Surfactant Alkyl Chain Research Articles

Photoresponsive arylazopyrazole surfactant/PDADMAC mixtures: reversible control of bulk and interfacial properties.

In many applications of polyelectrolyte/surfactant (P/S) mixtures, it is difficult to fine-tune them after mixing the components without changing the sample composition, e.g. pH or the ionic strength. Here we report on a new approach where we use photoswitchable surfactants to enable drastic changes in both the bulk and interfacial properties. Poly(diallyldimethylammonium chloride) (PDADMAC) mixtures with three alkyl-arylazopyrazole butyl sulfonates (CnAAP) with -H, -butyl and -octyl tails are applied and E/Z photoisomerization of the surfactants is used to cause substantially different hydrophobic interactions between the surfactants and PDADMAC. These remotely controlled changes affect significantly the P/S binding and allows for tuning both the bulk and interfacial properties of PDADMAC/CnAAP mixtures through light irradiation. For that, we have fixed the surfactant concentrations at values where they exhibit pronounced surface tension changes upon E/Z photoisomerization with 365 nm UV light (Z) and 520 nm green (E) light and have varied the PDADMAC concentration. The electrophoretic mobility can be largely tuned by photoisomerisation of CnAAP surfactants and P/S aggregates, which can even exhibit a charge reversal from negative to positive values or vice versa. In addition, low colloidal stability at equimolar concentrations of PDADMAC with CnAAP surfactants in the E configuration lead to the formation of large aggregates in the bulk which can be broken up by irradiation with UV light when the surfactant's alkyl chain is short enough (C0AAP). Vibrational sum-frequency generation (SFG) spectroscopy reveals changes at the interface similar to the bulk, where the charging state at air-water interfaces can be modified with light irradiation. Using SFG spectroscopy, we interrogated the O-H stretching modes of interfacial H2O and provide qualitative information on surface charging that is complemented by neutron reflectometry, from which we resolved the surface excesses of PDADMAC and CnAAP at the air-water interface, independently.

Study on the mechanism of the influence of surfactant alkyl chain length on the wettability of anthracite dust based on EDLVO theory and inverse gas chromatography

The dispersion of coal dust on roadways adversely affects the productivity of coal mines and threatens the lives of mine workers. Accordingly, it is crucial to enhance the wettability of coal dust to improve its suppression efficiency. Herein, the mechanism of the influence of the surfactant alkyl chain length on the wettability of anthracite was investigated by systematically analyzing the degree of modification of anthracite with sodium dodecyl, tetradecyl, hexadecyl, and octadecyl sulfates using the “macroscopic + mesoscopic + microscopic + theoretical calculation” method. First, the differences in the macroscopic effects of different surfactants on modified anthracite were investigated via contact angle, settling time, and water retention rate experiments. It was concluded that surfactants with shorter alkyl chains exhibit a stronger ability to enhance the wettability of anthracite. Second, the mesoscopic characterization of different coal samples via laser particle size distribution, zeta potential, X-ray photoelectron spectroscopy, and inverse gas chromatography surface energy analyses revealed that the adsorption amount and intensity of surfactants on the anthracite surface increased with shortening surfactant alkyl chains owing to the spatial site resistance effect. Furthermore, molecular dynamic simulations of the microscopic molecular mechanism of adding different surfactants to enhance the wettability of anthracite showed that the interaction energy between coal dust and water molecules as well as the number of hydrogen bonds formed in the system rapidly increased with the shortening of the alkyl chains of anionic surfactants, which had a stronger binding ability to water molecules. Finally, the extended Derjaguin, Landau, Verwey, and Overbeek theory was employed to explain the relationship between the variation in electrostatic interaction, van der Waals, hydrophobic interaction, and total interaction energies and confirm that the wettability of anthracite particles increases with their dispersion in water. The ability of the surfactants to improve the wettability of anthracite increased at different degrees with the shortening surfactant alkyl chains. This study can provide breakthrough inspiration for the fields of coal flotation and haze control.

Surface and thermodynamics properties of commercial fatty-alcohol ethoxylate surfactants

The present study provides the surface and thermodynamic properties data of commercial fatty-alcohol ethoxylate surfactants (FAEs) at different temperatures (25–60 °C). These compounds are a mixture of fatty-alcohol ethoxylate oligomers with different degree of ethoxylation (2.6–11) and length of the alkyl chain (C10-C18). In this work, we analyzed determinate the water content by the Karl-Fisher method and measured the surface tension using the Wilhelmy plate method. In addition, we studied the effect of their structural parameters (degree of ethoxylation and length of alkyl chain) and the temperature on the changes of the thermodynamic functions (Gibbs free energy, enthalpy, and entropy) for the processes of adsorption and micellization. It was found an exponential decrease of the critical micellar concentration (CMC) in molar scale with the length alkyl chain of the fatty-alcohol ethoxylate surfactants, and the CMC values and thermodynamic parameters agree with those values found in literature for pure compounds. Moreover, the micellization entropy increases with the degree of ethoxylation of the surfactant.

Spectrometric study on the hydrophobic hydration in the formation of Tween-60 micelles with curcumin

The hydrophobic hydration in the formation of Tween-60 micelles upon entrapping bioactive curcumin has been observed and studied. The atypically increased values of pyrene polarity index suggest that Tween-60/curcumin complexes with bigger bulk hydrophobic part have stronger hydrophobic hydration than curcumin alone. The low-field shifts of water proton by 1H NMR method can also confirm the formation of stronger hydrogen bond network of water molecules surrounding Tween-60/curcumin complexes. However, the hydrophobic aggregation of surfactant alkyl chains into Tween-60 premicelles and micelles may destroy the hydrophobic hydration of Tween-60/curcumin complexes, which is indicated by the decreasing change of pyrene polarity index with increasing Tween-60 concentration. The fluorescence anisotropy of curcumin is observed to have sharply decreased values for Tween-60/curcumin complexes, which correlates positively with the hydrogen bonding strength of water molecules around curcumin. The fluorescence anisotropy, fluorescence spectroscopy and stability of curcumin cooperatively suggest that there is gradually weakened contact of curcumin with water in the order of curcumin alone, Tween-60/curcumin complexes, curcumin with Tween-60 premicelles and micelles. This work demonstrates that the hydrophobic hydration plays an important role in the entrapment of curcumin from a polar medium of water to surfactant micelles.

Solubilization of α-tocopherol and curcumin by polyoxyethylene alkyl ether surfactants: Effect of alkyl chain structure

The effects of the structural characteristics of the alkyl chains of polyoxyethylene alkyl ether-type surfactants (Brij) on the solubilization of α-tocopherol and curcumin by surfactant micelles were investigated: Brij L23 (lauryl; C12:0); S20 (stearyl; C18:0); and Brij O20 (oleyl; C18:1). When α-tocopherol or curcumin were solubilized in Brij micelle solutions below their maximum solubilization concentrations (Cmax), the Brij L23 micelles exhibited the largest increase in dimensions due to the presence of the guest molecules. Above Cmax, excess α-tocopherol existed as microemulsion droplets whereas excess curcumin existed as insoluble crystals. Our results suggest that the guest molecules were preferentially located within the palisade layers of micelles, which can be attributed to the fact that they contained bother polar and non-polar moieties. These results may be important for the formulation of colloidal delivery systems to encapsulate and deliver oil-soluble vitamins and nutraceuticals.

A comprehensive methodology to study double emulsion stability

HypothesisThe stability of emulsions requires the fast formation of viscoelastic interfaces between water and oil phases. In double emulsions, two surfactant types (hydrophilic and lipophilic) are present and two interfacial films are involved. Understanding cooperative adsorption of these surfactants and its implication on properties of water/oil/water interfacial films will enable replacing the empirical methodologies used in designing double emulsion systems with a knowledge-based approach. Experiments and modelThe distribution of surfactants between the water/oil interfaces was investigated using single droplet diffusion experiments and simulation of equilibrium surfactant density profiles. The stability of the interfaces against coalescence was characterized by dye transport in a leach cell and coalescence time of single droplets in a model experiment. The conformation of the surfactants at an interface was then examined via surface rheology, sum frequency generation spectroscopy, and dissipative particle dynamics simulation. FindingsTwo selected hydrophilic surfactants combined with a lipophilic surfactant induce very different properties at water/oil interfaces and different dye release behaviour from their corresponding double emulsions. Competitive adsorption of sodium dodecyl sulfate and lipophilic surfactant results in the improvement of encapsulation efficiency, elasticity of the interface, and resistance against coalescence due to the intercalation of surfactant alkyl chains into the oil chains.

Activation of carbonated brine with surfactants and sulfate anion for enhanced oil recovery processes

CO2-based enhanced oil recovery (EOR) methods has gained special attention since they can extract trapped oil from depleted reservoirs and store CO2 in the ground. Considering these advantages, the current study aimed to investigate the effect of CO2 on the performance of both carbonated and activated (solution with tuned ions and surfactants) carbonated brine (CB) on the dynamic interfacial tension (DIFT) of crude oil, under constant temperature of 50 °C and pressure range of 0–3000 psi. In the first step, the IFT of CO2 and crude oil was measured to find the first and multiple contact miscibility (FCM and MCM) pressures. Then, two synthetic brines including synthetic sea water (SB) and tuned SB (called SB-2SO4, i.e. SB spiked with two times of SO42- and depleted from Na+ and Cl-) with the ionic strength of 0.8 M were prepared. Four surfactants including sodium luryl sulphate (SLS, anionic type), hexadecyltrimethyl ammonium bromide (CTAB, cationic type) and two ionic liquids (ILs) namely dodecyl-3-methyl imidazolium chloride ([C12 mim]Cl) and octadecyl-3-methyl imidazolium chloride ([C18 mim]Cl) were selected to examine the effect of surfactant type and alkyl chain length on the IFT concomitant with swelling factor in the presence and absence of CO2 in three different pressures including below, close to and higher than the MCM pressure. The best surface activity with very low IFT values and low adsorption time was obtained with C-SB-2SO4-CTAB, i.e. carbonated solution containing CTAB and tuned brine spiked with sulfate. Finally, the experimental data were used to model the dynamic IFT and to calculate the relaxation time.

Mixed-surfactant perovskites with enhanced photostability

Blue and green emitting methylammonium lead bromide perovskite particles with improved UV-light stability have been developed by tuning structure and stabilization with a mixture of different single- and double-tailed surfactants. The ratio of the long alkyl chain surfactants to the methyl ammonium bromide allows for tailoring of the emission color of ready to use perovskite particles without further purification processes. The combination of single and double tailed surfactants exceeds the properties and geometries of the perovskite particles obtainable with a single surfactant. With a mixture of octylammonium bromide and dimethyldioctadecyl bromide, the perovskite particles show a highly anisotropic shape with a layered pyramid structure. The effect of surfactant composition on the perovskite particles’ structure, morphology and light-emitting properties has been elucidated. As these mixed surfactant perovskites are more robust against UV-light than other perovskite particles, they bear great potential for applications in optical devices such as LEDs.

Preparation and Photocatalytic Activity of Hexagonal Plate-like ZnO Particles Using Anionic Surfactants.

Hexagonal plate-like ZnO particles with a high degree of c-face orientation have been synthesized using hydrothermal method in the presence of various anionic surfactants bearing different hydrocarbon chains. The c-face of the ZnO particles increased upon increasing the surfactant alkyl chain length. The photocatalytic activity of the as-obtained hexagonal plate-like ZnO particles was evaluated using the degradation of methylene blue (MB). Although the specific surface area of hexagonal rod-like particles is higher than that of hexagonal plate-like particles, the amount of MB adsorption on the ZnO particle surface was different for the hexagonal plate-like and rod-like particles. In addition, the hexagonal plate-like ZnO particles showed a significantly higher decrease in the MB concentration with the duration of ultraviolet light irradiation when compared to the hexagonal rod-like ZnO particles obtained in the absence of a surfactant. These results indicate that crystal-face-controlled ZnO with a high degree of c-face orientation exhibits high photocatalytic activity.

Self-assembly of ionic and non-ionic surfactants in type IV cerium nitrate and urea based deep eutectic solvent.

Understanding and manipulating micelle morphology are key to exploiting surfactants in various applications. Recent studies have shown surfactant self-assembly in a variety of Deep Eutectic Solvents (DESs) where both the nature of surfactants and the interaction of the surfactant molecule with the solvent components influence the size, shape, and morphology of the micelles formed. So far, micelle formation has only been reported in type III DESs, consisting solely of organic species. In this work, we have explored the self-assembly of cationic surfactant dodecyl trimethylammonium nitrate/bromide (C12TANO3/C12TAB), anionic surfactant sodium dodecyl sulfate (SDS), and non-ionic surfactants hexaethylene glycol monododecyl ether (C12EO6) and octaethylene glycol monohexadecyl ether (C16EO8) in a type IV DES comprising metal salt, cerium (III) nitrate hexahydrate, and a hydrogen bond donor, urea, in the molar ratio 1:3.5. C12TANO3, C12TAB, C12EO6, and C16EO8 form spherical micelles in the DES with the micelle size dependent on both the surfactant alkyl chain length and the head group, whereas SDS forms cylindrical micelles. We hypothesize that the difference in the micelle shape can be explained by counterion stabilization of the SDS headgroup by polycations in the DES compared to the nitrate/bromide anion interaction in the case of cationic surfactants or molecular interaction of the urea and the salting out effect of (CeNO3)3 in the DES on the alkyl chains/polyethoxy headgroup for non-ionic surfactants. These studies deepen our understanding of amphiphile self-assembly in this novel, ionic, and hydrogen-bonding solvent, raising the opportunity to use these structures as liquid crystalline templates to generate porosity in metal oxides (ceria) that can be synthesized using these DESs.

Adsorption of calixarene-based supramphiphiles at the solid–liquid interface monitored by QCM-D

ABSTRACT Supramolecular amphiphiles are a topic of widespread interest in supramolecular chemistry and the characterisation of their properties at the interfacesis at the basis of industrial and biotechnology applications. This work focuses on the determination of the adsorption features of supramolecular amphiphiles, formed by the host-guest complexation of a p-sulfonatocalix[4]arene with selected cationic surfactants, at the solid–liquid interface monitored by quartz crystal microbalance with dissipation monitoring (QCM-D) experiments. The adsorption process resulted to be favourite and strongly affected by the length of the surfactant alkyl chain and somehow by the nature of the polar head. The adsorption isotherms highlighted the key role played by the calixarene scaffold in the CMC value, the amount of material absorbed and the efficiency of the adsorption process on a gold substrate. Furthermore, the kinetic profiles provided significant insights on the different mechanisms of adsorption undergone by either conventional or supramolecular amphiphilic systems.

Superchaotropic nano-ions as foam stabilizers

HypothesisWeakly hydrated nanometric ions, called superchaotropes, were recently shown to adsorb strongly to non-ionic surfaces affecting drastically the surface’s physical–chemical properties due to a charging effect. Superchaotropic ions could serve as stabilizing agents for non-ionic colloidal systems, such as non-ionic surfactant foams. ExperimentsWe study foams of the non-ionic surfactant BrijO10 (C18:1E10) without and in presence of the superchaotropic Keggin-ion SiW12O404− (SiW). The foams are investigated under free drainage conditions by image analysis and conductimetry to reveal the effect of SiW on the foam stability, liquid drainage, and bubble size. Additionally, small angle neutron scattering on the same foams, but in a dry quasi-stationary state, provides insight into effects of SiW on the foam films. FindingsSiW strongly stabilizes non-ionic surfactant foams at millimolar concentrations by inducing electrostatic repulsions between foam film interfaces resulting in thicker and monodisperse foam films. A similar effect is observed with the ionic surfactant sodium dodecylsulfate (SDS) but to a lesser extent and with a different mechanism. At the foam films’ interface, SiW adsorbs to the polar non-ionic surfactant heads driven by the superchaotropic effect whereas DS− anchors between non-ionic surfactant alkyl chains by the hydrophobic effect. The potential of superchaotropic ions as foam stabilizers is herein demonstrated.

Preparation of β zeolite with intracrystalline mesoporosity via surfactant -templating strategy and its application in ethanol-acetaldehyde to butadiene

Abstract The conversion of ethanol to butadiene catalyzed by modified β zeolites has attracted wide attention. The construction of intracrystalline mesoporosity in β zeolite is a challenging way to improve the catalytic activity. In this work, a surfactant-template strategy was used to construct intracrystalline mesoporosity successfully in the alkali treatment of β zeolite using long-chain quaternary ammonium salt with different alkyl chain length (C10~C16) as the template. The intracrystalline pore size can be adjusted by varying the surfactant alkyl chain length (C10~C16) (1.9–3.4 nm). To get more information about this process, CTAB was chosen as the template in further investigations. The mesoporosity can be generated within 1 h. The BET surface area can reach up to 600 m2/g while the pore volume can reach up to 0.568 cm3/g, which are 1.23 and 1.5 times that of the parent zeolite, respectively. The template action of CTA+ is essential for forming mesoporosity, and CTA+ interacts with the zeolite during the alkali treatment process, protects the zeolite framework from being etched, and does not form a separated mesoporous phase. To demonstrate the effect of intracrystalline mesoporosity on the catalytic performance, Zr-β zeolite was prepared and used as the catalyst for ethanol-acetaldehyde conversion. The hierarchical Zr-β zeolite was prepared using a dealumination-metallization strategy, and both the zeolite crystallinity and the mesoporosity were preserved in this process. The total conversion increased by 10%, while the BD selectivity was well maintained. The catalytic performance showed that the introduction of mesoporosity effectively mitigated decreasing conversion while preserving BD selectivity.

Investigation on the effects of SiO2 nanoparticles with different surface affinity on the viscoelasticity of wormlike micelles

The effects of both hydrophilic and hydrophobic SiO2 nanoparticles (NPs) on the viscoelasticity of stearyltrimethylammonium bromide/sodium salicylate wormlike micelles (WLMs) solutions were investigated. The micelle-nanoparticle junctions obviously increased the contour length Lc of the WLMs to facilitate the viscoelasticity of WLMs solution, which could be reflected by cryo-TEM images and Maxwell model. The effects of SiO2 NPs on the zero-shear viscosity and the flow activation energies of WLMs with different surfactant alkyl chain lengths were explored in the controlled experiments. It was found that the viscoelasticity of WLMs/NPs mixture was associated with the strength of the hydrophobic effect between the SiO2 NPs and surfactant molecules in the micelle-nanoparticle junction. The number densities of micelle-nanoparticle junction in hydrophilic and hydrophobic SiO2 NPs systems were calculated by the mathematical model to confirm our proposed hypothesis.

Salt-tolerance of alkyl-glyceryl ether carboxylates hydrotropes and surfactants. Dramatic effect of the methylation of the glyceryl spacer

HypothesisThe insertion of polyether spacers between the anionic head and the alkyl chain of ionic surfactants significantly improves their salt-tolerance. The aim of this work is to study whether the petro-based polyethoxy spacer can be replaced by a glyceryl ether group for high salinity applications. ExperimentsA series of amphiphilic sodium salts of alkyl glyceryl ether carboxylates are synthesized with different alkyl chain lengths from 4 to 12 and various spacers between the glyceryl and the carboxylate groups. Their aggregation behavior is studied by tensiometry and their amphiphilicities are assessed by the PIT-slope method. The dramatic effect of the methylation of the glyceryl spacer on the salt-tolerance is highlighted, and rationalized by DFT calculations and molecular dynamics. FindingsIn contrast to the corresponding sodium soap, n-C6H13-CO2Na, and to the non-methylated counterpart, the sodium salt of 1-pentyl-3-methyl glyceryl ether methylene carboxylate ([5.0.1]-CH2CO2Na) exhibits an excellent salt-tolerance since it remains water-soluble with NaCl or CaCl2 concentrations greater than 20 wt% at 25 °C. Amphiphiles with short alkyl chains (<C8) act as hydrotropes whereas longer compounds behave as surfactants whose CMC are lower than their corresponding isomers with ethoxy spacers n-Ci(EO)2CH2CO2Na.

Influence of Quartz, Kaolin, and Organic Matter on the Critical Micelle Concentration of Tween Surfactants and their Application in Diesel‐Contaminated Soil Washing

AbstractSurfactant solutions are commonly used for the remediation of petroleum‐contaminated soil due to their good petroleum removal performance, time‐saving capability, and cost effectiveness. However, applying surfactants in excess concentrations could make oil recovery difficult. Moreover, residual surfactants in soil are toxic to microorganisms and plants. Thus, it is crucial to identify a suitable surfactant concentration for soil washing applications. The main objective of this study was to evaluate the effect of soil minerals (quartz and kaolin) and organic matter (OM) on the critical micelle concentration (CMC) of polyethoxylated sorbitan ester surfactants (Tween 20, 40, 60, and 80) and its effect on diesel removal from diesel‐contaminated soil by soil washing. The results showed that Tween surfactants with shorter carbon chain lengths required higher CMC for diesel removal from quartz, while those with longer chains needed higher CMC for kaolin cleanup. FTIR results illustrated that oxygenated functional groups of Tween surfactants played an important role in their adsorption on quartz, while alkyl chains of Tween surfactants were responsible for their adsorption on kaolin. At a certain OM concentration, quartz and OM exhibited antagonistic effects, resulting in CMC reduction. In soil washing application, maximum diesel removal could be achieved from kaolin, in the presence of which surfactants exhibited the highest CMC. Based on FTIR results, the adsorbed surfactant could reduce the hydrophobicity of the kaolin surface, thus preventing the re‐deposition of detached diesel.

Role of the cationic headgroup to conformational changes undergone by shorter alkyl chain surfactant and water molecules at the air-liquid interface

HypothesisSurfactants are commonly used as corrosion inhibitors for oil-and-gas pipelines. The alkyl chain of surfactants and their overall conformation contributes to the adsorption, flotation, and foam separation in the inhibition process. We hypothesize that the conformation of shorter alkyl chains and chemical nature of surfactants has an effect on the ordering of water molecules at the air-water interface which is not yet well understood. ExperimentsAlkyl (C4, C6, C8, C10, and C12) dimethylbenzylammonium bromides (Quats) were synthesized. Aqueous solutions at 0% and with different salt concentrations were studied at the air-liquid interface using sum frequency generation spectroscopy. Surface tension and pH measurement were also conducted for comparison. FindingsSurfactant solutions at 0%, 1%, and 10% salt showed a zigzag trend for the number of gauche defects. At 0% salt, an increasing trend of OH band intensity at 3182 cm−1 was observed from C6 to C12 SFG spectra. Yet, C4 showed a more prominent SFG signal from strongly hydrogen-bonded water molecules compared to C6. The headgroup’s chemical nature was found to play a role in the ordering of water molecules for a C4 alkyl chain length. The OH band intensity decreases with increasing ionic strength.

Molecular dynamics study of ACBP denaturation in alkyl sulfates demonstrates possible pathways of unfolding through fused surfactant clusters.

Anionic surfactants denature proteins at low millimolar concentrations, yet little is known about the underlying molecular mechanisms. Here, we undertake 1-μs-long atomistic molecular dynamics simulations of the denaturation of acyl coenzyme A binding protein (ACBP) and compare our results with previously published and new experimental data. Since increasing surfactant chain length is known to lead to more rapid denaturation, we studied denaturation using both the medium-length alkyl chain surfactant sodium dodecyl sulfate (SDS) and the long alkyl chain surfactant sodium hexadecyl sulfate (SHS). In silico denaturation on the microsecond timescale was not achieved using preformed surfactant micelles but required ACBP to be exposed to monomeric surfactant molecules. Micellar self-assembly occurred together with protein denaturation. To validate our analyses, we calculated small-angle X-ray scattering spectra of snapshots from the simulations. These agreed well with experimental equilibrium spectra recorded on ACBP-SDS mixtures with similar compositions. Protein denaturation occurs through the binding of partial micelles to multiple preferred binding sites followed by the accretion of surfactant monomers until these partial micelles merge to form a mature micelle and the protein chain is left disordered on the surface of the micelle. While the two surfactants attack in a similar fashion, SHS's longer alkyl chain leads to a more efficient denaturation through the formation of larger clusters that attack ACBP, a more rapid drop in native contacts, a greater expansion in size, as well as a more thorough rearrangement of hydrogen bonds and disruption of helices.

Effect of surfactant alkyl chain length on lyotropic uniaxial to biaxial cholesteric phase transitions.

Some ionic surfactant-based lyotropic mixtures, exhibiting cholesteric phases, were prepared to investigate the effect of the surfactant alkyl chain length on a) uniaxial-to-biaxial phase transitions and b) stabilization of different cholesteric phases. Potassium alkanoates, KCx, (potassium undecanoate, KC11, potassium dodecanoate, KC12, and potassium tridecanoate, KC13) were chosen as the surfactant molecules. The lyotropic mixtures, which were composed of KCx/potassium sulfate (K2SO4)/decanol (DeOH)/water/brucine, where brucine is a chiral dopant molecule, were studied. Partial phase diagrams were constructed to show how the surfactant alkyl chain affects the phase topologies in the phase diagrams. It was observed that the presence of a longer surfactant alkyl chain in the mixture favors the stabilization of the larger discotic cholesteric, ChD, and cholesteric biaxial, ChB, phase domains. The phase transitions from the uniaxial cholesteric to biaxial cholesteric phase were shifted to lower temperatures.

Guanosine-based thermotropic liquid crystals with tunable phase structures and ion-responsive properties

In this work, the thermotropic liquid crystals (LCs) composed of a biological molecule, guanosine 5′-monophosphate disodium salt (GMP), with different cationic surfactants were reported. When GMP interacted with the surfactants, the length of the surfactant alkyl chains was found to be of great importance in modulating the LC phase. The smectic A (SmA) phase and columnar rectangular (Colr) phase were formed upon increasing the length of the aliphatic chains due to the enlargement of the steric hindrance. Interestingly, K+ ions were observed to cause the phase transition of LCs from the SmA or Colr mesophase to a columnar hexagonal (Colh) mesophase in the GMP-surfactant complexes, which was attributed to the formation of G-quadruplexes. Accordingly, the chirality and fluorescence properties of the complexes also exhibited K+-responsive characters as the phase transition of the LCs emerged. Compared with the reported LCs containing guanosine groups, the thermotropic LCs with high elasticity and tunable mesophase structures in this study are easy to be prepared and are hopeful to provide potential applications for constructing stimuli-responsive luminescent materials, biocatalysis and biosensor devices.