Ordered to Isotropic Morphology Transition in Pattern-Directed Dewetting of Polymer Thin Films on Substrates with Different Feature Heights
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- 作者：Sudeshna Roy ; Rabibrata Mukherjee
- 刊名：ACS Applied Materials & Interfaces
- 出版年：2012
- 出版时间：October 24, 2012
- 年：2012
- 卷：4
- 期：10
- 页码：5375-5385
- 全文大小：617K
- 年卷期：v.4,no.10(October 24, 2012)
- ISSN：1944-8252
文摘
Controlled dewetting of a thin polymer film on a topographically patterned substrate is an interesting approach for aligning isotropic dewetted structures. In this article, we investigate the influence of substrate feature height (HS) on the dewetting pathway and final pattern morphology by studying the dewetting of polystyrene (PS) thin films on grating substrates with identical periodicity (位P = 1.5 渭m), but HS varying between 10 nm and 120 nm. We identify four distinct categories of final dewetted morphology, with different extent of ordering: (1) array of aligned droplets (HS 鈮?120 nm); (2) aligned undulating ribbons (HS 鈮?70鈥?00 nm); (3) multilength scale structures with coexisting large droplets uncorrelated to the substrate and smaller droplets/ribbons aligned along the stripes (HS 鈮?40鈥?0 nm); and (4) large droplets completely uncorrelated to the substrate (HS < 25 nm). The distinct morphologies across the categories are attributed to two major factors: (a) whether the as-cast film is continuous (HS鈮?/b> 80 nm) or discontinuous (HS鈮?/b> 100 nm) and (b) in case of a continuous film, whether the film ruptures along each substrate stripe (HS鈮?/b> 70 nm) or with nucleation of random holes that are not correlated to the substrate features (HS鈮?/b> 60 nm). While the ranges of HS values indicated in the parentheses are valid for PS films with an equivalent thickness (hE) 鈮?50.3 nm on a flat substrate, a change in hE merely alters the cut-off values of HS, as the final dewetted morphologies and transition across categories remain generically unaltered. We finally show that the structures obtained by dewetting on different HS substrates exhibits different levels of hydrophobicity because of combined spatial variation of chemical and topographic contrast along the surface. Thus, the work reported in this article can find potential application in fabricating surfaces with controlled wettability.