A hydrodynamic interaction model is presented to predict the behaviors of two droplets in a medium after application of large step shear strains. The model expresses the droplets by arrays of rigid spheres. Because of retraction rate e in time differentials for the rigid spheres, they move toward the center of mass of them in each array and this motion of the rigid spheres generates flow field in the medium similar to the field caused by recovery of droplets owing to the interfacial tension. The interaction between the rigid spheres is calculated using the hydrodynamic interaction tensor. The model predicts that the distance between the droplets in deformation direction decreases with increasing time and that the shape of the droplets becomes sigmoidal. In addition, the model calculation shows change in the distance in the deformation direction is independent of initial distance between the droplets providing that the initial distance is less than a certain value. These three predictions agree with the experimental results and strongly indicate that the origin of the interaction between the droplets is the hydrodynamic interaction.
To establish the evaluation method of tactile sensation of human hair, coincidence measurement of motion analysis and load measurements during hair brushing and finger combing were performed. Change in load profile from root to tip of hair by application of hair care products was examined. Change in the maximum load by hair damage and treatment and its correlation with sensory evaluation were also discussed. It was shown that the load during hair brushing which is considered to reflect the frictional property of human skin surface is useful to evaluate tactile feelings of human hair.
The behavior of the particle agglomerate in a polymer melt in dispersion and agglomeration processes was investigated. In the dispersion process of particle agglomerates, number of agglomerated particles and shear viscosity of the mixture were decreased in a similar manner, and the agglomerated number was well correlated by applied strain. On the other hand, in the agglomeration process of having reduced the shear rate applied, agglomerated number was increased after the increase in shear viscosity, when the mixture contained particles at a high volume fraction. Such a delay will be caused by the interaction between polymer entanglement structure and agglomerated particles. The internal structure of the mixture of particle and polymer was discussed in the consideration of frequency dependency of tanδ. When applying shear at shear rate more than the frequency where tanδ showed the maximum, particle agglomerate was dispersed well, and the interaction between polymer and single particle mainly governs rheological behavior. In addition, if smaller shear rate was applied to the mixture after that, relaxation of entanglement structure will induce particle agglomeration.
The sensitivity of the viscoelastic melt spinning process with respect to parameters has not been reported yet in the literature. The study on the sensitivity of the melt spinning process is quite important industrially because it is closely connected with the subject of productivity and product quality of the industrial process. In this study, we investigated sensitivity of the viscoelastic melt spinning process with respect to the velocity and temperature of the quench air, fiber length and the fluid characteristic relaxation time. Maxwell-Oldroyd model is used to describe the rheology of the polymeric materials. It has been found that the quality of the final product depends on the values of the parameters. Further, we have found that it is not possible to change the parameters arbitrary because it may yield irregular fiber or induce breakage of the individual filaments of the spinline.
Confined swirling flow of polymer solutions is investigated numerically using the finite volume method combined with a collocated mesh. The Simplified Phan-Thien-Tanner (SPTT) rheological model will be used as the constitutive equation of the fluid. It is assumed that the flow is steady, laminar, and axisymmetric. The effect of different parameters such as fluid's elasticity, mobility factor, retardation ratio, and the channel aspect ratio will be investigated on the velocity profiles and vortex structure within the cylinder and above the rotating disk. Numerical results are shown to be in good qualitative agreement with experimental data available for certain polymer solutions.
Linear viscoelastic behavior was investigated during a gelation process of two poly(dimethyl siloxane) prepolymers A and B of molecular weight Mw,pre = 3.5×104. The gelation occurred mainly through a reaction of monomethylsilyl groups (0.7 mol% in the backbone of the prepolymer B) and vinyl groups at the chain ends of A and B, giving a scarcely crosslinked gel having a large sol fraction (wsol = 0.58 on completion of gelation) and exhibiting the equilibrium modulus much smaller than a nominal modulus calculated from Mn,pre, (1-wsol)ρRT/Mn,pre with ρ = density. The reaction was conducted at a relatively low temperature, 50 °C, so that this reaction proceeded slowly and the viscoelastic changes during the gelation process were well resolved. The terminal flow behavior was observed at a reaction time tr ≤ 54 min (pre-gel stage), while the elasticity at low angular frequencies ω became prominent at tr ≥ 60 min (post-gel stage). The critical gelation behavior characterized with a power-law relationship between the storage/loss moduli and ω ,G' ∝ G" ∝ ωn (0 < n < 1), was not observed at tr between these stages, suggesting that the gelation did not occur through formation of a huge, self-similarly hyper-branched critical gel network. For further examination of this gelation process, the prepolymer mixture was collected at several reaction times tr and the molecular characteristics of toluene-soluble sol component therein and a number fraction of the remaining (unreacted) monomethylsilyl group nMeSi were examined. It turned out that the high-M tail of the sol became enriched with densely branched chains of M reaching 1×107 (≅ 300Mw,pre) and nMeSi rapidly decreased to ∼ 0.3 with increasing tr up to 65 min while the branch content/molecular weight of the sol decreased and nMeSi gradually approached 0 on a further increase of tr. These results suggested a gelation mechanism that densely branched pre-gel chains involving up to 300 prepolymer chains were first formed on consumption of the majority of the monomethylsilyl groups at tr ≤ 65 min and then these pre-gel chains were scarcely linked through a small amount of remaining monomethylsilyl groups to form the 3-dimensional gel at tr > 65 min. The lack of critical gelation behavior as well as the small equilibrium modulus (<<(1 - wsol)ρRT/Mn,pre) on completion of gelation are consistent with this mechanism.
The rheological properties of succinoglycan aqueous sodium chloride solution were investigated at the various temperatures ranging from 30 to 75 °C. The dynamic modulus of the sample solutions abruptly increased at around 65 °C during the cooling process. The critical temperature (Tc) at which the consistency changed sharply depended on the sodium chloride concentration, namely, Tc increased with the salt concentration. Succinoglycan takes a conformation of a semi-flexible single strand chain at above Tc. The spatial size of the polysaccharide at high temperature decreased with the salt concentration since the polysaccharide is a polyelectrolyte. The aqueous solution of the polysaccharide became a structured fluid after the cooling process. To make a quantitative characterization of the mechanical property of the structure fluid, the creep curve analysis was employed. The mechanical properties of the structured fluid can be quantitatively described by using 4- elements mechanical model. Moreover, the effect of the salt on the mechanical properties also emerged. Although the consistency of the sample at above Tc decreased with the salt concentration, it increased with the salt concentration after cooling below Tc. The result revealed that the consistency of the heat denatured succinoglycan aqueous solution was strongly affected with the salt concentration in the system.