Hole formation on the surface of thin block copolymer films is investigated as a function of time (t), temperature (T) and film thickness. The size of the holes, hs, approaches a steady state value at long times hs,∞ = hs(t -> ∞) and we introduce a simple kinetic model which gives a universal description of the kinetics of hole growth. The characteristic time, t, governing the rate of approach of hs to hs,∞ is observed to first decrease upon heating and then to increase sharply as the estimated film disordering temperature, Td, is approached from below. We also find a strong increase in hs,∞ with increasing T. These observations suggest that fluctuations associated with the film disordering transition cause a slowing down of the equilibration of the film to its steady state and a reduction of the surface elasticity of the outer block copolymer layer. This large change in the surface properties of block copolymer films near Td could have important ramifications for understanding transport property changes occurring in other amphiphilic films (e.g., lipid films comprising the membrane of cells) where non-monotonic mobility changes are observed near the respective disordering transition temperature.
Pub Type: Journals
block copolymer, combinatorial, ordering, thin film