Concentration and Conformation Dependence of Dynamic Viscoelastic Properties of Dilute Polymer Solutions

Abstract

Rouse and Zimm have derived theories of viscoelastic properties of random coil polymers in dilute solutions, and Kirkwood and Auer that for rodlike polymers. Comparing these theories with each other in the form of the normalized dispersion curve, we may obtain direct information on the degree of internal freedom of polymer molecules.Many experimental investigations on viscoelasticity of coiling polymers have been made for dilute and for concentrated solutions. Experimental results for dilute solutions show almost quantitative agreement with the theories of Rouse or Zimm, but those for concentrated solutions a systematic disagreement. From these results, it is clear that concentration effect on the viscoelasticity still remains somewhat ambiguous even in the region of dilute solutions. This is not surprising, because all these theories are concerned only with the intrinsic quantities corresponding to infinite dilution without taking account of intermolecular interaction.In this study the dynamic intrinsic viscosity and intrinsic rigidity, therefore, are defined experimentally as follows, [η']=limc→0(η'-ηs)/ηsc, [G']=limc→0G'/c.Considering that, with changing concentration, all relaxation times involved change to some extent as was pointed out by Ferry, we define also the limiting value of the terminal relaxation time as(τ1)0=limc→0τ1(c).The complex rigidities are obtained by means of the torsional crystal method at the frequency of 39.2kc and the temperature of 30.0°C. The relaxation times are derived from the steady shear viscosities measured by a Ubbelohde dilution viscometer.As an example of the random coil conformation, the solutions of the high molecular weight polymethyl methacrylate (Mv=2.1×106) in chloroform were studied. The measured values for G'/c, (G-ωηs)/c and τ1 were found to be in line with the concentration. The intrinsic rigidities and the limiting relaxation time were determined by extrapolating the experimental data to the zero concentration. The sets of the intrinsic rigidities and the limiting relaxation time thus determined were quantitatively in agreement with the values predicted by the Rouse theory.In the case of the rodlike conformation, poly-γ-methyl-D-glutamate (Mn=1.29×105) which was 100% α-helix in chloroform solutions was investigated. It was found that the measured values approached the theoretical dispersion curves due to Kirkwood and Auer as the concentration was lowered to infinite dilution.