Ming-Hsiang Cheng

Morphology control of three-dimensional nanostructures in porous templates using lamella-forming block copolymers and solvent vapors

The microphase separation behavior of block copolymers confined in cylindrical nanopores has been extensively investigated. Recently, the solvent-annealing-induced nanowetting in templates (SAINT) method has been demonstrated to be a versatile approach for the infiltration of block copolymers into the nanopores of porous templates. The function of the annealing solvents, however, is still not well understood, especially in the morphology control of the fabricated block copolymer nanostructures. In this work, we elucidate the function of the annealing solvents in the SAINT method using a lamella-forming block copolymer, polystyrene-block-polydimethylsiloxane (PS-b-PDMS), and anodic aluminum oxide (AAO) templates. By changing the composition of the annealing solvents, different morphologies such as the concentric lamellar morphology, the winding cylinder morphology, and the irregular hybrid morphology are observed, mainly caused by the annealing-solvent-induced volume change. The morphology of the block copolymer nanostructures can be further confirmed using an HF solution to remove the PDMS domain selectively.

Selective Template Wetting Routes to Hierarchical Polymer Films: Polymer Nanotubes from Phase-Separated Films via Solvent Annealing

We demonstrate a novel wetting method to prepare hierarchical polymer films with polymer nanotubes on selective regions. This strategy is based on the selective wetting abilities of polymer chains, annealed in different solvent vapors, into the nanopores of porous templates. Phase-separated films of polystyrene (PS) and poly(methyl methacrylate) (PMMA), two commonly used polymers, are prepared as a model system. After anodic aluminum oxide (AAO) templates are placed on the films, the samples are annealed in vapors of acetic acid, in which the PMMA chains are swollen and wet the nanopores of the AAO templates selectively. As a result, hierarchical polymer films containing PMMA nanotubes can be obtained after the AAO templates are removed. The distribution of the PMMA nanotubes of the hierarchical polymer films can also be controlled by changing the compositions of the polymer blends. This work not only presents a novel method to fabricate hierarchical polymer films with polymer nanotubes on selective regions, but also gives a deeper understanding in the selective wetting ability of polymer chains in solvent vapors.

Asymmetric Polymer Particles with Anisotropic Curvatures by Annealing Polystyrene Microspheres on Poly(vinyl alcohol) Films

Anisotropic polymer particles such as Janus particles have attracted significant attention in recent years because of their unique properties and unusual self-assembly behavior. Most anisotropic polymer particles synthesized so far, however, only have different chemical regions compartmentalized on the particles. It remains a great challenge to fabricate anisotropic polymer particles with different shapes within a single particle. A novel approach is developed to prepare anisotropic polymer particles that contain two hemispheres with different curvatures by annealing polystyrene microspheres on poly(vinyl alcohol) films. During the annealing process, the polymer microspheres gradually sink into the polymer films and transform to asymmetric polymer particles, driven by the surface and interfacial tensions of the polymers. Selective removal techniques are also used to confirm the morphologies of the asymmetric particles.

Hierarchical hybrid nanostructures: controlled assembly of polymer-encapsulated gold nanoparticles via a Rayleigh-instability-driven transformation under cylindrical confinement

We develop a novel route based on the solution wetting method using anodic aluminum oxide (AAO) templates to fabricate hierarchical hybrid nanostructures assembled from polystyrene-encapsulated gold nanoparticles (Au@PS NPs). Hybrid nanostructures including nanotubes and nanospheres can be reliably prepared, in which the spatial arrangement of the Au@PS NPs is determined by the pore diameters of the templates and the molecular weights of the thiol-ended polystyrene (PS-SH) ligands. In particular, the Rayleigh-instability-driven transformation plays a key role in the formation of the hybrid nanospheres.

Reversible morphology control of three-dimensional block copolymer nanostructures by the solvent-annealing-induced wetting in anodic aluminum oxide templates

ABSTRACT In this work, the authors study the fabrication of three-dimensional block copolymer nanostructures in which the morphologies can be reversibly controlled. Polystyrene-block-polydimethylsiloxane (PS-b-PDMS), a promising candidate for nanolithography, is introduced into cylindrical nanopores of anodic aluminum oxide (AAO) templates using a solvent annealing–induced nanowetting in templates (SAINT) method. Not only the morphologies of the infiltrated PS-b-PDMS nanostructures can be tuned by the annealing solvents, but also the solvent-vapor-controlled morphologies can be altered reversibly by annealing the samples repeatedly between different solvent vapors. GRAPHICAL ABSTRACT

Shaping the Light: The Key Factors Affecting the Photophysical Properties of Fluorescent Polymer Nanostructures

To manipulate the functions of nanomaterials more precisely for diverse applications, the controllability and critical influencing factors of their properties must be thoroughly investigated. In this work, the macroscopic and microscopic effects are studied on the photophysical properties of various pyrene-ended poly(styrene-block-methyl methacrylate) nanostructures. Fluorescent polymer nanospheres, nanorods, and nanotubes are prepared by different template-based methods using anodic aluminum oxide membranes. Chain arrangements and conformations are determined as the key factors affecting the photophysical properties of the fluorescent polymer nanostructures. This work not only gives a deeper understanding of the effects on the photophysical properties of polymer nanomaterials influenced by morphologies, chain arrangements, and chain conformations, but also provides a reference for designing proper fluorescent nanostructures for specific applications.