Phase Behavior of Styrene−Isoprene Diblock Copolymers in Strongly Selective Solvents

Abstract

The phase behavior of polystyrene−polyisoprene diblock copolymers diluted with solvents strongly selective for polyisoprene was investigated using variable-temperature small-angle X-ray scattering. Tetradecane was employed as a model selective solvent; its addition induced lyotropic order−order transitions, with as many as five ordered phases found in solutions of one diblock as tetradecane content was varied. The mesophases observed for tetradecane solutions of 10 different diblocks can be partially collapsed into a single two-dimensional map of segregation strength vs overall polystyrene content, as if the selective solvent simply alters the volume fraction of the soluble block. Among strongly selective solvents (tetradecane, tributylamine, squalane), measurable and even large differences in diblock−solvent phase behavior are revealed, in both the locations of lyotropic order−order transitions and the thermotropic order−disorder transition. The addition of squalane to polystyrene-rich diblocks actually elevates the order−disorder transition temperature relative to the diblock melt.

Phase Behavior of Polystyrene-block-poly(2-vinylpyridine) Copolymers in a Selective Ionic Liquid Solvent

“…The coexistence of microstructures persists after a long (24 h) preanneal at 145 "C prior to SAXS characterization and also after annealing the sample at 145 "C for 30 min on the SAXS beamline. In general, we find the microphase-separated structures observed in S2VP (13)(14)(15) periods of time. Samples stored 1-2 months at room temperature in the glovebox exhibit the same microphase-separated structure and thermodynamic transitions as samples prepared immediately prior to SAXS experiments.…”

“…Both PS and P2VP homopolymers are known to undergo a glass transition in the vicinity of 100-105 "C in the high molecular weight limit.56 It is thus not surprising that S2VP (13)(14)(15) (Table 1). Salt ions are known to induce physical cross-links in polymer matrices, which in turn lead to an increase in T,, e.g., LiC104/PE0 electrolytes.3s The @p = 0.93 sample exhibits two T, ' s at 95 and 120 "C. The phase with the high T, is likely the P2VP-rich microphase, in which most of the [Im][TFSI] is expected to reside.…”

20nm Pitch Directed Block Copolymer Assembly Using Solvent Annealing for Bit Patterned Media

“…Variation in feature periodicity with degree of swelling have been reported for other solvent annealed systems as well. [14][15][16][17] The annealing conditions discussed in chemical prepattern. In this case, the chemical prepattern is formed using an oxygen reactive ion etch to selectively damage a grafted PS brush layer in patterns created by e-beam lithography.…”

Crystalline free energies of micelles of diblock copolymer solutions

“…For clustered conditions, it has also been observed the occurrence of a transition between a disordered phase of dispersed clusters and a phase with long range spatial order in hexagonal (for cylindrical aggregates) or cubic (for spherical clusters) structures (ODT). Moreover thermotropic and lyotropic transitions between cubic crystals of different structure have been reported [7][8][9][10] and theoretically analyzed by mean field theoretical arguments [11][12][13].…”