Investigation of Nanoscopic Free Volume and Interfacial Interaction in an Epoxy Resin/Modified Clay Nanocomposite Using Positron Annihilation Spectroscopy

Abstract

Epoxy/clay nanocomposites are synthesized using clay modified with the organic modifier N,N-dimethyl benzyl hydrogenated tallow quaternary ammonium salt (Cloisite 10A). The purpose is to investigate the influence of the clay concentration on the nanostructure, mainly on the free-volume properties and the interfacial interactions, of the epoxy/clay nanocomposite. Nanocomposites having 1, 3, 5 and 7.5 wt. % clay concentrations are prepared using the solvent-casting method. The dispersion of clay silicate layers and the morphologies of the fractured surfaces in the nanocomposites are studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The observed XRD patterns reveal an exfoliated clay structure in the nanocomposite with the lowest clay concentration (≤1 wt. %). The ortho-positronium lifetime (τ(3)), a measure of the free-volume size, as well as the fractional free volume (f(v)) are seen to decrease in the nanocomposites as compared to pristine epoxy. The intensity of free positron annihilation (I(2)), an index of the epoxy-clay interaction, decreases with the addition of clay (1 wt. %) but increases linearly at higher clay concentrations. Positron age-momentum correlation measurements are also carried out to elucidate the positron/positronium states in pristine epoxy and in the nanocomposites. The results suggest that in the case of the nanocomposite with the studied lowest clay concentration (1 wt. %), free positrons are primarily localized in the epoxy-clay interfaces, whereas at higher clay concentrations, annihilation takes place from the intercalated clay layers.

Graphene networks and their influence on free-volume properties of graphene–epoxidized natural rubber composites with a segregated structure: rheological and positron annihilation studies

“…The o-Ps annihilation lifetime distributions obtained from CONTIN analysis can be transformed into free-volume hole distributions according to eqn (4) and (5) [74][75][76] …”

“…[75][76][77] The free-volume hole probability density function V f (pdf) is shown in Fig. [75][76][77] The free-volume hole probability density function V f (pdf) is shown in Fig.…”

“…The appearance of lower size freevolume holes can be attributed to the formation of GE networks which provide a high density interfacial region that is missing in the neat ENR. 75,76 Within the positron age of o-Ps, the S(t) of ENR-GE composites is lower than that of the pure ENR and decreases with an increase in the GE loading. 44,75 As shown in Fig.…”

The rheological behavior of ethylene vinyl acetate copolymer/rectorite nanocomposites during the melt extrusion process

“…Hence, the decrease in I 3 is corresponding to the increase in I 2 . It is the reason that the interfaces in epoxy/clay system were evaluated by I 2 in some previous literature . Therefore, in the present EVA/rectorite system, positron results imply that the number of interfaces increases with increasing rectorite content up to 2%, and then stays at a constant at the range of content from 3 to 5%.…”

Molecular packing of polyvinyl alcohol in PVA‐gold nanoparticles composites and its role on thermo‐mechanical properties

“…To invoke the structure‐property relationship in polymer nanocomposites, conventional techniques like X‐ray diffraction (XRD), Fourier transform infra‐red (FTIR), dynamical mechanical analysis, and electron microscopy techniques are used to infer changes in the polymer structure. Recently, we have used triplet state of positronium i.e., ortho ‐positronium ( o ‐Ps) as probe through positron annihilation lifetime spectroscopy (PALS) technique to investigate the molecular packing of polymer matrix in polymer nanocomposites . PALS is an established technique to measure the free volume hole size, density, and their size distribution in polymers.…”