Nucleating Pattern Formation in Spin-Coated Polymer Blend Films with Nanoscale Surface Templates

Abstract

We use Dip-Pen Nanolithography (DPN) to generate monolayer surface templates for guiding pattern formation in spin-coated polymer blend films. We study template-directed pattern formation in blends of polystyrene/poly(2-vinylpyridine) (PS/P2VP) as well as blends of PS and the semiconducting conjugated polymer poly(3-hexylthiophene) (P3HT). We show that acid-terminated monolayers can be used to template pattern formation in PS/P3HT blends, while hydrophobic monolayers can be used to template pattern formation in PS/P2VP blends. In both blends, the polymer patterns comprise laterally-phase separated regions surrounded by vertically separated bilayers. We hypothesize that the observed patterns are formed by template-induced dewetting of the bottom layer of a polymer bilayer during the spin-coating process. We compare the effects of template feature size and spacing on the resulting polymer patterns with predictions from published models of template-directed dewetting in thin films and find the data in good agreement. For both blends we observe that a minimum feature size is required to nucleate dewetting/phase separation. We find this minimum template diameter to be approximately 180 nm in 50/50 PS/P2VP blends, and approximately 100 nm in 50/50 PS/P3HT blends. For larger template diameters, PS/P2VP blends show evidence for pattern formation beginning at the template boundaries, while PS/P3HT blends rupture randomly across the template features.

Spatially Modulating Interfacial Properties of Transparent Conductive Oxides: Patterning Work Function with Phosphonic Acid Self‐Assembled Monolayers

“…[39] The microcontact printing of phosphonic acid modified catalysts for in situ poly mer growth [9,40] is also an area of significant future interest. Finally, while we have focused on LEDs as an easily visualizable test bed, the successful incorporation of microcontact printed phosphonic acid SAMs into solution-processed polymer diodes opens the door for the use of similar microcontact printed SAMs on a range of transparent conductive oxides [41] in OPV applications, perhaps to control film morphology, [39,42,43] in addition to local energy level alignment and carrier selectivity at a contact. [23,33] The lack of large topography (a) and uniformity of the CPD (b) are consistent with single layer coverage.…”

Directed Assembly of Polymer Blends Using Nanopatterned Templates

“…Ginger and coworkers reported phase separation into uniform geometries by patterned templates down to $150 nm by dip-pen nanolithography (DPN). [17,18] The disadvantage of DPN is that the sizes of templates that can be patterned are currently limited. To date, none of the published studies reported the preparation of complex, nonuniform patterns by directed assembly of polymer blends.…”

Multiscale Directed Assembly of Polymer Blends Using Chemically Functionalized Nanoscale‐Patterned Templates

“…In addition, polymer blends may enable fabrication of patterns with multiple length scales in a single substrate (or operation), which is very difficult to achieve using block copolymers 23, 33. Patterning of polymer blends,34–43 however, has been less studied in comparison to controlled self‐assembly of block copolymers 13, 14, 20–32…”

“…Their best polymer assembly occurred when the pattern periodicity and phase domain size were commensurate 34–37. Initial studies by Ginger and co‐workers38, 39 generated uniformly spaced dot patterns with dip‐pen nanolithography (DPN). They demonstrated assembly for PS/poly‐3‐hexylthiophene (P3HT) in patterns as small as 150 nm 38, 39.…”