Gerd Olofsson

Thermodynamics of ionization of water over wide ranges of temperature and pressure

We have summarized results of many experimental investigations of the thermodynamics of ionization of H2O(liq.) from 0–300°C and from 1.0 atm to nearly 8000 atm. Results of these investigations (equilibrium constants, enthalpies of ionization, heat capacities, partial molal volumes, and compressibilities) have been used for a number of thermodynamic calculations. It is particularly noteworthy that it is possible to use thermal data from 0–145°C with an equilibrium constant for 25°C in calculating reasonably accurate equilibrium constants for temperatures as high as 300°C. Similarly, it is possible to use volumetric data that refer to 1.0 atm in calculating useful equilibrium constants that apply for pressures as high as 2000 atm.

TITRATION CALORIMETRIC STUDY OF THE INTERACTION BETWEEN IONIC SURFACTANTS AND UNCHARGED POLYMERS IN AQUEOUS SOLUTION

The interaction between uncharged polymers (PEO, PPO, PVP, and EHEC) and ionic surfactants in dilute aqueous solution has been studied using isothermal titration microcalorimetry. The surfactants studied were lithium, sodium, and magnesium dodecyl sulfate, alkyltrimethylammonium halides (RTA+X- with R equal to C12, C14, and C16 and X either Br or Cl), and dodecylammonium chloride (DoAC). The critical aggregation concentration cac, the saturation concentration C2 and the amount of polymer-bound surfactant were derived from the calorimetric titration curves. The anionic surfactants interacted strongly with PEO while RTABr were indifferent. However, changing the counterion to chloride or modifying the headgroup to the unsubstituted ammonium ion gave observable interaction. The presence of extra salt lowered the cac and increased the C2 with a more pronounced effect for PPO and EHEC. An increase in temperature had no noticeable effect on cac and C2 although the shape of the calorimetric titration curves chang...

Interactions between surfactants and uncharged polymers in aqueous solution studied by microcalorimetry

The interaction between ionic surfactants and uncharged polymers in dilute aqueous solution has been studied by titration microcalorimetry. The resulting enthalpic titration curves give detailed information about polymer - surfactant interactions. While sodium dodecylsulfate interacts strongly with poly(ethy1ene oxide) and poly(viny1-pyrrolidone), the micelle formation of the cationic surfactants dodecyl-, tetradecyl-, and hexadecyl-trimethylammonium bromide is not measurably perturbed by the presence of these polymers. However, there is no significant difference between the interaction of the anionic and cationic surfactants with ethyl(hydroxyethy1)cellulose ethers. The aggregation of surfactants in polymer solutions shows clear similarities to the solubilization of small, polar molecules in ionic micelles. Preaggregation between surfactant monomers and polymers can be significant as indicated by sizeable endothermic enthalpy contributions from hydrophobic pair-wise interaction. Systems containing surfactants and water-soluble polymers are of great interest both for their widespread applications and for their inherently interesting properties. Polymer - surfactant complexes are used for instance in paints and coatings, in laundry detergents, cosmetic products, and in tertiary oil recovery. Systems containig nonionic polymers and ionic surfactants have been studied quite extensively during the last couple of decades so much is known about them. The various studies are summarized and discussed in several review articles ( ref 1-5 ). However, fundamental questions such as why and how surfactants form aggregates in the presence of polymers and how the polymer is involved in the aggregate formation are still unanswered.We became interested to see if results of calorimetric measurements could help to answer these questions and therefore, we started a study of some typical polymer - surfactant systems by titration microcalorimetry. EXPERIMENTAL Materials. Sodium dodecylsulfate SDS (BDH, 99%), dodecyltrimethylammonium bromide DoTAB (Aldrich, 99%), tetradecyltrimethylammonium bromide TTAB ( Sigma,99% ), and hexadecyltrimethylammonium bromide CTAB (Sigma, 99%) were used as received.Samples of poly(ethy1ene oxide) PEO with nominal molar masses of 4 000,8 000 ( two different samples ), 20 000, 100 000, and 1 500 000 were used without further treatment. Poly(N-vinylpyrrolidone) PVP with an average molar mass of 40 OOO ( Aldrich, special grade) and poly(propy1ene oxide) PPO with molar mass of 1 000 (Aldrich) were used as received. Samples of ethyl (hydroxy-ethy1)cellulose EHEC E230G and EHEC CST 103 ( Berol Nobel AB, Sweden) were dialyzed before use. The calorimetric measurements were made using the commercial microcalorimetric measuring channel of the 2277 TAM Thermal Activity Monitor system ( ThermoMetric AB, JMiilla, Sweden ) in a homebuilt high-precision thermostat bath (ref 6). The calorimetric titration experiments consisted of series of consecutive additions of concentrated surfactant solution to the calorimeter vessel initially containing 2.7 g of polymer solution. In some of the experiments concentrated polymer solution was added to surfactant solution in the vessel.The liquid samples were added in portions of 7 - 15 mg from a gas-tight Hamilton syringe through a thin stainless-steel capillary tube. A microprocessor-controlled motor-driven syringe drive was used for the injections. The fast titration procedure was used with six minutes between each injection (ref 7). The dynamic correction method used to deconvolute the potential signals was based on the simple Tian equation.

Isothermal microcalorimetric studies on starch retrogradation

In the present study, isothermal microcalorimetry was introduced as a tool to investigate properties of starch retrogradation during the first 24 h. The study was made on purified amylose and amylopectin from corn, as well as on native starches, such as wheat, potato, maize, waxy maize and amylomaize, differing in their amylose content. The results were obtained in the form ofP-t traces (thermal powervs. time), and integration of these traces gave a net exothermic enthalpy of reaction, caused by the crystallization of amylose and amylopectin. TheP-t traces reflected the quantities of amylose and amylopectin in the starch studied. Depending on the amylose content and the botanical source of the starch, the rate of crystallization of amylose was high and predominated over that of amylopectin during the first 5–10 h. The contribution from amylose crystallization to the measured exothermic enthalpy was very substantial during this period. After ∼10 h, amylose crystallized at a lower constant rate. During the first 24 h, amylopectin crystallized at a low steady rate. The exothermic enthalpies obtained by the isothermal microcalorimetric investigations during the first 24 h of retrogradation were generally low in relation to the endothermic melting enthalpies observed by differential scanning calorimetry (DSC) measurements after 24 h of storage. The discrepancies in enthalpy values between the two methods are discussed in relation to phase separation and the endothermic effects owing to the decrease in polymer-water interactions when polymer-rich regions in the starch gel separate. Besides the exothermic enthalpies obtained, theP-t traces also made it possible to study the initial gelation properties of amylose from different botanical sources. The present study further demonstrated that isothermal microcalorimetry can provide a possible way to investigate the antistaling effect of certain polar lipids, such as sodium dodecylsulphate (SDS) and 1-monolauroyl-rac-glycerol (GML), when added to starches of different botanical origin. The net exothermic heat of reaction for starch retrogradation during the first 24 h was decreased when GML or SDS was added to the starch gels. The recordedP-t traces also showed how the effect of the added lipid influenced different periods during the first 24 h of starch retrogradation, and that the effect depended mainly on the amylose content, the botanical source of the starch, and the type of lipid used. When GML or SDS was added to waxy maize, the isothermal microcalorimetric studies clearly indicated some interaction between amylopectin and the polar lipids. These results concerning the action of anti-staling agents are further discussed in relation to the helical inclusion complexes formed between amylose-polar lipid and amylopectin-polar lipid.

On the use of titration calorimetry to study the association of surfactants in aqueous solutions

Isothermal titration calorimetry is increasingly becoming a common tool for the investigation of surfactant association processes. This can be associated with the development of new, sensitive and easy-to-operate commercial equipment, allied with the advantage of producing simultaneous information on the main thermodynamic parameters associated with the process under investigation. However, a significant fraction of users are still unfamiliar with many aspects related with the use of these calorimetric techniques. This review intends to discuss the design of experiments to investigate surfactant self-assembly in water and in the presence of polymers (charged and uncharged), as well as on how to derive the most relevant thermodynamic parameters from these calorimetric titration curves. Some literature examples are discussed to illustrate the use of these techniques for different systems.

Thermodynamic and kinetic characterization of host-guest association between bolaform surfactants and alpha- and beta-cyclodextrins

The thermodynamics and kinetics of formation of host-guest complexes between a series of bolaform surfactants of type C n Me 6 (2+)2Br (-) ( n = 8, 10, and 12) and alpha-cyclodextrin and beta-cyclodextrin were studied with the aid of isothermal titration calorimetry (ITC) at 298.15 and 308.20 K. The association constant, the enthalpy, and the entropy of formation were determined. The obtained thermodynamic parameters are compared with parameters for the micelle formation of a related cationic surfactant. The difference in magnitude and sign between the parameters of the alpha-CD and beta-CD complexes is discussed based on the curvature of the cavity of the CD. We suggest that the water molecules inside the alpha-CD cavity are not able to maintain their hydrogen bond network. Upon complex formation these water molecules are expelled and reform their hydrogen bond network. The situation is different in the larger beta-CD cavity where water has the possibility of a more extensive hydrogen bonding. The kinetics for alpha-CD is slow, associated with high activation energies for both association and dissociation of the complex. The rates increased with a decrease in the number of methylene groups in the hydrocarbon chain. The slow kinetics is argued to originate from the fact that the charged headgroup needs to be pushed through a relative nonpolar cavity. A comparison is made with the Born energy.

Ionization Constants pKa of Cardiolipin

Cardiolipin is a phospholipid found in the inner mitochondrial membrane and in bacteria, and it is associated with many physiological functions. Cardiolipin has a dimeric structure consisting of two phosphatidyl residues connected by a glycerol bridge and four acyl chains, and therefore it can carry two negative charges. The pKa values of the phosphate groups have previously been reported to differ widely with pKa1 = 2.8 and pKa2 = 7.5–9.5. Still, there are several examples of experimental observations from cardiolipin-containing systems that do not fit with this dissociation behavior. Therefore, we have carried out pH-titration and titration calorimetric experiments on two synthetic cardiolipins, 1,1′,2,2′-tetradecanoyl cardiolipin, CL (C14∶0), and 1,1′,2,2′-tetraoctadecenoyl cardiolipin, CL (C18∶1). Our results show that both behave as strong dibasic acids with pKa1 about the same as the first pKa of phosphoric acid, 2.15, and pKa2 about one unit larger. The characterization of the acidic properties of cardiolipin is crucial for the understanding of the molecular organization in self-assembled systems that contain cardiolipin, and for their biological function.

Adsorption isotherms for cationic surfactants on silica determined by in situ ellipsometry

Abstract The adsorption of tetradecyltrimethylammonium bromide (C 14 TAB) on oxidized silicon plate has been determined in water and in 10 mmol·dm −3 NaBr solutions by in situ ellipsometry as a function of pH. The shape of the isotherms changes and the adsorbed amount increases as the pH of the solution is increased. Isotherms for C 14 TAB in water and in NaBr solution at pH 5 and for C 12 TAB in water at pH 9.6 obtained by ellipsometry are compared with results obtained by a different method (solution-depletion). The aggreement between the two methods is found to be satisfactory.

Thermodynamic quantities for the solution and protonation of four C6-amines in water over a wide temperature range

The enthalpies of solution ofn-hexyl- and cyclohexylamine have been determined at temperatures up to 125°C, of di-n-propylamine up to 100°C, and of triethylamine up to 75°C from reaction-solution calorimetric experiments. Quadratic polynomials were found to give good representations of the experimental values, implying a linear variation with temperature of the heatcapacity changes. The enthalpies of protonation of the aqueous amines have been determined in the same temperature range. Linear expressions give satisfactory representations of the protonation enthalpies of the hexylamines and dipropylamine, whereas a quadratic expression is required to represent the triethylamine values. The calorimetric results are used together with reported pKa values at 25°C to calculate the dissociation constants of the corresponding ammonium ions between 0 and 200°C. At 0°C triethylamine was found to be the weakest base, the relative base strengths being triethyl<cyclohexyl<n-hexyl<dipropyl, whereas above 60°C triethylamine was the strongest base, the order of the other amines being unchanged.

Phase behavior of synthetic amphiphile vesicles investigated by calorimetry and fluorescence methods

Abstract The understanding of biological membranes may be improved by investigating physical properties of vesicles from natural or synthetic amphiphiles. The application of vesicles as mimetic agents depends on the knowledgment of their structure and properties. Vesicles having different curvature and size may be obtained using different preparation protocols. We have used differential scanning calorimetry (DSC) and steady-state fluorescence to investigate the gel to liquid-crystal phase transition of vesicles prepared by sonication (SUV) and non-sonication (GUV) of the synthetic dioctadecyldimethylammonium bromide (DODAB) in aqueous solution. DSC thermograms for a non-sonicated dispersion show a well-defined pre- and main transition corresponding to two narrow peaks at 36 and 45°C in the first upscan, while in a second upscan, only the main peak was observed. The sharpness of the peaks indicate a cooperative phase behavior for GUV. For a sonicated DODAB dispersion, the first upscan shows a third peak at 40.3°C, whereas for the second upscan the peaks are not well-defined, indicating a less cooperative phase behavior. Alternatively, the fluorescence quantum yield (Φ f ) and the anisotropy ( r ) of trans, trans, trans -1-[4-(3-carboxypropyl)-phenyl]-6-[4-butylphenyl]-1,3,5-hexatriene (4H4A) and the ratio I 1 / I 3 of the first to the third vibronic peaks of the pyrene emission spectrum as function of temperature are used as well to describe the phase behavior of DODAB sonicated and non-sonicated dispersions. It is in good agreement with the DSC results that the cooperativity of the thermotropic process is diminished under sonication of the DODAB dispersion, meaning that sonication changes from homogeneous to heterogeneous populations of the amphiphile aggregates. The pre- and main transitions obtained from these techniques are in fairly good accord with results from the literature.