Hygroscopic hydrophobic coatings from cellulose: Manipulation of the aggregation morphology of water

Fogging and icing are common phenomena in nature, but they bring huge harm in the human life and production, such as the deterioration of optical devices, the detriment of vehicles operating, the destruction of power transmission lines. In this work, we designed and constructed a cationic cellulose derivative with both weak hygroscopicity and high hydrophobicity to achieve a spontaneous management of the aggregation morphology of interfacial water, via precisely controlling the chemical structure of cellulose derivatives. As a result, the resultant cationic cellulose derivative can be used as a transparent and water-resistant coating, which exhibits universal anti-fogging, excellent anti-icing and anti-bioadhesive properties. Under low humidity, the coating can effectively absorb water to form a pseudo-film due to the ionized structure and retained hydroxyl groups. Under high humidity, the coating can promote water droplets to roll off due to the high hydrophobicity. The coating with weak hygroscopic core and high hydrophobic surface thus has a universal anti-fogging performance. In addition, this ionized coating with weak hygroscopicity can adjust the interfacial water performance, so it can reduce the freezing temperature of water to −30 ℃, and the ice adhesion stress to 10 kPa at −30 ℃. The freezing time of water exceeds 2 h at −25 ℃. Furthermore, the bacterial killing percentage on this coating is more than 97 % for Staphylococcus aureus. Due to high hydrophobicity and low surface energy, this coating has outstanding water-resistance, self-cleaning property, anti-chlorella adhesion and anti-protein adhesion. Therefore, such a multifunctional coating prepared by a simple structure design from natural cellulose has a great potential in display devices, traffics, solar products, wind generator, agricultural greenhouse, and other fields.