Nanostrand Formation of Block Copolymers at the Air/Water Interface

Langmuir-Blodgett monolayers consisting of a network of nanostrands have occasionally been reported in the literature, but are often coexistent with other morphologies, which is not useful for potential applications With the use of PS-P4VP/PDP, a polystyrene poly(4-vinyl pyridine) diblock copolymer of 12 mol % VP content mixed with 3 pentadecylphenol, it is shown that the discordered nanostrand morphology cna be obtained reproducibly and uniformly over large surface areas by spreading chloroform solutions of relatively high copolymer concentration Use of a more slowly evaporating spreading solvent, 1,1,2,2 tetrachloroethane, and a low subphase temperature, 8-9 degrees C, results in much more densely aligned nanostrands Poorly spreading solvents such as nitrobenzene produce the well known fingerprint pattern often observed in spin- or dip-coated thin films of block copalymers A mechanism for nanostrand network formation is proposed that involves the momentary formation of a fingerprint morphology in spreding drops followed by its breakup at the level of the mobile P4VP/PDP stripes as spreading continues, leaving P4VP anchored PS nanostrands floating on the water surface