Progress in the self-assembly of organic/inorganic polyhedral oligomeric silsesquioxane (POSS) hybrids

This Review describes recent progress in the self-assembly of organic/inorganic POSS hybrids derived from mono-, di-, and multi-functionalized POSS cages. We highlight the self-assembled structures and physical properties of giant surfactants and chain-end- and side-chain-type hybrids derived from mono-functionalized POSS cages; main-chain-type hybrids derived from di-functionalized POSS cages; and star-shaped hybrids derived from multi-functionalized POSS cages; with various polymeric attachments, including polystyrene, poly(methyl methacrylate), phenolic, PVPh, and polypeptides.

Fluorine-containing nano-objects with the same compositions but different segment distributions: synthesis, characterization and comparison

PHOS-b-PPFS nano-objects and PPFS-b-PHOS nano-objects can be prepared by RAFT PISA and MISA processes, respectively. These nano-objects have the same compositions but different segment distributions and distinct hydrophilic/hydrophobic properties.

The block copolymer shuffle in size exclusion chromatography: the intrinsic problem with using elugrams to determine chain extension success

Is an increase in hydrodynamic volume always expected in block copolymer synthesis? Why SEC is sometimes not the last word.

High-throughput morphology mapping of self-assembling ternary polymer blends

Multicomponent blending is a convenient yet powerful approach to rationally control the material structure, morphology, and functional properties in solution-deposited films of block copolymers and other self-assembling nanomaterials. However, progress in understanding the structural and morphological dependencies on blend composition is hampered by the time and labor required to synthesize and characterize a large number of discrete samples. Here, we report a new method to systematically explore a wide composition space in ternary blends. Specifically, the blend composition space is divided into gradient segments deposited sequentially on a single wafer by a new gradient electrospray deposition tool, and characterized using high-throughput grazing-incidence small-angle X-ray scattering. This method is applied to the creation of a ternary morphology diagram for a cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymer blended with PS and PMMA homopolymers. Using “wet brush” homopolymers of very low molecular weight (∼1 kg mol⁻¹), we identify well-demarcated composition regions comprising highly ordered cylinder, lamellae, and sphere morphologies, as well as a disordered phase at high homopolymer mass fractions. The exquisite granularity afforded by this approach also helps to uncover systematic dependencies among self-assembled morphology, topological grain size, and domain period as functions of homopolymer mass fraction and PS : PMMA ratio. These results highlight the significant advantages afforded by blending low molecular weight homopolymers for block copolymer self-assembly. Meanwhile, the high-throughput, combinatorial approach to investigating nanomaterial blends introduced here dramatically reduces the time required to explore complex process parameter spaces and is a natural complement to recent advances in autonomous X-ray characterization.

Compositionally graded electrospray deposition combined with grazing incidence small angle X-ray scattering forms a high-throughput approach for mapping phase behavior in ternary mixtures as demonstrated here using block copolymer blends.

Simulation Study of Process-Controlled Supramolecular Block Copolymer Phase Separation with Reversible Reaction Algorithm

A supramolecular diblock copolymer formed by reversible bonds between the two blocks shows a rich microphase separation behavior and has great application potential in stimuli-responsive materials. We propose a novel method to describe supramolecular reactions in dissipative particle dynamics, which includes a reversible reaction to accurately reproduce the strength, saturation, and dynamic properties of the reversible bonds in the simulations. The thermodynamic properties and dynamic processes of the supramolecular diblock copolymer melts in both equilibrium and non-equilibrium states were studied using this method. The simulation results show that the method can faithfully characterize phase behaviors and dynamic properties of supramolecular diblock copolymer melts, especially in a non-equilibrium state, which provides a novel tool to unveil self-assembly mechanism and describe the properties of supramolecular block copolymers.

Glass Transition Behaviors of Poly (Vinyl Pyridine)/Poly (Vinyl Phenol) Revisited

We examined the composition and molecular weight dependence of the glass transition temperature in detail for two types of hydrogen bonding miscible blends: poly (2-vinyl pyridine)/poly (vinyl phenol) (2VPy/VPh) and poly (4-vinyl pyridine)/poly (vinyl phenol) (4VPy/VPh). Regarding the functional form of the glass transition temperature, Tg, as a function of the weight fraction, we found a weak deviation from the Kwei equation for 2VPy/VPh blends. In contrast, such a deviation was not observed for the 4VPy/VPh blend. By relating the difference in the functional forms of Tg between the two blend systems to the difference in hydrogen bonding ability, we proposed a modified version of the Kwei equation. As for the interaction parameter, q in the Kwei equation, clear molecular weight dependence was observed for 2VPy/VPh blends: the lower the VPh molecular weight in the oligomer level, the higher the q values, suggesting the higher hydrogen bonding formability near the polymer chain ends than the middle part of a polymer chain.

Hierarchical Self-Assembled Structures from Diblock Copolymer Mixtures by Competitive Hydrogen Bonding Strength

In this work we prepared poly(styrene⁻b⁻vinylphenol) (PS-b-PVPh) by sequential anionic living polymerization and poly(ethylene oxide-b-4-vinylpyridine) (PEO-b-P4VP) by reversible addition fragmentation chain transfer polymerization (RAFT) by using poly(ethylene oxide) 4-cyano-4-(phenylcarbonothioylthio)pentanoate (PEO-SC(S)Ph) as a macroinitiator with two hydrogen bonded acceptor groups. When blending with disordered PEO-b-P4VP diblock copolymer, we found the order-order self-assembled structure transition from lamellar structure for pure PS-b-PVPh to cylindrical, worm-like, and finally to PEO crystalline lamellar structures. Taking the advantage of the ΔK effect from competitive hydrogen bonding strengths between PVPh/P4VP and PVPh/PEO domains, it could form the hierarchical self-assembled morphologies such as core⁻shell cylindrical nanostructure.

Nitrogen reactive ion etch processes for the selective removal of poly-(4-vinylpyridine) in block copolymer films

Self-assembling block copolymer (BCP) patterns are one of the main contenders for the fabrication of nanopattern templates in next generation lithography technology. Transforming these templates to hard mark materials is key for pattern transfer and in some cases, involves selectively removing one block from the nanopattern. For poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP), a high χ BCP system which could be potentially incorporated into semiconductor nanofabrication, this selective removal is predominantly done by a wet etch/activation process. Conversely, this process has numerous disadvantages including lack of control and high generation of waste leading to high cost. For these reasons, our motivation was to move away from the wet etch process and optimise a dry etch which would overcome the limitations associated with the activation process. The work presented herein shows the development of a selective plasma etch process for the removal of P4VP cores from PS-b-P4VP nanopatterned film. Results have shown that a nitrogen reactive ion etch plasma has a selectivity for P4VP of 2.2:1 and suggest that the position of the nitrogen in the aromatic ring of P4VP plays a key role in this selectivity. In situ plasma etching and x-ray photoelectron spectrometry measurements were made without breaking vacuum, confirming that the nitrogen plasma has selectivity for removal of P4VP over PS.

Self-Assembled Structures of Diblock Copolymer/Homopolymer Blends through Multiple Complementary Hydrogen Bonds

A poly(styrene-b-vinylbenzyl triazolylmethyl methyladenine) (PS-b-PVBA) diblock copolymer and a poly(vinylbenzyl triazolylmethyl methylthymine) (PVBT) homopolymer were prepared through a combination of nitroxide-mediated radical polymerizations and click reactions. Strong multiple hydrogen bonding interactions of the A···T binary pairs occurred in the PVBA/PVBT miscible domain of the PS-b-PVBA/PVPT diblock copolymer/homopolymer blend, as evidenced in Fourier transform infrared and 1H nuclear magnetic resonance spectra. The self-assembled lamellar structure of the pure PS-b-PVBA diblock copolymer after thermal annealing was transformed to a cylinder structure after blending with PVBT at lower concentrations and then to a disordered micelle or macrophase structure at higher PVBT concentrations, as revealed by small-angle X-ray scattering and transmission electron microscopy.

Fabrication of Two-Dimensional Arrays of Diameter-Tunable PS-b-P2VP Nanowires at the Air/Water Interface

Composite thin films with well-defined and parallel nanowires were fabricated from the binary blends of a diblock copolymer polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) and several homopolystyrenes (h-PSs) at the air/liquid interface through a facile technique, which involves solution self-assembly, interface adsorption, and further self-organization processes. It was confirmed that the nanowires that appeared at the air/water interface came from the cylindrical micelles formed in solution. Interestingly, the diameters of the nanowires are uniform and can be tuned precisely from 45 to 247 nm by incorporating the h-PS molecules into the micellar core. This parallel alignment of the nanowires has potential applications in optical devices and enables the nanowires to be used as templates to prepare functional nanostructures. The extent to which h-PS molecules with different molecular weights are able to influence the diameter control of the nanowires was also systematically investigated.