Electric fields, block copolymers

Keywords Electric field Block copolymers Microdomain orientation In situ SFM Orientation mechanism... 

The alignment of a lamellar microstructure by electric fields has been reported [64], The electric fields were applied across a melt of a PS-PMMA block copolymer and were maintained throughout cooling down to below the glass transition point. SAXS studies show persuasive evidence that the microstructure was aligned by an electric field. 

As demonstrated above, the use of PS-PMMA block copolymers as precursors to nanoporous materials is quite well established. Electric field alignment... 

External fields have been widely used to align block copolymer microdomains. This approach relies on the ability to couple an external applied bias field to some molecular or supermolecular feature, and thus achieve directional control over the microdomains. External fields, such as an electric field [61-63], mechanical flow field [53-55], and temperature gradient [60], have been utilized to control the long-range orientation of block copolymers in the bulk state. 

Fig. 3 Schematic representation of control over block copolymer thin film orientation by applying an electric field to orient PS-6-PMMA cylinders perpendicular to the substrate (taken from [43])...

Fig. 10 Schematic representation of the nanoreplication processes from block copolymers, a Growth of high-density nanowires from a nanoporous block copolymer thin film. An asymmetric PS-fc-PMMA diblock copolymer was aligned to form vertical PMMA cylinders under an electric field. After removal of the PMMA minor component, a nanoporous film is formed. By electrodeposition, an array of nanowires can be replicated in the porous template (adapted from [43]). b Hexagonally packed array of aluminum caps generated from rod-coil microporous structures. Deposition of aluminum was achieved on the photooxidized area of the rod-coil honeycomb structure (Taken from [35])...

Chao CY, Li X, Ober CK, Osuji C, Thomas EL. Orientational switching of mesogens and microdomains in hydrogen bonded side-chain hquid-crystalline block copolymers using AC electric fields. Adv Funct Mater 2004 14 364-370. 

The dynamics of block copolymers melts are as intriguing as their thermodynamics leading to complex linear viscoelastic behaviour and anisotropic diffusion processes. The non-linear viscoelastic behaviour is even richer, and the study of the effect of external fields (shear, electric. ..) on the alignment and orientation of ordered structures in block copolymer melts is still in its infancy. Furthermore, these fields can influence the thermodynamics of block copolymer melts, as recent work has shown that phase transition lines shift depending on the applied shear. The theoretical understanding of dynamic processes in block copolymer melts is much less advanced than that for thermodynamics, and promises to be a particularly active area of research in the coming years. 

Effects of Electric Fields on Block Copolymer Nanostructures. 1... 

This chapter deals with the behavior of block copolymer nanostructures subjected to electric fields. We will consider the thin film behavior, elucidate the parameters governing the electric-field-induced alignment, and finally turn to bulk structures and show novel effects of high field strengths on block copolymer... 

To achieve in-plane alignment in a lamellar block copolymer thin film, the lamellae have to be oriented perpendicular to the plane of the film in the first place. As we have shown earlier, in the block copolymer system S47H10M4382 perpendicular alignment of the lamellae is achieved spontaneously at zero electric field [9, 17]. In short, a thin brush layer of the block copolymer is adsorbed onto the (polar) substrate via the PHEMA middle block, resulting in a stripe pattern of the two majority components PS and PMMA. In thicker films, this brush layer seems to serve as a template for perpendicular lamellae [21, 22], This can be seen in Fig. 2a, which shows SFM images of a thin S47H10M4382 film annealed for... 

Fig. 13 Effect of an electric field on the lamellar distance of a block copolymer solution, (a) 2D scattering pattern of a 50 wt% solution of SI51 dissolved in THF for different electric field strengths, (b) Dependence of the lamellar distance d of parallel (filled circles) and perpendicular (open circles) aligned lamellae, with respect to the electric field lines, on the electric field strength for the same solution, (c) Proposed chain stretching effect for lamellae aligned parallel to the field lines. Adapted with permission from Nature Materials [57]. Copyright (2008) Nature Publishing Group...

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