“Equatorial small-angle x-ray scattering study of porosity and pore-size distribution in polyester and their influence on dyeing behavior”

For explaining the dyeing behavior of polyester (PET) fibers, the important role played by pores has been speculated upon in modern dyeing theories. In the present work, an attempt has been made to characterize the pore size spectrum in morphologically very different PET fibers by means of equatorial small-angle X-ray Scattering (SAXS). The analysis of the scattering curves reveals that all the samples analyzed in the present work have a two-phase structure, consisting of pores of widely different sizes dispersed within a matrix of the polymer network. This polydispersity of pore sizes is revealed from Guinier plots, as well as from an analysis of intensities in the tail of the scattering curves, which are found to obey Porod's Law. Estimates have been made of pore radii, pore concentration in the substrate, and specific surface. The pore size distribution function has been obtained using a new procedure. Various parameters of the pore size spectrum are discussed in relation to the morphological structure of fibers, as well as their significance to dyeing. The diffusion behavior of solvent molecules within PET is also discussed.     

Configuration of cellulose trinitrate in solution

Cellulose trinitrate was prepared from cotton (Deltapine) under a variety of conditions and investigated in solution with ethyl acetate as solvent using the techniques of light scattering, osmometry and viscometry. The more mildly nitrated samples (e.g. 1 h at 20°C) exhibited downward curvature in the Zimm plots and a fractional precipitation experiment showed that this was due to the presence of large gel-like aggregates. Light scattering, viscometry, infra-red and ultracentrifuge measurements were made on the fraction of gel-like material and the effect of further nitration investigated. The possible nature of the aggregates is discussed. Light scattering measurements made on a mildly nitrated sample with this fraction removed yielded a straight line Zimm plot from which chain statistics similar to those found by other authors could be deduced. Samples obtained by more extensive nitration (2–25 h at 20°C) were considerably degraded but yielded straight line Zimm plots and osmotic pressure measurements showed the polydispersities to be low (DP_w/DP_n 1.3). Values of effective bond length, b, calculated from these Zimm plots (4.6 to 5.6 nm) were much larger than those found for the more mildly nitrated samples and those found by other authors. Also, in contrast to the results of other authors, second virial coefficients obtained by light scattering and osmotic pressure were found to be in fair agreement. The effect of gel-like material on measured second virial coefficients is discussed. It is suggested that the discrepancy in b arises because gel-like material remains in more mildly nitrated samples even after the larger aggregates have been removed by fractional precipitation. This material consists of particles denser than the single coils but of comparable or smaller size so that values obtained for the effective bond length are too low. The results of previous investigations on all the cellulosic polymers which have been investigated are discussed in the light of the present work with particular reference to the effect of gel-like material. It is suggested that the apparent disagreement between the conformational analysis of cellulose and experimental results arises from the presence of gel-like material in solutions rather than any fault in the molecular model.     

Small-angle X-ray scattering experiments and computer simulations to characterise anisotropy of activated carbons prepared from wood

Small-angle scattering was measured from activated carbon monoliths prepared from three different wood species (European beech, Pedunculate oak and Norwegian spruce). Substantial differences were found in the scattering images of axial and tangential slices, attributed to their characteristic phytogenic structures. The decrease in anisotropy in the nanostructured carbon matrix due to the activation process is also different among the three investigated types of wood. For quantitative characterization of the anisotropy and its decrease, the degree of alignment was calculated from the azimuthal scattering curves. A simple numeric model was constructed on the basis of direct information obtained by atomic force microscopy. Scattering patterns calculated from the model were compared with the experimental ones to explain the possible structural changes in the carbon skeleton.     

The Effects of Monomer Size Distribution on the Radiative Properties of Black Carbon Aggregates

Black carbon (BC), normally existing as aggregates, significantly affects the Earth radiative forcing, energy balance, and climate by scattering and absorbing both solar radiation and terrestrial emission. The BC particles are usually treated as fractal aggregates with same-sized monomers. However, experimental studies show that monomer diameters of BC normally obey a lognormal distribution ranging from 10 nm to over 100 nm. This study investigates the effects of monomer size distribution on the radiative properties of BC particles. The fractal aggregates are generated by a cluster–cluster aggregation (CCA) algorithm, and the Multiple Sphere T-Matrix (MSTM) method is used to simulate the radiative properties of randomly oriented aggregates. The integral radiative properties of aggregates with different-sized monomers have normal distributions with large standard deviations, and it requires to average radiative properties of over 60 aggregate realizations to represent their ensemble-averaged properties. The aggregates with different-sized monomers exhibit much stronger scattering and absorption than the aggregates with same-sized monomers and the geometric mean diameter, whereas the absorption cross section becomes comparable to that given by aggregates with same-sized monomer and the equivalent volume diameter. Similar phase matrix elements are obtained for the aggregates with different-sized and same-sized monomers. Furthermore, the Rayleigh-Debye-Gans (RDG) approach is significantly challenged for approximating the absorption and scattering cross sections of the aggregates with different-sized monomers, whereas it performs quite accurately for the phase matrix elements.

Copyright 2015 American Association for Aerosol Research     

Chain dimensions of crystallizable polymers in the solid and melt states

Small angle neutron scattering (SANS) data were obtained on hydrogenated polybutadiene, a crystallizable polymer (α_c≈0.4), which is equivalent in chemical microstructure to polyethylene with ca. 18 ethyl groups per 1000 main chain carbon atoms. One linear sample (M=62 400) and one 3-arm star (M=104 400) were used; labelled species were prepared by deuteration of the parent polybutadienes. Scattering curves were obtained in both the solid state and the melt with mixtures containing up to 30% of the labelled species. The results indicated random mixing in the melt and the rapidly crystallized solid, and only a very slight amount of segregation in the slowly crystallized solid. The scattering curves conformed to predictions for random coil molecules over a wide range of scattering vectors. The radius of gyration obtained was the same in the solid and melt states, and in close agreement with θ solvent values for polyethylene.     

CHARACTERIZATION OF PROTEINS DURING AGGREGATION II: USE OF MODEL MOLECULES FOR SPECTROSCOPY ANALYSIS

This study describes the progress made in the use of combined light scattering-spectral deconvolution techniques for the quantitative characterization of proteins in particular, pituitary and recombinant porcine somatotropin. Model molecules for the main ultraviolet chromophores contained in proteins (i.e., tyrosine, tryptophan, phenylalanine and cysteine) have been investigated as functions of ionic strength and denaturant concentration. The objective, in the use of model molecules for the representation of the spectra, is the identification and quantification of the spectral changes undergone by proteins during denaturation and renaturation reactions. Since the denaturation-renaturation reactions of porcine somatotropin involve aggregation processes, the effects of the combined absorption and scattering have been accounted for through the use of Mie and Rayleigh-Gans theories. It is demonstrated that quantitative information on the functional groups participating in the denaturation-renaturation reactions can be obtained through the use of combined light scattering-sped ral deconvolution techniques. The results suggest that not only quantitative size and composition information can be extracted from spectral data but, also, that an effective internal pH for the aggregates may be obtained. The aggregate size and the fraction of dissociated tyrosines estimated suggest that porcine somatotropin may not completely denatured in 6M guanidine/HCl. It is evident that if the appropriate corrections are not included, standard light scattering and uv-vis spectroscopy techniques may be misleading when used for the assessment of the denaturation-renaturation processes.     

Morphology of water-blown flexible polyurethane foams

A series of four TDI–polypropylene oxide (PO) water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of both the foams and plaques was investigated using dynamic mechanical spectroscopy (DMS), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM), swelling, wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS). A high degree of microphase separation occurs in these foams, and its degree is nearly independent of water (hard segment) content. In the foam with the lowest water content the morphology possesses many similarities to that of typical linear segmented urethane elastomers. Small hard segment domains are present with a correlation distance of about 7.0 nm. When the water content is increased a binodal distribution of hard segment material appears. There are the small hard segment domains typical of segmented urethane elastomers as well as larger “hard aggregates” greater than 100 nm in size. The larger domains are thought to be aggregates of rich polyurea that develop by precipitation during the foaming reaction. WAXS patterns of the foams suggest urea and possibly hard segment ordering that may be of a paracrystalline nature but certainly lacking in true 3-dimensional crystallinity.     

Small-angle X-ray scattering study of halato-telechelic polybutadienes

Summary The small-angle X-ray scattering curves of carboxy-telechelic polymers exhibit very strong scattering at the lowest angles which points to the presence of large aggregates in the samples. Beyond the position of the main scattering maximum, common to all ionomers, a faint modulation is observed at a position corresponding to a second diffraction order. These observations are discussed with respect to other data in the litterature.     

Waste Rapeseed Oil Used as a Binder for Masonry Units: NMR Spectroscopic Analysis

The chemistry of unsaturated oils used as binders for masonry units is under investigation, as it is likely to be relevant to their long term properties and may be used to improve the manufacturing requirements. The mixing process is followed by heat curing for 24 h, during which time the unit gains strength. The chemistry of this process has been assumed to be a complex series of oxidative and thermal reactions due to the double bonds present in the triacylglycerol (TAG) hydrocarbon chains, producing a heterogeneous, cross-linked solid matrix which encapsulates solid aggregates. A number of model samples and binder obtained from cured blocks were analysed via several NMR techniques. The reactions are characterised by consumption of polyunsaturated fatty acids (PUFA) and monounsaturated fatty acids (MUFA) and formation of oxygenated compounds, chain-shortened TAG, free fatty acids (FFA), di- and monoacylglycerols (DAG and MAG) and cross-linked material. The analysis facilitates identification of specific products and mechanisms of formation as the curing progresses, and evidence for instability of particular species in the matrix from samples retrieved after 6 months of storage.     

Composite inorganic membranes containing nanoparticles of hydrated zirconium dioxide for electrodialytic separation

The aim of the work was to elucidate the nature of charge-selective properties of macroporous composite inorganic membranes modified with nanoparticles of hydrated zirconium dioxide. The membranes have been investigated using methods of standard contact porosimetry, potentiometry, electron microscopy and small-angle X-ray scattering. The ion exchanger has been found to deposit inside pores of ceramics. Differential curves of pore volume distribution have been resolved using Lorentz functions; each maximum has been related to structure elements of the matrix and ion exchanger by means of calculations according to homogeneous and heterogeneous geometrical models. It was found that the voids, the radius of which is 4 to 8 nm, are responsible for charge selectivity of the composite membranes. These pores are formed due to blocking of macropores of ceramics with aggregates of nanoparticles of the ion exchanger; the radius of these aggregates is 20 to 24 nm. The membranes were applied to desalination of the solution containing NaCl. The removal degree of the salt from the solution reached 95% and 9% for the composite and unmodified membranes, respectively.     

Characterization of Polyglycerol Polyricinoleate Formulations Using NMR Spectroscopy, Mass Spectrometry and Dynamic Light Scattering

Three different analytical techniques, namely NMR spectroscopy, mass spectrometry and dynamic light scattering, were used to unravel the structure and morphology of polyglycerol polyricinoleate (PGPR). This material is used as an emulsifier in the preparation of chocolate and other confectionary products. The use of 1D and 2D NMR techniques led to the distinction of two separate entities in commercial ricinoleic acid (RA) and PGPR samples, namely the monomeric and oligomeric RA (estolides). ¹H and ¹³C spectra of PGPR confirmed the presence of polyglycerol moieties of various lengths being esterified by RA and estolides and to a lesser extent by oleic and linoleic acids. ¹³C-NMR DOSY experiments demonstrated the occurrence of several species in PGPR. Electrospray Ionization and tandem Mass Spectrometry succeeded in identifying the presence of over 30 glycerol/polyglycerol species containing n glycerol moieties with n = 1–6 esterified by monomeric and oligomeric RA molecules. Dynamic light scattering contributed to the characterization of PGPR morphology. The PGPR mixture contains relatively small-sized entities (monomers, dimmers, trimmers) and larger aggregates resulted from chain association. The percentage of larger aggregates is minimal compared to small-sized species.     

Electrospinning of nanofibers from non-polymeric systems: polymer-free nanofibers from cyclodextrin derivatives

High molecular weight polymers and high polymer concentrations are desirable for the electrospinning of nanofibers since polymer chain entanglements and overlapping are important for uniform fiber formation. Hence, the electrospinning of nanofibers from non-polymeric systems such as cyclodextrins (CDs) is quite a challenge since CDs are cyclic oligosaccharides. Nevertheless, in this study, we have successfully achieved the electrospinning of nanofibers from chemically modified CDs without using a carrier polymer matrix. Polymer-free nanofibers were electrospun from three different CD derivatives, hydroxypropyl-β-cyclodextrin (HPβCD), hydroxypropyl-γ-cyclodextrin (HPγCD) and methyl-β-cyclodextrin (MβCD) in three different solvent systems, water, dimethylformamide (DMF) and dimethylacetamide (DMAc). We observed that the electrospinning of these CDs is quite similar to polymeric systems in which the solvent type, the solution concentration and the solution conductivity are some of the key factors for obtaining uniform nanofibers. Dynamic light scattering (DLS) measurements indicated that the presence of considerable CD aggregates and the very high solution viscosity were playing a key role for attaining nanofibers from CD derivatives without the use of any polymeric carrier. The electrospinning of CD solutions containing urea yielded no fibers but only beads or splashes since urea caused a notable destruction of the self-associated CD aggregates in their concentrated solutions. The structural, thermal and mechanical characteristics of the CD nanofibers were also investigated. Although the CD derivatives are amorphous small molecules, interestingly, we observed that these electrospun CD nanofibers/nanowebs have shown some mechanical integrity by which they can be easily handled and folded as a free standing material.     

The Role of Pectobacterium atrosepticum Exopolysaccharides in Plant–Pathogen Interactions

The phytopathogenic bacterium Pectobacterium atrosepticum (Pba), one of the members of the soft rot Pectobacteriaceae, forms biofilm-like structures known as bacterial emboli when colonizing the primary xylem vessels of the host plants. The initial extracellular matrix of the bacterial emboli is composed of the host plant’s pectic polysaccharides, which are gradually substituted by the Pba-produced exopolysaccharides (Pba EPS) as the bacterial emboli “mature”. No information about the properties of Pba EPS and their possible roles in Pba-plant interactions has so far been obtained. We have shown that Pba EPS possess physical properties that can promote the maintenance of the structural integrity of bacterial emboli. These polymers increase the viscosity of liquids and form large supramolecular aggregates. The formation of Pba EPS aggregates is provided (at least partly) by the acetyl groups of the Pba EPS molecules. Besides, Pba EPS scavenge reactive oxygen species (ROS), the accumulation of which is known to be associated with the formation of bacterial emboli. In addition, Pba EPS act as suppressors of the quantitative immunity of plants, repressing PAMP-induced reactions; this property is partly lost in the deacetylated form of Pba EPS. Overall, our study shows that Pba EPS play structural, protective, and immunosuppressive roles during Pba–plant interactions and thus should be considered as virulence factors of these bacteria.     

Nanostructural features in silica-polyvinyl acetate nanocomposites characterized by small-angle scattering

Small-angle scattering (SAS) experiments were carried out on nanocomposites of poly(vinyl acetate) (PVAc) and fumed silica nanoparticles with different surface areas and chemical treatment, in the wave-vector (Q) range: 0.0002-1 Å⁻¹ . SAS data on composites with matrices of two different molecular weights indicate that the particle aggregation is independent of the molecular weight of the matrix for a fixed filler concentration and surface treatment. Particle size distributions derived from the SAS data suggest that particle aggregation is reduced when the native surface hydroxyl groups are blocked by various surface treatments, which also reduce the bonding strength to the polymer matrix. The unified exponential/power-law analysis of the SAS data shows three levels of hierarchy in the organization of silica particles. The first level consists of small aggregates of silica particles. At the second level we observe polydispersed aggregates resembling mass-fractal objects that is corroborated by TEM. The polydispersed aggregates further associate to form agglomerates at the third level. The relevance of these findings to the mechanism of nanofiller reinforcement of linear amorphous polymers above T_g is discussed.     

The analysis of lipids via HPLC with a charged aerosol detector

Because most lipid extracts are a mixture of saturated and unsaturated molecules, the most successful strategies for the quantitative analysis of lipids have involved the use of so-called “mass” or universal detectors such as flame ionization detectors and evaporative light scattering detectors. Recently a new type of HPLC “mass” detector, a charge aerosol detector (CAD), was developed and is now commercially available. This detection method involves nebulizing the HPLC column effluent, evaporating the solvents charging the aerosol particles, and measuring the current from the charged aerosol flux. In the present study, the CAD was evaluated with several normal phase and reverse phase HPLC methods commonly used for the quantitative analysis of lipid classes and lipid molecular species. The CAD detected common lipids such as triacylglycerols, diacylglycerols, glycolipids, phospholipids, and sterols. Lower molecular weight lipids such as free FA had smaller peak areas (50–80% lower). FAME were not detected by the CAD, probably because they were completely evaporated and did not form aerosol particles. The minimum limits of detection of the CAD with lipids varied with different mobile phase solvents. Using solvent systems that were predominantly hexane, the minimum limits of detection of triacylglycerols, cholesterol esters, and free sterols were about 1 ng per injection and the mass-to-peak area ratio was nearly linear from the range of about 1 ng to about 20 mg per injection. Three other solvents commonly used for HPLC lipid analysis (methanol, isopropanol, and acetonitrile) caused higher levels of background noise and higher minimum limits of detection. These experiments indicate that the CAD has the potential to become a valuable tool for the quantitative HPLC analysis of lipids. Long-term studies are needed to evaluate full instrument performance.     

Multilayered confinement of iPP/TPOSS and nylon 6/APOSS blends

A series of isotactic polypropylene and nylon 6 blends with silsesquioxane (POSS) additives were produced, then layered to nanometer thicknesses to test the effects of confinement upon polymer property modification. POSS is shown to be a poor filler, lacking solubility and favorable interaction with the polymer matrices. It was initially hypothesized that under extreme confinement and orientation, such as in melt-spun fibers, or confined within 2D nanoscale layers, that POSS would undergo forced-assembly into elongated, rebar-like reinforcement structures, or even act as crosslinking molecules for the polymer chains. The current results, however, show POSS existing as large, phase separated aggregates, in order to minimize interactions with the polymer matrix; the aggregates behave as debonded hard particles upon tensile deformation. POSS has been previously shown to enhance the properties of polymer matrices in which the POSS molecules have been grafted to, or copolymerized within the chain, but this is not the case for these POSS blends. In comparison to results from the iPP/DBS/TPOSS system, in which POSS is unable to directly interact with the polymer matrix, and the nylon 6/APOSS system, in which POSS can potentially form hydrogen bonds with the polymer matrix, the results are similar and reveal that POSS blends are largely incompatible with the polymer matrix. Small improvements in blend properties can be made via functionalization of the POSS cage, in order to enhance interactions, but these improvements are quite limited.     

Conformation of the molecules in drawn polypropylene revealed by neutron scattering studies

It has not been possible previously to do a complete study of drawn polyolefins using SANS techniques because of void scattering. In the case of polypropylene this can be reduced sufficiently to permit measurements with the Q-vector perpendicular and parallel to the draw direction. A complete analysis has been carried out with a draw ratio 8:1 in which the PPD molecules of narrow molecular weight distribution and molecular weights in the range 390 000 to 50 000 are molecularly dispersed in a drawable PPH matrix. The dimensional changes on drawing are to extend the molecule by a factor of 2 with a corresponding reduction in diameter to a maximum of 40%. We have interpreted the data at high Q on the basis that the molecule is not uniformly distributed but the majority is folded into sub-units and the number of these is proportional to the molecular weight of the polymer. A further feature of the sub-units structure is that its length is approximately two lamellae thick, this dimension is similar to the SANS scattering length (I_n) identified in the study of isotropic material. The double stems belonging to the same molecule have been concentrated by the drawing process some 16 times and a consequence of this is to markedly change the Kratky curves from the isotropic case. Notwithstanding, this increase in the packing of the molecule, the stems are still, on average, some 40 Å apart and surrounded by many stems belonging to other macromolecules. Similarly, each sub-unit is surrounded by sub-units belonging to neighbouring molecules.     

Fractal dimension of fumed silica: Comparison of light scattering and electron microscope methods

Due to the enormous increase in nanopowder production, it becomes necessary to find and develop adapted characterization techniques. In the case of nanostructured agglomerates, the structure of these particles has a direct impact on flowing, and handling, but also on end-use final product properties. In this work, a fractal approach is used to characterize the agglomerate structure using two different, commercially available and widely used, methods: static light scattering (SLS) and image analysis of scanning electron microscope (SEM) photographs of the aggregates. Fumed silica aggregates are used for this comparison. The results by image analysis show that fumed silica aggregates have a two-level structure, made of compact aggregates of open aggregates of nanoparticles. This structure is not detected by SLS. For such a structure, SLS seems to be less accurate than image analysis method, although it could be an interesting technique in more simple cases, since it is a much less time-consuming technique.     

Small-Angle X-Ray Scattering Analysis of Nucleation in Glass: I, Matrix Scattering and Sample Surface Effects

Two major sources of experimental error are examined in the analysis of small-angle X-ray scattering (SAXS) data from weakly scattering or nearly homogeneous multiphase glasses. The effect of sample surface structure and the importance of a well-polished surface are examined. There is also a contribution to the measured SAXS from the homogeneous matrix or solvent structure of the glass. This contribution arises from short-range frozen-in density fluctuations within the glass. A method for correcting this contribution before analyzing for particulate microstructure is described. In addition, SAXS curves for several commercial glasses are presented.     

Nondestructive Analysis of Total Nonvolatile Carbon by Forward Alpha Scattering Technique (FAST)

The oldest method of nuclear analysis, Rutherford scattering of alpha particles, is the basis of a technique we have developed that is capable of the quantitative nondestructive determination of carbon and all other elements lighter than sodium on an aerosol filter. Samples are collected on thin-stretched teflon filters, which are then placed in the 30-MeV alpha-particle beam of the Crocker Nuclear Laboratory's 193-cm cyclotron. Scattered alpha-particles are detected at the forward angles of 62 and 74 degrees, and the method has become known as FAST, for forward alpha scattering technique. The fluorine content of the air particles is assumed to be much less than the carbon content, and the filter blank carbon is subtracted from the known CF₂ ratio of teflon. Sensitivities for carbon are limited by the need to subtract the 70 μg/cm² of carbon in the filter, which can be done to ±5%, or ±3.5 μg/cm². This amounts to ±0.15 μg/m³ for the National Park Service aerosol samples. Since the FAST analysis is done in vacuum, only nonvolatile species are measured. This technique provides an alternative way to measure carbon without using artifact-prone quartz filters.