Power law rheology is of widespread occurrence in complex materials that are characterized by the presence of a very broad range of microstructural length and time scales. Although phenomenological models able to reproduce the observed rheological features exist, in general a well-established connection with the microscopic origin of this mechanical behavior is still missing. As a model system, this work focuses on a fractal colloidal gel. We thoroughly characterize the linear power law rheology of the sample and its age dependence. We show that at all sample ages and for a variety of rheological tests the gel linear viscoelasticity is very accurately described by a Fractional Maxwell (FM) model, characterized by a power law behavior. Thanks to a unique set-up that couples small-angle static and dynamic light scattering to rheological measurements, we demonstrate that the power law rheology observed in the linear regime originates from reversible non-affine rearrangements and discuss the possible relationship between the FM model and the microscopic structure of the gel.

Despite an abundant literature on epoxy-amine systems, a complete description of the curing kinetics in epoxy-phenol composites was still lacking. In this study, the curing kinetics of an epoxy-phenol composite relevant to microelectronics industry is probed by isothermal and non-isothermal differential scanning calorimetry. An isoconversional analysis of the data reveals a significant contribution of the diffusion of molecular species to the activation energy, at low temperature and high degrees of curing. A model-fitting of the kinetics is performed in two successive steps: high-temperatures data are fitted with Arrhenius law and nth order autocatalytic model (where the diffusion contribution is neglected), whereas low-temperature data are fitted using Rabinowitch and modified-Williams-Landel-Ferry models (considering a diffusion contribution related to the glass transition). The chemical and diffusion contributions to the rate constants are calculated at various temperatures, clarifying the kinetics regimes with precision. Finally, the kinetics regimes are summarized in an improved time-temperature-transformation diagram.

Contact-resonance atomic force microscopy (CR-AFM) is of great interest and very valuable for a deeper understanding of the mechanics of biological materials with moduli of at least a few GPa. However, sample surfaces can present a high topography range with significant slopes, where the local angle can be as large as ± 50°. The non-trivial correlation between surface slope and CR-frequency hinders a straightforward interpretation of CR-AFM indentation modulus measurements on such samples. We aim to demonstrate the significant influence of the surface slope on the CR-frequency that is caused by the local angle between sample surface and the AFM cantilever and present a practical method to correct the measurements. Based on existing analytical models of the effect of the AFM set-up's intrinsic cantilever tilt on CR-frequencies, we compute the non-linear variation of the first two (eigen)modes CR-frequency for a large range of surface angles. The computations are confirmed by CR-AFM experiments performed on a curved surface. Finally, the model is applied to directly correct contact modulus measurements on a durum wheat starch granule as an exemplary sample.

Recent experimental results using in particular small-angle scattering to characterize the self-assembly of mainly hard spherical nanoparticles into higher ordered structures ranging from fractal aggregates to ordered assemblies are reviewed. The crucial control of interparticle interactions is discussed, from chemical surface-modification, or the action of additives like depletion agents, to the generation of directional patches and the use of external fields. It is shown how the properties of interparticle interactions have been used to allow inducing and possibly controlling aggregation, opening the road to the generation of colloidal molecules or potentially metamaterials. In the last part, studies of the microstructure of polymer nanocomposites as an application of volume-spanning and stress-carrying aggregates are discussed.

Plastics are ubiquitous in the oceans and constitute suitable matrices for bacterial attachment and growth. Understanding biofouling mechanisms is a key issue to assessing the ecological impacts and fate of plastics in marine environment. In this study, we investigated the different steps of plastic colonization of polyolefin-based plastics, on the first one hand, including conventional low-density polyethylene (PE), additivated PE with pro-oxidant (OXO), and artificially aged OXO (AA-OXO); and of a polyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), on the other hand. We combined measurements of physical surface properties of polymers (hydrophobicity and roughness) with microbiological characterization of the biofilm (cell counts, taxonomic composition, and heterotrophic activity) using a wide range of techniques, with some of them used for the first time on plastics. Our experimental setup using aquariums with natural circulating seawater during 6 weeks allowed us to characterize the successive phases of primo-colonization, growing, and maturation of the biofilms. We highlighted different trends between polymer types with distinct surface properties and composition, the biodegradable AA-OXO and PHBV presenting higher colonization by active and specific bacteria compared to non-biodegradable polymers (PE and OXO). Succession of bacterial population occurred during the three colonization phases, with hydrocarbonoclastic bacteria being highly abundant on all plastic types. This study brings original data that provide new insights on the colonization of non-biodegradable and biodegradable polymers by marine microorganisms.

Non-aqueous Taylor dispersion analysis (TDA) was used for the size-characterization of natural and synthetic polyisoprenes (4 × 103–2 × 106 g/mol molar mass). Not only the weight-average hydrodynamic radius (Rh), but also the probability distribution of the hydrodynamic radius, were both derived from the Taylorgrams by a simple integration of the elution profile and by a more sophisticated constrained regularized linear inversion of the Taylorgram, respectively. Results in terms of size characterization (hydrodynamic radii between 2 and 100 nm) were compared to size exclusion chromatography coupled to a refractive index-based mass detector. Multimodal size distributions were resolved by TDA for industrial and natural polyisoprenes, with the advantage over the chromatographic technique that, in TDA, there is no abnormal elution of microaggregates (hydrodynamic radii ∼ 40–50 nm). Considering the importance and the difficulty of characterizing polyisoprene microaggregates, TDA appears as a promising and simple technique for the characterization of synthetic and natural rubber.

We investigated the complexation of thermoresponsive anionic poly(N-isopropylacrylamide) (PNiPAM) microgels and cationic ε-polylysine (ε-PLL) chains. By combining electrophoresis, light scattering, transmission electron microscopy (TEM) and dielectric spectroscopy (DS) we studied the adsorption of ε-PLL onto microgel networks and its effect on the stability of suspensions. We show that the volume phase transition (VPT) of microgels triggers a large polyion adsorption. Two interesting phenomena with unique features occur: a temperature-dependent microgel overcharging and a complex reentrant condensation. The latter may occur at fixed polyion concentration, when temperature is raised above the VPT of microgels, or by increasing the number density of polycations at fixed temperature. TEM and DS measurements unambiguously show that short PLL chains adsorb onto microgels and act as electrostatic glue above the VPT. By performing thermal cycles, we further show that polyion-induced clustering is a quasi-reversible process: within the time of our experiments large clusters form above the VPT and partially re-dissolve as the mixtures are cooled down. Finally we give a proof that the observed phenomenology is purely electrostatic in nature: an increase of the ionic strength gives rise to polyion desorption from the microgel outer shell.