Porous latex composite membranes: fabrication and properties

A new class of microfiltration (MF) and ultrafiltration (UF) membranes has been developed. By placing latex particles onto the surface of a microporous substrate and stabilizing the porous array, voids are formed between the particles which provide narrowly distributed pores that serve as separation channels. The size of the interstitial voids in the array is governed by the diameter of the latex particle. This aqueous based technology has advantages relative to other membrane fabrication processes in terms of the high asymmetry of the membranes, the facile adjustment of pore sizes, and the ability to easily modify pore surfaces during the synthesis of particles.A number of approaches were examined for placement of particles and stabilization of latex composite membranes (LCMs). Filtration of particles with reactive surface groups that provide covalent linkages at the contact points in the particle array proved most effective in obtaining stable membranes. These membranes had narrow size distributions in both the UF and MF range and were capable of being cleaned and backflushed. The membranes were characterized in terms of gas permeabilities, pure water permeabilities and electron microscopy. The rejection properties of LCMs were also examined during filtration of monodispersed latex particles and a broadly dispersed dextran mixture.     

Porous CuO superstructure: precursor-mediated fabrication, gas sensing and photocatalytic properties

A facile route was developed for the large-scale preparation of porous CuO superstructures based on a hydrothermal route with subsequent calcination. The CuO superstructures show "box-like" shape and are composed of microplatelets with high porosity resulting from the thermal decomposition of the precursor. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform spectroscopy (FT-IR) and Brunauer-Emmett-Teller N(2) adsorption-desorption analyses were employed to characterize the microstructure, size and crystalline phase of the porous cupric oxide product. The porous CuO superstructures with pore size of about 20 nm have a surface area of 18.2 m(2)/g. The gas-sensing measurements of the porous CuO superstructures demonstrate that the obtained CuO product exhibits higher sensing response to ethanol, propanol and acetone than commercial CuO powder. In addition, the enhanced photocatalytic activity of the porous CuO superstructures was also demonstrated with the photocatalytic degradation of methylene blue as a probe reaction. It is believed that the enhanced gas-sensing and catalytic properties are originated from their unique openly porous microstructure, which is highly beneficial to the reagent diffusion and mass transportation.     

Porous membranes of PLLA-PCL blend for tissue engineering applications

Porous membranes of polycaprolactone-poly(l-lactic acid) blends were prepared by a freeze-extraction process. This procedure was able to disperse homogeneously both components despite their amorphous phases being immiscible (as proven by the fact that the glass transition temperature of PCL in the blend is independent of blend composition) and both polymers crystallize. Thus, the porous membrane consists of amorphous and crystalline phases of both components. DSC and AFM were used to characterize the microstructure of the blends, whereas SEM and gravimetric methods enabled the porosity (around 70%) and pore architecture to be determined. Compression stress-strain experiments show the characteristic behaviour of porous materials with a yield stress that rapidly drops when the PCL content increases - whereas the deformation plateau zone enlarges.     

Conjugate polymer-based membranes for gas separation applications: current status and future prospects

Conjugate polymers provide the possibility of exploiting both the chemical and physical attributes of the polymers for membrane-based gas separation. The presence of delocalized π electrons provides high chain stiffness with low packing density, thus making the membrane a rigid structure that favors facilitated transport. Historically, the polymeric membranes were constrained by the tradeoff relationship between gas permeability and gas selectivity. So, different methods were investigated to prepare the membranes that can overcome the limitation. In recent years, electroconductive polymeric membranes have gained attention with their enhanced transportation properties combining the separation behavior depending on both molecular size discrimination as well as the facilitated transport. They offer better selectivity toward polar gases such as CO₂ because of the increased solubility. This review is aimed to provide a literature survey on gas separation using conjugate polymers such as polyaniline, polypyrrole, and some derivatives of polythiophenes. It contains various methods used by different researchers to enhance the gas separation properties of the membranes with improved mechanical and thermal stability such as changing the morphology and membrane preparation methods. In addition, it provides the pros and cons of various factors affecting the conjugate polymer membrane performance. The major challenges and future work that can be done in improving the transportation properties through the membrane to achieve viable membranes are also discussed so that they can be used for commercial and practical applications in the future.     

Patterned biomimetic membranes: effect of concentration and pH

Planar-supported lipid bilayers have attracted enormous attention because of their properties as model cell membranes, which can be employed in a variety of fundamental biological studies and medical devices. Furthermore, the development of patterned biological interfaces is of great practical and scientific interest because of their potential applications in the field of biosensors, drug screening, tissue engineering, and medical implants. In this study, mica-supported membranes were constructed from biomimetic peptide-amphiphiles and their mixtures with lipidated poly(ethylene glycol) (PEG120) molecules or 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) phospholipids using the Langmuir-Blodgett technique. The two peptide-amphiphiles used in this study were a fibronectin-mimetic with the PHSRN(SG)(3)SGRGDSP headgroup (referred to as PHSRN-GRGDSP) that contains both the primary (GRGDSP) and the synergy (PHSRN) recognition sites for alpha(5)beta(1) integrins and a peptide-amphiphile that mimics a fragment of the N-terminus of the fractalkine receptor (referred to as NTFR). Compression isotherms of the peptide-amphiphiles and their mixtures with PEG120 at the air/water interface were recorded and analyzed to evaluate the extent of miscibility in the two-component LB films. Domain formation in mica-supported bilayers constructed from mixtures of peptide-amphiphiles and lipidated PEG120 or DPPC was observed using atomic force microscopy. In PHSRN-GRGDSP/PEG120 mixtures deposited from an aqueous subphase at pH 7, concentration-dependent phase separation was observed on the AFM images. The NTFR/PEG120 and NTFR/DPPC mixtures deposited at pH 10 exhibited extensive lateral phase separation at all mixture compositions, whereas at deposition pH 7 the concentrations of NTFR/DPPC examined here were well mixed.     

Nanocrystals: fabrication,organization and collective properties

In this review, the control of size and shape of inorganic nanocrystals via colloidal solution is discussed. The nanocrystals are organized in 2D and 3D superlattices with formation of ‘supra’ crystals in fcc structure. Physical properties of nanocrystals organized in mesoscopic scale are neither those of the isolated nanocrystals nor that of the bulk phase but those of the film of nanocrystals. To cite this article: M.-P. Pileni, C. R. Chimie 6 (2003).     

Porous alumina membranes with branched nanopores as templates for fabrication of Y-shaped nanowire arrays

Porous anodic alumina membranes with Y-branched and double-branched nanopores were fabricated by the stepwise reduction of anodizing potential during the second step of anodization carried out in 0.3 M oxalic acid. The process of nanoporous layer formation and influence of anodizing parameters on structural features of as-obtained anodic aluminum oxide (AAO) membranes were discussed in detail. The pore rearrangement process occurring after the potential decrease was investigated on the basis of the current density vs. time curves, and results were correlated with the field-emission scanning electron microscope images of the pore bottoms taken after different anodizing durations. It was found that the reorganization of nanopores begins after 600 and 500 s from the time of the potential reduction to 42 and 30 V and the process seems to be completed after about 900 and 800 s, respectively. The through-hole AAO membranes were used as templates for the fabrication of gold and polystyrene nanowires via electrochemical deposition and simple immersing in the polymer solution, respectively. The arrays of hierarchically branched nanowires were synthesized, and the dimensions of nanowires were consistent with the shape and structure of used AAO templates.

     

Thioether-functionalized mesoporous fiber membranes: sol-gel combined electrospun fabrication and their applications for Hg2+ removal

Mesoporous polyvinylpyrrolidone (PVP)/SiO(2) composite nanofiber membranes functionalized with thioether groups have been fabricated by a combination method of sol-gel process and electrospinning. The precursor sol was synthesized by one-step co-condensation of tetraethyl orthosilicate (TEOS) and 1,4-bis(triethoxysilyl)propane tetrasulfide (BTESPTS, (CH(3)CH(2)O)(3)Si(CH(2))(3)S-S-S-S(CH(2))(3)Si-(OCH(2)CH(3))(3)), with the triblock copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (P123, EO(20)PO(70)EO(20)) as template. After the addition of PVP, nanofiber membranes were prepared by electrospinning. The membranes were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) images, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), N(2) adsorption-desorption isotherms, and an Elementar Vario EL analyzer. The composites were used as highly selective adsorbents for Hg(2+) due to the modification with thioether groups (-S-), and were conveniently separated from the waste water. The composite could be regenerated through acidification.     

Organohypervalent iodine: development, applications, and future directions

The synthetic utility of organohypervalent iodine reagents will be illustrated by their use in the alpha-hydroxydimethylacetal formation reaction from enolizable ketones, alpha-hydroxylation, alpha-tosyloxylation, alpha-alkoxylation and arylation of ketones, carbon-carbon bond formation, and intramolecular cyclopropanation using iodonium ylides. The uses of these reagents in the Hunsdiecker reaction of carboxylic acids and Hofmann rearrangement of carboxamides is presented. Specific transformation in the cubane series are discussed. The syntheses of a wide range of heterocycle structures are also presented. A unifying pathway for virtually all these diverse reactions is offered; the central features being initial attack at the iodonium center, ligand coupling, with reductive elimination of iodobenzene to yield the product.     

Porous,polyelectrolyte-filled membranes: Effect of cross-linking on flux and separation

A new type of membrane composed of a microfiltration substrate and a pore-filling polyelectrolyte has been produced by UV-induced grafting of 4-vinylpyridine (4VP) with varying amounts of divinylbenzene (DVB) onto polypropylene microfiltration membranes. Using the same irradiation conditions, it has been found that graft yield increases substantially in the presence of DVB. The increase in graft yield was shown to be accompanied by a substantial increase in the thickness of the grafted membranes and a small but significant decrease in water content. The composite membranes have very high charge densities and good mechanical properties.The membranes with various amounts of DVB were quaternized (methylated) and examined for reverse osmosis of various salts. In addition to an expected drop in flux due to the increased thickness and decreased water content, there was significantly different salt rejection for membranes with cross-linking. While, for example, there is practically no difference in rejection of NaCl by a membrane with 0.55% DVB and one having no cross-linker, the Na₂SO₄ rejection by the cross-linked membrane is, on average, twice as high as that by the non-cross-linked one. Large differences between the cross-linked and non-cross-linked membranes were found in the ratios of pure water to NaCl permeate fluxes of the membranes at various pressures. The results are discussed in terms of the physicochemical nature of the membranes and conformational changes of the pore-grafted poly(4-vinylpyridine).     

Biosurfactants: Formulations,properties, and applications

In this review, we attempt to give an overview on the recent progress made on biosurfactants, surface-active biomolecules produced by microorganisms, which are a sustainable alternative to synthetic surfactants. Different biosurfactants, their production techniques, and their physical and chemical properties are discussed. There is a focus on recent studies related to surface properties and rheology of biosurfactants, both being properties which affect their ability to take part in a stable formulation. Biosurfactants can have applications in multiple different industrial sectors, such as agriculture, medicine, personal care, food, petroleum, etc. The specific properties important for applications in these sectors are discussed in detail.     

Oxa-spirocycles: synthesis,properties and applications

A general approach to a new generation of spirocyclic molecules – oxa-spirocycles – was developed. The key synthetic step was iodocyclization. More than 150 oxa-spirocyclic compounds were prepared. Incorporation of an oxygen atom into the spirocyclic unit dramatically improved water solubility (by up to 40 times) and lowered lipophilicity. More potent oxa-spirocyclic analogues of antihypertensive drug terazosin were synthesized and studied in vivo.

A general practical approach to a new generation of spirocyclic molecules – oxa-spirocycles – is developed.     

Porous shape memory polymers: Design and applications

Porous shape memory polymers (SMPs) exhibit geometric and volumetric shape change when actuated by an external stimulus and can be fabricated as foams, scaffolds, meshes, and other polymeric substrates that possess porous three-dimensional macrostructures. These materials have applications in multiple industries such as textiles, biomedical devices, tissue engineering, and aerospace. This review article examines recent developments in porous SMPs, with a focus on fabrication methods, methods of characterization, modes of actuation, and applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1300–1318     

Ethylene glycol: properties, synthesis, and applications

Ethylene glycol (EG) is an important organic compound and chemical intermediate used in a large number of industrial processes (e.g. energy, plastics, automobiles, and chemicals). Indeed, owing to its unique properties and versatile commercial applications, a variety of chemical systems (e.g., catalytic and non-catalytic) have been explored for the synthesis of EG, particularly via reaction processes derived from fossil fuels (e.g., petroleum, natural gas, and coal) and biomass-based resources. This critical review describes a broad spectrum of properties of EG and significant advances in the prevalent synthesis and applications of EG, with emphases on the catalytic reactivity and reaction mechanisms of the main synthetic methodologies and applied strategies. We also provide an overview regarding the challenges and opportunities for future research associated with EG.     

Diatoms: self assembled silica nanostructures, and templates for bio/chemical sensors and biomimetic membranes

In this review we highlight recent advances in the understanding of biosilica production, biomodification of diatom frustules and their subsequent applications in bio/chemical sensors, and as a model membrane for filtration and separation.     

Split-luciferase complementary assay: applications,recent developments,and future perspectives

Bioluminescent systems are considered as potent reporter systems for bioanalysis since they have specific characteristics, such as relatively high quantum yields and photon emission over a wide range of colors from green to red. Biochemical events are mostly accomplished through large protein machines. These molecular complexes are built from a few to many proteins organized through their interactions. These protein–protein interactions are vital to facilitate the biological activity of cells. The split-luciferase complementation assay makes the study of two or more interacting proteins possible. In this technique, each of the two domains of luciferase is attached to each partner of two interacting proteins. On interaction of those proteins, luciferase fragments are placed close to each other and form a complemented luciferase, which produces a luminescent signal. Split luciferase is an effective tool for assaying biochemical metabolites, where a domain or an intact protein is inserted into an internally fragmented luciferase, resulting in ligand binding, which causes a change in the emitted signals. We review the various applications of this novel luminescent biosensor in studying protein–protein interactions and assaying metabolites involved in analytical biochemistry, cell communication and cell signaling, molecular biology, and the fate of the whole cell, and show that luciferase-based biosensors are powerful tools that can be applied for diagnostic and therapeutic purposes.