THE VISCOELASTIC PROPERTIES OF AQUEOUS POLY(METHACRYLIC ACID) SOLUTIONS AND THEIR RELATIONS TO THERMOREVERSIBLE GELATION

Influence of the gelation of concentrated aqueous poly(methacrylic acid) (PMA) solutions on the dynamic viscoelastic behavior was investigated. Dynamic shear moduli for aqueous PMA solutions (7.00-8.33 wt%) were determined over the frequency range from 0.0029 to 0.159 Hz and the tempemture range from 10 to 80-degrees-C by the method of torsion between coaxial cylinders. In order to classify the domain of the superposition principle, Cole-Cole diagrams in the complex viscosity were constructed considering temperature and frequency as variables. The complex viscosity was characterized by the circular arc based on the equation, eta* = eta0/[1 + (iomegatau)1-alpha], alpha = 0.26, in the sol region and by the skewed circular arc in the gel and unstable regions. The change in the relaxation from circular arc to skewed circular arc caused by the gelation was interpreted in terms of the partial change in the frequency dependency from the Maxwell type to the power law type. Data measured in the region that the gelation curve merge in the coexistence curve, that is, the data for the 7.33% solution at 70 and 80-degrees-C could not be combined by the superposition in the measured frequency range. In this case, the complex viscosities in the low frequency region were characterized by the facts that eta'' is nearly independent of frequency and eta' increases appreciably with decreasing frequency.