Lamellar structure and properties in poly(ethylene terephthalate) fibers

The fibrillar and the lamellar structures in a range of poly(ethylene terephthalate) fibers were studied by small-angle X-ray scattering. The intensity maxima in the lamellar peaks lie on a curve that can be described as an ellipse. Therefore, the two-dimensional images were analyzed in elliptical coordinates. The dimensions of the coherently diffracting lamellar stack, the dimensions of the fibrils, the interfibrillar spacing, and the orientation of the lamellar surfaces were measured in addition to the lamellar spacing. The orientation of the lamellar planes and the size of the lamellar stacks had a better correlation with mechanical properties of the fibers than did the lamellar spacing. In particular, longer and wider lamellar stacks reduced fiber shrinkage, as did the closer alignment of the lamellar normal to the fiber axis. These structural features were also associated with lower tenacity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2527–2538, 1998     

Structure Characterization of Surfactant Assisted Polymer Thickeners by Silica Nanocasting

The aggregation behavior of the hydrophobically modified polyelectrolytes which act in the interplay with special surfactant mixtures as a thickener is examined by replication of the different soft matter nanostructures into silica gels. The inorganic solidified replicas can be easily microtomed and analyzed by gas sorption measurements, quantitative small angle X‐ray scattering and transmission electron microscopy. The bare hydrophobically modified polyelectrolytes show a very homogeneous structure, free of larger aggregated moieties. In addition, a transition between a weakly‐ or unaggregated structure and an aggregated structure of the bare copolymer with hydrophobic moieties of ca. 3 nm diameter was found which depends on the degree of hydrophobic substitution, the concentration, and the salt content. The simultaneous presence of surfactant in the polymer solution leads to nanocasting of both spherical (ionic surfactant) and worm‐like (zwitterionic surfactant) micelles, which are essentially unperturbed by the incorporate the hydrophobic moieties of the polymer. Optimal thickening efficiency is obtained when each of those micelles is coupled to at least two of the polymers. The resulting sterical demands are best met by the presence of worm‐like surfactant micelles.     

SAXS/DSC/WAXD study of TiO2 nanoparticles and the effect of γ-radiation on nanopolymer electrolyte

Nanostructured polymer electrolytes are very attractive materials for components of batteries and opto-electronic devices. (PEO)₈ZnCl₂ polymer electrolytes and nanocomposites were prepared using Poly(ethylene oxide) (PEO) γ-irradiated with a selected dose of 529 kGy and with an addition of 10% of TiO₂ nanograins. The influence of the added nanosize TiO₂ grains on the polymer electrolytes and the effect of the γ-radiation from a Co-60 source were studied by small-angle X-ray scattering (SAXS) simultaneously recorded with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) at the synchrotron ELETTRA. Infrared (IR) and impedance spectroscopy (IS) were also performed [1]. It was shown by previously performed IS that the room temperature conductivity of the nanocomposite polymer electrolyte increased more than two times above 65 °C, relative to pure composites of PEO and salts. We observed all changes between 20 °C and 100 °C for treated and as prepared polymer electrolyte in the SAXS, DSC and WAXD spectra and especially during the phase transition to the super-ionic phase at 65 °C [2] and [3]. The SAXS/DSC measurements yielded insight into the temperature-dependent changes of the grains of the electrolyte as well as into the differences due to different heating and cooling rates. The crystal structure and the melting and crystallization temperatures of the nanosize grains were revealed by the simultaneous WAXD measurements.     

Structural characterization of novel gemini non-viral DNA delivery systems for cutaneous gene therapy

The structural and physicochemical properties of novel cationic lipid-based DNA complexes have been investigated for the purpose of designing micro/nano-scale self-assembling delivery systems for cutaneous gene therapy. DNA/gemini surfactant (spacer n?=?3–16; chain m?=?12 or 16) complexes (1?:?10 charge ratio), with or without dioleoylphosphatidyl-ethanolamine (DOPE), designed for cellular transfection, were generally in the range of 100–200?nm as demonstrated by atomic force microscopy and particle size analysis. Small-angle X-ray scattering measurements indicated that the DNA/gemini complexes lacked long-range order, whereas DNA/gemini/DOPE complexes exhibited lamellar and polymorphic phases other than hexagonal. Correlation studies using transfection efficiency data in PAM 212 keratinocytes and in vitro skin absorption indicated that formulations containing gemini surfactants having the ability to induce structures other than lamellar in the resulting complexes, generally exhibited greater transfection activity and cutaneous absorption.     

Size Distribution of Gold Nanoparticles Used by Small Angle X-ray Scattering

ABSTRACT

The size distribution of gold nanoparticles was estimated based on the scattering intensity data obtained from small angle X-ray scattering (SAXS) and compared with the result of micrographs by transmission electron microscopy. The slope of the Guinier plot was used to estimate the mean size assuming a narrow particle size distribution. When the size distribution is narrow, the mean size can be easily obtained from slope of a Guinier plot of scattering data within 10% error. Additionally, assuming a lognormal size distribution, the size distribution and the mean size can be calculated using the experimental SAXS data in the fitting analysis. The histogram method, which utilizes the coefficient matrix of scattering intensity, was also applied to the estimation of the size distribution, and this method could be useful for a rough estimate of the size distribution.     

Kinetic and stoichiometric characterisation of streptavidin-binding aptamers

Aptamers are oligonucleotide ligands that are selected for high-affinity binding to molecular targets. Only limited knowledge relating to relations between structural and kinetic properties that define aptamer-target interactions is available. To this end, streptavidin-binding aptamers were isolated and characterised by distinct analytical techniques. Binding kinetics of five broadly similar aptamers were determined by surface plasmon resonance (SPR); affinities ranged from 35-375 nM with large differences in association and dissociation rates. Native mass spectrometry showed that streptavidin can accommodate up to two aptamer units. In a 3D model of one aptamer, conserved regions are exposed, strongly suggesting that they directly interact with the biotin-binding pockets of streptavidin. Mutational studies confirmed both conserved regions to be crucial for binding. An important result is the observation that the most abundant aptamer in our selections is not the tightest binder, emphasising the importance of having insight into the kinetics of complex formation. To find the tightest binder it might be better to perform fewer selection rounds and to focus on post-selection characterisation, through the use of complementary approaches as described in this study.     

Supercritical fluid processing of Nafion® membranes: Methanol permeability and proton conductivity

Nafion® membranes commonly used in direct methanol fuel cells (DMFC) are typically limited by high methanol permeability. These membranes have phase‐segregated sulfonated ionic domains in a perfluorinated backbone, which make processing difficult and limited by phase equilibria considerations. This study used supercritical fluids (SCFs) as a processing alternative, since the gas‐like mass transport properties of SCFs allow for better penetration into the membranes and the use of polar cosolvents could also influence their morphology, thus fine‐tuning their physical and transport properties. The SCF processing was performed at 40°C and 200 bars using pure CO₂ and CO₂ with several polar cosolvents of different size and chemical functionalities like: acetic acid, acetone, acetonitrile, cyclohexanone, dichloromethane, ethanol, isopropanol, methanol, and tetrahydrofuran. Methanol permeability measurements revealed that the SCF processed membranes reduced the permeation of methanol by several orders of magnitude, especially with the use of some small polar cosolvents. Proton conductivity measurements, using AC electrochemical impedance spectroscopy, were on the order of 0.03–0.09 S/cm, which indicates that processing with SCF CO₂ plus some cosolvents maintained the high proton conductivity while reducing the methanol permeability. The results are explained using XRD and SAXS. XRD analysis of the SCF processed samples revealed an increasing pattern in the crystallinity, which influenced the transport properties of the membrane. SAXS measurements confirmed the morphological differences that led to the changes in transport properties of the SCF processed membranes. Finally, processing flow direction (parallel versus perpendicular flow) played a major role in the morphological changes of this anisotropic membrane. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of EVA/clay Nanocomposites with improved barrier performance

Poly (ethylene‐co‐vinyl acetate) (EVA)/clay nanocomposites containing two different organoclays with different clay loadings were prepared. The transport of gases (oxygen and nitrogen) through the composite membranes was investigated and the results were compared. These studies revealed that the incorporation of nanoclays in the polymer increased the efficiency of the membranes toward barrier properties. It was also found that the barrier properties of the membranes decreased with clay loadings. This is mainly due to the aggregation of clay at higher loadings. The morphology of the nanocomposites was studied by scanning electron microscopy, transmission electron microscopy and X‐ray scattering. Small angle X‐ray scattering results showed significant intercalation of the polymer chains between the organo‐modified silicate layers in all cases. Better dispersed silicate layer stacking and more homogeneous membranes were obtained for Cloisite® 25A based nanocomposites compared with Cloisite® 20A samples. Microscopic observations (SEM and TEM) were coherent with those results. The dispersion of clay platelets seemed to be maximized for 3 wt % of clay and agglomeration increased with higher clay loading. Wide angle X‐ray scattering results showed no significant modifications in the crystalline structure of the EVA matrix because of the presence of the clays. The effect of free volume on the transport behavior was studied using positron annihilation spectroscopy. The permeability results have been correlated with various permeation models. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Silicate-based polymer-nanocomposite membranes for polymer electrolyte membrane fuel cells

Proton-exchange membrane fuel cells have emerged as a promising emission free technology to fulfill the existing power requirements of the 21st century. Nafion^® is the most widely accepted and commercialized membrane to date and possesses excellent electrochemical properties below 80 °C, under highly humidified conditions. However, a decrease in the proton conductivity of Nafion^® above 80 °C and lower humidity along with high membrane cost has prompted the development of new membranes and techniques. Addition of inorganic fillers, especially silicate-based nanomaterials, to the polymer membrane was utilized to partially overcome the aforementioned limitations. This is because of the lower cost, easy availability, high hydrophilicity and higher thermal stability of the inorganic silicates. Addition of silicates to the polymer membrane has also improved the mechanical, thermal and barrier properties, along with water uptake of the composite membranes, resulting in superior performance at higher temperature compared to that of the virgin membrane. However, the degrees of dispersion and interaction between the organic polymer and inorganic silicates play vital roles in improving the key properties of the membranes. Hence, different techniques and solvent media were used to improve the degrees of nanofiller dispersion and the physico-chemical properties of the membranes. This review focuses mainly on the techniques of silicate-based nanocomposite fabrication and the resulting impact on the membrane properties.     

Long Spacing in Polyblock Poly(ether ester)s—Origin and Peculiarities

Abstract

Poly(ether ester)s (PEE) based on poly(butylene terephthalate) (PBT) as hard segments and poly(ethylene glycols) (PEG) with different molecular weight as soft segments are studied by means of WAXS and SAXS in the drawn and undrawn state after annealing at various temperatures (T_a ). The repeatedly reported strong increase of the long spacing L with T_a is confirmed once again. In the same time the directly measured by WAXS crystallite size of PBT remains insensitive to T_a and the increase of L with T_a is the stronger, the higher the PEG content. It is concluded therefore that the rise in L is due to the expansion of the amorphous intercrystalline layers rather than to crystal thickening, the latter being the case of semicrystalline homopolymers.

The observed much stronger increase of L with T_a in undrawn samples than in drawn ones is explained by melting of less perfect crystallites at higher T_a and dephasing processes in the amorphous regions. The conclusions drawn seem to be valid for other segmented polyblock copolymers and suggest some specific features of the block copolymers in comparison to homopolymers.