Anion exchange membranes with twisted poly terphenylene backbone Effect of the N cyclic cations

In order to investigate the relationship towards the cationic structures and ion exchange membrane performance, three kinds of twisted poly terphenylene based anion exchange membranes AEMs with N cyclic cations were prepared via facile Friedel Crafts type polycondensation and quaternization. The steric hindrance of the N cyclic cations is gradually increased from the small piperidinium to the sterically protected N spirocyclic quaternary ammonium QA . The twisted poly terphenylene s backbone promotes the self assembly of the polymer chain and forms a microphase separated morphology, resulting in a highest conductivity of 68.7 mS cm amp; 8722;1 80 C for the polymer tethered with piperidinium groups m TPNPiQA . The relative conductivity conductivity swelling ratio of m TPNPiQA is even higher than that of the commercial Fumapem FAA 3 50 membrane. Increasing the size of the QA is helpful to constrain water absorption and related swelling but has a negative effect on the chemical stability. amp; 946; Hofmann elimination degradation is observed for all of the AEMs during a stability test by 1H NMR analysis. The m TPNPiQA demonstrates less than 6 ionic exchange capacity loss after 240 h in 5 M NaOH solution at 80 C. The results demonstrated that the membrane performance is associated well with the features of the cationic groups. A high performance AEM can be achieved by grafting appropriate cations onto aryl ether free backbon

Ultra fast laser machined hydrophobic stainless steel surface for drag reduction in laminar flows

Hydrophobic surfaces have attracted much attention due to their potential in microfluidics, lab on chip devices and as functional surfaces for the automotive and aerospace industry. The combination of a dual scale roughness with an inherent low-surface-energy coating material is the pre-requisite factor for the development of an artificial superhydrophobic surfaces. Ultra short pulse laser (USPL) machining/structuring is a promising technique to obtain the dual scale roughness. Moreover, ultra short laser pulses allow machining without or with limited thermal effects. Flat stainless steel (AISI 304L) were laser machined with ultraviolet laser pulses of 6.7ps, at different laser processing parameters. Next, the samples were coated with a monolayer of\ud perfluorinated octyltrichlorosilane (FOTS) to get a superhydrophobic surface. The degree of hydrophobicity was accessed by static contact angle measurement. Laser patterned surface has longitudinal micro channels. Drag reduction in liquid flow can be obtained due to the shear free boundary condition at air-liquid menisci. The geometry of the patterns was analyzed with optical and scanning electron microscopy. Micro-Particle Image Velocimetry (μPIV) has been employed to measure and visualize the flow over such pattern

Comparing flat and micro-patterned surfaces: Gas permeation and tensile stress measurements

Micro-patterning is a suitable method to produce structured membranes that display increased flux compared to flat membranes. In this work we studied the permeation of four different gases (nitrogen, helium, oxygen and carbon dioxide) through Kraton™ polymer (SBS) membranes. It is possible to cast a micro-patterned membrane with 25 μm high and 30 μm wide lines that has a thickness of 5 μm at its thinnest point. Using this micro-pattern, the experimental diffusive gas flux was increased up to 59% compared to non-patterned membranes with the same polymer volume. Finite element simulations confirm this enhancement. Selectivities are similar for both flat and micro-patterned membranes and in accordance with literature. Tensile stress measurements confirm that the micro-patterned membranes yield only limited loss in mechanical strength. Although only one material and geometry is explored here, this principle is generally applicable to all diffusion-driven processes

Membranes and microfluidics: a review

The integration of mass transport control by means of membrane functionality into microfluidic devices has shown substantial growth over the last 10 years. Many different examples of mass transport control have been reported, demonstrating the versatile use of membranes. This review provides an overview of the developments in this area of research. Furthermore, it aims to bridge the fields of microfabrication and membrane science from a membrane point-of-view. First the basic terminology of membrane science will be discussed. Then the integration of membrane characteristics on-chip will be categorized based on the used fabrication method. Subsequently, applications in various fields will be reviewed. Considerations for the use of membranes will be discussed and a checklist with selection criteria will be provided that can serve as a starting point for those researchers interested in applying membrane-technology on-chip. Finally, opportunities for microfluidics based on proven membrane technology will be outlined. A special focus in this review is made on the membrane properties of polydimethylsiloxane (PDMS), since this material is frequently used nowadays in master replication

Modeling of gas-liquid reactions in porous membrane microreactors

This work provides a numerical model studying mass transport and heterogeneously catalyzed reactions in a porous membrane microreactor. The hydrogenation of nitrite over a Pd catalyst was used as a model reaction. The influence of liquid flow rates, initial nitrite concentration and catalytic membrane layer thickness (wetting thickness) on the conversion was studied. Firstly, a kinetic model was implemented based on the correlations available for reaction kinetics from literature. The results were validated using experimental results and it was found that the process is best described by Langmuir¿Hinshelwood reaction kinetics. Secondly, to obtain an optimized reactor geometry, boundary conditions were derived, which represent the reactant concentration at the microreactor inner wall as a function of catalytic layer properties. An optimum in conversion was found for varying catalytic membrane layer thickness. The initial increase in conversion with increasing catalytic layer thickness is due to enhanced catalyst area. The conversion later reduces due to gaseous reactant mass transfer limitation, for even thicker layers. This study provides detailed understanding of the mass transfer taking place in membrane microreactors. It also provides routes towards optimized reactor configurations, which allows for more efficient catalyzed gas¿liquid reaction processe

Microfluidic NF/RO separation: Cell design, performance and application

Microfluidics have seen a steady expansion of the operation toolbox over the last decade, which includes membrane separations as well. However, the latter are mainly limited to low-pressure operations such as dialysis, MF and UF with only very few reports focusing on high-pressure processes such as NF and RO. In this report a simple high-pressure microfluidic cell suitable for accommodating NF and RO membranes is described and critical design points are discussed. It is shown, both theoretically, using computational fluid dynamics (CFD) and Lévêque correlation, and experimentally, that a smaller height of the feed channel is beneficial for minimizing concentration polarization. Minimization of overall pressure losses, hydraulic and osmotic, indicates an optimal channel height of about 40–50 μm. The NF/RO microcell was tested as a concentrator for solution of a model peptide. The solution was successfully concentrated, however, a significant loss of peptide was observed, presumably, due to adsorption on the membrane or cell walls. This problem will need to be addressed in future studies of NF/RO microcells, however, this work demonstrates the potential and feasibility of implementing RO and NF operations in microfluidic technolog

Polymer-in-a-silica-crust membranes: macroporous materials with tunable surface functionality

We report on alkaline hydrolysis of tetraethoxysilane (Stöber synthesis) inside a macroporous polymer matrix resulting in a homogeneous coverage of silica onto the polymer surface. The encapsulation of the polymer struts by a continuous silica crust allows further functionalization with hydrophilic and hydrophobic silylating agents. The porous silica polymeric hybrid material combines the morphological control and mechanical flexibility of the polymeric matrix with the convenient surface modifications developed for glass and amorphous silica. This concept is applied to macroporous membranes where alteration in surface functionality allows tuning of hydrophobicity (contact angle and liquid entry pressure), streaming potential, and adsorption capacity of double-stranded DNA

Fouling behavior of microstructured hollow fibers in cross-flow filtrations: Critical flux determination and direct visual observation of particle deposition\ud

The fouling behavior of microstructured hollow fiber membranes was investigated in cross-flow filtrations of colloidal silica and yeast. In addition to the as-fabricated microstructured fibers, twisted fibers made by twisting the microstructured fibers around their own axes were tested and compared to round fibers. In silica filtrations, the three different fibers showed similar behavior and increasing Reynolds number increased the critical fluxes significantly. In yeast filtrations, the twisted fiber performed similar to the round fiber and better than the structured fiber. Among the three fibers, during yeast filtrations the critical flux for irreversibility was highest for the twisted fiber. The Reynolds number had little effect on the critical fluxes for particle deposition, which was attributed to the strong adsorption of yeast particles on the membrane. On the other hand, the critical fluxes for irreversibility increased with increasing Reynolds number for all three fibers. Direct visual observation of yeast particles on the surface of the three different hollow fibers revealed that for the structured and twisted fibers, the initial deposition rate on the fins is much lower than that in the grooves. This is attributed to the shear-induced migration of the yeast particles from areas of high shear (fins) to those of low shear (grooves). Furthermore, on the fins of the twisted fiber the deposition rate was lower than that on the fins of the structured fiber. This observation, together with the observed high critical fluxes for the twisted fiber led to the conclusion that the twisting induces a secondary flow in the liquid. This secondary flow is effective in depolarizing the buildup of micron-sized yeast particles since the diffusion of these particles is strongly effected by gradients in shear rate. On the other hand, for the silica colloids which are much smaller, shear-induced diffusion is not significant and twisting does not have an improving effect on filtratio