Hole nucleation in free-standing polymer membranes: the effects of varying molecular architecture

Abstract

Free-standing liquid films are generally unstable, failing whenever a hole or pore is created. The same is true of a polymer melt, although the details of the instability can be more complex and dependent on molecular architecture. Here, we compare the nucleation of holes in homopolymer films and films made from diblock co-polymers that can order into a cylindrical or lamellar phase. The different degrees of internal order (no long-range order, lamellar order, cylindrical order) has significant effects on the rate of hole formation. We find that lamellar order decreases the rate of film rupture by at least two orders of magnitude when compared to isotropic films. The hole formation is well described by a classical nucleation process. Notably, we find that the barrier to hole formation is identical for all samples studied here, favouring a simple capillary model. The vast differences in stability between films of differing internal structure is entirely quantified by the “attempt frequency” of barrier penetration and not the free energy barrier itself.