Fractal hole growth in strained block copolymer films

The evolution of surface topography in conformationally strained diblock copolymer films comprised of 3/2 lamellar bilayers was investigated by optical microscopy. Films of thickness 1.25D* < L < 1.5D* developed two-dimensional isotropic fractal holes with d_f = 1.67 following heterogeneous nucleation, where D* is the equilibrium lamellar spacing. A microscopic theory is presented that maps this hydrostatic tension driven hole growth instability onto the classical description of pattern formation during solidification.