title: Strong adhesion and cohesion of chitosan in aqueous solutions.
abstract: Chitosan, a load-bearing biomacromolecule found in the exoskeletons of crustaceans and insects, is a promising biopolymer for the replacement of synthetic plastic compounds. Here, surface interactions mediated by chitosan in aqueous solutions, including the effects of pH and contact time, were investigated using a surface forces apparatus (SFA). Chitosan films showed an adhesion to mica for all tested pH ranges (3.0-8.5), achieving a maximum value at pH 3.0 after a contact time of 1 h (Wad ~ 6.4 mJ/m(2)). We also found weak or no cohesion between two opposing chitosan layers on mica in aqueous buffer until the critical contact time for maximum adhesion (chitosan-mica) was reached. Strong cohesion (Wco ~ 8.5 mJ/m(2)) between the films was measured with increasing contact times up to 1 h at pH 3.0, which is equivalent to ~60% of the strongest, previously reported, mussel underwater adhesion. Such time-dependent adhesion properties are most likely related to molecular or molecular group reorientations and interdigitations. At high pH (8.5), the solubility of chitosan changes drastically, causing the chitosan-chitosan (cohesion) interaction to be repulsive at all separation distances and contact times. The strong contact time and pH-dependent chitosan-chitosan cohesion and adhesion properties provide new insight into the development of chitosan-based load-bearing materials.
authors.affiliation: Department of Chemical Engineering, University of California at Santa Barbara , CA 93106, United States.
authors.forename: Dong Woog
authors.initials: DW
authors.lastname: Lee
authors.forename: Chanoong
authors.initials: C
authors.lastname: Lim
authors.forename: Jacob N
authors.initials: JN
authors.lastname: Israelachvili
authors.forename: Dong Soo
authors.initials: DS
authors.lastname: Hwang
mesh_terms: D000268:Adhesiveness; D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry; D002236:Carbohydrate Conformation; D048271:Chitosan / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D012996:Solutions; D013997:Time Factors; D014867:Water / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D012996:Solutions; D014867:Water; D048271:Chitosan; C011934:mica