It was indicated that the viscoelastic measurements are useful tools for characterization of polymeric solids when they are employed in addition to the superstructural characterization. After crystalline relaxation was established by using single crystal mats, relaxation curves of highly oriented crystalline polymers were analyzed as a function of direction of external force. As a result the concept of tie molecule was proposed. One method for increasing the tie molecule fraction is to introduce the rigid rod-like molecules into the flexible chain matrix as reinforcements. Preparation methods, modulus evaluation and stress-strain behavior of molecular composites are discussed. Several successful examples are cited and the necessary conditions for the molecular composites are indicated. This method is similarly effective for reinforcing amorphous multiphase systems.
In order to improve the yield rate of wood used for piano soundboards, measurements were made of the dynamic mechanical properties for Sitka spruce (Picea sitchensis) wood pieces containing reaction wood, sapwood, indented rings, knot, resin streak, and resin pocket, which have been accepted to be defects according to the maker's own selection measure. In the present study the suitability of wood for soundboards was evaluated by using both the values of internal friction and specific Young's modulus in longitudinal direction; low internal friction and high specific Young's modulus were considered to be favorable for soundboards. The pieces containing intense reaction wood had higher value of internal friction and lower value of specific Young's modulus compared with those of slight reaction wood. The one with extremely low value of specific Young's modulus had large average microfibril angle in the cell wall. About half of the pieces containing slight reaction wood showed the acoustical properties comparable to those of defect-free high grade ones. Sapwood pieces had high value of internal friction and high specific Young's modulus. The high friction of sapwood was considered to result from their high moisture content. The acoustical properties of the pieces containing intense indented rings and resin streak were inferior to high grade ones. However, the acoustical properties of the pieces containing slight indented rings, knot, and resin pocket were almost comparable to those of high grade ones; probably these pieces are regarded as being inferior not because of their acoustical properties but because of their appearance. It was suggested that the selection based on the dynamic mechanical measurement is necessary to improve the yield rate of wood for piano soundboards.
Tensile and compressive plastic flows in glassy linear amorphous polymers have been investigated. The Eyring equation was applied to the lower yield value at which the stress becomes minimum after the yield point. This procedure allows to determine the variables such as the activation enthalpy, the activation entropy, and the activation volume for the plastic flow in the polymers as functions of temperature and stress. In previous papers it was already reported that experimental values of the activation enthalpy are explained well in terms of the Robertson theory when one assumes one-to-one correspondence between the molecular configuration and the activation enthalpy. In the present work, other Eyring coefficients, i. e., the activation entropy and the activation volume, were evaluated and discussed from the viewpoint of their relations to the polymer configurations. It was shown that the activation entropy for glassy polymers expressed as a function of Robertson's structural temperature θ1 was satisfactorily comparable with the activation entropy for polymer melts at temperature θ1. This means that the magnitude of the activation entropy depends to a considerable extent on the polymer configuration whether the polymer chain is in the state of glass or melt. By comparing the viscosity at θ1 calculated from the Eyring coefficients for the glasses with the viscosity measured for melts at temperature θ1, it was found that the magnitude of the activation volume was also closely associated with the polymer configuration.
Flow behavior of dilute red blood cell (RBC) suspension in a capillary was studied experimentally. Single RBC particle and rouleaux, i. e. two- or three-linearly connected RBCs, flowing through a glass capillary were observed using a microscope-16 mm cine-system. Image analysis was made on 16 mm cinefilm taken at a frame rate of 64/sec; the RBC velocity and flux were measured over the cross-section of the capillary by the method of“frame to frame”and by counting the number of RBC, respectively. The distribution in number density of RBC across the cross-section of capillary was determined on the basis of the RBC velocity and flux measured. The number density of rouleaux had a different distribution from that of single RBC; rouleaux had a tendency to flow in the central portion of capillary. This is probably due to the difference in shape, size, and deformability between single RBC and rouleaux.
The viscoelastic behavior of epoxy acrylate prepolymer during ultraviolet (UV) curing was studied by the use of an oscillating plate rheometer. The dynamic viscosity increases rapidly after a certain period of irradiation; the UV curing process has the minimum exposure energy required to start polymerization. Beyond the minimum exposure energy, the double logarithmic plots of dynamic viscosity against the exposure energy lie close to a straight line with a constant slope irrespective of sample thickness. The minimum exposure energy remarkably increases with sample thickness; this shows that the degree of curing under irradiation varies in the direction perpendicular to the plate. Curing efficiency depends on the light intensity at a given depth of the film. When UV light is applied through a UV filter, the curing behavior is analyzed by a single exponential decay of light with depth. The theoretical curve of dynamic viscosity shows a good agreement with the experimental results. On the other hand, when UV light from the UV lamp whose output spectrum is continuous, is applied, the initiation of polymerization can be explained by a combination of energy absorption at different wavelengths.
Literature data on the self-diffusion coefficient Ds of linear polymers in bulk and solution have been reexamined. The major conclusions are as follows: (a) The currently accepted relation for Ds as a function of polymer molecular weight M and concentration cp, i. e., Ds∝M-2,p-1.75 (i) is not exactly followed by the data, though it is usually taken as evidence for the reptation motion of a polymer chain assumed in the tube theory and also for the scaling theory. (b) The experimental data examined suggest that Ds tends to obey the relation Ds∝M-2.5 (ii) for M>Mc, the critical molecular weight for the onset of entanglement, and Ds∝M-1 (iii) for M<Mc, with a smooth transition between the two regions. Equation (ii) is consistent with the relation expected from viscoelastic data on polymer concentrates.
Self-diffusion coefficients Ds of chain molecules in highly entangled polymers were derived as a function of polymer molecular weight M and mass concentration cp, considering the“noodle effect”, i. e., the frictional resistance exerted on a moving chain by entangling chains, and postulating that flexible polymers in such systems wriggle as if they were in dilute solution (free chain model). For concentrated solutions of a mono-disperse polymer, Ds corrected for the segment friction coefficient is proportional to cp-1.5M-2.5. The corresponding results for binary blends of homologous monodisperse polymers are favorably compared with published data.
A semi-molecular theory of zero-shear viscosity η0 and steady-state compliance Je is worked out for monodisperse polymers and their binary blends, using basic relations in linear viscoelasticity and the expressions for self-diffusion coefficients derived in Part II of this series. For monodisperse systems, the result for η0 well explains the empirical viscosity law η0∝ζ0(cp)cp3.4M3.4 and that for Je is consistent with experimental Je which is independent of polymer molecular weight M and inversely proportional to the square of polymer mass concentration cp. The equation for η0 of binary blends can be brought to a close numerical agreement with the 3.4 power law by a suitable choice of one important parameter.
Viscoelastic properties and density of bone from the horse were studied. Two kinds of bone samples were used: one was taken from legs of horses suffering fracture in racing (fractured sample) and the other from legs of horses which were killed for other reasons (non-fractured sample). The dynamic stiffness and tan δ were measured by a viscoelastic spectrometer. A bone densitometer was used in density measurements. No substantial difference in values of dynamic stiffness and density was obseved in two kinds of samples. On the other hand, the values of tan δ for the fractured sample were definitely lower than those for the non-fractured one. It was inferred that the fractured sample was more brittle than the non-fractured sample.
The viscosity change of silica sol in the process of hydrolysis of ethylsilicate is measured by the falling ball method. With ethylsilicate 40, a pentamer on average of ethyl-silicate, as a starting material, the hydrolysis proceeds as Si5(OC2H5)12O4+12H2O→Si5(OH)12O4+12C2H5OH. With enough quantity of H2O for hydrolysis, the sol transforms to a gel quickly. In this study, the mole ratio H2O/ethylsilicate 40 is 1.83~2.83; the amount of water is smaller than that of the stoichiometric ratio. At temperatures below 25°C, viscosity increases to several poises in about 30 days, then due to the lack of water, the viscosity increases slowly as log η∝t for about 60 days up to about 100 poise. Finally the viscosity increase is remarkably accelerated.