Cloud Point Measurements Research Articles

Interaction of an Amphiphilic Drug Trifluoperazine Dihydrochloride with Pluronic Triblock Copolymers: A Physicochemical Study

In the present study, we report the interactional behavior of the phenothiazine drug trifluoperazine dihydrochloride (TFP) with Pluronics (L64, F68, and P123) using surface tension, cloud point and fluorescence measurements. Various micellar and interfacial parameters such as critical micellization concentration (cmc), interaction parameter (β), effectiveness of surface tension reduction (πcmc), maximum surface excess concentration (Γmax), and minimum area per molecule (Amin) at the air–water interface have been evaluated using surface tension technique. The phase separation behavior of the drug is studied in the presence of Pluronics, and the corresponding thermodynamic parameters such as Gibbs free energy (ΔG°c), standard enthalpy (ΔH°c), and entropy (TΔS°c) of clouding have been calculated. Employing the steady state fluorescence measurements, the interactions between the drug and Pluronics have been determined in terms of the number of binding sites for drug molecules (n), binding constants (Ka), and Stern–Volmer quenching constants (Ksv).

Role of lipid-based excipients and their composition on the bioavailability of antiretroviral self-emulsifying formulations

The objective of this study was to develop self-emulsifying drug delivery system (SEDDS) to improve solubility and enhance the oral absorption of the poorly water-soluble drug, nevirapine. This lipid-based formulation may help to target the drug to lymphoid organs where HIV-1 virus resides mainly. The influence of the oil, surfactant and co-surfactant types on the drug solubility and their ratios on forming efficient and stable SEDDS were investigated in detail. Two SEDDS (F1 and F2) were prepared and characterized by morphological observation, droplet size and zeta potential determination, cloud point measurement and in vitro diffusion study. The influence of droplet size on the absorption from formulations with varying concentration of oil and surfactant was also evaluated from two self-emulsifying formulations. Oral bioavailability of nevirapine SEDDS was checked by using rat model. Results of diffusion rate and oral bioavailability of nevirapine SEDDS were compared with marketed suspension. The absorption of nevirapine from F1 and F2 showed 1.92 and 1.98-fold increase (p < 0.05) in relative bioavailability, respectively, compared with that of the suspension. There was no statistical significant difference (p < 0.05) between F1 and F2 in their AUC and Cmax. This indicated that there was apparent poor correlation between the droplet size and in vivo absorption. However, nevirapine in SEDDS showed higher ex vivo stomach and intestinal permeability and in vivo absorption than the marketed suspension, suggesting that the SEDDS may be a useful delivery system for targeting nevirapine to lymphoid organs.

Synthesis and characterization of physically crosslinked N‐vinylcaprolactam, acrylic acid, methacrylic acid, and N,N‐dimethylacrylamide hydrogels

ABSTRACTPhysically crosslinked hydrogels based on N‐vinylcaprolactam/acrylic acid and N‐vinylcaprolactam/methacrylic acid were prepared via free radical polymerization. These temperature responsive hydrogels were characterized in terms of glass transition, phase separation temperature, potentiometric titration and swelling properties. Results showed that phase transition temperature was dependent on the pH value of the solution; increasing pH led to higher lower critical solution temperature (LCST) values which was related to the dissociative behaviors of the carboxylic group of MAc in the buffered solutions. Additionally, with the incorporation of N,N‐dimethylacrylamide into the system, cloud point measurements and MDSC showed an increased in the LCST. This increase was based on hydrophilicity, the hydrophilic–hydrophobic balance was disturbed, and consequently, the LCST behavior was shifted. The pKa of the copolymers ranged between 5.6 and 6.5, while for the terpolymers pKa ranged between 5.3 and 6. At high pH (&gt;10), the COOH group is deprotonated and negatively charged (COO−), while at low pH (1–3) the carboxylic group remains protonated which results in hydrogen bonding between the hydroxyl groups (from NaOH) and the excess of HCl. These results correlate with swelling studies where above the pKa value the hydrogels dissolved rapidly compared to below pKa they did not dissolve at all. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1555–1564

Integrally skinned PSf-based SRNF‐membranes prepared via phase inversion—Part B: Influence of low molecular weight additives

This paper is Part B of a two-paper series aiming at a better understanding of membrane formation via phase inversion process by means of immersion precipitation for hydrophobic, integrally skinned membranes. Four different polysulfone (PSf)/solvent systems, namely PSf/N-methyl-2-pyrrolidone (NMP), PSf/N,N-dimethylacetamide (DMAc), PSf/methyl sulfoxide (DMSO) and PSf/N,N-dimethylformamide (DMF), were used as base solutions to synthesize solvent resistant nanofiltration (SRNF) flat sheet membranes. The role of low molecular weight (MW) additives was studied with respect to performance of these SRNF membranes. In addition, their influence on the phase inversion process by means of immersion precipitation was studied fundamentally via viscosity and cloudpoint measurements to understand the role of the low MW additive in the formation process of integrally skinned SRNF‐membranes. The compositions of the membrane casting solutions were changed using different types of low MW additives in varied concentrations. They included: 1,4-dioxane (DIO), diethylene glycol diethyl ether (DGDE), dimethyl phthalate (DMPH), poly(ethylene glycol) dimethyl ether 250 (PEG-DME250), 2-propanol (IPA), acetone (AC), 2-butanol (BUT), γ-butyrolactone (γ-BUT), acetic acid (AA) and glycerol (GLY). The performance of the synthesized membranes was tested in SRNF by measuring iso-propanol (IPA) permeances and rejections of Rose Bengal (RB) in a high-throughput fashion. Performances were linked to membrane morphologies, as observed in scanning electron microscopy (SEM).

Integrally skinned PSf-based SRNF-membranes prepared via phase inversion—Part A: Influence of high molecular weight additives

This paper is Part A of a two paper series aiming at a better understanding of membrane formation via phase inversion process by means of immersion precipitation for hydrophobic, integrally skinned membranes. Polysulfone (PSf) was chosen to synthesize solvent resistant nanofiltration (SRNF) flat-sheet membranes and the role of high molecular weight (MW) additives was investigated in particular. The compositions of the membrane casting solutions were changed by adding different types of high MW additives in varied concentrations with a more detailed study on polyethylene glycol (PEG) as an additive. The Rose Bengal (RB) rejection and iso-propanol (IPA) permeance of the prepared membranes were determined by performing SRNF experiments in a high-throughput fashion and performances were linked to membrane morphology, as observed in scanning electron microscopy (SEM). Polymer casting solutions were characterized by viscosity and cloudpoint measurements to understand the fundamental thermodynamic and kinetic aspects of the formation process of integrally skinned SRNF-membranes.

Surface Activity of Novel Polymerizable Anionic Polyoxyethylene 4-Nonyl-2-Prpylene-Phenyl Ether Ammonium Sulfate Succinate Surfactants

Novel polymerizable surface-active monomers were synthesized by successive treatment of polyoxyethylene 4-nonyl-2-prpylene-phenyl ether ammonium sulfate with maleic anhydride in the presence of hydroquinone at temperature of 180°C. The molecular structures of the polymerizable surfactants were confirmed by 1H and 13C NMR spectroscopy. The surface tension isotherms on the air-water solution interface were obtained. The critical micelle concentrations (cmc) as well as the surface tension at the cmc were determined for these substances. The micellization and adsorption of the prepared anionic surfactants have been investigated by surface tension, and cloud point measurements. Surface parameters such as surface excess concentration (Γ max), the area per molecule at interface (A min) and the effectiveness of surface tension reduction (πCMC) were determined from the adsorption isotherms of the prepared surfactants.

Biolubricant basestocks from chemically modified plant oils: ricinoleic acid based-tetraesters

BackgroundPlant oils have been investigated as a potential source of environmentally favorable biolubricants because of their biodegradability, renewability and excellent lubrication performance. Low oxidation and thermal stability, poor low-temperature properties and a narrow range of available viscosities, however, limit their potential application as industrial lubricants. The inherent problems of plant oils can be improved by attaching functional groups at the sites of unsaturation through chemical modifications. In this article, we will demonstrate how functionalization helps overcome these disadvantages.ResultsIn this work, mono-, tri- and tetra-esters have been synthesized, including 10,12-dihydroxy-9-(stearoyloxy)octadecanoic acid 3; 9,10,12-tris(stearoyloxy)octadecanoic acid 4; and 18-(4-ethylhexyloxy)-18-oxooctadecane-7,9,10-triyl tristearate 5. Pour-point and cloud-point measurements have shown that these derivatives have improved low-temperature properties as compared to the precursor. The tetra ester compound, 18-(4-ethylhexyloxy)-18-oxooctadecane-7,9,10-triyl tristearate 5, had the lowest pour point (PP) (−44.37°C) and the lowest cloud point (CP) (−41.25°C). This derivatization also improved the compound’s thermo-oxidative stability, measured using pressurized differential scanning calorimetry (PDSC) and thin-film micro-oxidation (TFMO) testing. 18-(4-Ethylhexyloxy)-18-oxooctadecane-7,9,10-triyl tristearate 5 also had the highest onset temperature (OT) (282.10°C) and the lowest volatile loss and insoluble deposit (37.39% and 50.87%, respectively). Furthermore, the compounds’ tribological behaviors were evaluated using the four-ball method. 18-(4-Ethylhexyloxy)-18-oxooctadecane-7,9,10-triyl tristearate 5 also had the lowest coefficient of friction (μ) (0.44).ConclusionsThe results showed that, in general, these derivatives have good anti-wear and friction-reducing properties at relatively low concentrations under all of the test loads. Overall, the data indicates that these derivatives have significant potential to be used as biolubricant basestocks.

Measurement of cloud point temperature in polymer solutions

A temperature-controlled turbidity measurement apparatus for the characterization of polymer solutions has been instrumented and set up. The main features are the coupled temperature-light transmittance measurement and the accurate temperature control, achieved by means of peltier cells. The apparatus allows to measure cloud point temperatures by adopting different cooling protocols: low rate for quasi-equilibrium measurements and high rate for detect kinetic effects. A ternary polymeric solution was adopted as case study system showing that cooling rate affects the measured cloud point temperature.

The influence of polymer purity and molecular weight on the synthesis of integrally skinned polysulfone membranes

Polysulfones (PSf) from 10 different origins were chosen to prepare solvent resistant nanofiltration (SRNF) membranes by the non-solvent induced phase separation method via immersion precipitation. Besides synthesis of membranes with only one type of PSf, polymer blends were also synthesized. The effects of PSf molecular weight (MW), purity and polydispersity (PDI) on the structure and performance of the prepared asymmetric membranes were investigated by means of scanning electron microscopy (SEM) and SRNF experiments, the latter obtained by measuring Rose Bengal (RB) rejections from iso-propanol (IPA) solutions. Polymers were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) and thermogravimetric analysis (TGA) and the polymer casting solutions by viscosity and cloudpoint measurements.

Study of polymer concentration and evaporation time as phase inversion parameters for polysulfone-based SRNF membranes

The preparation of polysulfone (PSf) solvent resistant nanofiltration (SRNF) flat sheet membranes was investigated. Membranes were prepared via the phase inversion process by means of immersion precipitation. The membrane formation process was studied at the level of the casting solution composition (polymer concentration) as well as on the level of post-casting (evaporation time). Membrane preparation and filtration were performed in a high-throughput fashion. The performance of the synthesized membranes was tested in SRNF by measuring iso-propanol permeances and rejections of Rose Bengal. Rejections varied from 37% to 92% when the polymer concentration in the casting solution was increased from 13 to 25wt% and permeance decreased from 9.7 to 0.07L/m2h bar. When evaporation time increased from 0 to 120s, rejections increased from 47% to 76% and permeance decreased from 2.37 to 0.08L/m2h bar. Scanning electron microscopy (SEM) was used to investigate the morphology of the membrane cross sections. Viscosity measurements and light transmittance experiments were conducted in order to describe precipitation kinetics of PSf solutions. Depending on the evaporation time, polymer precipitation took place after 4–10s. Viscosity changed from 0.14 to 15.4Pas when the polymer concentration varied from 13 to 29wt%. Cloudpoint measurements were performed to determine the precipitation curve on a quasi-ternary diagram. The measurements were used to try to better understand the thermodynamic and kinetic aspects of membrane formation.

Test of Hofmeister-like series of anionic headgroups: clouding and micellar growth

Phenomenon of clouding in charged micellar solutions is a fairly recent addition to conventional phenomenon shown by aqueous nonionic micelles. In this paper, we have tested a Hofmeister-like ordering of charged headgroups in the context of cloud point (CP) and micellar growth. For this purpose, we have used various combinations of surfactant (sodium dodecyl sulfate, SDS; sodium dodecylbenzene sulfonate, SDBS; sodium salts of α-sulfonato myristic acid methyl ester, MES; and α-sulfonato palmitic acid methyl ester, PES) and tetra-n-butylammonium bromide (TBAB). Different surfactant concentrations and TBAB concentrations are used and CP measurements have been performed. CP values were found in the order SDBS < SDS < PES < MES for the same concentration of surfactant and TBAB. This order has been discussed in the light of water affinities of interacting ionic species (i.e., surfactant headgroup and TBA+ counterion). The ordering was found similar for the case of micellar growth studied by dynamic light scattering (DLS). A bimodal distribution of aggregate size was found that transforms to giant aggregates at CP. The micelles of roughly 10-nm size convert to aggregates of 1 μm. The study has a few novelties: (1) headgroup dependence of CP, (2) micellar growth on heating, and (3) confirmation of Hofmeister-like series of headgroup.

Switchable Phase Behavior of [HBet][Tf2N]–H2O upon Neodymium Loading: Implications for Lanthanide Separations

Task-specific ionic liquids (TSILs) present an opportunity to replace traditional organic solvents for metal dissolution or separation. To date, a thorough investigation of the physical properties of biphasic TSIL-H(2)O systems and the effects of metal loading is lacking. In this work, the change in the liquid-liquid equilibrium of [HBet][Tf(2)N]-H(2)O upon the addition of Nd(III) is investigated by cloud-point measurements. The addition of Nd(III), drops the upper critical solution temperature by over 20 °C. Further investigation of the [HBet][Tf(2)N]-Nd(III) system led to the formation of single crystals of [Nd(2)(H(2)O)(8)(μ(2)-Bet)(2)(μ(3)-Bet)(2)][(Cl)(2)(Tf(2)N)(4)] from the TSIL phase.

On the nature of volume-phase transitions in photo-cross-linked poly(cyclopropylacrylamide) and poly(N-vinylisobutyramide) coatings

Ellipsometry in an inverted configuration was used to characterize the temperature-dependent swelling of thin (100 nm) coatings of photo-cross-linked poly(cyclopropylacrylamide), or poly(CPAAm), and poly(N-vinylisobutyramide), or poly(NVIBAm). Both polymers contained 3 mol% of methacroylaminobenzophenone (MnBP) as the photo-cross-linking unit. Poly(CPAAm-co-MnBP) showed a continuous, 2nd order deswelling transition between 10 and 70 °C with no hysteresis. Poly(NVIBAm-co-MnBP), on the other hand, showed a discontinuous, 1st order deswelling transition at 45 °C with a hysteresis in the swelling curve. The two types of swelling transitions are consistent with the cloud-point measurements of the uncross-linked polymers, which both showed lower-critical solution temperature (LCST) behavior. The LCST for poly(CPAAm-co-MnBP) is located at almost zero polymer concentration, and hence cross-linked poly(CPAAm) cannot cross its cloud point curve during swelling or deswelling. The LCST for poly(NVIBAm-co-MnBP), in contrast, is located at a significant off-zero polymer concentration (>10 wt% polymer), meaning cross-linked poly(NVIBAm) can cross its cloud point curve and experience a discontinuous jump in swelling. Concurrent measurements of the infrared vibrations of the amide groups in both systems further revealed that the amide I band in poly(CPAAm-co-MnBP) showed a single sub-band throughout the swelling transition. Poly(NVIBAm-co-MnBP), on the other hand, showed two distinct sub-bands, one of which grew at the expense of the other throughout the swelling transition, which may explain the off-zero concentration in the cloud point curve and the discontinuous swelling transition.

Effect of urea on the aggregation behavior of gemini surfactants and their mixed micelles with Pluronic L64

The effect of urea on the perturbation of the molecular assembly of gemini surfactants viz. 12-2-12, 14-2-14, 16-2-16 and their mixed micelles with Pluronic L64 has been investigated using various experimental techniques, namely, surface tension, conductivity, small angle neutron scattering (SANS), dynamic light scattering (DLS), and cloud point measurements. Significant differences do exist between the three gemini surfactants: cmc of 12-2-12 increases whereas that of 14-2-14 and 16-2-16 decreases with increase in the concentration of urea. This behavior has been explained on the basis of various factors such as hydrophobic interactions, monomer stability in aqueous urea solution, solvation of head groups. The SANS and DLS data analysis has been employed to determine the effect of urea on the size and shapes of different aggregates formed. For further insights on the action of urea, various thermodynamic parameters such as the standard Gibbs free energy of micellization (ΔGmic°), Gibbs free energy of adsorption (ΔGads°) and standard Gibbs energy change of solubilization (ΔGs°) from surface tension and cloud point measurements have been evaluated. A direct mechanism for the action of urea has been accepted depending upon the inferences drawn from all the studies.

Supercritical carbon dioxide-soluble polyhedral oligomeric silsesquioxane (POSS) nanocages and polymer surface modification

In this work, a functionalized polyhedral oligomeric silsesquioxane (POSS) has been investigated for its solubility in supercritical carbon dioxide for the first time in literature. POSS nanocages, which can be functionalized with a wide variety of organic substituents, are most commonly studied as nanofillers in polymer nanocomposites and coatings. Solubility of trifluoropropyl POSS in supercritical carbon dioxide has been determined by cloud-point measurements performed in a high-pressure view cell. At temperature and pressure ranges of 308–323K and 8.3–14.8MPa, these fluorinated organic–inorganic hybrid nanocage structures exhibit solubility up to 4.4% by weight, which is promising for green material processing applications using the environmentally benign solvent. Solubility of CO2-philic POSS decreases with increasing temperature, while the solubility isotherms at two different temperatures converge. Choosing the processing conditions from the performed solubility studies, trifluoropropyl POSS–supercritical carbon dioxide system has been applied in high-pressure surface modification of a high-molecular weight, rigid poly(methyl methacrylate) (PMMA). Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) analysis of the processed PMMA sheet show that the functionalized nanoparticles were deposited on the PMMA surface, forming a uniform coating of POSS aggregates. This work proves that functionalized POSS with CO2-philic groups can be solubilized in supercritical CO2, which might allow them to be applied in a plethora of materials modification processes using supercritical carbon dioxide.

Tuning thermoresponsive behavior of diblock copolymers and their gold core hybrids: Part 1. Importance of placement of amphiphilic end groups on the diblock copolymers

We report the effects of use and placement of amphiphilic end groups as a valuable tool to achieve significant changes in the thermoresponsive properties of diblock copolymers without the need to resort to compositional changes. We prepared diblock copolymers of di(ethylene glycol) methyl ether methacrylate and oligo(ethylene glycol) methyl ether acrylate with phenyl dithioester and carboxylic acid chain ends and compared the effects of placement of these amphiphilic chain ends on the cloud points of the copolymers. All the copolymers were high molecular weight (greater than 20kDa) with a polydispersity between 1.1 and 1.2, and the cloud points were measured by UV–vis spectrophotometry and reported as the temperature at 50% normalized transmission. The thermoresponse showed a significant dependency on end group placement, reaching as much as a 28°C difference in measured cloud point simply by exchanging end group placement rather than compositional changes. The effect is attributed to changes in the solvation and mobility from chain end placement affecting the degree of association of the chains. The underlying effect is due to the hydrophilic/hydrophobic balance in combination with the use of amphiphilic chain end placement that can be applied to copolymers with different blocks at the chain ends. This work shows that substantial changes in thermo-response properties can be achieved by re-arranging monomer components rather than changing monomer composition. This may have value in biomedical materials where the range of acceptable monomers is limited.

UCST and LCST phase behavior of poly(trimethylene ether) glycol in water

AbstractWe describe the initial studies of the complex aqueous phase behavior of poly(trimethylene ether) glycol (PO3G), a renewably sourced polyether glycol. Cloud point measurement revealed that a low molecular weight PO3G exhibits both lower critical solution temperature (LCST) and upper critical solution temperature (UCST) in water in the temperature range between 30°C and 80°C. At low concentrations of PO3G, the polymer solutions exhibit LCST‐type phase behavior. In the intermediate concentration ranges, PO3G and water are immiscible. However, at higher concentrations of PO3G, the solutions show UCST‐type phase behavior. In addition, both the LCSTs and UCSTs can be easily tuned over a wide range by varying the amount of alcohol co‐solvents. These findings have potential applications in the design of personal care applications and in the development of thermosensitive “smart” materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Effect of different additives on the physical and chemical CO2 absorption in polyetherimide hollow fiber membrane contactor system

Porous asymmetric polyetherimide (PEI) hollow fiber membranes were fabricated via a phase-inversion method using ethanol, glycerol and acetone as the additives in the spinning dope. Also, hollow fiber PEI membrane without additives was fabricated. An aqueous solution of 1-methyl-2-pyrrolidone (80wt.%) was used as bore fluid to prevent forming of an inner dense skin layer. The precipitation rate of the polymer dopes with the different additives was studied using cloud point measurement. The effect of the additives on the resulting membrane structure, surface porosity, pore size, critical water entry pressure, collapsing pressure and physical and chemical CO2 absorption performance by distilled water and NaOH (1M) solution in a gas–liquid membrane contactor system were investigated and compared. Cloud point diagrams indicated that the precipitation rate of the polymer dopes increased following the trend of ethanol>acetone>glycerol. Results of gas permeation tests showed that ethanol and glycerol as additives provided the membranes with the largest and smallest pore size, respectively. Moreover, all the additives resulted in an increase in the effective surface porosity. The cross-section of the membranes was examined via a scanning electron microscopy. Ethanol in the spinning dope provided the membrane structure with a sublayer with finger-like macrovoids, originating from the inner and outer surfaces of the hollow fiber and extending to the middle section of the hollow fiber wall, which resulted in a larger pore size and higher CO2 absorption rate than the other PEI hollow fiber membranes.

Liquid-Liquid Extraction of 3FOx and 5FOx Polyoxetane Diols: Impact on Polyurethane Mechanical Properties, Surface Morphology, and Wetting Behavior

Laboratory prepared and commercial poly(2-2,2,2-trifluoroethoxy-2-methyl)oxetane, P[3FOx] and poly(2-2,2,2-pentafluoropropoxy-2-methyl)oxetane, P[5FOx] polyols contain varying amounts of cyclics and low molar mass (LMW) constituents as byproducts of ring opening polymerization. Guided by phase diagrams determined by cloud point measurements, P[3FOx] diol separation is achieved. The impact of purification is explored via the preparation of P[3FOx] and P[5FOx] polyurethanes from cyclic/LMW-free diols. Mechanical properties are improved because of higher polyurethane molecular weights. AFM revealed complex rugosity that is correlated with dynamic contact angles free from effects of water contamination.

Unusual Lower Critical Solution Temperature Phase Behavior of Poly(ethylene oxide) in Ionic Liquids

We describe the LCST-type phase behavior of poly(ethylene oxide) (PEO) dissolved in imidazolium-based tetrafluoroborate ionic liquids (ILs). Phase diagrams were determined by a combination of small-angle neutron scattering (SANS) and cloud point (CP) measurements. Unlike typical LCST phase diagrams of polymer solutions, the PEO/IL phase diagram is either roughly symmetric with a critical composition near 50% polymer or asymmetric with a critical composition shifted to an even higher concentration of PEO. As the molecular weight decreases from 20 500 to 4200 g/mol, the critical temperature (Tc) increases slightly (∼10 °C). However, a larger increase in Tc (27 °C) was observed as the molecular weight decreases from 4200 to 2100 g/mol, likely due to the increasing importance of hydrogen bonds between the −OH end groups of PEO and the fluorine atoms of the anions. This inference is supported by the strong dependence of the phase diagram on the identity of the PEO end groups (hydroxy vs methoxy). Furthermore, ...