Research progress on chitosan and its derivatives in the fields of corrosion inhibition and antimicrobial activity.

Chitosan stands out as the only known polysaccharide of its kind, second only to cellulose. As the second-largest biopolymer globally, chitosan and its derivatives are extensively used in diverse areas such as metal anti-corrosion prevention, food production, and medical fields. Its benefits include environmental friendliness, non-toxicity, cost-effectiveness, and biodegradability. Notably, the use of chitosan and its derivatives has gained substantial attention and has been extensively researched in the fields of metal anti-corrosion prevention and antibacterial applications. By means of chemical modification or synergistic action, the inherent limitations of chitosan can be substantially improved, thereby enhancing its biological and physicochemical properties to meet a wider range of applications and more demanding application requirements. This article offers a comprehensive review of chitosan and its modified composite materials, focusing on the enhancement of their anticorrosion and antibacterial properties, as well as the mechanisms by which they serve as anticorrosion and antibacterial agents. Additionally, it summarizes the synthesis routes of various modification methods of chitosan and their applications in different fields, aiming to contribute to the interdisciplinary development and potential applications of chitosan in various areas.

Effect of the Molecular Weight of Polyelectrolyte and Surfactant Chain Length on the Solid-Phase Molecular Self-Assembly.

Solid-phase molecular self-assembly (SPMSA) is emerging as an efficient approach, leading to scale-span self-assembled supramolecular films. With SPMSA, freestanding macroscopic supramolecular films can be formed upon mechanically pressing the precipitates formed with polyelectrolytes and oppositely charged surfactants. Herein, we report that the film formation ability and the mechanical strength of the resultant film depend highly on the surfactant chain lengths and the molecular weight of polyelectrolytes. A coarse-grained molecular dynamics study revealed that the longer surfactant chains are beneficial for the ordered assembly of surfactant bilayers in the film, whereas the larger molecular weight of PE favors the enhanced mechanical strength of the film by promoting the long-range order of the surfactant bilayers. The current results disclosed the physical insight of the surfactant chain length and the molecular weight of polyelectrolytes into the film structure and mechanical strength, which is of practical importance in guiding the creation of SPMSA materials.

High-performance corrosion resistance of chemically-reinforced chitosan as ecofriendly inhibitor for mild steel.

Finding new cost-effective and environmentally friendly anti-corrosion materials is a never-ending task. The present study is to prepare a new formulation based on chitosan derivatives with different degrees of substitution (chitosan-5-HMF) as an efficient green corrosion inhibitor to protect mild steel against corrosion in 1 M HCl. The inhibition performance of chitosan-5-HMF was determined by electrochemical tests coupled with theoretical study like as molecular dynamics (MD) simulations to assess the reactivity and adsorption mechanisms between chitosan-5-HMF and Fe. The obtained results revealed that chitosan-5-HMF3 performs excellently inhibition performance where its inhibition efficiency reached 97.01% at 200 mg/L, and it acted as an anode-based mixed inhibitor. SEM and contact angle analysis showed the formation of compact chitosan-5-HMF film on the steel surface. Molecular dynamic simulations also manifested that chitosan-5-HMF was absorbed more strongly on the metal surface in a parallel mode.

Physical Insight into the Conditions Required in the Solid-Phase Molecular Self-Assembly of SDS Revealed by Coarse-Grained Molecular Dynamics Simulation.

Molecular self-assembled materials have attracted considerable interest in recent years. As part of the efforts to overcome the shortcoming that the solution-based methods were hardly applicable in preparing bulk macroscopic molecular self-assemblies, Yan [ CCS Chem. 2020, 2, 98-106] developed a strategy of solid-phase molecular self-assembly (SPMSA) that allows scaling up the generation of massive supramolecular films. It is highly desired to understand the physical insight into the SPMSA at a molecular level. Here, in combination with the experimental study, we report molecular dynamics (MD) simulations on the SPMSA of the surfactant sodium dodecyl sulfate (SDS) using a coarse-grained method with the Martini force field model. The MD simulations clearly manifest that a small amount of water is required to endow the SDS molecules with sufficient mobility to self-assemble, and the smaller size of the preassembled SDS particles favors their further fusion into mesophases by reducing the total surface Gibbs free energy, while the smaller interparticle distance decreases the time for the particle fusion. The simulation results agree well with the conditions required in the experiment, confirming that SMPSA is a free-energy-favored process leading to bulk self-assembled materials.

In Situ Investigation of Dynamic Silver Crystallization Driven by Chemical Reaction and Diffusion.

Rational synthesis of materials is a long-term challenging issue due to the poor understanding on the formation mechanism of material structure and the limited capability in controlling nanoscale crystallization. The emergent in situ electron microscope provides an insight to this issue. By employing an in situ scanning electron microscope, silver crystallization is investigated in real time, in which a reversible crystallization is observed. To disclose this reversible crystallization, the radicals generated by the irradiation of electron beam are calculated. It is found that the concentrations of radicals are spatiotemporally variable in the liquid cell due to the diffusion and reaction of radicals. The fluctuation of the reductive hydrated electrons and the oxidative hydroxyl radicals in the cell leads to the alternative dominance of the reduction and oxidation reactions. The reduction leads to the growth of silver crystals while the oxidation leads to their dissolution, which results in the reversible silver crystallization. A regulation of radical distribution by electron dose rates leads to the formation of diverse silver structures, confirming the dominant role of local chemical concentration in the structure evolution of materials.