Effect of alkali metal cations on network rearrangement in polyisoprene ionomers

The effects of cations, Li⁺, Na⁺, and Cs⁺, on the structure of ionic aggregates and network rearrangement in carboxylated polyisoprene (PI) ionomers were studied. We found that network rearrangement via interaggregate hopping of metal carboxylates is improved with a decrease in cation size, even though density functional theory (DFT) calculation indicated the increase in the attractive interaction between metal carboxylates. At the same time, we also found that as the size of the cation decreases, the inclusion of the PI segment in the ionic aggregate increases. The DFT calculation suggested the cation-π interaction between the cation and double bonds in the PI segment as the cause for the inclusion. The inclusion of the PI segment with a low glass transition temperature (T_g) plasticizes the ionic aggregate and would sterically hinder the attractive interaction between metal carboxylates. In fact, the electron spin resonance measurement revealed a decrease in the T_g of the ionic aggregate with a decrease in cation size. Based on our findings, we proposed that the inclusion of PI segments in the ionic aggregate is the possible cause for the enhancement of network rearrangement in the carboxylated PI ionomers with a decrease in the cation size.

Self-Healing Materials for Electronics Applications

Self-healing materials have been attracting the attention of the scientists over the past few decades because of their effectiveness in detecting damage and their autonomic healing response. Self-healing materials are an evolving and intriguing field of study that could lead to a substantial increase in the lifespan of materials, improve the reliability of materials, increase product safety, and lower product replacement costs. Within the past few years, various autonomic and non-autonomic self-healing systems have been developed using various approaches for a variety of applications. The inclusion of appropriate functionalities into these materials by various chemistries has enhanced their repair mechanisms activated by crack formation. This review article summarizes various self-healing techniques that are currently being explored and the associated chemistries that are involved in the preparation of self-healing composite materials. This paper further surveys the electronic applications of self-healing materials in the fields of energy harvesting devices, energy storage devices, and sensors. We expect this article to provide the reader with a far deeper understanding of self-healing materials and their healing mechanisms in various electronics applications.

Highly stretchable and self-healing cellulose nanofiber-mediated conductive hydrogel towards strain sensing application

HYPOTHESIS

Hydrogel-based sensors have attracted considerable attention due to potential opportunities in human health monitoring when both mechanical flexibility and sensing ability are required. Therefore, the integration of excellent mechanical properties, electrical conductivity and self-healing properties into hydrogels may improve the application range and durability of hydrogel-based sensors.

EXPERIMENTS

A novel composite hydrogel composed of polyaniline (PANI), polyacrylic acid (PAA) and 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-oxidized cellulose nanofibrils (TOCNFs) was designed. The viscoelastic, mechanical, conductive, self-healing and sensing properties of hydrogels were studied.

FINDINGS

The TOCNF/PANI/PAA hydrogel exhibits a fracture strain of 982%, tensile strength of 74.98 kPa and electrical conductivity of 3.95 S m^-1, as well as good mechanical and electrical self-healing properties within 6 h at ambient temperature without applying any stimuli. Furthermore, owing to the high sensitivity of the TOCNF/PANI/PAA-0.6 hydrogel-based strain sensor (gauge factor, GF = 8.0), the sensor can accurately and rapidly detect large-scale motion and subtle localized activity. The proposed composite hydrogel is as a promising material for use as soft wearable sensors for health monitoring and smart robotics applications.

Extremely tough and healable elastomer realized via reducing the crystallinity of its rigid domain

We propose a new concept, called “toughening the rigidity”, for the field of self-healing materials.

Self-healing elastomers based on conjugated diolefins: a review

The introduction of dynamic covalent and physical crosslinks into diolefin-based elastomers improves mechanical and self-healing properties. The presence of dynamic crosslinks also helps in the reprocessing of elastomers.