The rheological behavior of a material is strongly related to the energy dissipation, and the understanding and modeling of dissipation are important from the view point of rheology. To study rheological properties with some mesoscopic and macroscopic dynamics models, the modeling of dynamic equation which appropriately incorporates the dissipation is important. Although there are several methods to construct mesoscopic and macroscopic dynamic equations, such as the Onsager's method, their validity is not fully clear. In this work, we theoretically analyze the dissipation in a mesoscopic Langevin equation in detail, from the view point of stochastic energetics. We show that the dissipative heat flow from the heat bath to the system plays an important role in the mesoscopic dynamics. The dissipative heat flow is unchanged under the variable transform, and thus it is a covariant quantity. We show that we can construct the Langevin equation and also perform a coarse-graining based on the dissipative heat flow. We can derive the mobility tensor from the dissipative heat flow, and construct the Langevin equation by combining it with the free energy. Our method can be applied to various systems, such as the dumbbell model and the diffusion type equation for the density field, to give the coarse-grained dynamic equations for them.
Analysis of ABA triblock copolymer in thermoplastic elastomer (TPE) using machine learning is conducted on the structure obtained by coarse-grained molecular dynamics simulation. ABA triblock copolymer formed the spherical micro phase separated structure takes the bridge or loop structures. The analysis of the bridge and loop chains are too complicated, and it takes a lot of tasks. We applied machine learning to this problem. Typical parameters for polymer chains, such as Rg2, R2 etc., are used as the descriptor, and the separation between bridge and loop chain is performed by SVC method. As a result, high prediction score can be obtained, and we can get the learning model for the separation of ABA chain conformation. Furthermore, we made the model to select the polymer chains which is especially elongated in the uniaxial deformation using the polymer chain parameters in the initial structure. Using this learning model, without the deformation test, we can predict the polymer chains which is especially elongated in the uniaxial deformation.
In this study, vulcanized isoprene rubber (IR) under uniaxial stretch was examined by two different methods. One was conventional dynamic mechanical analysis (DMA), while this attempt to perform DMA testing on largely deformed specimen was quite challenging and gave a new insight on the rheological behavior of stretched rubber molecules. Another was nanorheological atomic force microscope (AFM), which was developed by the authors. The method provided spatially-resolved images of storage modulus, loss modulus and loss tangent at wide frequency ranges. The IR vulcanizate exhibited heterogeneous structure visualized by AFM, in which stretched and non-stretched regions were visible, showing non-affine nature of the specimen. Viscoelastic properties were examined in terms of elongation ratios, frequencies with comparing macroscopic and microscopic responses, where both measurements gave almost similar results to each other. The storage modulus at rubbery plateau region was increased upon large deformation in both measurements. The main finding was that the viscous response was not enhanced until the specimen experienced large deformation.
The miscibility between two polymer species is important not only from a scientific viewpoint but also from an industrial perspective. The information on the morphology is not sufficient to understand their mixed states, and submicron-scale material properties must be clarified. A unique nanorheological atomic force microscopy (AFM) technique was utilized in this study to investigate the nature of a styrene-butadiene rubber (SBR)/butadiene rubber (BR) partially miscible polymer blend. The blend seemed to be immiscible according to scanning transmission electron microscopy and conventional AFM techniques. However, when both the storage modulus and loss modulus for the blends were compared with those for the homopolymers by using nanorheological AFM, values for both the SBR-rich and BR-rich regions did not coincide with those for the pure components. In particular, the BR-rich region, which might contain SBR due to their partial miscibility, exhibited a dynamic heterogeneity, where the frequency responses were much more complicated than those of the BR homopolymer, though differential scanning calorimetry measurement could not detect it as the change of glass-transition temperature.
In this study, the effect of clay particles on toughening behavior of poly(lactic acid) (PLA)/natural rubber(NR) blend is investigated. PLA and NR were blended in various compositions (70/30, 60/40 and 50/50 PLA/NR) with two types of clay, organoclay and natural clay (Montmorillonite). Linear viscoelasticity analysis and morphology observation of the blends were carried out to investigate change in the blend morphology in the presence of clay. As the NR content increases from 30 wt% to 50 wt%, the NR domains coarsens, changing the blend morphology from droplet to apparent co-continuous structure. With the change in the blend morphology, tensile behavior of the blend including tensile strength and elongation at break differs. Besides, the addition of clay to the blend affects the blend morphology in different way, especially depending on the localization and the clay content. Natural clay localized in the PLA phase induces coalescence of the NR droplets while organoclay reduces the NR drop size due to interfacial localization of clays in the PLA/NR blend. For the droplet morphology, toughening behavior of the PLA/NR blend improves (~ 60% elongation at break of 70/30 PLA/NR blend) only when a small amount of organoclay (0.5 wt%) is added. On the other hand, the 50/50 PLA/NR blend with the apparent co-continuous morphology improves the elongation at break as clay content increases regardless of the type of clay.
Rheological properties for binary polyolefin blends composed of linear low-density polyethylene (LLDPE) and long-chain branched polypropylene (LCB-PP), in which LCB-PP is the dispersed phase, were studied. Even though LCB-PP was in the dispersed phase, the blend showed marked strain-hardening behavior in the transient elongational viscosity. The deformed LCB-PP droplets acted as “rigid fibers” during the elongational flow owing to its strain-hardening behavior. Consequently, the blend behaved like a fiber-dispersion system and thus exhibited the enhanced elongational viscosity, originated from excess deformation of LLDPE located between fibrous LCB-PP droplets under the elongational flow. Under shear flow, the primary normal stress difference was not enhanced by the addition of LCB-PP. This is reasonable because LCB-PP droplets oriented to the flow direction did not provide excess deformation of a continuous phase greatly.
We constructed a low-calorie mayonnaise prototype in which part of the oil was replaced with agar micro-gels. The viscosity of a full oil mayonnaise (F-mayo) at the shear rate of 5s−1 was 36.0 Pa·s, while the value of a half oil mayonnaise (H-mayo) sharply decreased to 1.75 Pa·s. However, the value of an oil reduced mayonnaise containing agar micro-gels (A-mayo) recovered to 38.2 Pa·s. Furthermore, we obtained structural information in mayonnaise by analyzing dynamic modulus with a weak-gel model. The characteristic parameter, the coordination number (z), was 13.9 for F-mayo. However, the value of H-mayo was 6.54, which was almost half that of F-mayo. The z value of A-mayo was significantly improved to 11.7. From these results, it was suggested that the low oil mayonnaise blended with the agar microgel showed the similar rheological properties of the normal mayonnaise, that is, it is expected that a texture of A-mayo is similar to the normal mayonnaise.
A viscoelastic model for floc-forming suspensions considering the aggregation and breakage of flocs during flows was developed based on our previous model, in which a population balance equation was adopted to simulate the floc aggregation-breakage. Similarly to the previous model, a Krieger-Dougherty model was used to describe the dependence of viscosity on the volume fraction of flocs, and a White-Metzner type model was used to represent the effect of viscoelasticity. In addition, the dependence of the relaxation time on the volume fraction of flocs was introduced to the present model using an elastic modulus function that depends on the effective volume fraction of flocs. The rheological behavior of the present model was examined by performing the simulation of startup flows of simple shear. The results of the simulation indicated that the temporal change in the distribution of floc size greatly depended on the elastic modulus function. The temporal behavior of the first normal stress difference therefore exhibits differences just after the startup of flow, depending on the elastic modulus function. The present model will be a simple viscoelastic constitutive model for floc-forming suspensions that represents the dependence of both viscosity and relaxation time on the floc size distribution.
The flow-induced orientational changes of 0.5-wt% xanthan gum solution in a planar channel with an abrupt contraction followed by an abrupt expansion were examined by measuring the flow-induced birefringence and velocity fields. Four 4:1:4 abrupt-contraction-and-expansion channels with middle slit lengths of 1 mm, 2 mm, 3 mm, and 10 mm were tested in the experiments. How the flow-induced orientation developed near the centerline after the abrupt expansion was found to differ remarkably with the slit length. For slit lengths of 3 mm and 10 mm, the polymer molecules were temporally aligned perpendicular to the flow direction by negative elongational flows generated after the abrupt expansion. By contrast, no similar phenomenon was observed for the slit lengths of 1 mm and 2 mm. These results show that the typical flow-induced orientational changes in a polymer in a planar channel just after an abrupt expansion are affected substantially by the length of the middle slit.