Feature Size Modulation in Dewetting of Nanoparticle-Containing Ultrathin Polymer Films

Abstract

Ultrathin polymer films (thinner than ∼100 nm) undergo spontaneous rupture on a non-wetting surface with the appearance of random holes due to interfacial van der Waal’s interaction or disjoining pressure. These holes grow in size and coalesce into threadlike morphology, which subsequently disintegrate in an isotropic array of nearly equal-sized droplets, the size (d D) and periodicity (λD) of which scales with the initial film thickness (h F). We show that both λD and d D of the dewetted droplets can be modulated by adding trace amounts of nanoparticles (NPs) in the films. While addition of higher proportion of NPs is known to stabilize the films against dewetting, the presence of a lower amount of NPs leads to non-monotonic variation of λD and d D with h F, with the possible creation of miniaturized dewetted features under certain conditions. We also show that λD and d D of the dewetted films depend on whether dewetting is engendered by thermal annealing of the film beyond the glass transition temperature of the constituent polymer (T G) or by exposing the film to solvent vapor (SV). Our findings reveal that both λD and d D are much larger when the film (both with and without particles) is dewetted in the SV atmosphere, arguably due to penetration of the solvent into the film matrix, resulting in an increase in the effective thickness of the film during dewetting. We show that in SV-mediated dewetting, the much faster dynamics is attributed to solvent penetration through the film and its wetting the substrate, rather than a drastic drop in viscosity. We also observe that SV exposure not only leads to much faster dewetting dynamics, but it also successfully engenders dewetting in films with higher h F, which remain stable when annealed thermally.

Nanoparticle-Mediated Stabilization of a Thin Polymer Bilayer

“…The evolution of a PMMA25 film is, however, much slower as compared to a PS25 film, as morphological evolution in the PMMA25 film continued till t a ≈ 20 h, in comparison to complete dewetting of the PS25 film within t a ≈ 4 h. Although this study primarily deals with the PS25–PMMA25 bilayer, control experiments reveal that PS film having h F‑PS ≈ 65 nm and h F‑PMMA ≈ 38 nm dewetted fully on the hydrophobized silicon wafer substrates. Beyond these respective h F , only some scattered holes were observed in both types of films …”

“…Beyond these respective h F , only some scattered holes were observed in both types of films. 15 In Figure 1, we report dewetting of a PS25−PMMA25 particle-free bilayer. AFM images shown in frames A1−A8 of Figure 1 show the morphological evolution of the bilayer in the form of hole growth till frame A6 (t a ≈ 8.5 h), their coalescence in frame A7 (t a ≈ 19 h), and their disintegration into droplets in frame A8 (t a ≈ 23 h), with progressive TA.…”

“…Spontaneous instability in ultrathin polymer films has received significant attention ever since the pioneering contribution by Reiter in 1992, because of scientific complexities associated with the phenomenon as well as the potential nonlithographic technique for fabricating mesoscale structures spanning over large areas. Typically, ultrathin polymer films with thicknesses ( h F ) lower than ≈100 nm tend to become unstable and rupture because of the amplification of thermally excited surface capillary waves as a consequence of interfacial van der Waals interactions, or disjoining pressure. − Generally, spontaneous instability is best manifested in glassy polymer thin films coated on the non-wettable substrate as such films evolve and undergo dewetting when they are heated above the glass transition temperature of the constituent polymer ( T G ), − or exposed to solvent vapor (SVE) or immersed in a mixture of solvents and nonsolvents. − The evolution as well as structures can be frozen by quenching the samples under ambient conditions from the dewetting environment, and the solidified structures can be analyzed in detail using various advanced solid-state characterization techniques such as atomic force microscopy. Irrespective of the precise route by which dewetting is engendered, the generic morphological evolution pathway involves rupture of the film with the formation of fairly equal-sized holes, hole growth, merging of adjacent growing holes with the formation of cellular Voronoi tessellation patterns comprising interconnected threads, and their eventual disintegration into an isotropic array of nearly equal-sized droplets due to Rayleigh-Plateau instability, resulting in an isotropic structure .…”

Dewetting-Induced Hierarchical Self-Assembly of Block Copolymers Templated by Colloidal Crystals

“…The dewetting of thin films, which is a separation phenomenon induced by incompatible interfacial energies between the surface and film, is another useful method for micro/nanoscale separation or patterning of various materials, including metals, nanoparticles, and polymers [ 31 , 32 , 33 , 34 , 35 ]. In particular, the dewetting of BCP thin films has been shown to produce micro/nanoscale hierarchical patterns [ 36 , 37 ].…”

Assessing Polymer-Surface Adhesion with a Polymer Collection

“…Recent trends of integration and portability generate growing demand for miniaturized devices, which brings great opportunity to this field. However, the uncertainty of the polymer-surface adhesion slows down this evolution. , On the one hand, spontaneous dewetting phenomena of polymers on substrates make it hard to generate polymer microstructures with defined morphologies (e.g., size, thickness, and shape). − On the other hand, mismatched polymer–substrate pairs lead to poor adhesion, having a negative impact on device stability. Therefore, it is necessary to get a better control of polymer-surface adhesion.…”