Complex pattern formation by phase separation of polymer blends in thin films

Abstract

During spin coating of very thin Ðlms from a solution of incompatible polymers quite interesting lateral structures are forming. From scanning force microscopy (SFM) and X-ray reÑectometry it is concluded that a surface height modulation is present, which reÑects at the surface the phase separated morphology of the blend in the Ðlm. Those structures depend critically on di †erent parameters like relative concentration of the components, spinning parameters, solvent quality or compatibility of the blend. In blends of di †erent statistical copolymers of poly-styrene-stat-para-bromo-styrene the compatibility between the blended polymers depends on the di †erence in the degree of bromination. This allows a variation of the interaction parameter within a wide range. Besides relatively incompatible materials, also weakly incompatible mixtures are of interest. Such a system with an almost vanishing but still positive interaction parameter is realized with blends of poly-styrene and poly-para-methyl-styrene. Ultra thin polymer Ðlms with thicknesses between 2 to 4 were prepared by solvent quenches from R G homogeneous solution. The lateral structures created during the quench are examined with SFM. The SFM pictures are statistically analysed in terms of their Fourier components. From the power spectral density function the most prominent in-plane length scale is extracted. This analysis of a mean distance is complemented by the use of Minkowski measures.

Surface-directed phase separation in nanometer polymer films: self-stratification and pattern replication

“…Laterally separated phase domains present in solvent-quenched thin films (and corresponding to column-like morphologies in temperature-quenched samples with flat surfaces) are always accompanied by free surface undulations [39,[54][55][56][57][58][59][60][61][62]. Different theories, referring to various solvent effects, try to account for this phenomenon [59,[61][62].…”

“…5a). Such solvent quench [39,[54][55][56][57][58][59][60] accompanies the spin-casting process ( Fig. 5b-f) [38].…”

“…For homogeneous substrates simple strategies have been frequently used to alter the phase separation process by coarse modification of γ (e.g. by exchanging polymers [51,56]) or ∆γ (e.g. by changing the chemical nature of the substrate [9,11] Approaches using mixed SAMs [67] or end-grafted random copolymer brushes [68], both with variable composition, were used to tune the effective interactions between polymers and the substrate.…”

Highly Regular Polyampholytic Structures Adsorbed Directly from Solution

“…The used cantilevers were made from microfabricated silicon (Nanosen-sors). Measurements at several sample positions were performed with scan areas between 1 x 1 µm and 20 x 20 µm" To get a less pictoral view on the surface, the topographies observed by SFM were analyzed by a Fourier transformation [29] A better signal-to-noise ratio was reached in an additional next step with the calculation of the radially averaged power spectral density (PSD) from the Fourier transform: PSD = 1/2π|F(q)| 2 .If the PSD spectrum contained a peak, the peak position s* was extracted using a fit of a Gaussian line shape to the PSD [30]. From this position s* the dominant lateral length scale S* in the surface topography was then calculated:…”

Large-scale and local-scale structures in polymer-blend films: a grazing-incidence ultra-small-angle X-ray scattering and sub-microbeam grazing-incidence small-angle X-ray scattering investigation

“…in optics or sensors (Walheim et al, 1999). The morphology is altered and tailored by changing the ratio of the components in the blend (Gutmann et al, 1999). The characteristic structural size is modified through the amount of material deposited on the solid support and by the preparation technique used.…”