Temperature tunable micellization of polystyrene-block-poly(2-vinylpyridine) at Si-ionic liquid interface

Stability and Elasticity of Ultrathin Sphere-Patterned Block Copolymer Films

Sphere-patterned ultrathin block copolymer films are potentially interesting for a variety of applications in nanotechnology. We use self-consistent field theory to investigate the elastic response of sphere monolayer films with respect to in-plane shear, in-plane extension, compression deformations, and bending. The relations between the in-plane elastic moduli are roughly compatible with the expectations for two-dimensional elastic systems with hexagonal symmetry, with one notable exception: The pure shear and the simple shear moduli differ from each other by roughly 20%. Even more importantly, the bending constants are found to be negative, indicating that free-standing block copolymer membranes made of only a sphere monolayer are inherently unstable above the glass transition. Our results are discussed in view of the experimental findings.

Self-Assembly of Charge-Containing Copolymers at the Liquid-Liquid Interface

Quantitatively understanding the self-assembly of amphiphilic macromolecules at liquid-liquid interfaces is a fundamental scientific concern due to its relevance to a broad range of applications including bottom-up nanopatterning, protein encapsulation, oil recovery, drug delivery, and other technologies. Elucidating the mechanisms that drive assembly of amphiphilic macromolecules at liquid-liquid interfaces is challenging due to the combination of hydrophobic, hydrophilic, and Coulomb interactions, which require consideration of the dielectric mismatch, solvation effects, ionic correlations, and entropic factors. Here we investigate the self-assembly of a model block copolymer with various charge fractions at the chloroform-water interface. We analyze the adsorption and conformation of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) and of the homopolymer poly(2-vinylpyridine) (P2VP) with varying charge fraction, which is controlled via a quaternization reaction and distributed randomly along the backbone. Interfacial tension measurements show that the polymer adsorption increases only marginally at low charge fractions (<5%) but increases more significantly at higher charge fractions for the copolymer, while the corresponding randomly charged P2VP homopolymer analogues display much more sensitivity to the presence of charged groups. Molecular dynamics (MD) simulations of the experimental systems reveal that the diblock copolymer (PS-b-P2VP) interfacial activity could be mediated by the formation of a rich set of complex interfacial copolymer aggregates. Circular domains to elongated stripes are observed in the simulations at the water-chloroform interface as the charge fraction increases. These structures are shown to resemble the spherical and cylindrical helicoid structures observed in bulk chloroform as the charge fraction increases. The self-assembly of charge-containing copolymers is found to be driven by the association of the charged component in the hydrophilic block, with the hydrophobic segments extending away from the hydrophilic cores into the chloroform phase.

Engineering Hybrid Metallic Nanostructures Using a Single Domain of Block Copolymer Templates

Building complex nanostructures using a simple patterned template is challenging in material science and nanotechnology. In the present work, three different strategies have been exploited for the successful fabrication of hybrid dots-on-wire metallic nanostructures through combining an in-situ method with an ex-situ method. Basically, plasma etching was applied to generate a metallic wire-like nanostructure, and preformed nanoparticles could be placed through multiple means before or after the formation of the wire-like nanostructure. Various monometallic and bimetallic nanostructures have been obtained by utilizing only one functional domain of block copolymer templates. In these cases, full utilization of the functional domain or introduction of the molecular linker is critical to engineering hybrid metallic nanostructures. Other complex and multifunctional hybrid nanostructures can be developed via these strategies similarly, and these nanostructures are promising for useful applications such as optics and surface-enhanced Raman spectroscopy (SERS).

Temperature-triggered micellization of block copolymers on an ionic liquid surface

In situ neutron reflectivity was used to study thermally induced structural changes of the lamellae-forming polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer thin films floating on the surface of an ionic liquid (IL). The IL, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, is a nonsolvent for PS and a temperature-tunable solvent for P2VP, and, as such, micellization can be induced at the air-IL interface by changing the temperature. Transmission electron microscopy and scanning force microscopy were used to investigate the resultant morphologies of the micellar films. It was found that highly ordered nanostructures consisting of spherical micelles with a PS core surrounded by a P2VP corona were produced. In addition, bilayer films of PS homopolymer on top of a PS-b-P2VP layer also underwent micellization with increasing temperature but the micellization was strongly dependent on the thickness of the PS and PS-b-P2VP layers.