Surface Force Studies of Langmuir-Blodgett Cellulose Films

The interactions between cellulose surfaces, between chitosan-coated surfaces, and between one cellulose surface and one chitosan-coated surface have been studied using the interferometric surface force apparatus (SFA). The cellulose surfaces were prepared by depositing trimethylsilyl cellulose on hydrophobized mica using the Langmuir-Blodgett technique. The surfaces were desilylated in a humid HCl atmosphere to obtain regenerated cellulose. ESCA measurements and wetting studies demonstrated that the desilylation process was effective. Scanning force microscopy studies showed the cellulose surfaces to be smooth with a root-mean-square roughness of 0.16 nm. Surface force and ellipsometry measurements illustrate that the cellulose film swells considerably in humid air and in water, suggesting that it is mostly amorphous. The interaction between two cellulose surfaces is dominated by a steric repulsion caused by a few dangling tails. On separation an attractive force was present both between two cellulose surfaces and between one cellulose surface and one chitosan surface. The long-range interaction between cellulose and chitosan was shown to be attractive.