Gel-liquid Crystalline Research Articles

Influence of water on phase transition and rheological behavior of cellulose/ionic liquid/water ternary systems

ABSTRACTThe influence of water content on liquid crystalline (LC) gel formation and the rheological behavior of a ternary microcrystalline cellulose (MCC)/1‐ehtyl‐3‐methylimidazolium acetate (EmimAc)/water system was investigated using polarized optical microscopy (POM) and rheometry. POM indicated that the distinct water content range for forming a fully anisotropic LC gel with 14 wt % MCC was 4–10 wt %. Adding water to the MCC/EmimAc system resulted in enhanced complex viscosity and storage and loss moduli, and ultimately LC gel formation. Comparison of creep compliance vs. time revealed that the system without water showed representative viscoelastic behavior, while the time dependence of creep compliance disappeared as the water content increased, suggesting elastic‐solid behavior. Additionally, hydrogen bonding between cellulose and EmimAc weakened as water content increased, whereas the intra‐ and intermolecular hydrogen bonds of cellulose became stronger because of strong self‐association. This strong bonding caused aggregation, chain entanglement, and self‐supporting LC gel network formation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44658.

Self-Assembled Fibers Containing Stable Organic Radical Moieties: Alignment and Magnetic Properties in Liquid Crystals.

Macroscopically oriented stable organic radicals have been obtained by using a liquid-crystalline (LC) gel composed of an l-isoleucine-based low molecular weight gelator containing a 2,2,6,6-tetramethylpiperidine 1-oxyl moiety. The LC gel has allowed magnetic measurements of the oriented organic radical. The gelator has formed fibrous aggregates in liquid crystals via intermolecular hydrogen bonds. The fibrous aggregates of the radical gelator are formed and oriented on cooling by applying a magnetic field to the mixture of liquid crystals and the gelator. Superconducting quantum interference device (SQUID) measurements have revealed that both oriented and nonoriented fibrous aggregates exhibited antiferromagnetic interactions, in which super-exchange interaction constant J is estimated as -0.89 cm(-1) .

Rapamycin-loaded solid lipid nanoparticles: Morphology and impact of the drug loading on the phase transition between lipid polymorphs

Abstract In recent decades solid lipid nanoparticles (SLN) have become a well-performing tool for the site-targeted delivery of water-insoluble drugs. In this study, Compritol ® 888 ATO-based SLN, coated with polysorbate 80, were loaded with rapamycin (Rap), a lipophilic immunomodulator, broadly-used in therapies of cancer and neurodegenerative diseases. Rap-SLN were formulated using cold high-pressure homogenization and ultrasound-assisted emulsion. The exploitation of these methods yielded the nanoparticles of various values of zeta-potential (from −1 mV to −20 mV) and efficacies of the Rap entrapment (from 37.5 ± 2.3% to 77.0 ± 5.4%). The SEM and AFM imaging and shape-modeling by the combined DLS-SANS analysis revealed that the Rap-SLN of the hydrodynamic radius of ∼46 nm preserve the platelet-like or flat ellipsoidal structure with a thickness as large as 8–9 nm. These dimensions correspond to a single lipid bilayer, organized in a triclinic L β polymorph, and covered with a 1–2-nm shell of the surfactant. Consistently, FT-IR spectra acquired in the range 52–75 °C, showed that the Rap incorporation within the lipid matrix decreases the point of the gel-liquid crystalline (L β -L α ) phase transition. These outcomes imply a thermodynamically-driven mechanism of the Rap release from SLN.

FABRICATION AND CHARACTERIZATION OF ZALTOPROFEN LOADED LYOTROPIC LIQUID CRYSTALLINE GEL

In recent years, most of the non-steroidal anti-inflammatory drugs (NSAID’s) have been designed to deliver the drug in the form of topical gels, to avoid GIT irritation and to maximize drug concentration at the site of action. Liquid crystal phase has emerged as a novel material for the preparation of topical drug delivery system. For the preparation of liquid crystals, we have selected glycerol monooleate (GmO) because it is biocompatible, bioadhesive, a penetration enhancer and sustained release agent. It was proposed to develop zaltoprofen loaded lyotropic liquid crystalline gel. The optimized formulation of this system shows hexagonal phase identified by polarized microscopy and transmission electron microscopy. In vitro drug release kinetics shows that there was 70.45% drug release within 48 hrs. Textural properties like adhesiveness, cohesiveness, hardness and gumminess and texture profile analysis (TPA) of zaltoprofen loaded lyotropic liquid crystalline gel could be evaluated with the help of cT3 texture analyzer. In vivo evaluation of this formulation was done by carrageenan induced rat paw edema anti-inflammatory model.

Mesoscopically ordered and 3D printed nanocomposites inspired from the ligament-bone interface

Event Abstract Back to Event Mesoscopically ordered and 3D printed nanocomposites inspired from the ligament-bone interface Anand Rajasekharan1, Romain Bordes1 and Martin Andersson1 1 Chalmers University of Technology, Chemistry and Chemical Engineering, Sweden Introduction: The insertion site between soft and hard tissues such as the bone-ligament interface is crucial for muscoskeletal function and is highly prone to injuries. The interface tissues have a complex variation in structure and chemical-biological composition[1]. Modern grafts that support such injured interfaces lack necessary mechanical fixation and regenerative capacity. An important factor required from synthetic grafts for such applications is to transfer and minimize stress concentrations at the insertion site. Natural interfaces achieve this with the help of a well-ordered structure and chemical heterogeneity[1]. In light of this, we have developed a mesoscopically ordered nanocomposite with a mineral gradient that might act as a graft plug at injured interfaces. The composite is inspired from the matrix heterogeneity of the ligament-bone interface in terms of mesostructural order, anisotropy and chemical composition. Methods: Inspired by the collagen organization in bone and ligament, we use lyotropic liquid crystalline (LC) gels possessing a mesoscopically ordered structure as the matrix[2]. To create a macroscopic, porous material, the plug was fabricated via traditional molds and 3D printing by combining two distinct LC inks (figure 1A and 1B). The LC combination was covalently photo-crosslinked to form resilient and flexible polymerized liquid crystal matrices (PLCs). Next, a compositional gradient of bone-like hydroxyapatite (HA) was formed in-situ within the aqueous domains of the part of the PLC possessing calcium and phosphate ions, yielding a 3D, composite material with a graded mineral content (figure 1A). Figure 1(A) A traditionally molded and (B) 3D printed, porous, heterogeneous nanocomposite with mineral gradient (C) SAXS scattering confirms presence of mesoscopic order and anisotropy in both the mineralized and non mineralized sections (D) SEM image shows differences in morphology between mineralized and non-mineralized sections of the composite (E) Elemental scan shows increasing calcium to carbon ratio along the length of the composite shown in figure 1D Results: Small angle X-ray scattering (SAXS) data of the nanocomposite confirms the presence of meso-ordered (hexagonal) structure with long-range anisotropy similar to bone (figure 1C). Moreover cross-sectional electron microscopy images of composites show a clear gradient of the HA nanoparticles along macroscopic length scales of the PLC matrix (figure 1D and 1E). We have also shown the possibility to fabricate these heterogeneous structures via 3D printing with a porous architecture, possibilities towards scaffolding a biological heterogeneity of cells. Current work focuses on studying the composites in-vitro with different cell lines to assess cell behaviour on the heterogeneous surfaces. Conclusion: In this work, we have developed a heterogeneous nanocomposite possessing a mesoscopically ordered structure and a controlled gradient in mineral density and mechanical stiffness, inspired by the well-ordered matrix heterogeneity observed in natural bone-ligament interfaces. Knut and Alice Wallenberg Foundation; MAX-lab (Lund, Sweden)

Wavelength-tuneable laser emission from stretchable chiral nematic liquid crystal gels via in situ photopolymerization

We describe a technique for creating multi-coloured liquid crystalline laser gels which may be selectively and reversibly wavelength-tuned by applying a mechanical strain.

Functional liquid crystalline gels through multi-scale hierarchical self-assembly of LAPONITE® and amidodiol

Energy storage devices accomplished with efficient LAPONITE® liquid crystalline gel electrolytes.

Volume phase transitions of cholesteric liquid crystalline gels.

We present a mean field theory to describe anisotropic deformations of a cholesteric elastomer without solvent molecules and a cholesteric liquid crystalline gel immersed in isotropic solvents at a thermal equilibrium state. Based on the neoclassical rubber theory of nematic elastomers, we derive an elastic energy and a twist distortion energy, which are important to determine the shape of a cholesteric elastomer (or gel). We demonstrate that when the elastic energy dominates in the free energy, the cholesteric elastomer causes a spontaneous compression in the pitch axis and elongates along the director on the plane perpendicular to the pitch axis. Our theory can qualitatively describe the experimental results of a cholesteric elastomer. We also predict the first-order volume phase transitions and anisotropic deformations of a gel at the cholesteric-isotropic phase transition temperature. Depending on a chirality of a gel, we find a prolate or oblate shape of cholesteric gels.

Dispersability of Carbon Nanotubes in Biopolymer-Based Fluids

In this review the dispersability of carbon nanotubes in aqueous solutions containing proteins, or nucleic acids, is discussed. Data reported previously are complemented by unpublished ones. In the mentioned nanotube-based systems several different phases are observed, depending on the type and concentration of biopolymer, as well as the amount of dispersed nanotubes. The phase behavior depends on how much biopolymers are adsorbing, and, naturally, on the molecular details of the adsorbents. Proper modulation of nanotube/biopolymer interactions helps switching between repulsive and attractive regimes. Dispersion or phase separation take place, respectively, and the formation of liquid crystalline phases or gels may prevail with respect to dispersions. We report on systems containing ss-DNA- and lysozyme-stabilized nanotubes, representative of different organization modes. In the former case, ss-DNA rolls around CNTs and ensures complete coverage. Conversely, proteins randomly and non-cooperatively adsorb onto nanotubes. The two functionalization mechanisms are significantly different. A fine-tuning of temperature, added polymer, pH, and/or ionic strength conditions induces the formation of a given supra-molecular organization mode. The biopolymer physico-chemical properties are relevant to induce the formation of different phases made of carbon nanotubes.

Phytantriol-based in situ liquid crystals with long-term release for intra-articular administration.

The purpose of this study was to develop an injectable in situ liquid crystal formulation for intra-articular (IA) administration, and in situ forming a viscous liquid crystalline gel with long-term release of sinomenine hydrochloride (SMH) upon water absorption. The pseudo-ternary phase diagram of phytantriol (PT)-ethanol (ET)-water was constructed, and isotropic solutions were chosen for further optimization. The physicochemical properties of isotropic solutions were evaluated, and the phase structures of liquid crystalline gels formed by isotropic solutions in excess water were confirmed by crossed polarized light microscopy (CPLM) and small-angle X-ray scattering (SAXS). In vitro drug release studies were conducted by using a dialysis membrane diffusion method. The optimal in situ cubic liquid crystal (ISV2) (PT/ET/water, 64:16:20, w/w/w) loaded with 6 mg/g of SMH showed a suitable pH, showed to be injectable, and formed a cubic liquid crystalline gel in situ with minimum water absorption within the shortest time. The optimal ISV2 was able to sustain the drug release for 6 days. An in situ hexagonal liquid crystal (ISH2) system was prepared by addition of 5% vitamin E acetate (VitEA) into PT in the optimal ISV2 system to improve the sustained release of SMH. This ISH2 (PT/VitEA/ET/water, 60.8:3.2:16:20, w/w/w/w) was an injectable isotropic solution with a suitable pH range. The developed ISH2 was found to be able to sustain the drug release for more than 10 days and was suitable for IA injection for the treatment of rheumatoid arthritis (RA).

Stretchable light scattering display based on super strong liquid crystalline physical gels with special loofah-like 3D gel networks

A unique stretchable liquid crystal light scattering display is reported in this paper with clear images shown at a maximum strain of 145% of the original length, based on super strong liquid crystalline physical gels with special loofah-like 3D gel networks.

Photochromic and fluorescent LC gels based on a bent-shaped azobenzene-containing gelator

Photochromic liquid crystalline gels based on a low-molar-mass azobenzene-containing bent-shaped gelator and nematic liquid crystals were prepared.

The Structure and Function of Supramolecular Self-Assembling Binary Guanosine Gels

Binary liquid crystals of guanosine (GUO) and guanosine-5′-monophosphate (GMP) have been found to have unique and interesting properties in their ability to solubilize and selectively purify nanoparticles. The thermoassociative properties of these GMP-GUO g-gel phases have not been thoroughly explored and the mechanism of action is not understood. In the present study, nuclear magnetic resonance spectroscopy is used to probe the anisotropic properties of binary liquid crystals by employing deuterium nuclei. Deuterons have a quadrupolar moment that is normally averaged out by rapid molecular reorientation. In liquid crystals, however, the motion of the molecules is constrained such that quadrupolar effects are displayed in spectral data. To prevent other effects such as bulk exchange of deuterons from impacting the signal, 2H5-labeled aniline is employed to study the supramolecular structure of the liquid crystalline gels. This isotopomer of aniline has deuterons that are strongly bound to a rigid aromatic ring, allowing for study of solvent directed interactions without concern for conformation or bulk exchange effects. This study determines the anisotropy and order parameter of the binary liquid crystals to elucidate the structural and functional properties of the system.∗This research is supported by the Photosynthetic Systems Program, Office of Basic Energy Sciences, United States Department of Energy (DE-FG02-07ER15903).

A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4–5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

In Situ Observation of Ca2+ Diffusion-Induced Superstructure Formation of a Rigid Polyanion

Diffusion of multivalent metallic ions into aqueous solution of rigid, negatively charged macromolecules of high concentration is an effective approach to prepare macroscopically anisotropic hydrogels. However, the mechanism for superstructure formation is still not clear. By observing the mixing process of a small drop of CaCl2 solution with solution of a rigid polyanion, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), under the polarizing optical microscope, the diffusion profile of Ca2+ and detailed anisotropic gelation process of PBDT are revealed. Diffusion of Ca2+ into the surrounding PBDT solution immediately induces the formation of physical liquid crystalline (LC) gel with concentric alignment of PBDT. The thickness d of this region increases with diffusion time t, obeying the diffusion law d ∼ t1/2. A thin ring of constant width (∼100 μm) with radial alignment of PBDT appears at the diffusion/reaction front, ahead of the concentric alignment region. When two drops of CaCl2 fluxes me...

Solid-state NMR shows that dynamically different domains of membrane proteins have different hydration dependence.

Hydration has a profound influence on the structure, dynamics, and functions of membrane and membrane-embedded proteins. So far the hydration response of molecular dynamics of membrane proteins in lipid bilayers is poorly understood. Here, we reveal different hydration dependence of the dynamics in dynamically different domains of membrane proteins by multidimensional magic angle spinning (MAS) solid-state NMR (ssNMR) spectroscopy using 121-residue integral diacylglycerol kinase (DAGK) in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DMPG) lipid bilayers as a model system. The highly mobile and immobile domains of DAGK and their water accessibilities are identified site-specifically by scalar- and dipolar-coupling based MAS ssNMR experiments, respectively. Our experiments reveal different hydration dependence of the dynamics in highly mobile and immobile domains of membrane proteins. We demonstrate that the fast, large-amplitude motions in highly mobile domains are not triggered until 20% hydration, enhanced at 20-50% hydration and unchanged at above 50% hydration. In contrast, motions on submicrosecond time scale of immobile residues are observed to be independent of the hydration levels in gel phase of lipids, and at the temperature near gel-liquid crystalline phase transition, amplitude of whole-molecule rotations around the bilayer normal is dominated by the fluidity of lipid bilayers, which is strongly hydration dependent. The hydration dependence of the dynamics of DAGK revealed by this study provides new insights into the correlations of hydration to dynamics and function of membrane proteins in lipid bilayers.

Cholesteric liquid crystal gels with a graded mechanical stress

In cholesteric liquid-crystalline gels, the mechanical role of the polymer network over the structure of the whole gel has been ignored. We show that it is the stress gradient exerted by the network over the helical structure that drives the broadening of the optical band gap, as evidenced by the absence of a gradient in chiral species. Model calculations and finite-difference time-domain simulations show that the network acts as a spring with a stiffness gradient. The present results indicate a revision to the common understanding of the physical properties of liquid-crystalline gels is necessary when a concentration gradient in a polymer network is present.

NMR and Raman Spectroscopy Monitoring of Proton/Deuteron Exchange in Aqueous Solutions of Ionic Liquids Forming Hydrogen Bond: A Role of Anions, Self-Aggregation, and Mesophase Formation

The H/D exchange process in the imidazolium-based room temperature ionic liquids (RTILs) 1-decyl-3-methyl-imidazolium bromide- and chloride ([C10mim][Br] and [C10mim][Cl]) in D2O solutions of various concentrations was studied applying (1)H, (13)C NMR, and Raman spectroscopy. The time dependencies of integral intensities in NMR spectra indicate that the H/D exchange in [C10mim][Br] at very high dilution (10(-4) mole fraction of RTIL) runs only slightly faster than in [C10mim][Cl]. The kinetics of this process drastically changes above critical aggregation concentration (CAC). The time required to reach the apparent reaction saturation regime in the solutions of 0.01 mole fraction of RTIL was less 10 h for [C10mim][Br], whereas no such features were seen for [C10mim][Cl] even tens of days after the sample was prepared. The H/D exchange was not observed in the liquid crystalline gel mesophase. The role of anions, self-aggregation (micellization), and mesophase formation has been discussed. Crucial influence of Br(-) and Cl(-) anions on the H/D exchange rates above CAC could be related to the short-range ordering and molecular microdynamics, in particular that of water molecules. The concept of the conformational changes coupled with the H/D exchange in imidazolium-based ionic liquids with longer hydrocarbon chains can be rejected in the light of (13)C NMR experiment. The revealed changes in (13)C NMR spectra are caused by the secondary ((13)C) isotope effects not being the signal shifts due to the conformational trans-gauche transition.

Lehmann effects and rotatoelectricity in liquid crystalline systems made of achiral molecules

We discuss Lehmann effects and rotato-electricity for liquid crystalline phases made of achiral molecules. We point out that for static and dynamic Lehmann effects to exist, it is not necessary to have chiral molecules provided the overall structure has macroscopic chirality. This question is of direct relevance for liquid crystalline phases formed by bent-core molecules provided they have a sufficiently low symmetry. This includes systems which break parity symmetry and have overall C(2) or C(1) symmetry. We point out that for liquid crystalline gels and elastomers one should be able to observe rotato-electricity for systems with macroscopic chirality. Rotatoelectricity is associated with the relative rotations between two subsystems, namely, between the network and the director, in an external electric field. Candidates include gels and even monolayers prepared from bent-core molecules with sufficiently low symmetry.

Unique thermal behavior of sphingomyelin species with nonhydroxy and 2-hydroxy very-long-chain (C28-C32) PUFAs

In rat germ cells and spermatozoa, sphingomyelin (SM) contains molecular species with nonhydroxy (n) and 2-hydroxy (h) very-long-chain polyunsaturated fatty acids (V), the most abundant being SMs with (n- and h-) 28:4n-6, 30:5n-6, and 32:5n-6 as acyl chains. The aim of this study was to gain information about their thermotropic behavior and interactions with other lipids. After isolation from rat testis, multilamellar and giant unilamellar vesicles from these SMs were examined using fluorescent probes. Only n-32:5 SM and h-32:5 SM displayed a gel-liquid transition temperature (Tt ∼ 21-22°C), the rest remaining in the liquid state in the 5°C-45°C range. The degree of order was larger in bilayers of any of the h-V SMs than in those of their chain-matched n-V SMs. Both, but n-V SM relatively more than h-V SM, decreased the Tt of dimyristoylphosphatidylcholine as their proportion increased in binary phosphatidylcholine:SM liposomes. In contrast to the established ability of 16:0 SM to form lateral cholesterol/SM-rich ordered domains in ternary dioleoylphosphatidylcholine:cholesterol:SM bilayers, neither n-V SM nor h-V SM showed a tendency to do so. Thus, these SMs are in the fluid state and are not involved in this type of domains in spermatozoa at physiological temperatures. However, this state could be altered at the very low temperatures at which these gametes are usually preserved.