Interplay between domain microstructure and nematic order in liquid crystalline/isotropic block copolymers

Autor: Bernd Stühn, Rosina Staneva, Wolfram Gronski, Barbara Heck, Rouja Ivanova, Steffen Geppert, Bernd Walter
Rok vydání: 2004
Předmět:
Zdroj: Colloid & Polymer Science. 282:810-824
ISSN: 1435-1536
0303-402X
DOI: 10.1007/s00396-004-1128-x
Popis: The domain microstructure and the nematic LC mesophase in a series of side-chain liquid crystalline/isotropic (LC/I) diblock copolymers with systematically varied block volume fractions were studied in a broad temperature range (25–170 °C) by DSC, polarized microscopy, and wide and small angle X-ray scattering. At all temperatures the block copolymers are microphase separated. The PSLC block copolymers exhibit order at two length-scales: on one hand, a nematic LC mesophase with characteristic length-scale of 0.43 nm (intermesogen distance); on the other hand, lamellar, hexagonal or cubic domain microstructures with characteristic length-scales of 27–44 nm (lattice parameter). The LC block was either located in the matrix or confined inside the microdomains. The thermotropic behavior is characterized by the sequence g/~35 °C/n/~115 °C/i and is not affected by the domain microstructure and/or dimensions. Analysis of the lamellar dimensions showed that the LC chain is stretched. With increasing temperature, a thermal expansion of both blocks takes place followed by a retraction of the LC chain above TNI. The phase diagram is asymmetric and does not alter above TNI. No order-to-order transitions triggered by the nematic-isotropic transition are observed. It was shown that domain microstructures of low interfacial curvature (lamellar and hexagonal) are energetically favored over the geometrically expected ones of high interfacial curvature (micellar cubic) due to the presence of nematic LC mesophase in the matrix or in the microdomains. By comparison to theory a Kuhn segment length of the LC block b LC =0.86 nm was derived from the location of the lamellar/hexagonal phase boundaries.
Databáze: OpenAIRE
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