Graphene enhanced and in situ-formed alginate hydrogels for reducing friction and wear of polymers

2D materials for Tribo-corrosion and -oxidation protection: A review

The recent rise of 2D materials has extended the opportunities of tuning a variety of properties. Tribo-corrosion, the complex synergy between mechanical wear and chemical corrosion, poses significant challenges across numerous industries where materials are subjected to both tribological stressing and corrosive environments. This intricate interplay often leads to accelerated material degradation and failure. This review critically assesses the current state of utilizing 2D nanomaterials to enhance tribo-corrosion and -oxidation behavior. The paper summarizes the fundamental knowledge about tribo-corrosion and -oxidation mechanisms before assessing the key contributions of 2D materials, including graphene, transition metal chalcogenides, hexagonal boron nitride, MXenes, and black phosphorous, regarding the resulting friction and wear behavior. The protective roles of these nanomaterials against corrosion and oxidation are investigated, highlighting their potential in mitigating material degradation. Furthermore, we delve into the nuanced interplay between mechanical and corrosive factors in the specific application of 2D materials for tribo-corrosion and -oxidation protection. The synthesis of key findings underscores the advancements achieved through integrating 2D nanomaterials. An outlook for future research directions is provided, identifying unexplored avenues, and proposing strategies to propel the field forward. This analysis aims at guiding future investigations and developments at the dynamic intersection of 2D nanomaterials, tribo-corrosion, and -oxidation protection.

High Performance Conductive Hydrogel for Strain Sensing Applications and Digital Image Mapping

A hydrogel strain sensor can successfully transform its deformation into resistance changes, offering novel options for the Internet of Things (IoT) and artificial intelligence (AI). However, it remains challenging to prepare hydrogel sensors with superior performance (e.g., high conductivity). Here, we produced a conductive hydrogel (named PPC hydrogel) utilizing only three components, PVA (poly(vinyl alcohol)), PAAS (polyacrylate sodium), and CaCl₂, through freezing cross-linking and ion chelation. The PPC hydrogel is endowed with high electrical conductivity of approximately 5.2 S/m without the addition of highly conductive materials due to the unique ionic cluster mesh structure, thus enabling an outstanding performance of strain sensing. The PPC hydrogel also maintains electrical conductivity in frozen and underwater conditions and resists swelling in underwater environments, allowing it to be used under water for extended periods of time (more than 15 days). The PPC hydrogel-based strain sensor can be used as a flexible electrode for electrocardiogram (ECG) and electromyogram (EMG) examinations and sensitively monitor human activity as well as recognize handwriting. Moreover, we designed a python-based visualization program combined with a PPC hydrogel array to implement pressure-sensing digital image mapping for remote IoT monitoring. As a flexible sensor for biosafety, the PPC hydrogel has potential applications in the field of intelligent sensing, the IoT, and even Internet of Body systems.

Molecular dynamics simulation of hyaluronic acid hydrogels: Effect of water content on mechanical and tribological properties

BACKGROUND AND OBJECTIVE

Recently conducted biomedical studies have shown that the drug diffusivity of hyaluronic acid hydrogel plays an important role in the treatment of joint diseases. The drug diffusivity is closely related to the water content of hydrogel. In addition, different water content will not only affect its mechanical and tribological properties, but also change the effect of drug release.

METHODS

In this work, a Molecular dynamics simulation was used to investigate the effect of water content on spatial distribution, tribological and mechanical properties of a hyaluronic acid hydrogel network. This paper focuses on the analysis and calculation of the radial distribution function of 20, 40, 60, and 80% water content model and the friction force and mechanical parameters under the influence of different load and friction speed.

RESULTS

The results show that at 20 and 40% water content, the spatial distribution is loose and the intermolecular force is not strong, resulting in a major lack in tribological and mechanical properties; whereas at 60 and 80% water content, the spatial distribution becomes gradually compact and the intermolecular force is gradually increased. The tribological and mechanical properties manifest a marked improvement.

CONCLUSIONS

The calculations reveal that the hydrogel model has the best wear resistance, pressure resistance, and plastic deformation resistance at 80% water content. In the range of 20-80% water content, the mechanical properties and friction properties of hydrogels become better and better with the increase of water content.

Experimental Study on Properties of Ultrasonic Coupling Agent with Graphene in NDT

An ultrasonic coupling agent, as an acoustic medium between the ultrasonic probe and the surface of the specimens, is indispensable in Nondestructive Testing (NDT). Whether it is liquid, air, or solid coupling agent, the problem of improving the efficiency of ultrasonic propagation in a coupling agent is one worth studying. Glycerol and hydrogels are two common liquid coupling agents in NDT. This study intended to investigate the effect of graphene addition on the performance of these coupling agents in NDT. Firstly, based on the theory of acoustic impedance matching, the authors established an index system to evaluate the performance of ultrasonic coupling agent by experiments. Secondly, hydrogel–graphene and glycerol–graphene composite coupling agents were prepared by adding three-dimensional graphene structure powders with mass fraction of 0.25%, 0.5%, 0.75%, and 1% to CG-98 hydrogel coupling agent and HG-99 glycerol coupling agent, respectively. Corresponding experiments were conducted on these composite coupling agents. Peak-to-peak value, attenuation coefficient, and energy value of first echo are calculated at different frequencies. The experimental results showed that graphene can significantly improve the ultrasonic propagation performance of hydrogel and glycerin coupling agents. In addition, when the mass fraction of graphene added was 0.75%, the coupling agent had the best performance. Finally, we measured the acoustic impedance values of the composite couplings with different graphene contents to demonstrate the reliability of the experimental results.