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 ${1.25D}^{*}<L<\mathrm{}{1.5D}^{*}$ developed two-dimensional isotropic fractal holes with $d_f=1.67\mathrm{}$ 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.