Fluoride Substrates Research Articles

Hydrophobic SiO2 nanoparticle‐induced polyvinylidene fluoride crystal phase inversion to enhance permeability of thin film composite membrane

ABSTRACTThin film composite (TFC) membrane can get rid of small molecular contaminants and salts with a very high efficiency, thus exhibiting promising potential for addressing the emerging problem of a clean water shortage. In this work, a new type of TFC membrane was prepared by interfacial polymerization of two monomers (MPD and TMC) on surface of SiO2/polyvinylidene fluoride (PVDF) substrate. The maximum flux of 3.16 L m−2 h−1 Bar−1 was achieved for the optimized hydrophobic SiO2 nanoparticles well dispersed in PVDF substrate, which is 2.6 times higher than that of 1.21 L m−2 h−1 Bar−1 for the commercial cellulose triacetate reverse osmosis membrane. The improved performance of TFC membrane could be attributed to the higher compaction resistance of SiO2/PVDF substrate. Further analysis revealed that PVDF crystal phase inversion induced by superhydrophobic SiO2 nanoparticles obviously enhanced the intramolecular and intermolecular hydrogen bonds between PVDF polymer molecules. Additionally, the narrower finger‐like pore size and thicker pore wall of SiO2/PVDF substrate also played significant roles in enhancing the compaction resistance of PVDF membrane. This work also provides a proof‐of‐concept demonstration of high permeability substrates for effective flux enhancement of TFC membranes. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48204.

Confining migration of amine monomer during interfacial polymerization for constructing thin-film composite forward osmosis membrane with low fouling propensity

Forward osmosis (FO) membrane is paramount to the progress and implementation of FO process. However, typical FO membranes are confronted with many unsatisfactory issues, including the low water flux, high fouling propensity and the poor long-term operation stability in most cases, which confines the practical application of FO process to a large extent. This study proposes a feasible way to mitigate the internal concentration polarization (ICP) and optimize the polyamide (PA) layer structure of as-fabricated thin-film composite forward osmosis (TFC-FO) membranes simultaneously by incorporating phosphorylated titanium dioxide (p-TiO2) in polyvinylidene fluoride (PVDF) substrate. P-TiO2 nanoparticles with abundant phosphate groups were prepared through a chemical absorption approach followed by the thermal post-treatment. Superior water flux and the better antifouling properties of the resultant PVDF/p-TiO2 TFC-FO membrane was achieved, taking advantage of the more compact and smoother PA layer as a result of the confined migration of amine monomer during interfacial polymerization (IP). In addition, effects of p-TiO2 content on morphological changes and physicochemical properties of modified substrates and the construction of top PA layer are studied and elaborated systemically via many characterizations as well as the permeation tests. As a result, the water flux decline of PVDF/p-TiO2 TFC membrane is much lower (16.0%) than that (∼31.3%) of the pristine TFC membrane, in the long-term (20 h) dynamic fouling test against 500 ppm humic acid (HA) solution. Therefore, PVDF/p-TiO2 TFC-FO membrane with improved water flux and low fouling tendency is beneficial for wastewater treatment and desalination process, especially for the treatment of brackish water with high fouling tendency or under harsh conditions.

Synthesis of ZIF-8 based composite hollow fiber membrane with a dense skin layer for facilitated biogas upgrading in gas-liquid membrane contactor

Gas-liquid membrane contactor (GLMC) has been regarded as a promising alternative to conventional contacting processes for CO2 absorption. In this work, a composite hollow fiber (HF) membrane with an aminosilane-modified zeolitic imidazolate framework-8 (mZIF-8) based dense skin layer was designed and synthesized for high-efficiency biogas upgrading in the GLMC process, by dispersing mZIF-8 nanocrystals into poly(dimethylsiloxane) matrix and then depositing on a porous polyvinylidene fluoride (PVDF) substrate. (3-aminopropyl)triethoxysilane was introduced to modify the ZIF-8 nanocrystals, thereby enabling the chemical bonding with PDMS chains for avoiding interfacial voids and further enhancing hydrophobicity. Compared with the control membrane, the newly developed mZIF-8 based composite membrane with a dense skin exhibited competitive hydrophobicity with a contact angle of 130°, ensuring its anti-wetting ability. It exhibited an enhanced biogas upgrading performance with the absorption fluxes of 2.3 and 3.8 × 10−3 mol m−2·s−1 using water and 1 M monoethanolamine (MEA) as absorbents, respectively (liquid velocity = 0.25 m s−1). In particular, a comparable selectivity of CO2/CH4 with the value of ∼20 was achieved by using MEA as absorbent in the GLMC process. A robust long-term stability of the mZIF-8 based composite HF membrane was also achieved in a 15-day operation. This work offers a new perspective for promoting CO2 mass transfer with mZIF-8 based composite HF membranes, thereby improving the biogas upgrading performance in GLMC applications.

Native Nano-electrospray Differential Mobility Analyzer (nES GEMMA) Enables Size Selection of Liposomal Nanocarriers Combined with Subsequent Direct Spectroscopic Analysis.

Gas-phase electrophoresis employing a nano-electrospray differential mobility analyzer (nES DMA), aka gas-phase electrophoretic mobility molecular analyzer (nES GEMMA), enables nanoparticle separation in the gas-phase according to their surface-dry diameter with number-based concentration detection. Moreover, particles in the nanometer size range can be collected after size selection on supporting materials. It has been shown by subsequent analyses employing orthogonal methods, for instance, microscopic or antibody-based techniques, that the surface integrity of collected analytes remains intact. Additionally, native nES GEMMA demonstrated its applicability for liposome characterization. Liposomes are nanometer-sized, biodegradable, and rather labile carriers (nanoobjects) consisting of a lipid bilayer encapsulating an aqueous lumen. In nutritional and pharmaceutical applications, these vesicles allow shielded, targeted transport and sustained release of bioactive cargo material. To date, cargo quantification is based on bulk measurements after bilayer rupture. In this context, we now compare capillary electrophoresis and spectroscopic characterization of vesicles in solution (bulk measurements) to the possibility of spectroscopic investigation of individual, size-separated/collected liposomes after nES GEMMA. Surface-dried, size-selected vesicles were collected intact on calcium fluoride (CaF2) substrates and zinc selenide (ZnSe) prisms, respectively, for subsequent spectroscopic investigation. Our proof-of-principle study demonstrates that the off-line hyphenation of gas-phase electrophoresis and confocal Raman spectroscopy allows detection of isolated, nanometer-sized soft material/objects. Additionally, atomic force microscopy-infrared spectroscopy (AFM-IR) as an advanced spectroscopic system was employed to access molecule-specific information with nanoscale lateral resolution. The off-line hyphenation of nES GEMMA and AFM-IR is introduced to enable chemical imaging of single, i.e., individual, liposome particles.

Gradient nanoporous phenolics filled in macroporous substrates for highly permeable ultrafiltration

Highly permeable and cost-affordable membranes are highly desired in separation processes. Herein, such membranes are produced by designing gradient phenolics inside the macropores of polyvinylidene fluoride (PVDF) substrates. Solutions consisting of resol, poly(ethylene oxide)/poly(propylene oxide) copolymer and ZnCl2 are infiltrated into the macropores of PVDF. Phenolic nanoparticles and nanopores with increasing sizes are formed across the membrane thickness after fast solvent evaporation, ZnCl2-facilitated resol polymerization and acid soaking. The prepared gradient phenolic@PVDF membranes exhibit a permeance up to 1315 L/(m2 h bar), which is several times higher than that of other membranes with similar rejections to bovine serum albumin (91%) and lysozyme (71%). Moreover, the membranes are robust enough to withstand a pressure of at least 12.0 bar due to the interlaced structures of phenolics and PVDF. We demonstrate that thus-produced membranes can efficiently separate and concentrate gold nanoparticles with sizes down to 5 nm. This work suggests a new strategy for rational design of gradient porosities in macroporous substrates to produce robust membranes with high permeances and tight rejections.

Enhanced fluorescence in nano-multiferroic fluoride substrates attached with silver nanoparticles

Nano-multiferroic BaMF4 (M = Mn, Mg) are synthesized in pure-phase by hydrothermal method as fluoride substrates. The Mn2+ stokes emission and the Tm3+ anti-stokes emission are shown in BaMnF4 and BaMgF4: Yb3+, Tm3+ nanocrystals under 465 and 975 nm excitation respectively. By depositing silver nanoparticles with the AgNO3/BaMF4 ratio of 0.01:1, the 347&365, 455, 480, 640 and 700 nm emissions of Tm3+ are enhanced 27, 21, 6, 3 and 2 times respectively, also the 700 nm emission of Mn2+ is enhanced 2 time. The above mentioned enhancement factor versus emission wavelength is accordance with the nano-silver absorption wavelength, indicating the surface plasmon coupled emission (SPCE) inducted by excited luminescent ions.

Study of damage structure formation on aluminum film targets by picosecond soft X-ray laser ablation around threshold region

We irradiated soft X-ray laser pulses onto aluminum film targets, which were evaporated on silicon and lithium fluoride substrates. After laser irradiation, we observed irradiated surfaces and confirmed damage with nanometer scale-modified structures. These damage structures were the same as those formed on the aluminum bulk surface. In this article, we discuss a possibility of the growth process of damage structures on the Al surface based on the experimental results.

Construction of SiO2@MWNTs incorporated PVDF substrate for reducing internal concentration polarization in forward osmosis

This work provides a facile and effective way of incorporating SiO2@MWNTs in polyvinylidene fluoride (PVDF) substrate to alleviate the internal concentration polarization (ICP) impact of the resultant thin film composite forward osmosis (TFC-FO) membranes for the first time. The in-situ decoration of multi-walled carbon nanotubes (MWNTs) using tetraethyl orthosilicate (TEOS) as precursor was conducted, resulting in improved hydrophilicity and the excellent dispersion of synthesized SiO2@MWNTs in PVDF membrane substrates accordingly. Effects of the SiO2@MWNTs concentration on the morphologies and properties of the modified substrates, and further impact on the polyamide (PA) layer structure are investigated via various characterizations. Besides, the intrinsic separation properties and forward osmosis performance of resultant TFC-FO membranes are also systemically studied. In comparison with the control TFC membrane, SiO2@MWNT-modified TFC membranes exhibit higher water fluxes with the enhanced membrane selectivity, as indicated by the decreased JS/JV values (from 1.10 to 0.19 g/L). This work therefore presents an alternative approach to prepare TFC-FO membranes with enhanced water flux as well as increased selectivity.

Ultra-thin high-efficiency mid-infrared transmissive Huygens meta-optics

The mid-infrared (mid-IR) is a strategically important band for numerous applications ranging from night vision to biochemical sensing. Here we theoretically analyzed and experimentally realized a Huygens metasurface platform capable of fulfilling a diverse cross-section of optical functions in the mid-IR. The meta-optical elements were constructed using high-index chalcogenide films deposited on fluoride substrates: the choices of wide-band transparent materials allow the design to be scaled across a broad infrared spectrum. Capitalizing on a two-component Huygens’ meta-atom design, the meta-optical devices feature an ultra-thin profile (λ0/8 in thickness) and measured optical efficiencies up to 75% in transmissive mode for linearly polarized light, representing major improvements over state-of-the-art. We have also demonstrated mid-IR transmissive meta-lenses with diffraction-limited focusing and imaging performance. The projected size, weight and power advantages, coupled with the manufacturing scalability leveraging standard microfabrication technologies, make the Huygens meta-optical devices promising for next-generation mid-IR system applications.

Design and optimization of As2S5 chalcogenide channel waveguide for coherent mid-infrared supercontinuum generation

We numerically demonstrate mid-infrared supercontinuum generation in dispersion-engineered chalcogenide glass channel waveguide. The proposed ridge waveguide consists of arsenic pentasulfide (As2S5) strip deposited on magnesium fluoride (MgF2) substrate and air acting as an upper cladding. The structure parameters are calculated and optimized by using the fully vectorial finite-difference in the frequency-domain (FDFD) method Results indicates that the proposed waveguide exhibits an all normal dispersion (ANDi) profile over a wide spectral range with a zero dispersion wavelength (ZDW) around 2μm. By solving the generalized nonlinear Schrödinger equation, we demonstrate supercontinuum generation extending from the near infrared to the mid infrared region. Indeed, a broad and perfectly coherent ultra-flat supercontinuum spectrum spanning the region from 700 to 5200nm is successfully generated by using a 25kW peak power 100fs input pulse pumped at 2.5μm, in a waveguide of 5mm length.

Acyl Fluorides as Efficient Electrophiles for the Copper-Catalyzed Boroacylation of Allenes

The copper-catalyzed reaction of allenes with bis(pinacolato)diboron and acyl electrophiles is reported. In this transformation, acyl fluorides have been proven to be more efficient coupling partners than their chloride or carboxylate analogues. The optimized reaction conditions employed were shown to be compatible with a range of commonly used functional groups, thereby allowing the formation of a library of β-boryl β,γ-unsaturated ketones by varying the nature of the allene and acyl fluoride substrates.

Determination of stress-coefficient of magnetoelastic anisotropy in flexible amorphous CoFeB film by anisotropic magnetoresistance

Flexible magnetic devices are one of the indispensable flexible devices. However, the deformation of the magnetic devices will change the magnetic anisotropy of magnetic materials due to magnetoelastic anisotropy, which will decrease the performance of the devices. Therefore, it is essential to determine the stress-coefficient of magnetoelastic anisotropy in magnetic materials. Here, the magnetic anisotropy constants of an amorphous CoFeB film on a flexible polyvinylidene fluoride (PVDF) substrate in different stress states were quantitatively investigated by anisotropic magnetoresistance (AMR). The enhanced magnetic anisotropy of the CoFeB film at reduced temperature is due to magnetoelastic anisotropy induced by anisotropic thermal expansion of the PVDF substrate. Through fitting the AMR curves under variant fields in different stress states, the stress-coefficient of magnetoelastic anisotropy in the amorphous CoFeB film is obtained to be 170.7 × 103 erg cm−3 GPa−1.

Superoleophobic surface modification for robust membrane distillation performance

Inspired by mussels’ byssus with remarkable adhesive power that is neither degraded nor deformed in the marine environment, dopamine coating has emerged as an option for membrane surface modification. With its many advantages, direct-contact membrane distillation (DCMD) appears to hold potential for the recovery of high quality water from produced water. However, membrane fouling and pore wetting are challenging issues of long-term DCMD operations due to the presence of oils and surfactants in these waters. Hence, it is paramount to develop robust membranes with anti-fouling and anti-wetting properties for effective produced water treatment. In this study, we fabricated a composite hollow fiber membrane by single-step co-deposition of polydopamine (PDA)/polyethylenimine (PEI) onto the outer surface of a commercial hydrophobic polyvinylidene fluoride (PVDF) substrate. The successful co-deposition was verified using different characterization techniques. The composite membrane exhibited Janus wettability (Janus membranes have opposing properties at an interface) with its modified outer surface being in-air hydrophilic/underwater superoleophobic for preventing organics adhesion while insuring that unmodified pores beneath the surface remained hydrophobic for vapor transport. The anti-fouling and anti-wetting properties of the modified membrane were investigated via DCMD experiments by feeding a series of low surface tension solutions. In comparison to the pristine PVDF membrane, the modified membrane exhibited promising wetting resistant property against different surfactant types and excellent fouling resistant property against nonionic and cationic surfactants. Moreover, the modified membrane presented a promising long-term performance when feeding a cationic surfactant-stabilized petroleum-in-water emulsion mimicking produced water, during which a stable flux and excellent permeate quality were maintained throughout 7 days of operation. The efficacious combined effects of a hydration layer and protonated amine-functional groups on the PDA/PEI grafted layer could prevent membrane fouling and pore wetting. The results suggest that the mussel-inspired composite PVDF membrane could potentially be used for long-term water recovery from produced water via DCMD.

Improved performance of thin-film composite membrane with PVDF/PFSA substrate for forward osmosis process

In this work, a small amount of hydrophilic perfluorosulfonic acid (PFSA) is incorporated into the polyvinylidene fluoride (PVDF) substrate to develop the high-performance thin-film composite (TFC) membrane for forward osmosis applications. Because of the hydrophilicity and excellent compatibility with PVDF, PFSA not only significantly improves the wettability of the modified membrane substrate, but also well optimizes the pore size by changing the membrane morphology of PVDF/PFSA substrate. These two factors effectively mitigate the water transport resistance and favor the better formation of the polyamide (PA) layer during the interfacial polymerization, thus improving both the water flux and membrane selectivity of the resultant TFC membranes simultaneously. Effects of the PFSA concentration on the overall properties of the modified substrates and corresponding PVDF/PFSA TFC membranes are systematically investigated via various characterizations. Consequently, the PVDF/PFSA TFC membrane achieves a best water flux (JV) of 54.4 LMH and a reverse salt flux (JS) of 10.9 gMH in AL-DS mode, and a JV of 27.0 LMH with JS of 8.4 gMH in AL-FS mode using deionized (DI) water and 1M NaCl aqueous solution as the feed and draw solutions respectively. This work may provide a new orientation in developing TFC membranes on the hydrophobic substrate with its intrinsic advantages maximized.

Fluoride glass-based surface plasmon resonance sensor in infrared region: performance evaluation

Excitation parameters shown by a plasmonic structure are different in the near infrared (NIR) region as compared with that of the visible region. Fluoride-based glass materials show high transparency in the infrared (IR) region, which plays an important role from an experimental point of view. In order to explore optical sensors based on a heavy metal doped fluoride substrate, performance of a surface plasmon resonance (SPR) based sensor having HBL glass as the substrate material to couple direct light in the NIR region is discussed. The proposed sensor’s structure is based on Kretschmann configuration with gold (Au) deposited on an HBL glass substrate. Experimental refractive index values of water samples containing different NaCl concentrations are taken as the sensing medium for design and modelling of the sensor. The analysis was carried out for some different samples also. An HBL-based SPR sensor is able to provide significantly enhanced sensing performance compared with other conventional glass substrates operated in different spectral regions (SF10 in visible and SiO2 in NIR). The study paves the way for designing SPR sensor probes based on fluoride optical fibers in the IR region for different biological and chemical applications.

A specific spectral signature of serum and plasma-derived extracellular vesicles for cancer screening

In cancer, extracellular vesicles (EV) contribute to tumor progression by regulating local and systemic effects. Being released into body fluids, EV may be used in nanomedicine as a valuable source for diagnostic biomarkers. In this work, infrared and Raman spectroscopy were used for comprehensive comparative analysis of cancer versus non-cancer EV and patient screening. Two different EV fractions enriched in exosomes and microvesicles were isolated by differential centrifugation from serum and plasma of cancer and non-cancer patients and from serum and plasma of a healthy donor. The EV fractions were then subjected to drop-coating deposition and drying on calcium fluoride substrates. Reduction of alpha-helix-rich proteins and enhancement of beta-sheet-rich proteins as a cancer-specific blood EV signature was determined, and subsequently this feature was applied for a pilot study aiming to detect prostate cancer in a test cohort of patients with high-grade prostate carcinoma and benign hypoplasia.

SNSPDs on a Magnesium Fluoride Substrate for High System Efficiency and Ultra-Wide Band

We developed a superconducting nanowire single-photon detector (SNSPD) based on a magnesium fluoride (MgF2) substrate with the aim of producing a high system efficiency (SE) and wideband. The proposed SNSPD on a MgF2 substrate could simultaneously provide: 1) low lattice mismatching of the lattice constant between MgF2and superconducting niobium nitride (NbN) films; 2) a low reflection loss ( ${n}=1.37$ ); and 3) a wide transmission band (0.2– $7~\mu \text{m}$ ). Based on the designed structure, a simulation indicated that the maximum absorption efficiency of the designed SNSPD on the MgF2 substrate is 97%. An SE of 46% at 1064 nm was measured without maximizing the polarization. The SNSPD on the MgF2 substrate was examined in a long-haul laser ranging application over four months, expanding the possibilities for application such as for laser ranging of space debris.

Deposition of conductive polythiophene film on a piezoelectric substrate: effect of corona poling and nano-inclusions

Electrically conductive polythiophene (PTh) nanoparticles were deposited on poly(vinylidene fluoride) (PVDF) substrate by a facile and rapid chemical oxidative deposition in an organic solvent system. The process afforded conductivity to a piezoelectric PVDF film through deposition of conductive layer on the surface in 12 min. The produced final product was transparent, flexible, conductive and piezoelectric and a good candidate to be used in organic electronics especially as a sensor and capacitor. The effect of corona poling and inclusion of nanoparticles such as nanoclay and carbon nanotubes on electrical conductivity of piezoelectric substrates were studied with high precision. Corona poling modification of substrate made it susceptible for deposition of nanoparticles on surface and meanwhile induced higher orientation and crystallinity which led to higher capacitance. Electrical conductivity of the modified films, without extra doping, was in the order of 10−2 S/cm. Capacitance of the films was measured and the results were promising applications in flexible electronics. Surface morphology, average size, size distribution and samples surface roughness were measured by scanning electron microscopy and atomic force microscopy. It was observed that PTh surface morphology is an aggregation of globules with narrow size distribution ranging from 20 to 100 nm. EDX Technique was used to study the surface composition. The final product may find very promising applications in a wide range of organic electronics.

Characterization of different substrates for Raman spectroscopic imaging of eukaryotic cells

For Raman spectroscopic analyses of the cells and other biological samples, the choice of the right substrate material is very important to avoid loss of information in characteristic spectral features because of competing background signals. In the current study, Raman spectroscopy is used to characterize several potential Raman substrates. Raman vibrational bands of the substrate material are discussed. The surface topography is analyzed by atomic force microscopy, and the root mean square surface roughness values are reported. Biocompatibility of the substrates is tested with Hep G2 cells evaluating cellular morphology as well as live/dead staining. Calcium fluoride, silicon, fused silica, borofloat glass, and silicon nitride membranes support cell growth and adherence. Silicon, borofloat glass, and fused silica give rise to Raman signals in the region of interest. Calcium fluoride substrate (UV grade) is suitable for Raman spectroscopic investigation of living cells. Nickel foil is suitable substrate for Raman spectroscopic investigation but cellular adherence and viability depend on the quality of the foil. Silicon nitride membranes coated with nickel chrome is a suitable Raman substrate in closed microfluidic systems. Copyright © 2016 John Wiley & Sons, Ltd.

Mussel-Inspired Hybrid Coatings that Transform Membrane Hydrophobicity into High Hydrophilicity and Underwater Superoleophobicity for Oil-in-Water Emulsion Separation

We first report here mussel-inspired, hybrid coatings formed in a facile manner via simultaneous polymerization of mussel-inspired dopamine and hydrolysis of commercial tetraethoxysilane in a single-step process. The hybrid coatings can firmly adhered on hydrophobic polyvinylidene fluoride (PVDF) substrate, and the hydrophilicity of the coating can be tuned by adjusting silane concentration. The reason for the changed hydrophilicity of the coating is disclosed by a series of characterization, and was applied to rationally design optimized hybrid coatings that transform commercial PVDF microfiltration (MF) membrane hydrophobicity into high hydrophilicity with excellent water permeability and underwater superoleophobicity for oil-in-water emulsion separation. The PVDF MF membrane decorated with optimized coatings has ultrahigh water flux (8606 L m(-2) h(-1) only under 0.9 bar, which is 34 times higher than that of pristine membrane), highly efficient oil-in-water emulsion separation ability at atmospheric pressure (filtrate flux of 140 L m(-2) h(-1)) and excellent antifouling performance. More importantly, these membranes are extremely stable as underwater superoleophobicity are maintained, even after rigorous washings or cryogenic bending, disclosing outstanding stability. The simplicity and versatility of this novel mussel-inspired one-step strategy may bridge the material-induced technology gap between academia and industry, which makes it promising for eco-friendly applications.