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In this study, the preparation of a new, functional anion-exchange membrane (AEM), containing guanidinium groups as the anion-exchanging sites (Gu-100), is described as well as the membrane characterization by XPS, water uptake, permselectivities, and electrical resistances. The functional membrane was also employed in pH-dependent electrodialysis experiments using model dairy wastewater streams. The properties of the new membrane are compared to those of a commercially available anion-exchange membrane bearing conventional quaternary ammonium groups (Gu-0). Guanidinium was chosen for its specific binding properties toward oxyanions: e.g., phosphate. This functional moiety was covalently coupled to an acrylate monomer via a facile two-step synthesis to yield bulk-modified membranes upon polymerization. Significant differences were observed in the electrodialysis experiments for Gu-0 and Gu-100 at pH 7, showing an enhanced phosphate and citrate transport for Gu-100 in comparison to Gu-0. At pH 10 the difference is much more pronounced: for Gu-0 membranes almost no phosphate and citrate transport could be detected, while the Gu-100 membranes transported both ions significantly. We conclude that having guanidinium groups as anion-exchange sites improves the selectivity of AEMs. As the presented monomer synthesis strategy is modular, we consider the implementation of functional groups into a polymer-based membrane via the synthesis of tailor-made monomers as an important step toward selective ion transport, which is relevant for various fields, including water treatment processes and fuel cells.

A Micelle‐enhanced ultrafiltration (MEUF) separation process was investigated that can potentially be used for large‐scale enantioseparations. Copper(II)‐amino acid derivatives dissolved in nonionic surfactant micelles were used as chiral selectors for the separation of dilute racemic amino acids solutions. For the α‐amino acids phenylalanine, phenylglycine, O‐methyltyrosine, isoleucine, and leucine good separation was obtained using cholesteryl l‐glutamate and Cu(II) ions as chiral selector with an operational enantioselectivity (αop) up to 14.5 for phenylglycine. From a wide set of substrates, including four β‐amino acids, it was concluded that the performance of this system is determined by two factors: the hydrophobicity of the racemic amino acid, which results in a partitioning of the racemic amino acid over micelle and aqueous solution, and the stability of the diastereomeric complex formed upon binding of the amino acid with the chiral selector. The chiral hydrophobic cholesteryl anchor of the chiral selector also plays an active role in the recognition process, since inversion of the chirality of the glutamate does not yield the reciprocal enantioselectivities. However, if the cholesteryl group is replaced by a nonchiral alkyl chain, reciprocal operational enantioselectivities are found with enantiomeric glutamate selectors. Chirality 12:627–636, 2000. © 2000 Wiley‐Liss, Inc.

A Micelle-enhanced ultrafiltration (MEUF) separation process was investigated that can potentially be used for large-scale enantioseparations. Copper(II)-amino acid derivatives dissolved in nonionic surfactant micelles were used as chiral selectors for the separation of dilute racemic amino acids solutions. For the α-amino acids phenylalanine, phenylglycine, O-methyltyrosine, isoleucine, and leucine good separation was obtained using cholesteryl l-glutamate and Cu(II) ions as chiral selector with an operational enantioselectivity (αop) up to 14.5 for phenylglycine. From a wide set of substrates, including four β-amino acids, it was concluded that the performance of this system is determined by two factors: the hydrophobicity of the racemic amino acid, which results in a partitioning of the racemic amino acid over micelle and aqueous solution, and the stability of the diastereomeric complex formed upon binding of the amino acid with the chiral selector. The chiral hydrophobic cholesteryl anchor of the chiral selector also plays an active role in the recognition process, since inversion of the chirality of the glutamate does not yield the reciprocal enantioselectivities. However, if the cholesteryl group is replaced by a nonchiral alkyl chain, reciprocal operational enantioselectivities are found with enantiomeric glutamate selectors. Chirality 12:627–636, 2000. © 2000 Wiley-Liss, Inc.

The synthesis and characterization of liquid‐crystalline polymers with possible good adhesive properties is reported. These polymers are prepared by alternating copolymerization of maleic anhydride and mesogenic alkenes. The spacer length m is varied (m = 2, 3, 4, 6, 8 and 9) and methoxybiphenyl is used as the mesogenic group. The glass transition temperature decreases and the isotropization temperature increases with spacer length. Depending on the spacer length and temperature, SBand SAdmesophases can be observed. After annealing, spin‐coated films of these polymers show very regular layered structures with a layer spacing similar to that in the bulk.

Several polymeric materials were studied as membrane materials for potassium-selective ion-sensitive field-effect transistors (ISFETs) to overcome the problems related with the use of conventional plasticized poly(vinyl chloride) membranes casted on ISFET gate surfaces. Several acrylate materials, such as ACE, Epocryl and derivatives, showed no reproducible results. Three room-temperature vulcanizing (RTV)-type silicone rubbers were tested. The addition-type RTV-2 silicone rubber was not suitable as a membrane material, but the condensation-type RTV-1 and especially the RTV-2 silicone rubber showed good results. ISFETs with a Silopren membrane showed a durability of at least 2 months.

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 is an impractical situation as the effect of the surface roughness of reservoir rocks and its role in surfactant adsorption processes are not yet completely understood. The coupling of electrochemical techniques and QCM-D in one analysis setup (EQCM-D) provides a new methodology to explore complex surfactant adsorption processes. In this work, a uniform, rough, and well-covered model CaCO3surface was obtained on gold and platinum sensors to model carbonate rocks. This was achieved by the electrochemically formed hydroxide ions in the presence of bicarbonate and calcium ions, by which the controlled deposition of CaCO3resulted in sensor surface coverages in the range 35–40%. Before using the deposited CaCO3surfaces, the adsorption of anionic surfactant alcohol alkoxy sulfate (AAS) on a smooth commercially available CaCO3surface was studied with varying CaCl2concentrations. For the first time, the structure and characteristics of the formed AAS layer were quantitatively described, indicating the formation of an incomplete bilayer. Compared to the smooth CaCO3surface, an increase in the frequency shift from 5 to 15 times was observed in sensors covered with rough CaCO3deposit. This observation was primarily attributed to the rougher surfaces that possess more adsorption sites for AAS binding and also to the effect of liquid trapping, inducing additional frequency shifts. The obtained results show that surfactant adsorption on rough surfaces was vastly different from that on smooth surfaces, and they provide a better understanding of the adsorption behavior of surfactants to mineral surfaces.