Ring-Shaped Morphology in Solution-Cast Polystyrene−Poly(methyl methacrylate) Block Copolymer Thin Films

Abstract

We report observation of ring-shaped morphology formed in thin films of a cylinder-forming polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer cast from 1,1,2,2-tetrachloroethane (Tetra-CE) solution via relatively fast solvent evaporation rates, in which Tetra-CE is a good solvent for both blocks but preferential affinity for the minority PMMA block. We studied the microstructure of a set of solution-cast block copolymer films dried with different solvent evaporation rates, R. The control with different R leads to keeping microstructures in different solution concentrations (phi) and bringing mechanical strain fields with different strength in the film, for which faster evaporation rates result in microstructures of lower solution concentrations and mechanical strain fields of higher strength. As R decreases from rapid evaporation (approximately 0.1 mL/h), the film microstructure evolved from an intermediate ringlike morphology sequentially to ring-shaped morphologies including loose and tight rings and then inverted phase of PS spheres in a PMMA matrix and finally reached the equilibrium phase, namely, cylinders of PMMA in a PS matrix. In view of the influence of the film constraints, the microstructure of a film with a terraced free surface profile has been examined. The results indicate that the ring-shaped morphology can form as long as the film thickness is larger than a critical value of about one microdomain spacing. In the case where the film thickness is larger than that value, the nature of solvent and the kinetics of solvent evaporation are shown to be mainly responsible for the ring-shaped morphology formation.

Self‐Assembly of Fibers and Nanorings from Disulfide‐Linked Helix–Loop–Helix Polypeptides

“…In addition to extended fibers, the heterofibers occasionally assembled into closed loops (nanorings, Figure 4). Ringlike nanostructures have previously been described for a range of polymers and block copolymers,16–19 small organic molecules,20 and inorganic nanoparticles,21, 22 and a number of different mechanisms have been proposed to explain the formation of the rings 20–24. The assembly of ringlike structures of polypeptides as a result of folding has, to our knowledge, not been reported before.…”

Solvent-Induced Crystallization of PS-b-PEO-b-PS Block Copolymer Films

“…The effect of solvent on the film structure has also been studied by Han et al [6][7][8] Secondly, various ordered structures can be obtained by controlling the evaporation rate of the solvent from the film. He et al [9][10][11][12][13] designed an approach to control the solvent evaporation rate. Using freeze-drying, they were able to successfully freeze-in microstructures of solution-cast films at different times under extremely slow evaporation rates, which corresponded to frozen-in phase structures at qualitatively different block copolymer concentrations, ϕ. Thirdly, solvent vapor annealing after the polymer film has been prepared can lead to well-ordered film structures.…”

“…[38][39][40][41][42][43][44] However, in polymer films on the nanometer scale, what is the crystallization behavior induced by solvent? The ordered structure [9][10][11][12][13] and dewetting behavior [34,35] in thin films induced by solvent have been well researched and the corresponding mechanism has been deduced rather thoroughly, but the solvent-induced crystallization behavior has not yet been paid much attention. As a powerful annealing approach, its action on film crystallization is worthy of more attention.…”

The Influencing Factors on the Ring-shaped Morphology in PI-b-P2VP Diblock Copolymer

“…Jiang 等 [15] 观察到三嵌段共聚物 聚 4-乙烯基吡啶-聚苯乙烯-聚 4-乙烯基吡啶(P4VP-PS-P4VP)在二氧六环-水的共混溶液中可以形成环, 其成 环机理主要取决于搅拌速度: 在低速搅拌下, 环状胶束 主要通过柱状胶束的首尾相连形成; 而在高速搅拌下, 则经历了棒状胶束-球状胶束-囊泡-环状胶束的转 变过程. Gong 等 [16] 发现聚苯乙烯-聚甲基丙烯酸甲酯 (PS-b-PMMA)在溶剂 1,1,2,2-四氯乙烷(Tetra-CE)挥发速 最近, Chang 等 [20] 研究了聚异戊二烯-聚 2-乙烯基吡 啶两亲性嵌段共聚物(PI-b-P2VP)在四氢呋喃/乙醇共混 溶剂中的相行为. 通过向 PI-b-P2VP 的 THF 溶液中逐渐 滴加 P2VP 的选择性溶剂乙醇, P2VP 链段逐渐舒展而 PI 链段相互聚集, 形成形状和尺寸都非常均一的, 以 PI 为 核、 P2VP 为壳的环形胶束, 并提出 PI-b-P2VP 经历了从 球形胶束到环状胶束转变的机理.…”