**4. Materials and Methods**

### *4.1. Materials*

Polyvinyl alcohol (PVA, Mn ≈ 130,000, 99% hydrolysis), N,N'-methylenebisacrylamide (MBA), potassium persulfate (KPS) and acrylamide (AM) were obtained from Sigma-Aldrich (St. Louis, MO, USA) and used without further purification. Polyvinyl alcoholbearing styrylpyridinium group (PVA-SbQ) solution was purchased from Shanghai KCKI Printing Technology Co., Ltd., Shanghai, China (polymerization degree was 1700, and the concentration of SbQ was 0.03–0.05 mol kg−<sup>1</sup> ), and cellulose nanocrystal (CNC) aqueous suspension was prepared from cotton linters.
