W.F.C. Sager

Facilitated oxygen transport in liquid membranes: review and new concepts

In this paper, an overview is given on membranes with oxygen facilitated transport properties to enrich the oxygen content in air. Special emphasis is paid to recent developments of oxygen carrier systems and carrier containing membranes. Concepts leading to a structural evolution of supported liquid membranes are discussed in view of ion as well as gas separation processes. As a new concept, micro-encapsulated liquid membranes are introduced, in which a mobile carrier operates in the interior of liquid droplets that are encapsulated and dispersed in a solid polymer matrix and routes to prepare the new membranes described.

Preparation of ethylene vinylalcohol copolymer membranes suitable for ligand coupling in affinity separation

Hydrophilic microfiltration membranes with functional groups that can be used as coupling sites for ligands are of central interest in affinity separation, especially in view of biomedical applications. In this study, we employed ethylene vinyl alcohol copolymer (EVAL) to prepare macrovoid-free open cellular-type membranes with a high internal surface area and interconnectivity that can chemically be modified in aqueous and organic media. To tailor the required membrane morphology, we investigated the ternary water/DMSO/EVAL system and quaternary systems using a series of n-alcohols (n=2?12) as non-solvent additives in the casting solution. Addition of solvent (DMSO) to the coagulation bath (water) performed in the ternary system to delay the onset of liquid?liquid demixing, resulted in structures dominated by solid?liquid demixing before macrovoid formation was completely suppressed. The symmetric particulate membranes obtained did not display the necessary mechanical strength. Addition of medium chain alcohols (n=7?8) in the casting solution yielded macrovoid-free cellular membranes with a significantly higher pore interconnectivity and structural integrity upon drying. A model is proposed to understand the influence of the alcohol chain length and concentration on the membrane morphology.

A small angle x-ray scattering study of the droplet–cylinder transition in oil-rich sodium bis(2-ethylhexyl) sulfosuccinate microemulsions

A method for nonlinear fitting of x-ray scattering data from polydisperse mixtures was developed. It was applied to the analysis of the structural changes in the droplet phase of oil-rich water-in-oil (w/o) sodium bis(2-ethylhexyl) sulfosuccinate (AOT) microemulsions with increasing temperature or upon addition of salt. Data were collected at different temperatures (15 to 60 °C) and salt concentrations (up to 0.6% NaCl) within the one-phase region of the L2 phase (w/o microemulsion) for different droplet sizes (water/AOT molar ratio wo=25 to 56) and concentrations (droplet weight fraction cw=2% to 20%). This allowed us to distinguish between contributions from individual scattering particles, e.g., droplets and cylinders to the total scattering intensity. The complete data set containing over 500 scattering curves could be interpreted by fitting the scattering of weighted sums of AOT covered water droplets, long cylinders, and inverse AOT micelles containing bound water only, to the experimental scatterin...

Functionalised ethylene vinyl alcohol copolymer (EVAL) membranes for affinity protein separation

Hydrophilic microfiltration membranes with functional groups that can be used as coupling sites for ligands are of central interest in affinity separation, especially in view of biomedical applications. In this study we investigate covalent coupling of bovine serum albumin (BSA) as model ligand onto cellular-type poly(ethylene vinyl alcohol) (EVAL) microfiltration membranes. EVAL membranes prepared from the ternary water/DMSO/EVAL system are only suitable for activation and coupling reactions in aqueous media. Employing glutaraldehyde (GA) or oxiran to activate the secondary alcohol groups of the vinyl alcohol segments yielded a BSA-immobilization per internal area of 0.1–0.2 μg/cm2 (4–8 mg/g per membrane mass). Preparing microfiltration membranes from the quaternary water/1-octanol/DMSO/EVAL system, using 1-octanol as nonsolvent-additive in the casting solution, enabled to perform surface functionalization reactions in organic media as well as surface activation by a low-pressure glow discharge treatment. 0.3–0.45 μg/cm2 BSA per internal area (16–18 mg/g per membrane mass) was covalently coupled onto the porous membranes by applying trichloro-s-triazine (sTT) or sulfonyl chloride activation reactions, while a BSA-immobilization of 0.5–0.55 μg/cm2 (20–22 mg/g per membrane mass) was reached via plasma activation. To determine the degree of BSA-immobilization, the internal surface area of the membranes prepared was measured by BET. The formation of a BSA-monolayer is assumed on the pore surface as maximum immobilization. Such membranes can function as adsorptive devices for endotoxin removal from blood or blood plasma.

Dense Nanostructured t-ZrO2 Coatings at Low Temperatures via Modified Emulsion Precipitation

Nanostructured coatings on metals, plastics, and textiles have numerous applications, for example, as antifogging and self-cleaning coatings as well as protective coatings against corrosion, heat, or wear. Here the preparation at low temperature of dense nanostructured tetragonal ZrO2 coatings via a modified emulsion precipitation method is presented. The method, which involves the controlled preparation, crystallization, and densification of non-agglomerated ZrO2 nanoparticles, opens up the possibility of applying nanocoatings of high-melting oxides to steel or plastic, where low temperatures are required.

Controlled formation of nanoparticles from microemulsions

Droplet microemulsions and (reversed) micellar systems have been successfully used as reaction media for the synthesis of nanosized particles. Recently, other thermodynamically stable phases like bicontinuous microemulsions and liquid crystalline phases were also employed to prepare novel, functional materials with well-defined nanoscale structures.

Sphere to cylinder transition in a single phase microemulsion system: A theoretical investigation

The sphere to cylinder transition in a one-phase droplet microemulsion system is studied theoretically. Within the framework of the curvature energy model by Helfrich, it was already shown by Safran et al. [J. Phys. (France) Lett. 45, L-69 (1984)] that for a certain range of the curvature parameters (rigidity constants and spontaneous curvature), a transition occurs from spherical droplets to infinitely long cylinders through a region where both spheres and cylinders are present. Our aim is to further investigate this region in a quantitative way by including—in addition to curvature energy—translation entropy, cylinder length polydispersity, and radial polydispersity. In this way we are able to obtain structural information on the spheres and cylinders formed, their respective volume fractions, and polydispersity, and provide a more detailed comparison with experimental results.

Structure and dynamics of water in nonionic reverse micelles: A combined time-resolved infrared and small angle x-ray scattering study

We study the structure and reorientation dynamics of nanometer-sized water droplets inside nonionic reverse micelles (water/Igepal-CO-520/cyclohexane) with time-resolved mid-infrared pump-probe spectroscopy and small angle x-ray scattering. In the time-resolved experiments, we probe the vibrational and orientational dynamics of the O-D bonds of dilute HDO:H(2)O mixtures in Igepal reverse micelles as a function of temperature and micelle size. We find that even small micelles contain a large fraction of water that reorients at the same rate as water in the bulk, which indicates that the polyethylene oxide chains of the surfactant do not penetrate into the water volume. We also observe that the confinement affects the reorientation dynamics of only the first hydration layer. From the temperature dependent surface-water dynamics, we estimate an activation enthalpy for reorientation of 45 ± 9 kJ mol(-1) (11 ± 2 kcal mol(-1)), which is close to the activation energy of the reorientation of water molecules in ice.

Helfrich free energy for aggregation and adhesion

We present a theoretical study of the shape and free energy of a vesicle (or microemulsion droplet) adhered to a substrate (other droplet) based on the expression for the surface free energy by Helfrich. Analytical formulas are presented for the shape and free energy when the rigidity constant for bending, k, is small; i.e., when (k/σ)1/2, with σ the surface tension, is small compared to the typical dimension of the vesicle (k/σ)1/2≪V1/3, with V the vesicle volume. These formulas are compared with numerical solutions of the shape equations such as those first provided in the work by Seifert and Lipowsky. Results are presented when the exact formulas are applied to study the onset of microemulsion droplet aggregation, e.g., dimer formation, in terms of the usual coefficients in the Helfrich free energy expression, such as the rigidity constant for bending and the spontaneous curvature.

Vesicle adhesion and microemulsion droplet dimerization: Small bending rigidity regime

To study the vesicle-substrate unbinding transition and the onset of microemulsion aggregation, we calculate the curvature free energy of a vesicle adhered to a substrate and of two microemulsion droplets forming a dimer. Analytical expressions are derived in the small bending rigidity regime in which the length (k/σ)1/2, constructed from the rigidity constant of bending k and surface tension σ, is small compared to the typical size of the vesicle (droplet), (k/σ)1/2≪R. The leading contribution to the curvature free energy is shown to be proportional to k1/2. The formulas derived are used to understand the experimentally observed aggregation of microemulsion droplets occurring in the direction of vanishing spontaneous curvature. In this way we intend to bridge the gap between the liquid state theories used to describe aggregation processes in microemulsion systems and the bending energy concept originally introduced by Helfrich to describe vesicles shapes and fluctuations as well as phase diagrams of micr...