The Wetting Behavior of Polymer Droplets: Effects of Droplet Size and Chain Length

Monte Carlo computer simulations were utilized to probe the behavior of homopolymer droplets adsorbed at solid surfaces as a function of the number of chains making up the droplets and varying droplet sizes. The wetting behavior is quantified via the ratio of the perpendicular to the parallel component of the effective radii of gyration of the droplets and is analyzed further in terms of the adsorption behavior of the polymer chains and the monomers that constitute the droplets. This analysis is complemented by an account of the shape of the droplets in terms of the principal moments of the radius of gyration tensor. Single-chain droplets are found to lie flatter and wet the substrate more than chemically identical multichain droplets, which attain a more globular shape and wet the substrate less. The simulation findings are in good agreement with atomic force microscopy experiments. The present investigation illustrates a marked dependence of wetting and adsorption on certain structural arrangements and proposes this dependence as a technique through which polymer wetting may be tuned

Προσομοίωση συστημάτων πολυμερών και κολλοειδών

In this thesis we investigated two different problems using computer simulations. First we employed Monte Carlo simulations for the study of the conformations of polymer chains in bulk and close to surfaces near the ‘coil-to-globule’ transition as a function of solvent quality and surface energy. We provided a satisfactory insight into the peculiarities of the ‘coil-to-globule’ transition and the effect of the presence of an attractive surface to it. Our results are in close agreement with theoretical predictions in bulk, whereas, they supply useful information on the competition between chain adsorption and chain collapse. The second problem was the investigation of the temperature induced changes in the colloidal superstructure and star-polymer dynamics in suspensions, under marginal solvent conditions, by means of Molecular Dynamics simulations. Star polymers were modeled as ‘soft-spheres’, whose size increased with temperature, interacting via a theoretically developed potential of mean field. Our results show a transition towards a ‘glassy’ state at a temperature very close to the one reported experimentally. Furthermore, our findings illustrate the road to vitrification for these soft colloidal suspensions