Tuning of particle indentation by surface modification of polymer particles and substrates

We studied the influence of the chemical properties of the polymer particle and the polymer substrate on particle indentation. The polymer particles were arrayed over the polymer substrate and heat treatment (annealing) was conducted above the glass transition temperature (T_g) of bulk polymer to indent polymer particles into the polymer substrate. Surface topologies of particle-indented surfaces were observed with a field-emission scanning electron microscope (FE-SEM) and the degree of particle indentation (DI) was evaluated with a scanning probe microscope (SPM). The particle-arrayed substrate was placed upside down and then heat treatment was carried out. It was found that there was no effect of gravity on particle indentation. To prepare polymer particles with different chemical properties, surface grafting of hydrophobic, hydrophilic, cationic and anionic polymer chains was carried out by iniferter-initiated living radical polymerization. We found that the indentation of these particles was influenced by the outermost surface of the particle. Next, to investigate the effect of the substrate surface on particle indentation, sulfonation of the polystyrene (PS) substrate was carried out with concentrated sulfuric acid. We found that the surface property of the substrate also influenced particle indentation. From these results, we concluded that particle indentation would be determined by the interaction between the particle surface and the substrate surface. Finally, we intended to analyze the viscoelastic property of the substrate surface by particle indentation. We could estimate T_g values of PS and polyvinyl chloride (PVC) substrates by observing the particle indentation at the different annealing temperatures.