Phase Behavior of Binary Blends of Diblock Copolymers

Abstract

The phase behavior of binary blends of a long symmetric AB diblock copolymer and a short asymmetric AB diblock copolymer is studied using the self-consistent mean-field theory. The investigation focuses on blends with different short diblocks by constructing phase diagrams over the whole blending compositions and a large segregation regime. The influences of the chain length ratio (R) of the long and short diblock copolymers on their miscibility and on the stability of various ordered structures are explored. The theoretical results reveal that the blends have a much more complex phase behavior than each constituent copolymer. With the increase of the volume fraction of the short diblocks in the blends, multiple transitions from a long-period lamellar phase to phases with nonzero interfacial curvatures including cylindrical and spherical phases, and finally to a short-period lamellar phase or disordered phase, are predicted. In particular, consistent with experiments, the theory predicts that the cylindrical phase is stabilized over a wide blending compositions region in the strong segregation region, even though the two constituent diblock copolymers are both lamella-forming. When the ratio R is large enough, macrophase separation occurs over a wide range of blending compositions in a relatively strong segregation regime. Various coexisting phases, including those of lamellar and disorder, lamellar and cylindrical, cylindrical and cylindrical, cylindrical and disorder, spherical and disorder, and cylindrical and spherical, are predicted. In addition, the density profiles of the typical ordered structures are presented in order to understand the self-organization of the different copolymer chains.

Complex Macrophase‐Separated Nanostructure Induced by Microphase Separation in Binary Blends of Lamellar Diblock Copolymer Thin Films

“…The most interesting result of the AFM investigation is the absence of macrophase separation. According to both experimental and theoretical studies, macro­phase separation is expected for φ β = 0.3–0.7 for the blends studied here. Obviously, AFM only monitors the near‐surface structures, which may differ from the ones within the thin films.…”

Morphological Control Over Three‐ and Four‐Phase Superstructures in Blends of Asymmetric ABC and BAC Triblock Terpolymers

“…It has been shown before, that this ratio is not only essential for whether microphase or macrophase separation takes place, but it has also control over the resulting morphology. Wu et al . have demonstrated with the use of the SCFT how the phase diagram for binary blends of diblock copolymers dramatically changes when the chain length ratio R is altered.…”

“…It has been shown before, that this ratio is not only essential for whether microphase or macrophase separation takes place, [68,69] but it has also control over the resulting morphology. Wu et al [70] have demonstrated with the use of the SCFT how the phase diagram for binary blends of diblock copolymers dramatically changes when the chain length ratio R is altered. In our work, we have maintained this ratio at a nearly constant value but they are interchanged for both blend series: in series A the chain of SIM is 1.8 times longer than the chain of ISM and in series B the chain of ISM is 1.9 times longer than the chain of SIM.…”

Nonclassical Block Copolymer Self‐Assembly Resulting from a Constrained Location of Chains and Junctions

“…For example, Matsen [ 29 ] calculated the phase separation between two symmetric diblock blends and found that macrophase separation occurs if the chain length ratio of long diblock to short diblock is larger than 5, and the volume fraction of short copolymer larger than 0.2. Another interesting simulation study by Wu et al in 2010 [ 30 ] concerned the phase behavior of binary blends of a long symmetric AB diblock copolymer and a short asymmetric AB, where macrophase separation occurred when the chain length ratio was large enough (≈5.3).…”