Aqueous Solutions Of PEG Research Articles

Aqueous lubricating properties of charged (ABC) and neutral (ABA) triblock copolymer chains

Application of charged polymer chains as additives for lubricating neutral surfaces in aqueous environment, especially via polymer physisorption, is generally impeded by the electrostatic repulsion between adjacent polymers on the surface. In this study, we have investigated the adsorption and aqueous lubricating properties of an amphiphilic triblock copolymer, comprised of a neutral poly(ethylene glycol) (PEG) block, a hydrophobic poly(2-methoxyethyl acrylate) (PMEA) block, and a charged poly(methacrylic acid) (PMAA) block, namely PEG-b-PMEA-b-PMAA. After adsorption onto a nonpolar hydrophobic surface from aqueous solution, an equal and homogeneous mixture of neutral PEG and charged PMAA chains is formed on the surface, with an adsorbed polymer mass comparable to its fully neutral counterpart, PEG-b-PMEA-b-PEG. The lubricity of PEG-b-PMEA-b-PMAA showed significant improvement compared to fully charged polymer chains, e.g. poly(acrylic acid)-block-poly(2-methoxyethyl acrylate) (PAA-b-PMEA), which is attributed to dilution of charged moieties on the surface and subsequent improvement of the lubricating film stability.

Developing an in situ nanosuspension: A novel approach towards the efficient administration of poorly soluble drugs at the anterior eye

With about 50–60million cases in the US alone, dry eye disease represents a severe health care problem. Cyclosporin A (CsA) would be a potent candidate for a causal therapy. However, CsA is not sufficiently water soluble to be administrated via simple eye drops. We developed an in situ nanosuspension (INS) as a novel approach towards the administration of CsA to the cornea. It precipitates upon contact with the tear fluid and creates CsA nanoparticles that enter the cornea and release the drug by dissolution. We selected two liquid poly(ethylene glycols) (PEG) that dissolve CsA and create nanoparticles by precipitation of CsA upon water contact. Aqueous solutions of PEG and Solutol, a non-ionic surfactant, were well tolerated by primary human epithelial cells in vitro. To determine the critical water content needed for a precipitation, the solubility of CsA was investigated in quaternary systems of drug, solvent, surfactant and water. The best INS formulation showed a particle size of 505±5nm, a polydispersity index (PdI) of 0.23±0.03 and a neutral zeta potential of −0.07±0.05mV. After single administration to porcine eyes in vitro, 3165±597ngCsA/gcornea were detected in corneal tissue, while the levels of Restasis® a commercial formulation were, with 545±137ngCsA/gcornea, significantly lower (P<0.01). These results demonstrate that an INS is a promising, novel approach towards the causal treatment of inflammatory diseases at the anterior eye.

Titanium dioxide separation from water by PEG and Pluronic type polymers

Separation property of aqueous solutions of PEG (Mv=10,000) and poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers (F-68 and F-127), both in the absence and presence of salts, in a titanium dioxide suspension was evaluated. The separation process was performed by turbidity and zeta potential measurements and investigated with respect to some parameters such as the settling time, the polymer dose, the salt nature and concentration (sodium chloride (NaCl) and potassium chloride (KCl)) as well as polymer structure (ethylene oxide (EO) content). According to the turbidimetric results, a significant change in separation performance was noticed when salt solutions of PEG were used; the residual turbidity decreased with increasing salt concentration. F68 and F127 samples showed a much lower decrease of the residual turbidity over the entire range of polymer dose investigated, both in water and water containing salts. A zeta potential value close to zero at optimum polymer dose points to contribution from neutralization mechanism for destabilization of titanium dioxide suspension by PEG in 0.01M KCl. The viscosity behavior of the polymers under study was also investigated. In order to obtain the intrinsic viscosities, the experimental data were plotted in terms of the Wolf method. The results show that the experimental data fit well with the Wolf model.

Effect of temperature on volumetric and transport properties of nanofluids containing ZnO nanoparticles poly(ethylene glycol) and water

The nanoparticles of ZnO have been dispersed in base fluids of poly(ethylene glycol), PEG, and its aqueous solutions. Stability of these nanofluids has been verified with UV-Vis spectroscopy. Dynamic light scattering and size analyze laser methods were used to obtain particle size of the nanofluids investigated. The density, speed of sound and viscosity values for these nanofluids have been measured at T=(293.15,298.15,308.15 and 318.15)K. From these experimental data, the excess molar volume, VmE and isentropic compressibility, κs, have been determined. The behaviour of these values with temperature and concentration has been interpreted for clarifying the dispersion of ZnO nanoparticles in PEG and aqueous solution of PEG. The effects of ZnO nanoparticles and temperature have also been investigated on volumetric and transport properties of aqueous solutions of PEG. The VmE, was adequately fitted to the Redlich–Kister, Ott et al. and Singh et al. equations. The isentropic compressibility values were correlated with the polynomial equation. The Eyring-NRTL and Eyring-mNRF models have successfully been used for correlating the viscosity values of the nanofluids investigated with temperature dependency considered. The performance of the Einstein, Brinkman, Lundgren and Batchelor models in the prediction of viscosity values of the (ZnO+PEG) nanofluid has also been tested.

Poly-ethylene glycol induced super-diffusivity in lipid bilayer membranes

Fluorescence lifetime correlation spectroscopy (FLCS) has been used to probe the influence of PEG-8000 on the fluidity of fluorescently labeled planar supported lipid bilayers on ozone plasma treated glass. The lipid membrane compositions examined were; DOPC, DOPC/DOPS (80/20 mol/mol) and DMPC, with and without cholesterol. The lateral diffusion coefficients (D) for supported lipid bilayer films of these layers without cholesterol were 7.9 ± 0.2, 7.9 ± 0.4 and 5.5 ± 0.1 μm2 s−1 respectively. The high fluidity reflected the super-hydrophilicity (contact angle of 0) of the ozone treated plasma glass substrate. Using DOPE conjugated Atto 655 as a probe, exposure of the lipid bilayer to a 30% wt/wt aqueous solution of PEG, followed by washing, dramatically increased the diffusion coefficients of the probe within the film. For example, the diffusion coefficient for the DOPC bilayer increases by nearly an order of magnitude to 51.4 ± 2.6 μm2 s−1. The autocorrelation curves for DOPC/DOPS (80/20 mol/mol) and DMPC bilayers required a two-component model for adequate fit of their behaviour yielding both fast and slow components of the diffusion. In all cases, when hydrophilic DOPE–Atto 655 was used as the probe, treatment of the lipid bilayer with PEG resulted in non-Brownian diffusion. Importantly, the observed diffusion behavior observed depends on the identity of probe. In contrast, when a hydrophobic probe (DOPE–NapthBodipy) was employed PEG showed relatively little impact on the observed diffusion rates. This was attributed to orientation of the reporter probe in the lipid bilayer and its aqueous interface. Specifically, DOPE–Atto 655 is believed to associate strongly with PEG mesh at the aqueous interface of the lipid bilayer, its diffusion strongly influenced by the structure in this region, whereas DOPE–NapthBodipy remains in the interior of the bilayer where it is relatively uninfluenced by PEG.

Surface and adhesion properties of poly(ethylene glycol) on polyester(polyethylene terephthalate) fabric surface: Effect of air‐atmospheric plasma treatment

AbstractThe surface and adhesion properties of different molecular weight poly(ethylene glycol) (PEG) (400, 1500, and 3000 g/mol) on untreated and air‐atmospheric plasma‐treated PET woven fabrics were studied, with the aim of developing durable hydrophilic PET fibrous structures. PEG application was carried out by padding of the PET fabric in aqueous solution of PEG followed by curing and drying. The surface properties of the PEG‐coated PET fabrics were then characterized using wicking test to measure the water contact angle (θ°) and capillary weight (Wc), and using atomic force microscopy (AFM) images in the tapping mode. Results showed that without a prior air‐atmospheric plasma treatment of the PET fabric, the water contact angle decreased and capillary weight increased with the three PEGs, implying an increase in the hydrophilicity of both inner and outer PET fabric fiber surface. Air‐plasma treatment of the PET fabrics before PEG coating increases further the hydrophilicity of the inner fabric fiber surface: the capillary weight was almost doubled in the case of the three PEGs. Best results were obtained with PEG 1500: water contact angle decreasing from 82° to 51°, and the capillary weight increasing from 11 mg to 134 mg. Moreover, wash fastness test at room temperature and at 80°C confirms improved adhesion of PEG‐1500 to the plasma‐treated PET woven fabric surface, while under the same conditions the plasma‐treated PET without PEG loses completely its hydrophilic character. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

A Thermoresponsive Hydrogel Based on Telechelic PEG End‐Capped with Hydrophobic Dipeptides

The self-assembly in aqueous solution of PEG (1500 Da) telechelically end-capped with hydrophobic dipeptides has been investigated using spectroscopic, microscopic, scattering, and rheological methods. A self-assembled β-sheet fibril-based hydrogel has been identified (containing dityrosine end groups), which exhibits a gel-sol transition near body temperature. This thermo-responsive PEG-based biofunctional hydrogel is expected to have diverse potential uses in delivery or diagnostics for biomedical applications.

Diffusion of poly(ethylene glycol) and ectoine in NIPAAm hydrogels with confocal Raman spectroscopy

The diffusion behavior of poly(ethylene glycol) (PEG) in N-isopropylacrylamide (NIPAAm) hydrogels was investigated using confocal Raman spectroscopy with regard to temperature (25°C, 30°C and 35°C), PEG concentration (10 and 40 wt.%), PEG molecular weight (2,000 and 12,000 g/mol) and addition of the compatible solute ectoine (0.1 and 2 wt.%). Swelling and shrinking of the gels was observed by means of confocal Raman spectroscopy. The swelling behavior of NIPAAm gels in aqueous solutions of PEG and ectoine was found to resemble the swelling behavior in pure water with regard to temperature, i.e., the gel shrinks with increasing temperature. However, the presence and concentration of PEG and ectoine influence the swelling behavior by lowering the volume phase-transition temperature of the gel and facilitating shrinking. In some cases, a re-swelling of the gel was observed after the initial shrinking at the onset of PEG diffusion, which can be explained by PEG changing the chemical potential in the gel phase as it diffuses into the sample allowing the water to re-enter. The expulsion of water from the gel during shrinking and the so-caused increase of PNIPAAm and PEG concentrations in some cases led to the PEG diffusion seemingly being faster in more shrunken gels despite of their higher diffusion resistance.

Investigations on pre-treatment prior to freeze-drying of archaeological pine wood with abnormal shrinkage anisotropy

The current research is aimed at determining the nature of changes in the dimensions and hygroscopicity of archaeological Scots pine ( Pinus sylvestris L.) wood after treatment with polyethylene glycols and vacuum freeze-drying. The research was undertaken on mature sapwood with narrow annual rings and a small percentage of latewood. The experimental material used in a comparative assessment is characterised by a considerable degree of wood degradation, but low tangential and radial shrinkage and relatively high longitudinal shrinkage. The waterlogged samples were treated with aqueous solutions of PEG 300 with final concentrations: 8, 12, 16 and 20% (v/v), to which PEG 4000 with final concentration: 15, 20 and 25% (w/v) was added. After freeze-drying and seasoning of samples in the air at RH 30, 40, 50 and 65%, the water content of the samples and the degree of shrinkage of wood in three anatomical directions were determined. The dimensional stability of the samples was also determined on the basis of ASE values at RH 50%. After treatment of the samples with a mixture of PEG 300 and PEG 4000, vacuum freeze-drying and seasoning in the air, radial and longitudinal shrinkage of the pine wood was very low and stayed at the same general level, independent of the concentration of solutions and uptake of impregnating agents. More visible dimensional changes in wood were observed only in a tangential direction. On the basis of the results of the research on dimensional stability and the hygroscopicity of pine wood, it is suggested that the optimum method of pine wood conservation is vacuum freeze-drying, preceded with treatment with aqueous solution of 8–12% PEG 300 and 15–25% PEG 4000.

Using co-solvents and high throughput to maximize protein resistance for poly(ethylene glycol)-grafted poly(ether sulfone) UF membranes

The surface of poly(ether sulfone) (PES) membranes were modified to reduce protein fouling by grafting poly(ethylene glycol) methyl ether methacrylate (PEG) onto the membrane. Photo-induced graft polymerization (PGP) was used with a recently developed high throughput platform (HTP). To optimize and improve PEG protein resistance, four different co-solvent additives (dimethyl chloride (DCM), dimethylene formamide (DMF), dimethylene sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP)) were mixed with aqueous PEG solution in order to examine co-solvent effects on grafting and filtration performance of PES- g-PEG surfaces. Bovine serum albumin (BSA, 1 mg mL −1) was used as model “foulant” protein and DI water and PBS filtration resistance and protein sieving were measured. The intensity of fouling was quantified by a fouling index ( R) and correlated with the degree of grafting (DG) using FTIR-ATR spectra. Lower R values were observed for grafting PEG in the presence of co-solvents than in their absence. The lowest fouling index ( R = 0.03 ± 0.04) was with a 0.2 mol L −1 PEG and 0.15 mol L −1 DCM mixture, where the DG was 0.05 ± 0.005. As differences in Hansen solubility parameters reflect, the high affinity of co-solvent with PEG and with PES appears to result in lower fouling. Also, weak affinity between co-solvent and water helps maximize the fouling index suppression. The results reported here are significant because they demonstrate that co-solvents can increase the anti-fouling properties of PEG-grafted PES membranes beyond that possible with PEG alone (up to 86% decrease in R) and far better than that with commercial PES membranes (up to 97% decrease in R). Of the four PEG-solvent pairs used to modify the PES membranes, PEG–DMF and PEG–DCM exhibited lower fouling than the others and the control (PEG alone) at the expense of lower permeation flux, while PEG–DCM was the best compromise with respect to anti-fouling properties, permeability, and protein permeation, i.e. maximizing protein capture in the permeate.

Block sequence affects thermosensitivity and nano-assembly: PEG-l-PA-dl-PA and PEG-dl-PA-l-PA block copolymers

We are reporting triblock copolymers of (ethylene glycol)44–(L-alanine)9–(DL-alanine)9 (PEG–L-PA–DL-PA) with α-helical L-PA localized between flexible PEG and DL-PA, and (ethylene glycol)44–(DL-alanine)9–(L-alanine)9 (PEG–DL-PA–L-PA) with gradient flexibility in water. Aqueous solutions of PEG–L-PA–DL-PA underwent only sol-to-gel transition, whereas those of PEG-DL-PA-L-PA underwent sol-to-gel-to-squeezed gel transitions as the temperature increased. The L-PAs of both polymers have an α-helical secondary structure in water at low temperature. However, the α-helical structure of the PEG-DL-PA-L-PA changed into a random coil structure as the temperature increased above 40 °C, whereas the PEG-L-PA-DL-PA kept the α-helical secondary structure over the same investigated temperature range of 4 °C to 50 °C. Cryo-transmission electron microscopy images and dynamic light scattering suggested that the PEG-L-PA-DL-PA develops spherical micelles, whereas the PEG-DL-PA-L-PA develops cylindrical bundles as well as spherical micelles in water. Even though both block copolymers have a similar composition of (ethylene glycol)44, (L-alanine)9, and (DL-alanine)9, they showed significantly different temperature-sensitivities as well as different nano-assemblies in water. This report suggests that the block sequence of a polymer is very important in developing a specific nano-structure as well as in controlling thermosensitivity of the polymer, thus providing useful molecular information in designing a biomaterial.

Intermolecular interaction in aqueous solution of binary blends of poly(acrylamide) and poly(ethylene glycol)

AbstractThe interaction between poly(acrylamide) (PAM) and poly(ethylene glycol) (PEG) in their solid mixture was studied by Fourier transform infrared spectroscopy (FTIR); and their interaction in aqueous solution was investigated by nuclear magnetic resonance spectroscopy (NMR). For the solid PAM/PEG mixtures, an induced shift of the &gt;CO and &gt;NH in amide group was found by FTIR. These results could demonstrate the formation of intermolecular hydrogen bonding between the amide group of PAM and the ether group of PEG. In the aqueous PAM/PEG solution system, the PAM and PEG associating with each other in water, i.e., the amide group of PAM interacting with the ether group of PEG through hydrogen bonding was also found by 1H NMR. Furthermore, the effects of different molecular weight of PAM on the strength of hydrogen bonding between PAM and PEG in water were investigated systemically. It was found that the hydrogen bonding interaction between PAM and PEG in water did not increase with the enlargement of the PAM molecular weight as expected. This finding together with the viscosity reduction of aqueous PAM/PEG solution with the PAM molecular weight increasing strongly indicated that PAM molecular chain, especially having high molecular weights preferred to form spherical clews in aqueous PEG solution. Therefore, fewer amide groups in PAM could interact with the ether groups in PEG. Based on these results, a mechanism sketch of the interaction between PAM and PEG in relatively concentrated aqueous solution was proposed. The fact that the phase separation of aqueous PAM/PEG solution occurs while raising the temperature indicates that this kind of hydrogen bonding between PAM and PEG in water is weak and could be broken by controlling the temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

One-step preparation of amino-PEG modified poly(methyl methacrylate) microchips for electrophoretic separation of biomolecules

A simple method for a chemical surface modification of poly(methyl methacrylate) (PMMA) microchips with amino-poly(ethyleneglycol) (PEG–NH 2) by nucleophilic addition–elimination reaction was developed to improve the separation efficiency and analytical reproducibility in a microchip electrophoresis (MCE) analysis of biomolecules such as proteins and enantiomers. In our procedure, the PEG chains were robustly immobilized only by introducing an aqueous solution of PEG–NH 2 into the PMMA microchannel. The electroosmotic mobilities on the modified chips remained almost constant during 35 days with 37 runs without any recoating. The PEG–NH 2 modified chip provided a fast, reproducible, efficient MCE separation of proteins with a wide variety of isoelectric points within 15 s. Furthermore, the application of the modified chip to affinity electrophoresis using bovine serum albumin gave a good chiral separation of amino acids.

Dendrimers as Drug Carriers: Dynamics of PEGylated and Methotrexate-Loaded Dendrimers in Aqueous Solution

An investigation of the dynamics of aqueous solutions of PEG, PEGylated dendrimers, methotrexate, and PEGylated and drug (methotrexate)-loaded dendrimers was carried out with broadband dielectric relaxation spectroscopy (DRS). Two dielectric dispersions were observed in all systems, and the explanation of their molecular origin was offered. The lower frequency process, characterized by an activation energy of 52.2 kJ/mol, was attributed to motions in ice. The higher frequency process is of the Cole−Cole type and is assigned to bound water around PEG and methotrexate molecules. The effect of the average number of attached PEG chains and the average number of encapsulated methotrexate molecules was probed. Our results indicate that the dynamics are independent of these numbers but are a strong function of the composition of the complex. Spectral characteristics and temperature dependence of all relaxation processes are described.

Thermodynamic investigation of the systems poly(ethylene glycol) + sodium pentane-1-sulfonate + water and poly(vinyl pyrrolidone) + sodium pentane-1-sulfonate + water

Thermodynamic properties for aqueous solutions containing sodium pentane-1-sulfonate (C 5SO 3Na) in the absence and presence of poly(ethyleneglycol) (PEG) or poly(vinylpyrrolidone) (PVP) determined as a function of surfactant concentration from the density, sound velocity, viscosity, conductivity and vapor–liquid equilibria data, are reported here. Densities and sound velocities, allowing for the determination of apparent molar volumes and compressibilities, were measured at 288.15–313.15 K. Changes in the apparent molar properties upon micellization were derived using a pseudo-phase-transition approach and the infinite dilution apparent molar volumes and compressibilities of the monomer and micellar state of C 5SO 3Na in the investigated solutions were determined. The values of the infinite dilution apparent molar properties of micellar states of C 5SO 3Na in aqueous polymer solutions are larger than those in pure water. Vapor–liquid equilibrium data such as water activity, vapor pressure, osmotic coefficient, activity coefficient and Gibbs free energies were obtained through isopiestic method at 298.15 K. The variations of the critical micelle concentration (CMC) of C 5SO 3Na in water and in aqueous PEG and PVP solutions with temperature were obtained and a comparison between the CMC of C 5SO 3Na obtained from different thermodynamic properties was also made.

INITIAL DROPLETS FORMATION AND GROWTH PROCESS OF ACRYLAMIDE DURING AQUEOUS TWO-PHASE POLYMERIZATION IN AQUEOUS POLY(ETHYLENE GLYCOL) SOLUTION

In order to explore the droplet formation process of the aqueous two-phase polymerization of acrylamide(AM) in aqueous poly(ethylene glycol)(PEG) solution,dynamic light scattering(DLS) was employed to investigate the appearance,the size and size distribution of droplets in the initial stage of polymerization.The effects of PEG molecular weight and concentration on the droplets size and distribution were studied.It was found that the droplets stability in aqueous PEG solution decreased,and the droplets aggregated with each other to form larger and more uniform droplets with decreasing PEG molecular weight or PEG concentration.The morphology of the droplets rich in polyacrylamide(PAM) was observed with transmission electron microscopy(TEM).The droplets shape in the initial stage of polymerization is spherical but polydisperse.However,some oval droplets formed in the product,while the conversion was still very low,which indicated some coalescence of droplets in this stage.As the polymerization proceeds,the droplet size increased rapidly and the size distribution of droplets become uniform.These results were well in agreement with the DLS results.With using the spectrophotometer,the phase separation point was determined where the transparence of reaction solution declined suddenly.The effect of various parameters on the critical conversion of phase separation was measured by bromating method.It decreased with the increase of PEG molecular weight or PEG concentration.With raising temperature from 30℃ to 70℃,the critical conversion decreased at first,and then turned to increase when the temperature was at about 50℃.The critical molecular weight was also systemically investigated by gel permeation chromatogram(GPC).It could be seen that the evolution of critical molecular weight corresponded well with that of critical conversion at various reaction conditions.On the basis of above mentioned results,an initial droplet formation and growth mechanism of AM aqueous two-phase polymerization in aqueous PEG solutions was proposed.As the reaction starts,primary radicals,generated by decomposition of the initiator,grow in the continuous phase by the addition of monomer units until they reach their critical chain length.Then these polymer radicals precipitate and aggregate to form nuclei.The nuclei are not stable,and they will immediately aggregate with each other to form tiny droplets.Then monomer and initiator diffuse into the droplets rapidly,and polymerization takes place in both the continuous phase and the dispersed phase(inside the droplets).In the earlier stage,the PAM droplets are stable and grow mainly by polymerization inside the droplet.Because new smaller droplets generate from continuous phase at the same time,the droplet size distribution becomes wide.However,these droplets become unstable with the polymerization and aggregate with each other to make the droplet size distribution become narrow again.

A new technique for determination of melting temperature of poly(ethylene glycol) by ultrasonic velocimetry

Ultrasonic velocity and density of poly(ethylene glycol) (PEG) (mol. wt. 2000 and 8000) solutions in water and benzene have been studied as a function of temperature from which respective isentropic compressibility has also been calculated. The velocity (as well as isentropic compressibility) undergoes a sudden change near melting temperature, T m, of the solute polymer. Normally, we expect only one peak in viscoelastic properties at the T m of PEG. However, we see two peaks (T m1 and T m2) in the case of the aqueous solution of PEG while there is only one peak for the case of benzene solution. This has been interpreted on the basis that one of the peaks (T m1) is for unsolvated PEG and the other peak (T m2) is that of PEG with water solvation shell. Such solvation shell is not formed with the aprotic solvent (benzene).

Vapor−Liquid Equilibria, Density, Speed of Sound, and Refractive Index of Sodium Tungstate in Water and in Aqueous Solutions of Poly(ethyleneglycol) 6000

Vapor−liquid equilibrium data (water activity, vapor pressure, osmotic coefficient, and activity coefficient) of binary aqueous sodium tungstate solutions and ternary aqueous sodium tungstate−poly(ethyleneglycol) (PEG) solutions were obtained through the isopiestic method at T = 298.15 K. Density and speed of sound measurements were carried out on sodium tungstate in pure water and in aqueous solution of mass fraction 0.02 PEG at T = (288.15 to 308.15) K at atmospheric pressure. From the experimental density and speed of sound data, the apparent molar volume and isentropic compressibility values were evaluated and fitted to the Pitzer equation from which the apparent molar volume and apparent molar isentropic compressibility of the solutions at infinite dilution were calculated at each temperature. The results show a positive transfer volume and isentropic compressibility of sodium tungstate from pure water to an aqueous PEG solution. Furthermore, experimental refractive index data were measured for solutions of sodium tungstate in pure water and in aqueous solution of mass fractions 0.02 and 0.04 PEG as well as those for solutions of PEG in pure water and in aqueous solutions of mass fractions 0.02 and 0.04 sodium tungstate at T = 308.15 K.

Thermodynamic properties of surfactant sodium n-heptyl sulfonate in water and in aqueous solutions of poly(ethylene glycol) at different temperatures

The volumetric, compressibility and electrical conductivity properties of sodium n-heptyl sulfonate (C 7SO 3Na) in pure water and in aqueous poly(ethylene glycol) (PEG) solutions were determined at different temperatures below and above the micellar composition range. At each temperature, the infinite dilution apparent molar volumes of the monomer and micellar state of C 7SO 3Na in aqueous PEG solutions respectively are smaller and larger than those in pure water. However, the values of the infinite dilution apparent molar isentropic compressibility of both monomer and micellar states of C 7SO 3Na in aqueous PEG solutions are larger than those in pure water. Thermodynamic parameters of micellization of investigated surfactant in water and in aqueous solutions of PEG at different temperatures were estimated and it was found that the micelle formation process is endothermic and therefore, this process must be driven by entropy increase. The calculated Gibbs free energies of micellization for aqueous PEG solutions are more negative than those for pure water and become more negative by increasing temperature. The variation of the critical micelle concentration (CMC) of C 7SO 3Na in water and in aqueous PEG solutions with temperature was obtained and a comparison between the CMC of C 7SO 3Na obtained from different thermodynamic properties was also made.

Temperature dependent ultrasonic and conductivity studies in aqueous polymeric solution

Sound velocities, viscosity and density of aqueous solution of PEG of average molecular weight of 4000 g/mole have been measured as a function of temperature in the range 308–338 K at different frequencies. Isentropic compressibility, ultrasonic attenuation and acoustic impedance have been derived from the data. From velocity measurements it has been found that velocity changes near melting temperature due to change in the lattice of polymer. Changes in polymer lattice can also be monitored by complex impedance spectroscopy hence, real and imaginary part of the impedance of mixture of PEG with water were measured in the frequency range 40 Hz to 100 kHz in the same temperature range. From these data bulk electrical conductivity has been calculated. The results have been discussed in terms of molecular interaction occuring in the solution.