Rheology of Complex Fluid Films for Biological and Mechanical Adhesive Locomotion Randy H ...

143 Pages·2006·3.33 MB·English

Rheology of Complex Fluid Films for Biological
and Mechanical Adhesive Locomotion
by
Randy H. Ewoldt
B.S., Mechanical Engineering
Iowa State University (2004)
Submitted to the Department of Mechanical Engineering
in partial fulfillment of the requirements for the degree of
Master of Science in Mechanical Engineering
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
June 2006
(cid:176)c Massachusetts Institute of Technology 2006. All rights reserved.
Author ..............................................................
Department of Mechanical Engineering
May 12, 2006
Certified by..........................................................
Anette Hosoi
Assistant Professor, Mechanical Engineering
Thesis Supervisor
Certified by..........................................................
Gareth H. McKinley
Professor, Mechanical Engineering
Thesis Supervisor
Accepted by.........................................................
Lallit Anand
Chairman, Department Committee on Graduate Students
2
Rheology of Complex Fluid Films for Biological and
Mechanical Adhesive Locomotion
by
Randy H. Ewoldt
Submitted to the Department of Mechanical Engineering
on May 12, 2006, in partial fulfillment of the
requirements for the degree of
Master of Science in Mechanical Engineering
Abstract
Many gastropods, such as snails and slugs, crawl using adhesive locomotion, a tech-
niquethatallowstheorganismstoclimbwallsandwalkacrossceilings. Theseanimals
stick to the crawling surface by excreting a thin layer of biopolymer mucin gel, known
as pedal mucus, and their acrobatic ability is due in large part to the rheological prop-
erties of this slime. The primary application of the present research is to enable a
mechanical crawler to climb walls and walk across ceilings using adhesive locomotion.
A properly selected slime simulant will enable a mechanical crawler to optimally
perform while climbing in the horizontal, inclined, and inverted positions.
To this end, the rheology of gastropod pedal mucus is examined in greater detail
than any previously published work. The linear rheological response of pedal mucus
is examined with flow, oscillation, and creep tests. Nonlinear rheology is examined
with large amplitude oscillatory shear (LAOS), and analyzed with Lissajous curves,
Fourier transform rheology, and a new measure of non-linear elasticity. In addition,
pedal mucus is examined with a flexure-based microgap rheometer, which can test
the sample at the biologically relevant gap of 10-20µm, the measured thickness of
pedal mucus under a crawling slug.
Adhesive locomotion of a mechanical crawler is modeled in order to find the cri-
teria for an optimal slime simulant. After developing the selection criteria for the
ideal simulant, a range of candidate materials are examined including polymeric gels,
particulate gels, emulsions, composites, and field-responsive fluids. Two promising
simulants are examined in detail and compared with native gastropod pedal mucus.
Thesis Supervisor: Anette Hosoi
Title: Assistant Professor, Mechanical Engineering
Thesis Supervisor: Gareth H. McKinley
Title: Professor, Mechanical Engineering

Acknowledgments
I would like to thank the National Science Foundation Graduate Research Fellowship
Program for financial support and the freedom to pursue this research, Brian Chan
for his original idea to pursue a robotic snail, and my advisors Prof. Anette Hosoi
and Prof. Gareth H. McKinley for their enthusiasm, encouragement, and confidence
in me. Furthermore, I would like to thank Dr. Christian Clasen for his help with
microgap rheology, and my numerous lab mates, colleagues, and friends for their
support.
Finally, I am indebted to my wife Erin, who continues to be a constant source of
wisdom, encouragement, and strength. A.M.D.G.
R.H.E.

Contents
1 Introduction and Background 19
1.1 Adhesive locomotion . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.2 Mucus composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.2.1 Vertebrate mucus . . . . . . . . . . . . . . . . . . . . . . . . . 22
1.2.2 Invertebrate mucus . . . . . . . . . . . . . . . . . . . . . . . . 24
1.3 Prior work on the rheology of mucus . . . . . . . . . . . . . . . . . . 24
1.3.1 Vertebrate mucus . . . . . . . . . . . . . . . . . . . . . . . . . 24
1.3.2 Invertebrate mucus . . . . . . . . . . . . . . . . . . . . . . . . 26
2 Experimental Methods 29
2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
2.2 Linear viscoelasticity and steady-flow rheology . . . . . . . . . . . . . 30
2.3 Nonlinear oscillatory shear rheology . . . . . . . . . . . . . . . . . . . 32
2.3.1 Fourier transform rheology . . . . . . . . . . . . . . . . . . . . 33
2.3.2 Lissajous curves . . . . . . . . . . . . . . . . . . . . . . . . . . 34
2.3.3 Newly proposed quantitative measures for LAOS . . . . . . . 37
2.4 Microgap rheology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
2.4.1 Gap limits of bulk and microgap rheology . . . . . . . . . . . 42
2.4.2 FMR working principles . . . . . . . . . . . . . . . . . . . . . 44
2.4.3 FMR experimental range . . . . . . . . . . . . . . . . . . . . . 47
2.4.4 Theoretical models of LAOS rheology on the FMR . . . . . . 47
7
3 Results and Discussion: Rheology of Pedal Mucus from Terrestrial
Gastropods 55
3.1 Traditional rheology . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3.2 Nonlinear LAOS rheology . . . . . . . . . . . . . . . . . . . . . . . . 64
3.2.1 Viscoelastic moduli . . . . . . . . . . . . . . . . . . . . . . . . 64
3.2.2 Fourier transform rheology . . . . . . . . . . . . . . . . . . . . 66
3.2.3 Lissajous curves . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.2.4 Quantitative measure of stiffening . . . . . . . . . . . . . . . . 70
3.3 Microgap rheology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.4 Overview: the Pipkin diagram . . . . . . . . . . . . . . . . . . . . . . 76
4 Modeling Adhesive Locomotion: Criteria for Optimizing a Slime
Simulant 79
4.1 Adhesive locomotion model . . . . . . . . . . . . . . . . . . . . . . . 79
4.1.1 Velocity expression . . . . . . . . . . . . . . . . . . . . . . . . 81
4.1.2 Efficiency expression . . . . . . . . . . . . . . . . . . . . . . . 83
4.2 Horizontal locomotion simulation . . . . . . . . . . . . . . . . . . . . 85
4.3 Inclined locomotion model . . . . . . . . . . . . . . . . . . . . . . . . 88
4.3.1 Generalized Newtonian fluid . . . . . . . . . . . . . . . . . . . 89
4.3.2 Idealized yield stress fluid . . . . . . . . . . . . . . . . . . . . 90
4.3.3 Yield stress fluid with restructuring time . . . . . . . . . . . . 93
5 Survey of Possible Slime Simulants 101
5.1 Polymeric gels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
5.1.1 Material preparation . . . . . . . . . . . . . . . . . . . . . . . 103
5.1.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
5.2 Particulate gels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
5.2.1 Material preparation . . . . . . . . . . . . . . . . . . . . . . . 107
5.2.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
5.3 Emulsions, foams, and composites . . . . . . . . . . . . . . . . . . . . 109
5.3.1 Material preparation . . . . . . . . . . . . . . . . . . . . . . . 110
5.3.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
5.4 Field-responsive fluids . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.4.1 Material preparation . . . . . . . . . . . . . . . . . . . . . . . 113
5.4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114
6 Results: Detailed Rheology of Two Slime Simulants 115
6.1 Steady shear flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
6.2 Creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
6.3 Small amplitude oscillatory shear (SAOS) . . . . . . . . . . . . . . . 120
6.4 Nonlinear, large amplitude oscillation . . . . . . . . . . . . . . . . . . 120
6.5 Time dependency of yield stress . . . . . . . . . . . . . . . . . . . . . 125
6.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
7 Conclusions 131
A Biochemistry Reference 135