Origin of Surface Charge of Double Network Hydrogels Prepared by Sequential Polymerization

Understandingthe physicochemical properties of hydrogel surfacesand their molecular origins is important for their applications. Inthis paper, we elucidate the molecular origin of surface charges indouble-network hydrogels synthesized by two-step sequential polymerization.Synthesis of hydrogels by free-radical polymerization does not fullycomplete the reaction, leaving a small number of unreacted monomers.When this approach is used to synthesize double network (DN) hydrogelsby a two-step sequential polymerization from charged monomers forthe first network and neutral monomers for the second network, theunreacted first network monomers are incorporated into the secondnetwork. Since the surface of such DN hydrogels is covered with a & mu;m-thick layer of the neutral second network, the incorporationof a small amount of charged monomers into the second network increasesthe surface charge and, thereby, their repulsive/adhesive properties.Therefore, we propose a method to remove unreacted monomers and modulatethe surface charge density of DN hydrogels.

Automated summary

Understanding the molecular origin of surface charges in double network hydrogels is crucial for their applications. This paper investigates the incorporation of unreacted monomers from the first network into the second network, which results in an increase in surface charge and affects the repulsive/adhesive properties. The authors propose a method to remove unreacted monomers and modulate the surface charge density of double network hydrogels.