Specific AFM analytical methods were tested to the surface evaluation of wheat powders at micrometric scale in dry conditions. The objective was to evaluate the adhesion properties of particles based on the main wheat endosperm components (starch, protein, and arabinoxylan) that are characterized by large diversity in terms of chemical composition and particle characteristics. Experiments were conducted by using the force spectroscopy mode to determine interactions generated by the surfaces of particles that were glued on AFM tips, and two reference flat and smooth surfaces, a glass and a polysine slide. Particular care has been devoted to characterize the surfaces in contact since local contact radius is a key parameter in the interpretation of the interactions. The statistical analysis of the normalized adhesion forces have shown the sensitivity of the AFM technique for hydrophobic wheat components and their correlation with the surface tension of the particles.

An original method based on atomic force microscopy (AFM) in contact mode was developed to abrade progressively the surface of tablets made of starch or gluten polymers isolated from wheat. The volume of the material removed by the tip was estimated from the analysis of successive topographic images of the surface, and the shear force was measured by keeping a constant normal force. Our data together with a simple tribological model provide clear evidence for a higher hardness and shear strength of starch compared to gluten. Gluten appears to have mechanical properties close to soft materials, such as talc, whereas starch displays higher hardness close to calcite. Our results are in a better agreement with structural properties of gluten (complex protein network) and starch (granular and semi-cristalline structure) than earlier studies by micro-indentation. This work shows that the AFM scratching method is relevant for the characterization of any polymer surface, in particular in application to materials made of different polymers at the nano-scale.

We describe a single step preparation of nanostructures of poly(3,4-ethylenedioxythiophene), PEDOT, in the hydrophobic domains of cationic surfactant-based hexagonal mesophases via chemical oxidative polymerization of EDOT monomers using FeCl3 as an oxidizing agent. After polymerization, the hexagonal structure of the mesophases is preserved as demonstrated by polarized light microscopy and X-ray scattering measurements. After extraction from mesophases, the chemical structure of PEDOT is confirmed by Fourier transform infrared spectroscopy. Moreover, PEDOT morphology is checked by transmission and scanning electron microscopies. PEDOT nanostructures with spindle-like or vesicle-like shapes are obtained depending on the experimental conditions. In the original method, high resolution atomic force microscopy, coupled with infrared nanospectroscopy, is used to probe the local chemical composition of PEDOT nanostructures. Finally, the as-prepared PEDOT polymers are characterized by both good thermal stability up to 200 °C and a relatively high conductivity value up to 0.4 S cm−1 as determined by thermogravimetric analysis and four probe measurements respectively.

In this work, we experimentally investigate the ability of topological defects to guide interfacial assembly of spherical particles with homeotropic anchoring confined to nematic interfaces. We propose two different systems: In the first one, particles are trapped at an air/nematic interface where they spontaneously form various 2D patterns. We demonstrate that the phase transition between these patterns can be controlled by defects formed in the nematic bulk. In the second system, we explore the behavior of particles at the surface of bipolar nematic drops. We found that particles assemble into linear chains and interact with surface defects at the North and South poles of the drop, giving rise to the formation of star structures in a self-assembly process. We detail the mechanism that guides the behavior of particles and discuss the role of defects in the formation of the observed patterns.

Under certain conditions, the addition of small non-adsorbing polymers to a suspension of large hard spheres yields a depletion gel. It is expected that, provided that solvent quality issues do not lead to phase separation, thermodynamics imposes an invariance of the hard-sphere depletion gel upon heating. We show here that this is not the case for depletion gels of soft hairy nanoparticles. Using multiarm star polymers as a model that encompasses the key features of a huge range of grafted colloids, we show that their microstructural details make the difference. In particular, their hybrid nature, consisting of a carbosilane core and a polymeric shell, gives rise to a mismatch in thermal expansion upon heating, which affects the nanoparticle's conformation in a way analogous to a dry-to-wet brush transition, and hence leads to thermal melting of the gel. These results open the route for the molecular design of new materials, providing new opportunities to colloid chemistry and processing.

By employing rheological experiments, mode coupling theory, and computer simulations based on realistic coarse-grained models, we investigate the effects of small, hard colloids on the glassy states formed by large, soft colloids. Multiarm star polymers mimic hard and soft colloids by appropriately varying the number and size of their arms. The addition of hard colloids leads, depending on their concentration, to either melting of the soft glass or the emergence of two distinct glassy states.We explain our findings by depletion of the colloids adjacent to the stars, which leads to an arrested phase separation when the repulsive glass line meets the demixing binodal. The parameter-free agreement between experiment, theory, and simulations suggests the generic nature of our results and opens the route for designing soft-hard colloidal composites with tunable rheology.

We investigate the dynamics of alginate gels, an important class of biopolymer-based viscoelastic materials, by combining mechanical tests and non-conventional, time-resolved light scattering methods. Two relaxation modes are observed upon applying a compressive or shear stress. Dynamic light scattering and diffusive wave spectroscopy measurements reveal that these modes are associated with discontinuous rearrangement events that restructure the gel network via anomalous, non-diffusive microscopic dynamics. We show that these dynamics are due to both thermal activation and internal stress stored during gelation and propose a scenario where a hierarchy of cross-links with different life times is responsible for the observed complex behavior. Measurements at various temperatures and sample ages are presented to support this scenario.