Lyotropic Liquid Crystal Template Research Articles

Influence of Ionic Liquid and Light Intensity on a Polymer Nanostructure Formed in Lyotropic Liquid Crystalline Templates.

Utilizing self-assembled lyotropic liquid crystal (LLC) templates with radical photopolymerization shows promise in controlling polymer structure on the nanometer scale This control of nanostructure allows tailoring and enhancement of material properties not attainable in traditional polymerization in applications including hydrogels and stimuli-responsive systems. However, thermodynamically driven phase separation between the polymer and LLC templates often hinders the control of local polymer order and resultant polymer properties. This study investigates an alternative method to control the hydrogel nanostructure and avoid phase separation using imidazolium ionic liquids (ILs) in the LLC template while modulating the light intensity used in photopolymerization. The addition of the IL improves the thermodynamic stability and enhances the polymerization rate in the LLC system. The degree of LLC nanostructure retention is increased by increasing light intensities during polymerization. In addition, intermediate concentrations of cross-linker allow a balance between phase stability and cross-linking to lock in LLC morphology. With enhanced retention, the maximum water uptake is significantly higher compared with isotropic controls. These results demonstrate a method to increase the structure on the nanometer scale of a polymer by combining the addition of ILs with the proper selection of light intensity and cross-link density that allows access to unique hydrogel properties. These templated polymers demonstrate enhanced swelling and a stimuli response that show promise in applications ranging from drug delivery to water remediation.

Monitoring of Pore Orientation by in Operando Grazing Incidence Small-Angle X-ray Scattering during Templated Electrodeposition of Mesoporous Pt Films.

We have used in operando grazing incidence small-angle X-ray scattering (GISAXS) to monitor structural changes during templated electrodeposition of mesoporous platinum films on gold electrodes from a ternary lyotropic liquid crystalline mixture of aqueous hexachloroplatinic acid and the diblock copolymer surfactant Brij56. While the cylindrical micelles of the lyotropic liquid crystal (LLC) in the hexagonal phase have a center-to-center distance of 7.5 nm with a preferential alignment parallel to the electrode surface, the electrodeposited platinum films contain highly ordered mesopores arranged in a 2D hexagonal structure, with a center-to-center distance of about 8.5 nm and a preferential orientation perpendicular to the electrode surface. The progression of structural changes of the LLC template and the deposited mesoporous Pt could be monitored for the first time in operando by GISAXS: within the first 14 s of deposition, a nucleation burst of Pt coincides with a loss of preferential alignment of the LLC. Initially, the morphology of the 2-dimensionally nucleated Pt replicates the Au substrate. During the following 5 to 7 min, the growth morphology of the Pt film changes, and vertically aligned mesopores form. Our results indicate mutual interaction between the species involved in the electrodeposition and the LLC template, leading to a partial loss of horizontal orientation of the LLC during Pt nucleation before vertical rearrangement of the micelles to the electrode surface. The vertically aligned mesopores in the Pt and the possibility to produce freestanding films make these materials interesting in fields such as electrocatalysis, energy harvesting, and nanofluidics.

Thermoresponsive antifouling ultrafiltration membranes from mesophase templating

Nanostructured polymers synthesized by lyotropic liquid crystal (LLC) templates with normal hexagonal (H1) structure exhibit a 3D-continuous transport path, which makes them ideal for membrane separation application. Incorporating additional functionality, especially stimuli-responsiveness, in such an ordered structure provides even more application opportunities. In this work, we present the first successful synthesis of H1-structured thermoresponsive ultrafiltration (UF) membranes via LLC templating. The membrane contains thermoresponsive Pluronic P84 diacrylate (P84DA) which not only acts as the monomer and structure-directing amphiphile, but also enables the pore size change with temperature. Experimental studies reveal that the swelling capacity of H1-templated polymer as well as permeability and selectivity of the obtained membrane can be altered by changing the temperature. Increasing the temperature from 25 to 45 °C increases the normalized flux from 28 to 68 L m−2 h−1 μm and molecular weight cut-off (MWCO) from 2200 to 3900 Da. Furthermore, the membrane shows an outstanding fouling resistance against different solutes.

Lyotropic Liquid Crystal (LLC)-Templated Nanofiltration Membranes by Precisely Administering LLC/Substrate Interfacial Structure

Mesoporous materials based on lyotropic liquid crystal templates with precisely defined and flexible nanostructures offer an alluring solution to the age-old challenge of water scarcity. In contrast, polyamide (PA)-based thin-film composite (TFC) membranes have long been hailed as the state of the art in desalination. They grapple with a common trade-off between permeability and selectivity. However, the tides are turning as these novel materials, with pore sizes ranging from 0.2 to 5 nm, take center stage as highly coveted active layers in TFC membranes. With the ability to regulate water transport and influence the formation of the active layer, the middle porous substrate of TFC membranes becomes an essential player in unlocking their true potential. This review delves deep into the recent advancements in fabricating active layers using lyotropic liquid crystal templates on porous substrates. It meticulously analyzes the retention of the liquid crystal phase structure, explores the membrane fabrication processes, and evaluates the water filtration performance. Additionally, it presents an exhaustive comparison between the effects of substrates on both polyamide and lyotropic liquid crystal template top layer-based TFC membranes, covering crucial aspects such as surface pore structures, hydrophilicity, and heterogeneity. To push the boundaries even further, the review explores a diverse array of promising strategies for surface modification and interlayer introduction, all aimed at achieving an ideal substrate surface design. Moreover, it delves into the realm of cutting-edge techniques for detecting and unraveling the intricate interfacial structures between the lyotropic liquid crystal and the substrate. This review is a passport to unravel the enigmatic world of lyotropic liquid crystal-templated TFC membranes and their transformative role in global water challenges.

Improved mechanical properties of antimicrobial poly(N-[3-(dimethylaminopropyl)] methacrylamide) hydrogels prepared by free radical polymerization in the presence of cetyltrimethylammonium bromide as a lyotropic liquid crystal template

In this study, the effect of liquid crystal templates on improving the mechanical and antibacterial properties of poly(N-[3-(dimethylaminopropyl)] methacrylamide) hydrogels was investigated.

Synthesis of nano-ZnS by lyotropic liquid crystal template method for enhanced photodegradation of methylene blue

Layered liquid crystal templates were prepared in the ternary system of sodium dodecyl sulfate/n-amyl alcohol/water, supplemented with a homogeneous precipitation method to successfully prepare zinc sulfide nanomaterials. Various characterizations and photocatalytic degradation tests using methylene blue (MB) as a simulated pollutant were performed to analyze the fabricated samples. The results showed that the prepared ZnS nanomaterial with a cubic sphalerite structure and high purity obtained the particle size distribution between 60 and 200 nm due to the auxiliary effect of the solvent-liquid crystal template, resulting in high photodegradation performance for MB under xenon lamp irradiation, it showed.

Effect of the Duty Cycle of Flower-like Silver Nanostructures Fabricated with a Lyotropic Liquid Crystal on the SERS Spectrum.

Surface-enhanced Raman scattering (SERS) has been widely reported to improve the sensitivity of Raman spectra. Ordinarily, the laser is focused on the sample to measure the Raman spectrum. The size of the focused light spot is comparable with that of micro-nano structures, and the number of micro-nano structures contained in the light spot area (defined as duty cycle) will severely affect the spectrum intensity. In this study, flower-like silver nanostructures were fabricated with a soft lyotropic liquid crystal template in order to investigate the effect of duty cycle. They were observed under a scanning electron microscope, and their spectrum enhancement factor was computed with the obtained Raman spectrum. Then, their duty cycles were measured using a SERS substrate at different locations. A formula was derived to represent the relation between the duty cycle of the nanoflowers and the Raman spectral intensity. This work could promote the actual applications of SERS in high-sensitivity spectrum testing.

Simulated synthesis of silica nanowires by lyotropic liquid crystal template method

ABSTRACT Dissipative particle dynamics simulations were adopted to study the mechanism of lyotropic liquid crystal (LLC) formation and the synthesis process of silica nanowires by LLC template method. Simulation results show that the one-dimensional (1D) LLC channel can be formed at the Pluronic F127 concentration range of 61 ∼ 67%. With the increase of Pluronic F127 concentration, the diameter of LLC channel decreases and the deformation degree increases. The effect of PEO: PPO ratio on the diameter of LLC channel is slight. The appropriate PEO: PPO ratio of Pluronic is 40:70 for the formation of 1D LLC channel, as the deformation degree of channel is the smallest in this case. The effect of polymerisation degree on the diameter and deformation degree of LLC channel is both little. With the increase of TEOS concentration, the nanowire diameter increases rapidly at first, and then increases quite slowly. This work can provide guidance for silica nanowires synthesis by LLC template method.

Formation of ion gels by polymerization of block copolymer/ionic liquid/oil mesophases.

In this study, we introduce a new method of developing ion gels through polymerization of lyotropic liquid crystal (LLC) templates of monomer (styrene), cross-linker (divinylbenzene), ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate), and amphiphilic block copolymers (Pluronic F127). The polymerization of the oil phase boosts the mechanical properties of the ion-conducting electrolytes. We discuss the effect of tortuosity induced by crystalline domains and LLC structure on the conductivity of ion gels. The ion transport in polymerized LLCs (polyLLCs) can be controlled by changing the composition of the mesophases. Increasing the block copolymer concentration enhances the crystallinity of PEO blocks in the conductive domains, which slows down the dynamics of PEO chain and ion transport. We show that by adjusting the composition of LLC mesophases, the mechanical strength of ion gels can be increased one order of magnitude without compromising the ionic conductivity. The polyLLCs with 45/25/30 wt% (block copolymer/IL/oil) composition has storage modulus and ionic conductivity higher than 1 MPa and 3 mS cm-1 at 70 °C, respectively. The results suggest that LLC templating is a promising method to develop highly conductive ion gels, which provides advantages in terms of variety and processing.

Synthesis of mesoporous Co(OH)2 nanostructure film via electrochemical deposition using lyotropic liquid crystal template as improved electrode materials for supercapacitors application

Here we report synthesis of mesoporous structure containing two different phases of Co(OH)2 by different routes. The β-Co(OH)2 film and mesoporous α-Co(OH)2 powder synthesized using electrochemical deposition and chemical reduction methods, respectively using lyotropic liquid crystal (LLC) templates. These synthesized mesoporous β-Co(OH)2 film and α-Co(OH)2 powder were utilized as electrode materials for supercapacitors (SCs)application. The surface structure/morphology of these synthesized materials were analyzed by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), wide/low-angle X-ray diffraction (XRD) and Raman spectroscopy. The as-synthesized mesoporous β-Co(OH)2 film and mesoporous α-Co(OH)2 powder contain particles size in the range of 270–300 nm and 70–90 nm, respectively. For application as electrode in SCs, mesoporous β-Co(OH)2 film on FTO reveals enhanced electrochemical performance as compared to mesoporous α-Co(OH)2 powder in 1 M KOH electrolyte as high specific capacitance with a significant tremendous long-term cyclic stability. The specific capacitance of mesoporous β-Co(OH)2 film was 605 F/g at scan rate 10 mV/s and superior cyclic stability as capacitance retention of 94.4% over 2000 cycles. Uniform and homogeneous Co(OH)2 nanoparticles inside film enhance the electrochemical performance for SCs due to easy penetration and access of KOH electrolyte inside mesoporous structure. The reported synthesis method provides a suitable and fast approach to synthesize other kind of metal hydroxide mesoporous structure for electrode purpose for different energy storage devices.

Lyotropic liquid crystal directed synthesis of anisotropic copper microparticles and their application in catalysis

A simple, room-temperature approach for the synthesis of stable microparticles of copper in a lyotropic liquid crystal (LLC) template is described. The LLC phase having a hexagonal ordering is prepared using a mixture of non-ionic surfactant triton-X 100 and water in the ratio of 40:60 wt%. A controlled growth of copper particles is achieved in this medium by reducing cupric chloride using hydrazine hydrate under basic condition without the aid of any external stabilizing agent. Monodisperse, platelet-like copper microparticles (size ∼0.25 μm) are formed in this synthesis, which are well-dispersed in the lyotropic phase without aggregation. Besides, the copper particles are found to be stable for several months in the liquid crystalline medium. The LLC medium directed the growth of anisotropic microparticles and also acted as a stabilising agent. These micro platelets of copper are found to exhibit significant catalytic and electrocatalytic activity for the sodium borohydride mediated conversion of 4-nitrophenol to 4-aminophenol and for the reduction of hydrogen peroxide respectively.

Mesophase micelle-assisted electrodeposition and magnetisation behavior of meso-porous nickel films for efficient electrochemical energy and magnetic device applications

Mesoporous magnetic materials have found interesting potential applications in electrochemical energy harvesting and energy-efficient magnetic actuation device applications. Here we report on the electrodeposition and magnetic properties of mesoporous nickel films from lyotropic liquid crystal (LLC) templates formed by cetyltrimethylammoniumbromide (CTAB) cationic surfactant. Diffusion-controlled electrodeposition mechanism of nickel is determined. Films are electrodeposited under a constant current ranging from 1 to 7.5 mA cm−2 from an aqueous solution containing 0.1 M nickel sulphate, 0.2 M boric acid solution and CTAB with a concentration ranging from 0 to 50 wt.%. Mesopores develop an arranged hexagonal structure due to the micellar positional and orientational order reaching its highest value at 30 wt.% of CTAB at 2 mA cm−2. This is confirmed by transmission electron microscopy (TEM) and electrocatalytic surface area measurement. Electrodeposition current density and pH modify the mesoporous dimensions and therefore the magnetic properties change, tough hydrogen evolution as a side reaction influences the mesoporous structure. We observe an increased in-plane magnetic coercivity value to a maximum of 214 Oe for the mesoporous nickel film, which correlates with the increased interaction field. The widening of the coercivity distribution in first-order reversal curve (FORC) diagrams indicates that films with higher CTAB content have more inhomogeneous structure, which can lead to complex magnetization reversal mechanisms. The results of this study will help to exploit novel multifunctional magnetic and electrochemical energy materials and devices.

Responsive superabsorbent hydrogels via photopolymerization in lyotropic liquid crystal templates

In this work, stimuli-responsive, superabsorbent materials are created by copolymerization of stimuli-responsive poly(n-isopropyl acrylamide) (PNIPAM) in combination with superabsorbent sodium acrylate (SA) via photopolymerization in lyotropic liquid crystal (LLC) templates. Templating PNIPAM in LLC mesophases imparts nanostructure to the polymer that significantly increases transport and swelling when compared to isotropic hydrogels. These materials exhibit twice the equilibrium swelling of analogous non-templated materials and show a dynamic range between the swollen and deswollen state that is 5 times greater. To further augment this stimuli-responsive range, LLC-templated PNIPAM was combined with the superabsorbent monomer sodium acrylate (SA). As SA concentration is increased, significant structure changes are observed during polymerization that leads to less-defined nanostructure and lower stimuli response. Maximum swelling and temperature response are observed at low concentrations of SA (∼2 wt%). These LLC-templated copolymers exhibit stimuli-responsive volume transitions up to 40 times and equilibrium swelling ratios of 60 times their dry mass. This 600% increase in thermal response is due to the combined high swelling capabilities of SA with the enhanced thermal-response behavior induced by the LLC-templated nanostructure. Additionally, the nanostructure induces fast deswelling rates at temperatures above the lowest critical solution temperature of PNIPAM. The high dynamic range and quick response of this composition could allow for the development of superabsorbent, stimuli-responsive hydrogels in a variety of biomaterial, microfluidic, and water remediation applications.

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.

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.

Synthesis of three-dimensionally ordered macro-/mesoporous Pt with high electrocatalytic activity by a dual-templating approach

Three dimensionally ordered macro-/mesoporous (3DOM/m) Pt catalysts are fabricated by chemical reduction employing a dual-templating synthesis approach combining both colloidal crystal (opal) templating (hard-templating) and lyotropic liquid crystal templating (soft-templating) techniques. The macropore walls of the prepared 3DOM/m Pt exhibit a uniform mesoporous structure composed of polycrystalline Pt nanoparticles. Both the size of the mesopores and Pt nanocrystallites are in the range of 3–5 nm. The 3DOM/m Pt catalyst shows a larger electrochemically active surface area (ECSA), and higher catalytic activity as well as better poisoning tolerance for methanol oxidation reaction (MOR) than the commercial Pt black catalyst.

A versatile, one-pot synthesis of gold nanostars with long, well-defined thorns using a lyotropic liquid crystal template

We describe a simple, one-pot, silver-assisted synthesis of branched gold nanoparticles (GNPs) (nanostars) using Ag NO3 and the mild reducing agent, ascorbic acid, in the presence of a lyotropic liquid crystal (LLC) template formed by Triton X-100 in water either in the hexagonal phase or the micellar phase above the critical micellar concentration. The LLC template is found to assist in the formation of well-defined nanostars with long, twinned thorns and provides the necessary colloidal stability that prevents the final nanostars from irreversible aggregation. In addition, the length of the thorns on the nanostars can be tailored by controlling the Au/Ag ratio in the growth solution. We discuss the contributions of the competing mechanisms that result in an optimal concentration of AgNO3 for the synthesis of nanostars with considerably longer thorns, which is only possible in the LLC template that slows down the growth of the thorns on the initially formed GNP seeds.

Wide-spectrum optical hyperbolic metamaterial based on reverse hexagonal lyotropic liquid crystal

Reverse hexagonal lyotropic liquid crystal template is proposed to achieve optical hyperbolic metamaterial composed of silver nanowire arrays. All angle negative refraction is obtained during the wide wavelength range from near-infrared to visible light. Hyperbolic metamaterial incorporated with gain dye molecules is calculated to show the possibility of eliminating energy losses and the transmittance can be enhanced in the selected wavelength range.

Improved stimuli-response and mechanical properties of nanostructured poly(N-isopropylacrylamide-co-dimethylsiloxane) hydrogels generated through photopolymerization in lyotropic liquid crystal templates

Temperature-sensitive poly(N-isopropylacrylamide) (PNIPAM) hydrogels are widely studied stimuli-responsive systems due to their significant volume changes at biologically relevant temperatures and a potential wide range of applications including drug delivery, cell cultures, chemical sensors, and desalination. The successful performance of PNIPAM gels often requires a rapid response rate with a significant degree of deswelling when heated above the lower critical solution temperature. However, it is often difficult to design PNIPAM hydrogels with appropriate mechanical strength for the gels to remain functional in a working environment. Herein, lyotropic liquid crystals (LLCs) are utilized to generate a hexagonal nanostructure in PNIPAM hydrogels in order to improve material properties and transport characteristics. Cross-linked methacrylated poly(dimethylsiloxane) (PDMS) was incorporated into PNIPAM gels at varying concentrations through photopolymerization in the hexagonal LLC phase in order to modulate mechanical properties. The hexagonal LLC nanostructure dramatically increases the hydrogel deswelling rate compared to traditional isotropic PNIPAM–PDMS hydrogels of the same chemical composition. Additionally, the ordered LLC structure allows for considerable incorporation of PDMS into the hydrogel without significantly decreasing the water content of the gels. Interestingly, the hexagonal nanostructured hydrogels exhibit similar compressive moduli compared to isotropic hydrogel controls despite having considerably higher water content. These results may be utilized to generate stimuli-sensitive hydrogels with an appropriate rate and degree of deswelling while maintaining necessary mechanical integrity of the gel for use in numerous biomedical and industrial applications.