A new Landau free energy is derived for diblock copolymers of incompatible pairs based on the recently developed compressible random-phase approximation analysis. Finite compressibility of each block is generally allowed. The inhomogeneity of each block density and free volume is analyzed in the weak segregation regime. Free volume inhomogeneity fluctuates in two ways: One represents compressibility difference between blocks and the other stands for the screening of unfavorable cross-contacts. It is shown from the Landau energy that a continuous transition, observed in a symmetric block copolymer either incompressible or with no compressibility difference, disappears provided that one block is more compressible. Microphase transitions and their pressure response of commonly used diblock copolymers are calculated and compared with experimental results. A Flory-type interaction parameter which is suggested from the effective second-order vertex function in the free energy, is shown to be useful, owing to its compressible nature in understanding the phase behavior of various copolymers.
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15 September 2003
Research Article|
September 15 2003
A Landau free energy for diblock copolymers with compressibility difference between blocks
Junhan Cho
Junhan Cho
Department of Polymer Science & Engineering, and Hyperstructured Organic Materials Research Center, Dankook University, San-8, Hannam-dong, Yongsan-gu, Seoul 140-714, Korea
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Junhan Cho
Department of Polymer Science & Engineering, and Hyperstructured Organic Materials Research Center, Dankook University, San-8, Hannam-dong, Yongsan-gu, Seoul 140-714, Korea
J. Chem. Phys. 119, 5711–5721 (2003)
Article history
Received:
May 02 2003
Accepted:
June 18 2003
Citation
Junhan Cho; A Landau free energy for diblock copolymers with compressibility difference between blocks. J. Chem. Phys. 15 September 2003; 119 (11): 5711–5721. https://doi.org/10.1063/1.1599278
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