Effects of additives on the cloud points of selected nonionic linear ethoxylated alcohol surfactants

Effects of various additives including inorganic salts, nonionic and ionic surfactants, water-soluble polymers and alcohols on the cloud points of three linear nonionic surfactants, Tergitol 15-S-7, Tergitol 15-S-9 and Neodol 25-7, were investigated. These surfactants are readily biodegradable and either linear primary or secondary ethoxylated alcohols. Cloud points of these surfactants were functions of their concentrations and concentrations of additives. The cloud points of nonionic surfactant mixtures lay in between the cloud points of individual component surfactants. Presence of two ionic surfactants, sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB), increased the cloud point of 1 wt% Tergitol 15-S-7 micellar solution dramatically when concentrations of ionic surfactants approaching their critical micelle concentration. Addition of water-soluble polymers decreased the cloud point, while addition of inorganic salts can either increase or decrease the cloud points. However, the effect of an alcohol additive on cloud point was dependent on its chain length or its water solubility. Interestingly, synergistic effects between sulfate or phosphate and pentanol on depression of cloud points of Tergitol 15-S-9 were discovered. A linear model predicting cloud points of Tergitol 15-S-X (X = 7, 9 and 12) surfactants and Neodol 25-X (X = 7, 9 and 12) surfactants were proposed with a correlation to logarithm of their ethylene oxide numbers.     

Equilibrium partition of polycyclic aromatic hydrocarbons in a cloud-point extraction process

A cloud-point extraction (CPE) process using the nonionic surfactant Tergitol 15-S-7, a secondary ethoxylated alcohol, to extract selected polycyclic aromatic hydrocarbons (PAHs) from aqueous solutions is investigated. The CPE process is facilitated at the ambient temperature, ca. 22 degrees C, by the reduction of the cloud-point temperature of the surfactant solution by addition of sodium sulfate. It is observed that the preconcentration factor could be enhanced either by increasing the salt concentration or by decreasing the initial surfactant concentration in the micellar solution. A high preconcentration factor of about 40 was achieved at 1 wt% surfactant concentration with the addition of 0.6 M Na(2)SO(4). It is also noted that the equilibrium partition coefficients of the model PAHs are nearly independent of surfactant concentrations, up to 3 wt%, in this study. Correlations between the equilibrium partition coefficients K(p) of the PAHs and their octanol-water partition coefficients K(ow), as well as K(p) and the molar volume V(x) of these PAHs, indicate that the partition processes of the PAHs in the CPE processes are mainly governed by their hydrophobic affinities to the surfactant aggregates. Furthermore, the effect of added Na(2)SO(4) on the equilibrium partition coefficients is also studied. It is shown that addition of more Na(2)SO(4) to the surfactant solution gives more partition of the PAHs into the surfactant-rich phase.     

Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose solutions

Nonionic surfactant and temperature effects on the viscosity of hydrophobically modified hydroxyethyl cellulose (HMHEC) solutions are investigated experimentally. Weak shear thickening at intermediate shear rates takes place for HMHEC at moderate concentrations and becomes more significant at lower temperatures. While this amphiphilic polymer in surfactant-free solution does not turn turbid by heating to 95 degrees C, its mixture with nonionic surfactant shows a lower cloud point temperature than does a pure surfactant solution. For some mixture cases, phase separation takes place at temperatures as low as 2 degrees C. The drop of cloud point temperature is attributed to an additional attractive interaction between mixed micelles via chain bridging. With increasing temperature, the viscosity of an HMHEC-surfactant mixture in aqueous solution first decreases but then rises considerably until around the cloud point. The observed viscosity increase can be explained by the interchain association because of micellar aggregation.     

Solvent-polymer interactions in associative polymer/aqueous media systems

Light scattering measurements in the dilute regime (C<C*) of the amphiphilic hydrophobically modified hydroxyethyl cellulose (HMHEC) have shown a metastable equilibrium of solubility in pure water. As a consequence such ageing solutions present a great instability and in severe conditions of added NaCl or temperature, a demixion has been evidenced. In a more concentrated range of concentration, aqueous solutions of HMHEC possess higher viscosity than HEC precursor due to intermolecular hydrophobic associations. But in a 1M NaCl/ethanol mixture this effect is greatly weakened.     

Nonlinear rheology of aqueous solutions of hydrophobically modified hydroxyethyl cellulose with nonionic surfactant

Shear thickening and strain hardening behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC) aqueous solutions was experimentally examined. We focused on the effects of polymer concentration, temperature, and addition of nonionic surfactant. It is found that HMHEC shows stronger shear thickening at intermediate shear rates in a certain concentration range. In this range, the zero-shear viscosity scales with polymer concentration as eta(0) approximately c(5.7), showing a stronger concentration dependence than for more concentrated solutions. The critical shear stress for complete disruption of the transient network follows tau(c) approximately c(1.62) in the concentrated regime. Dynamic tests of the transient network on addition of surfactants show that the enhanced zero-shear viscosity is due to an increase in network junction strength, rather than their number, which in fact decreases. The reduction in the junction number could partly explain the weak variation of strain hardening extent for low surfactant concentrations, because of longer and looser bridging chain segments, and hence lesser nonlinear chain stretching.     

Synergistic effects in flows of mixtures of wormlike micelles and hydroxyethyl celluloses with or without hydrophobic modifications

This work presents experimental results on simple shear and porous media flow of aqueous solutions of two hydroxyethyl celluloses (HEC) and two hydrophobically modified hydroxyethyl celluloses (HMHEC) with different molecular weights. Mixtures of these polymers with a cationic surfactant, cetyltrimethylammonium p-toluenesulfonate (CTAT) were also studied. Emphasis was given to the range of surfactant concentrations in which wormlike micelles are formed. The presence of hydrophobic groups, the effect of the molecular weight of the polymers, the surfactant and polymer concentrations, and the effect of the flow field type (simple shear versus porous media flow) were the most important variables studied. The results show that the shear viscosity of HEC/CTAT solutions is higher than the viscosities of surfactant and polymer solutions at the same concentrations, but surface tension measurements indicate that no complex formation occurs between CTAT and HEC. On the other hand, a complex driven by hydrophobic interactions was detected by surface tension measurements between CTAT and HMHEC. In this case, the viscosity of the mixture increases significantly more (up to four orders of magnitude at high CTAT concentrations) in comparison with HEC/CTAT aqueous solutions. Increments in the molecular weight of the polymers increase the interaction with CTAT and the shear viscosity of the solution, but make phase separation more feasible. In porous media flow, the polymer/CTAT mixtures exhibited higher apparent viscosities than in simple shear flows. This result suggests that the extensional component of the flow field in porous media flows leads to a stronger interaction between the polymer and the wormlike micelles, probably as a consequence of change of conformation and growth of the micelles.     

Microviscosity of hydrophobically modified hydroxyethyl cellulose aqueous solutions

The microviscosity of hydrophobically modified hydroxyethyl cellulose (HMHEC) aqueous solutions is experimentally determined by conductometry with added ions as probe. Compared to its bulk viscosity, the microviscosity of HMHEC solution could be lower by four orders of magnitude. Since the electric conductivity reduction of added NaCl is almost the same for HMHEC and its unmodified counterpart at an equal weight concentration, one can conclude that the hydrophobic modification for the polymer hardly has any effect on the solution's microviscosity.     

The Influence of Nonionic Surfactant Adsorption on Enzymatic Hydrolysis of Oil Palm Fruit Bunch

Nonionic surfactants have been utilized to improve the enzymatic hydrolysis of lignocellulosic materials. However, the role of surfactant adsorption affecting enzymatic hydrolysis has not been elaborated well. In this work, nonionic surfactants differing in their molecular structures, namely the polyoxyethylene sorbitan monooleate (Tween 80), the secondary alcohol ethoxylate (Tergitol 15-S-9), and the branched alcohol ethoxylate (Tergitol TMN-6), were studied for their effects on the enzymatic hydrolysis of palm fruit bunch (PFB). The PFB was pretreated with a 10% w/v sodium hydroxide solution and then hydrolyzed using the cellulase enzyme from Trichoderma reesei (ATCC 26921) at 50 °C and pH 5. The optimal conditions providing similar yields of reducing sugar required Tween 80 and Tergitol TMN-6 at 0.25% w/v, while Tergitol 15-S-9 was required at 0.1% w/v. All the surfactants improved the enzymatic conversion efficiency and reduced unproductive binding of the enzyme to lignin. In addition, the adsorption isotherm of cellulase was fit well by the Freundlich isotherm, while adsorption of the three nonionic surfactants agreed well with the Langmuir isotherm. Adsorption capacities of the three nonionic surfactants were consistent with their enhancement efficiencies in hydrolysis. The critical micelle concentration was observed as a key property of nonionic surfactant for adsorption capacity.     

Clouding and phase behavior of nonionic surfactants in hydrophobically modified hydroxyethyl cellulose solutions

Clouding phenomena and phase behaviors of two nonionic surfactants, Triton X-114 and Triton X-100, in the presence of either hydroxyethyl cellulose (HEC) or its hydrophobically modified counterpart (HMHEC) were experimentally studied. Compared with HEC, HMHEC was found to have a stronger effect on lowering the cloud point temperature of a nonionic surfactant at low concentrations. The difference in clouding behavior can be attributed to different kinds of molecular interactions. Depletion flocculation is the underlying mechanism in the case of HEC, while the chain-bridging effect is responsible for the large decrease of cloud point for HMHEC. Composition analyses for the formed macroscopic phases were carried out to provide support for associative phase separation for the case of HMHEC, in contrast to segregative phase separation for HEC. An interesting three-phase-separation phenomenon was reported in some HMHEC/Triton X-100 mixtures at high surfactant concentrations.     

Thickening mechanism of associative polymers

Steady state viscosity and viscoelasticity of HMHEC solutions were studied. Viscosity increases with concentration due to a reinforcement of the micellar network. High shear rate viscosities are independent of temperature. Two relaxation processes were observed, the long one related to the lifetime of the hydrophobic junction and the short related to rapid Rouse-like relaxations of the free chains. When SDS is added, mixed micelles form that reinforce the network up to an optimum [SDS]/[HMHEC] ratio. Above this ratio, the micelles in excess isolate the polymer chains, the long relaxation process disappears and Rouse-like relaxations occur, corresponding to rapid movements of free chains.     

Determination of Carbamate Pesticides and Phthalates in Vegetables by a Cloud Point Extraction Process Using Tergitol 15-s-7 and High Performance Liquid Chromatography

An efficient and environmentally friendly analytical process based on cloud point extraction (CPE) has been developed for the determination of carbamate pesticides and phthalates in vegetables by high performance liquid chromatography (HPLC) separation and ultraviolet detection (UV). The readily biodegradable nonionic surfactant Tergitol 15-S-7 was chosen as the extraction solvent. To obtain optimum extraction efficiency, several experimental parameters including surfactant concentration, salt concentration, equilibration temperature, equilibration time, and sample pH were identified. Under the optimum conditions, the linear regression coefficients of the standard curves were greater than 0.9984. The limits of detection for carbaryl, pirimicarb, dimethyl phthalate (DMP), and diethyl phthalate (DEP) are 0.003, 0.015, 0.012, and 0.006 µg mL^?1, respectively. The intra-day and inter-day relative standard deviations are less than 5.75% and 6.97%. The proposed method has been proven to be an efficient, green, rapid, and inexpensive approach for extraction and determination of target analytes present in vegetable samples.     

Equilibrium partition of polycyclic aromatic hydrocarbons in cloud point extraction with a silicone surfactant

In the cloud point extraction (CPE) process with PEG/PPG-18/18 dimethicone, the flexible chain structure of the silicone surfactant efficiently decreased the water content remaining in the surfactant-rich phase, compared with conventional nonionic surfactants, represented by Triton X-114. Meanwhile, the phase volume ratio of surfactant-rich phase to aqueous phase obtained in the silicone surfactant CPE system was found to be maintained at a low value with increasing surfactant concentration; whereas a rapid increase tendency was commonly observed in that of other nonionic surfactants. Based on these advantages, the equilibrium partition of three polycyclic aromatic hydrocarbons (PAHs), anthracene, phenanthrene and pyrene, was studied in the CPE process with PEG/PPG-18/18 dimethicone. Equilibrium parameters, including preconcentration factor, distribution coefficient and recovery, were determined, and the performance was compared with that of another related CPE research, where Tergitol 15-S-7 was used. Due to the low surfactant-rich phase volume, higher concentrations of the three PAHs in the surfactant-rich phase, and the resulting higher preconcentration factors and distribution coefficients were able to be achieved at the same time. Moreover, the great performance was able to be maintained even at a high surfactant concentration or PAHs initial concentration.     

Interaction of surfactants with thickeners used in waterborne paints: a rheological study

Studies of the phase diagram and linear viscoelasticity of aqueous solutions of hydrophobically modified hydroxyethyl cellulose (HMHEC), a thickener used in water-based paints, and SDS reveal that SDS-HMHEC mixed micelles are formed that increase the number of hydrophobic junctions and enhance interpolymer association up to an [SDS]/[HMHEC] ratio. This fact produces a strong increase of viscoelasticity or a phase separation, depending on the [HMHEC]. At higher ratios the excess of micelles with predominant SDS isolates hydrophobes and disrupts the micellar network. Then, viscoelastic functions decrease and HMHEC behaves as a nonassociative polymer. TTAB and Brij30 also interact with HMHEC, but in a different way. No phase separation is observed with these surfactants. TTAB forms mixed micelles and new junction points in the same way as SDS. However, this surfactant does not stabilize the micelles as SDS does, presumably due to the different interaction between the OH from the cellulose and the charged groups. Results seem to indicate that Brij30 enters into the hydrophobic aggregates of HMHEC and stabilizes them, increasing relaxation time, but it does not form new junction points, since it forms quite big micelles.     

Mixed solutions of an associating polymer with a cleavable surfactant

Mixtures of hydrophobically modified hydroxyethyl cellulose (HMHEC) and alkali-sensitive cleavable betaine ester surfactants have been studied by viscometry, 1H NMR, absorbance measurements, and birefringence determinations. Before the hydrolysis, the surfactants behaved as conventional nondegradable surfactants in terms of the effect on the viscosity of increasing surfactant concentration. As the surfactants were hydrolyzed, systems with time-dependent viscosity were obtained. The viscosity either decreased monotonically or went through a maximum as a function of time, depending on the initial surfactant concentration. Different surfactant chain lengths gave rise to different viscosity profiles. The rate of hydrolysis, and thus the time-dependency of the surfactant concentration, could be controlled by changing the pH of the solution.     

Thermosensitive amphiphilic polyphosphazenes and their interaction with ionic surfactants

Temperature-responding physical hydrogels are promising materials as injectable drug delivery carriers which could hold useful bioactive materials inside the polymer networks for further controlled releases. Aimed at desired qualities at body temperature, those gel characteristics need to be adjusted carefully. In this point of view, surfactant is one of the useful molecules to be used by simple formulations without harmful chemical reactions. In this study, thermothickening of amphiphilic nonionic polyphosphazene solution is modified by anionic and cationic surfactants with different alkyl chains and counter-ions. Specified in the thermothickening system, a maximum viscosity (η_max) and a temperature at that point (T_max) are changed independently reflecting unique intermolecular interactions. At low concentration (1–9 mM) of the added surfactant, the η_max is maximized at 3 mM surfactant regardless of the surfactant type while the T_max is increased continuously along with the surfactant concentration. From a kinetic point of view, this 3 mM surfactant at the maximized η_max reflects a polymer-dominating interaction and highly favorable polymer–surfactant interaction with a low selectivity in the surfactant type. However, the magnitude of the maximum viscosity (η_max) is dependent on the surfactant tail, which reflects the lifetime and the strength of the hydrophobic domains of the polymer network affected by the surfactants. Meanwhile, the magnitude of the T_max depended on the surfactant head group, which means the interfacial tension of the polymer solutions changed by the surfactants. At high concentration (10 and 30 mM) of the cationic surfactants added to the polymer solutions with two different viscosities, the cationic surfactants are supposed to interact either with the hydrophobic parts of the aggregated polymer with high viscosity or on the backbone of the less- or non-aggregated polymer with low viscosity.Ionic surfactants change the thermothickening of the amphiphilic nonionic polyphosphazene solution in a unique tail- or head-dependent way. Moreover, the concentration of the added surfactants and the association pattern of the pure polymer solutions are also crucial for the thermothickening phase behaviors. Temperature-responsive polyphosphazenes in this work exhibit unique and controllable interactions with ionic surfactants.     

Solubilization of an organic solute in aqueous solutions of unimeric block copolymers and their mixtures with monomeric surfactant: volume, surface tension, differential scanning calorimetry, viscosity, and fluorescence spectroscopy studies

The ability of aqueous systems, formed by unimeric copolymers and their mixtures with a monomeric surfactant, in solubilizing large quantities of 1-nitropropane (PrNO2) was explored. The copolymers are F68 and L64, which differ for the hydrophilicity, and the surfactant is sodium dodecanoate. For a better understanding of the mechanism of solubilization, thermodynamic (volume and differential scanning calorimetry), spectroscopy (steady-state fluorescence), viscosity, and interfacial investigations were carried out. PrNO2 causes the micellization of the unimeric copolymer, and the required amount of PrNO2 depends on the composition, the copolymer nature, and the temperature. Large quantities of PrNO2 form mixed micelles where PrNO2 experiences an environment similar to its pure liquid state. The presence of the additive allows a decrease of the critical micellar temperature, evidence of which is quantitatively explained through a novel thermodynamic approach. A synergistic effect in solubilizing PrNO2 was observed when surfactant monomers were added to the unimeric copolymer solutions. The increased amount of PrNO2 leads to the complete self-assembling of both the copolymer and the surfactant; a process favored by temperature increase. For all of the investigated systems, the presence of PrNO2 generates a viscosity increase.     

Ethoxylated nonionic surfactants in hydrophobic solvent: interaction with aqueous and membrane-immobilized poly(acrylic acid)

Interaction between ethoxylated nonionic surfactants and poly(acrylic acid) (PAA) in aqueous solutions is well-documented in the literature. In the present study, pure ethoxylated surfactant solution in a hydrophobic solvent was permeated through a partially cross-linked PAA composite membrane to quantify the surfactant-PAA interaction in the heterogeneous system. Partitioning of the mixture of the surfactants (15-S-5) between the hydrophobic solvent and aqueous solution of PAA was also studied. The role of ethylene oxide group variation in the surfactant-PAA interaction for the heterogeneous system was established by performing experiments with pure surfactants having the same alkyl chain length but varying ethoxylate chain lengths. It was observed that the surfactants with a higher number of ethylene oxide groups per molecule exhibit stronger interaction with PAA. The literature data for adsorption of pure ethoxylated surfactants (C12E(n)) on a hydrophobic solid-water interface was correlated and compared with the data obtained in our study. It was calculated that resistance in terms of transfer of surfactant molecules from a hydrophobic solvent domain to PAA domain lowers the extent of PAA-surfactant interaction by an order of magnitude. Only 40% of available carboxyl groups were accessible for interaction with the ethoxylated nonionic surfactants due to diffusion limitations. Finally the pH sensitivity of the PAA-surfactant complex was verified by successful regeneration of the membrane on permeation of slightly alkaline water. The regeneration and reuse of membrane is especially attractive in terms of process development for nonionic surfactant separation from hydrophobic solvents.     

Anionic–Nonionic Mixed Surfactant Systems: Micellar Interaction and Thermodynamic Behavior

The interactions between an anionic surfactant, viz., sodium dodecylbenzenesulfonate and nonionic surfactants with different secondary ethoxylated chain length, viz., Tergitol 15-S-12, Tergitol 15-S-9, and Tergitol 15-S-7 have been studied in the present article. An attempt has also been made to investigate the effect of ethoxylated chain length on the micellar and the thermodynamic properties of the mixed surfactant systems. The micellar properties like critical micelle concentration (CMC), micellar composition (X_A), interaction parameter (β), and the activity coefficients (f_A and f_NI) have been evaluated using Rubingh's regular solution theory. In addition to micellar studies, thermodynamic parameters like the surface pressure (Π_CMC), surface excess values (Γ_CMC), average area of the monomers at the air–water interface (A_avg), free energy of micellization (ΔG_m), minimum energy at the air–water interface (G_min), etc., have also been calculated. It has been found that in mixtures of anionic and nonionic secondary ethoxylated surfactants, a surfactant containing a smaller ethoxylated chain is favored thermodynamically. Additionally, the adsorption of nonionic species on air/water interface and micelle increases with decreasing secondary ethoxylated chain length. Dynamic light scattering and viscometric studies have also been performed to study the interactions between anionic and nonionic surfactants used.     

Effects of nonionic surfactant and associative thickener on the rheology of polyacrylamide in aqueous glycerol solutions

The effect of a low molecular weight nonionic surfactant and an acrylic associative thickener on the rheology of polyacrylamide in aqueous glycerol solutions under steady shear was experimentally investigated. The nonionic surfactant (Tween20), associative thickener (Acrysol TT935) and polyacrylamide (Separan AP30) underwent complex molecular interactions in solution as reflected by rheological measurements. The surfactant also interacted with the glycerol solvent. The addition of surfactant in aqueous glycerol solutions reduced the surface tension, as well as the solution viscosity, at low surfactant concentration. The solution viscosity went through a minimum at certain surfactant concentration, depending on the composition of glycerol/water mixture, before increasing again. Similar behavior was found when the surfactant was added to the polyacrylamide solution, except there was an initial increase in the viscosity before the reduction. The associative thickener, Acrysol TT935 (an anionic acrylic emulsion copolymer) exhibited a strong affinity with polyacrylamide in solution, as indicated by a sharp increase in the solution viscosity. The dilute polyacrylamide solution became highly elastic in the presence of either the nonionic surfactant on the associative thickener. A threestage model was proposed to describe the surfactant/thickener/polymer interactions.