Flow simulations at reverse-roll coater using the VOF method were performed. In these simulations velocity fields and pressure fields were calculated in the gas phase and the liquid phase simultaneously. Concerning stream lines of the liquid phase, a large vortex and a small vortex are observed. Stream lines with various speed of the metering roll were simulated. Dynamic wetting line approaches to the center line of the nip with increasing the speed of the metering roll. Pressure distribution between the two rolls has two peaks which are a positive and a negative. Negative peak of pressure increases with the speed ratio S increases. Dynamic contact angle θD and dynamic wetting line position XD were calculated and compared with experimental data. The calculated value of θD and XD were in good agreement with the experimental value.
Although some experiments have addressed individual chain dynamics in the entangled state, the behavior of the quantity measured in the experiments, and its relation to chain conformation, deserves further study. In our previous work using primitive chain network simulations at equilibrium (Masubuchi et al, Nihon Reoroji Gakkaisi (J. Soc. Rheol. Jpn.) 36, 181, 2008), we examined the relaxation of the chain extension, x, which is the maximum distance between segments of any given chain. In this supplementary study we performed simulations under step shear deformations, away from the equilibrium state. It was found that the x relaxation under deformation is qualitatively similar to that of the relaxation modulus, where slow relaxation modes are insensitive to deformation while the intensity of fast modes is enhanced. As a result the longest relaxation time of x was found to be the same as the equilibrium state, and different from that of stress. For what concerns the behavior of the fast modes, less damping was observed for the relaxation of x than that for stress.
Startup flows of wormlike micellar solutions in an axisymmetric capillary channel were numerically studied using a modified Bautista-Manero (MBM) model as a constitutive equation. The values of model parameter of the MBM model decided for a CTAB/NaSal solution were employed. The velocity profile at steady state predicted by the numerical simulation agreed with corresponding experimental data. The present study treated startup flows at a constant pressure gradient, which corresponds to a stress-controlled-type flow. The flow rate increased with time until the flow reached a steady state. The velocity profile had an inflection point around which the velocity gradient rapidly changed. The position of inflection point slightly changed with time. Temporal changes in both fluidity and the micellar contribution to shear stress occurred within a wall side region of the inflection point, where a white turbidity phenomenon was observed in our previous experiments. These temporal responses are characteristic of the startup flow at constant pressure gradients.
A hybrid simulation of coarse-grained molecular dynamics (MD) simulation and self-consistent field (SCF) calculation has been conducted to examine the structure and strength of a polymer interface reinforced with block copolymers. We studied the interface of A-homo/AB-diblock/B-homo polymer systems, in which the B block in the copolymers was sufficiently short not to be entangled with other chains. In the coarse-grained MD simulation, the equilibrated structures in which block copolymers were concentrated at the interface were generated by our original algorithm, the density-biased Monte Carlo method. Stress-strain behavior was studied by elongating the unit cell during the coarse-grained MD simulation, and the fracture of interfaces was observed at around 4 % strain. The fracture energy was calculated by integrating the stress during elongation until the interfaces were completely separated. We found that the fracture energy was proportional to the volume fraction of block copolymer until the interface was saturated with block copolymer. The fracture energy was also proportional to the square of the length of the shorter block of the copolymer. These results were consistent with experimental results and theoretical predictions concerning the "pull-out" region, where one block of diblock copolymers was short enough not to become entangled.
We propose a highly coarse-grained dynamics simulation model for symmetric diblock copolymers based on the soft dumbbell model. We perform the simulations of microphase separation dynamics of diblock copolymer melts with and without shear flow and show that Brownian dynamics simulations for soft dumbbells can reproduce dynamics of microphase separated diblock copolymers qualitatively well with small computational costs. We also calculate the shear relaxation moduli for unoriented and oriented lamellar structures. It is shown that lamellars can be oriented to the perpendicular direction by shear flow, and the shear thinning behaviour is observed.
We performed three-dimensional viscoelastic analysis of multi-layer polymer flow by numerical simulation, and investigated the effects of the elongational properties on the encapsulation phenomenon in the coextrusion process. The K-BKZ model with multiple relaxation times was used as viscoelastic constitutive equation, and the PSM type damping function was used for this model. This model is convenient to investigate the effects of the elongational properties, because the parameter β in this model can control only the elongational properties. Also we can extract the effects only of the elongational properties, because the second normal stress difference in this model is zero. In this study, we assumed that multi-layer polymer flow of Fluid I (less viscous) and Fluid II (more viscous) flows in three kinds of channels with different taper angle (parallel, tapered contraction and tapered expansion). As a result, by increasing the β ratio between Fluid I and Fluid II (βI / βII) from 0.1 to 10.0, the degree of encapsulation (DE) hardly changed at confluence, increased at contraction part and decreased at expansion part. These results mean that the elongational properties clearly influence the encapsulation phenomenon especially at contraction part and expansion part.
Viscoelastic behaviour for entangled star polymer of 3 arms was investigated before and after the end-linking using computational linear rheology system of Branch-On-Branch(BOB) Rheology. The object of this study as an experimental system was poly(propylene sulfide) star (PPS star) with different arm length. The results of calculation were compared with the experimental data which has already been published and was supplied by the author of the original article. An additional function was incorporated into BOB-rheology which enables the calculation for polymers with the end-linking. The progress of end-link reaction was analysed by formulating the consumption of reactive groups in PPS star. The formulation produced the relation between the fraction of PPS star monomer and the connectivity extent in the end-link reaction. By comparing the experimental data with the calculation data for the monomer fraction, the unequal reactivity of end groups, also known as the substitution effect, was turned out to be negligible. As a result of calculation before the end-linking, the experimental data could be well reproduced by the viscoelasticity of 3 arm star polymer mixed with H-polymer rather than 3 arm star polymer alone. The results of calculation after the end-linking showed vertical shifts between the calculation and experimental data. The shifts were almost constant through the frequency range investigated and independent of the connectivity extent. Therefore, the expression of the plateau modulus (G0 = (4/5)·(dRT/Me), d:density, Me: the entanglement molar mass) is considered to underestimate the modulus appeared in the experimental data. Other features such as the cross point of G' and G", plateau region and terminal flow region were well reproduced by the calculation data.
The scanning probe microscopy experiment for the nanorheology and nanotribology of polymer surface is simulated by coarse grained molecular dynamics. The loading and the unloading process of the probe onto the polymer surface, and the lateral movement of the probe at the polymer surface are simulated with changing the temperature and the probe speed. The simulation gives the hysteresis loop in the force-displacement curve similar to what have been observed experimentally, and this effect is shown to be caused by a few polymer chains withdrawn from the bulk by the probe.
The specimen of a polymer melt in a rotational-type rheometer protrudes from the jigs when we measure the rheological characteristics of polymer melts by use of rotational-type rheometers. To clarify the effect of this protruding part size on the estimated rheological characteristics in the oscillatory flow, we tried to estimate the storage modulus G' and loss modulus G" using the viscoelastic flow simulation results in the parallel plate rheometer by the finite element method. The multiple mode Phan-Thien Tanner (PTT) model was employed as the constitutive equation. The estimated G' and G" increase with the protruding part size at the same frequency. The phase difference δ and the amplitude of shear stress τ0 need for the estimation of G' and G". The δ was almost independent of the protruding part size. While, the τ0 increased with the protruding part size because of shear stress rise near the edge of the jigs in case of large protruding part size. The absolute deviations of the estimated G' and G" using the simulation results were up to 20 % at the protruding part size of 1 mm when the plate radius is 12.5 mm and the distance between the plates is 2 mm.