We extend a model regarding the reinforcement of nanofilled elastomers and thermoplastic elastomers. The model is then solved by numerical simulations on mesoscale. This model is based on the presence of glassy layers around the fillers. Strong reinforcement is obtained when glassy layers between fillers overlap. It is particularly strong when the corresponding clustersfillers + glassy layerspercolate, but it can also be significant even when these clusters do not percolate but are sufficiently large. Under applied strain, the high values of local stress in the glassy bridges reduce their lifetimes. The latter depend on the history, on the temperature, on the distance between fillers, and on the local stress in the material. We show how the dynamics of yield and rebirth of glassy bridges account for the nonlinear Payne and Mullins effects, which are a large drop of the elastic modulus at intermediate deformations and a progressive recovery of the initial modulus when the samples are subsequently put at rest, respectively. These mechanisms account also for dissipative properties of filled elastomers. In particular, our results allowed also for explaining semiquantitatively the results obtained by Payne in his 1963 study. Our model opens the way for predicting mechanical behavior of nanofilled elastomers according to the filler structures and dispersion, polymer−filler interactions, and temperature, in order to prepare systems with tailored properties.

In this contribution, we study situations in which nanoparticles in a fluid are strongly heated, generating high heat fluxes. This situation is relevant to experiments in which a fluid is locally heated by using selective absorption of radiation by solid particles. We first study this situation for different types of molecular interactions, using models for gold particles suspended in octane and in water. As already reported in experiments, very high heat fluxes and temperature elevations (leading eventually to particle destruction) can be observed in such situations. We show that a very simple modeling based on Lennard-Jones (LJ) interactions captures the essential features of such experiments and that the results for various liquids can be mapped onto the LJ case, provided a physically justified (corresponding state) choice of parameters is made. Physically, the possibility of sustaining very high heat fluxes is related to the strong curvature of the interface that inhibits the formation of an insulating vapor film.interfaces ͉ liquids ͉ Kapitsa resistance S ubmicron-scale heat transfer is attracting a growing interest, motivated by both fundamental and technological points of view. In fluids, considerable attention has been devoted to the so-called nanofluids (1, 2), in which nanoparticles in dilute suspension appear to modify both bulk heat transfer and critical heat fluxes. Although the former effect can presumably be understood in terms of particle aggregation (3, 4), the latter is still poorly understood.More generally, heat transfer from nanoparticles or nanostructures to a fluid environment is a subject of active research, stimulated by the development of experimental techniques such as time-resolved optical absorption or reflectivity or photothermal correlation spectroscopy (5). Applications include, e.g., the enhancement of cooling from structured surfaces, local heating of fluids by selective absorption from nanoparticles, with possible biomedical hyperthermia uses (6, 7). Recent experiments demonstrated the possibility of reaching very high local temperatures by using laser heating of nanoparticles (8-10), even reaching the melting point of gold particles suspended in water. From a conceptual point of view, such experiments raise many interesting questions compared with usual, macroscopic heattransfer experiments. How are the phase diagram and heattransfer equations modified at small scales? How relevant is the presence of interfacial resistances, and how do they change with temperature?The case of nanofluids (11) is a good illustration of the role that can be played by molecular simulation in the interpretation of such complex situations. Although many interpretations have been proposed to explain the reported experimental results, it is only simulation of simple models that has been able to disprove some of these interpretations and to demonstrate the validity of the alternative, aggregation scenario. Interestingly, the use of complex models with accurate interaction force fields is not, in genera...

This work examines the initial growth and collapse stages of bubbles induced by laser ablation in liquids. First, the bubble shape and size are tracked using an ultrafast camera in a shadowgraph imaging setup. The use of an ultrafast camera ensures a high control of the reproducibility, because a thorough measurement of each bubble lifetime is performed. Next, an analytical cavitation-based model is developed to assess the thermodynamic bubble properties. This study demonstrates that the bubble evolution is adiabatic and driven by inertial forces. Surprisingly, it is found that the bubbles consist of significantly more solvent molecules than ablated matter. These results are valuable to the field of nanoparticle synthesis as they provide insight into the mechanics of laser ablation in liquids.

The cooling dynamics of glass-embedded noble metal nanoparticles with diameters ranging from 4 to 26 nm were studied using ultrafast pump-probe spectroscopy. Measurements were performed probing away from the surface plasmon resonance of the nanoparticles to avoid spurious effects due to glass heating around the particle. In these conditions, the time-domain data reflect the cooling kinetics of the nanoparticle. Cooling dynamics are shown to be controlled by both thermal resistance at the nanoparticule-glass interface, and heat diffusion in the glass matrix. Moreover, the interface conductances are deduced from the experiments and found to be correlated to the acoustic impedance mismatch at the metal/glass interface.2

We report on the formation and growth of nanobubbles around laser-heated gold nanoparticles in water. Using a hydrodynamic free-energy model, we show that the temporal evolution of the nanobubble radius is asymmetrical: the expansion is found to be adiabatic, while the collapse is best described by an isothermal evolution. We unveil the critical role of the thermal boundary resistance in the kinetics of formation of the nanobubbles: close to the vapor production threshold, nanobubble generation is very long, yielding optimal conditions for laser-energy conversion. Furthermore, the long appearance times allow nanoparticle melting before the onset of vaporization.

Thermo-osmotic and related thermophoretic phenomena can be found in many situations from biology to colloid science, but the underlying molecular mechanisms remain largely unexplored. Using molecular dynamics simulations, we measure the thermo-osmosis coefficient by both mechanocaloric and thermo-osmotic routes, for different solid-liquid interfacial energies. The simulations reveal, in particular, the crucial role of nanoscale interfacial hydrodynamics. For nonwetting surfaces, thermo-osmotic transport is largely amplified by hydrodynamic slip at the interface. For wetting surfaces, the position of the hydrodynamic shear plane plays a key role in determining the amplitude and sign of the thermo-osmosis coefficient. Finally, we measure a giant thermo-osmotic response of the water-graphene interface, which we relate to the very low interfacial friction displayed by this system. These results open new perspectives for the design of efficient functional interfaces for, e.g., waste-heat harvesting.

Recent experiments have demonstrated that the dynamics in liquids close to the glass transition temperature is strongly heterogeneous. The characteristic size of these heterogeneities has been measured to be a few nanometers at Tg. We extend here a recent model for describing the heterogeneous nature of the dynamics which allows both to derive this length scale and the right orders of magnitude of the heterogeneities of the dynamics close to the glass transition. Our model allows then to interpret quantitatively small probes diffusion experiments.

It has been shown over the past ten years that the dynamics close to the glass transition is strongly heterogeneous: fast domains coexist with domains three or four decades slower, the size of these regions being about 3 nm at T(g). The authors extend here a model that has been proposed recently for the glass transition in van der Waals liquids. The authors describe in more details the mechanisms of the alpha relaxation in such liquids. It allows then to interpret physical ageing in van der Waals liquids as the evolution of the density fluctuation distribution towards the equilibrium one. The authors derive the expression of macroscopic quantities (volume, compliance, etc.). Numerical results are compared with experimental data (shape, times to reach equilibrium) for simple thermal histories (quenches, annealings). The authors explain the existence of a "Kovacs memory effect" and the temporal asymmetry between down jump and up jump temperatures experiments, even for systems for which there is no energy barriers. Their model allows also for calculating the evolution of small probe diffusion coefficients during ageing.