Functional nanocomposites and dispersions: Synthesis, characterization and performance evaluation

Nanocomposites and nanoparticle dispersions offer unprecedented opportunities to develop advanced materials with tunable properties. This thesis presents synthesis strategies, characterization and laboratory performance evaluation of such material systems towards three applications of practical interest.;The first application features synthesis of flexible, wet-processed, superhydrophobic, polymer nanocomposite coatings with high adhesion to substrates, which is a major technological challenge. These nanocomposites, which consist of polymers and filler particles, are applied by means of spray atomization, which is potentially scalable to large areas. Judicious choice of blends of poly(vinylidene fluoride) (PVDF) with acrylic polymers as dispersant and binder for particle fillers helps achieve the desired properties. For binder, a novel blend of PVDF with ethyl 2-cyanoacrylate (ECA) is introduced by controlling the rapid polymerization of the ECA monomer. The effect of filler particle surface energy on liquid repellency is tested with water and water/alcohol mixtures. The feasibility of electrically conductive superhydrophobic coatings is also shown.;In another application, the thesis demonstrates conductive fibrous nanocomposites as flexible and permeable strain sensors prepared by electrospinning poly epsilon-caprolactone polymer solution with electrically conductive carbon black nanoparticles. The resulting nanocomposite mats show an increase in electrical resistance under uniaxial strain due to changes in geometry and nanoparticle percolation network, showing feasibility for strain sensing applications. A layered percolation model is formulated to account for both geometric and percolative changes under mechanical strain and interpret the observed strain/resistance relationships. A theoretical framework to detect local-clogging in large filters is also presented.;In the third application, elongational and shear mode rheological (fluid) properties of carbon nanotube (CNT) suspensions are investigated, to facilitate their emerging applications. A capillary self-thinning filament rheometer is used to determine the elongational properties using a novel quasi-1D theoretical model. The effects of CNT concentration, aspect ratio, filament diameter and host liquid viscosity are carefully analyzed. Comparison of elongational and shear parameters indicates the CNT suspension rheology to be fitting the Herschel-Bulkley model (i.e. power law fluid with yield stress). Our measurements also show flow dependent yield---stress for CNT suspensions suggesting extra care in using the flow properties of such suspensions.;The thesis demonstrates the enormous promise of nanocomposites and nanoparticle dispersions for advancing practical technologies.