Time effects on the rheological behavior of hydrophobically modified polyacrylamide aqueous solutions mixed with sodium dodecyl sulfate (SDS)

The transient response of hydrophobically modified polyacrylamides (HMPAM) aqueous solutions with sodium dodecyl sulfate (SDS) during step shear rate experiments was evaluated. The experimental protocol involved employing first a low shear rate for a specific time, followed by an abrupt increase in shear rate (applied for the same time) and then finally reducing the shear rate to the initial value and recording the sample relaxation with time. While the second step was characterized by a general anti-thixotropic behavior, a large viscosity peak was observed at the third step at very short times followed by a thixotropic relaxation of the viscosity value. This peak was interpreted as a consequence of the formation of a transient network during the relaxation process. A kinetic model was used to better understand and to describe the thixotropy of HMPAM solutions in the presence of SDS. The kinetic constants obtained from the model decrease in value when the shear rate applied during the second step increases, reflecting the increase in recovery time needed for the system to relax back to a lower strain rate. As expected, as the degree of hydrophobic association increases or the degree of fluid structuring increases, the kinetic constant values strongly decrease.     

Interfacial tension of ethylene and aqueous solution of sodium dodecyl sulfate (SDS) in or near hydrate formation region

The interfacial tensions between ethylene and an aqueous solution of SDS were measured using the pendant-drop method at 274.2 and 278.2 K and in the pressure range from 0.1 to 3.1 MPa, including hydrate formation points. The concentrations of sodium dodecyl sulfate (SDS) aqueous solution were 0, 100, 300, 500, 600, 700, 800, 900, and 1000 ppm. The effects of pressure on the critical micelle concentration (CMC) and the surface excess concentration were studied. It was demonstrated that both the CMC and the saturated surface excess concentration decreased with the increase of pressure.     

A solution-reaction isoperibol calorimeter and standard molar enthalpies of formation of Ln(hq)2Ac (Ln = La, Pr)

An on-line solution-reaction isoperibol calorimeter has been constructed. The performance of the apparatus was evaluated by measuring the molar enthalpy of solution of KCl in water at 298.15 K. The uncertainty and the inaccurary of the experimental results were within ±0.3% compared with the recommended reference data. Using the calorimeter, the molar enthalpies of reaction for the following two reactions: LaCl₃·7H₂O(s)+2Hhq(s)+NaAc(s)=La(hq)₂Ac(s)+NaCl(s)+2HCl(g)+7H₂O(l) and PrCl₃·6H₂O(s)+2Hhq(s)+NaAc(s)=Pr(hq)₂Ac(s)+NaCl(s)+2HCl(g)+6H₂O(l), were determined at T=298.15 K, as −(78.3±0.6) and −(97.3±0.5) kJ mol^−l, respectively. From the above molar enthalpies of reaction and other auxiliary thermodynamic quantities, the standard molar enthalpies of formation of La(hq)₂Ac and Pr(hq)₂Ac, at T=298.15 K, have been derived to be −(1535.5±0.7) and −(1536.7±0.6) kJ mol^−l, respectively.     

Crystal structure and thermochemical properties of 1-dodecylamine hydrochloride (C12H28NCl)(s)

Crystal structure of 1-dodecylamine hydrochloride (C₁₂H₂₈NCl)(s) has been determined by an X-ray crystallography. Lattice potential energy and the molar volumes of the solid compound and its cation were respectively obtained. The enthalpy of dissolution of the compound was measured by an isoperibol solution-reaction calorimeter at 298.15 K. The molar enthalpy of dissolution at infinite dilution was determined to be , and relative apparent molar enthalpies (Φ_L), relative partial molar enthalpies (L₂) of the compound and relative partial molar enthalpies (L₁) of the solvent (double distilled water) at different concentrations m (mol kg⁻¹) were obtained through fitted multiple regression equation by means of Pitzer's theory. Finally, hydration enthalpies of the substance and its cation were calculated by designing a thermochemical cycle in accordance with lattice potential energy and the molar enthalpy of dissolution at infinite dilution .     

Thermodynamics of complex formation equilibria between Ag(I) and thiocarbonyl ligands in propan-2-one (acetone) solution

Complex formation equilibria in propan-2-one between Ag(I) and thiourea (Tu), thioacetamide (Ta), N-methylthiourea (MeTu), N-ethylthiourea (EtTu), N,N′-diethylthiourea (Et₂Tu), N-phenylthiourea (PhTu), N, N′-diphenylthiourea (Ph₂Tu), and thiobenzanilide (TbAn) have been investigated by potentiometry at different temperatures t = 0–20 °C and self-determined ionic medium. Formation of mono-, bis-, and tris-coordinated AgL _n complexes (charges are omitted) has been detected, but for Ag(I)–Ph₂Tu system, where the occurrence of the mono-coordinate AgPh₂Tu and bis-coordinate Ag(Ph₂Tu)₂ has been found. The stability constants have been deduced. The standard enthalpy and entropy changes have been evaluated from the linear dependence of the free energies on temperature.     

Acetohydroxamatoiron(III) Complexes: Thermodynamics of Formation and Temperature Dependent Speciation

Studies of the thermodynamics of formation of the acetohydroxamatoiron(III) complexes were carried out in acidic media at temperatures ranging from 293 to 323 K. Through the isolation of the unique UV–visible spectra of all three complexes, it was possible to determine their formation constants and deduce enthalpies and entropies of formation as well as their molar absorptivities. The enthalpies of formation of the mono-, bis- and trisacetohydroxamatoiron(III) complexes were found to be −56.4, −17.09 and +19.74 kJ⋅mol⁻¹, respectively. Following the determination of the enthalpy and entropy of formation of these complexes, speciation diagrams were calculated for the complexes at temperatures ranging from 293 to 323 K.     

Effects of added dotab on thecmc and enthalpy of micelle formation at 298.2 K for CTAB(aq)

In a titration calorimetric study an aqueous solution held in a syringe and containing hexadecyltrimethylammonium bromide (CTAB; 15.4×10^–3 mol dm^–3) is injected in aliquots (5×l0^–3 dm³) into a sample cell containing initially water. Analysis of the data shows that thecmc equals 0.97×l0^–3 dm^–3 and the enthalpy of micelle formation equals –10.3 kJ mol^–1. When the solution in the syringe is replaced by a mixed surfactant solution, CTAB+dodecyltrimethylammonium bromide, at the same total concentration of surfactant, thecmc of CTAB decreases gradually with increasing mole fraction of DOTAB but the enthalpy of CTAB micelle formation is hardly affected. We conclude, therefore, that incorporation of DOTAB monomers into the CTAB micelles stabilizes entropically the CTAB micelles.We thank EPSRC for their support; the Commonwealth Scholarship Commission for an award to MCSS and the Royal Society for a grant awarded to PMC for the purchase of the Titration Microcalorimeter.     

The solution behavior of poly(vinylpyrrolidone): its clouding in salt solution, solvation by water and isopropanol, and interaction with sodium dodecyl sulfate

This article deals with the solution properties of poly(vinylpyrrolidone) (PVP) in salt and surfactant environment. The cloud point (CP) of PVP has been found to be induced by the salts NaCl, KCl, KBr, Na2SO4, MgSO4, and Na3PO4. On the basis of CP values for a salt at different [PVP], the energetics of the clouding process have been estimated. The effect of the surfactant, sodium dodecyl sulfate (SDS), on the salt-induced CP has also been studied, and reduction in CP at low [SDS] and increase in CP at high [SDS] have been observed. The water vapor adsorption of PVP has been determined by isopiestic method. The results display a BET Type III isotherm whose analysis has helped to obtain the monolayer capacity of PVP and formation of multilayer on it. The solvation of PVP in a solution of water and a water-isopropanol mixture has been determined by conductometry from which contribution of the individual components were estimated. The interaction of PVP with SDS in solution led to formation of a complex entity, which has been studied also by conductometry adopting a binding-equilibrium scheme. SDS has been found to undergo two types of binding as monomers in the pre- critical aggregation concentration (CAC) range and as small clusters in the post CAC region. The stoichiometries of binding and binding constant were evaluated.     

Low-temperature heat capacity and standard molar enthalpy of formation of the complex Zn(Thr)SO4·H2O (s)

Low-temperature heat capacities of the complex Zn(Thr)SO₄·H₂O (s) have been precisely measured with a small sample adiabatic calorimeter over the temperature range from 78 to 373 K. The initial dehydration temperature of the complex (T_d=325.50 K) has been obtained by analysis of the heat-capacity curve. The experimental values of molar heat capacities have been fitted to a polynomial equation by least square method. The standard molar enthalpy of formation of the complex has been determined from the enthalpies of dissolution (Δ_dH_m^Θ) of [ZnSO₄·7H₂O (s) +Thr (s)] and Zn(Thr)SO₄·H₂O (s) in 100 ml of 2 mol dm⁻³ HCl solvent as: Δ_fH_{m,Zn(Thr)SO4·H2O}^Θ=−2111.7±3.4 kJ mol⁻¹. These experiments were made by using an isoperibol solution calorimeter at 298.15 K.     

Micellar Behavior of Polystyrene-Poly(Ethylene Oxide) Diblock Copolymers in Aqueous Media: Effect of Copolymer Composition,Temperature, Salt,and Surfactants

Formation and structure of micelles from two amphiphilic polystyrene-block-poly(ethylene oxide) (PS-PEO) diblock copolymers (PS mol.wt. 1000; PEO mol.wt. 3000 and 5000) were examined by surface tension, viscosity, steady state fluorescence, dynamic light scattering (DLS), small angle neutron scattering (SANS), and cryo-transmission electron microscopy (cryo-TEM). The critical micelle concentration (CMC) of the copolymers in aqueous solution was ca. 0.05%; micelle hydrodynamic diameter was 30–35 nm with a narrow size distribution. SANS studies show that the copolymers form ellipsoidal micelles with semi major axis ～23 nm and semi minor axis ～8 nm. No significant change in the structure was found with temperature and presence of salt. The copolymer micelles interaction with the ionic surfactants sodium dodecyl sulphate (SDS) and dodecyltrimethylammonium bromide (DTAB) was also examined by DLS and SANS.     

S6 Isomer of C60(CF3)12: Synthesis,properties and thermodynamic functions

A crystalline form of S₆-С₆₀(CF₃)₁₂ was synthesized in an amount sufficient for reliable experimental investigation. We determined the enthalpy of combustion of S₆-С₆₀(CF₃)₁₂ in oxygen and its heat capacity, which made possible to derive the thermodynamic functions of S₆-С₆₀(CF₃)₁₂, namely the enthalpy of formation, the entropy and the Gibbs energy at T = 298.15 K. These experimental thermochemical data enabled estimation of the formation energy for a broad range of other trifluoromethylated compounds C₆₀(CF₃)_n, with n = (2–18; 24), on the basis of their DFT calculated relative energies.     

P NMR study of the stoichiometry, stability and thermodynamics of complex formation between palladium(II) acetate and bis(diphenylphosphino)ferrocene

The complexation reaction between palladium (II) acetate, and 1,1′-bis(diphenylphosphino)ferrocene, DPPF, was investigated in two different deuterated solvents CDCl₃ and DMSO at various temperatures using ³¹P NMR spectroscopy. The exchange between free and complexed DPPF is slow on the NMR time scale and consequently, two ³¹P NMR signals were observed. At metal ion-to-ligand mole ratio larger than 1, only one ³¹P NMR signal was observed, indicating the formation of a 1:1 Pd²⁺–DPPF complex in solution. The formation constant of the resulting 1:1 complexes was determined from the integration of two ³¹P signals. The values of the thermodynamic parameters (ΔH, ΔS and ΔG₂₉₈) for complexation were determined from the temperature dependence of stability constants. It was found that, in both solvents, the resulting complex is mainly entirely enthalpy stabilized and the ΔH compensates the TΔS contribution.     

Thermodynamics of complexation of zinc(II) with chloride,bromide and iodide ions in hexamethylphosphoric triamide

The complexation of zinc(II) with chloride, bromide and iodide ions has been studied by calorimetry in hexamethylphosphoric triamide (HMPA) containing 0.1 mol-dm^–3 (n-C₄H₉)₄NClO₄ as a constant ionic medium at 25°C. The formation of [ZnX_n]^(2–n)+ (n=1,2,3,4 for X=Cl; n=1,2 for X=Br, I) is revealed, and their formation constants, enthalpies and entropies were determined. It is proposed that the zinc(II) ion is fourcoordinated in HMPA and the coordinating HMPA molecules are stepwise replaced with halide ions to form [ZnX_n(hmpa)_4–n]^(2–n)+ (n=1–4), as is the case for the cobalt(II) ion. Furthermore, the formation of [ZnClI], [ZnBrI], [ZnBrCl] and [ZnBrCl₂]^– is revealed in the relevant ternary systems. It is found that the affinity of a given halide ion X^– to [ZnCl]⁺, [ZnBr]⁺ and [Znl]⁺ is practically the same.     

Dispersion of stratum corneum in an aqueous mixed solution of surfactants: the effect of a mixture of sodium dodecyl sulfate and N,N-dimethyldodecylamine oxide

Molecular interactions between sodium dodecyl sulfate (SDS) and N,N-dimethyldodecylamine oxide (C₁₂DMAO), whose mixtures were effective for dispersion of stratum corneum (SC) into intact corneocytes, were studied and found to be strongest at an SDS/C₁₂DMAO molar ratio of 1/3, when dispersion of SC was most effective and the sizes of the mixed micelles were largest.

This dispersion effect was confirmed as being caused by the stronger solubilizing power of molecular complexes formed between SDS and C₁₂DMAO in the binary mixed solutions by using ¹H NMR. The mechanisms for removing intercellular lipids such as ceramides, cholesterol and their derivatives, which play an important role as adhesives among the corneocytes, and for dispersing SC into intact cells were proposed on the basis of supporting data obtained from ¹H-NMR and light scattering measurements.     

Low-temperature heat capacities and standard molar enthalpy of formation of the solid-state coordination compound trans-Cu(Ala)2(s) (Ala = l-α-alanine)

Low-temperature heat capacities of the solid coordination compound trans-Cu(Ala)₂(s) have been measured by a precision automated adiabatic calorimeter over the temperature range from T = 78 K to 390 K. The experimental values of the molar heat capacities in the temperature region were fitted to a polynomial equation of heat capacities (C_p,m) with the reduced temperatures (X), [X = f (T)], by a least square method. The smoothed molar heat capacities and thermodynamic functions of the complex trans-Cu(Ala)₂(s) were calculated based on the fitted polynomial. The smoothed values of the molar heat capacities and fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated with an interval of 5 K. Enthalpies of dissolution of {Cu(Ac)₂·H₂O(s) + 2Ala (s)} and 2:1 HAc (aq) in 100 ml of 2 mol dm⁻³ HCl, respectively, and trans-Cu(Ala)₂(s) in the solvent [2:1 HAc (aq) + 2 mol dm⁻³ HCl] at T = 298.15 K were determined to be , , and by means of an isoperibol solution-reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as from the enthalpies of dissolution and other auxiliary thermodynamic data using a Hess thermochemical cycle.     

阳离子表面活性剂溶液的临界胶束浓度及扩散系数

在无探针分子条件下用循环伏安法(CV)研究了DTAB,TTAB,CTAB,OTAB水溶液体系胶束在玻碳电极(GCE)上的电化学行为,并用电位阶跃计时库仑法(CC)测定了胶束的扩散系数,进而得到第一与第二CMC,该方法简捷、快速、准确。对离子型表面活性剂的第二CMC提供了新的测定方法。     

Binding of sodium dodecyl sulfate to linear and star homopolymers of the nonionic poly(methoxyhexa(ethylene glycol) methacrylate) and the polycation poly(2-(dimethylamino)ethyl methacrylate): electromotive force, isothermal titration calorimetry, surface tension, and small-angle neutron scattering measurements

We investigated the binding of sodium dodecyl sulfate (SDS) to various linear and star polymers of the nonionic methoxyhexa(ethylene glycol) methacrylate (PMHEGMA) and the ionic 2-(dimethylamino)ethyl methacrylate (PDMAEMA), the latter being a polycation at low pH. The dodecyl sulfate ion selective electrode (EMF), isothermal titration calorimetry (ITC), and surface tension (ST) were applied to gain detailed information about interactions. In all cases there is evidence of significant binding of SDS over an extensive SDS concentration range spanning from ca. 10(-6) to 0.1 mol dm(-3). At pH 3, the polymer PDMAEMA is a strong polycation and here the binding is dominated by electrostatic 1:1 charge neutralization with the anionic surfactant. At their natural pH of 8.6, PMHEGMA and PDMAEMA polymers are essentially nonionic and bind SDS in the form of polymer-bound aggregates in the concentration range of ca. 1 x 10(-3) to 3 x 10(-2) mol dm(-3). All the polymers also bind SDS to a lesser extent at concentrations below 1 x 10(-3) mol dm(-3) reaching as low as 10(-7) mol dm(-3). This low concentration binding process involves the polymer and nonassociated SDS monomers. As far as we are aware, this is the first example that such a low concentration noncooperative binding process could be observed in SDS/neutral polymer systems by EMF and ST. We also showed that the nonionic surfactant hexa(ethylene glycol) mono-n-dodecyl ether (C12EO6) and the cationic cetyltrimethylammonium bromide (C16TAB) interact with star PDMAEMA. We believe that the interaction of C12EO6 and CTAB is of similar noncooperative type as the first SDS binding process in the range from ca. 10(-5) to 0.3 x 10(-3) mol dm(-3). At the high concentration binding limit Csat of SDS, the above polymers become fully saturated with bound SDS micelles. We applied small angle neutron scattering (SANS) to determine the structure and aggregation numbers of the star polymer/bound SDS micelles and calculated the stoichiometry of such supramolecular complexes. The SANS data on PDMAEMA star polymers in the presence of C12EO6 showed only a limited monomer binding in contrast to linear PDMAEMA, which showed monomer C12EO6 binding at low concentrations but micellar aggregates at 6 x 10(-3) mol dm(-3).     

Heat capacity and standard molar enthalpy of formation of crystalline 2,6-dicarboxypyridine (C7H5NO4)

Low-temperature heat capacity C_p,m of 2,6-dicarboxypyridine (C₇H₅NO₄; CAS 499-83-2) was precisely measured in the temperature range from (80 to 378) K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The thermodynamic functions [H_T − H_298.15] and [S_T − S_298.15] were calculated in the range from (80 to 378) K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined, and , by means of a precision oxygen-bomb combustion calorimeter at T = 298.15 K. The thermodynamic properties of the compound were further investigated through differential scanning calorimeter (DSC) and the thermogravimetric (TG) analysis.