Depletion-induced surface alignment of asymmetric diblock copolymer in selective solvents

Abstract

Phase separation of asymmetric diblock copolymer near surfaces in selective solvents is theoretically investigated by using the real-space version of self-consistent field theory (SCFT). Several morphologies are predicted and the phase diagram is constructed by varying the distance between two parallel hard surfaces (or the film thickness) W and the block copolymer concentration f(P). Morphologies of the diblock copolymer in dilute solution are found to change significantly with different film thicknesses. In confined systems, stable morphologies found in the bulk solution become unstable due to the loss of polymer conformation entropy. The vesicle phase region contracts when the repulsive interaction between the blocks is strong (strong segregation regime). The mixture of vesicles, rodlike and spherelike micelles and the mixture of vesicles and sphere-like micelles disappear in contrast to the weakly segregating regime. The walls strongly affect the phase separation of block copolymer in selective solvent, and the depletion layer near the surface contributes much to the micelle formation of the block copolymer. Interestingly, the self-assembled morphologies stay near the walls with the distance on the order of the radius of gyration of the block copolymer. The oscillation of the polymer distribution near the walls allows the surface phase separation to be observed due to the strong repulsion between the blocks A and B.

Three-Dimensional Multilayered Nanostructures with Controlled Orientation of Microdomains from Cross-Linkable Block Copolymers

“…Similar entropic domination in the interfacial tension has also been reported in the thin films of polystyrene- b -polybutadiene (PS- b -PB) on silicon wafer, where the Si/SiO x substrate is nearly nonselective to both blocks . In addition to nematic interaction, it should also be mentioned that there is another possibility of entropy-originated interactions arising from the depletion of polymer density in the vicinity of the surface. − The density depletion near the surface gives rise to a local decrease in either surface tension or interfacial tension at the A/B interface, which can also lead to an effective interaction of surface favoring L ⊥ over L ∥ . Such entropy-type interactions, either by nematic effect or by density depletion, can encourage the formation of L ⊥ .…”

Unusual structural properties of polymers confined in a nanocylinder

“…It can greatly affect conformation, [5][6][7][8][9][10][11] glass transition [12][13][14][15] of polymers, even the self-assembly of block copolymers. [16][17][18][19][20][21] The conformational properties of polymer glasses on planar surfaces are widely investigated experimentally and theoretically. [10][11][12] Even the curvature of the surface/interface is an important factor to change the phase behavior of polymers.…”