Influence of Substrate Wettability on the Morphology of Thin Polymer Films Spin-Coated on Topographically Patterned Substrates

Abstract

We show that the morphology of a thin polymer film spin coated directly on to a topographically patterned substrate is strongly influenced by the wettability of the substrate, in addition to other well-known parameters such as concentration of the polymer solution (c(n)), spin speed (RPM), and spin duration. Similar to spin coating on a flat surface, (1, 2) on a topographically patterned substrate as well, a continuous film forms only above a critical polymer solution concentration (c(t)*), for a specific RPM and dispensed drop volume. It is believed that for c(n) > c(t)*, the resulting continuous film on a topographically patterned substrate has an undulating top surface, where the surface undulations are in phase with the underlying substrate patterns. (3) On the basis of experiments involving spin coating of polymer thin films on topographically patterned grating substrates, we show that the surface undulations on the film are in phase with the substrate patterns only when the substrate is completely wetted (CW) by the solvent. In contrast, when the substrate is partially wetted (PW) by the solvent, then the undulations are 180° out of phase with respect to the substrate patterns. We further show that for c(n)< c(t)*, a variety of ordered and disordered structures, like array of aligned droplets, isolated strips of polymers, etc., result on both CW and PW substrates, depending on c(n).

Influence of Substrate Confinement on the Phase-Correlation in the Capillary Breakup of Arrays of Patterned Polymer Stripes

“…The corrugation of the PMMA layer was found to be in-phase with the underlying PS pattern, which was consistent with Mukherjee et al 40 Furthermore, according to Roy et al, the PMMA should have formed a continuous layer. 41 The surface morphology of the resultant bilayer system is shown in part a2 of Figure S6 of the Supporting Information.…”

Tamm plasmon- and surface plasmon-coupled emission from hybrid plasmonic–photonic structures

“…The spinning speed for the two PMMA layers was 8000 rpm. Due to the different surface properties of the top SiO 2 layer and the Ag layer, the thickness of the PMMA2 is slightly less than that of the PMMA1 layer [28,29]. Three samples were fabricated: the first one with the NB molecules doped only in the PMMA1 film, which was below the Ag film (this sample was named NB-1); the second one with the NB molecules doped only in the PMMA2 layer on the Ag film (NB-2); and the third one, which contained NB in both PMMA layers (PMMA1 and PMMA2, below and above the Ag film, respectively) (NB-3).…”

Hierarchically Built Hetero-superstructure Arrays with Structurally Controlled Material Compositions

“…45 This premise agrees with the correlation between film thickness and surface wettability observed in literature, for polystyrene thin films spin-coated from toluene solutions onto topographically patterned substrates. 46 Other related instances of the influence of humidity reported in the literature include, increase in volume of meniscus formed at the interface of a nanoscale probe and surface by capillary condensation 47 increase in transport rates for apolar inks in dip-pen lithography, 47 and drastic decrease in the nanoscopic sliding friction experienced by the tip on rough and hydrophilic surfaces. 44,48 To gain better insight into the potential influence of relative humidity on the outflow rates during spincoating, a control experiment was set up to determine sliding contact angles of a mineral oil on the substrates consisting of the Au nanoparticle arrays (the first level of hierarchy, or the A features as in Figure 1).…”