MECHANICS OF PARTICLE AND POLYMER ASSEMBLIES

This thesis reports a variety of developments in atomic force microscopy (AFM) methodology and surface preparation techniques. Methodologies of assembling colloidal particles into pre-designed patterns on surfaces were studied. Different interactions, such as electrostatic force, magnetic force, and capillary force of varied topography were used. In the topography-assisted particle assembly, the direct observations of the dynamics revealed that the particles are transported inside or toward the grooves of the pattern in the region where the liquid film is appropriately thin, and the particles¡¯ self-assembly inside the grooves is caused by a lateral capillary force. Scanning probe microscopy was used to examine topography assisted 2D self-assembly of micrometer-size latex particles in wetting films.Based on the adhesive interactions between an AFM tip and sample surfaces, an AFM method for measuring surface elasticity was proposed. The method is particularly useful when there is a large adhesion between the tip and soft samples, when the indentation method would be less accurate. For thin and soft samples, this method has much less interference from the substrate than is found using the indentation method because there is only passive indentation induced by tip-sample adhesion. The model was tested on PDMS polymers with different crosslink density. It was found that soft, less crosslinked PDMS polymers showed obvious viscoelastic behavior when interacting with AFM tips. Systematic studies of the viscoelastic effects found that energy dissipation occurs mainly in the bulk of polymer when an AFM tip indents into a polymer. When the tip is pulled out from the polymer, the energy dissipation occurs both in the bulk and interfaces, which causes a turning point of the adherence force of AFM tip with changes of scan rates. The multiple relaxation rates were characterized and compared with that from other methods.Using AFM imaging and indentation methods, the properties of barnacle adhesive were studied. A multilayered structure of barnacle adhesive plaque was proposed based on layered modulus regions measured by AFM indentation. Analysis shows that there is a strong correlation between the mean Young¡¯s moduli of the outmost softest adhesive layer and the barnacle shear strength, but no correlation for other higher modulus regions. Linear, quadratic, and Griffth¡¯s failure criterion regressions were used in the fit, and showed close correlation