The mechanism of the order-order transition in a block copolymer between spheres in a body-centered cubic lattice (bcc-spheres) and hexagonal cylinders was investigated by means of smallangle X-ray scattering (SAXS). The block copolymer studied is a polystyrene-block-polyisoprene diblock copolymer having a molecular weight of 4.40 × 10 4 and a weight fraction of polystyrene of 0.20. Cylindrical microdomains on a hexagonal lattice were observed up to 114.7 °C and changed to bcc-spheres above 116.7 °C. The OOT transition between the two microdomains reversibly occurred. Moreover, the repetitive OOT process (defined in the text) occurred with conservation of the grain structures and of orientation of the crystallographic axes in the grains. When the SAXS pattern from a single grain was examined, it was found that the cylinders are transformed into a series of spheres with the cylindrical axes corresponding to the [111] direction of the bcc-spheres upon heating and that the spheres along the [111] direction of the bcc lattice are deformed and interconnected to cylinders upon cooling, both without changing the grain structures.

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Introduction.The self-assembly of block copolymers below the order-disorder transition (ODT) temperature results in interesting nanostructures. An understanding of the methods of manipulating the orientation of the nanostructures in bulk sample is important both as a means of producing oriented materials of practical use and understanding the ordering process of these materials. Shear is an established method of controlling orientation, as is the use of flow. 1,2 Recently, there have been many reports concerning the effects of shear on the orientation of diblock copolymers forming lamellar morphology. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] In addition, electric fields 20 and surfaces 21-23 have been shown to cause alignment of block copolymer nanoscale patterns. However there are few (if any) experimental reports of using temperature gradient to align diblock copolymers. There are a few recent theoretical efforts concerning the effect of a temperature gradient, in the form of a propogating front, during the ordering process. A recent effort along these lines is Zhang et al.'s use of simulations to examine the effect of a shifting quench boundary on the orientation of lamella. 24 Previously, front propagation in a diblock copolymer system has been investigated numerically by Liu and Goldenfield. 25 Dynamics of front propagation were studied by Paquette. 26 Finally, Chen et al. 27 discussed front propagation rate selection. Since the effects of flow fields, surfaces, and electric fields have been shown to be important in aligning diblock copolymer, one naturally asks if the use of a temperature gradient is also important in orienting a diblock copolymer sample.In this communication, we report on the use of an applied temperature gradient to orient the lamellar structure formed by a diblock copolymer. To show the effect of temperature gradient (∇T effect), we need to clearly identify the effect of the sample surfaces on the lamellar orientation. This was achieved by placing a glass surface at an approximately 45°angle with respect to the temperature gradient. In this way, the surface effect will be dramatically tilted compared to the ∇T