Transformation from Rod-Like to Diamond-Like Micelles by Thermally Induced Nucleation Self-Assembly

Controllable Self-Assembly Morphologies of PPV-Based Block Copolymers

Poly(p-phenylenevinylene) (PPV) is a classic semiconducting π-conjugated polymer with outstanding optical and electronic properties, which shows important applications in the fields of optoelectronic, such as organic light-emitting diodes (OLEDs), organic solar cells (OSCs), and organic field-effect transistors (OFETs). In the working process of the device, the microstate of PPV decides its property. Therefore, it is significant to achieve ordered morphologies based on PPV at micro scale. Due to the long rigid backbone and large area of delocalized electron, PPV has a strong tendency towards ordered aggregation through intermolecular π-π interaction, and "rod-coil" type block copolymer (BCP) based on PPV with a corona chain to improve the solubility is always built for self-assembly in situ solution. However, obtaining regular PPV based micro-/nano-structures in a controllable and uniform form remains challenging. In this review, we summarize the progresses in constructing multi-dimensional regular self-assembly morphologies based on PPV BCPs and exploring the application potential of these delicate functional nanomaterials. The molecular design strategy and growth mechanism can be extended to regulate the aggregation state of functional semiconducting conjugated polymers, which is beneficial to improving their performance in application of microelectronics, optoelectronics, biology and so on.

Morphologically Tunable Rectangular Platelets Self-Assembled from Diblock Molecular Brushes Containing Azopyridine Pendants

Two-dimensional (2D) platelet structures are of growing importance as building blocks for the preparation of optical and electrical devices. However, the creation of morphologically tunable rectangular platelets through polymer self-assembly still remains a challenge. Herein, we describe a rational strategy for the fabrication of 2D rectangular platelets by stacking azopyridine-containing diblock molecular brushes in two dimensions in a selective solvent. Amphiphilic PEG-co-(PtBA-g-PAzoPy) DMBs with poly(ethylene glycol) (PEG) block, poly(t-butyl acrylate) (PtBA) backbone, and poly(6-(4-(4-pyridyazo)phenoxy)-hexyl methacrylate) (PAzoPy) brush were synthesized by sequential reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization. Various rectangular platelets were obtained via the solution self-assembly of PEG-co-(PtBA-g-PAzoPy) through a heating-cooling-aging process in which the morphology and size of platelets could be controlled by adjusting the composition of DMBs as well as the solvent polarity. In addition, we investigated the metal chelation ability and H-bonding-assisted co-assembly capability of PEG-co-(PtBA-g-PAzoPy). The results displayed that 2D hybrids and flower-like platelets were formed, respectively. Our study presents an efficient method to fabricate rectangular platelets with tunable morphologies.

Apparent symmetry rising induced by crystallization inhibition in ternary co-crystallization-driven self-assembly

The concept of apparent symmetry rising, opposite to symmetry breaking, was proposed to illustrate the unusual phenomenon that the symmetry of the apparent morphology of the multiply twinned particle is higher than that of its crystal structure. We developed a unique strategy of co-crystallization-driven self-assembly of amphiphilic block copolymers PEO-b-PS and the inorganic cluster silicotungstic acid to achieve apparent symmetry rising of nanoparticles under mild conditions. The triangular nanoplates triply twinned by orthogonal crystals (low symmetry) have an additional triple symmetry (high symmetry). The appropriate crystallization inhibition of short solvophilic segments of the block copolymers favors the oriented attachment of homogeneous domains of hybrid nanoribbons, and consequently forms kinetic-controlled triangular nanoplates with twin grain boundaries.

Regulation of the nanostructures self-assembled from an amphiphilic azobenzene homopolymer: influence of initial concentration and solvent solubility parameter

The control over the morphology and nanostructure of soft nanomaterials self-assembled from amphiphilic polymers is of high interest, but is still challenging. Herein, we manipulate the morphology of bowl-shaped nanoparticles by changing initial polymer concentrations, and prepare nanotubes and nanowires, both twisted and not, by using solvents with different solubility parameters. An amphiphilic azobenzene homopolymer (poly(4-(phenyldiazenyl)phenyl methacrylamide), PAzoMAA) is designed and synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization, which can self-assemble into bowl-shaped nanoparticles promoted by the synergy of hydrogen bonding and π-π interaction. More significantly, the opening size of the bowl-shaped nanoparticles can be controlled by changing initial polymer concentrations. Nanotubes and nanowires, both twisted and not, are also obtained using a solvothermal method in alcohols. The relationship between the structure of the nanomaterials and the solubility parameters of the alcohols is investigated, revealing the molecular arrangement patterns of PAzoMAA in different nanostructures. Overall, we propose a facile strategy to manipulate the microstructure of bowl-shaped nanoparticles and one-dimensional nanomaterials by adjusting initial polymer concentration and solvent solubility parameters. Our study may bring new avenues for controlling the nanostructures of soft nanomaterials.

Morphological transition and transformation of 2D nanosheets by controlling the balance of ππ stacking interaction and crystalline driving forces

Nanoscale organic two-dimensional (2D) materials of block polymers (BCPs) have attracted interest on account of their wide potential applications in a range of fields. Herein, we design a new poly(p-phenylenevinylene) (PPV) based BCP that contains a triisopropylsilyl side chain and poly (2-vinyl pyridine) (P2VP) corona, which could assemble into a series of 2D square and rectangular micelles in isopropanol. The aspect ratios and the scales of the 2D micelles can be tuned in two ways, including altering the ratios of the P2VP and PPV-TIPS blocks and their concentrations. By precisely controlling the aspect ratios, micro-scale rod-like micelles are also obtained. From in depth studies of the morphology transition from rectangular micelles to rod-like or square micelles, it is found that the BCPs initially organize into fibers and then assemble into final micelles by the combined forces of π-π interactions and the crystalline force from TIPS side chains. Based on the balance of the two interactions, 2D circle-like micelles are also achieved by heterogenous co-assembly of two kinds of polymers with different cores.

Morphologically Tunable Supramolecular Rectangular Microsheet and Microsaw Constructed by Hierarchical Self-assembly Based on Hydrogen Bonds

Amino acid derivative TDAV as new building blocks for two-dimensional (2D) supramolecular assembly has been designed. Various square and rectangular microsheets are achieved and the aspect ratios are precisely regulated by controlling the polarity of cosolvent or water content. By the introduction of chirality, the novel microsaw is also achieved. It provides a new approach to prepare various kinds of unique supramolecular 2D materials with controllable shapes and sizes for future biological applications. This article is protected by copyright. All rights reserved.

Transformation of Amorphous Nanobowls to Crystalline Ellipsoids Induced by Trans-Cis Isomerization of Azobenzene

The stimuli-responsive transition of nanostructures from amorphous to crystalline state is of high interest in polymer science, but is still challenging. Herein, we demonstrate the transformation of amorphous nanobowls to crystalline ellipsoids triggered by UV induced trans-cis isomerization, using an azobenzene-containing amphiphilic homopolymer (PAzoAA) as building block. The amide bond and azobenzene pendants are introduced to the side chain of PAzoAA to afford hydrogen bonding and π-π interaction, which promotes the formation of nanobowls rather than spherical nanostructures. Upon exposed to UV irradiation, trans-cis isomerization of azobenzene pendants occurs, leading to the increase of hydrophilicity and destruction of π-π interaction, further resulting in the disassembly of the nanobowls. Then the PAzoAA re-assembles to form crystalline ellipsoids instead of amorphous nanostructures when recovered at 70°C without UV light. We further confirm that the high incubation temperature after UV irradiation is critical for the cis-trans transformation and the high mobility of the polymer chains to facilitate the regular rearrangement of azobenzene pendants. Overall, we propose a facile method to achieve the transformation of amorphous nanobowls to crystalline ellipsoids, which may bring new insight into preparation of crystalline nanoparticles using amorphous precursors. This article is protected by copyright. All rights reserved.

Bottom-up supramolecular assembly in two dimensions

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. Attracted by the interesting properties of two-dimensional inorganic analogues, monomers of different chemical natures are being explored for the assembly of dynamic 2D systems. Although many important discoveries have been already achieved, great challenges are still to be addressed in this field. Hierarchical multicomponent assembly, directional non-covalent growth and internal structural control are a just a few of the examples that will be discussed in this perspective about the exciting present and the bright future of two-dimensional supramolecular assemblies.

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. This perspective discusses the main strategies to direct the supramolecular self-assembly of organic monomers in 2D.