Effect of Nonlinearity Strength in Chain Tension on Shear-Thickening of Associating Polymer Networks

概要

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The shear thickening phenomena observed in telechelic associating polymers are studied on the basis of the transient network theory. We investigate how the nonlinearity of the tension along the middle chains affects the stationary shear viscosity of the network under the following conditions: (i) the dissociation rate of the end chains from the network junctions is coupled to the middle-chain tension, and (ii) the generation rate of the chain in a loop conformation is enhanced by the middle-chain tension. A strong nonlinearity in the tension can cause shear thickening if the dissociation rate of the end chains is weakly coupled to the tension. If the nonlinearity of the tension is too strong, however, the dissociation rate is strongly coupled to the tension; moreover, dangling chains tend to be transformed into loop chains rather than bridge chains, thereby leading to shear thinning. The latter effect on the condition for thickening is shown to be small. Thus, the thickening condition is mainly determined by the balance between the nonlinearity strength in the middle-chain tension and the coupling intensity between the dissociation rate and the middle-chain tension.
2007-06-15