Microphase separation in mixtures of AC and ABC block copolymers

Within the random-phase approximation, a global analysis of the thermodynamic stability of homogeneous mixtures of diblock and triblock copolymers was performed. The corresponding phase portraits were constructed, and their examination allowed one to conclude whether, at given parameters of the mixtures under study, the tendency toward separation into macroscopic phases with different concentrations of the components dominated or microphase separation took place. At certain parameters of the mixtures, as a result of competition between the above tendencies, the homogeneous state of the mixture was broken down via simultaneous growth fluctuations with appreciably different wavelengths and, finally, an ordered alternation of triblock copolymer layers in the ordered diblock copolymer matrix was achieved. The importance of the development of such ordered suprastructures was discussed from the viewpoint of the fundamental technological problem of photon crystals.