Phase Transitions in Sphere-Forming Polystyrene-block-polyisoprene-block-polystyrene Copolymer and Its Blends with Homopolymer

Abstract

Phase transitions in sphere-forming polystyrene-block-polyisoprene-block-polystyrene (SIS triblock) copolymer and its blends with polystyrene (PS) were investigated using oscillatory shear rheometry, transmission electron microscopy, and small-angle X-ray scattering (SAXS). For the investigation, a commercial grade of high-molecular-weight SIS triblock copolymer (Vector 4113, Dexco Polymers) and a low-molecular-weight SIS triblock copolymer (SIS-100) synthesized in our laboratory were used. It is found from oscillatory shear rheometry and SAXS that both Vector 4113 and SIS-100 undergo order−disorder transition (ODT) having a characteristic feature of lattice disordering/ordering transition (LDOT) of spheres, giving rise to a phase consisting of micelles with short-range liquidlike order at thermal equilibrium above ODT and demicellization/micellization transition (DMT), as a pseudo phase transition, giving rise to a micelle-free phase with only thermal composition fluctuations. The LDOT temperature (T LDOT) of Vector 4113 is found to be ca. 205 °C, and the DMT temperature (T DMT) is much higher than 220 °C, the highest experimental temperature employed to avoid thermal degradation/cross-linking reactions. The addition of various amounts of low-molecular-weight PS enabled us to estimate, via extrapolation, the T DMT of Vector 4113 to be ca. 260 °C. On the other hand, SIS-100 is found to have T LDOT of 85 °C and T DMT of 105 °C. Transmission electron microscopy confirmed the existence of disordered micelles in both Vector 4113 and SIS-100 between T LDOT and T DMT. Phase diagrams for (SIS-100)/PS blends were constructed using T LDOT, T DMT, and cloud point measurements.

Self-assembled block copolymers: Bulk to thin film

“…With a further increase in temperature, disordered micelles are transformed into the micelle-free disordered phase with thermally induced compositional fluctuation at the critical micelle transition (or demicellization transition). The existence of the disordered micelles above the lattice disordering transition was verified experimentally [134][135][136][137][138] and theoretically. 139 From Figure 1 (b), the experimentally determined χN at f = 0.5 is ~ 17, which is distinctly larger than the theoretically predicted value (10.495).…”

“…133 It should be noted that the phase transition of highly asymmetric block copolymers is distinctly different from that of symmetric (or nearly symmetric) block copolymers. [134][135][136][137][138][139] Namely, lamellar microdomains directly lose the long range ordering and become disordered state with thermally induced concentration fluctuation at the T ODT , whereas the spherical microdomains lose long-range ordering at the lattice disordering transition and become disordered micelles with short-range ordering. With a further increase in temperature, disordered micelles are transformed into the micelle-free disordered phase with thermally induced compositional fluctuation at the critical micelle transition (or demicellization transition).…”

Effect of Surface‐Hydroxylated CdS Nanoparticles on the Morphological Transformation of Polystyrene‐block‐Poly(ethylene oxide) Thin Films

“…[1][2][3][4][5][6][7][8][9][10] Hence, selfassembled block copolymers in a bulk form serve as good carriers for bringing nanoparticles into an ordered nanostructure. [11][12][13][14][15] More complicated block copolymer morphologies, involving the incorporation of nanoparticles into block copolymers, have been predicted by Balazs'group.…”

Effects of substrate-blocks interactions on the phase behaviors of cylinder-forming block copolymers

“…At a given molecular weight of PS homopolymer and temperature, the symmetric SI diblock copolymer showed the following morphological type variations as the homopolymer concentration increased (in other words, as the compositional asymmetry increased): lamellae, the ordered bicontinuous double-diamond morphology, cylinders on a hexagonal lattice, spheres on a cubic lattice, disordered micelles of various shapes, and macrophase separation. 11 Similar homopolymer-blending effects have also been identified in the cases of cylinder-or sphere-forming asymmetric block copolymers, [4][5][6][11][12][13][14] i.e., the size and periodic spacing of microdomains increased as the molecular weight and/or volume fraction of blended minority homopolymer increased. In this case, however, the size and periodic spacing could not be significantly enlarged in comparison to those of neat asymmetric block copolymer because the macrophase separation between the block copolymer and homopolymer frequently occurs at a considerably lower homopolymer molecular weight and/or volume fraction.…”

“…[2][3][4][5][6][7] The phase behavior of a binary blend of block copolymer and homopolymer is primarily governed by the length of homopolymer chain compared to its counterpart block in the block copolymer and the amount of blended homopolymer. [8][9][10][11][12][13][14] Three different phase behaviors have been experimentally identified, depending on the degree of polymerization of homopolymer A, N AH , and that of the corresponding component of the block copolymer, N AC . If N AH < N AC , the homopolymer A tends to be localized towards the center of A domain, which can lead to a swelling of the A blocks, and hence causes a change in overall domain spacing and morphology.…”