Gel Crystallization Research Articles

The cyanobacterial polysaccharide sacran: characteristics, structures, and preparation of LC gels

To shift from a petroleum-dependent society to a sustainable society using eco-friendly materials, polysaccharides from natural products are important candidates as alternative materials. We have researched one cyanobacterial polysaccharide, “sacran”, which is extracted from Aphanothece sacrum. In this review, the unique characteristics and structures of sacran and the preparation of liquid crystal gels are introduced: polymer properties such as megamolecular weight, that is, a weight > 107 g/mol; characteristic viscosity; liquid crystallinity (LC); fiber structures on the nanometer/micrometer scale; gel formation with heavy metal ions; photoshrinking in gels composed of metal ions; anisotropically swelling gels; orientation upon drying of the air-LC interface; meniscus splitting; and membrane formation with uniaxial orientation, which are the results of self-organization. These matters are discussed particularly from the perspectives of polymer science, colloidal science, gel science, etc. We expect that sacran will be applicable in a variety of fields, such as tissue engineering, pharmacodynamics, and biomedical materials, with possible contributions to the development of a sustainable material society. To shift from a petroleum-dependent society to a sustainable society using eco-friendly materials, polysaccharides from natural products are important candidates as alternative materials. We have researched one of the cyanobacterial polysaccharides, “sacran,” which is extracted from Aphanothece sacrum. In this review, the unique characteristics, structures, and preparation of sacran LC gels are introduced. These matters are discussed especially from the perspectives of polymer science, colloidal science, gel science, etc. We hope that sacran will be used in a variety of fields, such as tissue engineering, pharmacodynamics, and biomedical materials, with possible contributions to the development of a sustainable material society.

Synthesis, Structure, and Properties of Zirconia-Modified Aluminosilicate Glass-Ceramics

Strontium aluminosilicate glass-ceramics modified with zirconia additions in the presence of yttria as a stabilizing oxide and without it have been prepared by a sol–gel process. Increasing the zirconia content from 5 to 15 wt % has been shown to reduce the gelation time of the starting solutions, lower the gel crystallization onset temperature, activate the glass-ceramic sintering process, and increase the critical stress intensity factor (KIc) of the glass-ceramics by more than a factor of 2. The present results confirm that the increase in KIc on the addition of ZrO2 is due to transformation toughening. At the same time, the addition of yttria as a stabilizing oxide has been shown to hinder the martensitic transformation of tetragonal ZrO2 into the monoclinic phase.

Synthesis of large single crystal of ZnAlPO4-15 by using melamine as structure directing agent

We report effects of crystallization conditions and gel composition on the hydrothermal synthesis of large zinc-doped AlPO4-15 (ZnAlPO4-15) single crystals by using melamine (MA) as structure directing agent (SDA). By optimizing the following synthesis conditions: amount of MA, molar ratio of ZnO/Al2O3, molar ratio of P2O5/Al2O3, crystallization temperature and duration, the pure phase of ZnAlPO4-15 (size up to 95 μm) with good optical transparency can be obtained at 200 °C with 40 h in the system of Al2O3:1.07MA:0.27ZnO: 1.15P2O5:667H2O. To the best of our knowledge, it is the first report of synthesizing ZnAlPO4-15 by using MA as SDA.

Using Dates Leaves Midribs to Prepare Hierarchical Structures Incorporating Porous Carbon and Zeolite A Composites for Cesium137Cs Ion Exchange

This study synthesized zeolite 4A, and hierarchical composite structure consisting of zeolite 4A- carbon were successfully prepared. Hydrothermal method was used to grow a layer of zeolite 4A over porous carbon surfaces to enhance mass transfer and increase surface area of zeolite. The products then were used to remove radioactive cesium137Cs from liquid wastewater. Iraqi dates leaves midribs (DM) were used as locally available agricultural waste to prepare low- cost porous carbon, using carbonization method in tubular furnace at 900C for two hours. Hierarchical porous structures including zeolite are prepared by mechanically activating the carbon surface via Ultrasonicating nanoparticles suspension of ground zeolite type 4A.For preparing nanoparticles suspension, commercial zeolite has been milled using 0.3-0.4 mm diameter glass balls as grinding media. Nanoparticles of zeolite 4A acting as seeding (nucleation centers) increase the crystallization of amorphous aluminosilica gel on modification carbon surface. The products of the syntheses zeolite 4A and the hierarchal composite materials (DMZ) were characterized using Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Nitrogen sorption (BET) and Energy dispersive X-ray spectrometer (EDX) to check the morphology, structure, surface area, and the chemical composition respectively. The products were used to treat radioactive wastewater contaminated with radioactive cesium 137Cs collected from destroyed building of the Radiochemistry Laboratories (RCL) in AL-Tuwaitha Nuclear Site. The activity concentration for the contamination water pre and after the treatment were measured using gamma spectroscopy system supplied with a high purity germanium detector (HPGe) with 60% relative efficiency. The results showed that the radioactivity concentration after the treatment process decreased significantly from 4800 Bq/L to 186 and Bq/L,121 Bq/L using 0.045 gm from synthesized zeolite 4A and DMZ respectively.

Hierarchical Structures Incorporating Carbon and Zeolite to Remove Radioactive Contamination

Synthesis, characterization and application of hierarchical zeolites are becoming a subject of an increasing interest among scientists and researchers. Hierarchical structures incorporating zeolites possess secondary porosity at meso- and macrolevel to overcome problem of mass transport, which occurs with using conventional zeolites.
 In this study, the porous carbon surface was prepared by carbonization of the locally available agricultural waste of the Iraqi Nut shell (NS) using a carbonization method in a tubular furnace at 900ËšC for two hours. Hierarchicalpours structures including zeolite were prepared by the mechanical activation of the carbon surface using ultrasonication with a nanoparticles suspension of ground commercial zeolite type 4A. Zeolite was milled using 0.3-0.4 mm diameter glass balls as grinding media to prepare nanoparticles seeding, which increases the crystallization of the amorphous aluminosilica gel on the modified carbon surface during the hydrothermal method. The Product of the syntheses of zeolite 4A and the hierarchal composite material were characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Nitrogen-Adsorption /desorption isotherms (BET), Energy Dispersive Spectroscopy (EDX), and Thermo Gravimetric Analysis (TGA) to determine the structure, morphology, surface area, chemical composition, and percentage weight of zeolite on carbon, respectively. The products were applied to remove the radioactive hazardous cesium isotope Cs137 from the radioactive wastewater provided by the destroyed building of Radiochemistry laboratories (RCL) in AL-Tuwaitha Nuclear Site. Gamma spectroscopy system with high purity germanium detector (HPGe) was used to measure the activity concentration for the contamination water before and after the treatment. The results showed that the activity concentration decreased from 4800 Bq/L to 186Bq/L and 100Bq/L using pure zeolite 4A and NSZ.respectively. The results also showed that the composite materials could be used effectively to remove radioactive 137Cs from a real wastewater, with ease of separation and recovery from the solution compared with the pure zeolite 4A.

Ultra-low switching reverse mode liquid crystal gels.

This research investigates the electro-optical properties of reverse mode liquid crystal gel (LC-gel) scattering films. The LC-gel has been fabricated through the fibrous self-assembly of the gelator 12-hydroxydodecanoic acid (G12) and mesogen monomer (RM257) in nematic LC HTW106700-100 (HTW). Adding RM257 monomer improves the transparency in the OFF state and enhances scattering effects in the ON state. Moreover, an extremely low switching voltage (∼ 1 V) is demonstrated.

Создание и получение композиционного вещества лантанилоксалата бария на основе золь-гель технологии

This article explored a method for producing a compound of the type perovskite composition. Ba0.5X×Ox1X (where X=0.5:0.5=1). A multi-component composition was obtained during coagulation and gel formation (xerogel) of pH 5.5, acidic medium, at a temperature of 45–50 °C, mechanical stirring for 10 hours. The sol–gel crystallization of the compound was determined at a temperature of 400–500 °C and the previously obtained substance was named Barium Lanthanyloxalate.

Halogen bonding in the co-crystallization of potentially ditopic diiodotetrafluorobenzene: a powerful tool for constructing multicomponent supramolecular assemblies.

Halogen bonding is emerging as a significant driving force for supramolecular self-assembly and has aroused great interest during the last two decades. Among the various halogen-bonding donors, we take notice of the ability of 1,4-diiodotetrafluorobenzene (1,4-DITFB) to co-crystallize with diverse halogen-bonding acceptors in the range from neutral Lewis bases (nitrogen-containing compounds, N-oxides, chalcogenides, aromatic hydrocarbons and organometallic complexes) to anions (halide ions, thio/selenocyanate ions and tetrahedral oxyanions), leading to a great variety of supramolecular architectures such as discrete assemblies, 1D infinite chains and 2D/3D networks. Some of them act as promising functional materials (e.g. fluorescence, phosphorescence, optical waveguide, laser, non-linear optics, dielectric and magnetism) and soft materials (e.g. liquid crystal and supramolecular gel). Here we focus on the supramolecular structures of multicomponent complexes and their related physicochemical properties, highlight representative examples and show clearly the main directions that remain to be developed and improved in this area. From the point of view of crystal engineering and supramolecular chemistry, the complexes summarized here should give helpful information for further design and investigation of the elusive category of halogen-bonding supramolecular functional materials.

Incorporation of fluorescent microgels inside calcite single crystals

Single crystals have been shown to incorporate guest materials (e.g., gel networks and functional particles) and the incorporated materials endow the crystal hosts with non-intrinsic properties. The acquisition of the non-intrinsic crystal properties impels us to diversify the incorporated guest materials and thus to spread the potential applications of single-crystalline materials. Here, fluorescent NIPAM-based microgels have been selected as the guest materials to be incorporated into the crystal hosts. In the presence of microgels, calcite crystallize from either solution or gel media have been examined. Solution-grown crystals exclude the microgels, while two gel-grown methods have proved effective for incorporating these microgels inside calcite single crystals. On one hand, an additional macroscopic agarose gel-network is introduced to trap the microgels. Crystallization in the agarose gel leads to incorporation of agarose gel-network together with the trapped microgels. The microgel concentration in the crystal reaches 33 mg/mL. On the other hand, dispersions of microgels are concentrated to about 352 mg/mL and the microgels aggregate into non-flowing macroscopic gels (termed as macrogels). Crystallization in a macrogel results in its incorporation. By showing the incorporation of microgels through physical entrapment, this work provides a new platform to functionalize single crystals by the microgels.

Comparison of three in-situ gels composed of different oil types

A phospholipid-based phase separation in-situ gel (PPSG) system, which consists of phospholipids, medium chain oil (triglyceride) and ethanol as basic ingredients, has been previously developed in our lab. In addition, glycerol monooleate (monoglyceride) and glycerol dioleate (diglyceride) were also reported to be able to form liquid crystal gels. Monoglyceride, diglyceride and triglyceride have different degrees of hydroxyl substitution in glycerol and therefore different amphiphilic properties, which may cause different properties of gels composed of them. In this experiment, glycerol monooleate (GMO), glycerol dioleate (GDO) and glycerol trioleate (GTO) were selected to prepare three kinds of PPSGs. We systematically studied their in-vitro and in-vivo physicochemical properties and investigated their drug release behavior with octreotide (OCT) as the model drug. The results showed that PPSG composed of GTO (GTO-gel) had a different microstructure, a slower solvent diffusion speed and the less irritation to skin. In addition, the drug release result showed that the GTO-gel group had a lower initial release rate and a more stable release profile. All results above indicated that GTO-gel had a greater potential as a drug delivery system.

Hydrothermal synthesis of large single crystals with ATS topology in a F− free system and fabrication of SWCNTs@ATS materials

Abstract In this paper, large single ZnAPO4-36 crystals with ATS topology have been hydrothermally synthesized by using tripropylamine as structure-directing agent in a F− free system. The effect of gel composition and crystallization conditions on the growth of ZnAPO4-36 have been discussed in detail. The degree of intergrowth can be greatly reduced by properly lowering the crystallization temperature. To our best knowledge, this is the largest single crystals synthesized with ATS topology (150 μm × 30 μm) so far. What's more, ultrasmall single-walled carbon nanotubes (SWCNTs) have been successfully fabricated inside the prepared ZnAPO4-36 crystals.

In Situ Incorporation of Zn into Hierarchical ZSM-5 Zeolites for Olefin Hydroisomerization

Zn species were incorporated into hierarchical ZSM-5 zeolite (Zn-ZSM-5) via in-situ hydrothermal crystallization of alumino-silicate gel containing zinc metal salts. Compared to bulk ZSM-5 zeolite,...

Effect of the Aging Temperature of Gel on the Synthesis and Properties of the Silicoaluminophosphate Molecular Sieve SAPO-11

The effect of the aging temperature of the starting silicoaluminophosphate gel on the crystallization of the SAPO-11 molecular sieve was studied. When pseudoboehmite was used as an aluminum source, a gel containing di-n-propylamine phosphate, undissolved pseudoboehmite, and amorphous silicoaluminophosphate were formed. An increase in the aging temperature of the gel from 25 to 90°C led to an increase in the fraction of the amorphous phase in the latter. Crystallization of the silicoaluminophosphate gel aged at 90°C allows crystallization of SAPO-11 of high phase purity and nearly 98% crystallinity. High activity and selectivity for linear dimers (86%) of SAPO-11 in the dimerization of α-methylstyrene was shown.

Bioinspired underwater locomotion of light-driven liquid crystal gels

Soft-bodied aquatic invertebrates, such as sea slugs and snails, are capable of diverse locomotion modes under water. Recapitulation of such multimodal aquatic locomotion in small-scale soft robots is challenging, due to difficulties in precise spatiotemporal control of deformations and inefficient underwater actuation of existing stimuli-responsive materials. Solving this challenge and devising efficient untethered manipulation of soft stimuli-responsive materials in the aquatic environment would significantly broaden their application potential in biomedical devices. We mimic locomotion modes common to sea invertebrates using monolithic liquid crystal gels (LCGs) with inherent light responsiveness and molecular anisotropy. We elicit diverse underwater locomotion modes, such as crawling, walking, jumping, and swimming, by local deformations induced by selective spatiotemporal light illumination. Our results underpin the pivotal role of the physicomechanical properties of LCGs in the realization of diverse modes of light-driven robotic underwater locomotion. We envisage that our results will introduce a toolbox for designing efficient untethered soft robots for fluidic environments.

Liquid Crystal Chambers: A Single‐Step Dual Stabilization of Smart Window by the Formation of Liquid Crystal Physical Gels and the Construction of Liquid Crystal Chambers (Adv. Funct. Mater. 4/2020)

Liquid Crystal Chambers: A Single‐Step Dual Stabilization of Smart Window by the Formation of Liquid Crystal Physical Gels and the Construction of Liquid Crystal Chambers (Adv. Funct. Mater. 4/2020)

Surfactant-based lyotropic liquid crystal gels – the interplay between anisotropic order and gel formation

Surfactant-based lyotropic liquid crystal gels (LLCGs) are soft materials which combine the anisotropic order of a surfactant-based lyotropic liquid crystal with the mechanical stability of a gel.

Biaxial stretchable liquid crystal light scattering display based on uniform energy dissipation in non-oriented assembly of gel networks

Different from the traditional uniaxial stretchable displays, biaxial stretchable devices are herein reported based on a dynamic supramolecular liquid crystal gel network that showed good innovation in a new dimension of the original stretch to obtain the “true stretchable display”.

Interconnection of smectic domains by polyethylene oxide networks for long-range conducting channels towards efficient and thermally stable dye-sensitized solar cells.

The development of an efficient electrolyte that combines fast charge transport and high stability for advanced energy devices remains a huge challenge because these two qualities are traded off during the normal design process. Nanostructured liquid crystals have shown potential as efficient charge transport media. However, the reported liquid crystal electrolytes showed limited performance in energy devices probably due to the charge transport barrier at the domain interfaces. Herein, a novel approach was proposed to construct self-assembled long-range charge transport channels in liquid crystal electrolytes by interconnecting the liquid crystal domains via flexible polymer networks. A liquid crystal gel electrolyte was prepared by solidifying a smectic electrolyte using polyethylene oxide (PEO) networks, and applied to improve the performance of the dye-sensitized solar cells (DSSCs). In the gel electrolyte, the smectic assembly formed lamellar nanostructures for charge transport at the intra-domains, while the PEO networks aggregated amorphously at the domain interfaces, acting as bridges to interconnect the smectic domains for charge transport over the inter-domains. Based on the coordination of the smectic assembly and PEO aggregation, the charge transport in the liquid crystal gel electrolyte was greatly improved despite a higher viscosity. Conversely, the photovoltaic efficiency of the DSSC prepared from the liquid crystal gel electrolyte was about two times enhanced, with a champion efficiency of 7.2%, compared with that from the smectic electrolyte without PEO. The liquid crystal gel-based DSSC showed superior stable performance within a wide temperature range from 30 to 70 °C, and stored after 5000 h. Our work here provides a novel and convenient approach to break the trade-off for high-performance electrolytes towards efficient and stable energy devices.

The Influence of Temperature of Gel Ageing on Synthesis and Properties of the Silicoaluminophosphate Molecular Sieve SAPO-11

The influence of temperature of ageing of the initial silicoaluminophosphate gel on crystallization of the molecular sieve SAPO-11 was studied. It was established that with pseudoboehmite used as the source of aluminum, a gel containing di-n-propylamine phosphate, non-dissolved pseudoboehmite and amorphous silicoaluminophosphate was formed. Elevation of the gel ageing temperature from 25 to 90 °C was shown to result in an increase in the proportion of the amorphous phase in the gel. Crystallization of the silicoalumophosphate gel at 90 °C allowed SAPO-11 to be crystallized at high phase purity and close to 98 % crystallinity. A high activity and selectivity (86 %) of SAPO-11 to linear dimmers was observed during dimerization of α-methylstirene.

A Single‐Step Dual Stabilization of Smart Window by the Formation of Liquid Crystal Physical Gels and the Construction of Liquid Crystal Chambers

AbstractSmart windows are very attractive because they not only provide comfortable indoor conditions for cars and buildings, but also protect privacy. However, current smart windows have problems such as high energy consumption, slow response time, and poor stability. To solve these problems, a single‐step dual stabilization (SSDS) is newly proposed for the fabrication of robust liquid crystal (LC) smart windows switching fast at low voltage. Upon irradiating ultraviolet light on the selected area of the nematic (N) LC optical cell with photoisomerizable macrogelators (B3AZ) and photopolymerizable monomers, NLC physical gels (LCPGs) and partition walls are simultaneously constructed. LCPGs play a role of light shutter under a low electric field (9.6 Vpp) which is ten times lower than that of the conventional polymer‐stabilized LC‐based smart windows. Partition walls constructed by the selected area photopolymerization significantly enhance the mechanical stabilities. Based on the experimental results, it is realized that the NLC layer generated near the partition walls makes the LCPGs respond to a low voltage. Robust SSDS smart windows could open new doors for the development of high‐performance smart windows.