Progress in control of microdomain orientation in block copolymers – Efficiencies of various external fields

Abstract

a b s t r a c tRecent progresses in control of orientation for block copolymer microdomains using external fields, such as force fields, electric fields, and magnetic fields will be reviewed. Since it has been more recognized that such explicit external fields are not necessarily required, implicit (unconscious) external fields, which mean those imposed automatically onto block copolymers, irrespective of intention, will also be covered under categories of ''surface fields'' and ''directional fields'', where self-organizing abilities of block copolymers are utilized for performance of spontaneous orientation (or in other words selforientation). Although some of these phenomena of the self-orientation have been already used in application-oriented researches towards nanotechnology, the mechanisms of self-orientation still remain ambiguous. Moreover, although there have been reported interesting and significant findings on the selforientation in the recent decades, it cannot be stated that the individual findings are well correlated with each other to draw formulated cognition. Therefore, in this feature article, we systematically discuss them under the new categories of the implicit external fields for a better understanding of phenomena and hopefully mechanisms of microdomain orientation.

Self-organized two-dimensional onions

“…Magnetic field induced alignment was reported in 1998; 19 a 2.4 T magnetic field was imposed on a diblock copolymer comprising both block chains of liquidcrystalline polymers, resulting in a weak orientation order. Similar alignment has also been demonstrated for semicrystalline polymers in the presence of a strong magnetic field of 30 T. [20][21][22][23] Due to the small interaction energies magnetic reorientation requires immense fields that are technologically unrealistic. Here we demonstrate that low magnetic field annealing of a directed assembly of a homogeneous diblock copolymer with multiferroic Pb 1.1 ͑Zr 0.53 Ti 0.47 ͒O 3 ͑PZT͒ and CoFe 2 O 4 ͑CFO͒ precursors produces a well-developed selforganized two-dimensional ͑2D͒ "onion" nanostructure.…”

Spontaneous Enhancement of Packing Regularity of Spherical Microdomains in the Body-Centered Cubic Lattice upon Uniaxial Stretching of Elastomeric Triblock Copolymers

“…Thus, they are referred to as a thermoplastic elastomer [1]. The microphase-separated structures in block copolymers have been studied for many decades and much has been uncovered [2][3][4][5][6][7][8][9][10], such as that spherical microdomains regularly order in the body-centered cubic (bcc) lattice [6]. We also have studied why the block copolymers favor the bcc over the face-centered cubic (fcc) lattice, and have been able to demonstrate a very rare case of spherical microdomains exhibiting the fcc lattice [9].…”

“…This fact seems to imply that mechanical stretching can play the role of an external field. However, the ability to enhance the packing regularity of spherical microdomains is exclusive to the mechanical stretching, bearing in mind that other external fields are generally effective for alignment or orientation of microdomains [7,8,10]. It should be further mentioned that a cycle of stretching-and-releasing plays an important role from analogy of densification of packing in granules upon shaking.…”

Mutual Alignment of Block Copolymer−Magnetic Nanoparticle Composites in a Magnetic Field

“…12,13 There has also been a fair amount of work using magnetic fields to orient block copolymers, although it is necessary to use copolymers which contain moieties or semicrystalline domains with appreciable magnetic susceptibility. 5,[14][15][16][17] In the absence of such a condition, we introduced the rod-shaped nanoparticles, which are capable of being magnetically aligned. Using this kind of scheme to induce reorientation in lyotropic liquid crystal/nanomagnet composites has also been demonstrated.…”