Crosslinking Kinetics and Application of Chitosan-Genipin Nanogel
The natural crosslinking agent genipin can crosslink chitosan in a dilute solution to obtain biocompatible nanogel particles.The particles can be used as the emulsifier of Pickering emulsion.This study examines the conformation and structural evolutions using asymmetric flow field-flow fractionation(AF4)combined with multiple detectors.The nanogel particles show an extremely wide molecular weight distribution but a much narrower size distribution.To explore the universality of this behavior,we adjusted the molecular weight of the prepolymer chain and the crosslinker concentration,respectively.The nanogels obtained from prepolymers with different molecular weights exhibit similar molecular weight and size distributions,but the characteristic size decreases with decreasing M of the prepolymers.This latter trend is due to the higher crosslinking density and accordingly the higher internal density for the nanogel based on prepolymer of the lower M.For a given prepolymer,the characteristic size first decreases and then increases with the crosslinker concentration.The former decrease is caused by the enhancement of intrachain crosslinking,whereas the later increase is attributable to the excessive crosslinkers that attach to the polymer chain as dangling molecules,which suppresses the further intra-or interchain crosslinking reaction.Finally,the nanogel particles obtained in this study turn out to be an efficient emulsifier in preparing high internal phase emulsion due to its uniform size,high specific surface area and balance between hydrophilicity and lipophilicity:a Pickering emulsion with oil content of up to 90％can be stabilized using only 0.57 wt％of the nanogel particles.
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