Roughness and hydrophobicity studies of nanofiltration membranes using different modes of AFM

Exploring the Challenges of Characterising Surface Topography of Polymer-Nanoparticle Composites

Nanomechanical testing plays a crucial role in evaluating surfaces containing nanoparticles. Testing verifies surface performance concerning their intended function and detects any potential shortcomings in operational standards. Recognising that nanostructured surfaces are not always straightforward or uniform is essential. The chemical composition and morphology of these surfaces determine the end-point functionality. This can entail a layered surface using materials in contrast to each other that may require further modification after nanomechanical testing to pass performance and quality standards. Nanomechanical analysis of a structured surface consisting of a poly-methyl oxazoline film base functionalised with colloidal gold nanoparticles was demonstrated using an atomic force microscope (AFM). AFM nanomechanical testing investigated the overall substrate architecture's topographical, friction, adhesion, and wear parameters. Limitations towards its potential operation as a biomaterial were also addressed. This was demonstrated by using the AFM cantilever to apply various forces and break the bonds between the polymer film and gold nanoparticles. The AFM instrument offers an insight to the behaviour of low-modulus surface against a higher-modulus nanoparticle. This paper details the bonding and reaction limitations between these materials on the application of an externally applied force. The application of this interaction is highly scrutinised to highlight the potential limitations of a functionalised surface. These findings highlight the importance of conducting comprehensive nanomechanical testing to address concerns related to fabricating intricate biomaterial surfaces featuring nanostructures.

Development of superhydrophobic and superoleophilic CNT and BNNT coated copper meshes for oil/water separation

In this research, chemical vapor deposition (CVD) method was used to synthesize boron nitride nanotube (BNNT) powder. This method involves heating multi-walled carbon nanotube (MWCNT) and boric acid in the presence of ammonia gas up to 1000 °C. Then MWCNT and synthetic BNNT were coated on the copper mesh via dip-coating method separately to prepare nano-structured membranes for efficient oil/water separation. Various analyzes were performed to identify the synthetic BNNT properties (X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and prepared coated membranes (FESEM, atomic force microscopy (AFM), water contact angle (WCA), oil contact angle (OCA) and oil/water separation process). Water and oil contact angle analyzes showed the super-oleophilic properties of both membranes with the underwater OCA of about 128°. For the separation process, a dead-end filtration setup was used, and free oil water mixture and o/w emulsion were prepared. So, in the separation process water was retained and decalin passed through both prepared membranes. The flux of CNT coated membrane was about 458 L m2 h-1, while this amount was 1834 L m2 h-1 for BNNT coated membrane and 99% separation efficiency was achieved by both of them. This four-fold increase in flux is due to the fact that the inner diameter of boron nitride nanotubes synthesized is four times larger than the inner diameter of MWCNT.

Fabrication of a sustainable superhydrophobic surface of Ag-NPs@SA on copper alloy for corrosion resistance, photocatalysis, and simulated distribution of Ag atoms

Artificial superhydrophobic surfaces that do not absorb water, like the lotus leaf, show tremendous promise in numerous applications. However, superhydrophobic surfaces are rarely used because of their low stability and endurance. A stable organic superhydrophobic surface (SHS) composed of novel morphology Ag-nanoparticles (NPs) has been fabricated on a copper alloy via etching, immersion, spraying, and annealing treatment, along with a static water contact angle (WCA) of 158 ± 1° and sliding angle (SA) less than 2°. The surface texture, composition, and morphology of the substrate surfaces were explored by using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, and DFT-based Ag atom distribution. The anti-corrosion study of non-coated and Ag-NP-coated copper alloy was undertaken using electrochemical impedance spectroscopy. Ag-NPs +SA@SHS enhanced the corrosion resistance as compared with bare Cu alloy. The water droplet rolled down the coated Cu alloy, removed the chalk powder from the surface, and indicated an excellent self-cleaning function. Photodegradation of Congo red (CR) and methylene blue (MB) dye samples was assessed by measuring the absorbance through UV-Visible spectrophotometry, where the Ag-NPs coated on the copper alloy were used as a catalyst. The performance of the SHS@Ag-NPs in the aqueous solution was 99.31% and 98.12% for industrial pollutants (CR and MB), with degradation rates of 5.81 × 10-2 s-1 and 5.89 × 10-2 s-1, respectively. These findings demonstrated a simple, rapid, and low-energy fabrication technique for SHS@Ag-NPs. This research reveals a valuable approach for the fabrication of SHS@Ag-NPs on various substrates to extend the superhydrophobic surfaces with ultra-fast self-healing properties, for outdoor applications such as anti-corrosion, for an innovative approach for the remediation of polluted water treatment, and for industrial applications.

Fabrication of antibacterial polydopamine-carboxymethyl cellulose-Ag nanoparticle hydrogel coating for urinary catheters

Urinary tract infections caused by catheter insertion are prevalent in hospital clinics, which can induce serious complications such as bacteriuria and sepsis, and even lead to patient death. The disposable catheters currently used in clinical practice suffer from poor biocompatibility and high infection rate. In this paper, we developed a polydopamine (PDA)-carboxymethylcellulose (CMC)-Ag nanoparticles (AgNPs) coating with both good antibacterial and anti-adhesion properties to bacteria on the surfaces of a disposable medical latex catheter by a simple dipping method. The antibacterial efficiency of the coated catheters against Gram-negative E. coli and Gram-positive S. aureus bacteria was evaluated with both inhibition zone tests and fluorescence microscopy. Compared with the untreated catheter, the PDA-CMC-AgNPs coated catheters showed both good antibacterial and anti-adhesion properties to bacteria, which inhibited the adhesion of live bacteria and dead bacteria by 99.0% and 86.6%, respectively. This novel PDA-CMC-AgNPs composite hydrogel coating has great potential in applications in catheters and other biomedical devices to reduce infections.

Application of Optical Coherence Tomography (OCT) to Analyze Membrane Fouling under Intermittent Operation

There is increasing interest in membrane systems powered by renewable energy sources, including solar and wind, that are suitable for decentralized water supply in islands and remote regions. These membrane systems are often operated intermittently with extended shutdown periods to minimize the capacity of the energy storage devices. However, relatively little information is available on the effect of intermittent operation on membrane fouling. In this work, the fouling of pressurized membranes under intermittent operation was investigated using an approach based on optical coherence tomography (OCT), which allows non-destructive and non-invasive examination of membrane fouling. In reverse osmosis (RO), intermittently operated membranes were investigated by OCT-based characterization. Several model foulants such as NaCl and humic acids were used, as well as real seawater. The cross-sectional OCT images of the fouling were visualized as a three-dimensional volume using Image J. The OCT images were used to quantitatively measure the thickness of foulants on the membrane surfaces under different operating conditions. The results showed that intermittent operation retarded the flux decrease due to fouling compared to continuous operation. The OCT analysis showed that the foulant thickness was significantly reduced by the intermittent operation. The decrease in foulant layer thickness was found to occur when the RO process was restarted in intermittent operation.

Single Solution-Phase Synthesis of Charged Covalent Organic Framework Nanosheets with High Volume Yield

Covalent organic framework nanosheets (COF-NSs) are emerging building blocks for functional materials, and their scalable fabrication is highly desirable. Current synthetic methods suffer from low volume yields resulting from confined on-surface/at-interface growth space and complex multiple-phase synthesis systems. Herein, we report the synthesis of charged COF-NSs in open space using a single-phase organic solution system, achieving magnitudes higher volume yields of up to 18.7 mg mL^-1 . Charge-induced electrostatic repulsion forces enable in-plane anisotropic secondary growth from initial discrete and disordered polymers into large and crystalline COF-NSs. The charged COF-NS colloidal suspensions are cast into thin and compact proton exchange membranes (PEMs) with lamellar morphology and oriented crystallinity, displaying outstanding proton conductivity, negligible dimensional swelling, and good H₂ /O₂ fuel cell performance.

Multi-Step Extracellular Matrix Remodelling and Stiffening in the Development of Idiopathic Pulmonary Fibrosis

The extracellular matrix (ECM) of the lung is a filamentous network composed mainly of collagens, elastin, and proteoglycans that provides structural and physical support to its populating cells. Proliferation, migration and overall behaviour of those cells is greatly determined by micromechanical queues provided by the ECM. Lung fibrosis displays an aberrant increased deposition of ECM which likely changes filament organization and stiffens the ECM, thus upregulating the profibrotic profile of pulmonary cells. We have previously used AFM to assess changes in the Young's Modulus (E) of the ECM in the lung. Here, we perform further ECM topographical, mechanical and viscoelastic analysis at the micro- and nano-scale throughout fibrosis development. Furthermore, we provide nanoscale correlations between topographical and elastic properties of the ECM fibres. Firstly, we identify a softening of the ECM after rats are instilled with media associated with recovery of mechanical homeostasis, which is hindered in bleomycin-instilled lungs. Moreover, we find opposite correlations between fibre stiffness and roughness in PBS- vs bleomycin-treated lung. Our findings suggest that changes in ECM nanoscale organization take place at different stages of fibrosis, with the potential to help identify pharmacological targets to hinder its progression.

Fractal Analysis on Surface Topography of Thin Films: A Review

The topographies of various surfaces have been studied in many fields due to the significant influence that surfaces have on the practical performance of a given sample. A comprehensive evaluation requires the assistance of fractal analysis, which is of significant importance for modern science and technology. Due to the deep insights of fractal theory, fractal analysis on surface topographies has been widely applied and recommended. In this paper, the remarkable uprising in recent decades of fractal analysis on the surfaces of thin films, an essential domain of surface engineering, is reviewed. By summarizing the methods used to calculate fractal dimension and the deposition techniques of thin films, the results and trends of fractal analysis are associated with the microstructure, deposition parameters, etc. and this contributes profoundly to exploring the mechanism of film growth under different conditions. Choosing appropriate methods of surface characterization and calculation methods to study diverse surfaces is the main challenge of current research on thin film surface topography by using fractal theory. Prospective developing trends are proposed based on the data extraction and statistics of the published literature in this field.

Soft Surface Nanostructure with Semi-Free Polyionic Components for Sustainable Antimicrobial Plastic

Surface antimicrobial materials are of interest as they can combat the critical threat of microbial contamination without contributing to issues of environmental contamination and the development drug resistance. Most nanostructured surfaces are prepared by post fabrication modifications and actively release antimicrobial agents. These properties limit the potential applications of nanostructured materials on flexible surfaces. Here, we report on an easily synthesized plastic material with inherent antimicrobial activity, demonstrating excellent microbicidal properties against common bacteria and fungus. The plastic material did not release antimicrobial components as they were anchored to the polymer chains via strong covalent bonds. Time-kill kinetics studies have shown that bactericidal effects take place when bacteria come into contact with a material for a prolonged period, resulting in the deformation and rupture of bacteria cells. A scanning probe microscopy analysis revealed soft nanostructures on the submicron scale, for which the formation is thought to occur via surface phase separation. These soft nanostructures allow for polyionic antimicrobial components to be present on the surface, where they freely interact with and kill microbes. Overall, the new green and sustainable plastic is easily synthesized and demonstrates inherent and long-lasting activity without toxic chemical leaching.

Cacao Pod Husk Extract Phenolic Nanopowder-Impregnated Cellulose Acetate Matrix for Biofouling Control in Membranes

The ultrafiltration membrane process is widely used for fruit juice clarification, yet the occurring of fouling promotes a decline in process efficiency. To reduce the fouling potential in the membrane application in food processing, the use of natural phenolic compounds extracted from cocoa pod husk is investigated. The cocoa pod husk extract (CPHE) was prepared in phenolic nanoparticles form and added into the polymer solution at varying concentrations of 0.5 wt%, 0.75 wt%, and 1.0 wt%, respectively. The composite membrane was made of a cellulose acetate polymer using DMF (dimethylformamide) and DMAc (dimethylacetamide) solvents. The highest permeability of 2.34 L m⁻² h⁻¹ bar⁻¹ was achieved by 1.0 wt% CPHE/CA prepared with the DMAc solvent. CPHE was found to reduce the amount of Escherichia coli attached to the membranes by 90.5% and 70.8% for membranes prepared with DMF and DMAc, respectively. It is concluded that CPHE can be used to control biofouling in the membrane for food applications.

Effect of Silica Nanoparticles Blocked with Epoxy Groups on the Crosslinking and Surface Properties of PEG Hydrogel Films

Silica nanoparticles (G-SiNPs) blocked with 3-glycidoxypropyl trimethoxysilane (GPTS) were newly applied to hydrogel films for improving film coating properties and to distribute the epoxy groups on the film surface. The effects of the content of epoxy-functionalized G-SiNPs on the crosslinking features by photo-induced radical polymerization and the surface mechanical properties of the hydrogel films containing poly(ethylene glycol) dimethacrylate (PEGDMA) and glycidyl methacrylate (GMA) were investigated. The real-time elastic modulus of various PEG hydrogel mixtures with prepared particles was monitored using a rotational rheometer. The distribution of epoxy groups on the crosslinked film surface was directly and indirectly estimated by the elemental analysis of Si and Br. The surface mechanical properties of various hydrogel films were measured by nano-indentation and nano-scratch tests. The relationship between the rheological and surface properties of PEG-based hydrogel films suggests that the use of small amounts of G-SiNPs enhances the surface hardness and crosslinked network of the film and uniformly distributes sufficient epoxy groups on the film surface for further coating applications.

Comparative Anaerobic Decolorization of Azo Dyes by Carbon-Based Membrane Bioreactor

This study used a novel integrated technology of ceramic supported carbon membrane (CSCM) to degrade azo dyes through an anaerobic mixed culture. The CSCM worked simultaneously as biofilm support, redox mediator, and nano-filter to enhance the dye decolorization efficiency. The decolorization of Acid Orange 7 (AO7) was initially investigated with and without microorganisms in both ceramic support (CS) and CSCM reactors. The CSCM bioreactor (B-CSCM), operated with microorganisms, gave a maximum decolorization of 98% using a CSCM evolved from 10% weight (wt.) of Matrimid 5218 solution. To know the influence of permeate flow, feed concentration, and dye structure on the decolorization process, different B-CSCMs for dye removal experiments were studied over monoazo AO7, diazo Reactive Black 5 (RB5), and triazo Direct Blue 71 (DB71). The highest color removal, operated with 50 mg·L−1 feed solution and 0.05 L·m−2·h−1 of permeate flux, was 98%, 82%, and 72%, respectively, for AO7, RB5, and DB71. By increasing these parameters to 100 mg·L−1 and 0.1 L·m−2·h−1, the decolorization rate of dye solution still achieved 37% for AO7, 30% for RB5, and 26% for DB71. In addition, the system was run for weeks without apparent loss of activity. These findings make evident that the combined phenomena taking place in CSCM bioreactor result in an efficient, cost-effective, and ecofriendly azo dye decolorization method.

Bioactive Cellulose Nanocrystal-Poly(ε-Caprolactone) Nanocomposites for Bone Tissue Engineering Applications

3D-printed bone scaffolds hold great promise for the individualized treatment of critical-size bone defects. Among the resorbable polymers available for use as 3D-printable scaffold materials, poly(ε-caprolactone) (PCL) has many benefits. However, its relatively low stiffness and lack of bioactivity limit its use in load-bearing bone scaffolds. This study tests the hypothesis that surface-oxidized cellulose nanocrystals (SO-CNCs), decorated with carboxyl groups, can act as multi-functional scaffold additives that (1) improve the mechanical properties of PCL and (2) induce biomineral formation upon PCL resorption. To this end, an in vitro biomineralization study was performed to assess the ability of SO-CNCs to induce the formation of calcium phosphate minerals. In addition, PCL nanocomposites containing different amounts of SO-CNCs (1, 2, 3, 5, and 10 wt%) were prepared using melt compounding extrusion and characterized in terms of Young's modulus, ultimate tensile strength, crystallinity, thermal transitions, and water contact angle. Neither sulfuric acid-hydrolyzed CNCs (SH-CNCs) nor SO-CNCs were toxic to MC3T3 preosteoblasts during a 24 h exposure at concentrations ranging from 0.25 to 3.0 mg/mL. SO-CNCs were more effective at inducing mineral formation than SH-CNCs in simulated body fluid (1x). An SO-CNC content of 10 wt% in the PCL matrix caused a more than 2-fold increase in Young's modulus (stiffness) and a more than 60% increase in ultimate tensile strength. The matrix glass transition and melting temperatures were not affected by the SO-CNCs but the crystallization temperature increased by about 5.5°C upon addition of 10 wt% SO-CNCs, the matrix crystallinity decreased from about 43 to about 40%, and the water contact angle decreased from 87 to 82.6°. The abilities of SO-CNCs to induce calcium phosphate mineral formation and increase the Young's modulus of PCL render them attractive for applications as multi-functional nanoscale additives in PCL-based bone scaffolds.

Understanding the Role of Pattern Geometry on Nanofiltration Threshold Flux

Colloidal fouling can be mitigated by membrane surface patterning. This contribution identifies the effect of different pattern geometries on fouling behavior. Nanoscale line-and-groove patterns with different feature sizes were applied by thermal embossing on commercial nanofiltration membranes. Threshold flux values of as-received, pressed, and patterned membranes were determined using constant flux, cross-flow filtration experiments. A previously derived combined intermediate pore blocking and cake filtration model was applied to the experimental data to determine threshold flux values. The threshold fluxes of all patterned membranes were higher than the as-received and pressed membranes. The pattern fraction ratio (PFR), defined as the quotient of line width and groove width, was used to analyze the relationship between threshold flux and pattern geometry quantitatively. Experimental work combined with computational fluid dynamics simulations showed that increasing the PFR leads to higher threshold flux. As the PFR increases, the percentage of vortex-forming area within the pattern grooves increases, and vortex-induced shielding increases. This study suggests that the PFR should be higher than 1 to produce patterned membranes with maximal threshold flux values. Knowledge generated in this study can be applied to other feature types to design patterned membranes for improved control over colloidal fouling.

Grain analysis of atomic force microscopy images via persistent homology

Atomic force microscopy (AFM) is an established technique in nanoscale grain analysis due to its accuracy in producing 3-dimensional images. Even though height threshold and watershed algorithms are commonly used to determine the grain size and number of grains, they mostly require image processing that result in the change of topographical features of the surface that generates misleading conclusions. In this study, we use persistent homology, a method of representing topological features, to obtain more accurate information about the granular surfaces from unprocessed AFM images than the conventional methods. The method is also useful as a robust alternative to common parameters describing the topography of the AFM images. Most of these parameters such as arithmetic roughness and root-mean-squared roughness are represented by a single number which results in uncertainty in characterization of different surfaces. Persistent homology provides more precise summary about surface properties than a single parameter.

Enhancing Polyvalent Cation Rejection Using Perfluorophenylazide-Grafted-Copolymer Membrane Coatings

Surface modification offers a straightforward means to alter and enhance the properties and performance of materials, such as nanofiltration membranes for water softening. Herein, we demonstrate how a membrane's surface charge can be altered by grafting different electrostatically varying copolymers onto commercial membrane surfaces using perfluorophenylazide (PFPA) photochemistry for enhanced ion separation performance. The native membrane's performance-i.e., in terms of divalent cation separation-with copolymer coatings containing a positively charged quaternary ammonium (-N(Me)₃⁺), a negatively charged sulfonate (-SO₃^-), and an essentially neutral zwitterion (sulfobetaine, -N(Me)₂R₂⁺, and -SO₃^-), respectively, indicates that: (a) the sulfonated polymer induces robust Coulombic exclusion of divalent anions as compared to the negatively charged native membrane surface on account of its higher negative charge; (b) the positively charged ammonium coating induces exclusion of cations more effectively than the native membrane; and significantly, (c) the zwitterion polymer coating, which reduces the surface roughness and improves wettability, in spite of its near-neutral charge enhances exclusion of both divalent cations and anions on account of aperture sieving by the compact zwitterion polymer that arises from its ability to limit the size of ions that transport through the polymer along with dielectric exclusion. The outcomes thereby inform new pathways to achieve size- and charge-based exclusion of ionic, molecular, and other species contained in liquid streams.

Solid-supported lipid bilayers - A versatile tool for the structural and functional characterization of membrane proteins

The cellular membrane is central to the development of single-and multicellular life, as it separates the delicate cellular interior from the hostile environment. It exerts tight control over entry and exit of substances, is responsible for signaling with other cells in multicellular organisms and prevents pathogens from entering the cell. In the case of bacteria and viruses, the cellular membrane also hosts the proteins enabling invasion of the host organism. In a very real sense therefore, the cellular membrane is central to all life. The study of the cell membrane and membrane proteins in particular has therefore attracted significant attention. Due to the enormous variety of tasks performed by the membrane, it is a highly complex and challenging structure to study. Ideally, membrane components would be studied in isolation from this environment, but unlike water soluble proteins, the amphiphilic environment provided by the cellular membrane is key to the structure and function of the cell membrane. Therefore, model membranes have been developed to provide an environment in which a membrane protein can be studied. This review presents a set of tools that enable the comprehensive characterization of membrane proteins: electrochemical tools, surface plasmon resonance, neutron scattering, the surface forces apparatus and atomic force microscopy are discussed, with a particular focus on experimental technique and data evaluation.

Robustness of Surface Roughness against Low Number of Picture Elements and Its Benefit for Scaling Analysis

Surface roughness is widely used in the research of topography, and the scaling characteristics of roughness have been noticed in many fields. To rapidly obtain the relationship between root-mean-squared roughness (Rq) and measurement scale (L) could be helpful to achieve more understandings of the surface property, particularly the Rq-L curve could be fitted to calculate the fractal dimension (D). In this study, the robustness of Rq against low number of picture elements was investigated. Artificial surfaces and the surfaces of two actual samples (a silver thin film and a milled workpiece) were selected. When the number of picture elements was lowered, Rq was found to be stable within a large portion of the concerned scope. Such a robustness property could validate the feasibility of Rq-L curve obtained by segmenting a single morphological picture with roughness scaling extraction (RSE) method, which was proposed in our previous study. Since the traditional roughness (TR) method to obtain Rq-L curves was based on multiple pictures, which used a fixed number of picture elements at various L, RSE method could be significantly more rapid than TR method. Moreover, a direct comparison was carried out between RSE method and TR method in calculating the Rq-L curve and D, and the credibility and accuracy of RSE method with flatten order 1 and 2 was verified.

Nanohybrid Membrane Synthesis with Phosphorene Nanoparticles: A Study of the Addition, Stability and Toxicity

Phosphorene is a promising candidate as a membrane material additive because of its inherent photocatalytic properties and electrical conductance which can help reduce fouling and improve membrane properties. The main objective of this study was to characterize structural and morphologic changes arising from the addition of phosphorene to polymeric membranes. Here, phosphorene was physically incorporated into a blend of polysulfone (PSf) and sulfonated poly ether ether ketone (SPEEK) doping solution. Protein and dye rejection studies were carried out to determine the permeability and selectivity of the membranes. Since loss of material additives during filtration processes is a challenge, the stability of phosphorene nanoparticles in different environments was also examined. Furthermore, given that phosphorene is a new material, toxicity studies with a model nematode, Caenorhabditis elegans, were carried out to provide insight into the biocompatibility and safety of phosphorene. Results showed that membranes modified with phosphorene displayed a higher protein rejection, but lower flux values. Phosphorene also led to a 70% reduction in dye fouling after filtration. Additionally, data showed that phosphorene loss was negligible within the membrane matrix irrespective of the pH environment. Phosphorene caused toxicity to nematodes in a free form, while no toxicity was observed for membrane permeates.

Monitoring film coalescence from aqueous polymeric dispersions using atomic force microscopy: Surface topographic and nano-adhesion studies

The aim of the investigation was to develop the use of topographic and nano-adhesion atomic force microscopy (AFM) studies as a means of monitoring the coalescence of latex particles within films produced from a pharmaceutically relevant aqueous dispersion (Eudragit^ⓇNE30D). Films were prepared via spin coating and analysed using AFM, initially via tapping mode for topographic assessment followed by force-distance measurements which allowed assessment of site-specific adhesion. The results showed that colloidal particles were clearly observed topographically in freshly prepared samples, with coalescence detected on curing via the disappearance of discernible surface features and a decrease in roughness indices. The effects of temperature and humidity on film curing were also studied, with the former having the most pronounced effect. AFM force measurements showed that the variation in adhesive force reduced with increasing curing time, suggesting a novel method of quantifying the rate of film formation upon curing. It was concluded that the AFM methods outlined in this study may be used as a means of qualitatively and quantitatively monitoring the curing of pharmaceutical films as a function of time and other variables, thereby facilitating rational design of curing protocols.

Comparison of different cationic polymers efficacy in fabrication of alginate multilayer microcapsules

In past decades, alginate-based multilayer microcapsules have been given important attention in various pharmaceutical investigations. Alginate-poly l lysine-alginate (APA) is studied the most. Due to the similarity between the structure of polyethyleneimine (PEI) and poly-L-lysine (PLL) and also lower price of PEI than PLL, this study was conducted to compare the efficacy of linear (LPEI) and branch (BPEI) forms of PEI with PLL as covering layers in fabrication of microcapsules. The microcapsules were fabricated using electrostatic bead generator and their shape/size, surface roughness, mechanical strength, and interlayer interactions were also investigated using optical microscopy, AFM, explosion test and FTIR, respectively. Furthermore, cytotoxicity was evaluated by comparing the two anionic final covering layers alginate (Alg) and sodium cellulose sulphate (NCS) using MTT test. BPEI was excluded from the rest of the study due to its less capacity to strengthen the microcapsules and also the aggregation of the resultant alginate-BPEI-alginate microcapsules, while LPEI showed properties similar to PLL. MTT test also showed that NCS has no superiority over Alg as final covering layer. Therefore, it is concluded that, LPEI could be considered as a more cost effective alternative to PLL and a promising subject for future studies.

Determination of Surface Energy Parameters of Hydrophilic Porous Membranes via a Corrected Contact Angle Approach

While the contact angle is a well-applied indicator of membrane hydrophobicity and surface energy, the interference of surface roughness and porosity in contact angle measurement and surface energy calculation has been long neglected in the field of porous membrane study. We propose an improved method to straightforwardly derive the surface energy of the porous membrane from contact angles with the interference effect corrected. A linearized model was established combining the Young-Dupré and Cassie-Baxter equations, from which the surface energy (Lifshitz-van der Waals and Lewis acid/base components) and roughness index (surface area difference) can be solved simultaneously at a given porosity using contact angles measured with a set of standard polar/nonpolar test liquids. The model solution was examined using hydrophilic microfiltration membranes with different pore morphologies (including perforated plate-like PCTE, irregular particulate bed-like PVDF, and fibrous mesh-like PTFE membranes), with the robustness of the results evaluated via Monte Carlo simulation. In comparison with the verified results of the model solution, it was found that the Lifshitz-van der Waals Lewis acid/base energy values for the tested membranes would deviate by 50-87, 30-160, and 52-97%, respectively, if surface roughness and porosity were neglected in the calculation. The profound effect of roughness and porosity on surface energy determination was further confirmed via theoretical analysis of the Young-Dupré and Cassie-Baxter relationships. This improved approach may apply to the surface energy characterization of hydrophilic rough porous membranes (e.g., hydrophilic microfiltration membranes).

Hybrid Hollow Fiber Nanofiltration-Calcite Contactor: A Novel Point-of-Entry Treatment for Removal of Dissolved Mn, Fe, NOM and Hardness from Domestic Groundwater Supplies

Groundwater (GW) is one of the main potable water sources worldwide. However, the presence of undesirable compounds and particularly manganese (Mn) and iron (Fe) (mainly co-existing in GWs) are considered as objectionable components of potable water for both health and aesthetic issues. As such, individual dwellings supplied by domestic wells are especially threatened by these issues. Current domestic treatment technologies are complicated to operate and even dangerous if improperly maintained (e.g., catalytic filtration) or consume salts and produce spent brine which pollutes the environment (i.e., ion exchange resins). Therefore, it is of prime importance to design a simple and compact, yet robust, system for Mn and Fe control of the domestic GW sources, which can reliably guarantee the desired Mn limit in the finished water (20μg/L). In the course of this study, we demonstrated, for the first time, that a hybrid hollow fiber nanofiltration (HFNF)–calcite contactor process is a promising alternative for treating domestic GWs with elevated levels of Mn, Fe, natural organic matter (NOM) and hardness. The efficacy of the HFNF membranes in terms of removal of Mn, Fe, NOM and fouling was compared with commercially available NF270 and NF90 membranes. The results revealed that HFNF (100–200 Da) and NF90 maintained considerably high rejection of Mn, Fe and NOM due to their dominant sieving effect. In contrary, the rejections of the above-mentioned components were decreased in the presence of high hardness for the looser HFNF (200–300 Da) and NF270 membranes. No membrane fouling was detected and the permeate flux was stable when the hard GW was filtered with the HFNF membranes, regardless of their molecular weight cut-off and transmembrane pressure, while the permeability of the NF270 and NF90 membranes steadily decline during the filtration. Integrating a calcite contactor, as a post filtration step, to the HFNF process yielded further Mn, Fe and NOM removals from the HFNF permeate and adjustment of its hardness level. The best performance was achieved when a blend of Calcite–CorosexTM (90/10wt.%) was used as a post-treatment to the tight HFNF (100–200 Da).

Performance of thin-film composite hollow fiber nanofiltration for the removal of dissolved Mn, Fe and NOM from domestic groundwater supplies

Groundwater (GW) is one of the most abundant water resources and around 1.5 billion people rely on GW as their main water supply. Manganese (Mn) and iron (Fe) are very common GW contaminants. Even though their presence is considered mainly as an organoleptic and operational nuisance, water with elevated Mn content may also lead to adverse health impacts. Amongst the most common treatment processes currently used to treat domestic GW supplies: catalytic filtration may lead to Mn leaching if improperly maintained; while ion exchange consumes a considerable amount of salt and produces a brine waste which pollutes the environment. Thus, it is proposed to design a simple, yet robust treatment system which can be implemented in small/remote communities or even domestic applications. To this end, the main objective of this investigation was to assess the potential application of novel outside-in sulfonated polyethersulfone thin-film composite hollow fiber nanofiltration (HFNF) membranes to remove dissolved Mn, Fe and natural organic matter (NOM) from domestic GW supplies. Of particular interest was the impact of GW matrix on performance of the HFNF membranes. Our experimental findings demonstrated that, in absence of hardness and the cumulative throughput of 1.9 L/m², above 90% of Mn, Fe and NOM were retained by the examined HFNF membranes (MWCO ∼ 200 Da) regardless of their initial concentrations in the feed solution (250-1000 μ g/L). In contrast, increasing the hardness level reduced the removal of Mn and Fe ions. XPS analysis revealed that the surface properties of the HFNF membranes were altered when the membranes were exposed to calcium and magnesium salts. These observations were attributed to the propensity for Ca and Mg ions to bind to the sulfonic groups present on the surface of the HFNF membranes which, subsequently, weakens rejection by charge exclusion. On the other hand, in the absence of GW hardness, charge exclusion was mainly responsible for rejection of dissolved Mn and Fe. It was also found that GW hardness had no marked impact on the NOM rejection as the later was mostly removed by size exclusion.

Smoothening of wrinkles in CVD-grown hexagonal boron nitride films

Hexagonal boron nitride (h-BN) is an ideal substrate for two-dimensional (2D) materials because of its unique electrically insulating nature, atomic smoothness and low density of dangling bonds. Although mechanical exfoliation from bulk crystals produces the most pristine flakes, scalable fabrication of devices is still dependent on other more direct synthetic routes. To date, the most utilized method to synthesize large-area h-BN films is by chemical vapor deposition (CVD) using catalytic metal substrates. However, a major drawback for such synthetic films is the manifestation of thermally-induced wrinkles, which severely disrupt the smoothness of the h-BN films. Here, we provide a detailed characterization study of the microstructure of h-BN wrinkles and demonstrate an effective post-synthesis smoothening route by thermal annealing in air. The smoothened h-BN film showed an improved surface smoothness by up to 66% and resulted in a much cleaner surface due to the elimination of polymer residues with no substantial oxidative damage to the film. The unwrinkling effect is attributed to the hydroxylation of the h-BN film as well as the substrate surface, resulting in a reduction in adhesion energy at the interface. Dehydroxylation occurs over time under ambient conditions at room temperature and the smoothened film can be restored back with the intrinsic properties of h-BN. This work provides an efficient route to achieve smoother h-BN films, which are beneficial for high-performance 2D heterostructure devices.

Functional graphene oxide membrane preparation for organics/inorganic salts mixture separation aiming at advanced treatment of refractory wastewater

Some refractory organic matters or soluble microbial products remained in the effluents of refractory organic wastewater after biological secondary treatment and need an advanced treatment before final disposal. Graphene oxide (GO) was known to have potential to be the next generation membrane material. The functional organics/inorganic salts separation GO membrane preparation and application in wastewater advanced treatment could reduce energy or chemicals consumption and avoid organics/inorganic salts mixed concentrate waste problems after nanofiltration or reverse osmosis. In this study, we developed a novelty GO membrane aiming at advanced purification of organic matters in the secondary effluents of refractory organic wastewater and avoiding the organics/inorganic salts mixed concentrate waste problem. The influence of preparation conditions including pore size of support membrane, the number of GO layers and the applied pressure was investigated. It was found that for organics/inorganic salts mixture separation membrane preparation, the rejection and flux would achieve balance for the support membrane at a pore size of ~0.1μm and the number of GO layers of has an optimization value (~10 layers). A higher assemble pressure (~10bar) contributed to the acquisition of a higher rejection efficiency and lower roughness membrane. This as prepared GO membrane was applied to practical secondary effluent of a chemical synthesis pharmaceuticals wastewater. A good organic matter rejection efficiency (76%) and limited salt separation (<14%) was finally obtained. These results can promote the practical application of GO membrane and the resourcelized treatment of industrial wastewater.

Single Step Double-walled Nanoencapsulation (SSDN)

A quick fabrication method for making double-walled (DW) polymeric nanospheres is presented. The process uses sequential precipitation of two polymers. By choosing an appropriate solvent and non-solvent polymer pair, and engineering two sequential phase inversions which induces first precipitation of the core polymer followed by precipitation of the shell polymer, DW nanospheres can be created instantaneously. A series of DW formulations were prepared with various core and shell polymers, then characterized using laser diffraction particle sizing, scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry (DSC). Atomic force microscopy (AFM) imaging confirmed existence of a single core polymer coated with a second polymer. Insulin (3.3% loading) was used as a model drug to assess its release profile from core (PLGA) and shell (PBMAD) polymers and resulted with a tri-phase release profile in vitro for two months. Current approaches for producing DW nanoparticles (NPs) are limited by the complexity and time involved. Additional issues include aggregation and entrapment of multiple spheres and the undesired formation of heterogeneous coatings. Therefore, the technique presented here is advantageous because it can produce NPs with distinct, core-shell morphologies through a rapid, spontaneous, self-assembly process. This method not only produces DW NPs, but can also be used to encapsulate therapeutic drug. Furthermore, modification of this process to other core and shell polymers is feasible using the general guidelines provided in this paper.

Atmospheric CO2 capture for the artificial photosynthetic system

The aim of these studies is to evaluate the ambient CO₂ capture abilities of the membrane contactor system in the same conditions as leafs, such as ambient temperature, pressure and low CO₂ concentration, where the only driving force is the concentration gradient. The polysulfone membrane employed was made by a phase inversion process and characterized by ESEM micrographs which were used to determine the thickness, asymmetry and pore size. Besides, the porosity of the membrane was measured from the membrane and polysulfone density correlation and the hydrophobicity was analyzed by contact angle measurements. Moreover, the compatibility of membrane and absorbent was evaluated, in order to exclude wetting issues by meaning of swelling, dynamic contact angle and AFM analysis. The prepared membranes were introduced into a cross flow module and used as contactors between CO₂ and the absorbing media, a potassium hydroxide solution. The influence of the membrane thickness, absorbent stirring rate, solution pH and absorption time on CO₂ capture were evaluated. Absorbent solution stirring rate showed no statistically significant influence on absorption. We observed a non-linear correlation between the capture rate and the increase of absorbent solution pH as well as absorption time. The results showed that the efficiency of our CO₂ capture system is similar to stomatal carbon dioxide assimilation rate, achieving stable value of 20μmol/m²·s after 1h of experiment.