Influence of binding interface between active and support layers in composite PDMS membranes on permeation performance

Effect of the binding interfaces of composite polydimethylsiloxane (PDMS) membranes on their pervaporation performance was studied. The membranes were made up of PDMS as active skin layer and polysulfone (PSF) or polyamide (PA) as supporting layer. PDMS‐PSF membrane was numbered 1, and PDMS‐PA membrane numbered 2. The pervaporation experiments were carried out by using the composite membranes and dilute ethanol–water mixture. The experimental measurements for the permeation performance under various operating conditions (e.g., feed concentration and temperature) showed that the specific permeation rate of membrane 2 was over membrane 1 by seven times at least. A resistance‐in‐series model was applied to formularize the transport of the permeants. Influence of the binding interfaces between the active skin layer and support layers in these membranes on pervaporation performance was analyzed. The cross section morphology of the membranes and chemical element distribution along membrane thickness were examined by using SEM and EDS. It was found that, although the PDMS intrusion layer into PSF near the interface was only about 2 μm, it gave significant effect on the permeation performance. It implied that the resistance produced by the intrusion layer into PSF was apparently larger than that of PDMS intruding PA and over intrinsic PDMS resistance. These should be probably attributed to structures and formation of the binding interfaces. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2468–2477, 2007     

Hybrid sol–gel membranes of polyacrylonitrile–tetraethoxysilane composites for gas permselectivity

Sol–gel reaction of tetraethoxysilane (TEOS) with fumed silica–polyacrylonitrile (PAN) membrane was carried out to prepare hybrid gas permeable membranes for oxygen and nitrogen separation. Various amounts of fumed silica microparticles with a few μm diameters were compounded in PAN–dimethylsulfoxide (DMSO) solution. After casting of the viscous compound solution on a flat sheet with 100 μm thickness, DMSO was evacuated under vacuum at 80°C. Then, the silica–PAN composite membranes were treated with TEOS for 1 day at 40°C in methanol. Air permeation was examined and compared in silica–PAN composite membranes with and without TEOS treatment. The latter hybrid membranes showed selective oxygen permeability, which depended on amounts of fumed silica in the membrane. The TEOS hybrid PAN membranes have a high ability of oxygen permselectivity for O₂/N₂ gas mixture with α(O₂/N₂) = 13–17, when the silica content was in the range of 13–20 wt %. This is attributed to siloxane network formation in hybrid silica–PAN composite membranes. Favorable siloxane network formation resulted in high oxygen permeability of the hybrid composite membranes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1752–1759, 2003     

Rheological behavior and network dynamics of silica filled vinyl‐terminated polydimethylsiloxane suspensions

Present article reports the rheological properties and network dynamics of fumed silica filled vinyl‐terminated polydimethylsiloxane suspensions. The results reveal that as filler loading increases, the span of the linear viscoelastic region with constant dynamic storage modulus is narrowed with increase in strain amplitude while the relaxation time of the compounds get shifted to longer time scales. The dynamics of filler‐network indicated significant Payne effect due to fumed silica incorporation into the PDMS matrix. Further, strain‐induced agglomeration of fumed silica particles, characterized by a peak in the dynamic loss modulus curve could also be observed. High loss‐tangent was observed for lower contents of filler in the suspension, an effect with an apparent relationship to the loosely formed filler‐network. The formation of a saturated network structure of fumed silica particles was evident from the dynamic modulus and complex viscosity data, that remained unaffected with frequency till a critical amount of fumed silica loading. Han plots (storage modulus versus loss modulus) revealed the microstructural changes for various filled systems that was attributed to build‐up of the filler‐network causing an apparent evolution of yielding phenomenon. Van Gurp‐Palmen plots (complex modulus versus phase lag) showed that flow behavior of the filled PDMS suspensions resembled to that of typical viscous fluids. POLYM. ENG. SCI., 57:973–981, 2017. © 2016 Society of Plastics Engineers     

Modified ZSM‐5/polydimethylsiloxane mixed matrix membranes for ethanol/water separation via pervaporation

In this article, chlorosilane‐modified ZSM‐5 particles were incorporated into polydimethylsiloxane (PDMS) to form mixed matrix membranes (MMMs) for ethanol/water mixture separation via pervaporation (PV). The membranes were characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, and mechanical performance testing. The maximum loading and dispersion of ZSM‐5 into PDMS were improved by chlorosilane modification. To evaluate the PV performance, the MMMs were used to separate an aqueous ethanol solution. The effect of zeolite loading and operational conditions on PV performance was investigated in detail. The separation factor of the composite membranes filled with modified ZSM‐5 increased considerably versus unmodified membrane, while the total flux decreased to some degree. Of all the chlorosilane‐modified membranes, dodecyltrichlorosilane modified ZSM‐5 filled PDMS showed the best separation factor of 15.8 for ethanol. POLYM. COMPOS., 37:1282–1291, 2016. © 2014 Society of Plastics Engineers     

Effect of nano‐silica filler on the rheological and morphological properties of polypropylene/liquid‐crystalline polymer blends

A fumed hydrophilic nano‐silica‐filled polypropylene (PP) composite was blended with a liquid‐crystalline polymer (LCP; Rodrun LC5000). The preblended polymer blend was extruded through a capillary die; this was followed by a series of rheological and morphological characterizations. The viscosity of the PP matrix increased with the addition of the hydrophilic nano‐silica. At shear rates between 50 and 200 s^?1, the composite displays marked shear‐thinning characteristics. However, the incorporation of LC5000 in the PP composite eliminated the shear‐thinning characteristic, which suggests that LC5000 destroyed the agglomerated nano‐silica network in the PP matrix. Although the viscosity ratio of LCP/PP was reduced after the addition of nano‐silica fillers, the LCP phases existed as droplets and ellipsoids. The nano‐silicas were concentrated in the LC5000 phase, which hindered the formation of LCP fibers when processed at high shear deformation. We carried out surface modification of the hydrophilic nano‐silica to investigate the effect of modified nano‐silica (M‐silica) on the morphology of the PP/LC5000 blend system. Ethanol was successfully grafted onto the nano‐silica surface with a controlled grafting ratio. The viscosity was reduced for PP filled with ethanol‐M‐silica when compared to the system filled with untreated hydrophilic nano‐silica. The LC5000 in the (PP/M‐silica)/LC5000 blend existed mainly in the form of fibrils. At high shear rates (e.g., 3000 s^?1), the LC5000 fibril network was formed at the skin region of the extrudates. The exclusion of nano‐silica in the LC5000 phase and the increased viscosity of the matrix were responsible for the morphological changes of the LCP phase. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1484–1492, 2003     

Preparation and characterization of novel polydimethylsiloxane composites used POSS as cross‐linker and fumed silica as reinforcing filler

A series of novel polydimethylsiloxane (PDMS) composites were prepared using octa[(trimethoxysilyl)ethyl]‐POSS (OPS) as cross‐linker and fumed silica as reinforcing filler. The cross‐linked networks, morphologies, thermal and mechanical properties of these novel PDMS composites were examined by attenuated total reflection infrared spectroscopy and the extraction/swelling experiment, scanning electron microscope, thermogravimetric analysis, and universal tensile testing machine, respectively. It was found that both the resistance to thermal degradation and mechanical properties of the novel PDMS composites were improved greatly by adding fumed silica. The prominent improvements in resistance to thermal degradation and mechanical properties of novel PDMS composites were likely attributed to the enhanced interaction of PDMS chains and aggregated particles resulted from synergistic effect between POSS and fumed silica. Meanwhile, we also found that the resistance to thermal degradation of the PDMS composites was lowered slightly with the further increment in loading fumed silica, but their mechanical properties were enhanced. The slight decrease in trend of the resistance to thermal degradation of the novel PDMS composites was likely ascribed to the increasing amount of hydroxyl groups resulting from fumed silica. And the improving mechanical properties were mainly attributed to the increasing interaction of PDMS chains and aggregated particles originated from synergistic effect between POSS and fumed silica. POLYM. COMPOS., 34:1041–1050, 2013. © 2013 Society of Plastics Engineers     

Preparation and characterization of Silicalite‐1/PDMS surface sieving pervaporation membrane for separation of ethanol/water mixture

To improve the pervaporation performance of Silicalite‐1/PDMS composite membrane by adding a small amount of Silicalite‐1 zeolite, novel Silicalite‐1/PDMS surface sieving membranes (SSMs) were prepared by attaching Silicalite‐1 particles on the PDMS membrane surface. The obtained membranes and traditional mixed‐matrix membranes (MMMs) were characterized by SEM, XRD, TGA, FT‐IR, and pervaporation separation of ethanol–water mixture. Effects of Silicalite‐1 particles content, feed temperatures, and feed compositions on the separation performance were discussed. From the cross‐section view SEM images of SSMs, a two‐layer structure was observed. The thickness of the Silicalite‐1 layer was about 300 nm to 2 μm. The TGA analysis indicates that the zeolite concentration in 3 wt % SSM is lower than 10 wt % MMMs. In the ethanol/water pervaporation experiment, the separation factor of Silicalite‐1/PDMS SSMs increased considerably compared with pure PDMS membrane. When the suspensions concentrations of Silicalite‐1 particles reached 3 wt %, the separation factor was about 217% increase over pure PDMS membrane and 52.9% increase over 10 wt % Silicalite‐1/PDMS MMMs. As the ethanol concentration in the feed increases, the separation factor of SSMs increases, whereas permeation flux decreases. At the same time, with increasing operating temperature, the permeation flux of SSMs increased. The stability of SSMs at high temperature is better than the traditional MMMs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42460.     

Hybrid organic inorganic nylon‐6/SiO2 nanocomposites: Transport properties

Organic‐inorganic hybrid membranes of nanosized SiO₂‐filled polyamide composites were prepared via film casting and their transport properties were studied. Gas permeation measurements were performed at room temperature, and the membrane exhibited an increase in membrane permeability performance. In contrast to the performance of traditional dense filled polymer systems, the permeability increased with an increased number of nanosilica particles. The nanocomposites were studied using positron annihilation lifetime spectroscopy (PALS). From the ortho‐positronium (o–Ps) lifetime (τ₃), the size of the local free volume (holes) was estimated. The increase in permeability is ascribed to the additional free volume obtained. This is created by the presence of nanoparticles that alter the PA chain packing. Furthermore, wide angle X‐ray diffraction (WAXD) patterns revealed that the incorporation of silica induced the structural modification of polymer chains by modifying the degree of crystallinity in comparison with the neat polymer. Polym. Eng. Sci. 44:1240–1246, 2004. © 2004 Society of Plastics Engineers.     

Characterization of graft polymerization of fluoroalkyl methacrylate onto PDMS hollow‐fiber membranes and their permselectivity for volatile organic compounds

Polydimethylsiloxane (PDMS) hollow‐fiber membranes grafted with 1H,1H,9H‐hexadecafluorononyl methacrylate (HDFNMA), which is a fluoroalkyl methacrylate, using a ⁶⁰Co irradiation source, were characterized and applied to pervaporation. The PDMS hollow‐fiber membranes were filled with N₂ gas and sealed. The membranes and the HDFNMA solution were then irradiated simultaneously. In the HDFNMA solution, graft polymerization was performed. The degree of grafting of the outside surface of the hollow fiber was greater than that in the inside surface of the hollow fiber. In the grafted PDMS hollow‐fiber membranes, the best separation performance was shown due to the introduced hydrophobic polymer, poly(HDFNMA). The grafted membrane had a microphase‐separated structure, that is, a separated structure of PDMS and graft‐polymerized HDFNMA. The permeability of molecules in the poly(HDFNMA) phase was so low that the diffusion of molecules was prevented in the active layer with many poly(HDFNMA) domains, as the feed solution was introduced through the inside of the hollow fibers and the outside was vacuumed. As the feed solution was introduced through the outside of the hollow fibers and the inside was vacuumed, the diffusion of molecules was not prevented in the active layer with few poly(HDFNMA) domains. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1573–1580, 2003     

硅溶胶填充改性PDMS—PA复合膜

在聚二甲基硅氧烷（PDMS）中填充质量分数为20wt％、25wt％和30wt％的疏水纳米二氧化硅溶胶作为表面皮层,以聚酰胺（PA）为支撑层,制备出改性硅橡胶-聚酰胺（PDMS—PA）复合膜。扫描电镜（SEM）观察发现二氧化硅颗粒均匀分布在PDMS基体中,改性皮层与PA支撑层结合紧密。用5％的乙醇水溶液对改性膜在不同温度下进行渗透汽化测试,发现填充比例为20wt％的膜的分离因子较未改性膜可提升25％,而填充比例为25wt％和30wt％时,膜的分离因子却低于未改性膜。这显示在PDMS中填充某种比例的硅溶胶可改善膜的分离性能。     

Effect of functionalization on dispersion of POSS‐silicone rubber nanocomposites

The nanocomposite of PDMS using functionalized fumed silica and nonreactive POSS as fillers were prepared by blend method in a planetary mixer. Fumed silica was functionalized by aliphatic and aromatic groups to study the filler–filler interactions with the aliphatic and aromatic POSS fillers and consequently their influence on the properties in the PDMS matrix. Transmission electron microscope (TEM) showed a good dispersion in the systems having the silica and POSS fillers with similar modifications. However, aliphatic and aromatic filler combinations showed more aggregated structures. Moreover, aliphatic POSS despite of good dispersion at higher loadings, act as lubricant, which is attributed to the disturbance in the PDMS‐ silica filler interaction and also the filler–filler interaction within fumed silica. There is a decrease in complex viscosity with the functionalization of fumed silica and with the aromatic/aliphatic POSS fillers. The thermal stability of aromatic functionalized fillers improves owing to the thermally stable phenyl groups. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

纳米白炭黑填充硅橡胶复合膜的制备与渗透汽化分离性能

制备以聚酯(PET)为支撑层,白炭黑填充的聚二甲基硅氧烷(PDMS107)为皮层的硅橡胶复合膜,并以乙醇水物系为料液,对比分析白炭黑增强硅橡胶复合膜的渗透蒸发分离性能,分离因子比空白膜有所提高,在乙醇浓度为3%～5%时,分离因子可达16.09,渗透通量为75.39 g/m2·h;测定填充白炭黑硅橡胶复合膜的拉伸强度,结果表明:拉伸强度可达1.828 MPa,相当于空白膜(0.368 MPa)的5倍.     

Ethanol/water mixture pervaporation performance of b‐oriented silicalite‐1 membranes made by gel‐free secondary growth

b‐oriented silicalite‐1 membranes on porous silica supports were synthesized using gel‐free secondary growth. The porous silica supports were made by pressing crushed quartz fibers followed by sintering and polishing, and further modified by slip‐coating three layers of Stöber silica particles (1000, 350, and 50 nm). The b‐oriented seed layers were prepared by rubbing silicalite‐1 particles (2 μm × 0.8 μm × 3 μm along a‐, b‐, and c‐axis, respectively) after depositing a polymeric layer on the support. After silicalite‐1 seed deposition, a final coating of spherical silica particles was applied. Well‐intergrown, μm‐thick, b‐oriented membranes were obtained, which, after calcination, exhibited ethanol permselectivity in ethanol/water mixture pervaporation. At 60°C and for ～5 wt % ethanol/water mixtures, the best membrane exhibited overall pervaporation separation factor of 85 (corresponding to membrane intrinsic selectivity of 7.7) and total flux of 2.1 kg/(m²·h). This performance is comparable to the best performing MFI membranes reported in the literature. © 2015 American Institute of Chemical Engineers AIChE J, 62: 556–563, 2016     

Monolayer and bilayer graphene on polydimethylsiloxane as a composite membrane for gas‐barrier applications

We report the preparation of centimeter‐scale composite membranes formed by monolayer or bilayer graphene and polydimethylsiloxane (PDMS). Graphene was synthesized on copper foils by chemical vapor deposition (CVD), and two methods for transferring the graphene layers from the Cu to the PDMS were tested. The method based on the use of poly(methyl methacrylate) as a sacrificial support layer was more effective in producing membranes with significant gas‐barrier properties, in which the gas permeability values for CO₂ and N₂ were reduced by up to 30% as compared to blank PDMS membranes. Raman spectroscopy maps and atomic force microscopy revealed that, on the microscopic scale, graphene is preserved upon transfer, but the presence of extended defects such as folds and tears still limits further increases in the composite barrier properties. The deleterious effect of such defects is reduced by using more than one graphene layer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45521.     

Pervaporation membranes based on imide‐containing poly(amic acid) and poly(phenylene oxide)

Three imide‐containing poly(amic acids) were synthesized and used for homogeneous and composite membrane preparation. The transport properties of composite membranes consisting of an imide‐containing poly(amic acid) top layer on an asymmetric porous poly(phenylene oxide) support were studied in the pervaporation of aqueous solutions of organic liquids (ethanol, isopropanol, acetone, and ethylacetate) and organic/organic mixtures (ethylacetate/ethanol, methanol/cyclohexane). For most of the aqueous/organic mixtures, the composite membranes exhibited dehydration properties. Dilute aqueous solutions of ethylacetate were an exception. In these solutions, the composite membranes exhibited organophilic properties, high permeability, and selectivity with respect to ethylacetate. In the pervaporation of methanol/cyclohexane mixtures, methanol was removed with very high selectivity. To account for specific features of pervaporation on the composite membranes, the sorption and transport properties of homogeneous membranes prepared from polymers comprising the composite membrane [imide‐containing poly(amic acids) and poly(phenylene oxide)] were studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2361–2368, 2003     

Water–alcohol separation by pervaporation through zeolite‐modified poly(amidesulfonamide)

Pervaporation membranes were fabricated by blending different amount of zeolite NaA or NaX with three types of poly(amidesulfonamide) (PASA). The zeolite‐filled membranes were characterized by IR spectroscopy, SEM, sorption measurements, and wide‐angle X‐ray diffraction. By adding the proper amount of NaA into the polymer casting solutions, the resultant zeolite‐filled membranes exhibited improvement in both selectivity and permeability in the separation of 10% aqueous solutions of ethanol and propan‐1‐ol, as compared with the zeolite free membrane. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1323–1329, 2001     

Polydimethylsiloxane‐modified polyurethane–poly(ɛ‐caprolactone) nanofibrous membranes for waterproof,breathable applications

In this study, we prepared polydimethylsiloxane (PDMS)‐modified polyurethane–poly(?‐caprolactone) nanofibrous membranes with excellent waterproof, breathable performances via an electrospinning technique. Field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and mechanical testing were used to characterize the morphologies and properties of the composite nanofibers. The fiber diameter and porous structure of the membranes were regulated by the adjustment of the temperatures of thermal treatment and the PDMS concentrations. The fibrous membranes obtained at a typical temperature of 70 °C possessed an optimized fibrous structure with a diameter of 514 ± 2 nm, a pore size of 0.55–0.65 µm, and a porosity of 77.7%. The resulting nanofibrous membranes modified with 5 wt % PDMS were endowed with good waterproof properties (water contact angle = 141 ± 1°, hydrostatic pressure = 73.6 kPa) and a high breathability (air permeability rate = 6.57 L m^?2 s^?1, water vapor transmission rate = 9.03 kg m^?2 day^?1). Meanwhile, the membranes exhibited robust mechanical properties with a high strength (breakage stress = 11.7 MPa) and excellent thermal stability. This suggests that they would be promising candidates for waterproof, breathable applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46360.     

Recovery of alcohols from water using polydimethylsiloxane–silica nanocomposite membranes: Characterization and pervaporation performance

Different polydimethylsiloxane (PDMS) nanocomposite membranes were synthesized by incorporating various contents of nanosized silica particles to improve the PDMS pervaporation (PV) performance. A uniform dispersion of silica nanoparticles in the PDMS membranes was obtained. The nanocomposite membranes were characterized morphologically by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that surface roughness increases by incorporating silica, and this decreases absorption of penetrants on the membrane. Swelling studies showed that the presence of silica nanoparticles into the PDMS membranes decreases degree of swelling, which can be attributed to rigidification of the PDMS matrix. Additionally, the results revealed that helium permeability decreases through the nanocomposite membranes, due to the more polymer chains packing. Effects of silica on recovery of isopropanol (IPA) from water mixtures were also investigated. Based on the results, incorporating silica nanoparticles promotes significantly the PDMS membrane selectivity because the polymer chains are rigidified and also the polymer free volume decreases. However, permeation flux decreases as diffusion of the penetrants reduces in the presence of silica nanoparticles within the PDMS membranes. As PV performance depends on operating conditions, effects of feed composition, and temperature were also studied. Moreover, recoveries of IPA, ethanol, and methanol from water mixtures were compared using the PDMS‐silica nanocomposite membranes. The results demonstrated that polarity and solubility of alcohols affect permeation flux and selectivity resulting in the higher permeation flux and selectivity for IPA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Ethanol‐responsive characteristics of polyethersulfone composite membranes blended with poly(N‐isopropylacrylamide) nanogels

Ethanol‐responsive smart membranes with different microstructures are prepared from blends of polyethersulfone (PES) and poly(N‐isopropylacrylamide) (PNIPAM) nanogels by immersion precipitation phase inversion method in a convenient and controllable manner. The introduction of PNIPAM nanogels forms the microporous structures on the surface of the top skin layer and on the pore walls of the finger‐like porous sublayer of membranes. The ethanol‐responsive characteristics of the proposed PES composite membranes are systematically investigated. With increasing ethanol concentration in the range from 0 to 15 wt %, the trans‐membrane flux of ethanol solution increases. The microstructures and the resultant ethanol‐responsive characteristics of the composite membranes can be regulated by the content of PNIPAM nanogels blended in the membranes. The more the content of PNIPAM nanogels blended in the membranes, the more the number of the submicron pores is, and thus the better the ethanol‐responsive characteristics of the composite membranes. The proposed ethanol‐responsive smart membranes are expected to be combined with the traditional pervaporation membranes as a smart vavle to achieve continuous and highly efficient ethanol production during the biological fermentation. The preparation technique and results in this study provide valuable guidance for further design and the industrial‐scale fabrication of novel composite membranes for application in ethanol separation systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41032.     

Polyhedral oligomeric silsesquioxane/silica/polydimethylsiloxane rubber composites with enhanced mechanical and thermal properties

Composites of polydimethylsiloxane (PDMS) rubber modified by three kinds of polyhedral oligomeric silsesquioxanes (POSSs) as well as fumed silica were prepared through solution blending and then open two‐roll mill blending with curing agent. Subsequently, the influences of POSS on mechanical and thermal properties of the resulting composites were investigated in detail. The addition of POSS significantly enhanced the tensile strength and elongation at break of the composite but lowered the tensile modulus, which could be ascribed to the interruption of silica–silica and silica–PDMS interactions. Octamethylsilsesquioxane (OMS)/silica/PDMS and octaphenylsilsesquioxane (OPS)/silica/PDMS composites did not show desirable mechanical and thermal properties. Nevertheless, heptaphenylvinylsilsesquioxane (VPS)/silica/PDMS composite with 5 wt % VPS exhibited enhanced glass transition temperature (T_g), mechanical properties, and thermal stability. Further studies revealed that more VPS unfavorably affected properties of the composite. Scanning electron microscope and X‐ray diffraction demonstrated that owing to the grafting reaction, 5 wt % VPS in the rubber matrix could form microcrystal domains the most effectively. Thus, the improved mechanical properties and thermal stability just resulted from the the formation of microcrystal domains and the increase in stiffness of PDMS chains because of the graft of VPS onto PDMS. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42173.