Small Angle X-ray Spectroscopy Research Articles

Acquiring reliable hydrogen crossover data of hydrated ion exchange membranes to elucidate the ion conducting channel morphology

The morphology of ion channels within ion exchange membranes (IEM) has long been disputed by researchers. Several accepted models include the Gierke’s discrete spherical cluster model, continuous parallel cylinder model, and flat-layered model. The primary experimental data to support each model were mostly small-angle X-ray spectroscopy (SAXS). In this work, we propose that hydrogen permeability (i.e. crossover) data of hydrated IEMs could provide valuable insights into understanding the ion channel connectivity and continuity within the membrane. We re-derived the two-phase Maxwell-Eucken transport models to predict the hydrogen crossover of hydrated IEMs. The model accurately predicted the hydrogen crossover of Nafion and in-house BPSH membrane series within 10% error range. The predicted results were experimentally validated using the pressure decay method (PDM) developed in our group specifically for this purpose. By comparing the degree of change in hydrogen crossover between the dry and hydrated membranes, it was possible to extract semi-qualitative information about the membrane’s controversial ion-conducting channel morphology. Interestingly, our experimental data and model prediction corroborates with the Gierke’s conjecture that the water phase within the ion channel exists as discrete spherical clusters, not as the continuous percolated phase (the parallel cylinder model). Although there is yet no consensus on the internal morphology of ion channels, our work suggests that hydrogen crossover data can be useful in elucidating the ion channel morphology.

Microwave-induced band gap attenuation of novel manganese zinc aluminum sulfide kesterite nanomaterials for optimal photovoltaics

Recently, kesterite (copper zinc tin sulfide, CZTS) have emerged as a promising alternative active layer to cadmium telluride and copper indium gallium selenide for low-cost thin films for solar cell applications due to its high absorption coefficient, direct band gap, natural abundance, and low toxicity. The photovoltaic power conversion efficiency achieved with CZTS is still very low when compared to silicon, thereby hindering its commercialization. Developing new materials with improved optical and photovoltaic properties is, therefore, encouraged. Here, we report for the first time the microwave-assisted solvothermal synthesis of novel manganese zinc aluminum sulfide using chlorides, sulfates, nitrates and a mixture of chlorides, nitrates, and sulfates in ratio 1:1:1 as cation precursor salts. The influence of microwave reaction temperatures from 100 to 190 °C for 5–60 min were investigated on the crystal structure, morphology, composition, optical, and electrochemical properties. It has been found out that the microwave reaction temperature and time have potential effect on the overall reaction. The optimum temperature and time were found to be 190 °C for 5 min and 150 °C for 20 min for our studies. The obtained powder samples were analyzed using X-ray diffraction, Raman spectroscopy, energy-dispersive X-ray spectroscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared, ultraviolet-visible, cyclic voltammetry, and electrochemical impedance spectroscopy. Structural characterization using X-ray diffraction revealed that the samples synthesized with chlorides, nitrates, and mixtures of the precursor salts were all amorphous while samples synthesized with sulfate precursor salts have a kesterite crystal structure. Raman spectroscopy shows major intense peaks between 326 and 331 cm for all the nanomaterials which could be assigned to the Raman A mode of kesterite CZTS. The morphological features revealed spherical shapes with little agglomeration for all the synthesized materials except for that synthesized with sulfate precursor salts at 190 °C revealing a rod-like morphology with a width of 0.780–1.200 μm, a length of 1.90–2.5 μm and attached to the surface are agglomerated nanospheres. Small-angle X-ray spectroscopy revealed a core-shell shape for most of the nanomaterials with an average particle size between 10 and 100 nm. Electrochemical impedance spectroscopy revealed that electron transfer is faster in the nanomaterials synthesized with the chloride precursor salts at both temperatures studied. The band gap falls within the range of 1.2–1.7 eV. The nanomaterials presented in this study possess the desirable properties for application in photoelectrochemical and solar cells.

Membrane composition of polymer-lipid hybrid vesicles

Hybrid vesicles (HVs) assembled from phospholipids and amphiphilic block copolymers (BCPs) are a more recent alternative to liposomes and polymersomes. We aim to change the properties of the HV membranes by varying the chemical composition of the hydrophobic block in the BCPs that have poly(carboxyethyl acrylate) (PCEA) as the hydrophilic part. To this end, statistical copolymers of cholesteryl methacrylate and either butyl methacrylate (BuMA) or 2-hydroxyethyl methacrylate (HEMA) as well as the corresponding homopolymers were synthesized and used as macroinitiator for the extension with PCEA. All the BCPs allowed for the assembly of small and giant HVs with soybean L-α-phosphatidylcholine. The extend of the co-extisting micellar populations varied as shown by transmission electron microscopy and small-angle X-ray spectroscopy. Although the membrane packings derived from spectra when using Laurdan as an environmentally sensitive fluorescent probe were comparable between the different HVs, their permeability towards 5(6)-carboxy-X-rhodamine or carboxyfluorescein depended on the membrane composition, i.e., HEMA-containing membranes had higher permeability than membranes containing the other tested BCPs for small and giant HVs. Further, membranes with BuMA offered the most suitable environment for the association with β-galactosidase illustrated by the efficient substrate conversion. Taken together, the hydrophobic block is a relevant mean to control the morphologies and membrane properties of HVs.

Porosity of Rigid Dendrimers in Bulk: Interdendrimer Interactions and Functionality as Key Factors.

The porous structure of second- and third-generation polyphenylene-type dendrimers was investigated by adsorption of N2, Ar, and CO2 gases, scanning electron microscopy and small-angle X-ray spectroscopy. Rigid dendrimers in bulk are microporous and demonstrate a molecular sieve effect. When using CO2 as an adsorbate gas, the pore size varies from 0.6 to 0.9 nm. This is most likely due to the distances between dendrimer macromolecules or branches of neighboring dendrimers, whose packing is mostly realized due to intermolecular interactions, in particular, π–π interactions of aromatic fragments. Intermolecular interactions prevent the manifestation of the porosity potential inherent to the molecular 3D structure of third-generation dendrimers, while for the second generation, much higher porosity is observed. The maximum specific surface area for the second-generation dendrimers was 467 m2/g when measured by CO2 adsorption, indicating that shorter branches of these dendrimers do not provide dense packing. This implies that the possible universal method to create porous materials for all kinds of rigid dendrimers is by a placement of bulky substituents in their outer layer.

Design of Nanosystems for the Delivery of Quorum Sensing Inhibitors: A Preliminary Study.

Biofilm production is regulated by the Quorum Sensing system. Nowadays, Quorum Sensing represents an appealing target to design new compounds to increase antibiotics effects and avoid development of antibiotics multiresistance. In this research the use of liposomes to target two novel synthetic biofilm inhibitors is presented, focusing on a preformulation study to select a liposome composition for in vitro test. Five different liposome (LP) formulations, composed of phosphatidyl choline, cholesterol and charged surfactant (2:1:1, molar ratio) have been prepared by direct hydration and extrusion. As charged surfactants dicetyl phosphate didecyldimethylammonium chloride, di isobutyl phenoxy ethyl dimethyl benzyl ammonium chloride and stearylamine (SA) and have been used. Liposome charge, size and morphology were investigated by zeta potential, photon correlation spectroscopy, small angle x-ray spectroscopy and electron microscopy. LP-SA was selected for the loading of biofilm inhibitors and subjected to high performance liquid chromatography for entrapment capacity evaluation. LP-SA loaded inhibitors showed a higher diameter (223.6 nm) as compared to unloaded ones (205.7 nm) and a dose-dependent anti-biofilm effect mainly after 48 h of treatment, while free biofilm inhibitors loose activity. In conclusion, our data supported the use of liposomes as a strategy to enhance biofilm inhibitors effect.

Design and Characterization of Ethosomes for Transdermal Delivery of Caffeic Acid.

The present investigation describes a formulative study aimed at designing ethosomes for caffeic acid transdermal administration. Since caffeic acid is characterized by antioxidant potential but also high instability, its encapsulation appears to be an interesting strategy. Ethosomes were produced by adding water into a phosphatidylcholine ethanol solution under magnetic stirring. Size distribution and morphology of ethosome were investigated by photon correlation spectroscopy, small-angle X-ray spectroscopy, and cryogenic transmission electron microscopy, while the entrapment capacity of caffeic acid was evaluated by high-performance liquid chromatography. Caffeic acid stability in ethosome was compared to the stability of the molecule in water, determined by mass spectrometry. Ethosome dispersion was thickened by poloxamer 407, obtaining an ethosomal gel that was characterized for rheological behavior and deformability. Caffeic acid diffusion kinetics were determined by Franz cells, while its penetration through skin, as well as its antioxidant activity, were evaluated using a porcine skin membrane–covered biosensor based on oxygen electrode. Ethosome mean diameter was ≈200 nm and almost stable within three months. The entrapment of caffeic acid in ethosome dramatically prolonged drug stability with respect to the aqueous solution, being 77% w/w in ethosome after six months, while in water, an almost complete degradation occurred within one month. The addition of poloxamer slightly modified vesicle structure and size, while it decreased the vesicle deformability. Caffeic acid diffusion coefficients from ethosome and ethosome gel were, respectively, 137- and 33-fold lower with respect to the aqueous solution. At last, the caffeic acid permeation and antioxidant power of ethosome were more intense with respect to the simple solution.

Nano to microblend formation in poly(ethylene-co-methyl acrylate)/ poly(vinylidene fluoride) blend and investigation of its anomalies in rheological properties

Polymer blending is a classical approach to develop new generation materials. The investigation of material rheological and microstructure properties of the blend is essential for product development with optimized properties. In this study, poly(ethylene-co-methyl acrylate)/poly(vinylidene fluoride) (EMA/PVDF) blend prepared by melt-mixing in which PVDF concentration is varied from 10 to 40 wt%. The morphology studies of the blends using electron microscopy revealed the formation of matrix-droplet architecture. PVDF nano-droplets were dispersed in the EMA matrix, and droplet coalescence observed with the increase in PVDF concentration. The storage modulus was increased after 150 s in the time resolved modulus studies indicates the presence of specific interactions and possible physical crosslinking during the processing. Fourier transform infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC) analysis delineate the specific interactions formed during the processing. The shift in the characteristic stretching peak of the carbonyl group from 1732 to 1738 cm−1 and the formation of an exothermic peak at 100 °C during the heating cycle of the calorimetric study demonstrated the presence of the anomalies during processing. Optical microscopy and small-angle X-ray spectroscopy (SAXS) were employed to study the time resolve crystallization of EMA under isothermal condition. The increase of crystals formation with time was observed from the optical microscopy. SAXS study demonstrates that the average hard block thickness (159 Å), and the long period (134 Å) values were found maximum when the EMA samples were kept under isothermal condition at 64 °C

Theory of Optical Coupling Effects Among Surfactant Au Nanoparticles Films

In previous reports, Dalfovo et al. showed experimentally that thin films of Au nanoparticles (NP) with organic coating change their optical properties when exposed to several analytes in the vapor phase (Anal Chem 84:4886–4892 2012; J Phys Chem C 119:5098–5106 2015). This optical behavior was associated with changes in the mean distance between nanoparticles, which resulted in a displacement of their plasmon bands towards blue or red in the presence of toluene (Tol) or ethanol (EtOH) vapors, respectively. In the report by Dalfovo et al. (J Phys Chem C 119:5098–5106 2015), in-situ grazing-incidence small-angle X-ray spectroscopy (GISAXS) was performed to determine changes in the inter-NP distance within the film. In the present work, we perform theoretical calculations to interpret the results obtained by Dalfovo et al. (Anal Chem 84:4886–4892 2012; J Phys Chem C 119:5098–5106 2015). For this purpose, we employ two different theoretical approaches, a quasi-static method (QS) and the Korringa-Kohn-Rostoker method (KKR), in order to describe the plasmon resonance shift as a function of the inter-NP distance changes during exposure to Tol and EtOH vapors. Both theoretical approaches describe qualitatively the behavior observed in previous experimental results that correlate the plasmon resonant wavelength with the inter-NP distance obtained by GISAXS. Our theoretical results show that the plasmon resonant wavelength strongly depends on the ratio between the inter-particle distance and the diameter of the nanoparticles and consequently, these films could be used for optical tuning.

Concentration dependent morphology and composition of n-alcohol modified cetyltrimethylammonium bromide micelles

Cetyltrimethylammonium bromide (CTAB) is one of the most commonly used surfactants in nanoparticle synthesis and stabilization. Usually, CTAB is used in high concentrations besides co-surfactants leading to well defined products but the complex mesoscopic CTAB structures stay mostly unknown. N-alcohols for instance are widely used co-surfactants which modify the properties of native CTAB dispersions. In this paper we report about a detailed structure analysis of n-alcohol modified CTAB micelles. In particular, n-pentanol and n-hexanol exhibit a significantly different influence on the size, shape and composition of CTAB micelles. Using a combination of small-angle x-ray spectroscopy (SAXS) and neutron scattering spectroscopy (SANS), we applied a method for a complete structural characterization of such micelles. The incorporation of n-pentanol into CTAB micelles generally does not influence the morphology but enhances the number of micelles due to the volume of the added alcohol. N-hexanol, however, leads to an elongation of the micelles as a function of its concentration. It was found by extended contrast variation measurements that this difference is caused by a different distribution of the alcohols between the micellar core and shell. N-pentanol molecules are generally located at the core–shell interface of the CTAB micelles with not only the head group but also two additional methylene bridging groups located in the micellar shell. This leads to an increase of its effective head group volume. In comparison, in n-hexanol modified micelles the whole alkyl chain is located within the micellar core. The detailed structure for n-alcohol modified CTAB micelles is described herein for the first time. The knowledge of the structural details found is indispensable for an in-depth understanding of CTAB–n-alcohol–water interfaces in general which is relevant for the synthesis of many functional nanostructures like mesoporous silica and gold or silver nanoparticles.

Plasmon-actuated nano-assembled microshells

We present three-dimensional microshells formed by self-assembly of densely-packed 5 nm gold nanoparticles (AuNPs). Surface functionalization of the AuNPs with custom-designed mesogenic molecules drives the formation of a stable and rigid shell wall, and these unique structures allow encapsulation of cargo that can be contained, virtually leakage-free, over several months. Further, by leveraging the plasmonic response of AuNPs, we can rupture the microshells using optical excitation with ultralow power (<2 mW), controllably and rapidly releasing the encapsulated contents in less than 5 s. The optimal AuNP packing in the wall, moderated by the custom ligands and verified using small angle x-ray spectroscopy, allows us to calculate the heat released in this process, and to simulate the temperature increase originating from the photothermal heating, with great accuracy. Atypically, we find the local heating does not cause a rise of more than 50 °C, which addresses a major shortcoming in plasmon actuated cargo delivery systems. This combination of spectral selectivity, low power requirements, low heat production, and fast release times, along with the versatility in terms of identity of the enclosed cargo, makes these hierarchical microshells suitable for wide-ranging applications, including biological ones.

Preparation, characterization and X-ray attenuation property of Gd2O3-based nanocomposites

In an attempt to develop an alternate to lead-based X-ray shielding material, we describe the X-ray attenuation property of nanocomposites containing Gd2O3 as nanofiller and silicone resin as matrix, prepared by a simple solution-casting technique. Gd2O3 nanoparticles of size 30 and 56 nm are used at concentrations of 25 and 2.5 wt%. The nanoparticles and the nanocomposites are characterized using X-ray diffraction (XRD) studies, small angle X-ray spectroscopy (SAXS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and atomic force microscopy (AFM). The X-ray attenuation property of nanocomposites, studied using an industrial X-ray unit, shows that nanocomposites containing nanoparticles of size 56 nm (G2) exhibit better attenuation than nanocomposites containing nanoparticles of size 30 nm (G1), which is attributed to the greater interfacial interaction between the G2 nanofillers and silicone matrix. In the case of nanocomposites containing G1 nanoparticles, the interfacial interaction between the nanofiller and the matrix is so weak that it results in pulling out of nanofillers, causing voids in the matrix, which act as X-ray transparent region, thereby reducing the overall X-ray attenuation property of G1 nanocomposites. This is further corroborated from the AFM images of the nanocomposites. The weight loss and heat flow curves of pure silicone matrix and the nanocomposites containing Gd2O3 nanoparticles of size 30 and 56 nm show the degradation of silicone resin, due to chain scission, between 403 and 622 °C. The same onset temperature (403 °C) of degradation of matrix with and without nanoparticles shows that the addition of nanofillers to the matrix does not deteriorate the thermal stability of the matrix. This confirms the thermal stability of nanocomposites. Therefore, our study shows that nanocomposites containing G2 nanoparticles are potential candidates for the development of X-ray opaque fabric material.

Characterization and comparison of iron oxyhydroxide precipitates from biotic and abiotic groundwater treatments

Removal of iron is an important step in groundwater treatment for drinking water production. It is performed to prevent organoleptic issues and clogging in water supply systems. Iron can be eliminated with a purely physico-chemical (abiotic) method or biotically with the help of iron-oxidizing bacteria (FeOB). Each of the purification methods requires different operating conditions and results in formation of iron oxyhydroxide (FeOOH) precipitates. Knowledge about the differences in composition and properties of the biotic and abiotic precipitates is desirable from a technical, but also scientific point of view. In this study, a broad spectrum of analytical methods was employed to describe in detail the differences between FeOOH produced on a number of Danish waterworks using either the purely physico-chemical or the biological variation of the iron removal method. According to the results from X-ray diffraction (XRD), small angle X-ray spectroscopy, and visible light microscopy, the precipitate formed with the help of FeOB was more microcrystalline and consisted of agglomerated particles. The purely physico-chemical precipitate was more amorphous and, typically, was composed of smaller particles.

Investigations of rapid thermal annealing induced structural evolution of ZnO: Ge nanocomposite thin films via GISAXS

In this work, we present in depth structural investigations of nanocomposite ZnO: Ge thin films by utilizing a state of the art grazing incidence small angle x-ray spectroscopy (GISAXS) technique. The samples have been deposited by sequential r.f. and d.c. sputtering of ZnO and Ge thin film layers, respectively, on single crystal Si(100) substrates. Transformation of Ge layers into Ge nanoparticles (Ge-np) has been initiated by ex-situ rapid thermal annealing of asprepared thin film samples at 600 °C for 30, 60, and 90 s under forming gas atmosphere. A special attention has been paid on the effects of reactive and nonreactive growth of ZnO layers on the structural evolution of Ge-np. GISAXS analyses have been performed via cylindrical and spherical form factor calculations for different nanostructure types. Variations of the size, shape, and distributions of both ZnO and Ge nanostructures have been determined. It has been realized that GISAXS results are not only remarkably consistent with the electron microscopy observations but also provide additional information on the large scale size and shape distribution of the nanostructured components.

Silver-functionalized methyl-silica hybrid materials as antibacterial coatings on surgical-grade stainless steel

Development of new materials enriched with noble metal ions, such as silver, cobalt or copper, is of great interest in the field of commercial and medical products due to its action against fungus and bacteria. Although a large number of products are chemically active against microorganisms, they are usually limited to fabrics for medical bandages and sportswear in order to avoid, respectively, infections and odors. On the other hand, sol-gel technology becomes the preparation of hybrid materials possible with introduction of different components, as inorganic salts or organic additives within its structure bringing up the possibility to develop functional materials for different purposes. In this work, the development of an antibacterial coating for metallic substrates is presented. The coating consists in a hybrid organic-inorganic sol-gel material doped with silver. The relation between the structure of the hybrid matrix, aggregation state of silver ions, and biocide behavior is analyzed as a function of the densifying thermal treatment. Sol-gel materials were synthesized through hydrolytic condensation, in acidic conditions, of tetraethoxysilane (TEOS) and methyl-triethoxysilane (MTES). Silica nanoparticles were added in order to give a mechanical reinforcement and silver nitrate as the supplier of Ag+ ions. Coatings were deposited on 316L stainless steel and microscope glass slides by the dip-coating process at a constant withdrawal rate and densified at 50, 150 and 450 °C. X-ray photoelectron spectroscopy, small angle X-ray spectroscopy and electrochemical impedance spectroscopy were used as characterization techniques in order to elucidate silver aggregation and its influence on the structural evolution of the hybrid matrix, as a function of the thermal treatment. At the same time, the biocide behavior, as a function of silver state, particles size and thermal treatment, was studied by inhibitory halo identification on Escherichia-coli cultures in agar diffusion tests.

Chitin hydrogel reinforced with TiO2 nanoparticles as an arsenic sorbent

In this work chitin hydrogels were reinforced with TiO2 nanoparticles acting as fillers. The mechanical and physicochemical characteristics of these hydrogels were studied by oscillatory rheology, infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Small Angle X-ray Spectroscopy (SAXS). Adsorption showed to be higher at pHs below the TiO2 point of zero charge (pH≈6.9). The equilibrium was achieved within 4h following an Elovich kinetic model. The equilibrium assay showed a maximum capacity of 3.1mg/g with better fitting for the Langmuir model. Moreover, the homogeneity/heterogeneity parameters of the Sips, Toth and Redlich–Peterson models were close to a value of 1, indicating a homogeneous sorbent/sorbate interaction. Typical natural water ions competed with As(V) for the sorption sites, being sulfate the most relevant interference. This interference was also evidenced in As(V) adsorption from natural water samples where the sorption capacity varied depending the anion composition of the sample. The reutilization of the hybrid gel was assessed up to five adsorption cycles.

Comparative Study of Nb-Incorporated Cubic Mesoporous Silicates as Epoxidation Catalysts

Niobium in varying amounts was successfully incorporated into SBA-16 material via a one-pot direct synthesis technique. Complementary small angle X-ray spectroscopy (SAXS), wide-angle X-ray diffraction (XRD), N2 sorption isotherms, and high resolution transmission electron microscopy (HR-TEM) imaging results confirm the structural features and integrity of the prepared materials. The Nb-SBA-16 materials possess high surface areas (829–1060 m2/g) and pore volumes (0.69–0.82 cm3/g) that decrease with increasing niobium content. Niobium exists mostly as tetrahedral NbO4 and oligomeric NbO4 species. NH3-TPD results reveal that Nb insertion imparts Lewis acidity to the SBA-16 supports, with the acidity increasing with Nb loading. The Nb-SBA-16 materials show good cyclohexene epoxidation activity with H2O2 as oxidant, with the epoxide selectivity decreasing at higher Nb loadings due to ring-opening and other side reactions of the epoxide, attributed to increased acidity. The Nb-SBA-16 materials generally show s...

Improving the Electrochemical Performance of Li4Ti5O12 Anode through Confinement into Ordered Bimodal Porous Carbon Frameworks

Li4Ti5O12 (LTO) was confined into bimodal mesoporous carbon (BMC) framework, and the confinement effects of BMC on the crystal structure and electrochemical performances of LTO were comprehensively investigated by means of X-ray diffraction, small-angle X-ray spectroscopy, Brunaer–Emmett–Teller analysis, transmission electron microscopy, and electrochemical analysis for the first time. In comparison to bulk Li4Ti5O12 the rate capability and the cycling performance of Li4Ti5O12 confined in BMC (Li4Ti5O12@BMC) were largely improved. The rate capability of Li4Ti5O12@BMC was enhanced about 50 mA·h/g at each current rate. Li4Ti5O12@BMC showed a good cycling performance (about 245 mA·h/g at 0.5 C and 165 mA·h/g at 10 C) and high Coulombic efficiency. The enhanced properties can be attributed to the confinement effect of the hierarchical porous carbon which offered much more electrode/electrolyte interface owing to the large surface area, favored the Li+ and electron transportation due to the hierarchical bimodal pore structure, shortened the diffusion path of both Li ions and electrons, avoided the particle aggregation, and increased the conductivity of the matrix.

Membranes with Highly Ordered Straight Nanopores by Selective Swelling of Fast Perpendicularly Aligned Block Copolymers

Membranes with uniform, straight nanopores have important applications in diverse fields, but their application is limited by the lack of efficient producing methods with high controllability. In this work, we reported on an extremely simple and efficient strategy to produce such well-defined membranes. We demonstrated that neutral solvents were capable of annealing amphiphilic block copolymer (BCP) films of polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) with thicknesses up to 600 nm to the perpendicular orientation within 1 min. Annealing in neutral solvents was also effective to the perpendicular alignment of block copolymers with very high molecular weights, e.g., 362 000 Da. Remarkably, simply by immersing the annealed BCP films in hot ethanol followed by drying in air, the originally dense BCP films were nondestructively converted into porous membranes containing highly ordered, straight nanopores traversing the entire thickness of the membrane (up to 1.1 μm). Grazing incident small-angle X-ray spectroscopy confirmed the hexagonal ordering of the nanopores over large areas. We found that the overflow of P2VP chains from their reservoir P2VP cylinders and the deformation of the PS matrix in the swelling process contributed to the transformation of the solid P2VP cylinders to empty straight pores. The pore diameters can be tuned by either changing the swelling temperatures or depositing thin layers of metal oxides on the preformed membranes via atomic layer deposition with a subnanometer accuracy. To demonstrate the application of the obtained porous membranes, we used them as templates and produced centimeter-scale arrays of aligned nanotubes of metal oxides with finely tunable wall thicknesses.

Phase behavior of hierarchical mesoporous silicas prepared using ABC triblock copolymers as single templates

In this study we found that complicated mesostructures featuring bimodal mesopore distributions could be fabricated through simple evaporation-induced self-assembly when employing lab-made poly(ethylene-b-ethylene oxide-b-ε-caprolactone) (PE-PEO-PCL) triblock copolymers as single templates without any other additives. Using this approach, we produced two kinds of ultra-complicated hierarchical mesoporous silica samples as a result of the unusual composition of the ABC-type triblock copolymer: hydrophobic segments at the termini and a hydrophilic segment in the middle. Notably, by adjusting the amount of tetraethyl orthosilicate (TEOS) in the reaction medium, we obtained a series of silica samples with well-defined morphologies and two types of well-ordered hierarchical mesostructures, namely “alternate body-centered cubic” and “tetragonal cylinder alternated with face-centered cubic.” Using small-angle X-ray spectroscopy, transmission electron microscopy, and isothermal N2 adsorption–desorption experiments, we studied the phase behavior of the mesoporous silica samples templated by a series of PE-PEO-PCL triblock copolymers at various TEOS-to-PE-PEO-PCL-to-HCl weight ratios. Notably, we report the first example of the fabrication and characterization of the special “alternate body-centered cubic” mesostructure (E1T40).

Photophysical studies of CdTe quantum dots in the presence of a zinc cationic porphyrin

The photophysical properties of 2.3 nm thioglycolic acid (TGA) coated CdTe quantum dots (QDs) prepared by a reflux method have been studied in the presence of cationic meso-tetrakis(4-N-methylpyridyl) zinc porphyrin (ZnTMPyP4). Addition of the CdTe QDs to the porphyrin in H(2)O results in a marked red-shift and hypochromism in the porphyrin absorption spectrum, indicative of a non-covalent binding interaction with the QD surface. Only low equivalents of the quantum dot were required for complete quenching of the porphyrin fluorescence revealing that one quantum dot may quench more than one porphyrin. Similarly addition of porphyrin to the quantum dot provided evidence for very efficient quenching of the CdTe photoluminescence, suggesting the formation of CdTe-porphyrin aggregates. Definitive evidence for such aggregates was gathered using small angle X-ray spectroscopy (SAXS). Ultrafast transient absorption data are consistent with very rapid photoinduced electron transfer (1.3 ps) and the resultant formation of a long-lived porphyrin species.