Reliability of Intrinsic Viscosity Estimated by Single Point Procedure at High Concentrations

Abstract

k’ is typically 1/3 for good solvents, and as temperature approaches θ or as M decreases, k’ tends to 1/2. Measurement of [h ] based on the extrapolation to zero concentration is one of the most precise measurements in polymer science although it is also the simplest and cheapest method. However, the extrapolation method cannot be applied to some cases. For example, some polymers can associate and form molecular assemblies. Since [h ] can be related with hydrodynamic volume of solute, we can define [h] of these molecular assemblies hypothetically to represent the size of assemblies. The size of assemblies will vary with concentration as well as [h] of assemblies. In principle, the extrapolation to zero concentration corresponds to [h ] of the molecularly dispersed single chain, and therefore we cannot use the extrapolation method to determine [h ] of assemblies. Alternative methods are desired to determine [h] of the assembly. In this context, the length (molar mass) of thread-like micelles in aqueous solution also varies with concentration. Einaga et al. estimated intrinsic viscosity of thread-like micelles formed by polyoxyethylene alkyl ether, CiEj in the finite concentration regime with the following equation. [ ] [ ] c k c sp 2 η η η ′ + = (1)