synopsisThe storage and loss shear moduli, G , and G", have been measured for solutions of three samples of poly-y-benzyl-L-glutamate with molecular weights from 16 to 57 X lo4, by use of the Birnboim-Schrag multiple-lumped resonator. The frequency range was 106 to 6060 Hz, the concentration range 0.0015-0.005 g/ml, and the temperature 25OC. Two helicogenic solvents with widely different viscosities, dimethylformamide and m-cresol, were used to provide a broader effective frequency range. The intrinsic moduli, extrapolated to infinite dilution, were compared with the predictions of the theory of Ullman for rigid rods; agreement was rather good at the lowest frequencies, but unsatisfactory at high frequencies. The data over the entire frequency range of three logarithmic decades could be described closely by a relaxation spectrum consisting of one terminal relaxation time separated by a gap from a sequence of relaxtion times spaced as in the Zmm theory. The terminal time agrees approximately with that calculated for end-overend rotation of a rigid rod. The additional relaxation mechanisms are tentatively attributed to modes of flexural deformation of the helix.

The shear-wave field generated in a linear viscoelastic medium confined between parallel plates (one fixed, the other oscillating sinusoidally in its own plane) has been evaluated and presented in a graphical form convenient for determination of the role of wave propagation effects in dynamic rheological measurements. The transition from closely spaced planes (“gap loading”) to the freely propagating plane wave (“surface loading”) limit is examined; the importance of deviations in magnitude and phase of the gradient profile from the gap loading limit is discussed in terms of high precision dynamic rheological experiments; significant deviations occur for shear wavelength to gap width ratios of 30 or less.

The storage (O') and loss (G") shear moduli of solutions of four polystyrenes with narrow-distribution weightaverage molecular weights (M) from 19,800 to 860,000 have been measured over a frequency range frpm 0.02 to 634 Hz. The solvents were two Aroclors (chlorinated diphenyls) with a viscosity range from 2 to 7000 P over a temperature range from -

Theoretical predictions are presented for the operating characteristics of a quartz crystal microbalance (QCM) system consisting of the crystal, an attached viscoelastic sample layer, and a surrounding viscoelastic bath medium. Predictions are given for the spatial variation of “particle” velocity and velocity gradient throughout the sample layer, for the characteristic mechanical impedance acting on the crystal surface due to the viscoelastic sample layer plus surrounding bath medium, and for the resultant changes, Δfr, in the resonance frequency of the QCM. Errors introduced by employing the usual simple Sauerbrey-type Δfr/sample-layer–mass relationship, together with a constant frequency offset to approximate the effect of the viscoelastic bath medium, are explored. In general, the viscoelastic properties of both the sample and bath media can substantially affect the apparent thickness (mass) of the sample layer if it is obtained by employing the typical Sauerbrey-type approximation noted above.

SynopsisOscillatory flow birefringence (OFB) measurements have been carried out for an extensive series of solutions containing narrow-distribution, atactic, linear polystyrenes PS (10,000 or 390,000 M,) or poly(cu-methylstyrene) PMS (400,000 M,) in a high-viscosity solvent, Aroclor 1248. The concentration ranges examined are such that the concentration dependence is obtained in both the "dilute" and "semidilute" regimes; the data are sufficiently precise to permit extrapolation to obtain for the first time the infinite-dilution properties. Various plotting formats are explored to determine an appropriate extrapolation procedure. The infinite-dilution OFB properties are compared with the bead-spring model (Zimm) theory which predicts quantitatively the frequency dependence of the observed properties for the PS and PMS solutions studied except for the high-frequency regime. The sensitivity and precision of the OFB experiment is such that the extrapolation curves-and the resulting infinite-dilution properties-show substantially less scatter than comparable viscoelasticity (VE) data. There is no evidence of a change in the character of the concentration dependence for the range of concentrations studied.