Lamellar Diblock Copolymer Thin Films Investigated by Tapping Mode Atomic Force Microscopy:  Molar-Mass Dependence of Surface Ordering

Abstract

Using tapping mode atomic force microscopy, we studied the influence of molar mass (13.9−183 kg/mol) on the lamellar orientation at the surface of thin films of symmetric polystyrene−polybutadiene diblock copolymers prepared via spin-coating and by slow solvent-casting. The ratio between film thickness and lamellar thickness was varied between 0.5 and 10. Whereas for film thicknesses between 1 and 10 times the lamellar thickness, a lamellar orientation parallel to the film surface is preferred for low molar masses (below ∼55 kg/mol), high molar mass samples (above ∼90 kg/mol) rather form lamellae oriented perpendicular to the surface. For film thicknesses equal to the lamellar thickness, the films do not exhibit any texture, whereas for film thicknesses equal to half the lamellar thickness, a weak surface structure could be observed. This is consistent with symmetric wetting, i.e., the same block adsorbs at both film interfaces, but their selectivity is only weak. Thus, entropic contributions like chain stretching along a wall and the enrichment of free chain ends at the interface become important, and both parallel and perpendicular orientations of lamellae in thin films can occur.

Structural and electronic properties of pentacene-fullerene heterojunctions

“…[57][58][59] AFM phase imaging can provide high contrast due to variations in local attractive forces and stiffness and can therefore be used as tool to discriminate between areas covered by different chemical compounds in blended films. [60][61][62] The phase image in Fig. 7͑f͒ reveals comparably the same phase angle values ͑ ͒ in the meandered lamellae ͑1͒ and the round islands ͑2͒, however, with high contrast to the surrounding smooth matrix in ͑2͒ ͓white areas in Fig.…”

Morphology of Symmetric Diblock Copolymers Confined Between Two Stripe‐Patterned Surfaces – Tilted Lamellae and More

“…At equilibrium, symmetric diblock copolymers A-B exhibit a lamellar structure characterized by alternating A-and B-rich layers. Over the past decade, symmetric diblock copolymers confined between two homogeneous and hard (impenetrable) surfaces have been extensively studied by experiments, [4][5][6][7][8][9][10] molecular simulations, [11][12][13][14][15][16][17][18] and various theories. [11,13,14,17 -31] Surfaces have several effects on the thin-film morphology: first, they generally Summary: We report the first Monte Carlo simulations on the thin-film morphology of symmetric diblock copolymers confined between either symmetrically or antisymmetrically stripe-patterned surfaces.…”

Nanostructured Morphologies by Self-Assembly of Diblock Copolymers: A Review

“…Lamellar morphology can be used to create line and space patterns on substrates by controlling their orientation. Lamellar orientation depends on several parameters and/or factors such as the substrate used for film preparation [16,17], thermal or solvent vapor annealing treatments [15,17,18], chain length or molar mass [16,17,19], pressure application during annealing [20] or the use of graphoepitaxial techniques for film preparation [21][22][23]. Thus, different orientations have been obtained for different block copolymers by controlling those parameters.…”

“…Chain length and molar mass of copolymers also are key factors in order to obtain lamellar structures with different orientations [16,17,19]. For films of PS-b-PMMA prepared in a neutral substrate [16], it was found that the orientation of lamellar microdomains was strongly influenced by the molecular weight of the copolymer and film thickness.…”

“…In the other hand, the as-cast thin film of copolymers with higher molecular weights showed a mixture of parallely and perpendicularly oriented lamellae. The effect of chain length has also been studied for PS-b-PB copolymer thin films, together with that of film thickness [19], varying film thickness/lamellar thickness ratios from 0.5 to 10. For ratios between 1 and 10, lamellae paralelly oriented to the surface were obtained for low molar masses (below 55 kg/mol), while perpendicularly oriented lamellae were obtained for copolymers with higher molar masses (above 90 kg/mol).…”