam52

CHAPTER 5: SIMULATION RESULTS AND DISCUSSION56

Beam bending of LCP laminated with substrates56

CHAPTER 6: CONCLUSIONS62

REFERENCES65

ABSTRACT

Photochromic liquid crystal polymer (LCP) films can undergo spontaneous mechanical deformations upon light illuminations. The light-induced strain is due to photoisomerization and the nematic-isotropic phase transition. A gradient strain exists due to absorption decay of the light intensity and will produce bending of LCP strips. Beam bending models are studied for single layered and bilayered LCP strips with substrate. The results show that the multilayered structures can have much larger bending curvature due to the utilization of the average light-induced contractions which were mostly not active for single-layered LCPs. Some structural optimizations for bilayered laminate are also discussed.

CHAPTER 1: INTRODUCTION

Liquid crystal polymers (LCPs) are a class of ordered polymers with liquid crystal (LC) moieties. Crosslinked LCPs include weakly linked liquid crystal elastomers (LCEs) and heavily linked liquid crystal glasses (LCGs). These LCPs exhibit many entirely new effects that are not simply enhancements of native liquid crystals or polymers (Lin & Huo, 2010: 41). This type of synthetic new material can undergo spontaneous mechanical deformation in response to some external stimulus such as thermal, electric, magnetic, chemical, and optical fields. LCPs are emerging as attractive candidates for many applications including remote con-trollable implementations and especially micro-mechanical devices such as actuators and sensors.

Currently, most studies have concentrated on monodomain nematic LCPs that possess a uniaxial orientation with the director n associated with aligned rod-like LC molecules. A nematic order parameter Q is introduced to measure the molecular alignments. Chromatic ordered nematic LCPs that are blended with light-sensitive chromophores (such as azobenzene or stilbene moieties) can undergo reversible mechanical deformation in response to a specific light wavelength. In fact, the idea of photo-induced mechani-cal responses in polymeric materials was first proposed by Lovrien in 1967 (Hogan & Tajbakhsh, 2002: 65). Most of the early work focused on the synthesis of azobenzene-based polymeric materials. Despite the considerable effort, the maximum light-induced strain was relatively limited (~1%). A breakthrough came in 2001 when Finkelmann et ...