Poly (vinyl alcohol)/sodium alginate hydrogels were prepared by freeze‐thaw followed by calcium ion crosslinking. Chloramphenicol release behavior from the poly (vinyl alcohol)/sodium alginate hydrogels in mimic conditions of gastrointestinal tract was examined. The effects of composition, number of freeze‐thaw cycles and calcium ion concentration on drug release process were investigated. The results showed that the cumulative release amount of chloramphenicol from the hydrogels (crosslinked through 4 freeze‐thaw cycles and immersed in 2 % calcium chloride solution) decreased from 84.3 % to 72.3 % as sodium alginate content increased from 0 % to 75 %. For the hydrogels containing 50 % sodium alginate and immersed in 2 % calcium chloride solution after the freeze‐thaw cycles, cumulative release amount of chloramphenicol decreased from 83.5 % to 76.6 % as the freeze‐thaw cycles increased from 2 to 6. Cumulative release amount of chloramphenicol from the hydrogels containing 50 % sodium alginate and with 4 freeze‐thaw cycles decreased from 79.8 % to 75.6 % when concentration of calcium chloride solution increased from 1 % to 4 %.

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Transparent underwater superoleophobic coatings were prepared by blending chitin nanofibers (ChNFs) and polyvinyl alcohol (PVA) and then cross‐linked with glutaraldehyde (GA). The interactions among ChNFs, PVA, and GA in the coatings were analyzed via FT‐IR and XPS. Results of SEM observation and AFM analysis showed that higher concentrations of ChNFs and GA gave rise to rougher surface and lower transmittance of the coatings. By adjusting ratios of ChNFs, PVA, and GA, the coating surface could possess underwater superoleophobicity with oil (1, 2‐dichloroethane) contact angle up to 159.2° and slide angle ~3°, meanwhile, transmittance of the coatings in the wavelength range of 400–800 nm could be maintained between 40% and 90%. This work provides a new route to prepare environmentally friendly transparent underwater superoleophobic coatings.