EPR and Rheological Study of Hybrid Interfaces in Gold–Clay–Epoxy Nanocomposites

Abstract

With the aim to obtain new materials with special properties to be used in various industrial and biomedical applications, ternary "gold-clay-epoxy" nanocomposites and their nanodispersions were prepared using clay decorated with gold nanoparticles (AuNPs), at different gold contents. Nanocomposites structure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Rheology and electron paramagnetic resonance (EPR) techniques were used in order to evaluate the molecular dynamics in the nanodispersions, as well as dynamics at interfaces in the nanocomposites. The percolation threshold (i.e., the filler content related to the formation of long-range connectivity of particles in the dispersed media) of the gold nanoparticles was determined to be ϕp = 0.6 wt % at a fixed clay content of 3 wt %. The flow activation energy and the relaxation time spectrum illustrated the presence of interfacial interactions in the ternary nanodispersions around and above the percolation threshold of AuNPs; these interfacial interactions suppressed the global molecular dynamics. It was found that below ϕp the free epoxy polymer chains ratio dominated over the chains attracted on the gold surfaces; thus, the rheological behavior was not significantly changed by the presence of AuNPs. While, around and above ϕp, the amount of the bonded epoxy polymer chains on the gold surface was much higher than that of the free chains; thus, a substantial increase in the flow activation energy and shift in the spectra to higher relaxation times appeared. The EPR signals of the nanocomposites depended on the gold nanoparticle contents and the preparation procedure thus providing a fingerprint of the different nanostructures. The EPR results from spin probes indicated that the main effect of the gold nanoparticles above ϕp, was to form a more homogeneous, viscous and polar clay-epoxy mixture at the nanoparticle surface. The knowledge obtained from this study is applicable to understand the role of interfaces in ternary nanocomposites with different combinations of nanofillers.

Essential Nanostructure Parameters to Govern Reinforcement and Functionality of Poly(lactic) Acid Nanocomposites with Graphene and Carbon Nanotubes for 3D Printing Application

“…Therefore, it is important to estimate the relaxation processes in polymer systems by calculation of the relaxation-time spectra using linear viscoelastic data from experimental rheology and constitutive equation models [ 4 , 19 ]. Researchers reported that the interface phenomena might cause local or global changes in the polymer relaxation associated with the strength of the interfacial polymer-filler interactions [ 4 , 20 , 21 ]. Herewith, the relaxation-time spectrum, was calculated by fitting the generalized Maxwell-type model, Equations (4) and (5), to data of the experimental dynamic moduli by using Advantage software (TA Instruments).…”

Morpho-chemical characterization and surface properties of carcinogenic zeolite fibers

“…Our aim is to investigate the relationships between morphology, mineralogy, crystal chemistry, BET specific surface area, and interacting ability of these zeolites surfaces, providing a background for future experiments on the biological activity of erionite and offretite. The analysis of the EPR spectra of selected spin probes has already demonstrated to be very useful to provide information about surface and interfacial properties of zeolites and other solids [46][47][48]. In the present case, these information are precious because they may be related to the eventual carcinogenicity of the fibrous zeolites.…”

“…In the present case, these information are precious because they may be related to the eventual carcinogenicity of the fibrous zeolites. Therefore, the scope of this study is to investigate the morphology and the chemical and surface properties of these zeolites, mainly providing information on the interacting ability of the surface at the liquid/solid interface using selected spin probes -4-trimethylammonium, 2,2,6,6 tetramethyl-piperidine-1oxyl Bromide (CAT1) and 4-octyl dimethylammonium, 2,2,6,6 tetramethyl-piperidine-1oxyl Bromide (CAT8) -which well mimic specific moieties of biocompounds and have been successfully employed for investigations in surfaces and interfaces characterization studies [10,11,46]. The chemical formulas of the spin probes are reported in the Supplementary data.…”

Composition dependence in surface properties of poly(lactic acid)/graphene/carbon nanotube composites

“…Wetting of nanofiller by surrounding polymer media is necessary in order to transfer the unique properties of the nanofiller to the matrix polymer. The interfacial interactions and the percolation threshold of nanofillers are determinant for the nanocomposite properties [14][15][16]. If the interface is weak, the composite has low strength and stiffness, but high resistance to fracture, while the strong interface interactions result in a brittle material with high strength [15].…”