Real Space Structure and Scattering Patterns of Model Polymer Nanocomposites

Microscopic polymer liquid state theory is employed to study the real space pair correlation functions and collective scattering structure factors of melt polymer nanocomposites composed of hard spheres and adsorbing homopolymers over length scales ranging from monomeric to macroscopic. Increasing filler volume fraction has a profound effect on the polymer matrix, inducing oscillatory reorganization on a length scale commensurate with the nanoparticle diameter. The near contact interfacial monomer−filler pair correlations are suppressed by nanoparticle addition, but on larger scales power law correlations emerge with filler imprinted oscillatory features. Increased nanoparticle volume fraction also substantially changes interfiller packing, inducing a transition from a highly bridged or sterically stabilized type of organization in the infinite dilution limit to more diffuse liquidlike packing characterized by many-particle clustering. Distinctive modifications of the collective polymer structure factor include an increase in the osmotic compressibility, the emergence of a large bound layer or microphase-separation-like scattering peak on a length scale controlled by filler size indicative of distinct bound polymer layers, and a local rarefaction and suppression of the coherence of the monomer cage scale packing. All the real and Fourier space correlations depend in distinctive manners on the physical and chemical variables (filler size, volume fraction, strength and spatial range of the interfacial cohesion) and proximity to the contact aggregation and bridging phase separation boundaries. The bulk modulus of the nanocomposite generically softens with the addition of fillers corresponding to enhanced total density fluctuations.