Creation of Hierarchically Ordered Nanophase Structures in Block Polymers Having Various Competing Interactions

Photo-induced bond breaking during phase separation kinetics of block copolymer melts: a dissipative particle dynamics study

Using a dissipative particle dynamics (DPD) simulation method, we study the phase separation dynamics in block copolymer (BCP) melts in d = 3, subjected to external stimuli such as light. An initial homogeneous BCP melt is rapidly quenched to a temperature T < T_c, where T_c is the critical temperature. We then allow the system to undergo alternate light "on" and "off" cycles. An on-cycle breaks the stimuli-sensitive bonds connecting both the blocks A and B in the BCP melt, and during the off-cycle, the broken bonds recombine. By simulating the effect of light, we isolate scenarios where phase separation begins with the light off (set 1); the cooperative interactions within the system allow it to undergo microphase separation. When the phase separation starts with the light on (set 2), the system undergoes macrophase separation due to bond breaking. Here, we report the role of alternate cycles on domain morphology by varying the bond-breaking probability for both set 1 and set 2, respectively. We observe that the scaling functions depend upon the conditions mentioned above that change the time scale of the evolving morphologies in various cycles. However, in all the cases, the average domain size respects the power-law growth: R(t) ∼t^φ at late times, where φ is the dynamic growth exponent. After a short-lived diffusive growth (φ∼ 1/3) at early times, φ illustrates a crossover from the viscous hydrodynamic (φ∼ 1) to the inertial hydrodynamic (φ∼ 2/3) regimes at late times.

Different Modes of Deformation of Soft Triangular Honeycombs at the Sub-5 nm Scale

Patterning on the sub-5 nm length scale is a contemporary challenge for further miniaturization of microelectronic circuits. Here, the first soft self-assembled triangular patterns are reported showing transitions between regular and two different kinds of isosceles (acute and obtuse angled) triangles on this length scale, formed by liquid crystalline honeycombs of polyphilic block molecules involving a fluorinated oligo(para-phenylene ethynylene) core. The type of formed triangular pattern depends on the degree and position of fluorination and on temperature. They are the first soft honeycombs combining tilted and nontilted organizations in a uniform nanostructure, where the tilted molecules in only one or two sides of the triangular prismatic cells dominate the shape and the size of the morphology.

Phase Behavior and Phase Diagram of Polystyrene-b-Poly(Perfluorooctylethyl Acrylates)

Fluorocontaining polymers bearing special properties are unique and important materials in modern society. In this work, we focused on the phase behavior and phase diagram of poly(styrene-block-perfluorooctylethyl acrylate) with a volume fraction varying from 0.2 to 0.8. Small-angle X-ray scattering and transmission electron microscopy showed the phase formation in the sequence of hexagonally packed cylinders (HEX) to lamellar layers (LAM) to inverse hexagonally packed cylinders (iHEX) in this series of block polymers. Wide-angle X-ray diffraction experiments proved that the fluorodomains of the LAM phases and the matrix of iHEX phases contained layered structures formed by the crystallization of fluorosegments. During heating, the self-assembled lattice remained intact even after the melting of fluorodomain, with barely changed lattice parameters. Such hierarchical structural formation was understood by chain conformation and domain interaction, which may provide new insight into the molecular design of advanced materials.

Patchy particles by self-assembly of star copolymers on a spherical substrate: Thomson solutions in a geometric problem with a color constraint

Confinement or geometric frustration is known to alter the structure of soft matter, including copolymeric melts, and can consequently be used to tune structure and properties. Here we investigate the self-assembly of ABC and ABB 3-miktoarm star copolymers confined to a spherical shell using coarse-grained dissipative particle dynamics simulations. In bulk and flat geometries the ABC stars form hexagonal tilings, but this is topologically prohibited in a spherical geometry which normally is alleviated by forming pentagonal tiles. However, the molecular architecture of the ABC stars implies an additional 'color constraint' which only allows even tilings (where all polygons have an even number of edges) and we study the effect of these simultaneous constraints. We find that both ABC and ABB systems form spherical tiling patterns, the type of which depends on the radius of the spherical substrate. For small spherical substrates, all solutions correspond to patterns solving the Thomson problem of placing mobile repulsive electric charges on a sphere. In ABC systems we find three coexisting, possibly different tilings, one in each color, each of them solving the Thomson problem simultaneously. For all except the smallest substrates, we find competing solutions with seemingly degenerate free energies that occur with different probabilities. Statistically, an observer who is blind to the differences between B and C can tell from the structure of the A domains if the system is an ABC or an ABB star copolymer system.

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.

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.

Precise syntheses of structurally possible all tetrablock quaterpolymers by a methodology combining living anionic polymerization with linking chemistry using 1 : 1 addition reaction

A methodology combining living anionic polymerization with linking chemistry using 1 : 1 addition reaction has been developed for the syntheses of tetrablock quaterpolymers composed of A, B, C, and D blocks.

Fabrication of Ordered Nanopattern by using ABC Triblock Copolymer with Salt in Toluene

Ordered nanopatterns of triblock copolymer polystyrene-block-poly(2-vinylpyridine)-block- poly (ethylene oxide)(PS-b-P2VP-b-PEO) have been achieved by the addition of lithium chloride (LiCl). The morphological and structural evolution of PS-b-P2VP-b-PEO/LiCl thin films were systematically investigated by varying different experimental parameters, including the treatment for polymer solution after the addition of LiCl, the time scale of ultrasonic treatment and the molar ratio of Li⁺ ions to the total number of oxygen atoms (O) in PEO block and the nitrogen atoms (N) in P2VP block. When toluene was used as the solvent for LiCl, ordered nanopattern with cylinders or nanostripes could be obtained after spin-coating. The mechanism of nanopattern transformation was related to the loading of LiCl in different microdomains.

Self-Assembled Morphologies of Linear and Miktoarm Star Triblock Copolymer Monolayers

Monolayers of linear and miktoarm star ABC triblock copolymers with equal A and C blocks were investigated using self-consistent field theory. Monolayers of ABC triblock copolymers were formed between two parallel surfaces that were attractive to the A and C blocks. The repulsive interaction parameter χ_ACN between the A and C blocks was chosen to be weaker than the A/B and B/C interactions, quantified by χ_ABN and χ_BCN, respectively, such that the B blocks were confined at the A/C interface, resulting in various B domains with different geometries and arrangements. It was observed that two variables, namely, the strength of the surface fields and the film thickness, were dominant factors controlling the self-assembly of the B blocks into various morphologies. For the linear triblock copolymers, the morphologies of the B domains included disks, stripes (parallel cylinders), and hexagonal networks (inverse disks). For the miktoarm star triblock copolymers, the competition between the tendency to align the junction points along a straight line and the constraint on their arrangement from the surface interactions led to richer ordered morphologies. As a result of the packing of the junction points of the ABC miktoarm star copolymers, a counterintuitive phase sequence from low-curvature phases to high-curvature phases with increasing length of B block was predicted. The study indicates that the self-assembly of monolayers of ABC triblock copolymers provides an interesting platform for engineering novel morphologies.

Formation of Nonclassical Ordered Phases of AB-Type Multiarm Block Copolymers

The formation of ordered phases from block copolymers is driven by a delicate balance between the monomer-monomer interaction and chain configurational entropy. The configurational entropy can be regulated by designed chain architecture, resulting in a new entropy-driven mechanism to control the self-assembly of ordered phases from block copolymers. An effective routine to regulate the configurational entropy is to utilize multiarm architecture, in which the entropic contribution to the free energy could be qualitatively controlled by the fraction of bridging configurations. As an illustration of this mechanism, the phase behavior of two AB-type multiarm block copolymers, B0-(Bi-Ai)m and (B1-Ai-B2)m where the minority A blocks form cylindrical or spherical domains, are examined using the self-consistent field theory (SCFT). The SCFT results demonstrate that the packing symmetry of the cylinders or spheres can be controlled by the length of the bridging B blocks. Several nonclassical ordered phases, including a novel square array cylinder with p4mm symmetry, are predicted to form from the AB-type multiarm block copolymers.

Hydrogen bonding strength effect on self-assembly supramolecular structures of diblock copolymer/homopolymer blends

The steric hindrance effect on the hydrogen bonding strength and self-assembly supramolecular structures of the PS-b-PVPh diblock copolymer when blended with P4VP and P2VP homopolymers was investigated.

Ionic Liquid-Triggered Redox Molecule Placement in Block Copolymer Nanotemplates toward an Organic Resistive Memory

The integration of functional components such as metal nanoparticles, metal salts, or ionic liquids with well-defined block copolymer (BCP) nanotemplates via noncovalent bond interactions has afforded hybrid functional materials. Here, we designed an ionic liquid (IL)-functionalized redox-active TEMPO (2,2,6,6-tetramethylpiperidine-N-oxy) radical (guest), investigated phase-selective incorporation/placement into host BCP nanostructured matrices, and established a rational approach to functionalize BCP templates. On-demand domain functionalization of poly(styrene-b-ethylene oxide) (PS-b-PEO) was triggered by ion-ionophore interaction, as verified by the suppression of PEO melting transition in DSC, and the swelling behavior of the PEO spherical domain in AFM, TEM, and X-ray scattering characterizations. The obtained BCP layer containing the redox-active TEMPO and IL was utilized as an active layer in the diode-structured memory device, which exhibited on/off resistive switching (on/off ratio >10³). Systematic placement of TEMPO and IL in the BCP spherical domain allowed for tuning of the switching characteristics and revealed that the formation of a discontinuous redox-active domain was critical for rewritable resistive switching.