Crystal growth transition from flat-on to edge-on induced by solvent evaporation in ultrathin films of polystyrene-b-poly(ethylene oxide).
The transition of lamellar crystal orientation from flat-on to edge-on in ultrathin films of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) via solvent vapor (toluene) treatment was investigated. When the as-prepared film was treated in saturated solvent vapor, breakout crystals could form quickly, and then they transformed from square single crystals (flat-on lamellae) to dendrites and finally to nanowire crystals (edge-on lamellae). Initially, heterogeneous nucleation at the polymer/substrate interface dominated the structure evolution, leading to flat-on lamellar crystals orientation. And the transition from faceted habits to dendrites indicated a transition of underlying mechanism from nucleation-controlled to diffusion-limited growth. As the solvent molecules gradually diffused into the polymer/substrate interface, it will subsequently weaken the polymer-substrate interaction. In this case, lower free energy lamellae of an edge-on orientation could be obtained by the gain of free volume of the soluble PS block.
Yang
Ping
P
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Graduate University of the Chinese Academy of Sciences, Changchun 130022, P. R. China.
Han
Yanchun
Y