Molecular-scale substrate anisotropy, crowding and division drive collective behaviours in cell monolayers.

The ability of cells to reorganize in response to external stimuli is important in areas ranging from morphogenesis to tissue engineering. While nematic order is common in biological tissues, it typically only extends to small regions of cells interacting via steric repulsion. On isotropic substrates, elongated cells can co-align due to steric effects, forming ordered but randomly oriented finite-size domains. However, we have discovered that flat substrates with nematic order can induce global nematic alignment of dense, spindle-like cells, thereby influencing cell organization and collective motion and driving alignment on the scale of the entire tissue. Remarkably, single cells are not sensitive to the substrate's anisotropy. Rather, the emergence of global nematic order is a collective phenomenon that requires both steric effects and molecular-scale anisotropy of the substrate. To quantify the rich set of behaviours afforded by this system, we analyse velocity, positional and orientational correlations for several thousand cells over days. The establishment of global order is facilitated by enhanced cell division along the substrate's nematic axis, and associated extensile stresses that restructure the cells' actomyosin networks. Our work provides a new understanding of the dynamics of cellular remodelling and organization among weakly interacting cells.

Design of Surface-Aligned Main-Chain Liquid-Crystal Networks Prepared under Ambient, Light-Free Conditions Using the Diels-Alder Cycloaddition.

Surface-aligned liquid-crystal networks (LCNs) offer a solution for developing functional materials capable of performing a range of tasks, including actuation, shape memory, and surfaces patterning. Here we show that Diels-Alder cycloaddition can be used to prepare the backbone of planar aligned LCNs under mild ambient conditions without the addition of additives or UV irradiation. The mechanical properties of the networks have robust viscoelastic modulus and stiffness with a reversible local free volume change upon physical aging. This study shows new opportunities to design surface-aligned LCNs based on additive free step-growth Diels-Alder polymerization and enables the potential to incorporate a wider range of photochromic materials into LCNs.

Controlled Diels-Alder "Click" Strategy to Access Mechanically Aligned Main-Chain Liquid Crystal Networks.

Aligned liquid crystal polymers are materials of interest for electronic, optic, biological and soft robotic applications. The manufacturing and processing of these materials have been widely explored with mechanical alignment establishing itself as a preferred method due to its ease of use and widespread applicability. However, the fundamental chemistry behind the required two-step polymerization for mechanical alignment has limitations in both fabrication and substrate compatibility. In this work we introduce a new protection-deprotection approach utilizing a two-stage Diels-Alder cyclopentadiene-maleimide step-growth polymerization to enable mild yet efficient, fast, controlled, reproducible and user-friendly polymerizations, broadening the scope of liquid crystal systems. Thorough characterization of the films by DSC, DMA, POM and WAXD show the successful synthesis of a uniaxially aligned liquid crystal network with thermomechanical actuation abilities.

Thermal Energy Harvest and Reutilization by the Combination of Thermal Conducting Reactive Mesogens and Heat-Storage Mesogens.

Utilizing a newly programmed and synthesized heat storage mesogen (HSM) and reactive mesogen (RM), advanced heat managing polymer alloys that exhibit high thermal conductivity, high latent heat, and phase transition at high temperatures were developed for use as smart thermal energy harvesting and reutilization materials. The RM in the heat-managing RM-HSM polymer alloy was polymerized to form a robust polymeric network with high thermal conductivity. The phase-separated HSM domains between RM polymeric networks absorbed and released a lot of thermal energy in response to changes in the surrounding temperature. For the fabrication of smart heat-managing RM-HSM polymer alloys, the composition and polymerization temperature were optimized based on the constructed phase diagram and thermal energy managing properties of the RM-HSM mixture. From morphological investigation and thermal analysis, it was realized that the heat storage capacity of polymer alloys depends on the size of the phase-separated HSM domain. The structure-morphology-property relationship of the heat managing polymer alloys was built based on the combined techniques of thermal, scattering, and morphological analysis. The newly developed mesogen-based polymer alloys can be used as smart thermal energy-harvesting and reutilization materials.

Hierarchical Hybrid Nanostructures Constructed by Fullerene and Molecular Tweezer.

For the construction of well-defined hierarchical superstructures of pristine [60]fullerene (C60) arrays, pyrene-based molecular tweezers (PT) were used as host molecules for catching and arranging C60 guest molecules. The formation of host-guest complexes was systematically studied in solution as well as in the solid state. Two-dimensional proton nuclear magnetic resonance spectroscopic studies revealed that PT-host and C60-guest complexes were closely related to the molecular self-assembly of PT. Ultraviolet and fluorescence spectroscopic titrations indicated the formation of stable 1:1 and 2:1 (PT/C60) complexes. From the nonlinear curve-fitting analysis, equilibrium constants for the 1:1 (log K1) and 2:1 (log K2) complexes were estimated to be 4.96 and 5.01, respectively. X-ray diffraction results combined with transmission electron microscopy observations clearly exhibited the construction of well-defined layered superstructures of the PT-host and C60-guest complexes. From electron mobility measurements, it was demonstrated that the well-defined hierarchical hybrid nanostructure incorporating a C60 array exhibited a high electron mobility of 1.7 × 10-2 cm2 V-1 s-1. This study can provide a guideline for the hierarchical hybrid nanostructures of host-guest complex and its applications.

Programmed Hierarchical Hybrid Nanostructures from Fullerene-Dendrons and Pyrene-Dendrons.

The construction of fullerene (C60 ) hierarchical nanostructures with the help of amphiphilic molecules remains a challenging task in nanoscience and nanotechnology. Utilizing the host-guest complex concept, sub-10 nm layered superstructures are constructed from a monofunctionalized C60 dendron (C60 D, guest) and tweezer-like pyrene dendron (PD, host). Since C60 D and PD are asymmetric shape amphiphiles having liquid crystal (LC) dendrons, both C60 D and PD construct head-to-head bilayer superstructures by themselves. From fluorescence titration experiments, it is realized that the host-guest complex shows 1:1 stoichiometric binding with a binding constant (Ksv = 2.45 × 105 m-1 ). Based on the morphological observations and scattering analyses, it is found that buckle-like asymmetric building blocks (C60 D·PD) are self-assembled by the host-guest complex and construct multilayer hybrid nanostructures. The hierarchical hybrid nanostructures consist of the self-assembled C60 D·PD bilayer with a 2D C60 ·P nanoarray sandwiched between LC dendrons. This advanced strategy is expected to be a practicable and rational guideline for the fabrication of programmed hierarchical hybrid nanostructures.

Kinetically Controlled Polymorphic Superstructures of Pyrene-Based Asymmetric Liquid Crystal Dendron: Relationship Between Hierarchical Superstructures and Photophysical Properties.

To understand the relationship between kinetically controlled hierarchical superstructures and photophysical properties, pyrene-based asymmetric liquid crystal (LC) dendrons (abbreviated as PD) were newly synthesized by covalently attaching a pyrene moiety (P) at a biphenyl-based LC dendritic group (D). The phase transition behavior of PD has been systematically studied with a combined technique of thermal analysis, microscopy, spectroscopy, and scattering analysis. PD formed two different crystalline structures depending on the cooling rate: a stable crystalline phase (Ks , slow cooling) and a metastable crystalline phase (Kms , quenching). The kinetically controlled molecular packing structures of PD depend on the competition and cooperation of intermolecular physical interactions with nanophase separation. Upon slow cooling, the PD dimer formed by intermoelcular H-bonding constructed a layered hierarchical structure with the help of nanophase separation. Owing to the strong π-π stacking (J-aggregation) with weak H-bondings, the PD dimer in the layer was slightly tilted to give a monoclinic layered structure with a periodic layer d-spacing of 6.6 nm. In contrast, the metastable Kms phase formed by the quenching process showed a significant tilt of the PD dimer in the layer (d-spacing=4.4 nm) due to the weak π-π stacking (H-aggregation) and the strong H-bondings.

Interfacial Engineering for the Synergistic Enhancement of Thermal Conductivity of Discotic Liquid Crystal Composites.

To develop an advanced heat transfer composite, a deeper understanding of the interfacial correlation between matrix and filler is of paramount importance. To verify the effect of interfacial correlations on the thermal conductivity, the conductive fillers such as expanded graphite (EG) and boron nitride (BN) are introduced in the discotic liquid crystal (DLC)-based polymeric matrix. The DLC matrix exhibits better interfacial affinity with EG compared to BN because of the strong π-π interactions between EG and DLC. Thanks to its excellent interfacial affinity, the EG-DLC composites show a synergistic increment in thermal conducting performance.

Azobenzene Molecular Machine: Light-Induced Wringing Gel Fabricated from Asymmetric Macrogelator.

To develop light-triggered wringing gels, an asymmetric macrogelator (1AZ3BP) was newly synthesized by the chemically bridging a photoisomerizable azobenzene (1AZ) molecular machine and a biphenyl-based (3BP) dendron with a 1,4-phenylenediformamide connector. 1AZ3BP was self-assembled into a layered superstructure in the bulk state, but 1AZ3BP formed a three-dimensional (3D) network organogel in solution. Upon irradiating UV light onto the 3D network organogel, the solvent of the organogel was squeezed and the 3D network was converted to the layered morphology. It was realized that the metastable 3D network organogels were fabricated mainly due to the nanophase separation in solution. UV isomerization of 1AZ3BP provided sufficient molecular mobility to form strong hydrogen bonds for the construction of the stable layered superstructure. The light-triggered wringing gels can be smartly applied in remote-controlled generators, liquid storages, and sensors.

Construction of Polymer-Stabilized Automatic MultiDomain Vertical Molecular Alignment Layers with Pretilt Angles by Photopolymerizing Dendritic Monomers under Electric Fields.

The synthesized itaconic acid-based dendritic amphiphile (Ita3C12) monomers and the methacryl polyhedral oligomeric silsesquioxane (MAPOSS) cross-linkers were directly introduced for the construction of automatic vertical alignment (auto-VA) layers in the host nematic liquid crystal (NLC) medium. The auto-VA layer can be stabilized by irradiating UV light. For the automatic fabrication of a polymer-stabilized multidomain VA (PS auto-MDVA) layer with a pretilt angle, Ita3C12 and MAPOSS were photopolymerized under the electric field by irradiating UV light on the multidomain electrode cell. Mainly because of the pretilted NLC at zero voltage, the electro-optic properties of the PS auto-MDVA cell were dramatically improved. From the morphological observations combined with surface chemical analyses, it was found that various sizes of protrusions on the solid substrates were automatically constructed by the two-step mechanisms. We demonstrated the PS auto-MDVA cell with the enhancement of electro-optic properties as a single-step process and investigated how the protrusions were automatically developed during the polymer stabilization.

Multifunctional Optical Thin Films Fabricated by the Photopolymerization of Uniaxially Oriented Lyotropic Liquid Crystal Monomers for Electro-Optical Devices.

A multifunctional optical thin film (MOTF) is fabricated by coating the newly synthesized perylene-based reactive mesogen (PBRM) and stabilized by the subsequent photopolymerization. Based on the spectroscopic results combined with morphological observations, it is found that nematic liquid crystal (NLC) is aligned parallel to the molecular long axis of PBRM not only due to the long-range physical anchoring effect but also due to the short-range molecular physical interactions between alignment layer and NLC molecules. From the electro-optical properties of LC test cells fabricated with the PBRM MOTF, it is clearly demonstrated that the PBRM MOTF can work as the planar LC alignment layer as well as the in-cell coatable polarizer. The coatable PBRM MOTF from lyotropic chromonic reactive mesogens can pave a new way for the flexible optoelectronic devices.

Heat Transfer Organic Materials: Robust Polymer Films with the Outstanding Thermal Conductivity Fabricated by the Photopolymerization of Uniaxially Oriented Reactive Discogens.

For the development of advanced heat transfer organic materials (HTOMs) with excellent thermal conductivities, triphenylene-based reactive discogens, 2,3,6,7,10,11-hexakis(but-3-enyloxy)triphenylene (HABET) and 4,4',4″,4‴,4'''',4'''''-(triphenylene-2,3,6,7,10,11-hexaylhexakis(oxy))hexakis(butane-1-thiol) (THBT), were synthesized as discotic liquid crystal (DLC) monomers and cross-linkers, respectively. A temperature-composition phase diagram of HABET-THBT mixtures was first established based on their thermal and microscopic analyses. From the experimental results, it was realized that the thermal conductivity of DLC HTOM was strongly affected by the molecular organizations on a macroscopic length scale. Macroscopic orientation of self-assembled columns in DLC HTOMs was effectively achieved under the rotating magnetic fields and successfully stabilized by the photopolymerization. The DLC HTOM polymer-stabilized at the LC phase exhibited the remarkable thermal conductivity above 1 W/mK. When the DLC HTOM was macroscopically oriented, the thermal conductivity was estimated to be 3 W/mK along the in-plane direction of DLC molecule. The outstanding thermal conductivity of DLC HTOM should be originated not only from the high content of two-dimensional aromatic discogens but also from the macroscopically oriented and self-assembled DLC. The newly developed DLC HTOM with an outstanding thermal conductivity as well as with an excellent mechanical sustainability can be applied as directional heat dissipating materials in electronic and display devices.

Self-Assembled Hierarchical Superstructures from the Benzene-1,3,5-Tricarboxamide Supramolecules for the Fabrication of Remote-Controllable Actuating and Rewritable Films.

The well-defined hierarchical superstructures constructed by the self-assembly of programmed supramolecules can be organized for the fabrication of remote-controllable actuating and rewritable films. To realize this concept, we newly designed and synthesized a benzene-1,3,5-tricarboxamide (BTA) derivative (abbreviated as BTA-3AZO) containing photoresponsive azobenzene (AZO) mesogens on the periphery of the BTA core. BTA-3AZO was first self-assembled to nanocolumns mainly driven by the intermolecular hydrogen-bonds between BTA cores, and these self-assembled nanocolumns were further self-organized laterally to form the low-ordered hexagonal columnar liquid crystal (LC) phase below the isotropization temperature. Upon cooling, a lamello-columnar crystal phase emerged at room temperature via a highly ordered lamello-columnar LC phase. The three-dimensional (3D) organogel networks consisted of fibrous and lamellar superstructures were fabricated in the BTA-3AZO cyclohexane-methanol solutions. By tuning the wavelength of light, the shape and color of the 3D networked thin films were remote-controlled by the conformational changes of azobenzene moieties in the BTA-3AZO. The demonstrations of remote-controllable 3D actuating and rewritable films with the self-assembled hierarchical BTA-3AZO thin films can be stepping stones for the advanced flexible optoelectronic devices.

Butterfly-Shaped Diphenylpyrimidine Molecule: Tunable Photophysical Properties by Molecular Self-Assembly Pathways.

To understand the relationships between chemical structures, molecular packing structures, and photophysical properties of organic materials, a butterfly shaped diphenylpyrimidine molecule (abbreviated as DPP-6C12) was newly synthesized [Park, M.; Choi, Y.-J.; Kim, D.-Y.; Hwang, S.-H.; Jeong, K.-U. Cryst. Growth Des. 2015, 15, 900-906]. By breaking the molecular symmetry and coplanarity of DPP-6C12, peculiar monotropic phase transitions were observed. Based on two-dimensional wide-angle X-ray diffraction and selected area electron diffraction, the molecular packing structures of ordered phases were identified, which were further confirmed by the computer simulations in the real and reciprocal spaces. Finally, we demonstrated that the photophysical properties of DPP-6C12 can be tuned by controlling the molecular packing structures with simple thermal treatments.

Multi-responsible chameleon molecule with chiral naphthyl and azobenzene moieties.

A photochromic chiral molecule with azobenzene mesogens and a (R)-configuration naphthyl moiety (abbreviated as NCA2M) was specifically designed and synthesized for the demonstration of chameleon-like color changes responding to multitudinous external stimuli, such as temperature, light and electric field. The basic phase transition behaviors of NCA2M were first studied by the combination of differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Based on the structure-sensitive X-ray diffraction results obtained at different temperatures, it was comprehended that the NCA2M molecule exhibited the tilted version of highly ordered smectic crystal phase with 5.45 nm layer thickness. Chiral nematic (N*) liquid crystals (LC) with helical superstructures were formed by doping the NCA2M photochromic chiral molecule in an achiral nematic (N) LC medium. By controlling the helical pitch length of N*-LC with respect to temperature, light and electric field, the wavelength of selectively reflected light from the N* photonic crystal was finely tuned. The light-induced color change of N*-LC film was the most efficient method for covering the whole visible region from blue to green and to red, which allowed us to fabricate remote-controllable photo-responsive devices.

Optically isotropic liquid crystal media formulated by doping star-shaped cyclic oligosiloxane liquid crystal surfactants in twin nematic liquid crystals.

The formation of optically isotropic liquid crystal (LC) media has been investigated by doping the star-shaped LC molecular surfactants (SiLC) into the rod-shaped twin LC host molecules (DiLC). The experimental phase diagram was constructed on the basis of differential scanning calorimetry (DSC) and then a theoretical calculation was conducted through a combined Flory-Huggins (FH)/Maier-Saupe-McMillan (MSM)/phase field (PF) model to account for the experimental results. The phase diagram of the SiLC/DiLC mixtures revealed the broad coexistence regions such as smectic A + crystal (SmA1 + Cr2), liquid + crystal (L1 + Cr2), and liquid + nematic (L1 + N2) at the intermediate composition along with the narrow single phase crystal (Cr2), smectic (SmA1), and nematic (N2) regions. The morphologies and structures of these coexistence regions were further confirmed by polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). At the 80/20 SiLC/DiLC composition, the optical anisotropy was induced under an alternating current (AC) electric field above its isotropization temperature. The formation of an optically isotropic LC medium in mixtures of the SiLC molecular surfactants and nematic LC host may allow us to develop new electro-optical devices.

Photoresponsive carbohydrate-based giant surfactants: automatic vertical alignment of nematic liquid crystal for the remote-controllable optical device.

Photoresponsive carbohydrate-based giant surfactants (abbreviated as CELAnD-OH) were specifically designed and synthesized for the automatic vertical alignment (VA) layer of nematic (N) liquid crystal (LC), which can be applied for the fabrication of remote-controllable optical devices. Without the conventional polymer-based LC alignment process, a perfect VA layer was automatically constructed by directly adding the 0.1 wt % CELA1D-OH in the N-LC media. The programmed CELA1D-OH giant surfactants in the N-LC media gradually diffused onto the substrates of LC cell and self-assembled to the expanded monolayer structure, which can provide enough empty spaces for N-LC molecules to crawl into the empty zones for the construction of VA layer. On the other hand, the CELA3D-OH giant surfactants forming the condensed monolayer structure on the substrates exhibited a planar alignment (PA) rather than a VA. Upon tuning the wavelength of light, the N-LC alignments were reversibly switched between VA and PA in the remote-controllable LC optical devices. Based on the experimental results, it was realized that understanding the interactions between N-LC molecules and amphiphilic giant surfactants is critical to design the suitable materials for the automatic LC alignment.

Hierarchical superstructures from a star-shaped molecule consisting of a cyclic oligosiloxane with cyanobiphenyl moieties.

Unconventional star-shaped liquid crystals (abbreviated as SiLCs) were successfully synthesized by chemically connecting four cyanobiphenyl anisotropic mesogens to the periphery of a super-hydrophobic and ultra-flexible cyclic tetramethyltetrasiloxane ring with flexible hexyl chains. Based on the combined experimental techniques of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), solid-state carbon-13 ((13)C) nuclear magnetic resonance (NMR) spectroscopy and one-dimensional (1D) wide-angle X-ray diffraction (WAXD), it was found that the SiLC molecule exhibited the monotropic phase transition from a LC phase to a crystalline phase. The crystalline phase was only detected during slow heating processes above its glass transition temperature, while a LC phase was formed both during cooling and during heating processes. The hierarchical superstructures were identified from the structure-sensitive 2D WAXD of the macroscopically oriented SiLC film and confirmed by selected area electron diffraction (SAED) of the SiLC single crystals. The molecular packing symmetry in the monoclinic unit cell was further investigated by computer simulations on the real and reciprocal spaces. Macroscopically oriented SiLC hierarchical superstructures on the different length scales may provide the targeted physical properties, which can allow us to apply SiLC molecules in the fields of electro-optical devices and nonlinear optics.

Dual photo-functionalized amphiphile for photo-reversible liquid crystal alignments.

Without the conventional polymer-based liquid crystal (LC) alignment process, a newly synthesized dual photo-functionalized amphiphile (abbreviated as ADMA1 ) was successfully applied as a robust photo-reversible LC alignment layer by self-assembly and photo-polymerization. The LC alignment layer constructed by directly adding dual photo-functionalized amphiphiles into LC media significantly cuts the manufacturing cost as well as opens new doors for the fabrication of novel electro-optical devices.