Simultaneously enhancing interfacial adhesion and pervaporation separation performance of PDMS/ceramic composite membrane via a facile substrate surface grafting approach

A facile substrate surface silane-grafting approach was demonstrated to enhance both interfacial adhesion and pervaporation separation performance of PDMS composite membrane. With C₁₆ grafted ceramic substrate, the PDMS/ceramic composite membrane exhibited up to 1.7 times stronger interfacial adhesion force between separation layer and substrate layer, meanwhile 1.5 times larger butanol/water separation factor that is higher than state-of-the-art membranes. This novel approach paves a new avenue to developing composite membranes with high and stable separation performance.     

A new technique for preparation of PDMS/ceramic nanocomposite membrane for gaseous hydrocarbons separation

A novel composite membrane using polydimethylsiloxane (PDMS) as a top active layer and ceramic nanocomposite as the support layer was developed for the gaseous hydrocarbons separation. For the fabrication of hybrid membranes, nanocomposite technology applied for manufacturing ceramic supports with controllable microstructures. Also, a new method was used for coating a uniform and no penetrated polymeric layer. Top layer of ceramic support with nanocomposite microstructures was fabricated using 5 wt % α‐Al₂O₃‐SiO₂ bidispersed suspensions with optimum weight fraction of second phase (SiO₂) based on the fractional collision frequency theory. PDMS selective layer was coated on the outer surface of the porous ceramic nanocomposite support by dip‐coating method. In this respect, the effect of several parameters such as pretreatment temperature, PDMS solution concentration, and number of coated polymeric layers on prepared layers morphology and hybrid membrane performance in the separation of condensable hydrocarbons (iso and n‐butane) from hydrogen were investigated. The results showed that the membranes fabricated at 140°C as pretreatment temperature and three polymeric layers by 7, 15, and 15 wt % PDMS concentration, respectively, had a high selectivity (>25 at 2 bar)) in C₄H₁₀/H₂ separation. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Optimization of coating solution viscosity of hollow fiber‐supported polydimethylsiloxane membrane for CO2/H2 separation

To optimize the CO₂ permeation and CO₂/H₂ separation performance of hollow fiber‐supported polydimethylsiloxane (PDMS) membranes, the effect of the viscosity of the PDMS coating solution on surface morphologies, thickness of PDMS layer, and solution intrusion into surface pores of hollow fiber supports was investigated. Increases in both stirring time and standing time could increase the viscosity of the PDMS solution. The PDMS layer thickness increased when the coating solution viscosity increased, whereas the surface roughness of the PDMS layer markedly decreased and then slightly changed. Moreover, when the stirring time of the PDMS coating solution was 9 min and the standing time was increased from 2 min to 25 min, the CO₂ permeance first decreased, then increased to ～2250 GPU probably due to the decreased intrusion depth, and finally decreased because of the substantially increased thickness of the PDMS layer. However, the CO₂/H₂ selectivity increased to 3.4 with an increase in coating solution viscosity. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45765.     

陶瓷支撑的有机复合膜及其在渗透汽化中的应用(英文)

Pervaporation(PV),as an environmental friendly and energy-saving separation technology,has been received increasing attention in recent years.This article reviews the preparation and application of macroporous ceramic-supported polymer composite pervaporation membranes.The separation materials of polymer/ceramic composite membranes presented here include hydrophobic polydimethylsiloxane(PDMS) and hydrophilic poly(vinyl alcohol)(PVA),chitosan(CS) and polyelectrolytes.The effects of ceramic support treatment,polymer solution properties,interfacial adhesion and incorporating or blending modification on the membrane structure and PV performance are discussed.Two in-situ characterization methods developed for polymer/ceramic composite membranes are also covered in the discussion.The applications of these composite membranes in pervaporation process are summarized as well,which contain the bio-fuels recovery,gasoline desulfuration and PV coupled proc-ess using PDMS/ceramic composite membrane,and dehydration of alcohols and esters using ceramic-supported PVA or PVA-CS composite membrane.Finally,a brief conclusion remark on polymer/ceramic composite mem-branes is given and possible future research is outlined.     

Influence of support layer and PDMS coating conditions on composite membrane performance for ethanol/water separation by pervaporation

A systematic study was performed on the combination of support properties and polydimethylsiloxane (PDMS) coating conditions for the lab‐scale preparation of a defect‐free, thin film composite membrane for organophilic pervaporation. Support layers having comparable surface porosities were prepared from three polymers with different chemical composition (PVDF, PSF, PI). Their exact role on the deposition of the PDMS coating (i.e., wetting and intrusion) and the final membrane performance (i.e., effect on mass transfer of the permeants) was studied. The crosslinking behavior of dilute PDMS solutions was studied by viscosity measurements to optimize the coating layer thickness, support intrusion and wetting. It was found essential to pre‐crosslink the PDMS solution for a certain time prior to the coating. Dip time for coating the PDMS solution on the supports was varied by using automated dip coating machine. The performance of the synthesized membranes was tested in the separation of ethanol/water mixtures by pervaporation. Both flux and selectivity of the membranes were clearly influenced by the support layer. Resistance of the support layers increased by increasing the polymer concentration in the casting solutions of the supports. Increasing the dip time of the PDMS coating solution led to increased selectivity of the composite membranes. Scanning Electron Microscopy analysis of the composite membranes showed that this leads to a minor increase in the thickness of the PDMS top layer. Top layer thickness increased linearly with the square root of the dip time (t^0.5) at a constant withdrawal speed of the support. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43670.     

Surface modification of nanocomposite ceramic membranes by PDMS for condensable hydrocarbons separation

PDMS/ceramic nanocomposite membranes were fabricated via dip-coating method. Tubular porous nanocomposite ceramic supports were used as membrane substrates and polydimethylsiloxane was applied as a top active layer. The hybrid membranes were characterized morphologically by scanning electron microscopy (SEM) and their gas transport properties were measured using single gas permeation (butane and hydrogen) at ambient temperature and different pressures. SEM micrographs confirmed the penetration of polymeric layer into ceramic support pores at low concentrations of PDMS solution. Experimental results clearly indicated that the undesirable penetration during the dip-coating stage could be avoided by increasing the concentration of PDMS coating solution. This led to the formation of a uniform and dense coating layer without penetration into pores of the support. These hybrid membranes showed higher permeability combined to a suitable selectivity in comparison with dense homogeneous PDMS membrane. In addition, at low pressures, the high selectivity of PDMS/ceramic nanocomposite membranes for condensable hydrocarbons separation revealed that the dominant mechanism is solution-diffusion.     

聚偏氟乙烯/聚二甲基硅氧烷渗透气化膜在丁醇分离中的应用

通过相转化法制备PVDF多孔支撑膜,在其上涂覆致密的PDMS分离层制备得到PVDF/PDMS复合膜,用于丁醇的分离纯化。以丁醇水溶液为原料液,流速为1.6 L·min^-1,丁醇浓度为15 g·L^-1,温度为37℃时, PVDF/PDMS复合膜的总通量为158.2 g·m^-2·h^-1,分离因子为17.3。向丁醇水溶液中按丁醇：丙酮：乙醇比例为6：3：1添加丙酮和乙醇模拟发酵液,PVDF/PDMS复合膜的总通量升高到189.5 g·m^-2·h^-1,分离因子降低到14.8。进一步考察了以丙酮-丁醇-乙醇（ABE）发酵液为原料液的渗透气化膜分离性能,发酵液中不存在菌体时,PVDF/PDMS复合膜的总通量和分离因子分别为120.2 g·m^-2·h^-1和19.7,而菌体存在时,复合膜的总通量和分离因子分别为122.1 g·m^-2·h^-1和16.7。与PDMS均质膜相比,PVDF/PDMS复合膜在丁醇分离过程中的分离性能有了显著的提升, 具有潜在的应用价值。     

Effect of Cu and Zn elements on morphology of ceramic particles and interfacial bonding in TiB2/Al composites

The 50 vol% TiB₂/Al composites with different alloying elements (Cu and Zn) were prepared by hot pressing sintering. The effects of Zn and Cu on the micromorphology of TiB₂ ceramic particles and interfacial behavior between TiB₂ ceramic and Al matrix as well as the mechanical properties of composites were investigated. Results indicated that the addition of Zn and Cu not only significantly enhanced the interfacial bonding strength between TiB₂ ceramic particles and Al matrix but also facilitated the reaction by reducing the reaction temperature in the Al–Ti–B system. Furthermore, the yield strength (719 MPa) and ultimate compressive strength (1130 MPa) of TiB₂/Al-6wt.%Cu composite increased by 48.8% and 26.4%, respectively, compared with that of the composite without alloy element. For the TiB₂/Al-6wt.%Zn composite, the yield strength and ultimate compressive strength increased by 15.3% and 7.8%, respectively. The improvement on the mechanical properties can be attributed to solid solution strengthening and second phase strengthening.     

The effect of kaolin addition on the characteristics of a sintered diatomite composite support layer for potential microfiltration applications

Porous ceramic membranes have lately become a subject of special interest due to their outstanding thermal and chemical stability. We prepared a sintered diatomite composite support layer with the addition of kaolin, which enhanced the mechanical strength of the diatomite composite matrix while retaining acceptable permeation properties. We also discussed whether the sintered diatomite composite support layer could serve as a separation layer to minimize processing difficulties as well as the feasibility of using a sintered diatomite composite layer without a separation layer as a porous ceramic membrane for microfiltration. The pore characteristics of the sintered diatomite specimens were studied by scanning electron micrography, mercury porosimetry, and capillary flow porosimetry.     

Fabrication of PEBA/ceramic nanocomposite membranes in gas sweetening

Poly (ether-block-amide) (PEBA)/ceramic nanocomposite hybrid membranes were fabricated by dip-coating of ceramic nanocomposite porous support in PEBA solution and their performance in gas separation (CO₂ and N₂) was examined. Tubular supports were used as substrates for hybrid membranes and Poly (ether-block-amide) was applied as a selective layer. PEBA based on N6 and PEO was synthesized via a two step process. The formation of new ester bond between N6 and PEO in the synthesized copolymer was proved by FT-IR spectroscopy. AFM micrographs indicated that the morphology is the dispersion of high stiffness nanostructured PA domains in the amorphous region of PEO matrix. Experimental results showed that at high concentration of coating solution, a uniform PEBA layer was formed on the porous ceramic support with higher performance for the separation of CO₂/N₂ binary gas mixture.     

Effect of the type of plasma on the polydimethylsiloxane/collagen composites adhesive properties

Polydimethylsiloxane (PDMS) films were treated with either oxygen (O₂), nitrogen (N₂) or argon (Ar) plasma between 40 W and 120 W for 5–15 min and their surface properties studied by contact angle measurements, infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Lower contact angles and increases in surface roughness, assessed by SEM and AFM, were observed for all used gases when plasma power and time increased, with argon treatment being the one that showed the most significant change in roughness.PDMS/collagen type I composites obtained after treating PDMS with oxygen at 80 W for 13 min or nitrogen and argon at 80 W for 14 min showed a peel strength of 0.1N/mm (oxygen plasma), 0.08 N/mm (nitrogen plasma) and 0.09 N/mm (argon plasma). In all cases, peel strength was higher than that measured for the untreated bilayer composite. An increase in adhesion strength, after oxygen and nitrogen plasma, was mostly attributed to chemical interaction between functional groups introduced on the PDMS surface and the functional groups on collagen as detected by FTIR. In contrast, the high peel strength observed on PDMS treated with argon plasma was attributed to its increased roughness which in turn increased mechanical interlocking. The properties of these composites render them suitable for adhesive free skin substitutes.     

Zirconia ceramic and Nb joints brazed with Mo-particle-reinforced Ag-Cu-Ti composite fillers: Interfacial microstructure and formation mechanism

Zirconia (ZrO₂) ceramic and Nb were successfully brazed using a Mo-particle -reinforced Ag-Cu-Ti composite filler. The effect of the Mo content of the composite filler on the interfacial microstructures and mechanical properties of ZrO₂/Nb-brazed joints was investigated. The calculated Ti activity initially increased and then decreased as the Mo content was increased from 1 to 40 wt%, and played a decisive role in the evolution of interfacial products formed adjacent to the ZrO₂ ceramic. When 40 wt% Mo particles were added to the composite filler, TiO+Ti₃Cu₃O reaction layers formed adjacent to the ceramic substrate. By decreasing the Mo content of the filler, the TiO layer became thinner or even vanished, whereas the thickness of the Ti₃Cu₃O reaction layer increased gradually with decreasing Mo content. Concurrently, a bulky TiCu compound grew near to the ZrO₂ ceramic, and further fine TiCu particles were observed in the brazing seam. This microstructure evolution, as well as the mechanism for the formation of joints brazed with composite fillers of differing Mo content, is discussed based on TEM analyses. The shear strength of the brazed joint is clearly improved when a suitable amount of Mo is added to the Ag-Cu-Ti filler. A maximum shear strength of 370 MPa was obtained when ZrO₂/Nb joints were brazed with Ag-Cu-Ti+5 wt% Mo composite filler.     

Effect of B4C,TiB2 and ZrSiO4 ceramic particles on mechanical properties of aluminium matrix composites: Experimental investigation and predictive modelling

This paper focuses on the influence of processing temperature and inclusion of micron-sized B₄C, TiB₂ and ZrSiO₄ on the mechanical performance of aluminium matrix composites fabricated through stir casting. The ceramic/aluminium composite could withstand greater external loads, due to interfacial ceramic/aluminium bonding effect on the movement of grain and twin boundaries. Based on experimental results, the tensile strength and hardness of ceramic reinforced composite are significantly increased. The maximum improvement is achieved through adding ZrSiO₄ and TiB₂, which has led to 52% and 125% increase in tensile strength and hardness, respectively. To predict the effect of incorporating ceramic reinforcements on the mechanical properties of composites, experimental data of mechanical tests are used to create 3 models named Levenberg–Marquardt Algorithm (LMA) neural networks. The results show that the LMA- neural networks models have a high level of accuracy in the prediction of mechanical properties for ceramic reinforced-aluminium matrix composites.     

Introducing all‐polyamide composite coated fabrics: A method to produce fully recyclable single‐polymer composite coated fabrics

Novel all‐polyamide composite (APC) has been developed to replace traditional coated fabrics with good interfacial adhesion and enhanced recyclability. The composite is fully recyclable since it contains no other materials except polyamide. APC was prepared by partially dissolving a polyamide fabric by treatment with a film‐forming polyamide solution. The effect of the polyamide solution concentration and gelling time on tensile and viscoelastic properties of APCs was investigated to explore the optimum processing parameters for balancing the good interfacial adhesion. The composite properties were studied by dynamic mechanical thermal analysis (DMTA), tensile testing and scanning electron microscopy (SEM). The results showed a good adhesion between the coating and the fabric. A new method was introduced to convert a low value added textile waste to a high value‐added product. The composite is tunable, in terms of having a dense or a porous top‐layer depending on the end‐use requirements. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42829.     

Interfacial microstructure and mechanical properties of porous-Si3N4 ceramic and TiAl alloy joints vacuum brazed with AgCu filler

Porous Si₃N₄ ceramic was firstly joined to TiAl alloy using an AgCu filler alloy. The effects of brazing temperature and holding time on the interfacial microstructure and mechanical properties of porous-Si₃N₄/AgCu/TiAl joints were studied. The typical interfacial microstructure of joints brazed at 880 °C for 15 min was TiAl/AlCu₂Ti/Ag-Cu eutectic/penetration layer (Ti₅Si₃+TiN, Si₃N₄, Ag (s, s), Cu (s, s))/porous-Si₃N₄. The penetration layer was formed firstly in the brazing process. With increasing brazing temperature and time, the thickness of the penetration layer increased. A large amount of element Ti was consumed in the penetration layer which suppressed the formation and growth of other intermetallic compounds. The penetration layer led the fracture to propagate in the porous Si₃N₄ ceramic substrate. The maximum shear strength was ~13.56 MPa.     

Improvement of interfacial adhesion between oxide ceramic nanoparticles and epoxy resin by wet-jet milling

Although ceramic/polymer composites are useful for various applications, such as sensors, electronics, automobiles, and aerospace, the aggregation of nanoparticles can lead to the degradation of the mechanical and functional properties of the composites. To mitigate this, the interfacial adhesion between epoxy resin and the oxide ceramic nanoparticles γ-aluminum oxide (Al₂O₃), silicon dioxide, and magnesium oxide was strengthened by wet-jet milling (WJM) treatment without a chemical modifier. The WJM treatment of the slurry containing nanoparticles and epoxy resin led to the good adsorption of epoxy resin onto the nanoparticle surface, which significantly improved the mechanical properties of the composites. Throughout this process, the amount of epoxy resin adsorbed on the nanoparticle surface and the composite mechanical properties increased with increasing WJM processing pressure, owing to the increased contact between the nanoparticles and epoxy resin droplets and the reduced droplet size. Furthermore, poor solvent was found to be effective for the dispersal of the nanoparticles because the epoxy resin droplets in the slurry were more stable on the nanoparticle surfaces than those in the solvent. When Al₂O₃ nanoparticles were used as a filler, the amount of epoxy resin adsorbed increased from 3.7 to 70.6 mg g⁻¹, and the composite tensile strength increased from 67.1 to 100.3 MPa in poor solvent and under high WJM processing pressure. This optimized WJM treatment will lead to improvements in the mechanical and functional properties of various composite materials.     

Effect of coating method on gas separation by PDMS/PES membrane

In this study, polydimethylsiloxane (PDMS)‐coated polyethersulfone (PES) composite membrane was prepared for gas separation. “Film casting” and “dip‐coating” techniques were used for producing selective PDMS layer on the surface of the PES support. The effects of coating technique and conditions including coating solution concentration and curing temperature on permselectivity of CO₂, CH₄, and N₂ were investigated. The prepared PES support did not provide any selectivity to the gases. When the concentration of PDMS coating solution was increased, initially permeability of CO₂ was rapidly dropped and then gradually reached to an almost constant value. The optimum concentration of coating solution was 5 wt%. Curing temperature showed no pronounced effect on the CO₂ permeability and selectivity. In “film casting” method, double coating showed superior permeability and selectivity. However, triple “dip‐coating” was promising. The selectivity of composite membrane prepared by “dip‐coating” was higher than “film casting” method. CO₂/N₂ and CO₂/CH₄ selectivity of five sequential dip‐coated composite membranes was 45.5 and 9.3, respectively. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Polar bear hair inspired ternary composite ceramic aerogel with excellent interfacial bonding and efficient infrared transmittance for thermal insulation

Highly porous, heat resisting ceramic aerogels are considered as promising materials for high-temperature insulation. However, the general structural characteristics of ceramic aerogel, such as poor mechanical strength and transparency to infrared radiation, pose a major obstacle to their practical application. In this paper, we report a general strategy to prepare hollow mullite fiber (HMF) structures by coaxial electrostatic spinning and grow TiO₂ nanorods (TiO₂/NAs) in situ on HMF. The ternary composite ceramic aerogel material was prepared by filling the pores of HMF-TiO₂/NAs with SiCN aerogel. The TiO₂/NAs increased the fiber/aerogel interfacial bonding of the composite (0.392 MPa, 30% strain) and improved the IR transmittance (∼0%, 1200 ℃) without sacrificing their low density and thermal conductivity. In addition, low thermal conductivity (0.041 W/(m·K), 1200 °C) and excellent high-temperature insulation properties allow the composite aerogel to meet the urgent need for lightweight, high-strength, high-temperature insulation systems for spacecraft.     

Effects of THF as cosolvent in the preparation of polydimethylsiloxane/polyethersulfone membrane for gas separation

Polydimethylsiloxane/polyethersulfone (PDMS/PES) asymmetric membranes are widely applied in gas separation. However, the effects of common cosolvent on these membranes remain unknown. In order to study the changes in membrane morphology and gas separation properties, asymmetric PDMS/PES membranes were prepared. The studied parameters were types of cosolvents, tetrahydrofuran (THF) concentration, evaporation time, and PDMS concentration. Membrane morphology was examined using scanning electron microscopy and gas separation was conducted using pure CO₂, N₂, CH₄, and Hat 25°C. The addition of cosolvent into the polymer solution decreased the dope viscosity and delayed liquid–liquid demixing during phase inversion. Macrovoids formation was observed in substructure layer after adding THF and these macrovoids elongated with the reduction in THF content. There were microvoids formed on top of macrovoids and microvoids layer became thicker due to the increasing evaporation time of solvents before coagulation in nonsolvent. The PDMS coating on the PES membrane formed a dense skin layer and exhibited higher selectivity compared to the uncoated membrane. Membrane contained THF cosolvent with 60 s evaporation time and 3 wt% coated PDMS is the optimum membrane among other membranes in this work. The CO₂/N₂ selectivity was enhanced by 73.3% with CO₂ permeance of 44.86 GPU. POLYM. ENG. SCI., 54:2177–2186, 2014. © 2013 Society of Plastics Engineers     

Influence of clay modification on the reinforcement of vinyl‐terminated polydimethylsiloxane networks

A novel method was attempted to reinforce a vinyl‐terminated polydimethylsiloxane (PDMS) with two commercially available clays, sodium montmorillonite and Cloisite^® 25A. The two clays were functionalized with bis(3‐triethoxysilylpropyl)tetrasulfide (TESPT) to prepare Na⁺MMTS₄ and C25AS₄, respectively. Incorporation of the tetrasulfide group‐containing clays, especially Na⁺MMTS₄, was found to be effective for the enhancement of the interfacial interaction between PDMS and the clays by way of a plausible chemical reaction between the tetrasulfide groups (TSS) and the vinyl‐terminated PDMS. Compounding of PDMS with the TESPT‐modified clays improved the mechanical properties significantly. In particular, the elongation at break of PDMS/Na⁺MMTS₄ composite was almost twice as high as that of neat PDMS, even if the silicate layers were not fully exfoliated in the PDMS matrix. The tear strength of PDMS was also improved greatly as a result of the incorporation of Na⁺MMTS₄. According to toluene swelling test results, the crosslinking density of the composites was lower than that of neat PDMS, indicating that the improved mechanical properties of the composites arise from enhanced compatibility between the constituents and not from increased crosslinking density. Copyright © 2009 Society of Chemical Industry