Atom transfer radical polymerization (ATRP): A versatile and forceful tool for functional membranes

The progress in atom transfer radical polymerization (ATRP) provides an effective means for the design and preparation of functional membranes. Polymeric membranes with different macromolecular architectures applied in fuel cells, including block and graft copolymers are conveniently prepared via ATRP. Moreover, ATRP has also been widely used to introduce functionality onto the membrane surface to enhance its use in specific applications, such as antifouling, stimuli-responsive, adsorption function and pervaporation. In this review, the recent design and synthesis of advanced functional membranes via the ATRP technique are discussed in detail and their especial advantages are highlighted by selected examples extract the principles for preparation or modification of membranes using the ATRP methodology.     

Dendrimer as nanocarrier for drug delivery

Dendrimers are novel three dimensional, hyperbranched globular nanopolymeric architectures. Attractive features like nanoscopic size, narrow polydispersity index, excellent control over molecular structure, availability of multiple functional groups at the periphery and cavities in the interior distinguish them amongst the available polymers. Applications of dendrimers in a large variety of fields have been explored. Drug delivery scientists are especially enthusiastic about possible utility of dendrimers as drug delivery tool. Terminal functionalities provide a platform for conjugation of the drug and targeting moieties. In addition, these peripheral functional groups can be employed to tailor-make the properties of dendrimers, enhancing their versatility. The present review highlights the contribution of dendrimers in the field of nanotechnology with intent to aid the researchers in exploring dendrimers in the field of drug delivery.     

Composition-dependent phase segregation and cocrystallization behaviors of blends of metallocene-catalyzed octene-LLDPE(D) and LDPE(H)

The morphological structures of slowly cooled blends of deuterated metallocene-catalyzed octene linear low-density polyethylene (O-mLLDPE(D)), and hydrogenous low-density polyethylene (LDPE(H)) were studied by using small angle neutron scattering in combination with complementary small angle X-ray scattering and differential scanning calorimetry. The phase segregation, which is more nanoscale than macroscale, and cocrystallization behaviors were found to vary with the blend composition. Phase-segregated O-mLLDPE(D) lamellae are predominantly formed in LDPE(H)-rich compositions. In contrast, few segregated O-mLLDPE(D) lamellae form in O-mLLDPE(D)-rich compositions, and instead O-mLLDPE(D) lamellar stacks are extensively cocrystallized with LDPE(H) mostly in the interlamellar amorphous region.     

Investigation of the microstructure of alkali-activated cements by neutron scattering

Significant research has been devoted to understanding and modeling the neutron scattering behavior of Portland cement pastes. The present work examines the potential of neutron scattering to noninvasively evaluate the properties of alternative cementitious materials encountered in the field. To interpret the scattering of both alkali-activated and slag-cement systems, alternative models to those typically adopted for Portland cement pastes were considered. Investigation of alkali-activated and slag-cement coupons were conducted for different sample thickness (∼0.5, 1, 2, 4, 6, 8 and 12 mm) over a wide scattering vector (Q) range (0.0005<Q>0.03 nm⁻¹ and 0.04<Q>4 nm⁻¹) on both ultra (USANS) and conventional small-angle neutron scattering (SANS) spectrometers. This wide Q range allowed determination of the fractal properties of the microstructure as well as the radius of the main scattering particle in the material. An empirical correction for multiple scattering was made based on the Dexter-Beeman equation and demonstrated that for thicker sample widths the theory correlated reasonably well. Alkali-activated fly ash was found to have the largest R value while the OPC and slag mix exhibited the largest Guinier radius. This difference was attributed to variations in the extent of multiple scattering for the samples. Successful application of this model was limited to sample thickness ≥1 mm. A combined power law-Sabine expression was also utilized to successfully model the SANS data over a Q range of 0.04-4 nm⁻¹.     

Salt influence upon the structure of aqueous solutions of branched PEO-PPO-PEO copolymers

Triblock copolymers composed of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), present an amphiphilic character in aqueous solution. Since PPO is less hydrophilic than PEO and since their solubilities decrease when the temperature increases, the copolymers self-assemble spontaneously, forming micelles at moderate temperature. For higher temperature or concentration, these solutions can form lyotropic liquid crystalline phases. In order to improve their properties for particular applications, these solutions are often used in the presence of salts. The influence of the salts nature is qualitatively well described for linear copolymer solutions of PEO-PPO-PEO type. The presence of a ‘salting out’ electrolyte shifts the cloud point and the critical micelle temperature to lower temperature while ‘salting in’ electrolyte induces opposite effects. In this article, we study the influence of the presence of sodium chloride (NaCl) on the structure of aqueous solutions of a four-branched copolymer. First, we show by viscosimetric studies that NaCl has a ‘salting out’ effect with these star copolymers as with theirs linear counterparts. Secondly, small angle neutron scattering studies make it possible to determine quantitatively the influence of the NaCl amount on the equilibrium unimers-micelles. These experiments allow obtaining the radius of micelles, their volume fraction and their aggregation number. These informations are compared with the data obtained with salt-free solutions. SANS results are also used to demonstrate that the micelles form bcc polycrystals in a significant zone of the phase diagram. The cell parameter of these crystals is determined according to the salinity of the solution. At last, we observe that the solution presents at high temperature a phase separation. Our results show clearly that this phenomenon is due to the dehydration of the PEO external layer of the micelles.     

Synthesis,aggregation and adsorption behaviour of a thermoresponsive pentablock copolymer

Poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer (Pluronic F127) was modified by introducing poly(N‐isopropylacrylamide) (PNIPAM) at both the PEO ends, and the pentablock copolymer (PNIPAM₄₁–F127–PNIPAM₄₁, PN41) so prepared was characterized using gel permeation chromatography and ¹H NMR spectroscopy. The degree of polymerization of NIPAM blocks at the two ends was 41. The solution behaviour and microstructure of PN41 aggregates in water were examined using UV–visible spectroscopy, micro‐differential scanning calorimetry and small‐angle neutron scattering (SANS) and compared with F127. Two lower critical solution temperatures (LCSTs) were observed for the pentablock copolymer, corresponding to PPO and PNIPAM blocks, respectively. The adsorption of PN41 on thiol‐grafted hydrophobic gold surfaces at various temperatures was investigated using a quartz crystal microbalance. It was found that the adsorption behaviour and mechanism of PN41 were mainly determined by the interactions of the pentablock copolymers with different chain conformations in dilute aqueous solutions at various temperatures. SANS measurements were used to determine the temperature‐dependent structural evolution of polymer micelles in aqueous solution. A NOESY study revealed that above the LSCT of PNIPAM, the interaction of PPO and PNIPAM protons increases and the distance between PPO and PNIPAM decreases. © 2019 Society of Chemical Industry     

Investigating Structural Alterations in Pyrogallol[4]arene‐Pyrene Nanotubular Frameworks

Small‐angle neutron scattering (SANS) and diffusion NMR studies are performed to investigate the stability and geometry of hydrogen‐bonded pyrene‐guest‐containing C‐hexylpyrogallol[4]arene (PgC₆‐pyrene) nanotubular frameworks in solution. In the solid state, hydrogen‐bonded pyrogallol[4]arene tubes are formed; however, the scattering data for PgC₆‐pyrene assemblies in acetone are best modeled as dimeric spheres of PgC₆ with no pyrene guest. The result of diffusion NMR study also indicates the rearrangement of tubular entity into spherical framework in acetone. This is the first example of structural transformation of pyrogallol[4]arene nanotubes (guest‐exo) in solution. Individual hydrogen‐bonded spheres of PgC₆ exhibits a uniform radius of ca. 8.6 Å and a diffusion coefficient of 9.12 × 10^?10 m² s^?1 in acetone. The diffusion NMR measurements further gave, for the first time, insights into how the type of solvent (acetone vs. methanol vs. acetontitrile/D₂O) governs the structural differences in these nanoassemblies. Solution‐phase structural alteration observed for PgC₆‐pyrene gives evidence of enhanced stability of pyrogallol[4]arene nanocapsules over nanotubes.     

Small-angle neutron scattering characterization of the structure of nanoporous carbons for energy-related applications

We used small-angle neutron scattering (SANS) and neutron contrast variation to study the structure of four nanoporous carbons prepared by thermo-chemical etching of titanium carbide TiC in chlorine at 300, 400, 600, and 800 °C with pore diameters ranging between ∼4 and ∼11 Å. SANS patterns were obtained from dry samples and samples saturated with deuterium oxide (D₂O) in order to delineate origin of the power law scattering in the low Q domain as well as to evaluate pore accessibility for D₂O molecules. SANS cross section of all samples was fitted to Debye-Anderson-Brumberger (DAB), DAB-Kirste-Porod models as well as to the Guinier and modified Guinier formulae for cylindrical objects, which allowed for evaluating the radii of gyration as well as the radii and lengths of the pores under cylindrical shape approximation. SANS data from D₂O-saturated samples indicate that strong upturn in the low Q limit usually observed in the scattering patterns from microporous carbon powders is due to the scattering from outer surface of the powder particles. Micropores are only partially filled with D₂O molecules due to geometrical constraints and or partial hydrophobicity of the carbon matrix. Structural parameters of the dry carbons obtained using SANS are compared with the results of the gas sorption measurements and the values agree for carbide-derived carbons (CDCs) obtained at high chlorination temperatures (>600 °C). For lower chlorination temperatures, pore radii obtained from gas sorption overestimate the actual pore size as calculated from SANS for two reasons: inaccessible small pores are present and the model-dependent fitting based on density functional theory models assumes non-spherical pores, whereas SANS clearly indicates that the pore shape in microporous CDC obtained at low chlorination temperatures is nearly spherical.     

A SANS Study of Organoclay Dispersions

Small-angle neutron scattering (SANS) is used to investigate the dispersion in toluene of various forms of the complex, Cloisite C15A. Cloisite is a commercially important exchanged clay prepared from montmorillonite and the cation di-tallow ammonium. Points discussed include estimates of the extent to which the complex is dispersed, the amount of organic clay platelet surface layer coverage, and possible network formation of the complex in the solvent. From power-law plots of the scattered neutron intensity versus the wave vector, it is estimated that C15A is well dispersed into clusters which consist of a stack of between three and seven di-tallow-coated montmorillonite platelets. The removal of excess di-tallow from the surface layer reduces the number of platelets in the cluster. Substitution of dimethydioctodecyl ammonium for the di-tallow molecule promotes network formation. It is demonstrated that SANS is a powerful tool for examining these complicated organic/inorganic systems.