Antibubble lifetime: influence of the bulk viscosity and of the surface modulus of the mixture

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2010)

The CMC-like behaviour of bile salts as probed by photoexcited Rose Bengal

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2009), 339

The onset of the aggregation process in aqueous bile salt (BS) solutions remains a debated question. This study aimed at investigating this point through the detection of BS monomers and small aggregates ... [more ▼]

The onset of the aggregation process in aqueous bile salt (BS) solutions remains a debated question. This study aimed at investigating this point through the detection of BS monomers and small aggregates using the dye Rose Bengal. Results showed that a few small BS aggregates led to a red shift of the absorption spectrum, while the BS monomer reacted with the photo-induced semi-oxidized dye and decreased its decay rate constant. The dye was dissolved in aqueous solution (10 mmol dm-3 NaOH) of sodium cholate (NaC), deoxycholate (NaDC), chenodoxycholate (NaCDC), dehydrocholate (NaDHC), glycocholate (NaGC) glycodeoxycholate (NaGDC), taurocholate (NaTC), taurodeoxycholate (NaTDC) and the zwitterionic analogue of sodium cholate called CHAPS. BS aggregates were detected at concentrations well below the concentration above which any added bile salt molecules participate in the aggregation process for all trihydroxy bile salts and for CHAPS but not for the dihydroxy bile salts. No aggregation of NaDHC could be observed in the studied concentration range (≤ 10 mmol dm-3). The presence of 150 and 600 mmol dm-3 sodium ions lowered the concentration below which BS are mainly monomers for dihydroxy but not for trihydroxy bile salts. As already proposed by others, the use of the concept of Micellar Dissociation Concentration (MDC) is suggested here instead of the classical Critical Micelle Concentration (CMC). [less ▲]

Formation mechanism of Y-junctions in arrays of multi-walled carbon nanotubes

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2008), 327

Transmission electron microscopy of arrays of multi-walled carbon nanotubes reveals the presence of numerous Y-junctions. The diameter distributions of the samples are found to be bimodal, with one mode ... [more ▼]

Transmission electron microscopy of arrays of multi-walled carbon nanotubes reveals the presence of numerous Y-junctions. The diameter distributions of the samples are found to be bimodal, with one mode corresponding to the branches and the other mode to the trunk of the Y-junctions. The analysis of the micrographs shows that the junctions form via the merger ofmetal particles during the tip-growth of the tubes. [less ▲]

Rheological determination of the sol-gel transition during the aqueous synthesis of resorcinol-formaldehyde resins

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2007), 293(1-3), 224-228

The sol-gel transition of organic gels prepared by polycondensation of resorcinol (R) with formaldehyde (F) in presence of sodium carbonate (C) was monitored by small amplitude oscillatory measurements ... [more ▼]

The sol-gel transition of organic gels prepared by polycondensation of resorcinol (R) with formaldehyde (F) in presence of sodium carbonate (C) was monitored by small amplitude oscillatory measurements, at a single frequency. The gelation time (t(g)) was determined from the evolution of the storage (G) and loss (G") moduli versus time. The influence of two synthesis variables, the resorcinol/sodium carbonate ratio (R/C) and the synthesis temperature (7), was investigated. The gelation time was found to decrease with increasing synthesis temperature and decreasing R/C ratio. The apparent activation energy of the reactional system leading to the gelation, calculated from the gelation times obtained between 50 and 90 degrees C, was found to be close to 80 kJ mol(-1) and independent of the R/C ratio. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Self-formation of hierarchical micro-meso-macroporous structures: Generation of the new concept "Hierarchical Catalysis"

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2007), 300(1-2 SPEC. ISS.), 70-78

The self-formation phenomenon of hierarchy with multiple-scaled porosity is reported. The structures of various chemical compositions, such as ZrO2, TiO2, Al2O3, Y2O3, Nb2O5, Ta2O5 ZrO2-SiO2, ZrO2-TiO2 ... [more ▼]

The self-formation phenomenon of hierarchy with multiple-scaled porosity is reported. The structures of various chemical compositions, such as ZrO2, TiO2, Al2O3, Y2O3, Nb2O5, Ta2O5 ZrO2-SiO2, ZrO2-TiO2, ZrO2-Y2O3, aluminosilicates, aluminophosphates, silicoaluminophosphates, metallophosphates, are made of macrochannels (0.5-5 μm in diameter) with mesoporous or microporous walls. The hierarchically porous structures are prepared by just controlling the hydrolysis and polycondensation rates of the pre-selected inorganic sources. The textural, structural as well as morphological properties of each material are carefully studied by using a large series of techniques, such as XRD, NMR, TEM, SEM, N2 adsorption-desorption, Hg porosimetry, optical microscopy. On the basis of these multimodal porous structures, a new concept "Hierarchical Catalysis" has been proposed. This new concept can allow the realisation of a multiple steps reaction in one single catalyst in a cascade way without any separation processes. © 2007 Elsevier B.V. All rights reserved. [less ▲]

Investigation of SDS, DTAB and CTAB micelle microviscosities by electron spin resonance

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2006), 290(1-3), 206-212

Electron spin resonance spectroscopy (ESR) of the nitroxide labelled fatty acid probes (5-, 16-doxyl stearic acid) was used to monitor the micelle microviscosity of three surfactants at various ... [more ▼]

Electron spin resonance spectroscopy (ESR) of the nitroxide labelled fatty acid probes (5-, 16-doxyl stearic acid) was used to monitor the micelle microviscosity of three surfactants at various concentrations in aqueous solution: sodium dodecyl sulphate (SDS), dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB). At low surfactant concentration, there is no micelle, the ESR probe is dissolved in water/surfactant homogeneous phase and gives his microviscosity. At higher surfactant concentration, an abrupt increase in microviscosity indicates the apparition of micelles and, the solubilization of the probes in micelles. The microviscosity of the three surfactants, in a large surfactant range, was obtained as well as the critical micelle concentration (CMC). The microviscosity increased slightly with the increase in surfactant concentration. Phosphate buffer lowered the CMC value and generally increased the microviscosity. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

About the methods of preparation of poly(ethylene oxide)-b-poly(epsilon-caprolactone) nanoparticles in water. Analysis by dynamic light scattering

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2004), 242(1-3), 203-211

Self-assembly of nonionic amphiphilic poly(ethylene oxide)-b-poly(ε-caprolactone) (PEO-b-PCL) and poly(ethylene oxide)-b-poly(γ-methyl-ε-caprolactone) (PEO-b-PMCL) has been studied in water by dynamic ... [more ▼]

Self-assembly of nonionic amphiphilic poly(ethylene oxide)-b-poly(ε-caprolactone) (PEO-b-PCL) and poly(ethylene oxide)-b-poly(γ-methyl-ε-caprolactone) (PEO-b-PMCL) has been studied in water by dynamic light scattering (DLS). The aqueous solutions have been prepared by three methods, i.e., dialysis of solutions in a common organic solvent against water, rapid addition of water to organic solutions, and rapid addition of organic solutions into water. Several common organic solvents have been used: tetrahydrofuran (THF), dimethylformamide (DMF), dimethylacetamide (DMAc) and dimethylsulfoxide (DMSO). The dialysis method is not reproducible and leads to very large and polydispersed particles (~1µm). In contrast, nanoparticles are formed by the two other methods with a low polydispersity and a size in the 30-10 nm range, depending on the organic solvent used. The particle size increases when the concentration in the organic solvent is decreased. The effect of temperature and length of the hydrophobic block has also been studied. [less ▲]

Comparison of different methods for characterizing multi-walled carbon nanotubes

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2004), 241(1-mars Sp. Iss. SI), 155-164

Four complementary and independent methods are used to characterize nanotube samples: (i) TEM observation coupled with image analysis, (ii) nitrogen and krypton adsorption isotherm analysis, (iii ... [more ▼]

Four complementary and independent methods are used to characterize nanotube samples: (i) TEM observation coupled with image analysis, (ii) nitrogen and krypton adsorption isotherm analysis, (iii) thermogravimetry and (iv) wide angle X-ray scattering. The methodology is discussed on the basis of two multi-walled carbon nanotube samples produced by the CCVD technique with very different reaction rates. It is shown that the total amount of deposited carbon is larger for the sample produced at the higher rate, that the fraction of nanotubes in the deposited carbon does not seem to be significantly different, but that the crystallinity of the nanotubes wall is larger for the sample produced at the lowest reaction rate. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Pore structure evolution of highly ordered mesoporous silica CMI-1 during boiling water treatment: A multi-technique investigation

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2004), 241(1-3), 87-93

The structural, textural and morphological evolution of calcined surfactant-free mesoporous molecular sieves treated in boiling water was investigated and explained by a three-step mechanism. The ... [more ▼]

The structural, textural and morphological evolution of calcined surfactant-free mesoporous molecular sieves treated in boiling water was investigated and explained by a three-step mechanism. The materials, prepared by a non-ionic surfactant [C16(EO)10] templating pathway, undergo a sharp decrease in surface area and pore size at the initial stage due to the partial hydrolysis of the silica walls. Then, the dissolution of the resulting branched (Si-O-)n chains attached to the internal surface of the pores results in a gain of surface area and pore size. Finally, the loss in surface area and the sharp increase in pore sizes is due to the destruction of the pore walls and thus of the materials. © 2004 Elsevier B.V. All rights reserved. [less ▲]

Mercury porosimetry applied to porous silica materials: successive buckling and intrusion mechanisms

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2001), 187

Some silica low-density xerogels exhibit two successive volume variation mechanisms, compaction and intrusion when submitted to mercury porosimetry. The position of the pressure of transition P-t between ... [more ▼]

Some silica low-density xerogels exhibit two successive volume variation mechanisms, compaction and intrusion when submitted to mercury porosimetry. The position of the pressure of transition P-t between the two mechanisms is characteristic of the tested material and allows to compute the buckling constant used to determine the pore size distribution in the compaction part of the experiment. The analysis of the mercury porosimetry data of a low-density xerogel wrapped in a tight membrane by the buckling law (intrusion is prevented and the sample is crushed during the whole porosimetry experiment) leads to a continuous unimodal distribution similar to the distribution of the unwrapped sample obtained by applying the buckling law below P-t and the intrusion law above P-t. This experiment confirms the validity of the use of the buckling law. The behaviour of the low-density xerogels can be related to one of their morphological characteristics. As the size of the aggregates of silica particles increases, the strength towards crushing increases and the change of mechanism from crushing to intrusion takes place at a lower pressure. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]