Asymmetric block copolymers confined in a thin film

Abstract

We have used a dynamic density functional theory ͑DDFT͒ for polymeric systems, to simulate the formation of micro phases in a melt of an asymmetric block copolymer, A n B m ( f A ϭ1/3), both in the bulk and in a thin film. In the DDFT model a polymer is represented as a chain of springs and beads. A spring mimics the stretching behavior of a chain fragment and the spring constant is calculated with the Gaussian chain approximation. Simulations were always started from a homogeneous system. We have mainly investigated the final morphology, adopted by the system. First, we have studied the bulk behavior. The diblock copolymer forms a hexagonal packed array of A-rich cylinders, embedded in a B-rich matrix. Film calculations have been done by confining a polymer melt in a slit. Both the slit width and surface-polymer interactions were varied. With the outcomes a phase diagram for confined films has been constructed. Various phases are predicted: parallel cylinders (C ʈ ), perpendicular cylinders (C Ќ ), parallel lamellae (L ʈ ), and parallel perforated lamellae (CL ʈ ). When the film surfaces are preferentially wet by either the A or the B block, parallel oriented microdomains are preferred. A perpendicular cylindrical phase is stable when neither the A nor B block preferentially wets the surfaces. The predicted phase diagram is in accordance with experimental data in the literature and explains the experimentally observed differences between films of asymmetric block copolymers with only two parameters: the film thickness and the energetic preference of the surface for one of the polymer blocks. We have also observed, that confinement speeds up the process of long range ordering of the microdomains.

Block Copolymer Membranes for Aqueous Solution Applications

“…If there is no strong enthalpic motivation for surface preferential wetting, the largest block tends to accumulate on the surface and an entropic balance will guide the placement of the smaller block. Cylinders to lamellae or cylinder to perforated transitions are then promoted 72 . The predictions were focused on thin films, but do not exclude the occurrence in thicker systems.…”

Influence of substrate interaction and confinement on electric-field-induced transition in symmetric block-copolymer thin films

“…6b) indicates the second possibility where circular domains coexist at the center simultaneouly with the wetting layers. The presence of such hybrid structures (combination of two different phases) have previously been reported in cylinder forming systems at similar film thickness [63]. However their transition in electric field has not been reported previously.…”

Synthesis and Catalytic Applications of Non-Metal Doped Mesoporous Titania

“…The hypothesis underlying this approach is that orthogonal alignment of the HCP mesophase can be achieved in EISA-derived ceramic film by modifying the substrate surface so that it interacts equally with both blocks of the P123 template, making it chemically "neutral" towards the template surfactant. Monte Carlo simulations [111,112] have shown that this is the expected outcome for mixtures of surfactants and small molecules, and not just for neat block copolymers [108]. A related epitaxial orientation procedure was demonstrated by Tolbert and coworkers, where HCP film was cast onto a cubic template film to induce orthogonal alignment [113].…”

“…By analogy with surface chemistry strategies used to orient block copolymer films [104][105][106][107][108][109], the Rankin group has reported the synthesis of mp-TiO 2 thin films with orthogonally tilted HCP (o-HCP) cylindrical nanopores using EISA with P123 as structure directing agent and titanium(IV) ethoxide as titania precursor [83,110]. The hypothesis underlying this approach is that orthogonal alignment of the HCP mesophase can be achieved in EISA-derived ceramic film by modifying the substrate surface so that it interacts equally with both blocks of the P123 template, making it chemically "neutral" towards the template surfactant.…”