We have been able to design model filled rubbers with exactly the same chemical structure but different filler arrangements. From these model systems, we show that the particle arrangement in the elastomeric matrix controls the strain softening at small strain amplitude known as the Payne effect, as well as the elastic modulus dependence on the temperature. More precisely, we observed that the Payne effect disappears and the elastic modulus only weakly depends on the temperature when the particles are well separated. On the contrary, samples with the same interfacial physical chemistry but with aggregated particles show large amplitudes of the Payne effect and their elastic modulus decreases significantly with the temperature. We discuss these effects in terms of glassy bridge formation between filler particles. The observed effects provide evidence that glassy bridges play a key role on the mechanical properties of filled rubbers.

A new method based on the combination of small-angle scattering, reverse Monte Carlo simulations, and an aggregate recognition algorithm is proposed to characterize the structure of nanoparticle suspensions in solvents and polymer nanocomposites, allowing detailed studies of the impact of different nanoparticle surface modifications. Experimental small-angle scattering is reproduced using simulated annealing of configurations of polydisperse particles in a simulation box compatible with the lowest experimental q-vector. Then, properties of interest like aggregation states are extracted from these configurations and averaged. This approach has been applied to silane surface-modified silica nanoparticles with different grafting groups, in solvents and after casting into polymer matrices. It is shown that the chemistry of the silane function, in particular mono- or trifunctionality possibly related to patch formation, affects the dispersion state in a given medium, in spite of an unchanged alkyl-chain length. Our approach may be applied to study any dispersion or aggregation state of nanoparticles. Concerning nanocomposites, the method has potential impact on the design of new formulations allowing controlled tuning of nanoparticle dispersion.

The microstructure of polymer nanocomposites made with disordered silica filler (Zeosil(R) 1165MP) of industrial relevance and various coating agents is quantitatively analyzed using a combination of SAXS, TEM, and a recently developed structural model. The polymer matrix is formed by an endfunctionalized styrene-butadiene statistical copolymer capable of covalent grafting on the silica nanoparticles. The effect of the coating agents with different alkyl chain length (C 8 , C 12 , and C 18 ) on filler structure quantified in terms of aggregate formation, for different concentrations (up to 8%wt with respect to silica), and the effect of a commonly added catalyzer, DPG, are studied using the structural model. As a result we show that a strongly synergetic effect of both DPG and coating agent exist. Our findings open the road to a fundamental understanding and rational design of model and industrial nanocomposite formulation with optimized coating agents.

We took advantage of pseudopartial wetting to promote the spreading of precursor films whose surface density smoothly decays to zero away from a sessile droplet. By following the spreading dynamics of semidilute precursor films of polybutadiene melts on silicon wafers, we measure molecular diffusion coefficients for different molar masses and temperatures. For homopolymers, chains follow a thermally activated 2D Rouse diffusion mechanism, with an activation energy revealing polymer segment interactions with the surface. This Rouse model is generalized to chains with specific terminal groups.

In polymer nanocomposites, particle-polymer interactions play a key role both in the processing and in the final properties of the obtained materials. Specifically, for silica, due to the surface polarity, surface modification is commonly used to improve the compatibility with apolar polymer matrices, in order to prevent agglomeration.In this work, a new way to investigating the polymer-silica affinity and determining dispersibility parameters (HDP) of silica particles in the 3D Hansen space using a solvent approach is proposed. These parameters are estimated from the assessment of the stability of suspensions in a set of organic solvents. Based on the respective locations of the solvent, polymer and silica representative points in the 3D Hansen space, the adsorption of a given polymer in solution in a given solvent can be predicted. This is shown with the industrial precipitated silica Zeosil ® 1165MP in combination with polystyrene and polybutadiene. It is shown that silanization of the silica particles 1 decreases the adsorption of polystyrene, even though due to this surface treatment silica comes closer to polystyrene in the Hansen space. This counter-intuitive effect is rationalized based on the consideration of an adsorption parameter χ S computed from the relative locations of the solvent, polymer and particles in the 3D Hansen space. Basically, this parameter is related to the respective distances of the solvent and polymer representative points to that of the particle in Hansen space.

Nanometer-thick supported films of polymer melts spontaneously form and spread around sessile droplets that are deposited on oxidized silicon wafers. At steady state, the films become dense and adopt a uniform thickness, which is equal to twice the gyration radius of the free polymer. Remarkably, this law applies to a wide variety of melts and does not depend on the polymer chemistry nor on the surface state (oxide layer thickness, temperature, presence of water adsorbed, etc.). We show that existing theoretical descriptions cannot reproduce this experimental result. Conversely, the evolution toward this equilibrium state witnesses the specificity of the interactions at stake in these confined polymer films. The chain spreading dynamics can be modeled by taking into account both the polymer/surface friction and the polymer/polymer friction.

We investigate the evolution over time of the space profiles of precursor films spreading away from a droplet of polymer, in the poorly explored pseudo-partial wetting case. We use polystyrene melt droplets on oxidized silicon wafers. Interestingly, the film thicknesses measured by ellispometric microscopy are found in a 0.01 to 1 nm range. These thicknesses were validated by atomic force microscopy (AFM) measurements performed on the textured film obtained after a quench in temperature. From this, an effective thickness is obtained and compares well to the thicknesses measured by ellipsometry, validating the use of an optical method in this range of thickness. Ellipsometric microscopy provides a height resolution below the ångström with lateral resolution, image size and framerate well adapted to spreading precursor films. From 1 this, we demonstrate that precursor films of polystyrene consist of polymer chains with a surface density decreasing to 0 away from the droplet. We further find that the polymer chains follow a simple diffusive law with diffusion coefficient independent of density. This demonstrate that polystyrene chains spread independently in precursor films in pseudo partial wetting condition. This behavior differs significantly from the case of chains spreading in total wetting, for which the diffusion coefficient was found in the literature to depend on surface density or thickness.

An innovative rotary tribometer was developed in order to reproduce the abrasive wear of reinforced rubber materials for tire. The device allows performing accelerated, quantitative friction and wear tests which mimic real usage conditions in terms of kinematics and dynamics of the contact, temperature and open cycle conditions, specifically in low severity conditions, which often represent a challenge to mimic and study. The specific point emphasized here is the strong impact of wear debris accumulated in the contact zone on the measured wear rate. To quantify this phenomenon, the amount of wear debris in the contact was varied by changing the frequency at which debris are eliminated. It was found that the presence of more debris in the contact zone generally decreases the wear rate. Two distinct types of wear debris were identified, which are likely to correspond to two distinct mechanisms of wear. Within a transitory period at the beginning of the tests, wear debris essentially consist in a sticky layer of soluble (thus decrosslinked elastomer material). Further on, a steady regime (representative of wear in real low severity conditions) occurs, with a well established ridge pattern, in which the predominant wear mechanism consists in tearing away material fragments of micrometric sizes. The proposed test method allows discriminating quantitatively these mechanisms.