Nascent Holes on Spin-Coated Polymer Nanofilms: Effect of Processing and Solvents

Abstract

The hole structure has great impact on the performance of polymeric film materials. In the current work, we focused on the formation mechanism and control of nascent holes that frequently appeared when preparing polymer films on poor wetting substrates. Number density and dewetting area of nascent holes on nanofilms of two model polymers, polystyrene and polymethyl methacrylate prepared from various solvents and spincoating conditions, were systematically studied. Sufficiently large spin speed and prolonged immersion time demonstrated both inducing more and larger holes as a result of high capillary stress and chain adsorption at the surface, respectively. Moreover, solvents played the most critical roles on the formation of nascent holes. Faster evaporative, intermediate Hassen parameter between the polymer and the solvent, and smaller surface tension of solvents promote the formation of more intact films. This work provided deeper understandings on the formation mechanism of polymer nanofilms and an effective approach for controlling nascent holes, which were both of particular importance in the fabrication of functional organic thin-film materials.

Dewetting Effects in Poly(vinylidene fluoride-trifluoroethylene) Thin Films on Poly(3-hexylthiophene) Substrates

“…As the solution wets better the substrate, the area exposed to evaporation is larger. In this way, the solvent would evaporate more efficiently, not allowing the polymer to be evenly distributed, and therefore producing a film with holes. , …”

“…In this way, the solvent would evaporate more efficiently, not allowing the polymer to be evenly distributed, and therefore producing a film with holes. 9,47 The origin of the observed effect of hole formation dependence with the P3HT layer thickness for the same PVDF-TrFE concentration must be found on the long-range interaction in the bilayer system. To further understand the differences between the final morphology depending on the characteristics of the bottom P3HT layer, the surface energy of the P3HT substrate for different thicknesses has been characterized, following the method described in the Supporting Information.…”

“…In this second stage, surface tension and viscose forces are the dominant ones. These forces depend strongly on the interaction between the system being deposited and the substrate. , Thus, polymer thin films prepared by spin coating are systems far away from thermodynamic equilibrium . From a processing point of view, the main parameters to be considered for spin coating preparation are (1) the volume dispensed, (2) the spinning speed, (3) the solution concentration, and (4) the spinning time.…”

Pattern Formation in Evaporating Polymer Solutions─Interplay between Dewetting and Decomposition

“…The spreading parameter for polystyrene on water is negative. 43,44 Thus, at later stages, we expect a complete dewetting of the thin film solution (Figure 1b). With an increase in the initial concentration, assuming a monotonic change in the spreading parameter, one may expect monotonic variation in the dewetting length scale.…”

“…Recent experiments reveal that chloroform evaporates at a rate of v ev ≈ 0.1 μm/s. 43 Using the values for the spreading parameter (|S| ≈ 10 −2 N/m), contact angle (θ ≈ 0.1), and viscosity (η ≈ 10 −3 Pa.s) from the literature, 43 we obtain the initial spreading velocity, 42 v spread ∼ |S|•θ 2 /η, to be of the order of cm/s. Of course, any presence of convective flow of air at the air−water interface may increase the evaporation rate considerably.…”