Effect of solvophobicity on the phase behavior of linear ABC triblock copolymers in selective solvents: a Monte Carlo study

Abstract

The microphase separation behavior of linear ABC triblock copolymers in A-selective solvents are studied using Monte Carlo simulation. The ABC triblock copolymer used in this study has a short solvophilic block A and two long solvophobic blocks B and C. The effects of the solvophobicity difference and the incompatibility between solvophobic blocks B and C on the micelle morphologies formed by linear ABC triblock copolymers are investigated, and phase diagrams as a function of the solvophobicity of blocks B and C are given at different repulsions between blocks B and C, respectively. A series of multicompartment micelles with distinct solvophobic parts is obtained, such as pupa-like multi-layered micelles, hamburger-like micelles and bumpy disks. Remarkably, when the solvophobicity of blocks B is much stronger than that of blocks C, a novel reverse core-shell-corona micelle with solvophilic blocks A located in the center of the micelle is obtained. Moreover, the results indicate that the competition between the effects of the incompatibility and solvophobicity difference between blocks B and C determines the microphase separation structures in the multicompartment micelles. These simulation results elucidate the mechanism of the formation of ABC triblock copolymer nanostructures and provide theoretical guidance for experimental studies.

Fig. 1. Typical morphologies formed by A₂B₅C₅ triblock copolymers in A-selective solvents as a function of the solvophobicity of blocks B (ε_BS) when the solvophobicity of blocks C and the repulsive interaction between block B and C are ε_CS = 2.0 and ε_BC = 2.0, respectively. (a)–(e) are the overall morphologies of the micelles. (a₁)–(e₁) and (e₂) are the cross-sections of the micelles and (b₂) is the solvophobic parts of the micelle shown in (b).

Fig. 2. Variations in the densities of components A, B, and C and solvents with the radii (r) around the mass center of the spherical micelles with different ε_BS in the case of ε_BC = 2.0 and ε_CS = 2.0. (a) ε_BS = 1, k_BC = 0.5; (b) ε_BS = 7, k_BC = 3.5; (c) ε_BS = 8, k_BC = 4.0; and (d) ε_BS = 10, k_BC = 5.0. For clarity, the corresponding cross-section of the typical micelle is given in each figure.

Fig. 3. Morphological phase diagram of A₂B₅C₅ triblock copolymers in A-selective solvents as a function of the solvophobicity of blocks B (ε_BS) and C (ε_CS) when the repulsive interaction between blocks B and C is ε_BC = 2.0. The same symbols in the phase diagram represent the same morphologies, and representative diagrams of the micelle morphologies are given in (a)–(f). (a₁)–(f₁), (d₂) and (e₂) are the cross-sections of the micelles shown in (a)–(f). (b₂) and (f₂) are the morphologies of the solvophobic parts of the micelles shown in (b) and (f), respectively.

Fig. 4. Morphological phase diagram of A₂B₅C₅ triblock copolymers in A-selective solvents as a function of the solvophobicity of blocks B (ε_BS) and C (ε_CS) when the repulsive interaction between blocks B and C is ε_BC = 4.0. The same symbols in the phase diagram represent the same morphologies, and representative diagrams of the micelle morphologies are given in (a)–(f). (a₁)–(f₁), (d₂) and (e₂) are the cross-sections of the micelles shown in (a)–(f). (b₂), (c₂) and (f₂) are the morphologies of the solvophobic parts of the micelles shown in (b), (c) and (f), respectively.

Fig. 5. Variations in the average contact numbers between blocks B and C (N_BC) with ε_BS in the case of (a) ε_BC = 2.0 and (b) ε_BC = 4.0, respectively. The solvophobicity of blocks C is ε_CS = 5.0. (a₁)–(a₉) and (b₁)–(b₉) are the morphologies of the solvophobic parts of the corresponding micelles.

Fig. 6. Variations in the average contact numbers N_BS and N_CS with simulation time (t) in the case of k_BC = ε_BS/ε_CS = 1.5 (in which ε_BS = 6.0 and ε_CS = 4.0). (a) ε_BC = 2.0 and (b) ε_BC = 4.0. For clarity, the morphologies of the solvophobic parts of the corresponding micelles are also given in this figure.

Fig. 7. Variations in the average contact numbers N_BS and N_CS with simulation time (t) in the case of k_BC = ε_BS/ε_CS = 2.5 (in which ε_BS = 5.0 and ε_CS = 2.0). (a) ε_BC = 2.0 and (b) ε_BC = 4.0. For clarity, the morphologies of the solvophobic parts of the corresponding micelles are also given in this figure.