Increase In Cloud Point Research Articles

Interaction of imidazolium chloride-based ionic liquids with Triton X-114 micelles

The effect of temperature and additives on the formation and structure of Triton X-114 (TX-114) micelles were studied using cloud point (CP technique), nuclear magnetic resonance (NMR), critical micellar concentration (CMC), micropolarity, and viscosity measurements. The clouding process of 2% (w/v) aqueous TX-114 in the presence of ionic liquids (ILs) was governed by the hydrophobic nature of the alkyl chains; the more hydrophobic the IL is, the more is the effect on the clouding process. ILs with hexyl and octyl group chains showed a drastic increase in cloud points supported by the exact reversal in trend obtained for viscosity measurements. An in-depth thermodynamic analysis of the clouding process helped to determine if it was entropy or enthalpy driven in each case. CMC of TX-114 slightly increased on the addition of ILs, accounting for strong interactions between the two, leading to delay in micellization. The impact of hydrophobicity was further studied using fluorescence spectrophotometry with pyrene as a solvatochromic probe. IL with octyl chain showed an increase in polarity, which could be attributed to the chain's deeper penetration inside the micelle. 1H NMR and Dynamic Light Scattering studies further confirmed the interaction and micellar size prediction, respectively.

Interaction of imidazolium based ionic liquids with aqueous Triton X-100 surfactant: Clouding, fluorescence and NMR studies

The micellar environment of aqueous Triton X-100 is dependent on its concentration and is driven by changes in the surfactant-water interactions. A mutual solubility curve is observed in clouding of Triton X-100 with a lower critical solution temperature at 339.5 K. Thermodynamic analysis indicate that the clouding process is entropy and enthalpy controlled below and above the lower critical solution temperature respectively. Enthalpy-entropy compensation effect has been invoked to discuss the clouding process. Addition of imidazolium based ionic liquids with variable alkyl chain length affect the micellar structure differently. The effect of different concentrations of ionic liquids on clouding of 2% Triton X-100 is studied to gauge their influence on the clouding process. The observed variations in clouding can be attributed to the hydrophobicity of the alkyl chain length of ionic liquids where, the hexyl and octyl alkyl chains results in substantial increase in cloud point for 2% Triton X-100. Fluorescence, 1H NMR and DLS studies are conducted to authenticate the changes occurring in the micellar systems. While fluorescence studies have shown a decrease in polarity of the micellar environment with increase in alkyl chain length, 1H NMR studies confirm the penetration of long alkyl chain ionic liquid in the micelles. DLS measurements show that ionic liquids are adsorbed on the micellar surface.

Structural changes in non-ionic surfactant micelles induced by ionic liquids and application thereof for improved solubilization of quercetin

We report the effect of concentration of 1-butyl-3-methylimidazolium ([C4mim]+) based ionic liquids (ILs) with different anions (Cl, BF4, CF3SO3, PF6, NTf2 and OS) on micelles of d-α-tocopheryl polyethylene glycol succinate (TPGS). A distinct series of ILs possessing identical anion (Cl−) but cation [Cnmim+) with increasing alkyl chain length (butyl, hexyl, octyl and decyl) was also tested. TPGS-IL mixed micelles were characterized through small angle neutron scattering (SANS).Depending upon IL-TPGS interaction, two distinct observations were recorded on clouding and aggregation of TPGS; (a) insignificant changes for ILs with short alkyl chain (C4mim), independent of concentration and type counter anions (Cl−, BF4−, CF3SO3−, PF6− and NTf2−), and (b) steep increase in cloud point, and reduction in size and aggregation number of micelles upon increasing the alkyl chain (C8 and C10) with concentration (10 to 200 mM). Our observations suggest that C4 (except C4mimOS) and C6mim ILs acted as solvent whereas C8mimCl, C10mimCl and C4mimOS served as secondary surfactants, thus promoting mixed micelle formation. For surface active ILs (C8 and C10), SANS parameters showed a progressive reduction in micelle size and increase in number density. Importantly, TPGS-C10mimCl association helped in improving the solubilization of quercetin (QCT) up to 700-fold. We speculate that high QCT solubilization resulted from the formation of small sized mixed micelles (hydrodynamic diameter ≈ 10 nm) at a high number density. Solubilization potential of TPGS-IL mixed system is practically exploitable for the development of injectable drug concentrates.

Viscosity-Temperature Behavior of Hydroxypropyl Cellulose Solution in Presence of an Electrolyte or a Surfactant: A Convenient Method to Determine the Cloud Point of Polymer Solutions

The viscosity of hydroxypropyl cellulose (HPC) solution with or without an additive has been measured continuously as a function of temperature with the help of a vibro-viscometer. The viscosity of the polymer solution showed a gradual decrease initially with increase in temperature until a particular point beyond which there was a sharp decrease in the viscosity, which coincided with the clouding of the solution. The cloud point temperature (CP) of the polymer solution was determined from the first derivative plot of viscosity vs. temperature. Effect of addition of an electrolyte or a surfactant on the CP of HPC solution has also been studied. While a decrease in CP of HPC solution in presence of fluoride, chloride, or bromide ions was observed, presence of iodide or thiocyanide ions led to an increase in the CP. However, presence of an ionic surfactant initially lowered the CP but beyond a particular surfactant concentration a sharp increase in cloud point was observed due to interaction of the surfactant with the polymer. The results suggest that surfactants with longer hydrophobic tail or more hydrophobic groups have more affinity for HPC.

Influence of Hydrophobic Anion on Solution Properties of PDMAEMA

The effect of bis(trifluoromethane)sulfonimide, NTf2, anion on solution properties of the thermoresponsive poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA, has been studied. Nonstoichiometric amounts of LiNTf2 were added to aqueous solutions of PDMAEMA, with or without a buffer in the pH range 6–10. Since PDMAEMA is a weak polybase, the interaction between PDMAEMA and NTf2 can be manipulated by the concentration of the anion and also by varying the degree of charging of PDMAEMA with pH. PDMAEMA has a well-known LCST behavior which can be modulated by the counterion. It was observed that the hydrophobic NTf2 anion not only decreases the cloud point of PDMAEMA but also triggers an upper critical solution temperature (UCST) type behavior in acidic pH. In a higher pH regime, NTf2 makes the cloud point increase because the anion turns PDMAEMA to a stronger base, presumably by effectively shielding the charges.

Aggregation and Phase Separation Phenomenon of Amitriptyline Hydrochloride Under the Influence of Pharmaceutical Excipients

AbstractThe interaction between the amphiphilic drug amitriptyline hydrochloride (AMT) and the nonionic surfactants used in drug delivery has been investigated. Herein, we report the micellization behavior of AMT in presence of ethoxylated alkyl phenols in aqueous medium and the clouding phenomenon in the absence and presence of different nonionic surfactants in buffer solution. The values of critical micelle concentration (CMC) of AMT obtained using the conductivity method, decrease as nonionic surfactant concentration increases. With an increase in temperature, the CMC first increases and then decreases. At 303.15 K, the maximum CMC values were obtained with or without nonionic surfactant. The results obtained indicate attractive interactions (synergism) between the two mixing amphiphiles in solution. The experimentally obtained critical micelle concentration (CMC) values are always lower than ideal CMC values. Micellar mole fraction (X1) values, calculated by different proposed models, show the contribution of nonionic surfactant concentration. At a fixed drug concentration (50 mmol kg−1) and pH (=6.7) nonionic surfactants show continuous increase in cloud point (CP). Increase in drug concentration and pH, in the presence of fixed amounts of nonionic surfactant, increases and decreases the CP, respectively.

Synergistic Effects of Skeletal Isomerization on Oleic and Palmitic Acid Mixtures for the Reduction in Cloud Point of Their Methyl Esters

Biodiesel is composed of saturated and unsaturated fatty acid esters, both of which have significant effects on the cloud point of biodiesel. These two classes of fatty acids also react differently to isomerization reactions for cloud point improvement. This study examines the effects of isomerization and hydroisomerization on the two most common saturated and unsaturated fatty acids that make up vegetable oils, i.e., palmitic and oleic acids, respectively. The two fatty acids are placed under two different reactions and analyzed both separately and mixed for the cloud point improvement of their esters. The two reactions, isomerization and hydroisomerization, are run at 250 °C and 1 MPa H2 and at 300 °C and 4 MPa H2, respectively. Negative and positive results were shown, i.e., cis to trans isomerization, causing an increase in cloud point, and branching, causing a reduction in cloud point. A 7.5 °C reduction in cloud point is achieved on the esters of a 55:45 (%) oleic acid/palmitic acid ratio, showing that isomerization and hydroisomerization reactions can successfully lower the cloud point of a mixture of fatty acid methyl esters.

Time-dependent increase in aqueous solubility caused by the gradual disruption of hydrophobic aggregation

We report the preparation of a thermoresponsive polymer whose solubility in water can be controlled simply by time elapse. Most importantly, we showed that the gradual disruption of hydrophobic aggregation originated from strong π–π stacking between side chain triazole rings resulting in an increase in the cloud point. As time progressed, hydrogen bonds between one of the triazole ring nitrogen atoms and water molecules became dominant. This caused disruption of the hydrophobic domains by breaking π–π stacking between the triazole rings, leading to a thermodynamically stable hydration state. The gradual disruption of hydrophobic aggregation induced a time-dependent increase in the apparent cloud point. This time-dependent increase in aqueous solubility was not driven by hydrolytic degradation of ester linkages. This behavior was carefully characterized using a number of techniques, including percent transmission analysis, UV-Vis spectroscopy and 1H-NMR spectroscopy, and dynamic light scattering (DLS) measurements, all supporting our hypothesis. This macromolecule, which offers tailored control over aqueous solubility, may be a unique potential platform for drug delivery scaffolds where the release of encapsulated molecules is controlled simply by time.

Solution thermal properties of a family of thermo-responsive N-isopropyl acrylamide-co- N-hydroxymethyl acrylamide copolymers – Aspects intrinsic to the polymers

A family of ( N-isopropyl acrylamide-co- N-hydroxymethyl acrylamide) copolymers, p(NIPAAm-co-HMAAm), was synthesised and characterised with respect to solution thermal behaviour. A notable increase in cloud point (CP) was observed as the concentration of the polymer solutions was lowered, though the effect of concentration on CP of pure p(NIPAAm), was relatively small. In all cases, the elevation of CP was most evident at low concentration between 0.1 wt.% and 0.01 wt.%. Both at fixed and decreasing concentrations of p(NIPAAm) solutions, a direct relationship between molecular weight and CP was observed, where CP shifted to higher temperatures as the molecular weight increased. The polymer coil size in solution below the CP in the concentration range studied was between 4 and 11 nm for all the polymers in this study, irrespective of the concentration and of the fraction of hydroxy monomer incorporated, but increased dramatically above the CP. CPs obtained by Dynamic Light Scattering (DLS) were lower than those obtained by UV absorbance as the latter is less sensitive. Copolymer compositions with more than 13% hydroxy monomer showed no thermal hysteresis, in contrast to pure p(NIPAAm). The rate of heating/cooling had almost no effect on the CP values recorded.

Effect of Polydispersity on the Phase Behavior of Polystyrene (PS)/Poly (Vinyl Methyl Ether) (PVME)

The thermodynamics and kinetics of phase separation in partially miscible blends of poly (vinyl methyl ether) (PVME) and two kinds of polystyrene (PS) with the same weight average molecular weight but different polydispersity were studied. The miscibility of PS/PVME with the monodisperse PS was better than that of PS/PVME with the polydisperse PS. Different morphology was observed for the two kinds of PS/PVME (10/90) blends during the nonisothermal phase separation process. The blend with monodisperse PS presented a co-continuous structure while the blend with polydisperse PS presented a viscoelastic phase separated network structure at a quench depth of 29°C. With increase of the heating rate, the increase of cloud point of PS/PVME (30/70) with polydisperse PS was smaller than that of PS/PVME (30/70) with monodisperse PS. During the isothermal phase separation of the critical composition (20/80) of PS/PVME with a quench depth of 30°C, it was found that the phase morphology of the two kinds of blends was nearly the same at the early stage of phase separation. However, as the dispersed phase, an approximately spherical droplet structure was observed in the blend with monodisperse PS at the late stage of phase separation, which did not appear in the blend with polydisperse PS.

Sequence control over thermo-triggered micellization and smart nanogels of copolymers based on PEGMA and aldehyde-functionalized monomer

This paper describes the sequence control over thermo-triggered micellization and the corresponding dynamic nanogels of copolymers of poly[poly(ethylene glycol) methyl ether methacrylate] (PEGMA) and 1,3-(4-formylphenoxy)-2-hydroxypropyl methacrylate (FPHPMA). To this end, the well-defined copolymers in the sequences of P(FPHPMA-ran-PEGMA), P(FPHPMA-ran-PEGMA)-b-PFPHPMA and P(FPHPMA-ran-PEGMA)-b-PPEGMA, at a molar ratio of [FPHPMA]:[PEGMA]≈1:1 and a fixed overall degree of polymerization or DP≈50, were synthesized via reversible addition-fragmentation chain transfer radical polymerization or RAFT polymerization under mild visible light radiation at 25 °C. The results demonstrated that altering the sequence from P(FPHPMA-ran-PEGMA) to P(FPHPMA-ran-PEGMA)-b-PPEGMA or P(FPHPMA-ran-PEGMA)-b-PFPHPMA led to an increase of cloud point and decrease of hydrodynamic diameter from hundreds of nm to tens of nm. Moreover, altering the copolymer sequence resulted in the thermo-triggered micellization mechanism changing from the insertion/expulsion of single chains to fusion/fission of their pre-assembled “polymerases”. The hysteresis and solvent isotopic effects varied with the sequence of copolymers. Moreover, the thermo-induced dehydration and the apparent reactivity of aldehyde functionalities in swollen micelles also varied with the sequence. These thermo-induced micelles could react with diamine to form dynamic nanogels. The pH- and/or thermo-triggered swellability of these nanogels could be adjusted by changing the sequence.

Physicochemical Behavior of Mixed Nonionic‐Ionic Surfactants in Water and Aqueous Salt Solutions

Cloud point, viscosity, and ultrasonic velocity of aqueous solutions of nonionic surfactants (Triton X‐114 and Triton X‐100) in the presence of ionic surfactants (anionic: sodium alkyl sulfate and cationic: alkytrimethylammonium bromides) are reported. The addition of ionic surfactant (at concentrations much less than CMC) to the salt‐free solution of nonionic surfactants increases the cloud point of nonionic surfactants. Such cloud point increase was dependant on the type and hydrophobic tail of surfactants and has been explained in terms of mixed micelles formation. However, in the presence of NaCl (≥0.3 M), the cloud point curve shows a deep minimum as a function of anionic surfactant concentrations. Such minima were not observed in lower concentrations of NaCl in the case of anionic surfactants and in the presence of cationic surfactants. It was seen that the stronger effect was obtained for anionic surfactant. The relative viscosity of this system increased markedly with the variation of the concentration of NaCl, which may be due to shape transition of the micelles. The relative sound velocity results are found to be in agreement with the viscosity results.

Effect of different additives on the cloud point of a polyethylene oxide‐polypropylene oxide‐polyethylene oxide block copolymer in aqueous solution

AbstractCloud point studies on aqueous solutions of a polyethylene oxide (PEO)‐polypropylene oxide‐PEO triblock copolymer (Pluronic® L64: EO13PO30EO13, total m.w.=2900, PEO=40%; EO=ethylene oxide; PO=propylene oxide) in the presence of different additives show some interesting features. The effect of various inorganic salts was an increase or decrease in cloud point based on their salting in and salting out action and followed the Hofmeister lyotropic series. Nonelectrolytes and hydrotropes increased the cloud point by influencing water structure. Hydrotropes altered the cloud point of the copolymer at much lower concentrations than inorganic salts. Ionic surfactants produced a marked increase in the cloud point of copolymer solutions. The effect was greater for surfactants with greater hydrophobicity. Alcohols and other organic liquid additives that are infinitely miscible with water increase the cloud point of the copolymer, whereas additives that are partially miscible in water decrease the cloud point.

Nonionic Cellulose Ethers as Potential Drug Delivery Systems for Periodontal Anesthesia

Nonionic cellulose ethers displaying a lower consolute temperature, or cloud-point, close to body temperature were investigated as potential carrier systems for the delivery of local anesthetic agents to the periodontal pocket. The interaction between the polymers, i.e., ethyl(hydroxyethyl)cellulose (EHEC) and hydrophobically modified EHEC (HM-EHEC), and ionic surfactants was determined in the absence and in the presence of the local anesthetic agents lidocaine and prilocaine. The cloud-point and rheology data indicate interactions between the polymer and both anionic and cationic surfactants. More precisely, a number of ionic surfactants were found to result in an increase in cloud-point at higher surfactant concentrations, a surfactant-concentration-dependent thickening, and a temperature-induced gelation upon heating. Upon addition of the local anesthetic agents lidocaine and prilocaine in their uncharged form to EHEC and HM-EHEC, in the absence of surfactants, only minor interaction with the polymer could be inferred. However, these substances were found to affect the polymer–surfactant interaction. In particular, the drug release rate in vitro as well as the stability and temperature-dependent viscosity were followed for an EHEC/SDS system and EHEC/myristoylcholine bromide system upon addition of lidocaine and prilocaine. The data indicate a possibility of formulating a local anesthetic drug delivery system suitable for administration into the periodontal pocket where at least small amounts of active ingredients can be incorporated into the system without severely affecting the gelation behavior. The results found for the cationic myristoylcholine bromide system are particularly interesting for the application in focus here since this surfactant is antibacterial and readily biodegradable.

Effect of Inorganic Additives on Solutions of Nonionic Surfactants: X. Micellar Properties

The study of the interaction between electrolytes and nonionic surfactants was extended to the micellar properties of octoxynol 9 at 25°C. Density, surface tension, viscosity, and static and dynamic light scattering were measured in water (where dilute octoxynol solutions had a cloud point of 64°C), in a salting-out electrolyte, 0.40 m Na 2SO 4 (cloud point lowering = 28°C), and in the salting-in electrolytes 1.80 m NaSCN (cloud point increase = 27°C) and 2.00 m Mg(NO 3) 2 (cloud point increase = 14°C). The intrinsic viscosity of octoxynol in Na 2SO 4 was twice as large as in water and NaSCN, the diffusion coefficient was 2.5 times smaller, the micellar molecular weight was 5 and 14 times larger than in water and NaSCN, respectively, and the micellar hydration was at least twice as large. The micellar properties in Mg(NO 3) 2 differed from those in the other three media: The partial specific volumes in the latter were independent of surfactant concentration and had comparable values, while decreasing significantly with increasing surfactant concentration in the former. The micellar molecular weights and aggregation numbers were nearly the same in Mg(NO 3) 2 and NaSCN and amounted to ≈ 1 3 of the corresponding values in water; the intrinsic viscosities were 98 and 83% of that in water, respectively, while the micellar diffusion coefficients at infinite dilution were 59 and 120%. The apparent diffusion coefficients in Mg(NO 3) 2 increased slightly with increasing surfactant concentration while decreasing in the other three media. Only in Mg(NO 3) 2 did the micellar hydration increase with increasing surfactant concentration. These observations point to micellar binding of Mg(NO 3) 2, presumably via complexation of Mg 2+ ions by the ether oxygens of the micellar polyoxyethylene moieties, which rendered the surfactant somewhat cationic.

Counter ion condensation on mixed cationic/nonionic micellar systems: Bjerrum's electrostatic condition

The association of counter-ions with mixed ionic/nonionic micelles has been investigated in the case of dodecyl/tetradecyl/ and hexadecyl-trimethylammonium bromide with two nonionic surfactants: dodecylpolyoxyethylene 23 and Triton X-100. The degree of association has been measured by potentiometry using a Bromide ion-selective electrode. Previous results with sodium and copper dodecylsulfate suggesting that in the nonionic-rich composition domain, bare mixed micelles are formed without associated counter-ions have been confirmed. These results are in agreement with the prediction of Bjerrum's condition for ion association. The effect of copper dodecylsulfate on the cloud point of Triton X-100 has also been determined as a means of investigating mixed micelles with multivalent counter-ions. The dramatic cloud point increase observed, even larger than with sodium dodecylsulfate, has been discussed as evidence of the solvation of divalent ions by ether groups, a factor which complicates the analysis of multivalent counterion condensation on mixed micelles.

Effect of protein denaturants on cloud point and krafft point of nonionic surfactants

The effects of a variety of protein denaturants (seven ureas, three thioureas, acetamide, and guanidinium chloride) on the cloud point and Krafft point ofpolyoxyl 10 cetyl ether were investigated. All additives raised the cloud point in direct proprotion to their concentration in the range 0 to 0.5 m. From 0.5 to 1.0 m, the cloud point increases were less than proportional to additive concentration. Owing to increased micellar solubilization, higher degrees of alkylation of the ureas and thioureas resulted in greater cloud point increases. Urea, methylurea, thiourea, and acetamide did not change the Krafft point, while the more highly alkylated ureas and thioureas produced modest decreases. Cloud point increases and Krafft point decreases represent salting in of the nonionic surfactant. At comparable concentrations, all additives increased the cloud points of polyoxyl 10 cetyl ether and of octoxynol 9 to the same extent, even though octoxynol 9 is more polar owing to the presence of a benzene ring. This indicates that the changes in cloud point are due predominantly to the interaction of the protein denaturants with the hydrated polyoxyethylene shell of the nonionic micelles, and that the hydrocarbon core is not involved. The efficiency of denaturants to salt in nonionic surfactants, as shown by increases in cloud point, was proportional to their efficiency to denature proteins, as shown by reductions in the molar absorption coefficient of the Soret band. This observation documents the similarity between the clouding phenomenon of polyoxyethylated surfactants and the denaturation of proteins.

The effect of protein denaturants on the cloud point of a nonionic surfactant

The effect of various protein denaturants (11 urea and thiourea derivatives, acetamide, and guanidinium chloride) on the cloud point of a nonionic surfactant was investigated. In the range of 0.1–0.5 m, all but one additive increased the cloud point in direct proportion to their concentration. The proportionality constant b between cloud point increase and additive molality is a measure of the effectiveness of the additives to salt the surfactant in. It was proportional to the excess partial molal heat capacity of the additives at infinite dilution, which discloses the effect of the additives on the structure of water. Small b values were found for additives with negative excess heat capacities, which are structure breakers. The increase in b with increasing number and/or size of the alkyl groups in urea and thiourea is ascribed to increased micellar binding.

The relationship between the cloud points and the properties of micelles of nonionic detergents

Abstract The relationship between the cloud points and the properties of micelle of non-ionic detergents has been studied by the light-scattering and the surface-tension methods. With increase in cloud point, the critical micelle concentration increased, and the micellar weight decreased. These relationships were found to hold even in the presence of added salt or alcohol.

Factors affecting the solubility of nonionic emulsifiers

The effect of detergents, electrolytes, and organic liquids on the cloud point of Triton X-100, a nonionic emulsifier of the alkylphenol/polyethylene oxide type, is described. The lowering of the cloud point in dilute aqueous solution by electrolyte is a linear function of the ionic strength. The observed salting-out effect for the alkali metal and multivalent cations is roughly in the order of decreasing ion hydration. Crystalline nonelectrolytes cause only slight cloud point changes. Nonpolar liquids and anionic detergents significantly raise the cloud point of the nonionic emulsifier. As the polarity of the organic solubilizate is increased by introduction of double bonds and more polar constituent groups, the increase in cloud point is less marked. Aromatics and polar aliphatics even cause the cloud point to be sharply decreased. The cloud points of mixtures of nonionic emulsifiers lie intermediate between the cloud points of solutions of the pure components.