Performance of filled rubber, which depended on the application such as tires, engine mounts, belts, seismic isolation rubber and rubber rollers, was described in conjunction with properties, i.e. strength, elasticity, viscosity, hardness, durability, weather resistance, conductivity, etc. Factors to control the properties were discussed in detail, which was associated with the amount of filler, the primary structure of filler, the secondary structure of its aggregate, and its distribution. In particular, the properties were related to rubber-rubber, rubber-filler and filler-filler interactions, which were inherently held in the filled rubber. The state of art technology and evolutionary prospect were described to control performance of tires, engine mounts, belts, seismic isolation rubber, rubber rollers and so forth.

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Molecules are often assembled by themselves with a large aspect ratio, leading to the formation of network structure based on their entanglements. Such systems, so-called “supramolecular network systems” possess hierarchical structure with various length scales ranging from nanometer to micrometer. Thus, to give a better understanding of dynamics for the supramolecular network systems, it is necessary to examine the structure and physical properties at various length scales, and clarify the correlation. By using optical tweezers and particle tracking techniques, we here show the local rheological properties in a worm-like micelle solution and a supramolecular hydrogel, which are formed by the networks based on the self-assembly of the amphiphilic molecules in water. In these techniques, viscoelastic information can be accessed on the basis of the movement of probe particles dispersed in a sample to be measured. For the worm-like micelle solution, we found that the viscoelastic functions (G' and G" ) varied depending on the location measured and the location-dependent variation of G' and G" was observed only at the measurement timescale being shorter than the relaxation time. This can be understood by taking into account that there exists a concentration fluctuation in the solution. Such fluctuation can be regard as a spatial heterogeneity when one takes a snapshot of the solution at a time shorter than the relaxation time. Also, the heterogeneity in the rheological properties was observed in a sol obtained by physically disrupting the supramolecular hydrogel. The extent of the heterogeneity decreased as a sol-to-gel transition proceeded. Such homogenization was associated with the change in the network structure rather than that in the molecular assembled state, which remains comparable in the sol and gel.

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We investigate the effects of polymer volume fraction on the mechanical properties of polymer gels by varying the volume fraction of network at preparation (φ₀) and at interested state (φ_m). Furthermore, we investigate the effect of φ₀ on the degree of the equilibrium swelling. We employ the Tetra-PEG gels with precisely tuning network strand length and the polymer volume fraction at preparation (φ₀) as a model system. The φ₀-dependence of the elastic modulus is almost proportional to φ₀/N, which corresponds to the prediction of the classical rubber elasticity theory. The φ_m-dependence of the elastic modulus exhibits the crossover at φ*. The dependence in semi-dilute region is stronger than that in dilute regions. The φ₀-dependences of the elastic modulus and the polymer volume fraction at the equilibrium swollen state also exhibit the crossover at φ*. The dependences in semi-dilute region are weaker than those in dilute regions. The Obukhov model successfully describes these dependences by considering the excluded volume effect. On the other hand, the familiar C* theorem fails to explain the experimental results.

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The rheological properties of an industrial-grade sucrose stearate aqueous solution were studied. This solution at 1 to 8 wt % appeared translucent or turbid from 20 to 48 °C; however, it became transparent above 48 °C and its viscosity increased. Furthermore, the apparent viscosity of the sample solution increased with temperature, and showed peak value at 48 °C for all such samples. On the other hand, small angle laser-light scattering studies revealed that the molecular-assembly size of the surfactant abruptly decreased at the same temperature. The dynamic modulus of the sample at approximately 48 °C was successfully analyzed with a bimodal Maxwell model, which showed that sucrose stearate formed several types of molecular assemblies and the shape was dependent on temperature. In particular, the rheological properties at approximately 48 °C strongly suggest that the surfactant formed thread-like molecular assemblies.

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In theoretical models of viscoelastic properties of polymer networks, it is typical to assume that the network junctions move affinely when the network is subject to macroscopic deformations. Recently, we proposed an idea to implement fluctuations of junctions around the affine motion in single-chain models of polymer networks without creating any of several physical inconsistencies [Schieber, Indei and Steenbakkers, Polymers, 5, 643 (2013)]. We showed that if the domain of the fluctuations represented by virtual springs deform affinely in an upper-convected manner, which we call the generalized Ronca-Allegra dynamics, then the contribution from the virtual springs does not show up explicitly in the expression of the total stress of the network. In this paper, we study physically cross-linked networks of unentangled associating polymers by theory and Brownian dynamics simulations. It is shown that if the generalized Ronca-Allegra dynamics is assumed, then the dynamic modulus for small deformations is equal to that from the Green-Kubo formula defined only for the stress from the polymer chains. Thus the consistency of the two expressions of the dynamic modulus is guaranteed in terms of the chain stress alone. This is one of the benefits of the generalized Ronca-Allegra dynamics. The result holds true for entangled polymer melts.

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This paper studies the molecular mechanism of rheological behavior of mixtures of colloid particles and associating polymers with many stickers by using a non-equilibrium molecular dynamics (NEMD) simulation method. The steady shear viscosity obtained by the NEMD simulation exhibits strong shear thickening at moderate shear rates, and shear thinning at larger shear rates. The value of the viscosity in the shear-thickening regime is three times larger than that in the the Newtonian regime. By analyzing the simulation data, it is shown that strong shear-thickening is caused by the network formation induced by shear flow. The scenario of the shear-induced network formation is as follows. In the small shear-rate regime, polymer chains take compact conformations due to strong association with a few colloid particles, which suppress the network formation. In the shear-thickening regime, such associated structures are destroyed by shear flow, leading to expanded conformations of polymer chains. This conformational change promotes the intermoleular association of polymers bridging colloid particles, and as a result, the network formation is enhanced.

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We report on a novel wrinkle formation process of water absorbing hydrogel particles. When the hydrogel particles called Super Absorbent Polymer (SAP) are dropped onto water which is held in a cylindrical container, the particles rapidly swell at the air-water interface to form a sheet-like structure. Once the sheet-like structure reaches the wall of the container by its continuous in-plane expansion, it starts to buckle with a characteristic pattern of wrinkles. We applied a simple model to estimate the wavelength of the wrinkle, which was in agreement with experimental values. We also discussed the effect of buoyant force on the wrinkle formation.

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Several supramolecular ion gels were prepared by mixing a poly(4-vinylpyridine)-b-poly(3, 4, 5-trimethoxystyrene) -b-poly(4-vinylpyridine) triblock copolymer (M_n = 76000) and poly(4-hydroxystyrene) (PHS, M_n = 3500) in an ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imidide, abbreviated as IL. The weight ratio of three components, i.e., triblock copolymer:PHS:IL was varied as 10:X:90 within the range of 0.16 ≤ X ≤ 3.2. Temperature-ramp oscillatory shear measurements revealed that the storage modulus G' of most of samples was larger than the loss modulus G" at room temperature, whereas G' ＜ G" at high temperatures, indicating those samples are thermoresponsive gels. G'-G" crossover temperature reached the maximum when a molar ratio of phenol unit on PHS to pyridine unit on a triblock copolymer was nearly two. Dynamic frequency sweeps also revealed two relaxation modes with different time scales: one is associated with hydrogen bonding formation at lower frequencies and the other with friction among network strands at higher frequencies. Moreover, the sample with excesssive PHS provided a completely different relaxation mode, suggesting that incomplete network was formed between triblock copolymer and PHS.

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The relationship between a microphase-separated structure and dynamic viscoelastic properties of polyurethane elastomers (PUEs) prepared at various temperatures and cross-linking agent contents were investigated. The PUEs were synthesized with poly(oxytetramethylene) glycol (PTMG), 4,4’-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) and a mixture of BD and 1,1,1-trimethylol propane (TMP) by a prepolymer method. The PUEs are in the strong-segregation limit. The microphase-separated structure was investigated using Fourier-transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), small-angle x-ray scattering (SAXS) and atomic force microscope (AFM). The extent of microphase separation of the PUEs became stronger and weaker with increases in curing temperature and trifunctional TMP content, respectively. The consistent results obtained in this study would be quite helpful to design the desirable PUEs.

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