Structure factor of blends of solvent-free nanoparticle–organic hybrid materials: density-functional theory and small angle X-ray scattering

Abstract

We investigate the static structure factor S(q) of solvent-free nanoparticle-organic hybrid materials consisting of silica nanocores and space-filling polyethylene glycol coronas using a density-functional theory and small angle X-ray scattering measurements. The theory considers a bidisperse suspension of hard spheres with different radii and tethered bead-spring oligomers with different grafting densities to approximate the polydispersity effects in experiments. The experimental systems studied include pure samples with different silica core volume fractions and the associated mean corona grafting densities, and blends with different mixing ratios of the pure samples, in order to introduce varying polydispersity of corona grafting density. Our scattering experiments and theory show that, compared to the hard-sphere suspension with the same core volume fraction, S(q) for pure samples exhibit both substantially smaller values at small q and stronger particle correlations corresponding to a larger effective hard core at large q, indicating that the tethered incompressible oligomers enforce a more uniform particle distribution, and the densely grafted brush gives rise to an additional exclusionary effect between the nanoparticles. According to the theory, polydispersity in the oligomer grafting density controls the deviation of S(q) from the monodisperse system at smaller q, and the interplay of the enhanced effective core size and the entropic attraction among the particles is responsible for complex variations in the particle correlations at larger q. The successful comparison between the predictions and the measurements for the blends further suggests that S(q) can be used to assess the uniformity of grafting density in polymer-grafted nanoparticle materials.

Hidden Hyperuniformity in Soft Polymeric Materials

“…polymers and moderately branched star polymer melts are more closely related in their configurational and thermodynamic properties, as well as to ring polymer melts, than linear chain melts [33,40]. Similar suppression of density fluctuations has been observed in the packing of polymer-grafted nanoparticles in the absence of solvent, a novel type of materials that several studies demonstrated their have special properties related to hybrid character of the particles and the highly uniform packing configurations that these particles exhibit [41][42][43]. It is evident that branched molecules exhibit non-trivial correlations in their molecular packing and hyperuniformity can provide a valuable tool to probe these correlations.…”

Particle localization and hyperuniformity of polymer‐grafted nanoparticle materials

“…Hsiu‐Yu and Koch first argued that GNP materials in the absence of solvent should have small long‐wavelength density fluctuations, and this effect has already been confirmed by experiments and molecular dynamics simulations (for an overview of these materials see the following reviews ). If these density fluctuations are sufficiently suppressed, then a hyperuniform material can be expected.…”

Dynamics and yielding of binary self-suspended nanoparticle fluids

“…57,58 In particular, the strong chain mediated correlations among the core particles lead to higher primary peaks, while the space filling constraint suppresses concentration fluctuations and results in a more rapid decay and lower S values in the low q regime. 57,58 In particular, the strong chain mediated correlations among the core particles lead to higher primary peaks, while the space filling constraint suppresses concentration fluctuations and results in a more rapid decay and lower S values in the low q regime.…”