Spinodal of microphase separation in double comb copolymer melt

1. Spinodal of microphase separation in double comb copolymer melt Palyulin V.V., Potemkin I.I. Division of Physics of Polymers and Crystals, Department of Physics, Moscow State University Block copolymer molecules are excellent systems for studying phenomena related to molecular self-assembly. Usually, researchers choose to work with AB diblock architecture because it is the “simplest” and best understood one. However, if more than two different types of blocks are involved there are a lot of new features occurred. Monodisperse melts of ABC double comb copolymer are examined using the weak segregation theory (WST). The spinodal curves or curves of order-disorder transition (transition from homogeneous melt to microphase separated structure) are obtained. The architecture of double comb copolymer Double Comb Copolymer The number of side chains of each sort is n. The length of side chain types A and B is fN and (1-f)N respectively. The number of segments between the branch points is m. Interactions due to Flory-Huggins parameters: χAB, χBС,χAC In general, system has 7 independent parameters: χAB, χBС,χAC, N, m, f, n.Westudied all cases when only one interaction parameter is left. There are 5 such cases: χAB=χ, χBС=χАС=0;χAB=0, χBC=χAC=χ; χAB=χBC=0, χAC=χ; χAB=χBC=χAC=χ; χAB=χAC=χ, χBC=0. Thefraction of the backbone monomers fbb = m(n-1)/(Nn+n(m-1)) is additional parameter very useful for plotting and physical interpretations. CaseχAB = χ;χBС= χAC= 0 Only the interactions between side chains are exist. The molecule is number of connected diblock-copolymers linked by non-selective chain. CaseχAB= χBС= χAC= χ Spinodal curves for different values of n. Increasing the number of segments between the branch points Spinodal curves for different values of n. Changing the side chain composition. If Flory-Huggins parameters are equal to each other andf = 0.5, we have found the two-scale instability.With increasing of number of segments between branch pointswe see the kink on the spinodal curve and discontinues changing of wavelength in the spinodal point. The structure factor can have two minima. As in other cases spinodal curves have different shapes in the cases of small and large m. Plot of a2q2N/6versus backbone monomers composition fbb Spinodal curves for different values of f depending of the backbone monomers composition fbb CaseχAB=0; χBС= χAC= χ This is the case of double comb copolymer with side chains, composed from the same monomers. With the increasing of n and small m Flory-Huggins parameterχis raising, but if m is large, χis dropping with increasing n. χ(f) is symmetricand has maximum in the point of symmetric compositionf = 0.5 for all lengths of backbone. Spinodal curves for different values of n. Changing the relative side chain length. Plot of a2q2(N+m)/6versus relative side chains length Spinodal curves for different values of n. Changing the relative side chain length. Small m. Spinodal curves for different values of n. Changing the relative side chain length. Large m. Double Comb Polymer synthesis (Lit.) Synthesis and mechanical properties ofdouble comb copolymers are described for the case of side chains, composed from the same monomers [2]. Series of polystyrene-polyisoprene copolymers were synthesized using tetrafunctional branch points. CaseχAB = χАС=χ,χВC= 0 Spinodal curves for different values of n. Changing the relative side chain length. Small m. Spinodal curves for different values of f depending of the backbone monomers composition fbb Conclusions 1. Behavior of the system in most cases significantly depends on m. 2. There are two regimes: case of small m and case of large m. 3. The two-scale switching in the case χAB=χBC=χAC=χ is found. 4. The properties of the system have weak dependence on the parameter n, if this parameter exceeds 10. • References • Leibler L., Theory of Microphase Separation in Block copolymers, Macromolecules, 1980, 13, 1602-1617 • Zhu Y., Weildisch R., Gido S.P., Velis G., Hadjichristidis N., Morphologies and Mechanical Properties of a Series of Block-Double-Graft Copolymers and Terpolymers. Macromolecules, 2002, 35, 5903-5909 • Werner A., Fredrickson G.H.,Architectural Effects on the Stability Limits of ABC Block Copolymers, • J. Polym. Sci. Part B: Polym. Phys., 1997, 35, 849-864 CaseχAB=χBС=0; χAC= χ Spinodal curvesare analogousones in the caseχAB=0; χBС= χAC= χ and large m.