Spatial inhomogeneity, interfaces and complex vitrification kinetics in a network forming nanocomposite

Abstract

A detailed calorimetric study on an epoxy-based nanocomposite system was performed employing bisphenol A diglycidyl ether cured with diethylenetriamine as the polymer matrix and a taurine-modified MgAL layered double hydroxide as the nanofiller.

Calorimetric and Dielectric Investigations of Epoxy-Based Nanocomposites with Halloysite Nanotubes as Nanofillers

“…The peak at q = 29.8 nm −1 (averaged intermolecular distances of ca. 0.21 nm) can be correlated with regions in the network with lower crosslinking density than the average, as discussed in [ 11 ].…”

“…As the SAXS/WAXS data were scaled to absolute intensity, it was possible to perform a linear combination of Ep and HNT/m-HNT WAXS data to obtain a rough estimate of the volume fractions for both components [ 11 , 27 ]. For the HNT and m-HNT samples, data were collected using two different X-ray sources (Xenocs, Grenoble, France), in multiple sample positions, with no observed change in the ratio of peak intensities, indicating that the measured samples lack orientation, and a decent powder diffraction average signal was collected.…”

“…Due to the reduced dimensions of the filler, resulting in a high surface to volume ratio, there is an increased volume of interfacial area. For non-repulsive filler–matrix interactions, polymer segments are physically adsorbed to the nanofiller, with the formed interphase commonly referred to as the rigid amorphous fraction (RAF) [ 11 ]. The RAF can also be formed through chemical bonding of the nanoparticle surface to the matrix.…”

“…The term “rigid” refers to a restricted or even immobilized segmental mobility in the interface compared to the bulk matrix [ 12 ]. The different molecular mobility at the interface, compared to the bulk matrix, can be investigated using broadband dielectric spectroscopy (BDS) in some cases [ 11 , 12 , 13 , 14 ]. Moreover, BDS allows for the investigation of the dynamical processes of PNCs in dependence on the concentration of the nanofiller on spatial length scales ranging from local to segmental fluctuations in a broad frequency range (mHz to GHz) [ 15 ].…”

“…Epoxy-based materials have been reinforced with nanoparticles (NPs), such as silica, barium titanate [ 24 , 25 ] or boehmite NPs [ 26 , 27 ], layered materials [ 11 , 28 ], polyhedral oligomeric silsesquioxane (POSS) [ 29 , 30 ] and carbon nanotubes (CNT) [ 31 , 32 ], to achieve improved properties compared to the unfilled epoxy. CNTs have been used as a nanofiller due to their high aspect ratio, having a significantly larger length compared to the inner and outer diameters, ease of processing and their ability to be surface modified [ 33 ].…”