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Herein, we developed thermoresponsive gelation systems of amphiphilic random copolymer micelles in water. To establish the design of micelle nanodomains for the physical gels, we synthesized random...

The effects of polymerization concentrations and elementary reaction rates on the network structure and mechanical properties of gels synthesized by free radical copolymerization of monomers and cross-linkers are studied by a coarse-grained molecular dynamics simulation. The shear modulus, the number of elastically effective chains, and the number of trapped entanglements are calculated with varying the concentrations. The results reveal that the experimentally reported high cross-linking efficiency of the gels formed at high monomer concentrations and low cross-linker concentrations is due to the large number of trapped entanglements. The molecular mechanisms of changes in the network structure due to changes in the concentrations are elucidated by analyzing the detailed structure of network strands connecting adjacent cross-linking points. The results with systematically varying the elementary reaction rates indicate that the decrease in the propagation rate suppresses the formation of cyclic structures and reduces the influence of the trapped entanglements, i.e., improves the structural uniformity of the gels.

The effects of the primary structure of multifunctional reactive polymers on the network structure and the mechanical properties of gels formed by crosslinking the reactive polymers with crosslinkers are studied by a coarse-grained molecular dynamics simulation. When functional groups are randomly arranged on the polymers, the network structure, such as the number densities of elastically effective chains and entanglements, and the mechanical properties depend on the number average molecular weight of the polymers; however, these properties are almost independent of the molecular weight distribution and the functional group number distribution of the polymers. The control of the arrangement of functional groups on the polymers improves the uniformity and the mechanical properties. By changing the arrangement from a random one to a periodic one, the number of elastically effective chains and the shear modulus increase, and the occurrence of entanglement is suppressed. The detailed analysis of the network structure reveals that the improvement of the mechanical properties is mainly due to the reduction of intramolecular crosslinking.

The interest in emulsion fuel grows worldwide because it is potentially more environment friendly than its base fuel. Nonetheless, it has yet to be widely used as it is pricier than conventional diesel fuel due to its dependency on surfactant. This paper highlights the application of non-surfactant emulsion fuel in a light-duty truck (1 ton). The fuel is produced on demand with the so-called Real-Time Non-Surfactant Emulsion Fuel Supply System (RTES) just before being transferred into the engine. The emission characteristics and performance of the truck were then evaluated. To identify the optimum water percentage, the RTES is controlled to produce an emulsion with various water percentages during the testing. The experiment was performed on a chassis dynamometer using the West Virginia University (WVU) 5-Peak Cycle. The variants of fuel used throughout this experiment are Euro 5 diesel (D) and emulsion fuel based from it with varying water percentage of 5% (E5), 6.5% (E6.5), 10.8% (E10.8), and 30% (E30). The smoke number and nitrogen oxides, NOx emission of the truck are reduced with the use of emulsion fuel. E6.5 shows the highest average reduction of NOx at 45%. E30 emits higher carbon monoxide, CO than D while its carbon dioxide, CO2 is reduced by about 0.13%. E6.5's fuel consumption is the lowest; it is around 8.56% lower than D, followed by E10.8, E5 and E30. Overall, the concept of non-surfactant emulsion fuel appears to have the potential for application in diesel-powered vehicles to reduce harmful emissions.

We study the structures and the mechanical properties of nanocomposite networks consisting of disk-shaped particles and polymers by a coarse-grained molecular dynamics simulation. The disk-shaped particles and the polymers form tightly cross-linked network structures by the polymer adsorption on the disk-shaped particles and show high mechanical strength. We confirm the significance of the high polymerization degree for the large fracture elongations. Under the uniaxial elongation, at low elongation ratios, the networks maintain the cross-linked structures and indicate the sharp increase of the stress with the elongation. At large elongation ratios, the number of bridge chains decreases by the peeling of the adsorbed polymers from the disk-shaped particles. The decline of the bridge chains suppresses the increment of the stress. The orientation of the disk-shaped particles saturates prior to that of the polymers because of the slow orientation of the non-bridge chains. These results are consistent with reported experimental results.

We study the inclusion complex formation of cyclodextrins and a single polymer chain by a grand canonical Monte Carlo simulation and by a statistical-mechanical theory. The filling ratio of the polymer chain by threaded cyclodextrins is calculated and shows good agreement with reported experimental results. The adsorption isotherm of the filling ratio is also derived by the statistical-mechanical theory. We confirm the significance of hydrogen bonds between cyclodextrins for the inclusion complex formation. When hydrogen bonds can be formed between cyclodextrins, the filling ratio drastically increases at a certain concentration of the cyclodextrins, and inclusion complexes are formed. However, inclusion complexes are rarely formed without hydrogen bonds. We also find the expansion of size of the polymer chain with the development of one-dimensional aggregates constructed by threaded cyclodextrins along the polymer chain.

Microrheology based on diffusing-wave spectroscopy, dynamic light scattering (DLS), and macrorheology were performed on solutions of polyacrylamide-derivative associating polymer containing imidazole groups. By adding Ni ion, the physical gel is formed by metal-ligand bond. The physical gel point, where the percolation of a transient network is supposed to occur, was microrheologically determined. In the DLS measurement showing ergodicity at all the conditions studied, we observed three modes in the autocorrelation functions: fast, intermediate, and slow modes. The fast mode is the collective diffusion (gel mode), while the slow mode is attributed to the diffusion of clusters. For the intermediate mode, with increase in Ni ion concentration, the transition from diffusive mode to relaxation mode was observed near the microrheologically determined physical gel point. In postgel regime, intermediate mode can be attributed to the macroscopic relaxation since the activation energies are comparable with the relaxation energy estimated by macrorheology.

The use of water-in-diesel (W/D) emulsion as a diesel substitute has imposed significant interest due to its benefits to engine performance and exhaust emissions. However, the development on emulsification technology especially without using surfactant is still not widely known. Therefore, in this study, a study into the application of non-surfactant W/D emulsion has been done with the objective to analyze the potential of non-surfactant W/D emulsion made from low grade diesel as a substitute for higher grade diesel. This study was conducted using light-duty diesel vehicle, a 1 ton truck tested in a chassis dynamometer. A variety of test fuels was used, comprises of Diesel Euro 5 (DE5), Diesel Euro 2 (DE2) and emulsion made from Diesel Euro 2 (EDE2). EDE2 was produced real time just before it is injected into the diesel engine, with water percentage of 6.5% and no additional surfactant. The testing was executed on a chassis dynamometer in accordance to the West Virginia (WVU) 5 Peak-Cycle standard. Among the data collected are fuel consumption, exhaust temperature, gas emissions (NOx, CO and CO2) and smoke number. The results show that the EDE2 improved the engine fuel consumption by 7.39% compared to DE5. As for exhaust emissions, EDE2 produced slightly higher NOx and CO compared to DE5. However, CO2 and smoke of EDE2 were found to be lower. For that reason, with some adjustments, non-surfactant W/D emulsion fuel made from low grade diesel has a potential to be applied in road transport with some adjustment in order to replace the high grade diesel.

Chemically modified polyrotaxanes by methylation are water-soluble and show high-temperature gelation in water. To elucidate the molecular mechanism, we developed a theoretical model incorporating the following contributions: hydration–dehydration of cyclic molecules, formation of one-dimensional aggregates composed of a various number of cyclic molecules along the polymer chain, and formation of junction structures by associating between the aggregates. We numerically calculated the sol–gel transition line, the average aggregate length, the average junction multiplicity, the heat capacity change of the solution, the hydration ratio of cyclic molecules, and the translational entropy of cyclic molecules along the chain. We compared our results with the previously reported experimental data, and we discussed the molecular mechanism of the high-temperature gelation and the formation of the junction structures based on the sliding feature of cyclic molecules.

The present study constructs a theory of physical gels consisting of bifunctional molecules, f-functional molecules, and solvent. This theory considered the formation of loops (i.e., the smallest cycles). First, the association state in the equilibrium state was investigated. Unlike the previous theory proposed by the authors, the present theory was able to describe the effect of functionality on the association state. Second, the dynamics of gelation was studied. As a result, the authors found two regimes: one where the characteristic time of gelation is governed by the association of associative groups and another where it is governed by the dissociation of them. Finally, theoretical results and the existing experimental results were compared in terms of gelation time and the time development of elasticity. With parameters set reasonably, the theory succeeded in the quantitative description of the experimental results.

Magnetorheological (MR) valve is widely applied in a lot of applications that utilizes the flow mode, which is one of the working modes available for MR fluid devices. This paper introduces the serpentine flux path method in an MR valve, whereby using this method it can help to increase the effective region of the valve. The magnetic flux is guided into the annular gap of the valve, as the magnetic flux can be weaved by alternating the magnetic and non-magnetic materials. The method is simulated using Finite Element Method Magnetics to see the effects of weaving steps and thicknesses of non-magnetic materials to the magnetic flux distribution and pressure drop change in the valve. The results show that MR effective region can be increased with the serpentine flux path method, and the additional steps and thicknesses of non-magnetic materials help to further increase the pressure drops within the valve.

International audience; When the polymer chains are cross-linked by physical bonds having a finite lifetime, the relaxation time and viscosity do not diverge at the gel point though percolation occurs. These undivergent quantities are related to the finite-sized "largest relaxed cluster," which can relax before it breaks. Its size is the key rheological parameter characterizing of the critical physical gels. In order to evaluate this characteristic size, we propose here a generalized phenomenological model for the viscoelasticity of critical physical gels. We apply the theory to the previously reported experimental result for the physical gel consisting of polyacrylamide-derivative associating polymers containing imidazole groups cross-linked by coordination bonds with Ni ions. We successfully estimate the size of the largest relaxed cluster and the fractal dimension. The size is in good agreement with that estimated from the mean-square displacement of probe particles at the gel point by microrheological measurement. We also compare this system with the poly(vinyl alcohol) hydrogel cross-linked by borate ions, and show that the difference in the cluster structures is originating from the differences of precursor chain properties such as overlap concentration and radius of gyration and of the cross-linking states in these systems.

The structures and the mechanical properties of networks formed by end-linking of two types of tetra-arm star polymers are studied by a coarse-grained molecular dynamics simulation. The formation efficiency of elastically effective chains is improved by increasing the length of the arms and the volume fraction of the star polymers at the preparation stage. When the uniaxial elongation is applied to the networks in the as-prepared state, the shear modulus is proportional to the number density of the elastically effective chains and indicates an intermediate value between the phantom and affine network models. In the equilibrium swollen state, the shear moduli of the networks prepared at high volume fractions are significantly enhanced by trapped entanglements. The networks formed from the tetra-arm star polymers show higher number densities of the elastically effective chains than networks consisting of telechelic functional polymers and cross-linkers.

We studied addition effect of sodium tetraphenylborate (NaBPh4), an organic salt with multiple hydrophobic sites, on thermoresponsive behavior of aqueous methylcellulose (MC) solution. By means of simultaneous measurements of viscosity and light transmittance during heating, it was clarified that the concentration of added NaBPh4 determines which of gelation and phase separation occurs first. Aqueous MC solution without NaBPh4 formed gels below the phase separation temperature, and therefore the phase separation remained incomplete. With increasing the concentration of added NaBPh4, the gelation temperature monotonously increased, whereas the phase separation exhibited complicated behavior. The phase separation temperature in gel phase drastically increased by addition of small amount of NaBPh4 in similar fashion to the gelation temperature, although the phase separation in gel phase faded away when the concentration of NaBPh4 exceeded ca. 0.05 M. Alternatively, liquid-liquid phase separation appeared. In contrast to the phase separation in gel phase, the liquid-liquid phase separation occurred essentially below the gelation temperature and proceeded completely to form macroscopic binary domains. Temperature of the liquid-liquid phase separation decreased initially, but it turned upward when the concentration of added NaBPh4 exceeded ca. 0.15 M and increased drastically with the further addition. In other words, the addition effect of NaBPh4 to the liquid-liquid phase separation switched from salting-out to salting-in. The liquid-liquid phase separation in progress was immobilized by application of additional heating above the gelation temperature. These various structure developments depending on the concentration of added NaBPh4 were observed by optical microscopy (OM) and small-angle light scattering (SALS). On the basis of the experimental results, we proposed a mechanism of the addition effects of organic anion with multiple hydrophobic sites on the gelation and the phase separation of aqueous MC.