Volume 27, Issue 3, June 1983
Index of content:
27(1983); http://dx.doi.org/10.1122/1.549704View Description Hide Description
Measurements of the viscosity of a suspension of monodisperse polystyrene particles as a function of volume fraction at two fixed values of (3.13 and 8.24) and various values of the electrokinetic (ζ−) potential permit a test of current theories of the primary electroviscous effect. The results reveal a major discrepancy which may be real but which is more likely attributable to the presence of a “gel‐like” layer on the surface of these particles.
27(1983); http://dx.doi.org/10.1122/1.549724View Description Hide Description
This article establishes a link between molecular theories that predict the macroscopic behavior of certain viscoelastic media and an empirically developed fractional calculus approach to viscoelasticity. The molecular theory addresses the viscoelastic properties of polymer solids with no crosslinking. It is shown that the results of these molecular theories are equivalent to constitutive relationships written in terms of the fractional calculus. Such relationships, developed previously from an empirical base, have been shown to be useful tools for engineering analyses. The establishment of a theoretical basis for these new constitutive relationships enhances their value, as they may now be used with increased confidence.
An Experimental Study of Asphalt Concrete Based on a Multiple‐Integral Representation of Constitutive Equation of a Nonlinear Visoelastic Solid27(1983); http://dx.doi.org/10.1122/1.549713View Description Hide Description
This article deals with the determination of mechanical response of a nonlinear viscoelastic solid based on a Frechet expansion. A modified superposition principle suggested earlier by various authors is used to simplify the constitutive equation. It is then shown that the resulting stress‐strain equations are consistent with mechanical behavior of asphalt concrete. The inadequacy of linear viscoelasticity theory for these materials is also demonstrated. Practical laboratory determination of the kernel functions of the material is described.
Rheology of Ternary Mixtures of Styrene‐Butadiene Diblock Copolymer, Homopolybutadiene, and n‐Tetradecane27(1983); http://dx.doi.org/10.1122/1.549725View Description Hide Description
The effects of adding low‐molecular‐weight homopolybutadiene (hB) into solutions of a styrene‐butadiene (SB) diblock copolymer in n‐tetradecane (C14) on their rheology and microdomain structure are examined. In solutions of SB in C14, SB molecules form micelles with precipitated S blocks as the rigid cores and soluble B blocks as the cilia. These micelles form a macrolattice. The macrolattice is stabilized by a thermodynamic force that tends to keep the local concentration of B segments in the matrix phase as uniform as possible. Such a micellar solution having a macrolattice exhibits nonlinear dynamic behavior as well as plastic flow in steady shear. When hB is added to the solution, the solution loses its plasticity and becomes a linear viscoelastic liquid and the macrolattice becomes disordered. The mechanism of such a transition may be a result of the fact that the added hB acts as a buffer to compensate for the local concentration change induced by the lattice deformation and makes the macrolattice unstable. Solutions of SB in pure hB (with concentration below 35 wt % SB) are no longer plastic but linear viscoelastic. The solutions exhibit some slow relaxation processes, which are often called the second plateau. The mechanism of the SB in hB solutions that exhibit the second plateau is also discussed.
27(1983); http://dx.doi.org/10.1122/1.549705View Description Hide Description
Stress relaxationmeasurements were conducted in three different modes: after an “instantaneous” deformation, after a constant rate of deformation, and after the cessation of steady‐state flow. In addition, dynamic oscillatory measurements, stress‐rise measurements at constant rates of deformation, and steady‐state flow measurements were made. A Rheometrics mechanical spectrometer was used at 100°C with a cone‐and‐plate fixture. Samples were an ethylene‐propylene copolymer (EP) Mooney index 40 and two butadiene‐acrylonitrile copolymers (BN) Mooney index 35. The EP sample exhibited melt flow behavior at the testing temperature and the BN samples were in the rubbery region at the testing condition. The viscoelastic behavior observed with the above measurements were correlated systematically. In the correlation the EP sampler obeyed linear viscoelasticity theory. With the BN samples the applicability of a strain‐time shift is demonstrated, whereby the nonlinear data were reduced to their linear equivalents. A method is presented for estimating strain and the strain‐time shift factor for the stress relaxation after the cessation of flow.
27(1983); http://dx.doi.org/10.1122/1.549706View Description Hide Description
Measurements were taken of the bulk rheological properties of concentrated suspensions of particulates in unsaturated polyester resins using a cone‐and‐plate rheometer. Over the range of shear rates investigated, suspensions of calciumcarbonate showed Newtonian behavior, whereas suspensions of clay showed both yield behavior at low shear rates and shear‐thinning behavior at high shear rates. Suspensions of both calciumcarbonate and clay together exhibited no normal stress effects. However, suspensions of polyethylene powders were found to exhibit positive values of normal stress at low concentrations, but negative values of normal stress at and above a certain critical concentration. In view of the fact that negative values of normal stress were observed at low shear rates the possibility of inertial effects is ruled out because we observed inertia‐induced negative values of normal stress with three different Newtonian liquids at very high shear rates, say above Having checked the possibilities of other probable sources that might have caused the negative normal stresses observed, we have concluded that the negative values of normal stress observed with concentrated suspensions of polyethylene powders in unsaturated polyester resin are real, not an artifact. Interestingly enough, the normal stress effects observed with concentrated suspensions of polyethylene powders very much resemble the observation reported by Kiss and Porter, who used liquid crystalline polymer solutions.
27(1983); http://dx.doi.org/10.1122/1.549733View Description Hide Description