Cloud Point Measurements Research Articles

Thermo‐sensitive amphiphilic poly(N‐vinylcaprolactam) copolymers: synthesis and solution properties

AbstractThermo‐sensitive amphiphilic copolymers, PVCL‐PTrpAMT and PVCL‐PVP‐PTrpAMT of hydrophilic N‐vinylcaprolactam (VCL), N‐vinylpyrrolidone (NVP), and hydrophobic N‐t‐Boc‐tryptophanamido‐N′‐methacryl thioureas (TrpAMT) monomers, were synthesized and characterized by 1H NMR, UV‐spectroscopy, and GPC‐MALLS. The cloud point (CP) measurement showed that hydrophobic PTrpAMT and hydrophilic PVP segments significantly altered the phase transition temperature of PVCL with comparable molecular weight in aqueous solution. The CP of PVP‐PTrpAMT solution was 38.0°C, lower by 5.0°C than that of unmodified PVCL. In the presence of phosphate buffer saline (PBS), the CP value of the PVCL polymer decreased by ∼2.0°C in comparison to that of the aqueous solution. Fluorescent spectroscopy and TEM studies revealed that PVCL‐PTrpAMT and PVCL‐PVP‐PTrpAMT self‐assembled into the spherical micelles, 30–70 nm in diameter, at concentrations over their CMCs in an aqueous solution. Cytotoxicity tests demonstrated that the PVCL copolymers were not harmful to cell viability, which may favor the use of the copolymers as potential thermo‐sensitive polymers in pharmaceutical applications. Copyright © 2009 John Wiley & Sons, Ltd.

Study of micellar and phase separation behavior of mixed systems of triblock polymers

Cyclic voltammetric (CV) techniques have been employed to study the mixed micellar behavior of binary mixtures of triblock polymers (TBP) such as F127+P85, F127+P85, F88+P85, and F88+P123 using 2,2,6,6-tetramethyl-1-piperidinyloxy (Tempo) as an electroactive probe. Critical micellar concentration (cmc) has been obtained for pure triblock polymers and their mixed systems from the plots of peak current ( i p) variation versus the total concentration. Diffusion coefficients of the electroactive species have been determined from the Randles–Sevcik equation. The interaction parameter ( β) for the mixed micelles was obtained from the regular solution theory. The values of β suggest that the synergism does exist especially with the F88+P123 system. Cloud point measurements have also been made on the binary mixtures of triblock polymers following similar mixing criteria. An effort has been made to correlate the micellar behavior and phase separation (cloud point) phenomenon. From the correlation, it can be concluded that in the systems studied, an increase in cmc increases the cloud point of mixed systems of triblock polymers.

Lubricant properties of Moringa oil using thermal and tribological techniques

The increasing application of biobased lubricants could significantly reduce environmental pollution and contribute to the replacement of petroleum base oils. Vegetable oils are recognized as rapidly biodegradable and are thus promising candidates for use as base fluids in formulation of environment friendly lubricants. Although many vegetable oils have excellent lubricity, they often have poor oxidation and low temperature stability. Here in, we report the lubricant potential of Moringa oil, which has 74% oleic acid content and thus possess improved oxidation stability over many other natural oils. For comparison, Jatropha oil, cottonseed oil, canola oil and sunflower oil were also studied. Among these oils, Moringa oil exhibits the highest thermo-oxidative stability measured using PDSC and TG. Canola oil demonstrated superior low temperature stability as measured using cryogenic DSC, pour point and cloud point measurements. The friction and wear properties were measured using HFRR. Overall, it was concluded that Moringa oil has potential in formulation of industrial fluids for high temperature applications.

Thermosensitive polylactide‐glycolide delivery systems for treatment of narcotic addictions

AbstractEnvironmental switches may be fabricated for the controlled release of pharmaceutical drug using a thermally responsive polymer with the intrinsic chemical and physical nature of stimuli‐sensitive smart materials. Particularly, much attention has been paid to the biomedical applications of poly(N‐isopropyl acrylamide) (PNIPAAm) because of its unique reversible transition at a specific lower critical solution temperature (LCST).Thermally sensitive block copolymers, poly(N‐isopropyl acrylamide‐b‐poly(L‐lactide‐co‐glycolide) (PNIPAAm‐b‐PLGA), and polyethylene glycol‐poly (lactide‐co‐glycolide) (PEG‐PLGA) triblock copolymers with different compositions and length of PLGA block were synthesized via ring‐opening polymerization of lactide and glycolide in the presence of OH‐terminated PNIPAAm or PEG. The composition and structure of the polymer were determined by NMR and FTIR. The effect of important factors, such as ionic strength, pH, and polymer concentration on the phase transition behavior of temperature‐sensitive polymers, were investigated by cloud point measurements. The resulting thermosensitive polymers were used for the entrapment of a narcotic antagonist drug, naltrexone, as the model drug. The loading efficiency and drug release behavior of naltrexone‐loaded hydrogels were investigated. The naltrexone loaded thermosensitive polymers were able to sustain the release of naltrexone for different periods of time, depending on the polymer composition, and concentration. In vitro release studies showed that these thermosensitive polymers are able to deliver naltrexone in biologically active forms at a controlled rate for 3–8 weeks. Copyright © 2009 John Wiley & Sons, Ltd.

Cloud-point measurement for (sulphate salts + polyethylene glycol 15000 + water) systems by the particle counting method

The phase separation of (water + salt + polyethylene glycol 15000) systems was studied by cloud-point measurements using the particle counting method. The effect of three kinds of sulphate salt (Na 2SO 4, K 2SO 4, (NH 4) 2SO 4) concentration, polyethylene glycol 15000 concentration, mass ratio of polymer to salt on the cloud-point temperature of these systems have been investigated. The results obtained indicate that the cloud-point temperatures decrease linearly with increase in polyethylene glycol concentrations for different salts. Also, the cloud points decrease with an increase in mass ratio of salt to polymer.

Hydrogenated monoterpenes as diesel fuel additives

Myrcene and limonene were hydrogenated to their fully saturated forms, 2,6-dimethyloctane and 1-isopropyl-4-methylcyclohexane, respectively. Mixtures of diesel fuel and up to 10% of each saturated hydrocarbon were tested by ASTM D975 to evaluate the 2,6-dimethyloctane and 1-isopropyl-4-methylcyclohexane as diesel fuel additives. The results showed that all tested mixtures were within the acceptable ranges specified by ASTM for diesel fuel and that the additives lowered the measured cloud point, compared to the base diesel fuel. Saturated limonene had positive effects on viscosity, as well. As myrcene and limonene are produced naturally in plants, these species represent a renewable route to fuel additives.

Binodal curve measurements for (water + propionic acid + dichloromethane) ternary system by cloud point method

The binodal (solubility) curves and tie line data for ternary systems of (water + propionic acid + dichloromethane) at 91.3 kPa and T = (277.15, 284.15, and 294.15) K are reported. The binodal curve results were determined by cloud point measurements method. A simple titration method has been used for determining of the concentration of propionic acid in the both liquid phases at equilibrium. The results obtained were successfully correlated with the UNIQUAC activity coefficient model. The deviations between experimental and calculated compositions in both phases for the ternary system using this model are reported. The partition coefficients of propionic acid and the selectivity factor of dichloromethane for extracting of propionic acid from water were calculated and are reported. The phase diagrams for the ternary system studied including both the experimental and correlated tie lines are presented.

Formation mechanism and crystallization of poly(vinylidene fluoride) membrane via immersion precipitation method

Poly(vinylidene fluoride) (PVDF) membranes were prepared by immersion precipitation method at different coagulation bath temperatures. Effects of coagulation bath temperature on the morphology and crystal structure of PVDF membranes were studied. The phase diagram of PVDF/DMAc/H 2O ternary system was divided into three regions: one phase region, liquid–liquid two phase region and gelation region. Binodal line and spinodal line of phase inversion were calculated based on the thermodynamics equations of membrane formation, and the gel phase boundaries of the systems at 25 and 60°C were determined via cloud point measurement. Based on the phase diagram analysis and experiment results, it was found that gelation is the dominate membrane formation mechanism at low temperature, but the bicontinuous structure of the formed membrane at 60°C is attribute to spinodal decomposition. Moreover, the thermal behavior and crystal structure of membranes prepared using different coagulation bath temperatures were examined by differential scanning calorimetry (DSC) and wide angle X-ray diffusion (WAXD). The results shows that the PVDF membrane precipitated at 60°C had a typical ‘‘α’’ form crystal structure. While at 15°C, the PVDF crystallites are a mixture of ‘‘α’’ and ‘‘ β’’ form crystal structure. The crystallization degree of the prepared membrane has not increased with the coagulation bath temperature decreasing.

Bicontinuous Polymeric Microemulsions from Polydisperse Diblock Copolymers

Polymeric bicontinuous microemulsions are thermodynamically stable structures typically formed by ternary blends of immiscible A and B homopolymers and a macromolecular surfactant such as an AB diblock copolymer. Investigations of these bicontinuous morphologies have largely focused on model systems in which all components have narrow molecular weight distributions. Here we probe the effects of AB diblock polydispersity in ternary blends of polystyrene (PS), polyisoprene (PI), and poly(styrene-b-isoprene) (PS-PI). Three series of blends were prepared using the same PS and PI homopolymers; two of them contain nearly monodisperse components while the third includes a polydisperse PS-PI diblock. The PS and PI homopolymers and two of the PS-PI diblocks were prepared by anionic polymerization using sec-butyllithium and have narrow molecular weight distributions. The polydisperse PS-PI diblock was prepared by anionic polymerization using the functional organolithium 3-tert-butyldimethylsilyloxy-1-propyllithium; this diblock has a polydisperse PS block (Mw/Mn = 1.57) and a nearly monodisperse PI block (Mw/Mn < 1.1). The phase behavior of the three series of blends was probed using a combination of dynamic mechanical spectroscopy, small-angle X-ray scattering, and cloud point measurements, and a bicontinuous microemulsion channel was identified in each system. These results prove that monodisperse components are not required to form bicontinuous microemulsions and highlight the utility of polydispersity as a tool to tune polymer blend phase behavior. The random-phase approximation, originally advanced by de Gennes, and self-consistent field theory are used to provide a theoretical supplement to the experimental work. These theories are able to predict the directions of the polydispersity-driven shifts in domain spacing, order-disorder transition temperatures, and the location of the microemulsion channel. Self-consistent field theory is also used in conjunction with the experimental data from a series of nearly monodisperse blends to probe the variations of chi with temperature. A single linear relation of the form chi = alpha/T + beta does not describe chi at all blend compositions. Rather, two separate relations describe chi as a function of temperature; one is obtained from data on the diblock-rich side of the bicontinuous microemulsion channel while the other is obtained from data on the homopolymer-rich side of the channel. The blend morphology, rather than the composition (homopolymer fraction), apparently dictates whether the system is in the "diblock chi" or "homopolymer chi" regime. These results reinforce the notion that a true understanding of chi still eludes the polymer science community.

Surfactant-Mediated Modulation of Hydrophobic Interactions in Associative Polymer Solutions Containing Cyclodextrin

The ability of nonionic surfactants to modulate the rheological characteristics of comblike hydrophobically modified associative polymer solutions containing cyclodextrin (CD) is examined. Addition of either alpha- or beta-CD to these polymers results in a marked decrease in solution viscosity and viscoelastic properties because of the encapsulation of the polymer hydrophobes by CD. Nonionic surfactants, introduced to such a system, alter the hydrophobic interactions by competing with the polymer hydrophobes for complexation with the CDs. In this regard, nonylphenol ethoxylates (NPe) with different ethylene oxide chain lengths, which determine the hydrophilic-lipophilic balance (HLB) of the surfactant, are used. Our results reveal that the extent and rate of recovery of zero shear viscosity as well as dynamic moduli are strongly influenced by the type of CD (alpha versus beta) as well as the HLB of the surfactant. For polymer solutions containing alpha-CD, recovery is observed solely in the presence of a low-HLB surfactant (NP6 and NP8). Additionally, in the case of NP6, the viscosity increases monotonically above the original hydrophobically modified alkali-soluble emulsion viscosity with surfactant addition, whereas for that of a higher HLB surfactant (NP15), the viscosity shows no appreciable change. In the case of beta-CD, on the other hand, a complete recovery as well as further enhancement of rheological properties is achieved using the above surfactants. However, the trends of viscosity modulation are dissimilar for different surfactants as we witness a monotonous increase in the case of NP6 while a maximum in viscosity is observed in the presence of NP8 and NP15. The contrasting observations can be explained in terms of varying affinities of alpha- and beta-CDs to bind with NP surfactants and the existence of different micellar structures in solution as governed by surfactant HLB. These results are further confirmed by UV/vis spectroscopy and cloud point measurements.

Effect of coagulation bath temperature on formation mechanism of poly(vinylidene fluoride) membrane

AbstractEffects of coagulation bath temperature on the membrane formation mechanism and the morphologies of the formed membranes were studied. The binodal and spinodal lines in the phase diagrams of water/DMAc/Poly(vinylidene fluoride) (PVDF) were calculated based on the thermodynamics equations of membrane formation, and the gel phase boundaries of the systems at 25°C and 60°C were determined via cloud point measurement. The obtained ternary phase diagrams of water/DMAc/PVDF contain three regions: the one‐phase region, the liquid–liquid two‐phase region, and the gel region. In the phase diagrams, the liquid–liquid demixing line (binodal) is located inside the gelation line. At low temperature, there exists a wide region between gelation line and binodal line. Gelation could occur in the absence of liquid–liquid demixing, and becomes the dominant membrane formation mechanism. At high temperatures (60°C), however, the gelation line approaches the binodal line, which results in a much smaller gelation zone. The kinetics of the solvent out‐flux and water influx were enhanced, liquid–liquid demixing is the dominant mechanism. The membrane formation mechanisms at different temperature were confirmed by the light transmission measurements during membrane forming process and the morphologies of the membranes examined by SEM imaging. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.

Liquid−Liquid Equilibrium of Aqueous Two-Phase Systems Containing Some Synthetic Polyelectrolytes and Polyethylene Glycol

Experimental results are presented for the liquid−liquid equilibrium of aqueous two-phase systems containing a synthetic polyelectrolyte (polysodium acrylate, polysodium methacrylate, and polysodium ethylene sulfonate) and polyethylene glycol at (298.2 and 323.2) K. A total of 40 phase diagrams were obtained, comprising data both of the binodal curve (obtained through cloud-point measurements) and of equilibrium compositions. The influences of temperature, the nature of the polyelectrolyte monomer unit, and the chain length of both types of polymers are analyzed and discussed.

Influence of Binary Surfactant Mixtures on the Rheology of Associative Polymer Solutions

Hydrophobically modified alkali-soluble emulsion polymers (HASE) are a class of comblike associative polymers that can impart high viscosities to aqueous solutions. The rheology of HASE solutions can be tuned by the addition of surfactants, such as nonylphenol ethoxylates (NP e), where e is the length of the hydrophilic (ethoxylate) chain. While previous studies have considered individual surfactants, our focus here is on binary surfactant mixtures. We find that equimolar NP4-NP12 mixtures significantly enhance the zero-shear viscosities of HASE solutions as compared to equivalent amounts of NP8, especially at high overall surfactant concentrations. Dynamic rheological measurements suggest that the higher viscosities are due to increases in the lifetime of hydrophobic junctions in the polymer-surfactant network. In contrast to the above results, equimolar NP4-NP8 mixtures are rheologically identical to equivalent solutions of NP6. The differences between the two sets of mixtures are further correlated with cloud point measurements and thereby with the overall hydrophilic-lipophilic balance (HLB) of the surfactant system.

Organic Additives and Electrolytes as Cloud Point Modifiers in Octylphenol Ethoxylate Solutions

AbstractCloud point measurements of nonionic surfactant Triton X‐100, an octylphenol ethoxylate, were carried out in the absence and presence of various organic additives such as n‐alkanols (methanol, ethanol, propanol and butanol), glycols (ethylene glycol, diethylene glycol and triethylene glycol), glycol ethers (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether and ethylene glycol monobutyl ether (EGMBE)) and electrolytes (LiCl, KCl, NaF, NaCl, NaBr, NaI, MgCl2 and AlCl3). The combined effect of these organic additives and electrolytes on cloud point (CP) measurement was also investigated. The effect of nature of cation, anion and valency of cation on CP is also reported. Among the n‐alkanols and glycol ethers as additives, n‐butanol and EGMBE were found to decrease the CP while all other additives increase the cloud point. The addition of electrolytes (LiCl, NaCl and KCl) to the solution of Triton X‐100 (TX‐100) decreases the CP but the rate of decrease in CP with concentration does not follow the lyotropic series of effect. Sodium halides (except NaI) also decrease the CP and the rate of decrease follows the lyotropic series of effect even in the presence of organic additives. NaI is a water structure breaker, hence it increases the cloud point. Further, cations of increasing valency lessen the depression in CP of TX‐100 with the rate of decrease in CP following the order Na+ &gt; Mg2+ &gt; Al3+ even in the presence of organic additives.

The Effects of Salts and Ionic Surfactants on the Micellar Structure of Tri‐Block Copolymer PEO‐PPO‐PEO in Aqueous Solution

The micelles of two poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) block copolymers, P123 and F127 (same mol wt of PPO but different % PEO) in aqueous solution in the absence and presence of salts as well as ionic surfactants were mainly examined by dynamic light scattering (DLS). The study is further supported by cloud point and viscosity measurements. The change in cloud point (CP), as well as the size of micelles in aqueous solution in presence of salts obeys the Hofmeister lyotropic series. Addition of both cationic cetylpyridinium chloride (CPC) and anionic sodium dodecylsulfate (SDS) surfactants in the aqueous solution of P123 show initial decrease of micellar size from 20 nm to nearly 7 nm and then increasing with a double relaxation mode, further in the presence of NaCl this double relaxation mode vanishes. The effect of surfactant on F127, which has much bigger hydrophilic part is different than P123 and have no double relaxation. The relaxation time distributions is obtained using the Laplace inversion routine REPES. Two relaxation modes for P123 are explained on the bases of Pluronic rich mixed micelles containing ionic surfactants and the other smaller, predominantly surfactant rich micelles domains.

Probing the Melt Miscibility of a Commercial Polyethylene Blend by Small-Angle Light Scattering

Small-angle light scattering (SALS) was used to determine the binary interaction parameter χ in a molten blend of linear polyethylene (LPE, M w = 52 kg/mol, PDI = 2.9) and linear low-density polyethylenes (LLDPEs) based on homogeneous ethylene-1-butene copolymers (LLDPE-1, 18.7 mol% butane branches, M w = 58.1 kg/mol, and LLDPE-2, 5.9 mol% butene branches, M w = 70 kg/mol). Traditional cloud point measurements (cooling at 0.5–3°C/min) and melt annealing/isothermal measurements under V V (parallel-polarized) optical alignment were used to evaluate the melt miscibility and determine the binary interaction parameter χ (7.74 × 10−4 at 423 K). This value of χ is consistent with the value (7.69 × 10−4 at 423 K) determined by earlier small-angle neutron scattering (SANS) measurements obtained by Crist and Rhee on polyethylene blends with the same branching-density difference (Δ y = 0.187). In addition, it was shown that SALS can be used to determine directly the melt miscibility of undeuterated polyolefin blends over branching-density differences (Δ y > 0.06), with results that are similar to the range obtained by neutron scattering. Our results are significant because they show that the low optical contrast between coexisting phases in polyolefin blends does not limit the determination of phase boundaries by SALS as was previously assumed. The blends studied exhibit upper critical solution temperature behavior.

Investigation of the role of electrolytes and non-electrolytes on the cloud point and dye solubilization in antidepressant drug imipramine hydrochloride solutions

Antidepressant drug imipramine hydrochloride (IMP) is amphiphilic which shows surfactant-like behavior in aqueous solutions. We have studied the effect of adding electrolytes and non-electrolytes on the micellar behavior of IMP by making cloud point (CP) and dye solubilization measurements. The CP of a 100 mM IMP solution (prepared in 10 mM sodium phosphate (SP) buffer) was found to decrease with increasing pH, both in the absence as well as presence of added salts. Increase in pH increased the visible absorbance of Sudan III dye solubilized in the drug micelles, implying micellar growth. Addition of increasing amounts of salts to 100 mM IMP solutions (at pH 6.7) caused continuous increase in CP due to micellar growth. On the basis of these studies, the binding-effect orders of counter- and co-ions have been deduced, respectively, as: Br − > Cl − > F − and Li + < Na + < K + < NH 4 +. The trend of increasing CP with addition of increasing amounts of quaternary salts (tetramethylammonium bromide, TMeAB; tetraethylammonium bromide, TEtAB; tetra- n-propylammonium bromide, TPrAB; tetra- n-butylammonium bromide, TBuAB; tetra- n-pentylammonium bromide, TPeAB) to 100 mM IMP solutions (at pH 6.7) was found to be dependent upon the alkyl chain length of the particular salt. Ureas caused CP depression, which was found to be dependent upon the number of methyl groups present in the molecule. Contrary to this, thioureas increased the CP slightly, but the presence of methyl group(s) had effect similar to that of alkylureas. The visible absorbance due to solubilized dye increased/decreased with addition of electrolytes/ureas. The overall behavior has been discussed in terms of electrostatic interactions, micellar growth, and mixed micelle formation.

Phase-equilibrium measurement and modeling of the PMMA/MMA/carbon dioxide ternary system

In this paper phase-equilibrium measurements for the poly(methyl methacrylate)/methyl methacrylate/carbon dioxide ternary system are presented. The experimental data were obtained by cloud-point measurements and by applying a novel spectroscopic device. The influence of temperature, pressure and the polymer molecular weight on the phase behavior of the ternary system was investigated. Modeling with the PC-SAFT equation of state shows a very good agreement with the experimental data.

Temperature/Light Dual‐Responsive Inclusion Complexes of α‐Cyclodextrins and Azobenzene‐Containing Polymers

Three kinds of photoresponsive copolymers with azobenzene side chains were synthesized by radical polymerization of N‐4‐phenylazophenylacrylamide (PAPA) with N‐isopropylacrylamide (NIPAM), N,N‐diethylacrylamide (DEAM) or N,N‐dimethylacrylamide (DMAM) respectively. Their structures were characterized by FT‐IR, 1H‐NMR and UV/Vis spectroscopy. Their reversible photoresponses were studied with or without α‐cyclodextrin (α‐CD), which showed that both the copolymers and their inclusion complexes with α‐CD underwent rapid photoisomerization. The lower critical solution temperature (LCST) of the copolymers and their inclusion complexes with α‐CD were investigated by cloud point measurement, which showed that the LCST of three kinds of copolymers increased largely after adding α‐CD. After UV irradiation on the solutions of copolymers and their inclusion complexes, the LCST of the copolymers increased slightly with the absence of α‐CD, while decreased largely with the presence of α‐CD. Furthermore, the LCST reverted to its originality after visible light irradiation. This change of LCST could be reversibly controlled by UV and visible light irradiation alternately. In particular, in the copolymer of PAPA and DMAM, the reversible water solubility of the inclusion complexes could be triggered by alternating UV and visible light irradiation.

Ester hydroxy derivatives of methyl oleate: Tribological, oxidation and low temperature properties

Five branched oleochemicals were prepared from commercially available methyl oleate and common organic acids; and their lubricant properties were determined. These branched oleochemicals are characterized as 9(10)-hydroxy-10(9)-ester derivatives of methyl oleate. These derivatives show improved low temperature properties, over olefinic oleochemicals, as determined by pour point and cloud point measurements. The derivatization also increased thermo-oxidative stability, measured using both pressurized differential scanning calorimetry (PDSC) and thin film micro oxidation (TFMO) methods. Branched oleochemicals were used as additives both in soybean oil and in polyalphaolefin. Their lubrication enhancement was evaluated by both four-ball and ball-on-disk wear determinations. These derivatives have good anti-wear and friction-reducing properties at relatively low concentrations, under all test loads. Their surface tensions were also determined and a trend was observed. The materials with larger side chain branches had lower surface tension than those containing smaller side chain branches. An exception to this trend was found when studying the compound with the carbonyl containing levulinic acid side chain, which had the highest surface tension of the branched oleochemicals studied. Overall, the data indicate that some of these derivatives have significant potential as a lubricating oil or fuel additives.