Improving interparticle contacts via photothermal heating of the particle

Large aspect ratio particle-polymer composites are desirable for properties such as electrical and thermal conductivity, resulting from a sample-spanning particle network. Such properties are strongly influenced by interparticle contacts. However, during composite fabrication, particles are coated with surfactant and/or matrix to enhance dispersion. These materials remain within particle-particle junctions and detrimentally affect desired composite properties. Ideally, particle-matrix interactions would be initially strong and then altered to favor particle-particle contact and expel inter-particle material after solidification. We present results utilizing photothermal heating of multiwalled carbon nanotubes (CNT) to explore this paradigm. In photothermal heating light is absorbed by nanoparticles resulting in localized heat: illuminating a composite causes significant temperature increase around each particle (and interparticle junction) while regions far from the particles remain cool. We observe relative increased electrical conductivity after treating solid CNT-polymethylmethacrylate composites that depends primarily on light intensity (and thus likely the temperature at the interparticle-junction) and is largely independent of dispersion and concentration. We discuss proposed chemistry and phase transitions at junctions and provide observations on how the particle-matrix interaction can be manipulated with localized heat.