Effects of added nonionic surfactant and inorganic salt on the rheology of sugar surfactant and CTAB aqueous solutions

The effect of adding tri(oxyethylene) dodecyl ether (C₁₂EO₃) on the phase and rheological behavior of sucrose hexadecanoate and CTAB aqueous solutions in the presence of added salt (NaBr) was investigated. Viscoelastic solutions are formed in CTAB and C₁₆SE systems upon addition of lipophilic nonionic surfactant C₁₂EO₃. The zero-shear viscosity shows a maximum at a certain mixing fraction of C₁₂EO₃, except in the case of the aqueous CTAB/C₁₂EO₃ system in the absence of salt. The rheological properties are strongly affected by the addition of salt to the CTAB systems but they remain unaltered in the case of C₁₆SE systems. In ionic systems, the mixing fraction of C₁₂EO₃ for the maximum viscosity depends on salt concentration.     

Rheology of viscoelastic anionic micellar solutions in the presence of a multivalent counterions

The growth and structure of anionic micelles sodium dodecyl trioxyethylene sulfate (SDES) in the presence of a multivalent counter-ion, Al³⁺, were investigated by means of rheological methods and the technique of freeze-fracture transmission electron microscopy. It was found that wormlike micelles and network structures could be formed in SDES/AlCl₃ aqueous micellar solutions, according to the measurements of the zero-shear viscosity, the complex viscosity and the dynamic moduli (storage modulus and loss modulus), and the application of the Cox–Merz rule and a Cole–Cole plot. The cyclic shear test, the plateau modulus and the relaxation time were also studied to express the rheological properties of the wormlike micellar solutions. The structure was of a character of a nonlinear viscoelastic fluid and departed from the simple Maxwell model. Received: 23 November/2000 Accepted: 31 January 2001     

Studies on the self-assembly behavior of the amphiphilic block copolymer of PSt-b-PAA in apolar solvents with polar fluorescent probe

The block copolymer of polystyrene-b-poly(butyl acrylate) (PSt-b-PBA) with a well-defined structure was synthesized by atom transfer radical polymerization (ATRP); its structure was characterized, and the living polymerization was also validated by gel permeation chromatography, Fourier transform infrared, and ¹H NMR measurements. Then, the amphiphilic block copolymer of polystyrene-b-poly(acrylic acid) (PSt-b-PAA) has been prepared by hydrolysis of PSt-b-PBA, and copolymers of PSt-b-PAA with longer PSt blocks and shorter PAA blocks were obtained by controlling the conditions of ATRP polymerization. The reversed micelle solution of PSt-b-PAA in toluene was prepared by using the single-solvent dissolving method, and the reverse micellization behavior of PSt-b-PAA in toluene was mainly investigated in this paper. The fluorescent probe technique was used by using polar fluorescence compound N-(1-Naphthyl)ethylenediamine dihydrochloride (NEAH) as a polar fluorescent probe to study the reverse micellization behavior of PSt-b-PAA. It was found that the reverse micellization behaviors of PSt-b-PAA in toluene can be clearly revealed by using NEAH as a polar fluorescence probe, and the critical micelle concentrations (cmcs) can be well displayed. The experimental results showed that the self-assembling behavior of PSt-b-PAA in toluene depends apparently on the microstructure of the macromolecules and is also influenced by the temperature. For the copolymers of PSt-b-PAA with the same length of hydrophobic PSt blocks, the copolymer with a longer hydrophilic block PAA has lower cmc, and at higher temperature, the copolymer has lower cmc.     

Rheological Properties of Anionic Surfactant Solutions in the Presence of Al3+ Counterion

Aqueous solutions of ionic surfactants with strongly binding counterions exhibit wormlike or network properties. The properties of anionic micelles of sodium dodecyltrioxyethylene sulfate (AES) in the presence of multivalent counterion Al³⁺ were investigated by dynamic rheological methods. The steady-shear viscosity and stress, the zero-shear viscosity, the complex viscosity, and the dynamic shear modulus have been determined as a function of the surfactant and salt concentrations. Some interesting and noticeable results have been obtained, which can express the micellar growth and structure. The formation of wormlike micelles or network structure in surfactant solutions becomes much easier with increasing surfactant and salt concentrations. The Cox-Merz rule and the Cole-Cole plot are not applicable perfectly to the systems studied. The nonlinear viscoelasticity and non-Newtonian behavior can be found in all solutions according to the comparison with the simple Maxwell model. The technique of freeze-fracture transmission electron microscopy (FF-TEM) was also applied to confirm the formation of these interesting structures.     

Rheological properties of wormlike micelles formed in the sodium oleate/trisodium phosphate aqueous solution

Aqueous solution of anionic surfactant,sodium oleate（NaOA）,was studied by means of steady-state shear rheology and dynamic oscillatory technique.The system of NaOA/Na3PO4 showed high viscosity,strong viscoelasticity and good ability of countering Ca^2＋,Mg^2＋.The Maxwell model and Cole-Cole plot were applied to study the dynamic viscoelasticity of wormlike micelles.The microstructures of the wormlike micelles were characterized by FF-TEM.     

Rheological behavior of associating ionic polymers based on diallylammonium salts containing single-, twin-, and triple-tailed hydrophobes

The cycloterpolymerizations of N,N-diallyl-(4-octyloxy)benzyl-, N,N-diallyl-(3,5-dioctyloxy)benzyl-, and N,N-diallyl-(3,4,5-trioctyloxy)benzyl-ammonium chloride (0-8 mol%) with hydrophilic monomer N,N-diallyl-N-carboethoxymethylammonium chloride and sulfur dioxide afforded a series of cationic polyelectrolytes (CPE). The CPEs were treated with HCl and NaOH to produce the corresponding pH-responsive cationic acid salts (CAS) and polybetaines (PB), anionic polyelectrolytes (APE) as well as polymers PB/APE containing various proportions of zwitterionic (PB) and anionic fractions (APE) in the polymer chain. Likewise, the cycloterpolymerizations of these single-, twin-, and triple-tailed hydrophobes (0-12 mol%) with hydrophilic monomer diallyldimethylammonium chloride and sulfur dioxide afforded a series of CPE in excellent yields. The polymers were characterized by different techniques including NMR and IR. The solution properties of the series of CPE were investigated by rheological techniques. The studied water soluble polymers showed different rheological behavior depending on their structure (hydrophobe type and content) as well as salinity and pH. The high shear thinning and the formation of networks at low shear would likely promote the use of such polymers in enhanced oil recovery applications.     

Rheological and photorheological effects in aqueous solutions of cetyltrimethylammonium bromide containing 9-anthrylalkanols

Viscosities, flow properties, and static low-angle light scattering of dilute (250 mmol/dm³) aqueous micellar solutions of cetyltrimethylammonium bromide were measured in the presence of various amounts of 9-anthrylmethanol (AM), 2,2,2-trifluoro-1-(9-anthryl)ethanol (TFAE), 1-(9-anthryl)ethanol (AE), 9-methylanthracene (MA), and 9-ethylanthracene (EA). At room temperature the solubilization of AM induces an increase of viscosity and a rise in aggregation numbers (as determined from low-angle light scattering). Both features are reverted upon in in situ photodimerization of AM. After lowering the temperaure, non-Newtonian flow is detected by means of a rotating viscometer. The solubilization of AE and EA, respectively, leads to analogous observations, while no viscoelastic features were obtained with solubilized MA. TFAE containing systems at room temperature show non-Newtonian flow accompanied by viscoelasticity which can be ascribed to the formation of long rod-like micelles. Raising the temperature as well as photodimerization diminish the lengths of the micelles and the non-Newtonian features.     

Electrostatic hierarchical co-assembly in aqueous solutions of two oppositely charged double hydrophilic diblock copolymers

The formation of spherical micelles in aqueous solutions of poly(N-methyl-2-vinyl pyridinium iodide)-block-poly(ethylene oxide), P2MVP-b-PEO and poly(acrylic acid)-block-poly(vinyl alcohol), PAA-b-PVOH has been investigated with light scattering-titrations, dynamic and static light scattering, and ¹H 2D Nuclear Overhauser Effect Spectroscopy. Complex coacervate core micelles, also called PIC micelles, block ionomer complexes, and interpolyelectrolyte complexes, are formed in thermodynamic equilibrium under charge neutral conditions (pH 8, 1 mM NaNO₃, T = 25 °C) through electrostatic interaction between the core-forming P2MVP and PAA blocks. 2D ¹H NOESY NMR experiments show no cross-correlations between PEO and PVOH blocks, indicating their segregation in the micellar corona. Self-consistent field calculations support the conclusion that these C3Ms are likely to resemble a ‘patched micelle’; that is, micelles featuring a ‘spheres-on-sphere’ morphology.     

Association under shear flow in aqueous solutions of pectin

Effects of oscillatory and steady shear flows on intermolecular associations in dilute and semidilute aqueous solutions of pectin in the absence and presence of the hydrogen bond breaking agent urea are reported. A weak oscillatory shear perturbation builds up, depending on polymer concentration, multichain aggregates or networks in the course of time and these association structures are mainly stabilized through hydrogen bonds. The association effect is more pronounced at higher concentrations, and the growth of intermolecular interactions is inhibited by the addition of urea. Steady shear measurements on the pectin-water solutions reveal shear thickening at low shear rates for all the concentrations, except the lowest one, and disruption of intermolecular junctions at high shear rates. In the presence of urea, no shear thickening is detected. The polymer concentration dependence of the viscosity at a low shear rate can be described by a power law η ∼ c^x, with x = 1.9 and 1.4 without and with urea, respectively. When a low constant shear rate is applied to pectin solutions and this monitoring shear rate is interrupted periodically by transitory high shear rates perturbations during a short time, prominent association structures evolve upon return to the monitoring shear rate. This effect is more evident at a lower polymer concentration, and in the presence of urea, the growth of the association complexes is damped. The shear-induced alignment and stretching of polymer chains and the formation of hydrogen-bonded structures are analyzed in the framework of a model, where cooperative zipping of stretched chains play an important role. Viscosity enhancement is found for a semidilute pectin-water solution in the presence of moderate levels of salt addition (NaCl), suggesting that partial screening of electrostatic interactions promotes growth of energetic cross-links.     

Rheological properties of multisticker associative polyelectrolytes in semidilute aqueous solutions

Multisticker associative polyelectrolytes of acrylamide (≈86 mol %) and sodium 2‐acrylamido‐2‐methylpropanesulfonate (≈12 mol %), hydrophobically modified with N,N‐dihexylacrylamide groups (≈2 mol %), were prepared with a micellar radical polymerization technique. This process led to multiblock polymers in which the length of the hydrophobic blocks could be controlled through variations in the surfactant‐to‐hydrophobe molar ratio, that is, the number of hydrophobes per micelle (N_H). The rheological behavior of aqueous solutions of polymers with the same molecular weight and the same composition but with two different hydrophobic block lengths (N_H = 7 or 3 monomer units per block) was investigated as a function of the polymer concentration with steady‐flow, creep, and oscillatory experiments. The critical concentration at the onset of the viscosity enhancement decreased as the length of the hydrophobic segments in the polymers increased. Also, an increase in the N_H value significantly enhanced the thickening ability of the polymers and affected the structure of the transient network. In the semidilute unentangled regime, the behavior of the polymer with long hydrophobic segments (N_H = 7) was studied in detail. The results were well explained by the sticky Rouse theory of associative polymer dynamics. Finally, the viscosity decreased with an increase in the temperature, mainly because of a lowering of the sample relaxation time. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1640–1655, 2004     

Study of maleated ethylene-propylene copolymers by fluorescence: Evidence for succinimide induced polar associations in an apolar solvent

A maleated ethylene-propylene copolymer (EP-MAH) was labelled with 1-naphthalene- and/or 1-pyrenemethylamine to yield an EP copolymer bearing succinimide pendants all labelled with a chromophore. The labelled EPs were reacted with LiAlH₄ so that the polar succinimide linker group between the EP backbone and the chromophore was converted into apolar pyrrolidine units. The resulting products were purified through a gel permeation chromatography column to remove the cleaved off chromophores. FT-IR spectroscopy revealed that after reduction, the peak assigned to the succinimide carbonyls was strongly diminished. UV-vis absorption and steady-state and time-resolved fluorescence measurements were performed in hexane and THF. The reduction of the succinimide carbonyls was found to have a significant effect on the luminescence properties of the labelled EPs. The polar associations taking place between the succinimide moieties in hexane were found to be dramatically decreased after reduction as shown by UV-vis absorption, steady-state excitation and emission fluorescence, time-resolved fluorescence, and fluorescence resonance energy transfer. These results demonstrate that the presence of pyrene aggregates for EP-MAH labelled with 1-pyrenemethylamine is due primarily to the polar succinimide moieties rather than the aromatic pyrene.     

Composition dependence of ordered structures in mixed micellar aqueous solutions of hydrophobically modified poly(ethylene glycol)s

Ordered structures of micellar aqueous solutions of poly(ethylene glycol) (PEG) monododecylether mixtures [octaethylene glycol monododecylether (C12E8) and poly(ethylene glycol) monododecylether (C12E25)] have been investigated as a function of the C12E8/C12E25 composition by means of X‐ray scattering. C12E8 and C12E25 have different chain lengths of corona PEG, that is, 8 and 25 repeating units, respectively. The following results have been obtained. First, in the C12E8‐rich and C12E25‐rich regions, the mixtures take hexagonal and cubic phases, respectively. The hexagonal phase remains over a wider range of compositions and is more stable for the mixing of the other component than the cubic phase. Second, in the C12E8‐rich region of the cylindrical hexagonal packing, the nearest‐neighbor micellar distance increases, whereas the association number density remains constant, with an increasing amount of mixed C12E25 possessing longer corona chains. Third, in contrast to this, the nearest‐neighbor micellar distance of the body‐centered cubic packing exhibits almost no change, whereas the association number increases as C12E8 of shorter corona chains is increasingly incorporated. Fourth, self‐consistent field calculations reasonably reproduce the experimental findings of the second and third observations. We discuss the phase stability and the structural changes with the composition in terms of differences in the PEG corona‐chain length. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2474–2483, 2005     

Rheological and microcalorimetric studies of a model alkali‐soluble associative polymer (HASE) in nonionic surfactant solutions

Rheological experiments were carried out on a 1 wt % hydrophobically modified alkali‐soluble emulsion (HASE) solutions at pH ∼ 9 in the presence of nonionic polyoxyethylene ether type surfactant (C₁₂EO₂₃). The low shear viscosity and dynamic moduli increases at c > cmc until they reach a maximum at a critical concentration, c^m of approximately 1 mM (∼17 times the cmc of free surfactant) and then decrease. The dominant mechanism at cmc < c < c^m is an increase in the number of intermolecular hydrophobic junctions and a strengthening of the overall associative network structure. Above c^m, the disruption of the associative network causes a reduction in the number of junctions and strength of the overall network structure. The influence of C₁₂EO₂₃ on HASE before cmc could not be detected macroscopically by the rheological technique. However, isothermal titration calorimetry enables the determination of complex binding of surfactant to the polymer. Isothermal titration of C₁₂EO₂₃ into 0.1 wt % HASE indicates that the C₁₂EO₂₃ aggregation in water and 0.1 wt % HASE polymer solutions is entropically driven. A reduction in the critical aggregation concentration (cac) confirms the existence of polymer–surfactant interactions. The hydrophobic micellar junctions cause a decrease in the ΔH and ΔS of aggregation of the nonionic surfactant. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2019–2032, 2000     

Dynamics of solutions of triblock copolymers in a selective solvent: Effect of varying copolymer concentration

We have used static and dynamic light scattering and pulsed field gradient NMR to study the effect of varying concentration on the dynamics of the triblock copolymer, polystyrene block poly(ethylene, butylene) block polystyrene (PS‐PEB‐PS), dissolved in n‐heptane, a selective solvent for the middle block. The correlation function for a dilute solution with c = 0.49 % (w/v) corresponds to the translational diffusion of micelles. At intermediate concentrations [1.1 ≤ c ≤ 2.6 % (w/v)], the correlation functions can be fitted to the sum of a single exponential and stretched exponential functions. The slower mode is due to the diffusion of polydisperse clusters formed by random association of triblock copolymer molecules and the faster one again represents micelles. A complex behavior is observed in the semidilute region [4.0 ≤ c ≤ 6.9 % (w/v)]. Three dynamic processes can be extracted from the correlation function: (i) The fast diffusive mode is the collective diffusion mode in the physical gel, (ii) the middle, relaxational mode, is probably due to the local movement of insoluble domains trapped in the network of the physical gel, and (iii) the slow diffusive mode implies the existence of large‐scale inhomogeneities in the system. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1312–1322, 2000     

Scaling and structural properties of a polymer in a simple solvent: A study based on integral equations

We present a statistical mechanical theory for polymer–solvent systems based on integral equations derived from the polymer Kirkwood hierarchy. Integral equations for pair monomer–monomer, monomer–solvent, and solvent–solvent correlation functions yield polymer–solvent distribution, chain conformation in three dimensions, and scaling properties associated with polymer swell and collapse in athermal, good, and poor solvents. Variation of polymer properties with solvent density and solvent quality is evaluated for chains having up to 100 bonds. In good solvents, the scaling exponent v has a constant value of about 0.61 at different solvent densities computed. For the athermal solvent case, the gyration radius and scaling exponent decrease with solvent density. In a poor solvent, the chain size scales as N^v with the value of the exponent being about 0.3, compared with the mean field value of ⅓. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3025–3033, 1998     

Self-organization in aqueous solutions of thermosensitive statistical copolymers based on N-(dimethylamino)ethyl methacrylate

Thermo- and pH-responsive statistical copolymers of N-(dimethylamino)ethyl methacrylate and lauryl methacrylate were synthesized by free radical copolymerization. Obtained samples differed in content of hydrophobic components (3 and 6?mol. %). Their molar masses were close to 30,000?g/mol. Self-organization in buffer solutions of copolymers were studied using light scattering and turbidimetry. It was found that copolymers as well as of poly(N-(dimethylamino)ethyl methacrylate) were thermosensitive at pH?>?7. Phase separation temperatures of investigated solutions decreased with dilution and pH increasing. Growth of lauryl methacrylate content in copolymers caused the decrease in phase separation temperatures.     

Cationic polymerization of 1,3-pentadiene : IV. Initiation by aluminum chloride in an apolar solvent: effect of various electron donors

The polymerization of 1,3-pentadiene (PD) initiated by aluminum trichloride in nonpolar solvent was carried out in the presence of various electron donors (EDs) such as ethyl acetate, (EtOAc) tert-butyl acetate, dimethyl phthalate (DMP), N,N-dimethyl formamide, N,N-dimethyl acetamide and dimethyl sulfoxide. Addition of an ED whatever its nature to the polymerization medium, in a one-to-one molar ratio relatively to the Lewis acid, resulted in a decrease of the overall yield and an increased proportion of crosslinked polymer. The molecular weight distribution of the soluble fraction was narrower than that of polymerizations carried out without ED. The microstructure of the soluble polymers can be tuned using different EDs, showing that they are interacting with the active species. For instance EtOAc increased polymer isomerization while DMP increased polymer cyclization. Thus, the nature of the chemical functions borne by the ED does not seem to be the only parameter explaining its influence on the polyPD microstructure. If crosslinking efficiency seems to be roughly correlated to the donicity scale of the EDs, termination reaction is not. It was shown that the complexation between the Lewis acid and the EDs containing a carbonyl group involved the carbonyl oxygen atom. The decrease of polymerization yield when using the EDs was assigned to this complexation between the ED and AlCl₃.     

Anionic polymerization of 1,3‐cyclohexadiene with alkyllithium/amine system in an aromatic hydrocarbon solvent: Predominant formation of 1,2‐addition product

Steric hindrance of the amine strongly affected the formation of the dominant 1,2‐addition product from the anionic polymerization of 1,3‐cyclohexadiene (1,3‐CHD) initiated by the alkyllithium (RLi)/amine system in an aromatic hydrocarbon solvent. 1,2‐Cyclohexadiene (1,2‐CHD)/1,4‐cyclohexadiene (1,4‐CHD) unit molar ratios from 85/15 to 93/7 were obtained using an RLi/N,N,N′,N′‐tetramethylethylenediamine (TMEDA) system in toluene. The C? Li bonds of poly(1,3‐cyclohexadienyl)lithium (PCHDLi)/TMEDA complex in toluene appeared to be strongly polarized with small steric hindrance. Intermolecular forces contributing to the aggregation were strong for high‐molecular‐weight poly(1,3‐cyclohexadiene) (PCHD) consisting of almost all 1,2‐CHD units. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6604–6611, 2008     

Prediction of solvent diffusion coefficient in amorphous polymers based on an equation‐of‐state

This study develops a modified free‐volume model to predict solvent diffusion coefficients in amorphous polymers by combining the Vrentas–Duda model with the Simha–Somcynsky (S‐S) equation‐of‐state (EOS), and all the original parameters can be used in the modified model. The free volume of the polymer is estimated from the S‐S EOS together with the Williams‐Landel‐Ferry fractional free volume, and the complex process of determining polymer free‐volume parameters in the Vrentas–Duda model and measuring polymer viscoelasticity can be avoided. Moreover, the modified model includes the influence of not only temperature but also pressure on solvent diffusivity. Three common polymers and four solvents are employed to demonstrate the predictions of the modified model. The calculation results are generally consistent with the experimental values. It is reasonable to expect that the modified free‐volume model will become a useful tool in polymer process development. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1000–1009, 2006