Understanding the Static Interfacial Polymer Layer by Exploring the Dispersion States of Nanocomposites

Abstract

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 preadsorption 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. Preadsorbed 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 *

Resolving Segmental Polymer Dynamics in Nanocomposites by Incoherent Neutron Spin–Echo Spectroscopy

“…To quantify these aspects, the structure of polymer nanocomposites is usually characterized by transmission electron microscopy (TEM), [13][14][15][16] and in particular small-angle X-ray or neutron scattering (SAXS or SANS), 17 combined with appropriate modelling approaches, [18][19][20][21] possibly including simulations. [22][23] The dynamical properties of PNCs may be studied by broadband dielectric spectroscopy (BDS) [24][25][26][27] or NMR. [28][29] These techniques average over the macroscopic response of the samples to external fields, without spatial resolution.…”

Direct Structural Evidence for Interfacial Gradients in Asymmetric Polymer Nanocomposite Blends

“…big) NPs, indicating similar density. The spatial distribution of NPs in nominally identical PNCs has been investigated previously 2 showing the formation of zones slightly denser than the average for PNC blends of low chain mass, whereas a homogeneous (non-aggregated) hard-sphere dispersion was found at the highest masses. We now compare the polymer structure in pure H/D blends to nanocomposites made with the same blends.…”

“…Our rationale is that differences observed in dynamics have been related to the presence of polymer surface layers with different properties than the bulk, like a different composition in terms of chain mass, 35 or a different mass density close to the surface. 2 The latter very subtle effect has been revealed by a SAXS analysis, and it will be shown below that it is too weak to affect our SANS data. The first effect, however, would be reflected in our experiments by a different isotopic composition, and should lead to signatures visible in SANS.…”

Viscosity reduction in polymer nanocomposites: Insights from dynamic neutron and X‐ray scattering

“…The mobility of the IL and its entanglement with the bulk of the polymer matrix determine the behavior of the PNC. 14,[18][19][20][21][22][23][24] However, the detailed knowledge of these phenomena required for the rational design of new materials is still lacking, with multiple parameters such as size, shape, and surface chemical nature likely playing a role. 25,26 Among the many properties of PNC, probably the most well-known is the mechanical reinforcement resulting from NP addition, where the mechanical and rheological properties of PNC still attract a lot of attention for potential applications.…”

“…It is also commonly accepted that in well dispersed PNC the polymer interfacial layer (IL) plays a fundamental role; 10–17 where the IL can be loosely but intuitively defined as the fraction of the polymer matrix surrounding the NP, on the order of 1 to a few nanometers thick, whose segments are in contact with the particle surface. The mobility of the IL and its entanglement with the bulk of the polymer matrix determine the behavior of the PNC 14,18–24 . However, the detailed knowledge of these phenomena required for the rational design of new materials is still lacking, with multiple parameters such as size, shape, and surface chemical nature likely playing a role 25,26…”