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 dynamic and static properties of the interfacial region between polymer and nanoparticles have wide-ranging consequences on performances of nanomaterials. The thickness and density of the static layer are particularly difficult to assess experimentally due to superimposing nanoparticle interactions. Here, we tune the dispersion of silica nanoparticles in nanocomposites by pre-adsorption of polymer layers in the precursor solutions, and by varying the molecular weight of the matrix chains. Nanocomposite structures ranging from ideal dispersion to repulsive order or various degrees of aggregation are generated and observed by small-angle scattering. Pre-adsorbed chains are found to 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-ray and neutron scattering. Only in ideally well-dispersed systems a static interfacial layer of reduced polymer density over a thickness of ca. 2 nm is evidenced based on the analysis with a form-free density profile optimized using numerical simulations. This interfacial gradient layer is found to be independent of the thickness of the initially adsorbed polymer, but appears to be generated by out-of-equilibrium packing and folding of the pre-adsorbed layer. 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. This study thus promotes the fundamental understanding of the interplay between effects which are decisive for macroscopic material properties: polymer-mediated interparticle interactions, and particle interfacial effects on surrounding polymer.

We apply a recently developed optimization scheme to obtain effective potentials for alkali andalkaline-earth aluminosilicate glasses that contains lithium, sodium, potassium, or calcium asmodifiers. As input data for the optimization, we used the radial distribution functions of theliquid at high temperature generated by means of ab initio molecular dynamics simulations anddensity and elastic modulus of glass at room temperature from experiments. The new interactionpotentials are able to reproduce reliably the structure and various mechanical and vibrationalproperties over a wide range of compositions for binary silicates. We have tested these potentialsfor various ternary systems and find that they are transferable and can be mixed, thus allowing toreproduce and predict the structure and properties of multi-component glasses.