The Influence Of Salt On Viscometric Behavior Of Collagen Solutions

The concentration of the collagen solution, temperature, ionic strength, pH, shearrate, and a variety of metal ions can affect the rheological behavior of collagensolution, and thus can affect the applications of collagen. In this work, the rheologicalbehaviors of the collagen solutions were systematically studied by viscosity method,and rheometer. The main specific contents are as follows:(1) The reason of abnormal behavior of collagen solutions was clarified. First, thecapillary inner-surface of the viscometer was coated with dimethyl dichlorosilane toprevent the solution from being adsorbed on the glass surface of the capillary. Andthen an investigation of the influences of the adsorption, electrolyte, shear rate andtemperature on the viscometric behavior of collagen solutions was performed using aphotoelectric viscometer. The experimental results showed an abnormal behavior ofthe reduced viscosity (ηsp/C) of dilute collagen solutions can be found by a viscometerwith or without a hydrophobic surface treatment; this phenomenon can be completelyeliminated by increasing the concentration of an added salt. It indicated that theabnormal viscosity behavior was resulted from a long-ranged, inter-molecularelectrostatic force. The reduced viscosity decreased as the shear rate increased. Thephenomenon of shear-thinning was resulted from the high aspect ratio of the collagenmolecules. The reduced viscosity of the collagen solutions increased with an increasein temperature, which was due to the association of collagen molecules at hightemperature.(2) The viscosity behavior of collagen solution, with the addition of salt(Na2C2O4Na2SO4, Cr2(SO4)3)solutions was studied. The results indicate that when the pH ofthe solution is2.0, the influence of Na2SO4and Cr2(SO4)3on the viscosity of collagenare basically consistent. The reduced viscosity of collagen solution first increased andthen reduced with the increase of salt concentration, but the trend is contrast when thepH of the solution is4.0. The change of the reduced viscosity of collagen solution isdue to the two kinds of ionic interactions. In addition, the conclusions are also provedby AFM and DLS results.(3) The rheological behavior of collagen solutions were studied via a rheometer.When the pH of the collagen solution is equal to2.0, it showed a typical shearthinning behavior at higher concentrations. With the increase of Cr2(SO4)3 concentration, the G’ and G" crossover frequency evidently moved to higher valuesfirst and then the crossover frequency decreased. This indicated the characteristicsrelaxation time of the polymer solutions decreased first and then increased withCr2(SO4)3solution concentrations. But when the pH of the collagen solution is equalto4.0, the G’ and G" crossover point moved to low frequency region first and then thecrossover point were moved toward the high-frequency region. The results wereconsistent with that of viscosity results of collagen/Cr2(SO4)3solution.