If self-healing materials can be prepared via simple technology and methods using nontoxic materials, this would be a great step forward in the creation of environmentally friendly self-healing materials. In this paper, the specific structural parameters of the various hydrogen bonds between chitosan (CS) and polyacrylic acid (PAA) were calculated. Then, multilayer polyelectrolyte films were fabricated with CS and PAA based on layer-by-layer (LbL) self-assembly technology at different pH values. The possible influence of pH on the (CS/PAA) × 30 multilayer polyelectrolyte film was investigated. The results show that the interactions between CS and PAA, swelling capacity, microstructure, wettability, and self-healing ability are all governed by the pH of the CS solution. When the pH value of the CS solution is 3.0, the prepared multilayer polyelectrolyte film (CS3.0/PAA2.8) × 30 has fine-tuned interactions, a network-like structure, good swelling ability, good hydrophilicity, and excellent self-healing ability. This promises to greatly widen the future applications of environmentally friendly materials and bio-materials.

The consumption of fresh-cut apples has grown rapidly due to consumers' increasing willingness to enjoy prepared and ready-to-eat fruits. But fresh-cut apples tend to experience severe enzymatic browning which discourages people to taste. Chitosan (CS) coating containing ascorbic acid (AA) or calcium chloride (CaCl 2) were applied on fresh-cut apples in this work to observe their preservation effects. Their appearance, weight change were evaluated during the storage at room temperature, besides, AA content, soluble solid content were analyzed at the end of storage. CS-CaCl 2 coating has better preservation effect than CS-AA coating when they were applied on fresh-cut apples. CS-CaCl 2 coating showed lower weight loss and higher AA content of apple slices than CS-AA coating. CS-CaCl 2 coating was also good at anti-browning in terms of the appearance of coated apple slices.

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Recently, one-dimensional photonic crystals (1DPCs) have attracted considerable interest because they exhibit a material-specific response profile to external stimuli. In our previous work, TiO2/GO 1DPCs, the stopbands of which can be made to span the whole visible range, were fabricated by spin-coating technique. The prepared 1DPCs have a double response to both dimethyl sulfoxide and alkali solution. However, the response is slow, insensitive, and irreversible. To improve the responsiveness of the 1DPCs, poly(ethylene glycol) (PEG)-cross-linked poly((methyl vinyl ether)-co-maleic acid) (PMVE-co-MA) hydrogels were embedded in those crystals. The results demonstrated that modified 1DPCs with different stopbands could be obtained by controlling the speed of the spin-coating technique. The prepared 1DPCs have better responsiveness to external solution pH.

We developed a smart and reproducible fabrication of pH/temperature dually responsive sensor by taking advantage of one dimensional photonic crystals (1DPCs). TiO 2 /P(AA-bis-NiPAAm) 1DPCs were fabricated by spin-coating TiO 2 and copolymers P(AA-bis-NiPAAm) onto silicon wafers. When using the 1DPCs dually responsive polymer films as pH/temperature sensor, both refraction wavelength and peak refraction intensity values were derived, and the reproducible change could be observed by the naked eye through a change in color.

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