Search

In view of enhanced oil recovery, the adsorption behavior of surfactants is usually monitored on smooth model rock surfaces using quartz crystal microbalance with dissipation (QCM-D). However, this...

Surfactants have the ability to mobilize residual oil trapped in pore spaces of matrix rocks by lowering the oil-water interfacial tension, resulting in a higher oil recovery. However, the loss of surfactants by adsorption onto the rock surface has become a major concern that reduces the efficiency of the surfactant flooding process. In this study, the adsorption behavior of an anionic surfactant to a clay mineral surface was investigated by quartz crystal microbalance with dissipation monitoring upon variations with different cation conditions. Through recording the change of frequency and dissipation of clay-modified sensors, it allows us to do a real-time quantitative analysis of the surfactant adsorption with nanogram sensitivity. The results revealed that the surfactant adsorption increased in a Ca2+-containing solution with increasing pH from 6 to 11, whereas from a Na+-containing solution, more adsorption occurred at acidic conditions. The adsorbed amount went through a maximum (∼200 mM) as a function of the Ca2+ concentration, and the Voigt model suggested that multilayer adsorption of surfactants could be as many as 4-6 monolayers. Using mixed cation (Ca2+ and Na+) solutions, the amount of adsorbed surfactant decreased linearly with decreasing fraction of CaCl2, but Na+ competed for about ∼30% adsorption sites. The importance of the presence of CaCl2 for the surfactant adsorption was stressed in high-salinity and low-salinity solutions in the presence and absence of Ca2+. Furthermore, increasing the temperature from 23 to 65 °C shows first a small increase of surfactant adsorption followed by a reduction of about 20%. The obtained results contribute to a better understanding of surfactant adsorption on clay surfaces and a guide to optimal flooding conditions with reduced surfactant loss.

Hydrogen and oxygen surface-terminated nanocrystalline diamond (NCD) films are studied by the contactless time-resolved microwave conductivity (TRMC) technique and X-ray photoelectron spectroscopy (XPS). The optoelectronic properties of undoped NCD films are strongly affected by the type of surface termination. Upon changing the surface termination from oxygen to hydrogen, the TRMC signal rises dramatically. For an estimated quantum yield of 1 for sub-bandgap optical excitation the hole mobility of the hydrogen-terminated undoped NCD was found to be ∼0.27 cm(2)/(V s) with a lifetime exceeding 1 μs. Assuming a similar mobility for the oxygen-terminated undoped NCD a lifetime of ∼100 ps was derived. Analysis of the valence band spectra obtained by XPS suggests that upon oxidation of undoped NCD the surface Fermi level shifts (toward an increased work function). This shift originates from the size and direction of the electronic dipole moment of the surface atoms, and leads to different types of band bending at the diamond/air interface in the presence of a water film. In the case of boron-doped NCD no shift of the work function is observed, which can be rationalized by pinning of the Fermi level. This is confirmed by TRMC results of boron-doped NCD, which show no dependency on the surface termination. We suggest that photoexcited electrons in boron-doped NCD occupy nonionized boron dopants, leaving relatively long-lived mobile holes in the valence band.

We present a study of the random scission process of polymers, in which numerical simulations are com- bined with experimental investigations into the acid hydrolysis ofthepolysaccharidehyaluronan(HA),inparticularatpH1.1and 50 � C. As input for the simulations, an initial molecular weight distribution (MD(0)) and the hydrolysis rate constant (kh) are needed.The firstwasobtainedusingagarosegelelectrophoresis followed by densitometric analyses, by which we determined the evolution of the full molar-mass distribution during hydro- lysis. The rate constant was experimentally obtained by two independent techniques. Kinetic plots were obtained from both the number- and the weight-average molar mass (Mn and Mw, respectively), converted to degrees of polymerization (Nn and Nw, respectively),andfromthese,khvaluesforHAhydrolysiswerederived.Forconfirmation,khwasalsodeterminedfromtheevolution oftheconcentrationofreducingchainends.Experimentallydeterminedkhvalueswereusedasinputforthemodel,andtheevolution of MD during hydrolysis was simulated for various hypothetical MD(0) functions as well as for an experimentally determined MD(0) curve.Agreementbetweenexperimentalandsimulatedresultsdemonstratedconsistencyofthemodelandindicatesthatacidhydrolysisof hyaluronan can indeed be considered a random scission process. We show that for cases where the initial molar mass distribution is notoftheKuhn-type—whichisoftenthecase—thevalueforthekhdeterminedfromtheevolutionofMnismoreaccuratethanthat obtained from Mw.

The synthesis of the polymerizable fluorinated surfactant sodium 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoro-2-(4-vinylphenyl)ethoxy)ethanesulfonate (1) and a number of related fluorocarbon compounds is described. Compound 1 is synthesized using a copper-mediated cross-coupling reaction of 4-bromobenzaldehyde and sodium 5-iodooctafluoro-3-oxapentanesulfonate. The resulting benzaldehyde is converted to a styrene unit using a Wittig reaction with methyltriphenylphosphonium bromide in acetonitrile, using DBU as a base. This strategy for converting an iodo-functionalized fluorosurfactant to a styrene-containing fluorosurfactant is highly efficient because both reactions are performed in polar solvents and are compatible with the sulfonate moiety. In addition, the copper-mediated cross-coupling reaction is most efficient with electron-poor aryl bromides like 4-bromobenzaldehyde. We wish to employ 1 for the construction of nanostructured membranes by polymerization of 1 in a microemulsion or in lyotropic liquid crystalline phases.

A general method is presented to extract thermodynamic as well as structural information from calorimetric data on self-associating systems using existing statistical thermodynamic models. The method is illustrated with one simple and one complex ligand binding system taken from the literature. The method is also used to extract the aggregation number using a simple mass balance model for self-assembly of surfactant molecules, and experimental evidence is provided to support this.

The relation between the morphology, optical, and photoconductive properties of thin-film bulk heterojunctions of poly(3-hexylthiophene) (P3HT) with a series of electron-accepting siloxanes with a different number (x = 2, 4, 5) of pendant naphthalene diimide (NDIS) moieties is reported. All NDIS siloxanes show good electronaccepting properties, when blended with P3HT. Interestingly, the film (nano)morphology can be controlled by relatively small changes in the molecular structure of the NDIS siloxanes. Spin-coating from orthodichlorobenzene (ODCB) yields complex film (nano)morphologies, being correlated with the weight ratios of P3HT and NDIS siloxanes, and the molecular structure of the latter. On the other hand, all blends spincoated from chloroform (CHCl3) show good mixing of the components at the molecular level. It is inferred that the nanomorphology of the blends can greatly influence their photoconductive properties: samples spincoated from ODCB invariably display a higher photoconductance than corresponding samples spin-coated from CHCl3. This is explained in terms of a higher mobility of holes in samples spin-coated from ODCB, as measured by time-resolved microwave conductivity measurements. These data are useful to delineate the conditions for the research in strives for efficient organic photovoltaics. © 2009 American Chemical Society.

Small-angle neutron scattering measurements were performed on some cholic acid-based gel systems in order to gain detailed information about the network structure. The presence of thin fibers with a radius of about 10-20 Å was found for various gelators. Two types of interaction between different sorts of fibers were demonstrated, depending on the molecular structure of the gelator. The first type involves the presence of microcrystalline knots with a dimension of about 100-200 Å between the fibers. Upon heating, this network gradually disintegrates. The second type involves loose entanglements between flattened fibers. The occurrence of these types of interaction is related to the length of the alkyl tail attached to cholic acid.

The formation of soluble reversible coordination polymers with Zn2+ ions in aqueous solution was studied for two bifunctional ligands, differing in spacer length. Viscosity measurements were used to follow the formation of polymers as a function of the ratio between metal ions and ligands, the total ligand concentration, and the temperature. All the experimental findings could be reproduced and interpreted with a theoretical model that accounts for the formation of chains and rings. At low concentrations and at a 1:1 metal-to-ligand ratio, a large fraction of the ligand monomers are incorporated in small rings, with a small contribution to the viscosity. Rings are less important at higher concentrations or if one of the two components is in excess. The fraction of monomers in chains and rings could be estimated from 1H NMR measurements, which were in good agreement with the model predictions. With increasing temperature, the fraction of monomers in rings decreases. As a result, the reduced viscosity increases with increasing temperature

Enantioselectivity experiments for the binding to chiral Cu(II) complexes have been performed for several α-amino acids using isothermal titration calorimetry. To a system containing nonionic micelles, Cu(II) ions, and cholesteryl glutamate as chiral selector, either the d- or l-amino acid was titrated. The highest enantioselectivities (KD/KL) were measured for the amino acids with relatively bulky R-groups [phenylalanine (1.24) and phenylglycine (1.26)], while an increase in enantioselectivity from 1.00 to 1.21 was measured upon increasing the size of the R-group in the amino acids alanine to leucine. For serine, no enantioselectivity was measured. Reciprocal enantioselectivities have been measured with phenylalanine upon inversion of the chirality of the glutamate headgroup of the chiral selector. Finally, it was found that the binding of the amino acid to the chiral−metal selector is an entropically driven process.

The photopolymerization of spin-coated films of diacetylene derivatives containing phthalimido or naphthaldiimido moieties has been studied by monitoring the increase in the optical absorption in the visible region on irradiation at 308 nm. The phthalimido derivatives form blue polymers with absorption maxima at ca. 630 nm, corresponding to a highly conjugated, close to planar polydiacetylene (PDA) backbone configuration. The naphthaldiimido derivative yields a red polymer with an absorption maximum at 535 nm, indicating a backbone structure with a substantially reduced degree of -bond conjugation. The initial, "low-dose" quantum yields for monomer conversion, based on the total number of photons absorbed at 308 nm, range from 2 to 20. Monomer conversions up to ca. 50re found. The polymerized films are found to be photoconductive using the time-resolved microwave conductivity technique (TRMC). Mobile charge carriers are suggested to be formed via the triplet state of the arylimido moieties which undergoes long-distance charge transfer to polydiacetylene chains to form the arylimido radical anion and the mobile PDA radical cation or "hole". A maximum value of 1.4 x 10-2 cm2/(V s) for the product of the quantum yield for charge carrier formation and the hole mobility is found. The photoconductivity of the "blue" polymer is approximately an order of magnitude larger than for the "red" variety. This is attributed to a higher mobility of PDA holes in the former compound, resulting from the higher degree of backbone conjugation. The lifetime of the mobile carriers extends well into the microsecond region, which is considerably longer than previously found on direct ionization of PDA chains.

The formation and transfer of ordered layers of poly(maleic anhydride-alt-alkyl vinyl ether)s and poly(maleic acid-alt-alkyl vinyl ether)s with and without (cyanobiphenylyl)oxy moieties on aqueous subphases is studied by use of the Langmuir-Blodgett technique. The length of the spacers, flexibility of the polyelectrolyte backbone, pH of the subphase, and the presence of counterions determine the orientation of the polymers at the air-water interface. As counterions Cu 2+ , Mg 2+ , tetrabutylammonium, n-dodecyltrimethylammonium, and n-dodecyl sulfate are used. The increase in lift-off area proves the interaction of both cationic and anionic surfactants with the maleic acid copolymers. This is due to electrostatic interactions between the charged groups and hydrophobic interactions between the side chains of the polymer and surfactant tail. The π-A isotherms and Brewster angle microscopy of the maleic acid copolymers on water and on a 1 mM n-dodecyltrimethylammonium solution show the formation of a triple layer upon compression of the monolayer. Monolayers of the maleic acid copolymers on both subphases could be transferred onto hydrophilic glass and quartz slides in a Z-type fashion. However, second harmonic generation (SHG) measurements showed that the noncentrosymmetry is not maintained in the deposited multilayers.

Poly(sulfonylethylmaleic acid monoamide-co-alkyl vinyl ether)s carrying both a sulfonic acid and a carboxylic acid moiety are obtained by reacting the corresponding poly(maleic anhydride-co-alkyl v...

Two novel polymerizable double-chained ammonium amphiphiles carrying mesogenic cyanobiphenylyloxy units have been synthesized containing methacrylate in the headgroup or diacetylene groups in the hydrophobic tails. These compounds form bilayer vesicles upon dispersion in water. Polymerization increases the vesicle stability toward solubilization by a nonionic surfactant. The stacking of the cyanobiphenylyloxy units in the bilayer is directly monitored by the extent of the blue shift of the absorption maximum. Upon polymerization a decrease in blue shift is observed, reflecting a decrease in the ordering of the amphiphile molecules. This effect is stronger when polymerization occurs in the hydrophobic tails than in the headgroup region.

Side-chain liquid crystalline polyelectrolytes containing terminal (cyanobiphenylyl)oxy moieties were obtained through hydrolysis of the corresponding poly(maleic anhydride-co-alkyl vinyl ether)s with spacer lengths of 6-12 methylene groups. All polymers display a liquid crystalline phase. The transition temperatures are lower for the more rigid poly(maleic anhydride-co-alkyl vinyl ether)s. The enthalpy gain associated with the phase transition decreases with increasing rigidity of the polymeric backbone and with decreasing spacer lengths. In aqueous solution all polyelectrolytes have two distinct apparent pK a values, 3.3 and 6.5, indicative for strong nearest neighbor interactions within a maleic acid moiety. At neutral pH a blue shift of the absorbance maximum is observed which increases with increasing spacer length. Above pH 8 the blue shift decreases, indicating a conformational transition of the polyelectrolytes from more compact microdomains to a more extended chain conformation.

Conductivity, UV, and attenuated total reflectance IR measurements show that n-alkyltriphenylphosphonium amphiphiles adsorb on a Ndion 117 membrane. Approximately 20% of the Ndion protons are exchanged for a cationic amphiphile (n-hexadecyltriphenylphoephonium). Diffusion of amphiphile through the membrane was not observed. Once adsorbed, the amphiphiles did not leach from the membrane. Surface-sensitive techniques (x-ray photoelectrion spectroscopy, static secondary ion mass spectrometry) were used to investigate the presence, concentration, and distribution of the amphiphile in the Ndion membrane. Our experiments point to an incomplete monolayer coverage of the membrane, the molar ratio of amphiphile to sulfonate groups being only slightly less than 1 in the uppermost 2-5 nm. The amphiphile is bonded to the membrane, most likely via an ionic bond with the sulfonate groups. X-ray fluorescence measurements show that the amphiphile is also present in the bulk of the membrane, at least in the uppermost micrometer. However, in the bulk the concentration of amphiphile is significantly lower than the sulfonate groups. These results show that thin and stable amphiphilic layers can be made on a solid support material using adsorption of an amphiphile and coupling via an ionic bond.

Lipophilic ionophores, synthesized by coupling crown ethers 18-crown-6 and 12-crown-4 at the termini of polysiloxane backbones, have been tested as carriers in the transport of potassium perchlorate through a supported (Accurel) liquide membrane that contains o-nitrophenyl n-octyl ether (NPOE) as the membrane phase. The polysiloxane-coupled crown ethers are able to facilitate the ion transport. The stability of the membrane is enhanced in comparison with that of simple crown ethers like dibenzo-18-crown-6 by a least a factor of 25, because of the high partition coefficient (log P CE =4.7-27) of the carrier for which the contribution of one siloxane moiety to the value of log P CE is 0.6

The flux of guanidinium thiocyanate through a supported liquid membrane has been measured for substituted benzo crown ethers and dibenzo crown ethers. This flux depends on the water solubility of the carrier. The more lipophilic crown ethers show a higher flux and form more stable supported liquid membranes. The effect of the lipophilic substituents on the partition coefficient of the benzo crown ethers has been calculated and verified by partition experiments. The observed fluxes have been interpreted by a developed general model for the transport of salts through supported liquid membranes containing crown ethers. This thermodynamic model takes into account the interface equilibra, viz. the partition of crown ether and salt, as well as complexation equilibria in the membrane and aqueous phase

Synthese d'une serie de composes crown ayant entre 18 et 33 atomes dans le cycle et comportant des sous-unites catechol et xyleno-1,3. On montre que le cation guanidinium est completement encapsule par le dibenzo-[2,8]-30-crown-10. Et on etudie, le transport des ions guanidinium a travers des membranes de chloroforme, facilite par les composes crown

In the past decade, the role of complementary size, shape, and functionality in the molecular recognition of neutral molecules has been pointed out. Artificial receptor molecules have been designed with multiple recognition sites and a well-defined geometry, capable of strong and selective binding of the appropriate substrates by hydrogen bonding, ionic interaction, and/or hydrophobic interactions. 2-8 Rebek et al.2 have used molecular clefts with acidic functions for the complexation of diamines, such as imidazole. Our group has shown that additional hydrogen-bond donors9 or electrophilic metal centers,10 incorporated in the cavities of macrocyclic polyethers, improve strongly the complexation of urea. This type of cocomplexation of a neutral guest by a host molecule either by hydrogen bonding or by coordination with a metal ion, is frequently observed in (metal1o)enzymes.

Etude de la complexation de l'eau par des hotes charges positivement: pentaoxa [15]-, hexaoxa [18]- et heptaoxa [21] pyridinophaniums