Unravelling new phenomena in polymer science at both the ensemble and single-molecule levels
Date of Issue2011
School of Physical and Mathematical Sciences
Single-(macro) molecule tracking is used for the first time here to study the crystallization process in ultrathin layers of single poly(ethylene oxide) (PEO) chains. Diffusion trajectories of macromolecules diffusing toward the crystal followed by deposition onto the crystal-growth front display different types of motion, such as Brownian and directed motions, prior to crystallization. We show that PEO chains in the amorphous layer and in the less concentrated or depleted zone exhibit Brownian motion of different diffusion rates as a result of heterogeneities in the environment. The phase evolution of thin polymer blend film of polystyrene (PS) and poly(2-vinyl pyridine) (P2VP) triggered by solvent annealing is examined at both the bulk and single-(macro)molecule levels using wide-field microscopy (WFM). The transitions between different evolutionary stages in the nucleation and growth process are clearly visualized in real-time and without intermittent breaks. The nucleation of PS holes arises from the coalescence and growth of P2VP domains and the holes expand in a complex manner involving the dewetting of PS and the absorption of P2VP domains into the holes. The formation of multiring deposits of poly(2-vinyl pyridine) P2VP from the evaporation of a P2VP-(2,6-lutidine + water) drop on a glass substrate does not conform to the conventional pinning-depinning mechanism. Instead, ring-like deposits are formed when the droplet undergoes several cycles of spreading and receding where for each spreading event, a P2VP ridge is formed at the contact line when the polymer flows toward the outward advancing edge. A surface tension gradient created as a result of the solutal-Marangoni effect plays an important role in enhancing the droplet spreading rate.