Order—Disorder Transitions in Biocolloids

Abstract

The author's theory of order—disorder transitions in associative colloids is tested by comparison with measurements of the viscosity of different colloidal systems as a function of temperature or concentration. The theory predicts that an order—disorder transition from a random array of monomers to a segmented one‐dimensional helical rod will occur as the temperature is reduced to the one‐dimensional freezing point or the concentration increased to the critical micelle concentration. Under these conditions as enormous increase in the solution viscosity is predicted to occur. Semiquantitative agreement is obtained between theory and experiment for a variety of associative colloids. Fully quantitative agreement cannot be obtained because the solutions become birefringent upon aggregation of the monomers, due to the large rod lengths which are obtained. This birefringence is well known to be due to the fact that the rods bump into each other and do not have their full freedom of rotation. Although this situation more closely resembles the statistical mechanical theory which neglects rotation of the rods, there is unfortunately no adequate theory of the viscosity of such solutions and the Simha—Kuhn theory which we have used can only be approximate under these conditions.