Carboxyl-terminated butadiene acrylonitrile (CTBN) rubber/ epoxy (diglycidyl ether of bisphenol-A) / diamino diphenyl methane polymer blends with 60 wt% of CTBN were formulated to evaluate the viscoelasticity and the damping properties. When the blend resins had micro-phase separated morphologies composed of epoxy-rich dispersed phases larger than 500 nm in diameter surrounded by a rubber-rich continuous phase, the loss factors (η) of the steel laminates adhered with the resin significantly depended on the environmental temperature and the resonant frequencies. The resins with epoxy-rich phases smaller than 200 nm in diameter had broad glass-transition temperature range that resulted in the high loss factor (η > 0.1) of the steel laminates in the broad temperature range. Inhomogeneous nano-gel structures with 20∼30 nm sizes were observed in more compatible resins by scanning probe microscopy, although appreciable micro-phase separation was detected by none of SEM and TEM. Pulse NMR suggested that the fraction of interfacial phase in the resins increased with increasing the compatibility of the blends. The large interfacial phase in the inhomogeneous nano-gel structures seems to play an important role in the damping mechanisms.
The characteristics of strain-induced crystallization (SIC) are described on sulfur-crosslinked and peroxide-crosslinked natural rubber (NR) and synthetic isoprene rubber (IR). Simultaneous tensile and wide-angle X-ray diffraction measurements using synchrotron radiation systems were carried out in order to elucidate SIC, the rate of which was much faster than so called cold crystallization of NR. Onset strain of SIC of sulfur-crosslinked rubber was almost independent of network-chain density. The stretched molecular chains acted as initiating species of the crystallization, while surrounding chains contributed to the crystal growth. Deformation of crystal lattice with nominal stress was detected, which showed the strain-induced crystallites were responsible for the higher modulus upon stretching. A pantograph model describes the deformation mechanism of the rubber network. The effect of non-rubber components of NR on SIC was clearly detected, where the stress relaxation after high speed stretching gave the significant difference of SIC between NR and IR. Stearic acid did not accelerate SIC of sulfur-crosslinked NR and IR, oppositely with the cold or temperature-induced crystallization of them. The effect of carbon black filler on SIC of sulfur-crosslinked NR is also reviewed. For peroxide-crosslinked NR, SIC occurred when the deformation brought about a definite entropic state, this agrees with the theoretical prediction by Flory and is consistent with the classical theory of rubber elasticity.
In this work numerical simulation of a non-Newtonian fluid flow over a step has been studied by using mesh free method. The characteristic based split mesh free algorithm is used for numerical simulation of fluid flow. This mesh free algorithm has been developed based on the general characteristic based split finite element method. The mesh free results obtained from characteristic based split algorithm have been compared to those of the finite element. The effect of different fluid parameters on the solution has been discussed. Numerical results have been verified by experimental and other numerical data reported in literature.
Dynamic mechanical properties of binary and ternary blends of isotactic polypropylene (PP), atactic polystyrene (PS) and poly(styrene-b-ethylene-co-butylene-b-styrene (SEBS)) were investigated. The glass transition temperature of PS domains in PP/PS and PP/PS/SEBS composites becomes higher with PP content owing to the low activation entropy of the glass transition of PS domains. The PS domain size and the relaxation strength of the PS glass transition decrease by the increase of SEBS for PP/PS/SEBS composites with less than 2.5 phr SEBS content, while the domain size and the relaxation strength become constant for the composites with over 2.5 phr SEBS content.
Dielectric and viscoelastic behavior was examined for a 8/2 (wt/wt) blend of a cis-polyisoprene (PI; M = 19.9×103) and a low molecular weight (M) poly(p-t-butyl styrene) (PtBS; M = 16.4×103). In general, PtBS and PI exhibit the LCST-type phase behavior, but the blend examined was in the miscible region at temperatures examined, T = 30-70 °C. The dielectric loss ε" of the blend at low frequencies was exclusively attributable to the large-scale motion of the PI chains having type-A dipoles. The ε" data obeyed the time-temperature superposition, suggesting that all PI chains in the blend felt the same frictional environment. This result was in contrast to the failure of the superposition previously observed for the same PI chains in a 8/2 miscible blend with a higher-M PtBS (M = 69.5×103). This difference was attributed to a difference of the lifetime of the dynamic heterogeneity due to the concentration fluctuation of PtBS. In the blend with high-M PtBS, the terminal relaxation of PtBS was slower than that of PI and thus the concentration fluctuation was effectively frozen and the PtBS chains behaved as non-uniformly distributed frictional objects during the terminal relaxation of the PI chains. Then all PI chains could not feel the same segmental friction, which naturally resulted in the failure of the time temperature superposition. In contrast, in the blend with low-M PtBS examined in this study, the terminal relaxation was slower for PI than for PtBS. For this case, PtBS behaved as uniformly distributed frictional objects during the terminal relaxation of PI thereby allowing the PI chains to obey the superposition.
The total stress tensor for immiscible polymer blends is calculated based on the theoretical expression by Batchelor (1970), and Mellema and Willemse (1983) in the last stage of the stress relaxation under large step shear strains. In this stage, the shape of droplets is spheroid and the retraction of isolated droplets is calculated according to the theory developed by Okamoto et al. (1999). The calculated results are compared with experimental data for a polyisobutylene/polydimethylsiloxane blend. Contribution of the motion of the interface (the interface velocity term) to the total stress tensor in the theoretical expression for the isolated droplets is 37 % - 50 %, which cannot be neglected compared with the contribution of the pressure difference beyond the interface (the Laplace pressure term). The summation of both terms agrees well with the experimental data at step strain γ = 1, in which effects inherent in multiple droplet systems are the smallest. The γ dependence of the reduced stress appearing in the experimental data, which cannot be predicted by the theoretical calculation for the isolated droplets, is qualitatively explained by considering droplet size distribution in the theoretical calculation.
Non-Newtonian fluid can be encountered in many applications of Microdevices. In this study, two-dimensional non-Newtonian simulations of viscous micropump were performed. The viscous micropump consists of a rotating cylinder located eccentrically inside a microchannel. When the cylinder rotates, a net force is transferred to the fluid due to the unequal shear stresses on the upper and lower surfaces of the cylinder, thus causing the fluid to displace. Navier Stokes equations and modified Bingham model have been used to describe the fluid flow. Parameters as viscosity and stress used in the model are based on experimental data. It was found that Reynolds number is a predominant parameter on the variation of bulk velocity as a function of eccentricity. The stress and bulk velocity decrease with increasing the eccentricity at low Reynolds number. The changes in non-Newtonian fluid structure are related to Reynolds number, eccentricity and channel height. The pumping performance of non-Newtonian fluid is increasing with global pressure gradient and decreasing with the channel height.
Experimental studies were performed on the response under step changes in magnetic flux density of a magneto-rheological suspension consisting of carbonyl iron particles dispersed in silicone oil. The samples were subjected to a constant shear stress. It was found that the 30 % volume fraction suspension showed the expected changes in shear rate when the magnetic flux density was increased for a short period then reduced to the original value. The 24 % volume fraction suspension did not show this behavior, tending to maintain a lower value of the shear rate even after the flux density had been re-set to the original lower value, suggesting that this suspension may be more susceptible to some form of remnant aggregation of the particles.