Detection of obscured glass transitions by QiDSC

Determination of compatibility in the amorphous phase for a two component blend is usually accomplished by analyzing for whether one notes one or two glass transitions. This can be complicated when one of the components is semicrystalline and its melting peak obscures the second glass transition. Quasi-isothermal differential scanning calorimetry (QiDSC) can be used to detect an obscured glass transition by allowing the semicrystalline component to melt and relax revealing the underlying glass transition of the other component. QiDSC is accomplished by performing a modulated temperature DSC experiment at a particular temperature and step ramping through the transitions of interest. For this study two systems are investigated. The first system is a model system based on a blend of polystyrene (PS) and a copolymer of vinylidene fluoride and hexafluoropropylene, P(VF₂/HFP). The glass transition for the PS occurs at the same temperature as the melting point for the fluoro-copolymer. The second system is a fluoro-copolymer/acrylic dried latex. In both cases the hidden glass transition can be noted in the reversing heat capacity of the QiDSC analysis.     

Light scattering by polyhedral particles in the Rayleigh-Gans domain

Summary The light scattering properties of certain regular polyhedral particles in theRayleigh-Gans region are considered. The particle scattering factors are derived for dispersions of square pyramids and dispersions of octahedra, oriented at random to the incident beam. Numerical results are presented both for the average scattering factor and for the average 45° dissymmetry of arrays of such particles.

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Zusammenfassung Es wurde die Lichtstreuung pyramidenf?rmiger und oktaedrischer Teilchen imRayleigh-Gans-Bereich untersucht und Ausdrücke für den Teilchen-Streufaktor bei statistischer Orientierung solcher Teilchen abgeleitet. Für den mittleren Teilchen-Streufaktor und für die mittlere Dissymmetrie wurden numerische Ergebnisse angegeben.

     

Hard domain compression of triblock-copolymer gels by high pressure X-ray small-angle scattering

Small-angle X-ray scattering using synchrotron radiation at pressures up to 700 MPa has been performed on triblock-copolymer gels, polystyrene-rubber-polystyrene with poly(ethylene/butylene) as the rubber mid-blocks. A 2-stage pressure behaviour could be verified by comparison of the experimental data with the Tait-equation and a model of pressure screening.     

Inhibition assay of yeast cell walls by plasmon resonance Rayleigh scattering and surface-enhanced Raman scattering imaging

We report on plasmon resonance Rayleigh scattering (PRRS) and surface enhanced Raman scattering (SERS) imaging for inhibition assay of yeast cell walls. This assay reveals that the proteins having alkali sensitive linkage bound to β1,3 glucan frameworks in cell walls are involved in SERS activity. The result is further confirmed by comparison of genetically modified cells and wild type cells. Finally, we find that PRRS and SERS spots do not appear on cell walls when daughter cells are enough smaller than parent ones, but appear when size of daughter cells are comparable to parent cells. This finding indicates the relationship between expression of the proteins that generate SERS spots and cell division. These results demonstrate that PRRS and SERS imaging can be a convenient and sensitive method for analysis of cell walls.     

Mechanism of stabilization of polypropylene by ultraviolet absorbers

The ultraviolet screening properties of 2-hydroxyphenylbenzotriazoles and 2-hydroxybenzophenones in polypropylene film were investigated by using photochemical and spectroscopic techniques. The effect of light screening on polymer photostability was examined by using filter solutions, and the fraction of ultraviolet light absorbed by stabilized film was calculated and compared to flexural failure times. It was found that the 2-hydroxyphenylbenzotriazoles behave primarily as screeners of ultraviolet light whereas the 2-hydroxybenzophenones are both screeners and excited-state quenchers. The quenching characteristics of the latter have not been isolated and mechanistically examined, but it is probably similar in nature to that of the nickel chelate stabilizers.     

Chemical imaging by single pulse interferometric coherent anti-stokes Raman scattering microscopy

A single pulse interferometric coherent anti-Stokes Raman (CARS) spectroscopy method is used to obtain broadband CARS spectra and microscopy images of liquid and polymer samples. The pump, Stokes, and probe pulses are all selected inside a single broadband ultrafast pulse by a phase- and polarization-controlled pulse shaping technique and used to generate two spectral interference CARS signals simultaneously. The normalized difference of these two signals provides an amplified background-free broadband resonant CARS spectrum over the 400-1500 cm(-1) range with 35 cm(-1) spectral resolution. Chemically selective microscopy images of multicomponent polymer and liquid samples are investigated with this new CARS method. Multiplex CARS spectra at 10,000 spatial points are measured within a few minutes, and used to construct chemically selective microscopy images with a spatial resolution of 400 nm. The spectral bandwidth limits, sensitivity, homodyne amplification advantages, spatial resolution, depolarization, chromatic aberration, and chemical imaging aspects of this new technique are discussed in detail.     

Swallowtail bacteriochlorins. Lipophilic absorbers for the near-infrared

Bacteriochlorins absorb strongly in the near-infrared spectral region and hence are ideally suited for diverse photomedical applications, yet naturally occurring bacteriochlorins have limited stability and synthetic malleability. A de novo route has been exploited to prepare synthetic bacteriochlorins that bear a geminal dimethyl group in each pyrroline ring for stability and a symmetrically branched 1,5-dimethoxypentyl group attached to each pyrrole ring for solubility in lipophilic media.     

Determination of the width of the domain boundaries in polymer two-phase systems by X-ray small-angle scattering

An accurate determination of the width of domain boundaries presupposes an unambigous elimination of the intensity component due to density fluctuations within the domains. The theoretical aspects of this problem are discussed and an application is demonstrated in an SAXS study of a styrene-isoprene-styrene blockcopolymer. The widths of the domain boundaries depend on the history of the sample, its values are, in general, smaller than theoretically predicted. The domain sizes correspond to the theoretical values, its variance is of the same order as the variance of the molecular weight of the domain-building blocks.Dedicated to Prof. Dr. Dr. h. c. O. Kratky on the occasion of his 80th birthday.     

Frequency doubling scattering and second-order scattering spectra of phosphato-molybdate heteropoly acid-protein system and their analytical application

In the sulfuric acid medium, the reaction of heteropoly compounds with proteins could result in the enhancement of frequency doubling scattering (FDS) and second-order scattering (SOS). Based on the characteristic, a novel method for the determination of trace amounts of protein by using the FDS and SOS method has been developed. Their maximum scattering wavelengths, lambda(ex)/lambda(em), appear at 940/470 nm for FDS and 350/700 nm for SOS, respectively. In a certain range, the concentration of proteins is directly proportional to the enhanced intensity of FDS and SOS. The suitable reaction conditions, affecting factors as well as the influence of some coexisiting substances were investigated. The methods exhibited high sensitivity, and the detection limits were in the range of 8.6-39.3 ng ml(-1) depending on different methods. The method had good selectivity, and was applied to the determination of protein in synthetic samples and practical samples with satisfactory results.     

Interaction of ultraviolet absorbers

Ultraviolet absorbers (UVA) are used in various fields, and their interactions with other additives have been studied. However, the interaction between UVA has not been studied in detail. In this study, the interaction of two UVA having maximum absorption in the range of UV-A (320-400 nm) or UV-B (290-320 nm) was studied. It was found that the photo-oxidation occurs by the fluorescence, which is emitted by a photo-excited UVA-B, if it has enough high energy, that is, its wavelength is within UV-A range. When a UVA-A coexists with such a UVA-B, however, the mixture of both UVA may show a synergism, because the UVA-A absorbs the fluorescence from UVA-B to make it harmless. Particularly, the mixture of hydrogen transfer-type UVA and charge separation-type UVA shows remarkable synergism. The synergistic mechanism is discussed.     

Light scattering by cellulose. III. Morphology of wood

Radial, tangential and cross cuts of Eastern spruce are examined by a solid-state light-scattering method which allows study of light scattering due to fluctuations in density and fluctuations in anisotropy. All of the samples investigated show well-defined scattering maxima which are related to their anisotropic texture with limited contributions from random density fluctuations. The radial cuts give rise to scattering similar to that by a grating with orthogonal characteristic spacings. The gratinglike character is due mainly to the pit structure and their periodic spacings, which can be deduced from the “unit-cell” dimensions of the scattering pattern. The scattered intensity is maximum when the fiber direction is at 45° to the polarization direction; when it is either horizontal or vertical, a distinct “spherulitic” scattering is observed from which size and asymmetry of the pits can be deduced.     

Controllable source-object light scattering imaging in optical systems

Abstract

The imaging process in an ideal optical system with an essentially inhomogeneous source-object, based on a liquid crystal, is discussed.     

Numerical reconstruction of fine structure in obscured backscattering spectra

Revelation of details which are hidden in a backscattering spectrum due to finite apparatus resolution demands the numerical solution of a linear Fredholm integral equation of the first kind with only approximately known and near-singular kernel. Unphysical oscillations of the solution are largely avoided by properly chosen smoothness conditions. Adequate algebraization of the problem is achieved by approximation of the solution by a cubic spline function. Reliability of the approach is studied by mathematical experiments with realistic kernels.     

Surface enhanced resonance Raman scattering imaging of Langmuir-Blodgett monolayers of bis (benzimidazo) thioperylene.

The synthesis, spectroscopic characterization and surface-enhanced spectroscopy of a new electro active organic material bis (benzimidazo) thioperylene (Monothio BZP) are reported. Langmuir monolayers of Monothio BZP were successfully formed on water subphase and characterized by the pi-A surface-pressure area isotherm. Langmuir-Blodgett (LB) monomolecular layers of Monothio BZP were fabricated onto glass substrates and onto silver island films for surface-enhanced spectroscopic studies. The results of surface-enhanced resonance Raman scattering (SERRS), SERRS imaging and surface-enhanced fluorescence (SEF) studies for Monothio BZP LB monolayers are reported. Raman imaging (global imaging and point-by-point mapping) of the SERRS signal for a single monomolecular layer on silver islands were obtained using the 514.5 nm laser line. The SERRS imaging permits a visualization of the variation of the SERRS intensity across of the rough metal surface. The SEF was recorded for the excimer emission of aggregates in the LB film. The distance dependence and the enhancement factor of SEF were determined using fatty acid spacing layers. A temperature dependence study of the LB monolayer SERRS and SEF spectra was carried out between -190 degrees and + 200 degrees C confirming the thermal stability of the LB monolayer on silver. The specificity and the sensitivity of SERRS signal on metal island films was probed using mixed LB films with 0.01% molecular ratio of Monothio BZP in Arachidic Acid (AA). The micro-Raman SERRS spectra from ca. 10(-3) attomole of the dye were recorded.     

Quantitative chemical imaging with multiplex stimulated Raman scattering microscopy

Stimulated Raman scattering (SRS) microscopy is a newly developed label-free chemical imaging technique that overcomes the speed limitation of confocal Raman microscopy while avoiding the nonresonant background problem of coherent anti-Stokes Raman scattering (CARS) microscopy. Previous demonstrations have been limited to single Raman band measurements. We present a novel modulation multiplexing approach that allows real-time detection of multiple species using the fast Fourier transform. We demonstrate the quantitative determination of chemical concentrations in a ternary mixture. Furthermore, two imaging applications are pursued: (1) quantitative determination of oil content as well as pigment and protein concentration in microalgae cultures; and (2) 3D high-resolution imaging of blood, lipids, and protein distribution in ex vivo mouse skin tissue. We believe that quantitative multiplex SRS uniquely combines the advantage of fast label-free imaging with the fingerprinting capability of Raman spectroscopy and enables numerous applications in lipid biology as well as biomedical imaging.     

Direct imaging of surface-enhanced Raman scattering in the near field

By using near-field scanning microscopy/spectroscopy, we show that surface-enhanced Raman scattering (SERS) of rhodamine 6G deposited on self-affine silver colloidal film is localized to small, down to less than 200 nm, portions of the film. The locus of the SERS signals ("hot spots") does not necessarily reside in special topographic elements such as interstices and between nanoparticles. The local SERS enhancement is estimated to be over 3 orders of magnitude higher compared to the far-field measurements. Near-field imaging of SERS directly validates the theory of the optical response of self-affine fractal objects.     

Femtosecond laser ablation: Visualization of the aerosol formation process by light scattering and shadowgraphic imaging

The shockwave propagation and aerosol formation during femtosecond laser ablation (fs-LA) of dielectric materials (Li₂B₄O₇, Y:ZrO₂) in ambient air were monitored using shadowgraphy and light scattering. Three independent shockwave fronts were observed originating from (i) the instantaneous compression of ambient gas during the initial stage of fs-LA, (ii) a secondary compression caused by material ejection, and (iii) an air breakdown well above the target surface. In addition, particle size distributions were found to be multimodal implying the co-existence of condensational growth and supplementary particle production pathways such as phase explosion or critical point phase separation (CPPS). As a consequence, fs-LA of Li₂B₄O₇ resulted in the formation of primary aggregates reaching diameters of > 10 μm. In contrast, aggregates formed during fs-LA of Y:ZrO₂ covered a size range < 1 μm. Our data, furthermore, indicate the existence of a breakdown channel in the ambient atmosphere being capable to carry plasmatic, i.e. non-condensed matter beyond the primary shockwave barrier which may occasionally causes a spatial separation of material released. Assuming the Taylor-Sedov model of explosion to be valid the over-all energy dissipated in acoustic transients was found to exceed values of 50%.     

Inherent complexities of trace detection by surface-enhanced Raman scattering.

Surface-enhanced Raman scattering (SERS) and surface-enhanced resonance Raman scattering (SERRS) are powerful optical scattering techniques used in such frontier areas of research as ultrasensitive chemical analysis, the characterization of nanostructures, and the detection of single molecules. However, measuring and, most importantly, interpreting SERS/SERRS spectra can be incredibly challenging. This is the result of modifications to the measured spectra that are due to of a variety of instabilities and contributions. These interferences and modifications arise from the nature of the enhancement itself, as well as the conditions used to attain SERS spectra. The present report is an attempt to collect in one place the analytical interferences that are most commonly found during the collection of SERS/SERRS spectra.     

Neutron scattering by liquid crystals. A new analysis

Abstract

This paper presents a new analysis of all (old and new) quasi-elastic neutron scattering results obtained for seven members of the PAA series (n = 1,…, 7). The analysis is based upon a discussion of the parameter p, which is the deviation of the intensity of the elastic component from the intensity demanded by a reorientational model. If the value of this parameter is negative, it may be interpreted as an indication of an additional motion which has not been taken into account in the model. The first model analysed in this way for all seven substances in the nematic phase was that of the rotational diffusion of the whole molecule in its stretched (trans) conformation, around the long axis. A very large negative values of p (p ? -60 per cent) was obtained, clearly showing that some motions have been neglected. The second model was that of the rotational diffusion of moieties consisting of benzene rings plus alkoxy side-chains. The diffusion occurs around the benzene para-axes, and the alkoxy side-chains are assumed to be in their trans conformations. Less negative values of p (p ? -10 per cent) were obtained, indicating that other motions still exist. Since these must take place in the alkyl chains, we make a third step in the analysis, in which we retain the second model but now take substances which are alkyl-deuterated (which means masking for the neutron incoherent scattering method). Now values of p which are nearly zero are obtained which means that the motions previously ignored indeed exist in the alkyl chains. An even-odd effect observed in the dependence of p on n indicates that even molecules are more mobile than odd ones, probably due to less steric hindrance in more ordered, even substances.

A critical discussion on reorientational correlation times is also presented.