A Small-Angle Neutron Scattering Study of a Soft Model Nanofiller in an Athermal Melt

Abstract

We present a detailed small-angle neutron scattering investigation of mixtures of poly­(ethylene oxide) (PEO)/polyhedral oligomeric silsesquioxane (POSS) hybrids, a popular nanofiller, addressing the conformation of the model-grafted nanoparticles as well as their influence on the linear polymer matrix in which they are embedded. The nanofiller has a well-defined graft arm length and is monomolecular. Because of the identical chemical nature of the grafted arm and matrix chains, it can be considered as an ideal athermal mixture. We have introduced a random phase approximation approach with general application possibilities for other grafted nanofillers, combining the star-like and particle-like characteristics of the POSS nanofiller. The size of the nanofiller remained unaffected and Gaussian upon mixing with linear chains of various lengths, and no aggregation of the nanofiller was observed. This turns the POSS-based nanocomposite into an interesting model compound. The mixtures of PEO chains with the octafunctional PEO–POSS nanofiller were found to resemble those of a micellar system whereas within experimental uncertainty the radius of gyration of the embedding matrix remained basically unaltered despite some tendency toward shrinking.

Chain Dimension and Dynamics of Polymers in Well-Defined Non-sticky Nanocomposites of Molecular Nanoparticle Polyhedral Oligomeric Silsesquioxane/Poly(butylene oxide)

“…This argument seems consistent with some experimental results, for example, in the miscible phenyl coating silica/PS nanocomposite system, 15 pentyl-coated SiO 2 /PS, 14,17,22,23 and PEO-grafted POSS in the PEO matrix. 64 In our non-sticky athermal system, the unaltered chain dimension with introduction of nanoparticles is observed, consistent with above arguments regarding the screened excluded volume effects. In our PNCs, the concentration of the polymer is larger than 90 vol %, far beyond the critical overlapping concentration of polymers in the concentrated regime if POSS was treated as a regular solvent molecule.…”

“…The presence of nanoparticles would not be able to influence the chain dimension significantly. This argument seems consistent with some experimental results, for example, in the miscible phenyl coating silica/PS nanocomposite system, pentyl-coated SiO 2 /PS, ,,, and PEO-grafted POSS in the PEO matrix …”

“…Meanwhile, due to the decoupling of different x , y , z components of an ideal chain’s random walk, , constraint in one dimension would not necessarily perturb the conformation of an ideal chain in other dimensions. Recently, the unperturbed Gaussian statistics of polymer chains upon mixing with nanoparticles was verified by NS measurements in the intermediate-to-high q region. , A negligible change of the mean-square end-to-end distance of the polymer melt in neutral diblock copolymer single-crystal platelets has been also observed experimentally . Interestingly, the lattice Monte Carlo simulation demonstrated the unaffected overall Gaussian chain statistics regardless of the filler loading up to 27 vol %, despite the complex structures in the vicinity of the nanoparticle at the subchain level .…”

Structural Analysis of Ultrasoft PDMS-g-PDMS Shell-Only Particles

“…With increasing concentration of the bottlebrush polymers in the highest molecular weight host matrix, the osmotic pressure forces the bottlebrushes closer together which subsequently leads to a formation of another structural level, which can be seen as the start of cluster formation. , Similar behavior is known from polymer grafted nanoparticles. For polymer nanocomposites with M matrix ≫ 2 M graft the particle shell collapses, and subsequently, with increasing concentration of the polymer grafted nanoparticles, aggregation occurs. , …”

“…For polymer nanocomposites with M matrix ≫ 2M graft the particle shell collapses, and subsequently, with increasing concentration of the polymer grafted nanoparticles, aggregation occurs. 73,74 In solution a concentration dependence of the bottlebrush size was observed and predicted. 2,53 This directs our attention to the concentration-dependent size.…”