Aqueous Micellar Solutions Research Articles

Non-ionic fluorinated amphiphilic block copolymer via RAFT polymerization and their application as surfactant in emulsion polymerization

This investigation reports the synthesis of block copolymer of poly(ethylene glycol) methyl ether methacrylate (PPEGMA) with poly(heptafluorobutyl acrylate) (PHFBA). The blockcopolymer was prepared via reversible addition-fragmentation chain transfer polymerization (RAFT). The RAFT end-capped poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) macro-chain transfer agent (CTA) was prepared using 2-cyano-2-propyl dithiobenzoate (CPBT) as RAFT agent. The synthesized PPEGMA was later used as macro-RAFT agent for the polymerization of 2,2,3,3,4,4,4-heptafluorobutyl acrylate (HFBA) which yielded well-defined block copolymers of varied lengths. The PPEGMA-b-PHFBA block copolymer self-assembles in water produces spherical micelles with core-shell nano-structure where the core made of hydrophobic block (PHFBA) and shell is of hydrophilic block (PPEGMA). The synthesized block copolymers, PPEGMA−b−PHFBA, an amphiphilic block copolymers were used as surfactant in the surfactant free emulsion polymerization of styrene. Aqueous micellar solutions of the block copolymers were characterized by DLS and TEM analyses. The CMC value of polymeric surfactant was 0.046 mg. mL−1, determined by surface tension analysis. The block copolymers were characterized by GPC, 1H NMR, FT-IR, DSC analyses.

Spectroscopic and time-dependent density functional investigation of the role of structure on the acid-base effects of citrinin detection

A time-dependent density functional theory (TD-DFT) study was carried out on tautomers of the mycotoxin citrinin in the neutral, anionic, and cationic forms to gain insight into the role of chemical structure on detection. Steady-state fluorescence studies of citrinin in micellar aqueous solutions produced unusual results for ionic surfactants and the neutral Triton X-100 enhanced fluorescence emission. Ground-state and time-dependent density functional studies were carried out on five tautomers of citrinin using the B3LYP density functional and the 6-311+G(2df,2p) basis set. The investigation revealed that deprotonation is a major factor governing the shifts in fluorescence excitation and emission maxima. Moreover, the position of the lowest unoccupied molecular orbitals is removed from the fluorophore moiety of citrinin in the dianionic state which is consistent with the diminished fluorescence of the toxin in basic solutions. The ionic characteristics of certain chemosensors can influence the structure and intrinsic spectroscopic properties of citrinin.

Oil-in-Water Emulsion Templated and Crystallization-Driven Self-Assembly Formation of Poly(l-lactide)-Polyoxyethylene-Poly(l-lactide) Fibers.

A molecular solution of an amphiphilic block copolymer may act as an oil phase by dispersing into an aqueous micellar system of small-molecular surfactant, forming oil-in-water (O/W) emulsion droplets. In this paper, an as-synthesized triblock copolymer poly(l-lactide)-polyoxyethylene-poly(l-lactide) (PLLA-PEO-PLLA) was dissolved in tetrahydrofuran (THF) and then added to an aqueous micellar solution of nonaethylene glycol monododecyl ether (AEO-9), forming initially coalescent O/W emulsion droplets in the size range of 35 nm-1.3 μm. Along with gradual volatilization of THF and simultaneous concentration of PLLA-PEO-PLLA molecules, the amphiphilic copolymer backbones themselves experience solution-based self-assembly, forming inverted core-corona aggregates within an oil-phase domain. Anisotropic coalescence of adjacent O/W emulsion droplets occurs, accompanied by further volatilization of THF. The hydrophilic block crystallization of core-forming PEOs and the hydrophobic chain stretch of corona-forming PLLAs together induce the intermediate formation of rod-like architectures with an average diameter of 300-800 nm, and this leads to a large-scale deposition of the triblock copolymer fibers with an average diameter of ∼2.0 μm. Consequently, this strategy could be of general interest in the self-assembly formation of amphiphilic block copolymer fibers and could also provide access to aqueous solution crystallization of hydrophilic segments of these copolymers.

Multicenter Polyester Initiators for the Preparation of Graft Copolymers with Oligo(2‐Oxazoline) Side Chains

Multicenter polyester initiators intended for the cationic polymerization of oxazolines were synthesized via high‐temperature polycondensation of 2‐(4‐(2‐bromoethyl)phenyl sulfonyl hydroquinone with a number of aromatic and alkylene‐aromatic dichloroanhydrides. The Kuhn segment values, liquid‐crystalline properties, and molecular‐mass characteristics of the macroinitiators are determined. The synthesized macroinitiators were used in cationic ring‐opening polymerization to obtain hybrid comb polymers containing poly(2‐oxazoline) side chains. It was suggested the method for estimating the length of poly(oxazoline) side fragments and graft density. It was demonstrated that at a certain ratio between backbone length and side chain length (which depends on chemical structure of the initiator), comb copolymers The graft copolymers form aqueous micellar solutions with a narrow particle‐size distribution. They possess a lower critical solution temperature.

FRET-Mediated Zn2+ Sensing in Aqueous Micellar Solution: Application in Cellular Imaging and Molecular Logic Gate

Forster (fluorescence) resonance energy transfer (FRET) is an excellent method in generating characteristic fluorescence signals between two light sensitive molecules in the 1–10 nm range. On the other hand, studies of Zn2+ detection and imaging are also important, as zinc is the second most abundant transition metal ion in the human body and is involved in many biological activities and neurological functions. This work is a superposition between these two realities, which demonstrates the excellent performance of 4-(pyridine-2-yl)-3H-pyrrolo [2, 3-c] quinoline (PPQ) as a FRET sensor for Zn2+, entrapped in aqueous micellar solution, in presence of Rhodamine B (RB)/Rhodamine 6G (R6G). We show that easy, superior detection and molecular imaging of Zn2+ becomes possible via FRET, as PPQ nonradiatively transfers its energy to R6G/RB, only when it binds with Zn2+, over important biological cations including Na+, K+, Ca2+, Mg2+. During FRET, the Forster radius (R0) between the donor (PPQ) and the acceptor (RB/R6G) is calculated to be ≈ 4 nm, when they are encapsulated in sodium dodecyl sulphate (SDS) micelles at pH 6. Moreover, on careful observation of the fluorescence behavior of PPQ, we also demonstrate that PPQ functions like a monomolecular circuit in an INHIBIT logic gate, based upon two chemical inputs from Zn2+ and Rhodamine.

Characterization of Pyrene Solubilization in Selective Micellar Media of Novel Bio-degradable Natural Surfactant Saponin (Extracted from Soap Nut) and Conventional Surfactant SDBS in Presence and Absence of Common Salt NaCl

Abstract Solubilisation of pyrene (PAHs) in aqueous micellar solutions of natural surfactant saponin and conventional surfactant sodium dodecylbenzene sulfonate (SDBS) has been examined by UV-Vis and steady state fluorescence spectrometry at 30°C. The effect of addition of common salt NaCl on the I1/I3 of fluorescence has also been determined. The experiment concludes that the pyrene molecules were incorporated in the palisade layers of both micelles because of their hydrophobic character. The interaction of pyrene with a neutral saponin micelle resulted in a red shift of UV absorption spectra, while the negative headed surfactant SDBS showed no such phenomena. The resulting thermodynamic parameters proved the better efficiency of the bio-surfactant saponin for the solubilization of pyrene with respect to that of the conventional surfactant SDBS. With increasing ionic strength (on addition of NaCl) the solubilization of pyrene was found to be better and effective in both the surfactant mediums.

Character of Localization and Microenvironment of Solvatochromic Reichardt's Betaine Dye in Sodium n-Dodecyl Sulfate and Cetyltrimethylammonium Bromide Micelles: Molecular Dynamics Simulation Study.

The problem of using surfactant micellar aqueous solutions as reaction media centers on estimating the polarity of the micellar pseudophase. The most popular approach is the utilization of solvatochromic dyes. Among the last, the strongest ones are the dipolar pyridinium N-phenolate dyes. The complication of such approach, however, consists in the nonuniform character of the environment of the indicator fixed in the micellar pseudophase. The aim of this study is to reveal the character of localization and orientation of the standard solvatochromic pyridinium N-phenolate dye, 4-(2,4,6-triphenylpyridinium-1-yl)-2,6-diphenylphenolate, the so-called Reichardt's dye, within the micellar pseudophase of an anionic (sodium n-dodecyl sulfate, SDS) and cationic (cetyltrimethylammonium bromide, CTAB) surfactants using MD simulations. The locus and hydration of the dye are found to be dependent on the surfactant nature. New approaches are proposed to quantitatively describe the state of the dye within the pseudophase. The results confirm the experimental data, which indicate the higher polarity of the interfacial region in the case of the SDS micelles. Because this dye is also used as an interfacial acid-base probe, the corresponding study is simultaneously performed for its protonated, i.e., cationic form. The neutral and protonated forms of the dye are found to be localized and hydrated in a different way in both SDS and CTAB micelles. This should be taken into account when using the Reichardt's dye as an acid-base indicator for estimating the electrical surface potential of micelles. The presented approach may be recommended to shed light upon the locus of other solvatochromic and acid-base indicators in micelles and micellar-like aggregates.

Effect of Electrolyte (NaCl) and Temperature on the Mechanism of Cetyl Trimethylammonium Bromide Micelles

In the last few decades, surfactants and electrolyte interaction has gained considerable attention of researchers due to their industrial and domestic applications. In this work, the effects of electrolyte (NaCl) on the critical micelle concentration (CMC) of the cationic surfactant cetyltrymethyl ammonium bromide (CTAB) at different temperatures were investigated through different techniques such as conductometry, surface tensiometer and viscosimeter. The results showed that the values of CMC of CTAB decreased with the increase in temperature as well as with the addition of NaCl. The value of CMC for pure CTAB was calculated 0.98M at 303K, which was observed to decrease as temperature increased and got value of 0.95M at 318K. Moreover the addition of electrolyte NaCl into the surfactant lead to lowering of the CMC and obtained value of 0.90M at 3M of NaCl, indicating significant electrostatic interactions between surfactant and electrolyte. Moreover the degree of ionization(α) calculated for pure cationic surfactant CTAB was 0.219, which tends to increase with the addition of electrolyte, while that of counter ion binding values (β) was observed to decrease from 0.780 to 0.201. Furthermore, the conductivity of charged micelle of surfactant and free ions of electrolyte contributed to electric conductivity of aqueous micellar solution of surfactant. The results can be helpful to develop better understanding about interaction between electrolyte and surfactant.

Evolution of aqueous micellar solutions in the injection fluids of alkaline–surfactant–polymer and alkaline–surfactant floodings from injection to production

AbstractIn an effort to determine the sources of the nanomicron and submicron oil droplets in the produced water of an industrial ASP flooding project conducted at Daqing fields, evolution of the lower aqueous phases in artificial ASP and AS flooding injection fluids during aging in contact with crude oil and after dilution by reservoir brine was investigated by means of dynamic light scattering and oil content determination. Nanosize swollen micelles were identified in the lower aqueous phases of the artificial ASP and AS flooding injection fluids during aging in contact with crude oil. Slow solubilization of crude oil components by micelles in the lower aqueous phase was observed. Nanomicron and submicron oil droplets were detected in the artificially produced water, which were prepared by diluting the lower aqueous phases of aged artificial AS and ASP flooding injection fluids with reservoir brine to surfactant contents below critical micelle concentration. The nanomicron and submicron oil droplets identified in the blended produced water entering water treatment facilities of the ASP flooding project were determined to have evolved mainly from the swollen micelles in the injection fluid, which broke up when the surfactant content fell to bellow critical micelle concentration. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.

Diffusion of monoalkyl ethers of poly(ethylene glycols) and octyl-β-D-glucopyranoside in micellar solutions

Diffusion coefficients of monoalkyl ethers of poly(ethylene glycols), С8Е4 and С12Е5, and octyl-β-D-glucopyranoside have been measured in aqueous micellar solutions within wide ranges of temperatures and concentrations by dynamic light scattering. The study of the С12Е5–water system containing cylindrical micelles has been supplemented with viscosity measurements, which make it possible to better monitor structural transformations and phase transformations.

Hydrated Micellar Structure of Ethoxylated Nonyl Phenols from PGSE NMR

Abstract Solvent self-diffusion coefficients $D_{w}^{*}$ and Dw are respectively determined by PGSE NMR in the bulk solvent and in suitably prepared aqueous micellar solutions of a series of commercial ethoxylated nonyl phenols (ENPs) at 298 and 317 K. The capability of ENP micelles for obstructing the free diffusion of solvent molecules is characterized by the obstruction ratio $K = D_{w}/D_{w}^{*}$, which turns out to depend merely on the volume fraction of EO units present—regardless of significant changes in solute concentration, distribution of EO chain length, micellar aggregation number and temperature. The experiments are interpreted in terms of a renewed analytical model of ENP micellar structure, based on Tanford’s concept of hydrodynamic particle. The results from model fitting return the characteristic sizes of ENP monomers, support the ellipsoid shape of the micelles, indicate a stable EO shell, follow the trend in the variation of hydration number vs. the chain length predicted by thermal analysis in PEO solutions.

Incorporation of Lamotrigine Drug in the PEO–PPO–PEO Triblock Copolymer (Pluronic F127) Micelles: Effect of Hydrophilic Polymers

AbstractThe hydrophobic drug Lamotrigine (LTG) shows low bioavailability after oral administration. Work has been performed to improve the aqueous solubility of LTG using the micelles of amphiphilic block copolymers. Polyethylene oxide‐ polypropylene oxide‐ polyethylene oxide triblock copolymers (PEO–PPO–PEO), known as Pluronic®, have been the subject of current interest due to the versatile structural possibilities of varying PEO/PPO ratios. Incorporation of LTG in the aqueous micellar solutions of Pluronic® F127 was investigated using UV–visible spectroscopy. The shapes and size of the micelles with and without LTG have been ascertained using dynamic light scattering and small angle neutron scattering experiments. Results show increase in the Pluronic® micellar size with hard sphere radius with the incorporation of LTG. The effect of hydrophilic polymers (PEG1500 and F68) on the LTG‐incorporated Pluronic® F127 micelles was also studied and found inefficient for enhancement of the solubility of LTG. Solid forms of LTG‐incorporated Pluronic® F127 micelles with and without hydrophilic polymers, coded as LPMs, were successfully prepared through the thin‐film hydration method. Fourier transform infrared spectroscopy, X‐ray diffraction spectroscopy and thermogravimetric analysis have been used to ensure the compatibility of the LTG with Pluronic® F127 micelles in prepared LPMs. All the LPMs showed good incorporation efficiency, loading capacity and the sustained release profile of LTG. Results showed no specific improvement with the addition of hydrophilic polymers in the studied concentration range.

Escherichia coli removal from model substrates: Underlying mechanism based on nanofluid structural forces.

Understanding the interactions between bacteria and solid surfaces that result in bacterial adhesion and removal is of immense importance for reducing foodborne illness outbreaks. A nanofluid formulation comprised of a sodium dodecyl sulfate (SDS) micellar aqueous solution in the presence of an organic acid (as a pH controller) was used to test the E. coli K12 removal from two substrates, polyvinylchloride (PVC) and partially hydrophobic glass. We investigated the bacterial removal efficacy based on the combined effect of the nanofluid's structural forces and bacterial isoelectric point. To quantify the bacteria-PVC coverage, we used fluorescence microscope. The Langmuir isotherm at the low volume fraction was applied to estimate the adsorption energy of E. coli K12. We obtained a value of about 2.5±0.2kT. This value compared favorably with the value of 2.1kT reported previously for E. coli NCTC 9002 (Vanloosdrecht et al., 1989). We applied the dynamic light scattering method to estimate the radius of the gyration of E. coli K12. The radius of the gyration was used to estimate the limit of surface area covered by the bacterium and compared it to the surface area measured from the image taken with fluorescence microscope. We found that they are in good agreement with each other. We modeled the nanofluid oscillatory structural energy against the E. coli K12 adsorption energy by applying the statistical mechanics approach. Based on the model prediction, the oscillatory interaction energy was estimated at the vertex between a bacterium and the substrate (i.e., the wedge film's interaction energy at one particle layer). The evaluated film's repulsive energy due to the oscillatory structural forces (OSF) was about 15.6±4.4kT of the 0.02M SMNF (the SDS micellar nanofluid formulation) and several times higher than the bacterial adsorption energy, 2.5±0.2kT. The OSF of the 0.06M SMNF was measured by AFM (the oscillatory decay force curve). The period and number of oscillations versus distance was annualized and used to obtain information for the effective size of the nanoparticles and nanofluid's effective volume fraction. These findings suggest that the OSF is capable of bacteria/microorganism removal from contaminated substrates.

Synthesis of comb-shaped polymers via controlled cationic polymerization of oxazolines with polyester-type macroinitiator

On the basis of macroinitiators of polyester type, hybrid comb-shaped polymers with poly-2-isopropyl-2-oxazoline side fragments are prepared via ring-opening cationic polymerization. A method for estimating the length of polyoxazoline side chains and their grafting density is proposed. It is shown that, at the given ratio of the length of backbone and side chains, which depends on the chemical structure of the initiator, the graft copolymers are capable of formation of micellar aqueous solutions with a lower critical solution temperature.

Shear-induced structural and thermodynamic phase transitions in micellar systems.

In this contribution a methodology to compute and classify shear-induced structural and phase transitions in surfactant/water mixtures from rheological measurements is presented. Non-linear rheological experiments, considering variations in surfactant concentration and temperature, are analyzed. In particular, the parameters of the BMP (Bautista-Manero-Puig) model, obtained from the fitting of the shear stress versus shear rate data, which are functions of surfactant concentration and temperature, allow classifying structural and phase transition boundaries. To test this methodology, we consider the analysis of the shear-induced structural and phase transitions of two micellar systems, cetyltrimethylammonium tosylate (CTAT)/water as a function of CTAT concentrations and Pluronics P103/water as a function of temperature. We found that the CTAT/water system presents a first-order phase transition at 30 ° C, and around 31 to 32 wt.% from isotropic to nematic phases, whereas a 20 wt.% Pluronics P103 aqueous micellar solution has two second-order (structural) phase transitions, one from spherical to cylindrical micelles at 33.1 ° C, and another one from cylindrical micelles to a nematic phase at 35.8 ° C and one first-order phase transition around 37.9 ° C at high shear rates near to the cloud point previously reported. The proposed methodology is also able to identify the instability regions where the wormlike micelles are broken, producing the typical shear banding behavior.

Photophysical properties and interaction studies of Rose Bengal derivatives with biomimetic systems based in micellar aqueous solutions

Xanthene dyes are compounds extensively used in Photodynamic Therapy against infection caused by microorganisms, cancer and other diseases. In this study, structural changes in Rose Bengal (RBB) xanthene photosensitizer (PS) were performed in order to improve its interaction with biological substrates. In this way, hydrophobic RBB ester derivatives were obtained through insertion of a hydrocarbon chains containing 1, 4 and 10 carbons. The spectroscopic and photophysical properties of these compounds in homogeneous medium (water at physiological pH) and micro-heterogeneous micellar systems formed by sodium dodecyl sulfate (SDS), cetyl trimethylammonium bromide (CTAB) and Pluronic™ P-123 copolymeric surfactant were evaluated. The interaction between the PS and these micelles showed that association and location are significantly dependent on PS and micelle charges, length of the inserted hydrocarbon tail (hydrophobic effects) and the micellar structure. The binding constants (Kb) for the xanthenes in SDS, P-123 and CTAB micelles follow the same trend of the partition coefficients, which reveal the influence of the hydrophobic effects on PS/micelle interaction. Resonance Light Scattering (RLS) and fluorescence anisotropy studies showed the formation of pre-micellar aggregates of PS combined with CTA+ which justifies the high Kb values in this system. Comparative analyses of Stern-Volmer constant (KSV) confirm the pKa results showing that location of each PS into the micelles depends on both, its hydrophobicity and charge. Finally, singlet oxygen quantum yield (ΦΔ1O2) of the ester derivatives presented values from 0.83 to 0.89 such shows that they exhibit high potential to be applied in future photodynamic treatments.

Electrochemical Properties of Poly(Azure A) Films Synthesized in Sodium Dodecyl Sulfate Solution

Radicalization of azure A monomers, a phenothiazines class heterocyclic compound, was carried out by cyclic voltammetry in sodium dodecyl sulfate micellar aqueous solutions for the first time, which allowed poly(azure A) films (PAA(DS)) to be deposited on the electroactive surface of different electrodes. In particular, this work focused on the electrochemical behavior of PAA(DS) films deposited on screen-printed carbon electrodes. To this end, electrochemical techniques, including cyclic voltammetry and electrochemical impedance spectroscopy were employed. The Ru(NH3)63+/2+ redox probe was used to characterize the electroactive area of the PAA(DS)-modified electrodes, with the support of SEM images. The PAA(DS) electrochemical mechanism involves anions transfer and protons transfer in KCl solutions, where the anion transfer is probably slower than the proton transfer. The electrochemical reactivity of PAA(DS) films toward reduced nicotinamide adenine dinucleotide (β-NADH) was compared with other PAA films synthesized in the presence of different inorganic anions under identical experimental conditions. The obtained data showed that PAA(DS) films had better electrocatalytic properties than the same polymer electrogenerated with other inorganic anions, such as Cl−, F−, HPO2 −4, H2PO−4, NO−3 and SO2 −4. This opens up the possibility for further applications as new electrochemical sensing platforms with enhanced capabilities.

L-dopa co-drugs in nanostructured lipid carriers: A comparative study

This paper describes the production and characterization of nanostructured lipid carriers (NLC) containing four different levodopa (LD) co-drugs (PD), named PDA (3,4-diacetyloxy-LD-caffeic acid co-drug), PDB (lipoic acid-dopamine co-drug), PDC (lipoic acid-3,4-diacetoxy-dopamine co-drug), and PDD (dimeric LD co-drug containing an alkyl linker), with therapeutic potential in Parkinson's disease. These co-drugs were produced with the aim of prolonging the pharmacological activity of LD, enhancing its absorption and protecting it from metabolism. These compounds were characterized by very low water solubility that limits their systemic administration. To improve the solubility of these LDPD, NLC were considered.The obtained NLC showed acceptable particle size and a good stability up to two months from preparation. Cryo-TEM morphological characterization revealed no substantial differences between unloaded and co-drug loaded NLC. In vitro studies showed that the LDPD loaded NLC provided a controlled drug release. Moreover, the enhancement of LDPD stability on the hydrolysis catalysed by foetal calf serum (FCS) esterases or in the presence of lipases was evaluated as compared to a labrasol solution. In presence of esterases PDA-NLC and PDD-NLC showed half-lives higher >3-fold as compared to the corresponding aqueous micellar solution. In the case of PDB-NLC it was found that the stability exceeds the 19h. It can be concluded that NLC represent good strategies to encapsulate lipophilic LD co-drugs, although further studies aimed to deeply evaluate anti-parkinsonian effects in vivo have to be carried on.

Zinc(II) Ion Sensing in Aqueous Micellar Solution Using Modified Bipyridine-Based "Turn-On" Fluorescent Probes and its Application in Bioimaging.

The bipyridine-based constructs 4-(pyridine-2-yl)-3H-pyrrolo[2,3-c]quinoline (PPQ) and [6-(3H-pyrrolo[2,3-c]quinolin-4-yl)pyridin-2-yl]methanol (PPQ-OH) and their assemblies with surfactants are evaluated as turn-on fluorescent sensors for Zn2+ ions in aqueous solution. This study strives to overcome the problem of low water solubility of the hydrophobic PPQ and PPQ-OH by using micelles. Whereas the ligands show selective sensing behavior for Zn2+ over important biological cations including Na+ , K+ , Ca2+ , Mg2+ in anionic sodium dodecyl sulfate and non-ionic Tween 80 micelles, no Zn2+ sensing is observed in cationic cetyltrimethylammonium bromide micelles. Unlike in DMF, Cd2+ interference is observed in aqueous conditions, which can be avoided either by performing the study at pH≥9 or by carrying out a time-resolved fluorescence study. Analysis of the Job plot data, the fluorescence lifetimes, and experiments on varying micellar shape and pH, confirms that the coordination volume of the resulting octahedral metal complex and formation of a five-membered chelate ring are critical factors for Cd2+ interference. The described sensing systems are capable of detecting Zn2+ ions at the micromolar level. Additionally, it is shown that PPQ and PPQ-OH can be used to detect Zn2+ in HeLa cells under physiological conditions in bioimaging studies.

ChemInform Abstract: A Review on the Advancement of Ether Synthesis from Organic Solvent to Water

AbstractReview: 106 refs.