Effect of ionic impurities on the electric field alignment of diblock copolymer thin films

The effect of ionic impurities on the electric field alignment of lamellar microdomains in polystyrene-block-poly(methyl methacrylate) diblock copolymer thin films was studied using transmission electron microscopy (TEM) and atomic force microscopy (AFM). At lithium ion concentrations greater than similar to210 ppm, the microdomain morphology in block copolymers could be aligned in the direction of an applied electric field, regardless of the strength of interfacial interactions. Complete alignment of the copolymer microdomains, even those adjacent to the polymer/substrate interface, occurred by a pathway where the applied electric field enhanced fluctuations at the interfaces of the microdomains with a wavelength comparable to L-o, the equilibrium period of the copolymer. This enhancement in the fluctuations led to a disruption of the lamellar microdomains into smaller microdomains similar toL(o) in size, that, in time, reconnected to form microdomains oriented in the direction of the applied field.