Abstract
We demonstrate that the temperature-dependent phase behaviors of parallel and perpendicular cylinder-forming block copolymers are governed by domain-domain segregation forces inherently present in block copolymer material itself. With increasing temperature, a parallel cylinder-forming block copolymer experienced a parallel cylinder straightening process before the order-disorder transition (ODT) and did not show long-range composition fluctuations near the ODT temperature due to the weak segregation forces between the block domains. A perpendicular cylinder-forming block copolymer with a strong segregation force between the block domains displayed cylinder orientation transition from perpendicular to parallel below the ODT temperature. On the other hand, a perpendicular cylinder-forming block copolymer material with an exceptionally strong segregation force between the block domains maintained its initial perpendicular cylinder orientation up to near the ODT temperature. In both cases of perpendicular cylinder-forming block copolymers, submicrometer-scale long-range composition fluctuations were observed well above the ODT temperature due to their intrinsically strong segregation forces between the block domains.
Highlights
The majority of studies on temperature-dependent phase behaviors of block copolymers have concentrated on the phase behaviors of weakly ordered block copolymers near the lamellar-to-disorder, cylinder-to-disorder, cylinder-to-sphere or sphere-to-disorder transitions [1,2,3,4,5], even though information on phase behaviors of strongly ordered block copolymers is required for nanotechnological applications of block copolymers
We showed that the intrinsic preference for parallel or perpendicular cylinder orientation of a cylinder-forming block copolymer was readily controlled by adjusting the molecular weight of homopolymer blended
By using stable block copolymer cylinders oriented either parallel or perpendicular to the surface, we demonstrate that the temperature-dependent phase behaviors of cylinder-forming block copolymers depend on their preference for parallel or perpendicular cylinder orientation, whose strength is directly proportional to the strength of segregation force between the block domains
Summary
The majority of studies on temperature-dependent phase behaviors of block copolymers have concentrated on the phase behaviors of weakly ordered block copolymers near the lamellar-to-disorder, cylinder-to-disorder, cylinder-to-sphere or sphere-to-disorder transitions (i.e., in the relatively high temperature region) [1,2,3,4,5], even though information on phase behaviors of strongly ordered block copolymers is required for nanotechnological applications of block copolymers. In the molecular weight ratio between 1 and 2, on the other hand, overall perpendicular cylinder orientation was spontaneously produced even on an energetically preferential substrate when the thickness of miscible samples was smaller than ~ 10 μm Such parallelto-perpendicular cylinder orientation transition originated from the strong intermolecular interaction between the minority block component and its homopolymer blended, which significantly enhanced the enthalpic preference for the perpendicular cylinder orientation (as well as the incompatibility between the block components) to overcome the parallel cylinder-inducing interfacial interaction between the substrate and its preferential block component. By using stable block copolymer cylinders oriented either parallel or perpendicular to the surface, we demonstrate that the temperature-dependent phase behaviors of cylinder-forming block copolymers depend on their preference for parallel or perpendicular cylinder orientation, whose strength is directly proportional to the strength of segregation force (i.e., incompatibility) between the block domains
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