The morphology and structure of PS‐b‐P4VP block copolymer films by solvent annealing: effect of the solvent parameter

Abstract

Lamellae (symmetric) forming polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymers (BCPs) were used to produce nanostructured thin films by solvent (toluene) casting (spin‐coating) onto silicon substrates. As expected, strong micellization of PS‐P4VP in toluene results in poorly ordered hexagonally structures films. Following deposition the films were solvent annealed in various solvents and mixtures thereof. A range of both morphologies including micelle and microphase separated structures were observed. It was found that nanostructures typical of films of regular thickness (across the substrate) and demonstrating microphase separation occurred only for relatively few solvents and mixtures. The data demonstrate that simple models of solvent annealing based on swelling of the polymer promoting higher polymer chain mobility are not appropriate and more careful rationalization is required to understand these data. Analysis suggests that regular phase separated films can only be achieved when the copolymer Hildebrand solubility parameter is very similar to the value of the solvent. It is suggested that the solvent anneal method used is best considered as a liquid phase technique rather than a vapor phase method. The results show that solvent annealing methods can be a very powerful means to control structure and in some circumstances dominate other factors such as surface chemistry and surface energies. Copyright © 2009 John Wiley & Sons, Ltd.

Block copolymer micelle formation in a solvent good for all the blocks

“…1 and 2, the brighter area in the height image is usually darker in the phase image, which indicates that the higher area is softer [26]. It has also been argued for very long time which bock of PS-b-P4VP is softer [27][28][29]. Recently, Jiang et al [30] proved that in the AFM phase image, the brighter area corresponds to the PS phase and darker one corresponds to the P4VP phase because the PS block is harder than P4VP block in symmetric PS-b-P4VP films.…”

The influence of polarity of additive molecules on micelle structures of polystyrene-block-poly(4-vinylpyridine) in the fabrication of nano-porous templates

“…32HNA and 18NDM have correspondingly smaller degree of swelling as seen from light scattering and SAXS results. In the investigation of solvent annealing of PS-P4VP films, O'Driscoll et al reported micelle structure changes from spherical to elongated when the solvent used for annealing had Hildebrand solubility parameters (d) closest to that of P4VP [34]. They verified that toluene dissolves the PS block well since PS has d value of 18.6 MPa 1/2 and toluene, 18.3 MPa 1/2 .…”

“…They verified that toluene dissolves the PS block well since PS has d value of 18.6 MPa 1/2 and toluene, 18.3 MPa 1/2 . P4VP has an averaged d value of 23.0 MPa 1/2 [34]. However the polarity of the molecules complicates the evaluation as three dimensional solubility parameters need to be taken into consideration [35].…”

Combination of temperature and saturated vapor annealing for phase separation of block copolymer

“…The periodical pattern can be prepared by the annealing in solvent vapor, temperature annealing or directly during spin‐coating deposition from selective solvent mixtures . In the case of the solvent vapor annealing, there are several key issues which influence the resulting morphology: choice of the suitable solvent, method of solvent annealing (static or dynamic), applied temperature, duration of solvent treatment, substrate and film thickness …”

“…The resulting orientation of the nanodomains and the quality of a film play a crucial role for the further application. Thus far, many studies have been dealing with the aforementioned parameters, but standardization of this technique for utilization in mass production has not been presented yet.…”