Formation and rheological behavior of wormlike micelles in a catanionic system of fluoroacetic acid and tetradecyldimethylaminoxide

In situ formation and dispersion of lanthanide complexes in wormlike micelles

Lanthanide-containing, water-based fluids normally suffer from low photoluminescent (PL) and/or colloidal stability, which greatly hinders their applications. Herein, we report the preparation of PL fluids which contain in situ formed europium complexes in aqueous solution. The strategy first relies on the construction of wormlike micelles by mixing a zwitterionic surfactant (tetradecyldimethylaminoxide, C₁₄DMAO) and a tridentate ligand for a lanthanide cation (2,6-dipicolinic acid, DPA) in water. The addition of the dual-functionalized DPA to an aqueous solution of C₁₄DMAO (100 mol L^-1) induced non-monotonic rheological changes, with the expected formation of a pseudogemini surfactant at a DPA-to-C₁₄DMAO molar ratio of approximately 1 : 2. When a third component of EuCl₃ is introduced to this system, complexes formed in situ between Eu³⁺ and DPA, resulting in bright red-emission. Besides DPA, C₁₄DMAO is also involved in the complexation, which squeezes out water molecules and greatly improves the PL stability of the fluid. The synergetic effect among Eu³⁺, DPA and C₁₄DMAO leads to the high colloidal stability of the fluid, opening the door for a wide range of potential applications. Further tests indicate that this strategy can be easily expanded to other lanthanide cations such as Tb³⁺.

Synthesis and Study of a New Type of Fluorinated Polyether Demulsifier for Heavy Oil Emulsion Demulsification

To solve the problem of heavy oil demulsification difficulties in Liaohe Oilfield, phenolamine resin initiator was synthesized from p-trifluoromethyl phenol, and then FB series fluorinated polyether demulsifiers were synthesized by block polymerization using ethylene oxide (EO) and propylene oxide (PO) as raw materials. The demulsifiers were characterized by infrared spectroscopy, cloud point, hydrophilic-lipophilic balance (HLB) value, and surface tension. The demulsifying and dehydrating properties were tested by demulsifying and dehydrating experiments, the demulsification mechanism was analyzed by the microscopic demulsification process test, and the influence of demulsifier addition and demulsifying temperature on demulsifying performance was also studied. The results showed that under the condition of the optimum demulsification temperature of 60 °C and the optimum demulsifier dosage of 100 mg/L, the water removal (%) of fluorinated polyether demulsifier of FB 4 was the highest, and the overall water removal (%) of 50 mL crude oil emulsion in Liaohe Oilfield reached 90.33% within 2 h, which was better than the current demulsifier used in Liaohe crude oil.

Hydrogels Consisting of Vesicles Constructed via the Self-Assembly of a Supermolecular Complex Formed from α-Cyclodextrin and Perfluorononanoic Acid

The self-assembly of α-cyclodextrin (α-CD) mixed with a fluorocarbon surfactant, perfluorononanoic acid (PFNA), in aqueous solution was studied. Interestingly, the 1:1 inclusion complex, PFNA@α-CD, was verified to form by ¹H nuclear magnetic resonance measurement. Also as the building block, the PFNA@α-CD complex was further self-assembled into worm-like micelles under lower concentrations while hydrogels were self-assembled under higher concentrations. The hydrogels were composed of unilamellar vesicles with polydisperse size, which were clearly detected by freeze-fracture transmission electron microscopy measurements. Besides, the vesicle hydrogels showed high viscoelasticities and a substantial elastic characteristic. Also as revealed by the results of Fourier transform infrared measurements, the driving force for the vesicle and worm-like micelle formation was the hydrogen bonding between α-CD molecules. Then, these vesicles were densely packed to form hydrogels. As far as we know, the self-assembly of CDs and fluorocarbon surfactants based on host-guest inclusion in aqueous solution has been limitedly reported. Our work successfully constructed hydrogels consisting of vesicles through the self-assembly of the α-CD/PFNA complex for the first time and will also provide a better understanding and enrich the fundamental research of the self-assembly behavior of the CD/fluorosurfactant complex.

Surface charge tunable catanionic vesicles based on serine-derived surfactants as efficient nanocarriers for the delivery of the anticancer drug doxorubicin

Self-assembled vesicles composed of amino acid-based cationic/anionic surfactant mixtures show promise as novel effective drug nanocarriers. Here, we report the in vitro performance of vesicles based on cationic (16Ser) and anionic (8-8Ser) serine-based surfactants using a cancer cell model for the delivery of the anticancer drug doxorubicin (DOX). This catanionic mixture yields both negatively (0.20 in the cationic surfactant molar fraction, x16Ser) and positively (x16Ser = 0.58) charged vesicles, hence providing a surface charge tunable system. Low toxicity is confirmed for concentration ranges below 32 μM in both formulations. DOX is successfully encapsulated in the vesicles, resulting in a surface charge switch to negative for the (0.58) system, making both (0.20) and (0.58) DOX-loaded vesicles highly interesting for systemic administration. High uptake by cells was demonstrated using flow cytometry and confocal microscopy. Drug accumulation results in an increase of cell uptake up to 250% and 200% for the (0.20) and (0.58) vesicles, respectively, compared to free DOX and with localizations near the nuclear regions in the cells. The in vitro cytotoxicity studies show that DOX-loaded vesicles induce cell death, confirming the therapeutic potential of the formulations. Furthermore, the efficient accumulation of the drug inside the cell compartments harbors the potential for optimization strategies including phased delivery for prolonged treatment periods or even on-demand release.

Formation of polyhedral vesicle gels from catanionic mixtures of hydrogenated and perfluorinated surfactants: effect of fluoro-carbon alkyl chain lengths

The effects of alkyl chain length of anionic fluorinated fatty acid surfactants, CnF2n+1COOH (n = 7-11), mixed with one cationic hydrocarbon surfactant, tetradecyltrimethylammonium hydroxide (TTAOH), on the formation of polyhedral vesicle gels were investigated in aqueous solutions. On the basis of phase behavior mapping, C8F17COOH, C9F19COOH, C10F21COOH and C11F23COOH except C7F15COOH all formed polyhedral vesicle gels when they were mixed with TTAOH under certain mixed ratios, which was demonstrated by freeze-fracture transmission electron microscopy (FF-TEM) measurements. Meanwhile, the following observation was not observed: the longer the fluorinated alkyl chain, the more effective the formation of gels by fluorinated fatty acids. The formation of the faceted vesicle gels was determined both by the rigidity of the fluorinated alkyl chain and the co-crystallization of fluorocarbon chains and hydrocarbon chains, as revealed by the results of differential scanning calorimetry (DSC), wide angle X-ray scattering (WAXS) and 19F NMR measurements. Furthermore, the polyhedral vesicle gels showed high viscoelasticity, which increased clearly with increasing fluorinated alkyl chain length, indicating that the viscoelastic property of the polyhedral vesicle gel was a result of the crystalline state of the polyhedral vesicle bilayers at room temperature. As far as we know, such polyhedral vesicle gels formed from perfluorinated and hydrocarbon surfactant mixtures have been rarely reported. Our study can be a great advancement in fundamental research of surfactant vesicle gels.

Growth of wormlike micelles in nonionic surfactant solutions: Quantitative theory vs. experiment

Despite the considerable advances of molecular-thermodynamic theory of micelle growth, agreement between theory and experiment has been achieved only in isolated cases. A general theory that can provide self-consistent quantitative description of the growth of wormlike micelles in mixed surfactant solutions, including the experimentally observed high peaks in viscosity and aggregation number, is still missing. As a step toward the creation of such theory, here we consider the simplest system - nonionic wormlike surfactant micelles from polyoxyethylene alkyl ethers, C_iE_j. Our goal is to construct a molecular-thermodynamic model that is in agreement with the available experimental data. For this goal, we systematized data for the micelle mean mass aggregation number, from which the micelle growth parameter was determined at various temperatures. None of the available models can give a quantitative description of these data. We constructed a new model, which is based on theoretical expressions for the interfacial-tension, headgroup-steric and chain-conformation components of micelle free energy, along with appropriate expressions for the parameters of the model, including their temperature and curvature dependencies. Special attention was paid to the surfactant chain-conformation free energy, for which a new more general formula was derived. As a result, relatively simple theoretical expressions are obtained. All parameters that enter these expressions are known, which facilitates the theoretical modeling of micelle growth for various nonionic surfactants in excellent agreement with the experiment. The constructed model can serve as a basis that can be further upgraded to obtain quantitative description of micelle growth in more complicated systems, including binary and ternary mixtures of nonionic, ionic and zwitterionic surfactants, which determines the viscosity and stability of various formulations in personal-care and house-hold detergency.