Microstructure, elastic and electromagnetic properties of epoxy-graphite composites

Abstract

A set of epoxy resin-based composites filled with 0.25 – 2.0 wt.% of commercially available exfoliated graphite (EG) and thick graphene (TG), prepared by suspending EG particles in cyclohexane, and submitting the suspension to a series of grinding and ultrasonic dispersion steps, was produced. The microstructure of such epoxy-graphite composites has been studied by the impulse acoustic microscopy technique. According to acoustic microscopy data, exfoliated graphite microparticles have been well dispersed in the epoxy matrix. TG nanoflakes demonstrated persistent tendency to clustering and formation of agglomerates. The addition of graphite particles in small amount (0.25 – 2.0 wt.%) did not influence the bulk elastic properties of epoxy-graphite composite materials. Being extremely lightweight, 0.003 g cm−3, EG had a lower percolation threshold than TG, at the level of 1-1.5 wt.% against 2.1-3.2 wt.%, respectively. As a result, epoxy composites filled with 1.0-2.0 wt.% EG provided high electromagnetic (EM) interference shielding both at microwave and THz frequencies. In contrast, no significant influence of TG loading was observed at low weight fraction (up to 2 wt.%) on the EM performance of epoxy composites.

Cluster microstructure and local elasticity of carbon‐epoxy nanocomposites studied by impulse acoustic microscopy

“…The images are formed in an ultramicroscopic mode —sizes of some scatterers could be smaller than the wavelength; the presence of air in the conglomerates results in a high efficiency of ultrasonic scattering; according to estimations , conglomerates are effective scatterers. It has been revealed that both graphite nanoparticles (GNP) and nanotubes (MWCNT) possess a strong tendency to agglomeration . Depending on the filler content these agglomerates are formed and distributed over the material bulk.…”

“…Impulse acoustic microscopy is based on using focused ultrasonic beams and the raster principle of image formation . A focused ultrasonic beam interacts with a plane‐parallel object within its waist.…”

“…The value of a reflected echo‐pulse is displayed in a grayscale. The echo‐pulse pattern is employed for local measurements . Measuring time intervals between the echo signals reflected from the specimen face and bottom enables us to find local values of sonic velocities and elastic modules of the material under investigation.…”

“…Independent measurement of the material density ρ makes it possible to find elastic modules of the material. The ultrasonic technique is especially attractive in the case of the scanning impulse acoustic microscopy when employing focused ultrasound. Application of focused probe impulses enables one to measure local values of sonic velocities in inhomogeneous specimens with micron resolution and to find spatial distribution of elastic properties over the specimen bulk.…”

Theoretical investigations of the interfacial sliding and buckling of graphene on a flexible substrate

“…Graphene, a two-dimensional (2D) monolayer nanomaterial, has attracted significant attention in recent decades because of its unique electronic, thermal, and mechanical properties, and it is considered to have promising applications in the fields of nano-electronics, [1][2][3][4] flexible/stretchable electronics, 5,6 and nanocomposites, [7][8][9] etc. In graphene-based stretchable electronics and graphenereinforced nanocomposites, the interfacial failures between graphene and substrate materials is the main factor limiting their overall performance and reliability.…”