Structural relaxation in amorphous poly (ethylene terephthalate) (PET) quenched from various temperatures above and below the glass transition temperature Tg (ca 68°C) has been studied in terms of time dependence of the specific volume. Experimental results were analyzed using the phenomenological multiparameter model of Moynihan and co-workers to give numerical values of kinetic parameters characterizing the structural relaxation. The kinetics of PET struc-tural relaxation could be divided into two different processes. One was in a temperature range below Tg-20°C, where the kinetic parameters remained constant while the time (ta) and tempera-ture (Ta) of aging varied. The relaxation time of this process was strongly dependent on the instan-taneous state of the PET glass and showed a broad distribution. The other process was in a temperature range from Tg-20°C to Tg, where the kinetic parameters changed with Ta, and the re-laxation time showed an Arrhenius-like temperature dependence and a less broad distribution. Moreover, it was found that thermal pretreatment in the vicinity of Tg was likely to stabilize the glassy PET structure and lead to some extreme retardation in long-term segmental rearrangements and cooperative motions.
Coating color is a complicated system consisting of clay, calcium carbonate, starch, styrenebutadiene latex (SBL), water, etc. At rest the system forms a three dimensional network structure through the interactions between the components, however, the structure changes at high shear rates imposed upon the system during the blade coating process, only to recover its original structure after the shear is removed. Although the flow properties of coating color system, especially the viscosity at high shear rate, are known to affect the stability of blade coating process, the viscoelastic properties seem to be more important than the flow properties in steady shear because the former is sensitive to the structure change. To elucidate the process of the formation of the fluid structure of the coating color system, we measured the dynamic viscoelasticity as a function of the passage of time after the system was prepared. By estimating the increase in the storage modulus and decrease in the dynamic loss tangent, we proposed a model that the structure formation proceeds in three steps. In the first step, the formation of local aggregation of starch and SBL takes place. In the second step, a three dimensional network structure is formed and, in the third step, finally flocculation of pigments occurs. The structures of the first and second steps are strongly controlled by the polymer components. We also discuss the critical concentration of starch and SBL needed to form the network structure.
In a previous paper, we showed that the three dimensional network structure of a coating color system is significantly controlled by the polymer components. Here we analyse the data using a simple model. We introduce the mean interaction parameters between the components of the coating color such as starch and styrene-butadiene latex (SBL). Comparing the shear rate dependence of the viscosity of the coating color with that of the aqueous starch solution and/or aqueous SBL dispersion, we determine the interaction parameter assuming that the viscosity of each system increases exponentially with increasing weight fraction of starch and/or SBL. From this analysis we discuss the structure change of the coating color by shear and found at high shear rate, the clay-clay interaction increases due to the parallel orientation of the clay particles. We also found that the critical starch concentration needed to form the three dimensional network structure corresponds to that of the inflection point of starch concentration dependence of the coating color viscosity.
As a fundamental study on anisotropic channel flow, two-dimensional fiber orientation was investigated in a main flow as well as in a recirculating flow within a salient corner of a backward-facing step channel. For a large number of fibers (N=1800, aspect ratio γa=5 and 10000) having a random initial orientation, the orientation distribution after injection was computed with the Jeffery's equation along streamlines in Newtonian flows. This distribution, which was described by the second-order orientation tensor and the orientation ellipse determined on a statistical basis, was compared with the actual distribution found from experiments. For large γa, both experiments and computations indicated that steady orientation was achieved after several circulation and all fibers aligned almost completely along the streamlines in a recirculating flow. For small γa, the computations predicted that almost complete orientation was achieved at steady state but a preferred orientation angle lay obliquely to the streamlines. When fibers almost completely aligned along the streamlines flowed into an expanding part of a channel, this orientation state remained in a main flow at high Reynolds numbers Re, because of gradual divergence of main flow, but their preferred orientation angle lay obliquely to the streamlines in the central region of the channel. In contrast, for low Re that resulted in the main flow abruptly diverging at the expanding part, the fibers were less oriented and their preferred orientation angle in the central region increased just at downstream side of the expansion entrance. This worse orientation was expected to remain in a wider downstream region for lower Re. All above results provided a clue for rigorous computation of fiber suspension flows, which is carried out by coupling flow field with fiber orientation state, through a complex channel often inducing a recirculating flow.
Pressure characteristics were studied experimentally for a two cycle converging-diverging channel (a type of corrugated tube), using polyacrylamide water solutions as working fluids. Effects of the viscoelasticity on the pressure distribution along the channel wall were examined by comparing the data for polymer solutions with a Newtonian fluid. The experimental results for the two cycle channel were also compared with the data for one cycle channel having the same dimension. The total pressure drop for the two cycle channel with a dilute polymer solution was smaller than that of the Newtonian fluid in a region of lower Reynolds number, whereas no such a symptom was observed in the case of the one cycle channel. From the observation by a flow visualization technique in the laminar flow regime, there were found to exist five and four major flow modes in the converging and diverging parts of the channels, respectively, and hence there appeared, in total, thirteen flow states in the channels. Based on the flow modes, flow state maps are presented in the present study.
Extensional viscosities ηe(ε) of polystyrenes (PS) with high molecular weights in benzyl butyl phthalate (BBP; a good solvent for PS) and dioctyl phthalate (DOP; a θ solvent for PS) were studied in the dilute region for viscosity as a function of the extensional rate with an opposing jets extensional rheometer. The ηe(ε) data obtained with use of different orifice geometries agree with each other within experimental errors. The extensional viscosity at low ε limit, ηe0 is about three times larger than the corresponding zero-shear viscosity in accordance with Trouton's rule. In high ε region, the extensional-thickening was observed for all the solutions. The critical extensional rate ε* at which the ηe(ε) deviates from ηe0 is confirmed to be related to the longest relaxation time of the solutions.