A liquid-crystalline copolyester consisting of 1, 4-oxybenzoate and ethylene terephthalate groups was subjected to the injection molding using a rectangular mold 120×70×1mm with a slot gate of 0.5mm gap. The structures of injection-molded products were studied in detail by the X-ray diffraction method and the techniques of polarizing microscope. The molecules in the outer layers contiguous to both surfaces of injection-molded rectangular plate were highly oriented in the direction of injection and strongly birefringent, whilst the interior layer remained principally unoriented. The generation of characteristic binary structure with sharp boundaries was interpreted in terms of CAE data and the rheological behavior of the melt of liquid-crystalline polymer. The products of usual polymer made up of flexible molecules, on the contrary, gave isotropic products. The measurements of relaxation time afforded a key to an understanding of the difference between the behavior of liquid-crystalline polymer and that of usual polymer. The structural anisotropy of the products of liquid-crystalline polymer resulted in the anisotropy of mechanical properties. The structure produced by processing proved to be a determining factor for the mechanical propertties of products in preference to the material of which the product was composed.
Rheological properties of a thermotropic liquid crystalline copolyester which was synthesized from poly (ethylene terephthalate) and 60mol% p-hydroxybenzoic acid were investigated. The dynamic and steady flow properties above the rheological transition temperature (ca.270°C) were studied in detail. It has been found that the steady flow properties are not affected by thermal history in the anisotropic state. The following relations hold between steady flow and dynamic viscoelastic properties of the sample with a shearing history: |η*(ω)|=η(γ) at ω=γ, and limω→0G'(ω) =1/5 Limγ→0NNI(γ) In the anisotropic state, the thermotropic liquid crystalline copolyester shows a significant shear-thinning of viscosity even at very low shear rates and a first normal stress difference comparable with an isotropic copolyester melt which was synthesized from poly (ethylene terephthalate) and 28mol% p-hydroxybenzoic acid. The steady compliance (Js) of the liquid crystalline copolyester in the anisotropic state is about 10 times as large as that of the isotropic copolyester melt when compared at the same shear stress. It is shown that the storage compliance of various liquid crystalline polymers is about 10 times as large as that of liquid crystalline polymers in the isotropic state and of the crystalline copolyester in the molten state when compared at the same value of |G*|, the absolute value of complex dynamic modulus.
A modified concentric cylinder viscometer was used for the simultaneous measurement of thermal condutivity and apparent viscosity. The thermal conductivity of disperse medium is 100 times higher than that of carbon black particles, suggesting the particles behave as obstacles to thermal conductance. In flow field, heat transfer is mainly caused by forced convection and the effect of particle orientation on the thermal conductivity of the system becomes large. After cessation of shear flow, the thermal conductivity decreases drastically depending on the rate of shear before the cessation of flow, and recovers gradually with elapsed time. The process of thermal conductance at rest state is by radiation. The thermal conductivity of disperse system where the particles are dispersed uniformly agents. The thermal conductivity of system containing a small amount of dispersing comparatively low, but aggregation of particles results in an increase of conductance because of the path for thermal conductance. In the disperse system, aggregation of particles is depressed by the addition of dispersing agents. The thermal conductivtiy of system containing a small amount of dispersing agent does not change with time. With increasing concentration of disperse particles, the thermal conductivity of the system is reduced. The concentration dependence of thermal conductivity can be expressed by Hamilton's theory, qualitatively. However, in the higher concentration region, the experimental values of thermal conductivity are larger than the theoretical values, because highly developed flocculated structures are constructed.
The flow of a viscoelastic fluid through a 4:1 axisymmetric abrupt contraction was studied by means of the finite element method. The effects of elongational viscosity on vortex and entrance pressure drop were investigated in detail using the viscoelastic models which have different values of elongational viscosity by varying the model parameters. The Phan Thien-Tanner (PTT) type and the Giesekus type models with a single relaxation time were used as the constitutive equations. It is found that the vortex grows with the recoverable strain and the model with higher elongational viscosity predicts a larger and more intensive vortex. It seems that the vortex becomes more intensive as recoverable strain becomes larger if elongational viscosity curves coincide. The model with higher elongational viscosity gives larger values for the entrance correction in the PTT type model, while the Giesekus type model gives the opposite prediction. It seems that the magnitude of entrance correction can not be explained only from the elongational viscosity.
Zero-shear viscosity η0 and steady-state compliance Je of poly(α-methylstyrenes) in benzyl n-butyl phthalate (_??_=46°C) and polystyrene in dioctyl phthalate (_??_=22°C) were measured at temperatures lower than the _??_ points. Moreover, stress developments after onset of steady shear flow were measured and the strength of entanglement was estimated on the basis of network rupture model. The concentration and the molecular weight dependences of η0 at temperatures lower than the _??_ points are almost the same as those at the _??_ temperatures, but the magnitude of η0 increases with decreasing temperature. This suggests that the strength of entanglement increases with decreasing solvent power. On the other hand, Je values at the temperatures lower than the _??_ points are almost the same as those in good and _??_ solvents. This result indicates that the entangled structure of polymer solution effective to Je is almost independent of solvent power. Therefore, it is concluded that the gel-like behavior of polymer solution at temperatures lower than the _??_ points is caused by the long relaxation times due to the high viscosity.
The viscoelasticity and self-diffusion were investigated for aqueous solutions of cetyltrimethylammonium bromide (CTAB) containing sodium salicylate (NaSal). The concentration of CTAB, CD, was equal to that of NaSal, Cs. This system contains thread-like micelles and exhibits pronounced viscoelastic behavior. The storage modulus, G′, and loss modulus, G″, could be fitted with the Maxwell model of one relaxation time when CD<0.5M. The plateau modulus, GN, was proportional to CD2 over a wide range of CD. This property is similar to that of concentrated polymer solutions. The relaxation time, τ, was evaluated from the frequency at which G″ takes maximum. The self-diffusion coefficient, D, was measured by forced Rayleigh scattering measurement. The quantities D and τ-1 varied in a similar manner as a function of CD ; when CD<0.2M, they increased with CD and when CD<0.2M, they decreased with CD. This behavior is remarkably different from polymer solutions.The rate of diffusion may be controlled by the rate of the process where thread-like micelles cut across each other, a process proposed previously to describe the stress relaxation.