Recent advances in multi-layer composite polymeric membranes for CO_2 separation: A review

The development of multilayer composite membranes for CO_2 separation has gained increasing attention due to the desire for energy efficient technologies. Multilayer composite membranes have many advantages, including the possibility to optimize membrane materials independently by layers according to their different functions and to reduce the overall transport resistance by using ultrathin selective layers, and less limitations on the material mechanical properties and processability. A comprehensive review is required to capture details of the progresses that have already been achieved in developing multilayer composite membranes with improved CO_2 separation performance in the past 15-20 years.In this review, various composite membrane preparation methods were compared, advances in composite membranes for CO_2/CH_4 separation,CO_2/N_2 and CO_2/H_2 separation were summarized with detailed data, and challenges facing for the CO_2 separation using composite membranes,such as aging, plasticization and long-term stability, were discussed. Finally the perspectives and future research directions for composite membranes were presented.

Novel nanofiltration membranes with tunable permselectivity by polymer mediated phase separation in polyamide selective layer

Microstructure in selective layer has played a decisive role in permselectivity of nanofiltration(NF) membranes,and nanomaterials were well-known additives that had been applied to mediate the microstructure and permeability of polyamide NF membranes. However, nanoadditives generally displayed a poor dispersion in membranes or in fabrication process. To solve this problem, we showed an interesting concept that novel NF membranes with hybrid selective layer consisting of flexible polyisobutylene(PIB) and rigid polyamide could be fabricated from well-defined interfacial polymerization. The hydrophobic polymer mediated phase separation and microdomains formation in polyamide layer were found. The immiscibility between the rigid polyamide and flexible PIB as well as the resultant interface effect was interpreted as the reason for the polymer enhanced permselectivity, which was similar with the well-known thin film nanocomposite(TFN) membranes that nanoparticles incorporated contributed significantly to membrane permeability and rejection performance.Our results have demonstrated that novel NF membranes with enhanced performance can be prepared from immiscible polymers, which is a new area that has not been extensively studied before.

Fabrication and Properties of Porous Film / Fabric Composites for Vascular Scaffold Application

A composite vascular scaffold combining textile reinforced structure and biodegradable polymer is introduced, which may possess high porosity and connectivity.Moreover,the porous size could be controlled.The proposed scaffold consists of a warp-knitted poly( ethylene terephthalate)( PET) fabric with well-defined macropores, which is embedded with a porous biodegradable polymer membrane.The aim of this paper is to study the fabrication and properties of porous polymer membrane through optimizing the parameter of composite methods from freeze drying / particle leaching( FD/PL) and gas foaming /particle leaching( GF /PL),subsequently combining with the warp-knitted fabric.Weighing method was utilized to analyze the porosity of the samples and the scanning electron microscope( SEM) images were taken to observe the porous structure of the vascular membrane.In addition,the static contact angle( CA) was measured to estimate the hydrophilicity of the samples, and the tensile testing of the composites was performed on the universal mechanical tester.Furthermore, the water permeability of the membrane was also calculated.The results showed that the porosity and pore connectivity of the vascular membrane were diverse, because of solution concentration, particle size, ratio of content, etc.Meanwhile,the stress-strain curves and the bursting strength showed the different mechanical properties among composite scaffolds in different structures.

The Constitutive Relation of a Fabric Membrane Composite for a Stratospheric Airship Envelope Based on Invariant Theory

The study of stratospheric airships has become the focus in many countries in recent years,because of its potential applications in many fields.Lightweight and high strength envelopes are the keys to the design of stratospheric airships,as it directly determines the endurance flight performance and loading deformation characteristics of the airship.A typical envelope of any stratospheric airship is a coated-fabric material which is composed of a fiber layer and several functional membrane layers.According to composite structure,nonlinearity and viscoelasticity are the two main characteristics of such envelope.Based on the analysis on the interaction between the different components in the micro-mechanical model of the coated-fabric,several invariant values reflecting the characteristics of the envelope material are obtained according to invariant theory.Furthermore,the constitutive equation that describes the viscoelasticity of the envelope material is derived.The constitutive equation can represent both the individual roles of the warp and weft fibers,and their further coupled interactions.The theoretical computation results were verified by off-axial tension tests.The results can help gain a deeper understanding of the mechanical mechanism and provide a reference for structural design of envelope material.

On-Chip Fabrication of Carbon Nanoparticle–Chitosan Composite Membrane

The on-chip fabrication of a carbon nanoparticle-chitosan composite membrane （i.e. a sorbent membrane or a mixed matrix membrane） using laminar flow-based interfacial deprotonation technology was presented in this paper. In addition, the effects of carbon nanoparticles and reactant flow rates on membrane formation were investigated. Finally, the permeability and adsorption capacities of the membrane were discussed. During fabrication, an acidic chitosan solution and a basic buffer solution that contained carbon nanoparticles were introduced into a microchannel. At the flow interface, a freestanding composite membrane with embedded carbon nanoparticles was formed due to the deprotonation of the chitosan molecules. The membrane growth gradually stopped with time from upstream to downstream and the thickness of the membrane increased rapidly and then slowly along the reactant flow direction. The formation of the membrane was divided into two stages. The average growth rate in the first stage was significantly larger than the average growth rate in the second stage. Carbon nanoparticles in the basic solution acted as nucleating agents and made the membrane formation much easier. As the flow rate of the chitosan solution increased, the averaged membrane thickness and the membrane hydraulic permeability initially increased and then decreased. Because of the addition of carbon nanoparticles, the formed membrane had adsorption abilities. The carbon nanoparticle-chitosan composite membrane that was fabricated in this study could be employed for simultaneous adsorption and dialysis in microdevices in the future.

Recent advances in nanoporous graphene membrane for gas separation and water purification

Graphene is a one-atom-thick sheet of graphite comprising sp2-hybridized carbon atoms arranged in the hexagonal honeycomb lattices. By removing the honeycomb lattices and forming nanopores with specific geometry and size, nanoporous graphene has been demonstrated as a very high-efficiency separation membrane, due to the ultrafast molecular permeation rate for its one-atom thickness. This review focuses on the recent advances in nanoporous graphene membrane for the applications of gas separation and water purification, with a major emphasis on the molecular permeation mechanisms and the advanced fabrication methods of this state-of-the-art membrane. We highlight the advanced theoretical and experimental works and discuss the gas/water molecular transport mechanisms through the graphene nanopores accompanied with theoretical models. In addition, we summarize some representative membrane fabrication methods, covering the graphene transfer to porous substrates and the pore generation. We anticipate that this review can provide a platform for understanding the current challenges to make the conceptual membrane a reality and attracting more and more attentions from scientists and engineers.

Low-cost method of fabricating large-aperture,high efficiency,Fresnel diffractive membrane optic using a modified moir technique

To reduce the cost and achieve high diffraction efficiency, a modified moir@ technique for fabricating a large- aperture multi-level Fresnel membrane optic by a novel design of alignment marks is proposed. The modified moire fringes vary more sensitively with the actual misalignment. Hence, the alignment accuracy is significantly improved. Using the proposed method, a 20 μm thick, four-level Fresnel diffractive polyimide membrane optic with a 200 mm diameter is made, which exhibits over 62% diffraction efficiency into the ＋1 order, and an efficiency root mean square of 0.051.