The radial density profile of deuterated poly(N,n-propyl acrylamide) shell monomers within core-shell microgels has been studied by small angle neutron scattering in order to shed light on the origin of their linear thermally-induced swelling. The poly(N-isopropyl methacrylamide) core monomers have been contrast-matched by the H2O/D2O solvent, and the intensity thus provides a direct measurement of the spatial distribution of the shell monomers. Straightforward modelling shows that their structure does not correspond to the expected picture of a well-defined external shell. A multi-shell model solved by a reverse Monte Carlo approach is then applied to extract the monomer density as a function of temperature and of the core crosslinking. It is found that most shell monomers fill the core at high temperatures approaching synthesis conditions of collapsed particles, forming only a dilute corona. As the core monomers tend to swell at lower temperatures, a skeleton of insoluble shell monomers hinders swelling, inducing the progressive linear thermoresponse.

Nanofilms of thickness of about two nanometers have been formed at the air-water interface using functionalized castor oil (ICO) with cross-linkable silylated groups. These hybrid films represent excellent candidates for replacing conventional polymeric materials in biomedical applications, but they need to be optimized in terms of biocompatibility which is highly related to protein adsorption. Neutron reflectivity has been used to study the adsorption of two model proteins, bovine serum albumin and lysozyme, at the silylated oil (ICO)-water interface in the absence and presence of salt at physiologic ionic strength and pH and at different protein concentrations. These measurements are compared to adsorption at the air-water interface. While salt enhances adsorption by a similar degree at the air-water and the oil-water interface, the impact of the oil film is significant, with adsorption at the oil-water interface three-to four-fold higher compared to the air-water interface. Under these conditions, the concentration profiles of the adsorbed layers for both proteins indicate multilayer adsorption: The thickness of the outer layer (oil-side) is close to the dimension of the minor axis of the protein molecule, ~ 30 Å, suggesting a side-way orientation with the long axis parallel to the interface. The inner layer extends to 55-60 Å. Interestingly, in all cases, the composition of oil film remains intact without significant protein penetration into the film. The optimal adsorption on these nanofilms, 1.7-2.0 mg•m-2 , is comparable to the results obtained recently on thick solid cross-linked films using quartz crystal microbalance and atomic force microscopy, showing in particular that adsorption at these ICO film interfaces under standard physiological conditions is non-specific. These results furnish useful information towards the elaboration of vegetable oil-based nanofilms, in direct nanoscale applications or as precursor films in the fabrication of thicker macroscopic films for biomedical applications. 2

The hysteretic softening at small dynamic strains (Payne effect) related to the rolling resistance and viscoelastic losses of tires was studied as a function of particle size, filler volume fraction, and temperature for carbon black (CB) reinforced uncrosslinked styrene-butadiene rubber (SBR) and a paste-like material composed of CB-filled paraffin oil. The low strain limit for dynamic storage modulus was found to be remarkably similar for CB-filled oil compared to CB-filled SBR. Small-angle X-ray scattering (SAXS) measurements on the simple composites and detailed data analysis confirmed that the aggregate structures and nature of filler branching/networking of carbon black were virtually identical within oil compared to the high molecular weight polymer matrix. The combined dynamic rheology and SAXS results provide clear evidence that the deformation-induced breaking (unjamming) of the filler network – characterized by filler-filler contacts that are percolated throughout the material – is the main cause for the Payne effect. However, the polymer matrix does play a secondary role as demonstrated by a reduction in Payne effect magnitude with increasing temperature for the CB-reinforced rubber, which was not observed to a significant extent for the oil-CB system.

The peculiar linear temperature-dependent swelling of core-shell microgels has been conjectured to be linked to the core-shell architecture combining materials of different transition temperatures. Here the structure of pNIPMAM-core and pNNPAM-shell microgels in water is studied as a function of temperature using small-angle neutron scattering with selective deuteration. Photon correlation spectroscopy is used to scrutinize the swelling behaviour of the colloidal particles and reveals linear swelling. Moreover, these experiments are also employed to check the influence of deuteration on swelling. Using a form free multi-shell reverse Monte Carlo approach, the small-angle scattering data are converted into radial monomer density profiles. The comparison of ‘core-only’ particles consisting of identical cores to fully hydrogenated core-shell microgels, and finally to H core/D shell architectures unambiguously shows that core and shell monomers display gradient profiles with strong interpenetration, leading to cores embedded in shells which are bigger than their isolated ‘core only’ precursor particles. This surprising result is further generalized to different core cross linker contents, for temperature ranges encompassing both transitions. Our analysis demonstrates that the internal structure of pNIPMAM-core and pNNPAM-shell microgels is heterogeneous and strongly interpenetrated, presumably allowing only progressive core swelling at temperatures intermediate to both transition temperatures, thus promoting linear swelling behaviour.

Single-chain nanoparticles (SCNPs) are soft disordered nano-objects synthesized by intra-molecular bonding of linear polymer chains with a finite fraction of reactive groups allowing internal crosslinking of the molecule. They may be investigated as a mimick of, e.g., intrinsically disordered proteins, in particular with respect to the effect of the crowded cellular environment on macromolecular properties. Here the conformation of synthetic SCNPs in presence of linear polystyrene crowding molecules has been studied by small-angle neutron scattering under contrast-matching of the crowders[1]. A model describing the scattering of aggregating polydisperse SCNPs (see Figure 1) has been developed, resulting in the determination of the potentially squeezed size of the individual SCNPs within aggregates, their local chain statistics, and the average aggregation number, as a function of crowding. Two different crowders – of low and high molecular weight, respectively – are shown to have a different effect: while long chains tend to impede their aggregation above their overlap concentration, short ones are found to mediate depletion interactions leading to aggregation. Self-imposed crowding within the aggregates has a similar impact on chain conformation independently of the crowding of the surrounding medium. Our results are compared to recent simulations and is hoped to contribute to the microscopic understanding of the phase behavior of soft intrinsically disordered nano-objects, and in particular the effect of crowding on biomacromolecules. Figure 1: Schematic representation of the aggregation process of two SCNPs of monomer numbers i1 and i2 described by the addition of their individual SCNP masses, and obeying the same local chain statistics.References[1] Julian Oberdisse, Marina González-Burgos, Ander Mendia, Arantxa Arbe, Angel J. Moreno, José A. Pomposo, Aurel Radulescu and Juan Colmenero, under (favorable) revision in Macromolecules.

A combined small-angle scattering of neutrons (SANS) and X-rays (SAXS) study of thestructure of polymer layers pre-adsorbed on silica nanoparticles (NP) which are subsequentlyincorporated into polymer nanocomposites (PNCs) is presented. Pre-adsorbed chains are foundto promote ideal dispersion, before desorption in the late stages of nanocomposite formation.The microstructure of the interfacial polymer layer is characterized by detailed modeling of X-rayand neutron scattering. Only in ideally well-dispersed systems a static interfacial layer ofreduced polymer density over a thickness of ca. 2 nm is evidenced based on the analysis with aform-free density profile optimized using reverse Monte Carlo simulations. This interfacialgradient layer is found to be independent of the thickness and mass of the initially adsorbedpolymer, but appears to be generated by out-of-equilibrium packing and folding of the preadsorbedlayer. The impact of annealing is investigated to study the approach of equilibrium,showing that initially ideally well-dispersed systems adopt a repulsive hard-sphere structure,while the static interfacial layer disappears.In parallel, SANS and the use of zero average contrast conditions allow the measurement ofchain conformation in the PNCs with and without pre-adsorption. Surprisingly, we evidenced thespontaneous formation of thermally-stable adsorbed layers in PNCs containing matrix chains ofdifferent mass, whereas a symmetric matrix of identical chain masses does not show this effect.This study contributes thus to the fundamental understanding of the interplay betweeneffects which are decisive for macroscopic material properties: polymer-mediated interparticleinteractions, and particle interfacial effects on surrounding polymer.

The conformation of single-chain nanoparticles (SCNPs) in presence of linear polystyrene crowding molecules has been studied by small-angle neutron scattering under contrast-matching of the crowders. A model describing the scattering of aggregating polydisperse SCNPs has been developed, resulting in the determination of the potentially squeezed size of the individual SCNPs within aggregates, their local chain statistics, and the average aggregation number, as a function of crowding. Two different crowders – of low and high molecular weight, respectively – are shown to have a different effect: while long chains tend to impede their aggregation above their overlap concentration, short ones are found to mediate depletion interactions leading to aggregation. Self-imposed crowding within the aggregates has a similar impact on chain conformation independently of the crowding of the surrounding medium. Our results are compared to recent simulations and shall contribute to the microscopic understanding of the phase behavior of soft intrinsically disordered nano-objects, and in particular the effect of crowding on biomacromolecules.