Alkyl Chain Length Of Surfactant Research Articles

Photophysical Response of Propranolol in Biomimetic Micellar Media of Alkyltrimethylammonium Bromide Surfactants: Effect of pH and Alkyl Chain Length.

The photophysical behavior of a β-blocker drug propranolol (PPL) in micellar environments, formed by alkyltrimethylammonium bromide surfactants viz.; Cetyltrimethylammonium bromide (CTAB), Tetradecyltrimethylammonium bromide (TTAB), and Dodecyltrimethylammonium bromide (DTAB), has been investigated through fluorescence and UV-visible spectroscopic techniques at pH levels of 3.5, 7.4, and 10.4. The impact of pH on the critical micelle concentration (cmc) and micropolarity of micelles were assessed using pyrene as a photophysical probe. The cmc values were found to be lower at pH 10.4 compared to pH 7.4 and pH 3.5. Fluorescence emission intensities of PPL at 323nm, 338nm, and 352nm were significantly influenced by pH, hydrophobic alkyl chain length of surfactants, and their concentrations. Quenching experiments with Cetylpyridinium chloride (CpCl) indicated the localization of charged and uncharged forms of PPL within micelles, with quenching constant (Ksv) values dependent on alkyl chain length and pH. At pH < pKa, PPL is positioned near the Stern layer, whereas at pH 10.4, its naphthalene moiety resides near the hydrophobic micellar core. UV spectroscopy showed that the charged form of PPL interacted with micelles only above cmc, while the neutral form interacted even below the cmc. Density Functional Theory (DFT) reveals the HOMO of the surfactants to be localized on the hydrocarbon chains, and the LUMO localized around the quaternary ammonium unit. Upon complexation with PPL, both HOMO and LUMO shifted to the drug, thereby decreasing energy levels. The findings are explained based on weak noncovalent interactions, further supported and analyzed through Reduced Density Gradient (RDG) and Noncovalent Interaction (NCI) methods, confirming synergistic non-covalent interactions in surfactant-PPL complexes.

Polyelectrolyte-Surfactant Complex Nanofibrous Membranes for Antibacterial Applications.

Polyelectrolyte-surfactant complexes (PESCs) have garnered significant attention due to their extensive range of biological and industrial applications. Most present applications are predominantly used in liquid or emulsion states, which limits their efficacy in solid material-based applications. Herein, pre-hydrolyzed polyacrylonitrile (HPAN) and quaternary ammonium salts (QAS) are employed to produce PESC electrospun membranes via electrospinning. The formation process of PESCs in a solution is observed. The results show that the degree of PAN hydrolysis and the varying alkyl chain lengths of surfactants affect the rate of PESC formation. Moreover, PESCs/PCL hybrid electrospun membranes are fabricated, and their antibacterial activities against both Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) are investigated. The resulting electrospun membranes exhibit high bactericidal efficacy, which enables them to serve as candidates for future biomedical and filtration applications.

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.

Fabrication of the Pesticide-Attapulgite composites regulated by mixed-surfactants

The SB (DTAB, TTAB, CTAB, OTAB)-AP complex was obtained by modifying attapulgite (AP) with surfactant of SB (DTAB, TTAB, CTAB, OTAB). The structures were characterized by XRD, FT-IR, TGA/DTA and SEM. A new lamellar structure is formed by introducing surfactant. The basal spacing increases with the increase of alkyl chain length of cationic surfactants. Then, the beta-cypermethrin (BCT) composites of BCT/SB-AP, BCT/DTAB (TTAB, CTAB, OTAB)-SB-AP were prepared and investigated. The basal spacings of BCT composites were larger than those of SB-AP and the corresponding DTAB (TTAB, CTAB, OTAB)-AP. The existence of BCT and surfactants molecules into BCT composites was further confirmed. The BCT/DTAB (TTAB, CTAB, OTAB)-SB-AP have the smaller specific surface areas than DTAB (TTAB, CTAB, OTAB)-AP due to the increase of AP exfoliation in the presence of SB. Fabrication mechanism of BCT composites was put forward. Release behaviors of BCT were investigated and analyzed in different buffer solutions. The existence of mixed-surfactants influenced distinctly the release rates. BCT composites had the slow release property. The release behaviors were well fitted by pseudo second-order and parabolic diffusion models. This study provided a new approach to improve the utilization efficiency of pesticide and could be applied as a pesticide delivery system.

Effect of sodium alkyl sulfate chain length on foam stability: A molecular dynamics study

The alkyl chain length of surfactant plays an important role on its own performance. In this paper, the effect of sodium alkyl sulfate (SAS) with different alkyl chain lengths on the stability of foam film was studied by molecular dynamics (MD) method. The results showed that the increase of alkyl chain length enhances the interaction between SAS molecules, and increases the thickness of hydrated shell around the polar head. To investigate the effect of alkyl chain length on the drainage and rupture process of foam film, the steered molecular dynamics (SMD) study of foam liquid film with two external forces was also carried out. One external force is parallel to Z-axis and perpendicular to the liquid film, which can reflect the difficulty of foam drainage. The other is parallel to the horizontal direction of X-axis, which represents the stability of foam film. It was found that the longer the alkyl chain of SAS, the greater the external force required to destroy the foam surface. In addition, the free energy change profile of SAS from aqueous phase to SAS layer further indicates that the growth of alkyl chain can enhance the stability of foam film. This work aims to further understand the mechanism of foam film rupture and explore industrial methods to control foam stability.

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.

The effect of alkyl chain length of the imidazole ionic liquid surfactants on the improving lubricating properties of the hexagonal lyotropic liquid crystal composed of the [C16imCn]Br/hydrotalcite/H2O

The hydrotalcites were dispersed in the hexagonal lyotropic liquid crystals (LLCs) composed of 1-hexadecyl-3-alkyl imidazolium bromide ([C16imCn]Br, n = 1, 2 and 3) and H2O. The effects of the hydrotalcite concentration and the alkyl chain length of the [C16imCn]Br on the properties and the lubricant performance of the [C16imCn]Br/hydrotalcite hexagonal LLCs were studied by small angle X-ray diffraction measurements, rheology and tribology. Compared with the pure hexagonal LLCs, the incorporation of hydrotalcite into the [C16imCn]Br hexagonal LLCs can increase the interlayer distances and the viscoelasticity of the hybrid hexagonal LLCs gradually. However, the friction coefficient and wear volume decrease firstly and then increase with the increasing of hydrotalcite content. With the increase of the alkyl chain length of the [C16imCn]Br, the viscoelasticity, the interlayer distance and the water permeability of the mixed LLCs gradually increase which decreases the friction coefficient and wear volume at the moderate hydrotalcite content. The mechanism of the effective improvement of lubrication performance of the hybrid hexagonal LLCs is the tribofilm formed by the physical adsorption and tribochemical reaction of [C16imCn]Br/hydrotalcite LLCs on the steel surface.

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.

Transition from antagonistic to synergistic interaction in mixed micellar system by increase in alkyl chain length of alkyl trimethylammonium bromide

Herein, the electrical conductivity technique used to measure the critical micelle concentration (cmc) for pure cationic surfactants (Dodecyl/cetyltrimethylammonium bromides) and phenothiazine drug (Promethazine hydrochloride), as well as their different mole fractions in 10−3 ​mol/kg 1-methyl-3-octylimidazolium chloride (C8mim.Cl) at different temperatures. By using the cmc values the regular solution theory used to evaluate the micellar mole fraction for DTAB/CTAB-PMT mixed systems. The clint's model used to calculate the ideal critical micelle concentration (cmc∗) that helps to evaluate the ideal micellar mole fraction for studied mixed systems, both explain the deviation from ideality. In addition, interaction parameter βm helps to confirm the nature of interaction (either antagonistic or synergistic) for the studied systems. The calculated parameters confirm a transition in the binding nature from antagonistic to synergistic with the increase in alkyl chain length of cationic surfactant i.e., component of the binary mixed system. The ease of micellization for the studied systems discussed by the standard Gibb's energy of micellization (ΔGm0), as well as the standard enthalpy and standard entropy of micellization were (ΔHm0) and (ΔSm0), respectively to discuss the stability of the studied systems.

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.

Single-Use Electrochemical Platform for Monitoring of Antimicrobial Activity in Comparison to Minimum Inhibitory Concentration Assay

Determination of antimicrobial properties of (bio)molecules has been conventionally performed using minimum inhibitory concentration (MIC) assay based on visual monitoring of turbidity which may cause incorrect interpretations. Surfactants are widely used as disinfectants because of their antimicrobial properties, especially in todays’ world struggling with infections. In this study, surfactants are chosen as the model molecules for the fabrication of a voltammetric biosensor for monitoring antimicrobial activity for the first time in the literature. The antimicrobial effect of anionic and cationic surfactants on E. coli and S. aureus and the effect of alkyl chain length of cationic surfactants were investigated. Anodic peak current (Ia) value was measured by cyclic voltammetry (CV) in a redox probe containing K3[Fe(CN)6] and K4[Fe(CN)6] ions to understand the biointeraction mechanisms. The effect of the surfactants on the microorganisms was characterized by optical microscopy, SEM, and FTIR. The electrochemical biosensor could detect the antimicrobial properties of the surfactants by obtaining consistent results with MIC assay and spectroscopy. While cationic surfactants were more effective on the microorganisms, hexadecyltrimethylammonium bromide (CTAB) is the most effective surfactant by reaching a low MIC level. This article has novelty using disposable PGEs in combination with the CV technique for antimicrobial activity evaluation.

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.

Influence of the alkyl chain length of surfactant on adsorption process: A case study

To investigate the effect of alkyl chain length of surfactant on the adsorption process behavior, the present study was applied the adsorption of anionic methyl orange (MO) dye using mineral pumice (NP) as natural adsorbent, and Dodecyltrimethylammonium bromide (DTAB), Tetradecyltrimethylammonium bromide (TTAB), and Cetyltrimethylammonium bromide (CTAB) modified pumice as namely DMP, TMP, and CMP, respectively. Due to the differences in the alkyl chain length of the surfactants, the effect of chain length on the MO dye adsorption process can be evaluated. For an understanding of the physical and chemical structure of adsorbents, XRF, SEM, BET, and FTIR analyses were performed. The effect of contact time, initial MO concentration, adsorbent dosage, and solution pH was studied. Langmuir, Freundlich, Jovanovic and Temkin isotherm models were used for fitting of the experimental data. Based on the results of the isotherm models and also calculating the errors of each model, the highest match was obtained with Langmuir isotherm, and the maximum adsorption capacities for NP, DMP, TMP, and CMP were 6.43, 18.13, 28.60, and 31.73 mg/g, respectively. Also, the results of kinetic studies showed that the data are in maximum agreement with the pseudo-second-order kinetic model. Therefore, it can be concluded that an extended surfactant chain increases the adsorption capacity, and it can be found that one of the effective factors in the adsorption processes is the hydrophobic interactions of the modifiers.

Influence of the Alkyl Chain Length of Imidazole Ionic Surfactants on their behavior with Sodium Dodecyl Sulfate

Influence of the Alkyl Chain Length of Imidazole Ionic Surfactants on their behavior with Sodium Dodecyl Sulfate

Influence of the Alkyl Chain Length of the Imidazole Ionic Liquid-Type Surfactants on Their Aggregation Behavior with Sodium Dodecyl Sulfate.

The influence of the alkyl chain length of the ionic liquid surfactants 1-hexadecyl-3-alkyl imidazolium bromide [C16imCn]Br (n = 2-16) on their aggregation behavior with sodium dodecyl sulfate (SDS) in water was studied. The rheological properties, thermostability, and microstructure of the samples were characterized via a combination of rheology, cryo-transmission electron microscopy, polarization optical microscopy, and small-angle X-ray scattering. Upon the addition of SDS, the [C16imCn]Br (n = 2, 4, 6) rodlike micelles transit into the gels with high water content. The effects of molar ratio and alkyl chain length on the viscoelasticity and thermal stability of the SDS/[C16imCn]Br (n = 2, 4, 6) gels were studied. However, the [C16imCn]Br (n = 8, 10, 12, 14, 16) rodlike micelles precipitate with the addition of SDS. The [C16imCn]Br (n = 10, 12, 14, 16) gels transit to the rodlike micelles with the proper addition of SDS. The mechanism of the influence of the alkyl chain length of the [C16imCn]Br on their aggregation behavior with SDS was proposed.

Micellization of Ionic Liquid Surfactants Induced by Sodium Polystyrenesulfonate in Aqueous Solutions

The aggregation phenomena of two ionic liquid surfactants—1-decyl-3-methylimidazolium chloride (C10MeImCl) and 1-hexadecyl-3-methylimidazolium chloride (C16MeImCl) have been investigated in aqueous solutions in the presence of a polyelectrolyte, sodium polystyrenesulfonate (NaPSS), using electrical conductivity, surface tension, fluorescence and vapor pressure measurements. The counterion-condensation behavior of aqueous NaPSS has also been studied and approximately 62% of the counterions have been found to remain uncondensed in these solutions. The characteristic concentrations signifying different kinds of interactions, namely the critical aggregation concentration and the polymer saturation concentration, in the premicellar regime have been identified. Surface-active complexes with bound surfactant monomers onto the polyion backbone, non-surface active aggregates with small micellar units wrapped by polyion chains, and non-surface active micelles of ionic liquid surfactant monomers, were found to form in aqueous ionic liquid surfactant solutions in the presence of NaPSS. The surfactant concentration where polyelectrolyte–surfactant monomer complexes begin to form (cac), the concentration where the polyion chains get saturated with the small micellar units (psc), and the concentration where micelles of ionic liquid surfactant molecules begin to appear (cmc*) were identified in aqueous C16MeImCl solutions in the presence of NaPSS. Only two critical concentrations, namely the psc, and cmc* were, however, detected in aqueous C10MeImCl solutions in the presence of NaPSS. Effects of alkyl chain length of the ionic liquid surfactants, temperature, NaPSS concentration, and the charge parameter of NaPSS on the self-aggregation of the ionic liquid surfactants have been considered to elucidate the interactions in these mixed systems. The thermodynamics of micellization in these systems have also been studied and the spontaneity of the polyelectrolyte-induced micellization processes have been rationalized for the systems investigated, with the entropy terms superseding the enthalpy terms.

Effects of alkyl chain length on synergetic interaction and micelle formation between a homologous series of n-alkyltrimethylammonium bromides and amphiphilic drug propranolol hydrochloride

The aggregation behavior of a homologous series of n-alkyltrimethylammonium bromides (CnH2n+1TAB; n = 12, 14, and 16) in the presence of amphiphilic drug propranolol hydrochloride (PPL) in aqueous solutions were studied using conductometric technique. The critical micelle concentrations (CMCs) were determined for pure PPL and surfactant as well as mixed micelles [surfactant(1)/PPL(2)] using the Carpena method. Various physicochemical parameters such as ideal CMC (CMCid), degree of counter-ion binding (α), micellar mole fractions of surfactant (X1m and X1id), interaction parameter (βm), the activity coefficients of components (f1m and f2m), standard Gibbs free energy of micellization (ΔGmic0) and the excess free energy of micellization (GmicE) values have been calculated and compared in detail using Clint's and Rubingh's theories. The activity coefficients of surfactant and PPL are less than 1 (f1m < 1 and f2m < 1) and the values of βm are negative in all mixtures, which indicates the synergistic interaction between surfactant and PPL. Also, the results show that the synergistic effects of mixed micelles strongly depend on the chain length of cationic surfactant, and the values of interaction parameter increase with increasing the alkyl chain length of surfactant. Of the several interactive interactions, it seems hydrophobic interaction is the most dominant interaction between the molecules of the mixed systems among all observed interactive interactions in this study.

Formation of Drug-Participating Catanionic Aggregates for Extended Delivery of Non-Steroidal Anti-Inflammatory Drugs from Contact Lenses.

This paper focuses on extending drug release duration from contact lenses by incorporating catanionic aggregates. The aggregates consist of a long-chain cationic surfactant, i.e., cetalkonium chloride (CKC), and an oppositely charged anti-inflammatory amphiphilic drug. We studied three non-steroidal anti-inflammatory (NSAID) drugs with different octanol–water partition coefficients; diclofenac sodium (DFNa), flurbiprofen sodium (FBNa), and naproxen sodium (NPNa). Confirmation of catanionic aggregate formation in solution was determined by steady and dynamic shear rheology measurements. We observed the increased viscosity, shear thinning, and viscoelastic behavior characteristic of wormlike micelles; the rheological data are reasonably well described using a Maxwellian fluid model with a single relaxation time. In vitro release experiments demonstrated that the extension in the drug release time is dependent on the ability of a drug to form viscoelastic catanionic aggregates. Such aggregates retard the diffusive transport of drug molecules from the contact lenses. Our study revealed that the release kinetics depends on the CKC concentration and the alkyl chain length of the cationic surfactant. We demonstrated that more hydrophobic drugs such as diclofenac sodium show a more extended release than less hydrophobic drugs such as naproxen sodium.

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.

Growth of silica shell on hydrophobic upconverting nanocrystals – Mechanism and control of porosity

The method based on the oil/water biphasic system appears as the most effective for the growth of mesoporosus silica shell on hydrophobic nanocrystals. In this paper the influence of various synthesis parameters, such as catalyst, solvent, temperature or hydrophobic chain length of surfactant, on porosity and thickness of silica layer grown on up-converting nanocrystals (UCNPs) was systematically investigated. The key factor determining morphology of silica shell and allowing to control its porosity is a kind of solvent used for TEOS dilution. For solvents of low polarity index silica shell has dendrimeric structure with pore size of 4–5.5 nm, while for solvents with high polarity index the silica shell is non-porous. The pore size can be also controlled in the range from 2 to 5.5 nm through selection the catalysts type. The morphology of the silica shell is also influenced by alkyl chain length of the cationic surfactant as well as temperature. Based on these new experimental results the mechanism of formation of mesoporous silica shell on inorganic nanopaticles was proposed and discussed. It was also proved, that the organic dyes, like Rhodamine B can be effectively incorporated inside the pores of mesoporous UCNPs@SiO2 nanoparticles. This signify that such hybrid functional materials, which in addition exhibit stability of water dispersions and possibility of biofunctionalization, offer great potential for development of biomarkers or drug carriers.