Two-dimensional Marangoni-instability-induced periodic patterns of polymer blend films cast on tilted substrates

Two-dimensional periodic patterns were observed for PS/PVP blend films and the corresponding homopolymer films on tilted glass substrates. They were attributed to the Marangoni instability resulting from surface tension non-uniformity. For the 1:1 PS-1/PVP-1 blend films, two-dimensional regular arrays of the separated phases were observed, similar to those observed on homopolymer films from thickness variations. In addition, for the PS-2/PVP-2 blend films of 30/70 composition, one-dimensional strip patterns of separated phases were observed. The pattern formation mechanism is discussed and a characteristic parameter defined as the ratio of the final film thickness to initial solution viscosity, is found to correlate well with the pattern regularity through variation in polymer concentration.