Mohtada Sadrzadeh

A Novel Approach Toward Fabrication of High Performance Thin Film Composite Polyamide Membranes.

A practical method is reported to enhance water permeability of thin film composite (TFC) polyamide (PA) membranes by decreasing the thickness of the selective PA layer. The composite membranes were prepared by interfacial polymerization (IP) reaction between meta-phenylene diamine (MPD)-aqueous and trimesoyl chloride (TMC)-organic solvents at the surface of polyethersulfone (PES) microporous support. Several PA TFC membranes were prepared at different temperatures of the organic solution ranging from −20 °C to 50 °C. The physico-chemical and morphological properties of the synthesized membranes were carefully characterized using serval analytical techniques. The results confirmed that the TFC membranes, synthesized at sub-zero temperatures of organic solution, had thinner and smoother PA layer with a greater degree of cross-linking and wettability compared to the PA films prepared at 50 °C. We demonstrated that reducing the temperature of organic solution effectively decreased the thickness of the PA active layer and thus enhanced water permeation through the membranes. The most water permeable membrane was prepared at −20 °C and exhibited nine times higher water flux compared to the membrane synthesized at room temperature. The method proposed in this report can be effectively applied for energy- and cost-efficient development of high performance nanofiltration and reverse osmosis membranes.

Thin film composite polyamide membranes: parametric study on the influence of synthesis conditions

Preparation of thin film composite (TFC) polyamide (PA) membranes by interfacial polymerization (IP) reaction is remarkably sensitive to the interactions between synthesis parameters. Here we report the effect of the simultaneous change in four synthesis parameters, namely monomers concentrations (m-phenylenediamine, MPD, and trimesoyl chloride, TMC), reaction time and curing temperature, on the surface morphology and on the permeation properties of TFC membranes. By varying several synthesis parameters at the same time using a Taguchi robust design (L9 orthogonal arrays), it was found that monomers concentration and curing temperature significantly affected water permeation by creating a substantial change in morphology of the PA films. More importantly, a strong interaction between monomers concentration was observed, which demonstrates the importance of smart adjustment of these parameters in the preparation process. Permeation properties were justified by thickness and by the cross-link density of the synthesized films; the latter was found to be more influential. Based on analysis of variance (ANOVA), the contribution of the synthesis parameters towards change in water permeation was determined as: curing temperature (40.7%) > MPD concentration (28%) ∼ TMC concentration (27.8%) > reaction time (1.9%). The findings will provide valuable guidelines to develop practical low cost, robust and high performance membranes by changing the curing temperature and the monomer concentrations as critical parameters.

Methods for the Preparation of Organic–Inorganic Nanocomposite Polymer Electrolyte Membranes for Fuel Cells

In the last decade, the organic–inorganic nanocomposite polymer electrolyte membranes (PEM) have gained high technical relevance in a wide range of fuel cells applications. The significance of nanocomposite membranes fabrication is particularly highlighted by the fact that one of the major challenges of this century is to provide well-performing and cost-effective membrane materials for fuel cells applications. Many efforts have been made in the development of advanced membranes with the aim to outperform the most commonly used polymer membranes. With the advances in nanomaterials and polymer chemistry, the innovative nanocomposite membranes with superior properties can be designed by various techniques including blending of nanoparticles in a polymer matrix, doping, or infiltration and precipitation of nanoparticles and precursors, self-assembly of nanoparticles, layer-by-layer fabrication method, and nonequilibrium impregnation reduction. This study presents a brief overview of these techniques and discusses the encountered challenges, the problems to be overcome, the major findings and guidance for future developments.

Fundamentals and Measurement Techniques for Gas Transport in Polymers

Polymeric membranes have been widely used in various gas separation applications mainly due to their high performance regarding permeation and selectivity. Gas transport in a dense polymeric membrane is primarily described by solution-diffusion mechanism where gas dissolution on feed side and diffusion across the membranes play significant roles in overall gas separation process. Understanding the nature of transport phenomena and the precise evaluation of transport coefficients (permeability, solubility, and diffusivity) are therefore of fundamental and practical interest. This chapter provides fundamentals of membrane gas separation and critically reviews major techniques for measurement of gas permeation, sorption, and diffusion. The main purpose of this chapter is to lay out the basics for selecting appropriate measurement techniques by considering their pros and cons, especially in terms of membrane material properties and operating condition range.

Preparation and C3H8/Gas Separation Properties of a Synthesized Single Layer PDMS Membrane

In this paper, a new polydimethylsiloxane (PDMS) membrane was synthesized and its ability for separation of heavier gases from lighter ones was examined. Sorption, diffusion, and permeation of H2, N2, O2, CH4, CO2, and C3H8 in the synthesized membrane were investigated as a function of pressure at 35°C. PDMS was confirmed to be more permeable to more condensable gases such as C3H8. This result was attributed to very high solubility of larger gas molecules in hydrocarbon−based PDMS in spite of their low diffusion coefficients relative to small molecules. The synthesized membrane showed much better gas permeation performance than others reported in the literature. Increasing upstream pressure increased solubility, permeability and diffusion coefficients of C3H8, while these values decreased slightly or stayed constant for other gases. Local effective diffusion coefficient of C3H8 and CO2 increased with increasing penetrant concentration which indicated plasticization effect of these gases over the range of penetrant concentration studied. C3H8/gas solubility, diffusivity and overall selectivities also increased with increasing feed pressure. Ideal selectivity values of 4, 13, 18, 20, and 36 for C3H8 over CO2, CH4, H2, O2, and N2, respectively, at upstream pressure of 7 atm, confirmed the outstanding separation performance of the synthesized mebrane.

Treatment of an in situ oil sands produced water by polymeric membranes

AbstractCross-flow ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) were applied for the first time on a produced water obtained from a thermal in situ bitumen recovery process called steam-assisted gravity drainage (SAGD), with the intent to remove salt, silica, and dissolved organic matter (DOM) so that the produced water could be re-used as high-quality boiler feedwater. It was found that more hydrophilic and more negatively charged membranes were less susceptible to fouling. The UF membrane tested rejected a maximum of 30% of the salt and silica and 50% of the DOM. Nanofiltration with loose membranes removed more than 70% of the salt and DOM. The tight NF membranes tested removed more than 86% of the salt, silica, and DOM, and consumed less energy than RO, which showed almost the same rejection. An instantaneous increase in water flux resulting from a step change in feedwater pH demonstrated the critical role of pH in flux recovery and in fouling mitigation. Analysis of the fouled m...

Separation via Pervaporation Techniques Through Polymeric Membranes

This chapter attempts to delve into some of the recent progresses made by researchers and the present scope of future works in liquid separation area via pervaporation (PV) techniques using polymer membranes. Polymeric scientists have introduced numerous PV membrane materials, which could be divided into two main groups: water-selective polymeric membranes and apolar or organophilic polymer membranes. These polymeric materials as well as their separation properties are illustrated in this chapter. The key aim is to lay down the fundamentals for choosing polymers to fabricate PV membranes for various fields of liquid separation. Another purpose of this chapter is to overview various PV transport models. Realization and accurate estimation of mass transport are thus of basic and practical interest.

Compact micro/nano electrohydrodynamic patterning: using a thin conductive film and a patterned template.

The influence of electrostatic heterogeneity on the electric-field-induced destabilization of thin ionic liquid (IL) films is investigated to control spatial ordering and to reduce the lateral dimension of structures forming on the films. Commonly used perfect dielectric (PD) films are replaced with ionic conductive films to reduce the lateral length scales to a sub-micron level in the EHD pattering process. The 3-D spatiotemporal evolution of a thin IL film interface under homogenous and heterogeneous electric fields is numerically simulated. Finite differences in the spatial directions using an adaptive time step ODE solver are used to solve the 2-D nonlinear thin film equation. The validity of our simulation technique is determined from close agreement between the simulation results of a PD film and the experimental results in the literature. Replacing the flat electrode with the patterned one is found to result in more compact and well-ordered structures particularly when an electrode with square block protrusions is used. This is attributed to better control of the characteristic spatial lengths by applying a heterogeneous electric field by patterned electrodes. The structure size in PD films is reduced by a factor of 4 when they are replaced with IL films, which results in nano-sized features with well-ordered patterns over the domain.

Analytical solution for transient electroosmotic flow in a rotating microchannel

An analytical solution is developed for the unsteady flow of fluid through a parallel rotating plate microchannel, under the influence of electrokinetic force using the Debye–Huckel (DH) approximation. Transient Navier–Stokes equations are solved exactly in terms of the cosine Fourier series using the separation of variables method. The effects of frame rotation frequency and electroosmotic force on the fluid velocity and the flow rate distributions are investigated. The rotating system is found to have a damped oscillatory behavior. It is found that the period and the decay rate of the oscillations are independent of the DH parameter (κ). A time dependent structure of the boundary layer is observed at higher rotational frequencies. Furthermore, the rotation is shown to generate a secondary flow and a parameter is defined (β(t)) to examine the ratio of the flow in the y and x directions. It showed that both the angular velocity and the Debye–Huckel parameters are influential on the induced transient secondary flow in the y direction. At high values of the Debye–Huckel parameter and the rotation parameter the flow rates in the x and y directions are found to be identical. The analytical solution results are found to be in good agreement with the numerical method results and previously published work in this field.

Nonlinear deformation and localized failure of bacterial streamers in creeping flows

We investigate the failure of bacterial floc mediated streamers in a microfluidic device in a creeping flow regime using both experimental observations and analytical modeling. The quantification of streamer deformation and failure behavior is possible due to the use of 200 nm fluorescent polystyrene beads which firmly embed in the extracellular polymeric substance (EPS) and act as tracers. The streamers, which form soon after the commencement of flow begin to deviate from an apparently quiescent fully formed state in spite of steady background flow and limited mass accretion indicating significant mechanical nonlinearity. This nonlinear behavior shows distinct phases of deformation with mutually different characteristic times and comes to an end with a distinct localized failure of the streamer far from the walls. We investigate this deformation and failure behavior for two separate bacterial strains and develop a simplified but nonlinear analytical model describing the experimentally observed instability phenomena assuming a necking route to instability. Our model leads to a power law relation between the critical strain at failure and the fluid velocity scale exhibiting excellent qualitative and quantitative agreeing with the experimental rupture behavior.