Micellar and solubilizing behaviour of Pluronic L-64 in water

Mechanisms, performance optimization and new developments in demulsification processes for oil and gas applications

The present review discusses new developments and optimization of demulsification processes in oil and gas applications, and highlights the critical parameters. Discussed are the primary mechanisms of demulsification, as well as the strategies for developing optimum demulsifiers. Demulsification mechanisms are presented in the context of emulsion stability principles which are equally applicable to the destabilization of crude oil-water emulsions. The present paper is a concise overview of the various surfactant classes and their structure-activity relationship. It correlates demulsification optimization with surfactant properties and their applications. These classes include, but are not limited to pluronic block co-polymers, as well as amine- and siloxane based nonionic surfactants. The emphasis is on providing some strategies for achieving optimum crude oil-water separation efficiency by tuning the demulsifier to the intended application and crude oil properties. A brief overview of unconventional analytical techniques, which reach beyond the standard demulsifier evaluation methods, i.e., Near Infrared Spectroscopy (NIR), and in particular, low resolution NMR relaxometry, highlights their role in monitoring demulsification processes.

Influence of additives on thermoresponsive polymers in aqueous media: a case study of poly(N-isopropylacrylamide)

Thermoresponsive polymers (TRPs) in different solvent media have been studied over a long period and are important from both scientific and technical points of view.

Monitoring the aggregation behaviour of self-assembling polymers through high-resolution ultrasonic spectroscopy

Poloxamer 407 is a well-known self-assembling polymer with a wide range of temperature- and concentration-dependent phase behaviour, such as micellization and gelation. This work was carried out to demonstrate the potential of high-resolution ultrasonic spectroscopy in evaluating aggregation-deaggregation behaviour of self-assembling polymers. In order to achieve this objective, six different concentrations of Poloxamer 407 water dispersion were prepared and analysed between 5 and 35 degrees C using ultrasonic spectroscopy. For comparison, the same samples were also analysed by the DSC technique. The results showed that polymer aggregation process can be successfully monitored using both ultrasonic parameters of sound speed and attenuation. Furthermore, good agreement with DSC data was observed in terms of characteristic transition temperatures and also in terms of micellization kinetics and related parameters.

Phase behavior and micellar properties of carboxylic acid end group modified pluronic surfactants

The micellar behavior of three different carboxylic acid end standing (CAE) surfactants has been characterized using conductometry, differential scanning calorimetry, isothermal titration calorimetry, and dynamic light scattering. The CAE surfactants are modified high molecular weight Pluronic (PEO-PPO-PEO triblock copolymer) surfactants. The influence of pH and salt additives on the critical micellization temperature (CMT) and the cloud point of the CAE surfactants have been studied. Both the CMT and the cloud points of the CAE surfactants increase as a function of pH and decrease as a function of ionic strength. For the CAE surfactants, the CMT varies by about 5 degrees C, and the cloud point shows a variation in the order of 20-30 degrees C, as compared to the unmodified Pluronics. From the different experimental techniques, it follows that at low pH values (pH<3.5), the CAE surfactants show the same micellar behavior as the unmodified Pluronic, while at high pH values (pH>6), the micellar properties of the CAE surfactants are considerably different from those observed for the corresponding Pluronic. It has been demonstrated that the CAE micelles are capable of removing simultaneously divalent ions and phenanthrane. The CAE surfactants are the first known anionic surfactants that show cloud point behavior with the addition of low concentrations of simple salts, such as, for example, NaCl.

PEO−PPO Block Copolymer Vectors Do Not Interact Directly with DNA but with Lipid Membranes

Small angle neutron (SANS) and light scattering was used to study the interaction between fragments of double stranded deoxyribonucleic acid (DNA) and a synthetic triblock [poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)] amphiphilic polymer, known as L64, a potential vector for gene therapy. The mechanism of action of this vector is yet unknown. The contrast variation method was used to separate the partial structure factors of the different components in mixtures of triblock and DNA. It has been found that the copolymer and DNA molecules exhibit repulsive interactions. Further, the interaction between the copolymer and a model lipid membrane was investigated in order to explain the action of the vector. Electrical measurements on black lipid membranes indicated that the main effect of L64 as a vector is to permeabilize the cell's membrane.

Poly(ethylene oxide)-poly(propylene oxide) block copolymer micelles as drug delivery agents: improved hydrosolubility, stability and bioavailability of drugs

The low solubility in biological fluids displayed by about 50% of the drugs still remains the main limitation in oral, parenteral, and transdermal administration. Among the existing strategies to overcome these drawbacks, inclusion of hydrophobic drugs into polymeric micelles is one of the most attractive alternatives. Amphiphilic poly(ethylene oxide)-poly(propylene oxide) block copolymers are thermoresponsive materials that display unique aggregation properties in aqueous medium. Due to their ability to form stable micellar systems in water, these materials are broadly studied as hydrosolubilizers for poorly water-soluble drugs. The present review provides a concise description of the most important applications of PEO-PPO-based copolymers in the Pharmaceutical Technology field as means for attaining improved solubility, stability, release, and bioavailability of drugs.

Concentration, temperature, and salt-induced micellization of a triblock copolymer Pluronic L64 in aqueous media

The effect of copolymer concentration, temperature, and sodium halides (NaI, NaBr, NaCl, and NaF) on micellization and micellar properties of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic copolymer (Pluronic L64: EO13PO30EO13), was examined by different methods such as dye spectral change, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), small angle neutron scattering (SANS), dynamic light scattering (DLS), viscosity, and cloud point (CP). Temperature/polymer concentration/salt dependent aggregation behavior of L64 was observed. The data on critical micelle concentration (CMC), critical micelle temperature (CMT), (CP), micelle size, and shape are reported. The Fourier transform infrared (FTIR) showed temperature dependent changes in C-O-C stretching variation band towards higher wave numbers and broadening of band width during the micellization process; this was attributed to increase in proportion of the anhydrous methyl groups, while the proportion of the hydrated methyl groups was decreased. Differential scanning calorimetry (DSC) provides CMTs and CPs from the same experiment. CMC values derived from dye spectral change, decrease significantly with the addition of salt. The increases in salt/copolymer concentration lower the onset temperature of micellization (CMT). Halide anions influence both CMT and CP in the order of F- > Cl- > Br- > I- when total salt and copolymer concentration kept constant. SANS results show the increase of inter-micellar interaction due to the increase in temperature/salt concentration; this is supported by viscosity data.

Small-angle neutron scattering and theoretical investigation of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) stabilized oil-in-water microemulsions

The aim of this study is to determine the effects of oil solutes and alcohol cosolvents on the structure of oil-in-water microemulsions stabilized by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers. The systems investigated involved the solubilization of 1,3,5-trimethylbenzene or 1,2-dichlorobenzene by P123 (EO(20)-PO(70)-EO(20)) pluronic surfactant micelles in water and water + ethanol solvents. The structures of these swollen micelles were determined by small-angle neutron scattering (SANS). A thermodynamic model was employed to interpret the characterization data. The results of the thermodynamic model for micellization agreed well with the SANS data from samples of micelles swollen by both oils. The model predicted the size of the micelles within 5% accuracy using only one fitting parameter, the micelle polydispersity. Ethanol had significantly different effects on the polymer micelles that contained solubilized oil compared to pure polymer micelles. For pure polymer micelles, the addition of ethanol increased the solubility of the polymer and, therefore, decreased the total volume fraction of micelles, while for polymer-oil aggregates, ethanol tended to have a positive effect on the volume fraction of micelles. SANS results showed that the greatest divergence from pure aqueous solvent results occurred at oil concentrations above the microemulsion stability limit.

Effect of Salts on the Micellization, Clouding, and Solubilization Behavior of Pluronic F127 Solutions

We have examined the effect of NaCl, Na(2)SO(4), Na(3)PO(4), and NaSCN on F127 solutions; properties examined were critical micellization temperature (cmt), cloud point, and solubilization of a model hydrophobic drug, propyl paraben. Static light scattering showed that the first three salts lower the cmt of F127 in the order Na(3)PO(4)>Na(2)SO(4)>NaCl. The extent of lowering depends on the salt concentration and can be ascribed to the water structure-making properties of these salts. NaSCN, a water structure breaker, was found to increase cmt. Pyrene fluorescence was used to study the changes in micellar interior in the presence of salts. We found that the micellar micropolarity is not significantly changed by salts, evidenced by a constant I(1)/I(3) ratio of pyrene. However, the I(e)/I(3) ratio changes significantly with salts, being lower for NaCl, Na(2)SO(4), and Na(3)PO(4) and higher for NaSCN. This is consistent with an increase in the total hydrophobic micellar domain, in micellar microviscosity, or both. Solubilization of propylparaben increases in the presence of Na(3)PO(4), consistent with a larger hydrophobic domain for solubilization. The thermodynamics of micellization continue to be entropically driven in the presence of salts, evidenced by a positive entropy overcoming an unfavorable enthalpy. Copyright 2000 Academic Press.

Effects of inorganic salts on solubilization of estriol in an aqueous solution of poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymer

The effects of inorganic salts on the solubilization of estriol was studied in an aqueous solution of a poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) triblock copolymer (Pluronic L-64). The solubility of estriol increased with increasing Pluronic L-64 and salt concentrations. Furthermore, two clear transition points corresponding to the polymolecular micelle formation and a pronounced change in micellar structure of Pluronic L-64 were found on the solubility curves. The effectiveness of inorganic salts for increasing solubility of estriol followed approximately the lyotropic or Hofmeister series, except Li+.

Temperature Study of Sound Velocity and Volume-Related Specific Thermodynamic Properties of Aqueous Solutions of Poly(ethylene oxide)-Poly(propylene oxide) -Poly (ethylene oxide) Triblock Copolymers

A comprehensive study of sound velocity and apparent specific volume, and adiabatic compressibility and expansibility thermodynamic properties of aqueous solutions of a number of POE-POP-POE triblock copolymers has been carried out in the temperature range 10-45 degreesC. Three series of the above block copolymers were studied: one having similar relative molar masses but different POP/POE mass ratios (F38, P103, P85); another having the same POP/POE mass ratio but different relative molar masses (L64, P84, P104 and F38, F68, F108); and a series in which the copolymers have the same absolute POP content but different relative molar masses (P103, P104, P108). An abrupt transition in the temperature dependence of the volumetric and sound velocity properties occurs in the temperature range 10-45 degreesC for many of the copolymers. This is due to the self-aggregation of the copolymers. The results of this study show that the relative molar mass, POP/POE mass ratio and POP content of the copolymers are factors that play a role in the self-aggregation of these systems. The extensive study of the sound velocity property of these systems extends and confirms the few previous reports that it is a sensitive macroscopic probe of the onset of self-aggregation processes in these systems. The apparent specific volume data of the copolymers has been used to test current models of these aggregates. The results show that the POP core contains some water. Copyright 1997 Academic Press.