Volume 43, Issue 4

Commercial and synthesized sucrose fatty acid esters were qualitatively analyzed by atmospheric-pressure ionization MS with electrospray ionization. Straight-forward mass characterization of the complex mixtures could be achieved. By using methanol/tetrahydrofuran as solvent, the constituents were identified on the basis of quasi-molecular ions. Individual components could be observed as protonated molecular ions [M+Na] + and/or as their K + adducts in positive mode. The mass spectrometric investigation showed that the mixtures of sucrose fatty acid esters contained mono-, di-, tri-, tetra- or polyesters; the sucrose fatty acid esters are mixture of two types of nonionic surfactants: sucrose palmitates and sucrose stearates. The results indicate the atmospheric-pressure ionization MS with electrospray ionization analysis is an effective method for the analysis of sucrose esters composed of different isomers. The rapid and highly sensitive atmospheric-pressure ionization MS with electrospray ionization analysis technique proposed here is well suited for direct characterization of sucrose esters.

The pH-stat technique has been used to study the influence of several natural and synthetic additives containing carboxyl, phenolic, and sulfonic groups on the precipitation of calcium carbonate from supersaturated solutions (Ca=HCO 3 = 5.50 mM, NaCl=0.10 M, pH 8.50, 35°C). The additives investigated were natural i.e., green tea extract, GTE; sodium lignosulfonate, SLS and synthetic i.e., poly(acrylic acid), P-AA; poly(2-acrylamido-2-methyl-propane sulfonic acid), P-SA. It has been found that addition of low concentrations of additive has three fold effects: a) it delays the precipitation of calcium carbonate, b) it inhibits the rate of precipitation, and c) it influences the calcium carbonate polymorph. Based on the results obtained under the test conditions, the ranking in terms of decreasing effectiveness is: P-AA ≫ GTE>SLS ∼ P-SA. The results also indicate that the delay in precipitation increases with increasing additive concentration. SEM and X-ray diffraction studies of calcium carbonate precipitated in the presence of additives reveal that whereas P-AA and P-SA favor the formation of vaterite, GTE and SLS influence the formation of calcite. By contrast, the predominant polymorph formed in the absence of additive is vaterite. Kinetic analysis suggests Langmuir-type adsorption of added additive ions on the active growth sites of CaCO 3 crystals.

The dynamic surface tension of micellar surfactant solutions was measured using the maximum bubble pressure method. The chosen surfactants were carboxy- and sulfo-betaines. At the beginning, surface tension decay curves are consistent with a diffusion-controlled adsorption. However, at long times these curves were analyzed by using the Fainerman model. From these experiments, the rate constants for demicellization were obtained. The micelle dissociation rate constant depends of the surfactant concentration, the concentration dependence is interpreted by Aniansson's theory, and the micelle dissociation constant independent of surfactant concentration was calculated. The rate constants found in this work are of the same order of magnitude as those obtained using classical techniques for fast reactions.

The influence of small addition of ionic surfactant such as sodium dodecyl sulfate (SDS) and carboxylate ethoxyle (TDC) to nonionic surfactant hexaethylene glycol mono-n-dodecyl ether (C 1 2E 6 ) on the microemulsions formed in the system water/decane/surfactant was studied. An empirical description of the phase behaviour is presented that permits to determine the PIT, and what efficiency of the surfactants to expect. The investigation showed an expected rise in the temperature at which maximum solubility was observed (PIT), and a pronounced extension of the solubility area was also observed. In addition, the temperature stability of these microemulsions was improved. The structural study of the system water/(C 1 2E 6 +1% TDC) shows that the liquid crystal phase is lamellar at 45°C. It's structural parameters are determined by small angle X-ray scattering. The study of lamellar phase allows the description of the evolution of the surfactant chains conformation.

A series of new gemini surfactants having hydrophilic glucosides were synthesized from glucose via two different synthesis roads, including N,N′-didodecyl-N,N′-bis-(1-glucosyl-2-hydroxyl-propyl)-p-phthaloyl amide [B(DG)PA], N,N′-didodecyl-N,N′-bis(1-glucosyl-2-hydroxyl-propyl)-2,5-dicarboxylate p-phthaloyl amide [B(DGC)PA], N,N′-didodecanoyl-N,N′-bis-(1-glucosyl-2-hydroxyl-propyl) ethylenediamine [B(DG)EA], and N,N′-didodecanoyl-N,N′-bis-(1-glucosyl-2-hydroxyl-propyl) hexanediamine [B(DG)HA]. The final products were characterized by IR and NMR spectral measurements and by interfacial tension measurements. The critical micellar concentrations (cmc) of these gemini surfactants were determined to be 2.49 × 10 −6 , 1.93 × 10 −6 , 2.47 × 10 −6 and 1.66 × 10 −6 mol L −1 , respectively, which are about one order of magnitude lower than the corresponding monomeric surfactants (GHPDA). The results showed that these synthesized sugar-based gemini surfactants had high abilities to reduce the surface or oil-water interface tension. The high surface activity of these synthesized molecules was attributed to their unique structure where two optimally spaced hydrophobic chains and hydrophilic groups were present.

Al-δ layered sodium disilicate with high framework stability in hot water (60–80°C) has been successfully synthesized from the system of Na 2 O–Al 2 O 3 –SiO 2 –H 2 O. It was shown that the presence of aluminum can improve the purity of δ phase. After marinated in hot distilled water for 60minutes, Al-δ layered sodium disilicate still kept δ phase and had better Ca 2+ binding capacity and calcium binding rate. This property of Al-δ layered sodium disilicate may extend its application field. The samples were characterized by XRD, FT-IR, MAS NMR, Ca 2+ binding capacity and rate, The data of 27 Al MAS NMR and 29 Si MAS NMR showed that aluminum was incorporated essentially in tetrahedral framework position, and substitute for SiO 4 tetrahedron in sheet of δ layered sodium disilicate.