Rich Variety of Three-Dimensional Nanostructures Enabled by Geometrically Constraining Star-like Block Copolymers

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• 作者：Chao Wang ; Yuci Xu ; Weihua Li ; Zhiqun Lin
• 刊名：Langmuir
• 出版年：2016
• 出版时间：August 9, 2016
• 年：2016
• 卷：32
• 期：31
• 页码：7908-7916
• 全文大小：518K
• 年卷期：0
• ISSN：1520-5827

文摘

The influence of star-like architecture on phase behavior of star-like block copolymer under cylindrical confinement differs largely from the bulk (i.e., nonconfinement). A set of intriguing self-assembled morphologies and the corresponding phase diagrams of star-like (AB)_f diblock copolymers with different numbers of arms f (i.e., f = 3, 9, 15, and 21) in four scenarios (ϕ_A = 0.3 and V₀ > 0; ϕ_A = 0.3 and V₀ < 0; ϕ_A = 0.7 and V₀ > 0; and ϕ_A = 0.7 and V₀ < 0 (where ϕ_A is the volume fraction of A block) and V₀ < 0 and V₀ > 0 represent that the pore wall of cylindrical confinement prefers the inner A block (i.e., A-preferential) and B block (i.e., B-preferential), respectively) were for the first time scrutinized by employing the pseudospectral method of self-consistent mean-field theory. Surprisingly, a new nanoscopic phase, that is, perforated-lamellae-on-cylinder (denoted PC), was observed in star-like (AB)₃ diblock copolymer at ϕ_A = 0.3 and V₀ > 0. With a further increase in f, a single lamellae (denoted L₁) was found to possess a larger phase region. Under the confinement of A-preferential wall (i.e., V₀ < 0) at ϕ_A = 0.3, PC phase became metastable and its free energy increased as f increased. Quite intriguingly, when ϕ_A = 0.7 and V₀ > 0, where an inverted cylinder was formed in bulk, the PC phase became stable, and its free energy decreased as f increased, suggesting the propensity to form PC phase under this condition. Moreover, in stark contrast to the phase transition of C₁ → L₁ → PC (C₁, a single cylindrical microdmain) at ϕ_A = 0.3 and V₀ > 0, when subjected to the A-preferential wall (ϕ_A = 0.7), a different phase transition sequence (i.e., C₁ → PC → L₁) was identified due to the formation of a double-layer structure. On the basis of our calculations, the influence of star-like architecture on (AB)_f diblock copolymer under the imposed cylindrical confinement, particularly the shift of the phase boundaries as a function of f, was thoroughly understood. These self-assembled nanostructures may hold the promise for applications as lithographic templates for nanowires, photonic crystals, and nanotechnology.