The physical origin of reversible surface attachment in insects
File(s)
Author(s)
Attipoe, Andrea
Type
Thesis
Abstract
Insects can attach themselves on surfaces under an impressive range of environmental conditions using adhesive pads. Earlier studies indicated the contact under the pad is mediated by a thin layer of liquid secretion, which could produce adhesive forces through capillary bridges and viscous effects. Previous work found another source of viscous dissipation in the viscoelastic properties of the pad. This lead to the formulation of two main supposed mechanisms of adhesion: "wet" and "dry" models, where temperature and rate, following distinct laws, act as crucial factors influencing these models.
The wetting properties of the liquid secreted by the stick insect Carausius morosus were determined through interference reflection microscopy, and found to be weakly affected by temperature. Dewetting experiments indicated that the secretion’s viscosity is exponentially dependent on temperature.
The storage and loss moduli of the pad were determined through creep experiments, and were found to be weakly influenced by temperature when compared to typical amorphous polymers.
The resulting "wet" and "dry" models were compared to the adhesive forces produced by single pads during detachment at different temperatures and pulling rates. The measured forces were drastically affected by rate, while temperature had no significant effect.
The adhesive performance of insect pads can thus not be explained by "wet" models, due to the inconsistencies of capillary forces with rate dependence, and viscous forces with weak temperature influence. On the other hand, the rate dependence of the energy required to break adhesive bonds in viscoelastic fracture corresponded with the measured pull-off forces, and the weak temperature dependence of the viscoelastic properties of the pad was consistent with the similar performance of the pads. Hence, I argue that fracture mechanics theories of viscous dissipation offer a viable answer to the question of reversible surface attachment in insects.
The wetting properties of the liquid secreted by the stick insect Carausius morosus were determined through interference reflection microscopy, and found to be weakly affected by temperature. Dewetting experiments indicated that the secretion’s viscosity is exponentially dependent on temperature.
The storage and loss moduli of the pad were determined through creep experiments, and were found to be weakly influenced by temperature when compared to typical amorphous polymers.
The resulting "wet" and "dry" models were compared to the adhesive forces produced by single pads during detachment at different temperatures and pulling rates. The measured forces were drastically affected by rate, while temperature had no significant effect.
The adhesive performance of insect pads can thus not be explained by "wet" models, due to the inconsistencies of capillary forces with rate dependence, and viscous forces with weak temperature influence. On the other hand, the rate dependence of the energy required to break adhesive bonds in viscoelastic fracture corresponded with the measured pull-off forces, and the weak temperature dependence of the viscoelastic properties of the pad was consistent with the similar performance of the pads. Hence, I argue that fracture mechanics theories of viscous dissipation offer a viable answer to the question of reversible surface attachment in insects.
Version
Open Access
Date Issued
2023-01
Date Awarded
2024-03
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Labonte, David
Sponsor
Biotechnology and Biological Sciences Research Council (Great Britain)
European Research Council
Grant Number
BMPF P72408
BMPF P78382
Publisher Department
Bioengineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)