Low-molecular-mass gels responding to ultrasound and mechanical stress: towards self-healing materials

Abstract

In this review, we focus on the types of smart supramolecular gels whose self-assembly processes are affected or even triggered by physical forces including sonication and mechanical stress (mechanical force). The types of gels that are responsive to sonication and mechanical stress are examined and summarised. The gels exhibit non-covalent interactions among the gelator molecules and show dynamic and reversible properties controlled by the stimuli. Upon stimulation, the gelators cause instant and in situ gelation of organic solvents or water with different modes and outcomes of self-assembly. On the other hand, sonication and mechanical stress, as external factors, can give rise to dynamic changes in microscopic morphology, optical properties, etc. Certain thixotropic supramolecular gels exhibit perfect self-healing characteristics. The driving forces and the mechanism of the self-assembly process and the responsive outcome of morphological and spectroscopic changes are discussed. Those supramolecular gels responding to sonication and mechanical stress offer a wide range of applications in fields such as smart and adaptive materials, switches, drug control and release, and tissue engineering.

Interplay Between Mechanochemistry and Sonochemistry

“…These further assemble into three-dimensional networks that encapsulate the solvent and impede flow. This kind of supramolecular soft material which responds to sonication and stress may find numerous applications in biomedical research and the preparation of self-healing substances or mechanical switches [50,51].…”

“…However, unlike gels controlled by chemical stimuli, mechanical force and moderate sonication do not generally modify (or destroy) the structure of a molecule in the gel network. The role of sonication appears to be twofold [50]. Firstly, ultrasound can transform intramolecular interactions into favourable intermolecular interactions that lead to aggregation.…”

Photoisomerization-induced morphology and transparency transition in an azobenzene based two-component organogel system

“…Spontaneous self-assembly of small molecules into specific functional super-structures by various interactions is a powerful approach toward the development of smart materials and devices [1][2][3][4]. As a novel class of self-assembled materials, low molecular weight gels with three-dimensional networks capable of entrapping solvents through noncovalent interactions, including hydrogen bonds, p-p interactions and van der Waals contacts, have recently attracted considerable attention [5][6][7][8][9][10][11][12].…”

Smart Electrochemical Energy Storage Devices with Self‐Protection and Self‐Adaptation Abilities

“…[34,88] Motivated by living organisms whose injuries can be healed spontaneously by innate regenerative systems, smart energy storage devices with self-healing ability in response to external mechanical damage are very appealing, and are being studied intensely, [34,89,90] facilitated by the rapid development of healable materials. [91][92][93][94][95][96][97] As a consequence, the service time, reliability and durability of these devices can be significantly enhanced.…”