Interface Analysis of Composites Using AFM-Based Nanoscale IR and Mechanical Spectroscopy

Introduction Composite materials are becoming increasingly important in today’s world, where lighter materials with enhanced properties are in high demand. Carbon fibers, carbon black, graphite, graphine, carbon nanotubes, quartz particles, nanocrystalline cellulose, and clays are among the materials being added to bulk polymers in an effort to achieve better properties and performance. It is important not only to determine the size and locations of nanoparticle inclusions in bulk polymers, but also to characterize the important interphase region where the components interact. This article describes how an atomic force microscope (AFM) combined with infrared (IR) spectroscopy and mechanical spectroscopy can be used to not only locate and determine the size of inclusions, but also to characterize them chemically and mechanically. After introducing AFM-IR spectroscopy and Lorentz contact resonance (LCR) methodology for obtaining nanoscale mechanical spectra and images, results from three specific applications will be discussed. These applications include an isotactic poly(propylene) film with added SiO2 particles, a polymer with carbon black particles incorporated under different processing conditions, and a carbon-fiber/epoxy composite material. The first example uses AFM-IR spectroscopy and IR absorbance imaging. The second example employs LCR mechanical property spectroscopy and imaging. The final example includes a combination of AFM-IR and LCR to obtain corroborating information about the important interphase region between carbon fiber and epoxy domains.