Liquid Crystal Templating Research Articles

Enhanced Alignment of Water-Soluble Polythiophene Using Cellulose Nanocrystals as a Liquid Crystal Template.

Cellulose nanocrystals (CNCs) are bioderived, rodlike particles that form a chiral nematic liquid crystal (LC) in water. In this work, CNCs were used to induce long-range order in a semiconducting polymer, poly[3-(potassium-4-butanoate) thiophene-2,5-diyl] (PPBT). When mixed with CNCs, it was found that PPBT was incorporated into the liquid crystal "template" to form ordered structures with highly birefringent domains, as observed under polarized light. We show that the π-π interactions between polymer chains, which contribute considerably to the energetics of the semiconducting system, are directly influenced by the presence and packing of the liquid crystal phase. Upon increasing the concentration of CNCs from the isotropic to chiral nematic regime, we observe a bathochromic shift in the UV-vis spectra and the emergence of the 0-0 vibrational peak, suggesting enhanced π-π stacking leading to chain coplanarization. Furthermore, the chiral nature of the PPBT/CNC mixture was evidenced by a negative peak in circular dichroism (CD) spectroscopy, promoting the notion that the polymer chains followed the helicoidal twist of the chiral nematic liquid crystal host. At high temperatures, the peak height ratios and overall intensities of the UV-vis and CD spectra associated with PPBT decreased as the chiral nematic pitch grew larger in size.

Mesoporous silica materials from diluted and concentrated solutions of nonionic fluorinated and ionic hydrogenated surfactants mixtures

Herein, mesostructured silica materials have been prepared through both the cooperative self-assembly and liquid crystal templating mechanisms by using mixtures of polyoxyethylene fluoroalkylether and cationic quaternary ammonium surfactants as building blocks. The nonionic surfactant/ionic surfactant/water phase diagram shows that a micellar phase (L1) was formed. The SAXS spectra of the two surfactants micellar phases are different from that of micelles constituted of only one component. This provides informations about the nature of the micelles, which are really mixed. A detailed investigation of the liquid crystals domain was also conducted, and results indicate the presence of a hexagonal mixed phase.Then, mesoporous silica materials with high specific surface area have been synthesized, using surfactant mixtures, and characterized by small angle X-ray scattering, transmission electron microscopy and nitrogen adsorption-desorption analysis. The SAXS patterns show two hexagonal porous networks, showing the presence of the dual porosity.

Molecular Simulations of the Synthesis of Periodic Mesoporous Silica Phases at High Surfactant Concentrations

Molecular dynamics simulations of a coarse-grained model are used to study the formation mechanism of periodic mesoporous silica over a wide range of cationic surfactant concentrations. This follows up on an earlier study of systems with low surfactant concentrations. We started by studying the phase diagram of the surfactant–water system and found that our model shows good qualitative agreement with experiments with respect to the surfactant concentrations where various phases appear. We then considered the impact of silicate species upon the morphologies formed. We have found that even in concentrated surfactant systems—in the concentration range where pure surfactant solutions yield a liquid crystal phase—the liquid-crystal templating mechanism is not viable because the preformed liquid crystal collapses as silica monomers are added into the solution. Upon the addition of silica dimers, a new phase-separated hexagonal array is formed. The preformed liquid crystals were found to be unstable in the prese...

Photopolymerization kinetics in and of self‐assembling lyotropic liquid crystal templates

ABSTRACTPhotopolymerization in and of lyotropic liquid crystal (LLC) template phases shows great promise for generating nanostructure in organic polymers. Interestingly, the order imposed on the polymerization system in LLCs significantly alters polymerization kinetics. The rate of polymerization of hydrophilic monomers increases with increasing LLC order, primarily due to monomer/polymer association with surfactant and the resulting decrease of growing polymer chain diffusion. Conversely, as LLC order increases, hydrophobic monomers become less segregated as nonpolar volume increases, which decreases polymerization rate. The efficiency of initiators is also dependent on LLC template order, further contributing to polymerization rate changes. When reactive surfactants are used, LLC mesophase, location of reactive group, and aliphatic tail length also affect polymerization kinetics. Overall, these photopolymerization kinetics directly relate to the segregation behavior and local order of reactive groups and thus can be used to probe nanostructure evolution, facilitating understanding and control of ultimate polymer nanostructure. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 471–489

Lyotropic liquid crystal-assisted synthesis of micro- and nanoparticles of silver

ABSTRACTA simple, one-step approach for the synthesis of micro- and nanoparticles of silver by employing a lyotropic liquid crystal (LLC) template is described. Anisotropic silver particles are synthesised by reducing an appropriate amount of precursor silver nitrate using a mild reducing agent ascorbic acid in presence of a hexagonal LLC medium, without the aid of any external stabilising agents. In this synthesis, precursor concentration, type of the reducing agent and LLC phase are found to significantly influence the particle size and morphology. Either a decrease in the concentration of silver nitrate or a change in the reducing agent, from ascorbic acid to sodium borohydride in the same reaction medium, yielded quasi-spherical nanoparticles. Besides, replacing the hexagonal LLC medium with a lamellar phase during the synthesis using ascorbic acid also resulted in the formation of spherical particles in nanometre scale. As a comparison, gold nanoparticle synthesis is carried out in hexagonal and lamellar LLC phases. Similar to the observations made in the silver particle synthesis, branched anisotropic particles are formed in the hexagonal phase and quasi-spherical particles are produced in the lamellar phase. A possible growth mechanism for the formation of these particles based on the phase structure of the LLC medium is discussed.

Electrodeposited MoSx films assisted by liquid crystal template with ultrahigh electrocatalytic activity for hydrogen evolution reaction

MoSx as a promising electrocatalyst for hydrogen evolution reaction (HER) has the active sites of rims and edges and inert sites of basal plane. A strategy to activate MoSx is to produce more unsaturated S or S vacancies on the inert plane by designing unique nanostructure. Herein, we report a facile electrodeposition assisted by liquid crystal template (LCT) to prepare MoSx film on ITO substrate (MoSx (LCT)). XPS confirms the state of Mo and S of the obtained MoSx film. SEM shows that there are many uniform disk bulges with the diameter of about 100 nm on the surface of MoSx (LCT), which may provide more rims and edges of MoSx. While the electrodeposited MoSx film in water (MoSx (H2O)) is a smooth plane structure. The electrochemical measurements show MoSx (LCT) exhibits an ultrahigh activity for HER with the small onsetpotential very close to that of Pt/C, which may be due to not only the uniform disk bulges but also the more unsaturated S atoms of MoSx (LCT). The electrodeposition assisted by LCT may be a novel strategy to prepare novel nanostructure and activate MoSx-based electrocatalysts for HER.

Nonionic Fluorinated Surfactant Removal from Mesoporous Film Using sc-CO2.

Surfactant templated silica thin films were self-assembled on solid substrates by dip-coating using a partially fluorinated surfactant R8F(EO)9 as the liquid crystal template. The aim was 2-fold: first we checked which composition in the phase diagram was corresponding to a 2D rectangular highly ordered crystalline phase and second we exposed the films to sc-CO2 to foster the removal of the surfactant. The films were characterized by in situ X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS) under CO2 pressure from 0 to 100 bar at 34 °C. GISAXS patterns reveal the formation of a 2-D rectangular structure at a molar ratio R8F(EO)9/Si equal to 0.1. R8F(EO)9 micelles have a cylindrical shape, which have a core/shell structure ordered in a hexagonal system. The core contains the R8F part and the shell is a mixture of (EO)9 embedded in the silica matrix. We further evidence that the extraction of the template using supercritical carbon dioxide can be successfully achieved. This can be attributed to both the low solubility parameter of the surfactants and the fluorine and ethylene oxide CO2-philic groups. The initial 2D rectangular structure was well preserved after depressurization of the cell and removal of the surfactant. We attribute the very high stability of the rinsed film to the large value of the wall thickness relatively to the small pore size.

Liquid crystal templating as an approach to spatially and temporally organise soft matter

Chemistry quickly moves from a molecular science to a systems science. This requires spatial and temporal control over the organisation of molecules and molecular assemblies. Whilst Nature almost by default (transiently) organises her components at multiple different length scales, scientists struggle to realise even relatively straightforward patterns. In the past decades, supramolecular chemistry has taught us the rules to precisely engineer molecular assembly at the nanometre scale. At higher length scales, however, we are bound to top-down nanotechnology techniques to realise order. For soft, biological matter, many of these top-down techniques come with serious limitations since the molecules generally show low susceptibilities to the applied stimuli. A new method is based on liquid crystal templating. In this hierarchical approach, a liquid crystalline host serves as the scaffold to order polymers or assemblies. Being a liquid crystal, the host material can be ordered at many different length scales and on top of that, is highly susceptible to many external stimuli, which can even be used to manipulate the liquid crystal organisation in time. As a result, we anticipate large control over the organisation of the materials inside the liquid crystalline host. Recently, liquid crystal templating was also realised in water. This suddenly makes this tool highly applicable to start organising more delicate biological materials or even small organisms. We review the scope and limitations of liquid crystal templating and look out to where the technique may lead us.

Watching mesoporous metal films grow during templated electrodeposition with in situ SAXS.

In this paper, we monitor the real-time growth of mesoporous platinum during electrodeposition using small-angle X-ray scattering (SAXS). Previously, we have demonstrated that platinum films featuring the 'single diamond' (Fd3m) morphology can be produced from 'double diamond' (Pn3m) lipid cubic phase templates; the difference in symmetry provides additional scattering signals unique to the metal. Taking advantage of this, we present simultaneous in situ SAXS/electrochemical measurement as the platinum nanostructures grow within the lipid template. This measurement allows us to correlate the nanostructure appearance with the deposition current density and to monitor the evolution of the orientational and lateral ordering of the lipid and platinum during deposition and after template removal. In other periodic metal nanomaterials deposited within any of the normal topology liquid crystal, mesoporous silica or block copolymer templates previously published, the template and emerging metal have the same symmetry, so such a study has not been possible previously.

Porous conducting polymer prepared through liquid crystal template for drug delivery

Unlike conventional controlled drug delivery systems where drug is released at a constant pre-programmed rate, drug release from conducting polymers (CPs) can be controlled through electrical stimuli and adjusted based on the patient's needs. However, owing to their low drug loading capacity and limited electrical responsiveness CP systems cannot currently be applied for systemic drug delivery or to treat chronic disease. To overcome that obstacle one approach is to fabricate porous CP structures. In this work, polypyrrole (PPy) was used owing to its electrical responsiveness and biocompatibility. Liquid crystals were used as a template through which PPy was grown. Dexamethasone phosphate was loaded as a dopant into PPy during polymerisation and its release was quantified by HPLC after the removal of liquid crystal; release could be modified by electrical stimulus. This system has potential applications in conditions where required drug dosing changes with time, such as in age-related macular degeneration.

Widely tunable photonic bandgap and lasing emission in enantiomorphic cholesteric liquid crystal templates

Widely tunable reflection and lasing emission in a dye-doped nematic liquid crystal refilled gradient-pitched enantiomorphic cholesteric liquid crystal polymer template.

The structure-property relationship of oxovanadium(IV) complexes in the wall framework of PMOs and their catalytic applications

Oxovanadium(IV) species could be considered as effective active sites in the catalytic oxidation reactions, but in the traditional vanadium-containing catalysts, the unstable and undispersible status of these active sites cause great limitation in their application. In this study, we present a novel approach to utilize the co-condensation of the silica source with oxovanadium organic complexes through the liquid-crystal templating (LCT) process introducing the vanadium species into the framework of periodically meosporous organosilicas (PMOs). Oxovanadium organic complexes are successfully obtained by the coordination effect between vanadium species and organic complexes. Thus the vanadium-containing PMOs catalysts are accordingly synthesized; the model structure of as-prepared catalysts is proposed and further verified by different characterization measurements. These vanadium-containing PMOs catalysts display the extremely stable and well-dispersed oxovanadium(IV) species in the framework, and due to this advanced structure, the corresponding excellent catalytic properties of these catalysts in styrene oxidation reaction are obtained.

Concurrent Deposition and Exfoliation of Nickel Hydroxide Nanoflakes Using Liquid Crystal Template and Their Activity for Urea Electrooxidation in Alkaline Medium

Nickel hydroxide nanoflakes (Ni(OH)2-NF) were prepared by chemical deposition and in situ exfoliation of nickel hydroxide layers confined in the aqueous domain of the liquid crystalline hexagonal template of Brij®78 surfactant. Using excess of sodium borohydride as a reducing agent generates concurrent excessive dynamic hydrogen bubbles which exfoliated and fragmented the nickel hydroxide layers precipitated within the soft hexagonal template. The physicochemical characterizations of Ni(OH)2-NF by using surface area analyser, X-ray diffraction (XRD), XPS and transmission electron microscope (TEM) showed the formation of α-Ni(OH)2 nanoflakes with thickness of 2–3 nm and have about 450 m2 g−1 surface area which is 20 times higher than that for bare nickel (bare-Ni) deposited without surfactant template. The electrocatalytic activity of the Ni(OH)2-NF catalyst for urea electrolysis was studied by cyclic voltammetry and chronoamperometry techniques. The Ni(OH)2-NF has shown a superior activity for the electrochemical oxidation of urea in alkaline solution and exhibits more than tenfold increase in activity in comparison with the bare-Ni deposit. The enhancement of urea electrooxidation activity was related to the superficial enhancement in the electroactive surface area of Ni(OH)2-NF. This new approach of deposition and in situ exfoliation by using liquid crystal template and hydrogen bubbles offers a new platform to nanostructuring wide range of catalysts with better catalytic performance.

Quaternized Chitosan-Capped Mesoporous Silica Nanoparticles as Nanocarriers for Controlled Pesticide Release.

Nanotechnology-based pesticide formulations would ensure effective utilization of agricultural inputs. In the present work, mesoporous silica nanoparticles (MSNs) with particle diameters of ~110 nm and pore sizes of ~3.7 nm were synthesized via a liquid crystal templating mechanism. A water-soluble chitosan (CS) derivative (N-(2-hydroxyl)propyl-3-trimethyl ammonium CS chloride, HTCC) was successfully capped on the surface of pyraclostrobin-loaded MSNs. The physicochemical and structural analyses showed that the electrostatic interactions and hydrogen bonding were the major forces responsible for the formation of HTCC-capped MSNs. HTCC coating greatly improved the loading efficiency (LC) (to 40.3%) compared to using bare MSNs as a single encapsulant (26.7%). The microstructure of the nanoparticles was revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The pyraclostrobin-loaded nanoparticles showed an initial burst and subsequent sustained release behavior. HTCC-capped MSNs released faster than bare MSNs in the initial stage. Pyraclostrobin-loaded HTCC-capped MSNs with half doses of pyraclostrobin technical demonstrated almost the same fungicidal activity against Phomopsis asparagi (Sacc.), which obviously reduced the applied pesticide and enhanced the utilization efficiency. Therefore, HTCC-decorated MSNs demonstrated great potential as nanocarriers in agrochemical applications.

High catalytic activities of palladium nanowires synthesized using liquid crystal templating approach

Synthesis of palladium (Pd) nanoparticles of various morphologies using swollen liquid crystalline (SLC) phases as structure directing templates is described in the present paper. The Pd precursor, bisdibenzyledene acetone palladium (Pd(DBA)2) was dissolved in the oil phase of a hexagonal lyotropic liquid crystalline phase. The characteristic nature of the hexagonal mesophase was confirmed using polarized optical microscopy. The hexagonal mesophases were exposed to hydrogen gas for the synthesis of Pd nanoparticles. The nanomaterials were characterized using UV–vis spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). These nanowires showed very good catalytic activity for reduction of 4- nitrophenol to 4-aminophenol when compared to the spherical Pd nanoparticles. A comparative study revealed that the catalytic activity of the nanowires was much better than even very small Pd nanoparticles that are reported in the literature. The nanowires also had a very good catalytic activity in Suzuki-Miyaura coupling reactions for the synthesis of biphenyl even using aryl chlorides as reactant.

Directing Soft Matter in Water Using Electric Fields

Directing the spatial organization of functional supramolecular and polymeric materials at larger length scales is essential for many biological and molecular optoelectronic applications. Although the application of electrical fields is one of the most powerful approaches to induce spatial control, it is rarely applied experimentally in aqueous solutions, since the low susceptibility of soft and biological materials requires the use of high fields, which leads to parasitic heating and electrochemical degradation. In this work, we demonstrate that we can apply electric fields when we use a mineral liquid crystal as a responsive template. Besides aligning and positioning functional soft matter, we show that the concentration of the liquid crystal template controls the morphology of the assembly. As our setup is very easy to operate and our approach lacks specific molecular interactions, we believe it will be applicable for a wide range of (aqueous) materials.

Efficient photocatalytic degradation of acid orange 7 over N-doped ordered mesoporous titania on carbon fibers under visible-light irradiation based on three synergistic effects

N-Doped ordered mesoporous titania on carbon fibers (NOMT/CFs) has been prepared by a liquid-crystal template (LCT) method with the aid of supercritical deposition. The NOMT/CFs product has been characterized by X-ray diffraction analysis, scanning electron and transmission electron microscopies, X-ray photoelectron spectroscopy, N2 sorption, UV/Vis diffuse reflectance spectrophotometry, and photoluminescence. The photoactivity of the obtained product in the degradation of acid orange 7 (AO7) solution under visible-light irradiation has been evaluated. A photocatalytic mechanism involving three synergistic effects of NOMT/CFs is proposed, whereby the titania acts as an electron/hole generator with its ordered mesostructure facilitating electron–hole separation, N-doping enhances visible-light adsorption, and the CFs serve to concentrate the pollutant around the active sites, favor electron transfer, and facilitate convenient recycling. Gas chromatography and mass spectrometry have been used to analyze the intermediates generated in the conversion of AO7, allowing a tentative decomposition pathway to be proposed. The effects of catalyst amount, pH, and initial AO7 concentration have been examined as operational parameters. The photocatalytic reactions follow pseudo-first-order kinetics and are discussed in terms of a modified Langmuir–Hinshelwood model.

Mesoporous cobalt hydroxide prepared using liquid crystal template for efficient oxygen evolution in alkaline media

Active, stable and economical electro-catalysts are very necessary for hydrogen production through water splitting by electrolysis. This work reports the synthesis and characterization of highly porous cobalt hydroxide (meso-Co-OH) formed by a simple chemical precipitation within the interstitial space of liquid crystal template. The physicochemical properties of the meso-Co-OH were characterized by surface area analyzer, X-ray diffraction, XPS, scanning and transmission electron microscopes. The meso-Co-OH exhibits low crystallinity and high surface area of 457±5m2/g with a mesoporous structure and pore diameter of 4.0±1.0nm. As confirmed by the electrochemical characterizations, the meso-Co-OH is highly effective electro-catalyst for oxygen evolution reaction (OER) at low applied potential and shows superior activity and stability than iridium oxide during long term water electrolysis in alkaline media. The meso-Co-OH shows oxygen evolution current and onset potential comparable to the IrO2 catalyst and the current is enhanced by 10 times than the values of bulk cobalt hydroxide electrode. For meso-Co-OH catalyst the oxygen evolution overpotential of 1.55V (vs. RHE) at current density of 25mA cm2 has been achieved in 1.0M KOH. The enhanced OER activity was attributed to the substantial increase in the active catalyst surface area due to the formation of mesoporous network within the cobalt hydroxide framework.

Patterning of Soft Matter across Multiple Length Scales

Controlling the organization of functional supramolecular materials at both short and long length scales as well as creating hierarchical patterns is essential for many biological and electrooptical applications. It remains however an extremely challenging objective to date, particularly in water‐based systems. In this work, it is demonstrated that water‐processable self‐assembling materials can be organized from micrometers to centimeters in any direction using liquid crystal templating in combination with photoaddressable command layers. The structural assemblies that are prepared are readily transformed into optically active π‐conjugated polymers after photopolymerization. After this step, the template may be removed to leave the functional material well‐organized on the substrate. The advantage of this approach is that it lacks specific molecular interactions and uses simple techniques such as spin coating and photoillumination and it may therefore be applied to a wide range of (aqueous) materials.

Ordered Mesoporous Nickel Sphere Arrays for Highly Efficient Electrocatalytic Water Oxidation

We report the preparation and use of the three-dimensionally ordered mesoporous Ni sphere arrays (3D-OMNiSA) as a highly effective OER catalyst in alkaline electrolyte. The 3D-OMNiSA is fabricated through lyotropic liquid crystal templating within a polymer inverse opal. The prepared 3D-OMNiSA catalyst exhibits a low overpotential of 254 mV at 10 mA cm–2 and a small Tafel slope of 39 mV decade–1, better than the commercial precious RuO2 catalyst. The mass activity (166.5 A g–1) and turnover frequency (0.0281 s–1) of 3D-OMNiSA are about 4.3 and 2.2 times that of RuO2, respectively. Additionally, this 3D-OMNiSA catalyst shows a high durability under harsh water oxidation cycling test. The outstanding OER performance of the 3D-OMNiSA could be attributed to the large surface area, efficient mass and charge transport, and high structural stability arising from the unique 3D hierarchical porous structure of the 3D-OMNiSA consisting of ordered close-packed mesoporous spheres.