Confined Self-Assembly Enables Stabilization and Patterning of Nanostructures in Liquid-Crystalline Block Copolymers

Phase Behaviors and Photoresponsive Thin Films of Syndiotactic Side-Chain Liquid Crystalline Polymers with High Densely Substituted Azobenzene Mesogens

Azobenzene-containing polymers (azopolymers) are a kind of fascinating stimuli-responsive materials with broad and versatile applications. In this work, a series of syndiotactic C1 type azopolymers of Pm-Azo-Cn with side-chain azobenzene mesogens of varied length alkoxy tails (n=1, 4, 8, 10) and different length alkyl spacers (m=6, 10) have been prepared via Rh-catalyzed carbene polymerization. The thermal properties and ordered assembly structures of thus synthesized side chain liquid crystalline polymers (SCLCPs) have been systematically investigated with differential scanning calorimetry (DSC), polarized optical microscopy (POM) and variable-temperature small/wide-angle X-ray scattering (SAXS/WAXS) analyses. P10-Azo-C1 and P10-Azo-C4 with shorter alkoxy tails exhibited hierarchical structures SmB/Colob and transformed into SmA/Colob at a higher temperature, while P10-Azo-C8 and P10-Azo-C10 with longer alkoxy tails only displayed side group dominated layered SmB phase and transformed into SmA phase at higher temperatures. For P6-Azo-C4 with a shorter spacer only showed a less ordered SmA phase owing to interference by partly coupling between the side chain azobenzene mesogens and the helical backbone. More importantly, the series high densely substituted syndiotactic C1 azopolymer thin films, exhibited evidently and smoothly reversible photoresponsive properties, which demonstrated promising photoresponsive device applications.

Manipulation of photoresponsive liquid-crystalline polymers and their applications: from nanoscale to macroscale

We summarize the molecular design of photoresponsive liquid-crystalline polymers, manipulation at multiple scales and various applications based on their intrinsic properties, providing an opportunity for future development in this field.

High Mechanical Strength and Multifunctional Microphase-Separated Supramolecular Hydrogels Fabricated by Liquid-Crystalline Block Copolymer

The development of multifunctional supramolecular hydrogels with high mechanical strength and multifunction is in high demand. In this work, the diblock copolymer poly(acrylamide-co-1-benzyl-3-vinylimidazolium bromide)-block-polyAzobenzene is synthesized through reversible addition-fragmentation chain transfer polymerization. The dynamic host-guest interactions between the host molecule cucurbit[8] uril and guest units are used to fabricate a 3D network of supramolecular hydrogels. Investigations on the properties of the supramolecular hydrogels show that the tensile stress of the sample is 1.46 MPa, eight times higher than that of hydrogel without liquid-crystalline block copolymer, and the self-healing efficiency of the supramolecular hydrogels at room temperature is 88.3% (fracture stress) and 100% (fracture strain) after 24 h. Results show that microphase-separated structure plays a key role in the high-strength hydrogel, whereas the host-guest interaction endows the hydrogel with self-healing properties. The supramolecular hydrogels with high mechanical strength, photo-responsivity, injectability, and biocompatibility can be used in various potential applications.

Interfacial and confined molecular-assembly of poly(3-hexylthiophene) and its application in organic electronic devices

Poly(3-hexylthiophene) (P3HT) is a typical conducting polymer widely used in organic thin-film transistors, polymer solar cells, etc., due to good processability and remarkable charging carrier and hole mobility. It is known that the ordered structure assembled by π-conjugated P3HT chains could promote the performance of electronic devices. Interfacial and confined molecular-assembly is one effective way to generate an ordered structure by tuning surface geometry and substrate interaction. Great efforts have been made to investigate the molecular chain assembly of P3HT on a curved surface that is confined to different geometry. In this report, we review the recent advances of the interfacial chain assembly of P3HT in a flat or curved confined space and its application to organic electronic devices. In principle, this interfacial assembly of P3HT at a nanoscale could improve the electronic properties, such as the current transport, power conversion efficiency, etc. Therefore, this review on interfacial and confined assembly of P3HT could give general implications for designing high-performance organic electronic devices.

Mechanically mutable polymer enabled by light

Human skin is a remarkable example of a biological material that displays unique mechanical characters of both soft elasticity and stretchability. However, mimicking these features has been absent in photoresponsive soft matters. Here, we present one synthetic ABA-type triblock copolymer consisting of polystyrene as end blocks and one photoresponsive azopolymer as the middle block, which is stiffness at room temperature and shows a phototunable transition to soft elastics athermally. We have synthesized an elastics we term "photoinduced soft elastomer," where the photo-evocable soft midblock of azopolymer and the glassy polystyrene domains act as elastic matrix and physical cross-linking junctions, respectively. On the basis of the photoswitchable transformation between stiffness and elasticity at room temperature, we demonstrated precise control over nanopatterns on nonplanar substrates especially adaptable in the human skin and fabrication of packaged perovskite solar cells, enabling the simple, human-friendly, and controllable approach to be promising for mechanically adaptable soft photonic and electronic packaging applications.

Photo-controlled self-assembly behavior of novel amphiphilic polymers with a rosin-based azobenzene group

Novel ‘bola’ rosin-based photo-responsive amphiphilic polymers PMPn show an extremely high photoresponsive efficiency and various assembly morphological changes.

Supramolecular Chirality Transfer toward Chiral Aggregation: Asymmetric Hierarchical Self-Assembly

Self-assembly, as a typical bottom-up strategy for the fabrication of functional materials, has been applied to fabricate chiral materials with subtle chiral nanostructures. The chiral nanostructures exhibit great potential in asymmetric catalysis, chiral sensing, chiral electronics, photonics, and even the realization of several biological functions. According to existing studies, the supramolecular chirality transfer process combined with hierarchical self-assembly plays a vital role in the fabrication of multiscale chiral structures. This progress report focuses on the hierarchical self-assembly of chiral or achiral molecules that aggregate with asymmetric spatial structures such as twisted bands, helices, and superhelices in different environments. Herein, recent studies on the chirality transfer induced self-assembly based on a variety of supramolecular interactions are summarized. In addition, the influence of different environments and the states of systems including solutions, condensed states, gel systems, interfaces on the asymmetric hierarchical self-assembly, and the expression of chirality are explored. Moreover, both the driving forces that facilitate chiral bias and the supramolecular interactions that play an important role in the expression, transfer, and amplification of the chiral sense are correspondingly discussed.

Azopolymer-Based Nanoimprint Lithography: Recent Developments in Methodology and Applications

Nanofabrication on soft polymeric surfaces is an essential process in many fields, for example, chip manufacturing, microfluidics, high efficiency solar cells, and anticounterfeiting. In order to achieve these applications, various nanofabrication methods have been explored. Among them, nanoimprint lithography (NIL) has drawn worldwide attention because of its cheap and fast processability. In this minireview, an overview of azopolymer-based NIL is provided. Since their discovery, azopolymers have demonstrated versatile photoresponsive characteristics due to their unique physical and chemical properties that originate from the photoisomerization of azobenzene chromophores. As such, two aspects are reported in this minireview. On the one hand, various azopolymers showing photofluidization and photoswitchable glass transition temperatures have been developed, thus facilitating methodological advancements in NIL. On the other hand, these on-demand NIL methods provide greater opportunities for azopolymer-based applications, such as templating of optics, directional photo-manipulation of nanopatterns, and micro photo-actuators. Also the challenges are discussed that remain in this field.

Molecular engineering of stimuli-responsive, functional, side-chain liquid crystalline copolymers: synthesis, properties and applications

This review describes recent progress made in designing stimuli-responsive, functional, side-chain, end-on mesogen attached liquid crystalline polymers (LCPs).

Thermotropic Liquid Crystalline Polymers with Various Alkoxy Side Groups: Thermal Properties and Molecular Dynamics

Two series of thermotropic liquid-crystalline polymers (TLCPs) were synthesized by reacting various dialkoxy terephthalate units with hydroquinone (HQ) and 2,6-naphthalene diol (Naph). The dialkoxy terephthalate moieties used in this study include 2,5-diethoxyterephthalate, 2,5-dibutoxyterephthalate, and 2,5-dihexyloxy-terephthalate. All the TLCPs synthesized in this study formed nematic phases. The molecular motions according to the length of the dialkoxy side groups in the TLCPs were evaluated by 13C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy. The thermal properties and molecular dynamics of the TLCPs are found to be affected by the length of the dialkoxy side group and the aromatic diol unit in the main chain. Further, the thermal behaviors, liquid crystalline mesophases, and degree of crystallinity of the two series of TLCPs, i.e., HQ- and Naph-TLCPs, are compared.

Photoreversible Order-Disorder Transition in an Ionic Liquid Solvated Block Polymer

The structure of a solution of poly(methyl methacrylate)-block-poly(benzyl methacrylate-stat-(4-phenylazophenyl methacrylate)) in the ionic liquid 1-ethyl-3-methyl imidazolium bis(trifluoromethanesulfonylimide) can be controlled with light. We explored the phase behavior of this block polymer at a concentration of 30 wt % as a function of temperature. Remarkably, this solution shows ordering into hexagonally closed packed spheres (HCP) upon heating under visible light, as confirmed by small-angle X-ray scattering. Small amplitude oscillatory shear rheology was used to demonstrate that the system could readily be converted between HCP and disorder by switching between visible and UV light wavelengths at 100 °C. This switching was cycled six times, without any noticeable change in the ordered or disordered state. The dependence on illuminating wavelength arises from the changes in polarity of the azobenzene moiety, which modulates its solubility in this ionic liquid to a significant extent. This is the first example of reversible light-triggered ordering of a "coil-coil" block polymer, a phenomenon that has been previously observed only in liquid crystalline systems.

Photoresponsive polymers with multi-azobenzene groups

Photoresponsive polymers with multi-azobenzene groups are reviewed and their potential applications in photoactuation, photo-patterning, and photoinduced birefringence are introduced.