Mixed supercrystalline structures in mixtures of ABC-triblock and AB(BC)-diblock copolymers, 1. Lamellar structures in bicomponent mixtures

Abstract

The theory of lamellar superstructures in binary mixtures of AB diblock and linear ABC triblock copolymers under the condition of strong segregation between chemically different blocks is developed. This system is considered using Alexander-de Gennes (box-model) and self-consistent field (SCF) models. The formation of a mixed lamellar superstructure comprising both mixture components is proved. It is shown that a mixed lamella may be the only type of lamellae in the mixture, or it may coexist with pure diblock lamellae, depending on the mixture composition, local characteristics of blocks (thickness and Kuhn segment length), and surface tension coefficients at the A/B and B/C interfaces. Preliminary experimental results provide support of these theoretical estimations. The formation of mixed lamellae in a mixture of linear ABC and branched (AB) 2 C block copolymers is also considered.

Mixed Supercrystalline Structures in Mixtures of ABC Triblock and ab(bc) Diblock Copolymers, 3. Lamellar and Cylindrical Structures in Bicomponent Mixtures

“…The free energy of the mixed superstructure contains interfacial, conformational, and mixing contributions: [6] …”

“…The first paper of this series [6] is devoted to the initial problem: is a superstructure of ABC and ab mixed on a molecular level possible? To solve this problem, we restricted ourselves to the investigation of the mixed superstructure with lamellar morphology.…”

“…In the present paper the theory of binary (ABC + ab) mixtures developed in [6] will be extended. First, a larger number of equilibrium morphologies of the ABC and the ab superstructures are taken into consideration.…”

“…The factors determining the choice of one of these morphologies for the equilibrium superstructure was considered theoretically. [6,8] It is also well established [9 -16] that one of the main factors determining the choice of the equilibrium superstructure morphology in both diblock and triblock copolymers is the volume fraction of components in the copolymer f i = N i a 3 i = P i N i a 3 i , (i = A, B, and C for the triblock and i = a, b for the diblock). In the case of triblock copolymers, the ratio of interfacial tension coefficients at the A/B and the B/C interfaces, k (Equation (1)) is also very important.…”

“…Y i describes the difference in the local characteristics of blocks i and A. [6] Here a i and l i are the thickness and the persistence length of the i th block. It should be noted that experimentally triblock and diblock copolymers exhibit not only canonical but also more complicated superstructures in the region between LAM and C(A, C) (in diblock copolymers between lam and c (a) or c (b)) structures.…”