Date of Degree

9-2022

Document Type

Dissertation

Degree Name

Ph.D.

Program

Physics

Advisor

Xi Chen

Committee Members

Steven Greenbaum

M. Lane Gilchrist

Nicolas Giovambattista

Tong Wang

Subject Categories

Biological and Chemical Physics | Engineering Physics

Keywords

Peptidoglycan, Water-responsive materials, Evaporation energy harvesting, Nano-confined water

Abstract

Water-responsive materials that reversibly deform in response to humidity changes show great potential for developing muscle-like actuators for miniature and biomimetic robotics. This thesis demonstrates that peptidoglycan exhibits ultrahigh water-responsive actuation energy and power densities, which are orders of magnitude higher than those of frequently used actuators, such as piezoelectric actuators and dielectric elastomers. Surprisingly, peptidoglycan exhibits an energy conversion efficiency of ~66.8%, which could be attributed to its super-viscous nanoconfined water that efficiently translates water’s movement to peptidoglycan’s mechanical deformation. The systematic water-responsive characterizations of peptidoglycan from different microorganisms and peptide crystals indicate that enhanced H-bonding interactions in water-responsive materials are critical to the efficient energy conversion from chemical potential of water to materials’ mechanical motions, suggesting guidelines for designing water-responsive materials with higher performance. Using peptidoglycan, we developed water-responsive composite actuators that can be integrated into a range of engineering structures, including a robotic gripper and linear actuators, which illustrate the possibilities of using peptidoglycan as building blocks for high-efficiency water-responsive actuators.

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