University of Groningen
Light switchable surface topographies
Liu, Ling
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Publication date: 2018
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Liu, L. (2018). Light switchable surface topographies: Modelling and design of photo responsive topographical changes of liquid crystal polymer films. Rijksuniversiteit Groningen.
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Light Switchable Surface
Topographies
Modelling and Design of Photo Responsive Topographical
Changes of Liquid Crystal Polymer Films
PhD thesis
to obtain the degree of PhD at the
University of Groningen
on the authority of the
Rector Magnificus Prof. E. Sterken
and in accordance with
the decision by the College of Deans.
This thesis will be defended in public on
Monday 10 September 2018 at 11:00 hours
by
Ling Liu
born on 29 March 1988
in Jiangxi, China
Supervisors
Prof. Patrick R. Onck
Prof. Erik Van der Giessen
Assessment Committee
Prof. Albert P.H.J. Schenning
Prof. Mark Warner
iv
Cover image:
An imaginary image of an active surface featuring dynamic morphologies subject to sunlight. Fueled by the sun, the surface absorbs light within a wide range of wave-lengths and converts the sunlight energy into elastic and kinetic energy of the system. This type of surfaces with continuous light-fueled topographical deformations could function as perpetual actuators to achieve cargo transportation and self-cleaning.
This research forms a part of the research programme of the Dutch Polymer Institute (DPI), project #775 TOPSWITCH and Netherlands Organisation for Scientific Re-search (NWO), project 735.015.014.01.
This research was conducted in the Micromechanics of Materials group, Zernike In-stitute for Advanced Materials, University of Groningen.
ISBN 978-94-034-0739-5 (printed version) ISBN 978-94-034-0738-8 (electronic version)
CONTENTS v
Contents
Table of Contents v 1 General Introduction 1
1.1 Responsive morphological changes . . . 2
1.1.1 Background and motivation: inspiration by nature . . . 2
1.1.2 Functionalities of responsive materials . . . 4
1.2 Responsive liquid crystal polymers . . . 16
1.2.1 Liquid crystal glassy polymers . . . 17
1.2.2 Liquid crystal elastomers . . . 20
1.2.3 Light responsive liquid crystal polymers . . . 21
1.3 Morphological transformation mechanisms . . . 23
1.3.1 Folding and origami . . . 24
1.3.2 Topological Surface texture changes of substrated films . . . . 26
1.3.3 Surface and geometric instabilities . . . 27
1.4 Research objectives . . . 28
1.5 Outline of the thesis . . . 29
2 Topographical Changes in Photo-responsive Liquid Crystal films: A Computational Framework 33 2.1 Introduction . . . 34
2.2 Computational model . . . 36
2.2.1 Opto-mechanical constitutive equations . . . 36
2.2.2 Light attenuation model . . . 38
2.3 Numerical results . . . 40 2.3.1 Input parameters . . . 41 2.3.2 Light profiles . . . 41 2.3.3 Uniform films . . . 43 2.3.4 Linearly-patterned films . . . 45 2.3.5 Polydomain films . . . 54 2.3.6 Fingerprint films . . . 57
2.4 Discussion and conclusion . . . 61
Appendix 2.A Fitting of light parameters . . . 65
3 Travelling Waves on Photo-Switchable Polymer Films by Rotating Polarized Light 67 3.1 Introduction . . . 67
vi CONTENTS
3.2.1 Light attenuation model . . . 71
3.2.2 Optomechanical equations . . . 72
3.2.3 Roughness parameters . . . 72
3.3 Results . . . 73
3.3.1 Optimal wave amplitude at small and large film thicknesses . . 73
3.3.2 Thin films at low light intensity . . . 75
3.3.3 Thick films . . . 78
3.4 Discussion and conclusion . . . 79
Appendix 3.A Rotatory travelling waves on disclination patterns . . . 83
4 Light-driven Topographical Morphing of Azobenzene-doped Liq-uid Crystal Polymer Films via Tunable Photo-polymerization In-duced Diffusion 87 4.1 Introduction . . . 88
4.2 Modelling framework . . . 90
4.2.1 Photo-polymerization diffusion model . . . 90
4.2.2 Light penetration model . . . 93
4.2.3 Constitutive model . . . 97
4.3 Results . . . 100
4.3.1 Bending and twisting of cantilever films . . . 102
4.3.2 Patterned films . . . 106
4.3.3 Surface travelling wave . . . 111
4.4 Discussion and conclusions . . . 118
Appendix 4.A Diffusion schemes with varied mobilities . . . 125
5 Enhanced Deformation of Azobenzene-modified Liquid Crystal Poly-mers under Dual Wavelength Exposure: A Photophysical Model 129 5.1 Introduction . . . 130
5.2 Photophysics model . . . 130
5.3 Photo-mechanical response . . . 134
5.4 Optimal wavelength . . . 139
5.5 Conclusion . . . 141
Appendix 5.A Light attenuation parameterization . . . 143
Appendix 5.B Optimal wavelength . . . 145
Summary 149
Samenvatting 151
Bibliography 153
Curriculum Vitae 175 Acknowledgments 177
