Early studies of the present author and his collaborators on the viscosity and viscoelasticity of non-polymeric and polymeric liquid solutions are reviewed. The period covered is from 1947 to 1972. The subjects described are: (1) The mutual viscosity as a measure of the interaction between unlike molecules in non-polymeric solutions,(2) the Weissenberg effect and the nature of elastic deformation of polymer chains,(3) the dependence of steady shear compliance on molecular weight,(4) the characteristic ratio for polymer chains - its evaluation and compilation based on numerous data of intrinsic viscosity in ordinary solvents, and (5) the relaxation modulus of polymer solutions under large strain. The strain-dependent moduli observed for a concentrated solution of polystyrene were separable in the form of product of a universal strain function and a time function over a wide range of time longer than a critical value, and it provides a key to the solution of the nature of entanglement coupling between polymer molecules.
This paper summarizes an experimental study on an elongational rheometer and elongational viscosity measurements of polymer melt developed by the present author and his coworkers. The elongational viscosity increases with time by two steps: One is a gradual viscosity increase at small strain and the other is a rapid viscosity increase at large strain. The rapid viscosity increase behavior does not depend on strain rate, temperature, and average molecular weight, but does depend on molecular weight distribution and chain branching. These experimental results were explained by introduction of small amount of extremely long relaxation time mode into the normal relaxation spectrum which is estimated from linear viscoelastic data. The elongational rheometer can quickly detect the extremely long relaxation time mode.
This paper summarizes recent works in which the entanglement effect on diffusion and viscoelasticity was mainly studied on solutions of narrow-distribution polystyrene (PS) in dibutylphthalate (DBP) over a wide range of temperature T, concentration C and molecular weight M. The temperature dependence of the self diffusion coefficient Ds and the tracer diffusion coefficient Dtr was described by the WLF equation with values of the WLF coefficients same as found for the solution viscosity η. The effects of entanglements on the self diffusion behavior and the viscoelastic behavior were examined from data analysis in terms of the two parameters, the effective friction coefficient of a segment ζand the molecular weight between entanglements Me. The product Dsη/C was close to the theoretical prediction based on the free Rouse chain up to M/Me-1 and, for M/Me>10, showed universal behavior characterized by the linear proportionality to M/Me. The ratio of the two characteristic times for viscoelasticity and diffusion took approximately a constant value of 0.15±0.05 over the whole range of M/Me studied. Reduction of diffusion data on the basis of the two-parameter scheme was so successful that one master curve was obtained for each set of Ds and Dtr∞ data. The both master curves were proportional to (M/Me)-2.5 in the highly entangled region, being not in harmony with either the prediction of the reputation theory or the observation for PS melts. The tracer diffusion behavior in the unentangled concentrated solution was described by the partial-draining model.
Ferry and Stratton proposed a relation between a shift factor and a strain. They assumed compressibility of free volume on the basis of a sample volume. On the other hand, we defined the compressibility on the basis of the free volume, and derived a new relation between the shift factor and the strain (or stress). The equation we obtained was different in the formula from the Ferry-Stratton equation, but the properties of the equations were quite similar. Our equation could satisfactorily approximate a relation between the shift factor and the strain for relaxation curves of a polyethylene film, and also the relation between the shift factor and the stress for creep curves of monofilaments of nylon and poly (ethyleneterephthalate). Fractions of free-volume were estimated from these equations.
A low-density polyethylene (LDPE) sample and an isotactic polypropylene (PP) sample were chemically cross-linked in molten state with dicumyl peroxide using liquid 1,2-polybutadiene (L-PB) as an auxiliary for PP. The effects of the degree of cross linking on their capillary flow properties have been studied. The apparent viscosity ηa of LDPE system at a constant shear rate rapidly increases until a gel content of 1.1 wt%, which is due to the increase in molecular weight, and after that log ηa linearly increases with the gel fraction, which is due to an action of gel particles as filler. The dependence of ηa on the gel fraction is more notable at lower shear rate. The value of ηa at a constant shear rate of PP system with an L-PB content of 5 phr drops until a gel content of about 15 wt%, and after that shows a maximum at a gel fraction of about 25 wt%, and gradually decreases with the gel content. For the system of an L-PB content of 20 phr, ηa gradually increases with the gel fraction. The end correction coefficient ν shows a maximum in a range of gel fractions from 15 to 40wt%. The flow activation energy at a constant shear rate, ΔHγ, of LDPE system decreases with the gel fraction and the flow activation energy at a constant shear stress, ΔHτ, shows a maximum at a gel fraction of about 70wt%.
The surface pressure relaxation and area creep experiments were carried out for the myristic acid (C14), stearic acid (C18), and behenic acid (C22) monolayers on the water surface at 293K. The myristic acid monolayer is in an amorphous state on the water surface at 293K. In the case of π(t=0) =17 mN·m-1 for the myristic acid monolayer, little change of π was observed in the experimental range of 1000 sec. The large relaxation was observed both above and below 17 mN·m-1. On the other hand, the stearic and behenic acid monolayers are in crystalline states on the water surface at 293K. In the case of π(t=0)=26 mN·m-1 for the crystalline stearic acid monolayer, large relaxation of the surface pressure was not observed up to 100 sec. Also, in the case of π(t=0)=25mN·m-1 for the crystalline behenic acid monolayer, the surface pressure did not change within 1000 sec. The transmission electron microscopic(TEM)observation revealed that this stability of monolayer might be related to homogeneity of monolayer. Electron diffraction (ED) measurement also revealed that the origin of relaxation for crystalline monolayer at high surface pressure can be attributed to the collapse of monolayer and the sintering among crystalline domains of monolayer. On the other hand, the area creep measurement revealed that the magnitudes of constant pressure π0 which showed the smallest decrease of area were 17, 23, and 25 mN·m-1 for the myristic, stearic, and behenic acid monolayers, respectively. These surface pressure (π0) values are almost equal to the surface pressure π(t=0) at which the monolayer showed fairly small surface pressure relaxation.
In order to investigate the structural recovery of suspension of acicular γ-ferrite powder in mineral oil, viscoelastic properties were measured intermittently with small amplitude oscillatory shearing (strain at 0.3%, rate at 10 rad/sec). A couette test fixture was used for the measurements. Storage and loss moduli of the suspension immediately after cessation of large amplitude oscillatory preshearing (strain at 50-500%, rate at 50 rad/sec, for 20 min) increased with increasing strain amplitude of preshearing. The moduli of the suspension at the early stage of recovery were found to follow the scaling equation : G′ (or G″)-tn where t is resting time after cessation of preshearing. The moduli decayed after reaching the maximum, when larger amplitude preshearing had been applied. The phenomenon is interpreted from the view point of percolation using a two level (intra- and interfloc level) network model of flocculated suspensions.
The stress-optical rule (SOR) does not hold valid in the glassy and the glass-to-rubber transition zones of amorphous polymers. The birefringence and stress can be related through a modified SOR : The stress is composed of two components each of which contributes to the birefringence with different degree of effectiveness. Studies of Read (Polym. Eng. Sci., 23, 835 (1983)) and of the present authors (Macromolecules, 24,5670 (1991)) are based on different methods of assignment of the stress-optical coefficients for the two components. We show that the two component viscoelastic functions derived from the latter method are thermo-rheologically simple but those from the former are not.