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 df0ex0ex=0ex0ex1.67 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.