Electromechanical Couplings in Soft Matter and Biology
Zelisko, Matthew R
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The ability of certain materials to deform in response to an electrical field or, conversely, generate an electrical field due to mechanical stimuli has tantalizing implications in fields ranging from biology to engineering. Various forms of electromechanical (and related) couplings, e.g., piezoelectricity, pyroelectricity, Maxwell stress effect, and ferroelectricity among others, have found use in topics ranging from energy harvesting, soft robots, sensors, and artificial muscles to the understanding of biological phenomena like mammalian hearing. In this dissertation, using methods ranging from quantum mechanics based density functional theory, empirical force-field molecular dynamics, statistical mechanics and continuum mechanics, the following topics are addressed: (i) Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets: Using quantum mechanical simulations and qualitative arguments from continuum mechanics, the mechanisms that lead to the development of unexpected piezoelectricity in this 2D material are elucidated. (ii) What is the mechanism behind biological ferroelectricity?: The first evidence of ferroelectricity in biological materials was recently discovered in 2012. Biological materials shown to be ferroelectric are largely composed of the protein elastin, a large biopolymer found in the extracellular domains of most tissues. A new model and an explanation for this intriguing observation are presented. Based on a relatively simple hypothesis, an analytical statistical mechanics model is developed which, coupled with insights from molecular dynamics, provides a plausible mechanism underpinning biological ferroelectricity. Furthermore, piezoelectric properties of tropoelastin, a precursor/monomer of elastin are predicted for the first time. Specifically, it is found that the piezoelectric constant of tropoelastin is larger than any known polymer. (iii) Mammalian hearing mechanism: The mechanisms underpinning the role of the ion channel Prestin in mammalian hearing are explored. The conductance of the Prestin channel is found via molecular dynamics, an important parameter for the derivation of an analytical model of the hearing mechanism. (iv) A novel approach to estimate Gaussian modulus and edge properties of lipid bilayers: The Gaussian modulus is a largely neglected parameter of membranes which is difficult to find. A model is derived to relate the properties of the free edge of a membrane to its fluctuations.