Dynamics at the Polymer/Nanoparticle Interface in Poly(2-vinylpyridine)/Silica Nanocomposites

Abstract

The static and dynamic properties of poly(2vinylpyridine)/silica nanocomposites are investigated by temperature modulated differential scanning calorimetry, broadband dielectric spectroscopy (BDS), small-angle X-ray scattering (SAXS), and transmission electron microscopy. Both BDS and SAXS detect the existence of an interfacial polymer layer on the surface of nanoparticles. The results show that whereas the calorimetric glass transition temperature varies only weakly with nanoparticle loading, the segmental mobility of the polymer interfacial layer is slower than the bulk polymer by 2 orders of magnitude. Detailed analysis of BDS and SAXS data reveal that the interfacial layer has a thickness of 4−6 nm irrespective of the nanoparticle concentration. These results demonstrate that in contrast to some recent articles on polymer nanocomposites, the interfacial polymer layer is by no means a "dead layer". However, its existence might provide some explanation for controversies surrounding the dynamics of polymer nanocomposites.

Calorimetric evidence for a mobile surface layer in ultrathin polymeric films: poly(2-vinyl pyridine)

“…46 Moll and Kumar found only a small shift in T g for P2VP/ silica nanocomposites. 47 Holt et al 48 report also a study on P2VP filled with silica nano-…”

Unexpected Molecular Weight Effect in Polymer Nanocomposites

“…These adsorbed chains form an dynamic interfacial layer (DIL), which has distinct segmental mobility and other properties [7,[14][15][16][17][18][19][20][21][22][23], and is believed to directly correlate with many advanced macroscopic properties of PNCs [3,5]. However, despite the recent intensive discussions on the features of the DIL [18,19,[22][23][24][25][26][27][28], many of its characteristics, especially the basic relationship between the interfacial layer chain packing and the dynamics, are still missing. This strongly hinders our understanding of various phenomena in PNCs.…”

“…Adding silica nanoparticles to PVAc leads to several changes in the dielectric spectra (Fig.1) [15,[21][22][23]: (i) the α-relaxation peak (segmental dynamics) shifts slightly to lower frequency, broadens and decreases in amplitude; (ii) an additional contribution appears on the low-frequency side (α'-peak); (iii) the Maxwell-Wagner-Sillar's (MWS) polarization process appears at even lower frequency; and (iv) the conductivity changes. The α'-process, corresponding to the segmental dynamics in the interfacial layer [21,23] which was not resolved in previous studies [15,[21][22][23], is now clearly visible especially in the derivative spectra, ε' der (ω) = -π/2*∂ε'(ω)/∂ln(ω) (Fig.S2 in SM [33]), and the relaxation time distribution analysis (Fig.1b) (for details of this analysis see Ref. [41] and SM [33]).…”

Influence of filler/matrix interactions on resin/hardener stoichiometry, molecular dynamics, and particle dispersion of silicon nitride/epoxy nanocomposites

“…Consequently, in this particular system, the structure of the DGBEA molecules may reduce the impact of polymer/particle interactions on the segmental dynamics of the polymer layer surrounding the nanoparticles. However, different impact on the polymer dynamics could occur for different polymer chain structures, as reported elsewhere [37,43,45].…”

“…Instead of forming a completely rigid layer that does not contribute to the glass transition, other studies have claimed that strong filler/polymer interactions cause a broadening of the glass transition to higher temperatures [45][46][47] or result in additional glass transition steps at different temperature [45][46][47][48]. Therefore, the polymer/filler attachment might cause a restriction for the segmental dynamics of the surrounding polymer, and this effect gradually decreases with the distance from the particle surface.…”