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Abstract It is challenging to post-tune the sensitivity of a tactile force sensor. Herein, a facile method is reported to tailor the sensing properties of conductive polymer composites by utilizing the liquid-like property of dynamic polymer matrix at low strain rates. The idea is demonstrated using dynamic polymer composites (CB/dPDMS) made via evaporation-induced gelation of the suspending toluene solution of carbon black (CB) and acid-catalyzed dynamic polydimethylsiloxane (dPDMS). The dPDMS matrices allow CB to redistribute to change the sensitivity of materials at the liquid-like state, but exhibit typical solid-like behavior and thus can be used as strain sensors at normal strain rates. It is shown that the gauge factor of the polymer composites can be easily post-tuned from 1.4 to 51.5. In addition, the dynamic polymer matrices also endow the composites with interesting self-healing ability and recyclability. Therefore, it is envisioned that this method can be useful in the design of various novel tactile sensing materials for many applications.
Growth constitutes a powerful method to post-modulate materials’ structures and functions without compromising their mechanical performance for sustainable use, but the process is irreversible. To address this issue, we here report a growing-degrowing strategy that enables thermosetting materials to either absorb or release components for continuously changing their sizes, shapes, compositions, and a set of properties simultaneously. The strategy is based on the monomer-polymer equilibrium of networks in which supplying or removing small polymerizable components would drive the networks toward expansion or contraction. Using acid-catalyzed equilibration of siloxane as an example, we demonstrate that the size and mechanical properties of the resulting silicone materials can be significantly or finely tuned in both directions of growth and decomposition. The equilibration can be turned off to yield stable products or reactivated again. During the degrowing-growing circle, material structures are selectively varied either uniformly or heterogeneously, by the availability of fillers. Our strategy endows the materials with many appealing capabilities including environment adaptivity, self-healing, and switchability of surface morphologies, shapes, and optical properties. Since monomer-polymer equilibration exists in many polymers, we envision the expansion of the presented strategy to various systems for many applications.
Polymer networks with dynamic covalent bonds show properties and functions not achievable with covalently crosslinked systems. Among of the different polymers connected by dynamic covalent bonds, this Thesis is based on polydimethylsiloxane (PDMS) elastomers prepared via acid-catalyzed ring-opening polymerization of cyclic monomer and cross-link. This reaction presents different dynamic equilibrium reactions, such as polymer-oligomer equilibrium and bond exchange reaction. In this Thesis, I have developed three different functional materials based on acid-catalyzed PDMS. In Chapter 1, the basic concepts of dynamic bond chemistry and the state-of-the-art of dynamic covalent polymer networks are described. In Chapter 2, a new PDMS-based elastomer that can self-grow and self-degrow is presented. Chapter 3 describes how the acid-catalyzed PDMS was used to fabricate a strain sensor that could flexibly post-tailor the sensor properties. In the last part (Chapter 4), a gas-flow enhanced relaxation behavior observed in CB/dPDMS composite is described.
