Material science and engineering of polymers has not been well developed in contrast to that of metals, though polymeric materials are widely used. In order to relate the performance of polymeric materials to the molecular structures and properties, it is proposed that material characterization of polymers should be introduced in addition to molecular characterization and mechanical tests already used. Items for material characterization are tentatively presented. This report is a summary of the Symposium on “To Fill up a Gap between Basic Research and Technology on Polymeric Materials” held by Tokai-Kondankai, Tokai Division of the Society of Polymer Science, Japan.
The low temperature synthesis of glass through sol-gel process consisting of preparation of the starting solution, gelation of the solution and conversion of the gel to glass have been reviewed. Especially, the conditions required for gel fiber drawing and gel film forming from the solution have been discussed in this article. Silica gel formed from Si(OC2H5)4 was taken as an important example. It was shown that, in order for fiber drawing and film forming to be possible, the solutions have to exhibit spinnability and, accordingly, the one-dimensionally developed polymeric particles have to be formed in the course of hydrolysis and polycondensation of the alkoxide. It was shown by measurements of viscosities and molecular weights that one-dimensional polymeric particles are only formed in solutions with [H2O]/[Si(OC2H5)4] ratios less than 3-5. The nature of the one-dimensional particles has been discussed and it was tentatively concluded that linear polymers with triple-chains might be formed in the solution.
The muscle contraction is the process in which the chemical energy of ATP is transformed to the mechanical energy. Since it is very difficult to analyze quantitatively the chemical change accompanying mechanical work in a living muscle, the mechanochemical coupling of energy conversion was studied using a reconstituted motile system, “stream cell”. In the cell circulating flow could be induced by the interaction of heavy meromyosin (HMM) with attached polarized actin, both of which were extracted from skeletal muscle of a rabbit. Improving the way of attaching F-actin, a new biological motor, which was based on microscopic energy conversion, was also developed. The motor, “actomyosin motor”, has six blades, on which F-actin-HMM assembly is formed, and can rotate in a specific directon in the HMM solution. It was shown in these reconstituted systems that the assembly, not necessarily in the fibrous form, produces a vectorial force utilizing the energy of ATP hydrolysis. The physiological significance of these reconstituted systems depends on to what extent chemical and physical properties of the systems resemble those of muscle system under contraction. The reconstituted systems worked only when the physiological condition was the same as that of muscle. In the case of the stream cell, the ATPase activity at higher streaming velocity was higher than that at lower velocity. This corresponds to the Finn's effect in the muscle system. A close analysis of the relation between chemical and mechanical properties during active streaming led to a conclusion that the extent of self-organization of macroscopic streaming, or the resulting flow velocity, controls the molecular dynamics of the elementary cycles, namely, the ATPase activity of individual myosin molecules.
Mach-Zehnder interferometry, as applied to the stress analysis of solid materials, was employed to investigate the flow of viscoelastic fluids. With this method, secondary principal values of a refractive index ellipsoid can be measured because a reference light is used. This is in contrast to the birefringence method, in which only the difference of principal values can be evaluated. A Poiseuille flow between two parallel plates was selected as a flow field. Schemes for measurement of direct and transverse stress optical coefficients, C1 and C2, and absolute values of normal stresses were derived for each case where either poralized or nonpolarized light is led through the test section in the flow direction, the direction perpendicular to the shear plane, or the neutral direction. Such quantities can be evaluated if the phase difference can be measured as a function of shear stress and pressure on the wall and a stress optical coefficient C1-C2 is known in advance. Preliminary experiments for polyethylene and polystyrene melts were carried out with the polarized light perpendicular to the shear plane. However measurements accurate enough to allow evaluation of the normal stresses etc. have not been attained in this study.
Nonlinear viscoelastic properties of a carbon black - linseed oil suspension were investigated. Dynamic shear viscosity η′and rigidity G′ were measured using a newly constructed computer controlled rheometer, in which the amplitude of applied oscillatory shear could be held constant throughout the measurement. Measurements were performed at various strain amplitudes from 0.3% to 250% in the frequency range of 10-3-10 sec-1. The values of η′ decrease with increasing angular frequency w and the curve of log η′ vs. log ω shifts downward with increasing strain amplitude γ. The frequency dependence of G′ is very small, and G′ decreases markedly with increasing γ. G′ and η′ are both independent of γ in the small strain region. However, at strains larger than 1%, they decrease with increasing y and the strain dependence of G′ is more remarkable than that of η′. The non-linear viscoelastic properties of the suspension may be attributable to the characteristic strain dependence of a network structure formed from dispersed particles. Since the rigidity depends on the network density, the network structure itself may be reduced with increasing amplitude of oscillatory shear. A quantity ωγ was introduced in order to describe the effect of deformation rate on viscoelastic properties. The frequency dependence of G′ is rather strong, if the value of ωγ is kept constant. With increasing ωγ, the plot of log G′ against log ω shifts to higher frequency and the frequency dependence of η′ becomes weak. If the formation of network structure could be considered to be one of the relaxation mechanisms, the relaxation modes with longer relaxation times would be gradually diminished as the deformation rate increases.
A theory for the viscosity η of semi-dilute solutions of a linear flexible polymer was formulated on the postulate that η in this concentration regime is governed by the effective hydrodynamic volume per polymer segment and chain entanglement. The former was treated from a molecular point of view and the latter formulated phenomenologically. All the parameters in the theory can be estimated from dilute solution data and the asymptotic behavior of η for large molecular weight. It was found that the theory describes almost quantitatively the experimental data obtained by Adam and Delsanti and also by us for polystyrene in cyclohexane and in benzene.
Viscoelastic measurements have been carried out for both liquid crystalline and isotropic solutions of a helical synthetic polypeptide PBG (an equimolar mixture of L and D enantiomers of poly-γ-benzyl-glutamate) in m-cresol to study the viscoelastic properties of lyotropic liquid crystal of rodlike macromolecules. Dynamic viscoelastic functions, shear storage modulus G′ and shear loss modulus G″, were determined over angular frequency(ω) range of 0.005-3 (rad·sec-1) by oscillatory shear between cone and plate. The contour of stress-strain Lissajous' figure obtained for liquid crystalline solution and isotropic solution is almost elliptical within angular frequency range described above and it was not changed by increasing strain amplitude at least up to 80% and by repeated application of sinsoidal strain, which means linear viscoelastic response and no rheotropic behavior in the present system. The results of G′ and G″ revealed a distinct difference between liquid crystalline solution and isotropic solution. In the case of isotropic solution, G′ and G″ are proportional to ω2 and ω, respectively and independent of strain amplitude. On the other hand, in the case of liquid crystalline solution the dependence of G′ and G″ on ω becomes weaker with decreasing angular frequency in the lower angular frequency region, which implies the existence of relaxation mechanism attributed to polydomain texture. The trend is more remarkable in G′ than in G″. G′ and G″ are slightly, but not negligibly, affected by the amount of strain amplitude. For liquid crystalline solution G′ (G″) at different temperatures can be superposed into one composite curve only when the curves are shifted both horizontally and vertically.
Dielectric relaxation spectrum g(τ) for the normal mode process in undiluted cis-polyisoprene(cis-PI) was calculated from the dielectric data reported previously. The shape and the broadness of the spectra were in accord with the prediction by the 3 mode model. The following relationship between complex dielectric constant ε*(ωw) for the normal mode process and dynamic shear modulus G*(ω) in the terminal region was derived based on the tube theory by Doi: 1-ε*(ω)/Δε=G*(ω)/GN0 where ω is the angular frequency; Δε the dielectric relaxation strength; GN0 the plateau modulus in the rubbery region. To check this relationship, the relaxation spectrum H(τ) converted from the retardation spectrum reported by Nemoto et al. was compared with g(τ). The loss modulus G″(ω) reported by Carella et al. was also compared with the dielectric loss factor ε″(ω).