Film formation from latex: Hindered initial interdiffusion of constrained polystyrene chains characterized by small-angle neutron scattering

Bulk polystyrene film samples were made from a 50% deuterated latex with a molecular weight of 5.85 × 10⁶ g/mol and 38 nm particle diameter. Because of the high molecular weight and small particle size, these chains are constrained in dimensions by a factor of four. Mildly molded (compacted to full density) samples were annealed for increasing time periods and their small-angle neutron scattering (SANS) patterns recorded. The radii of gyration increase with time as segmental diffusion proceeds during film formation. The initial diffusion was hindered, as shown by a slower than expected relaxation of the chains. Residual interfacial effects were postulated to be the main cause. Chain interdiffusion between latexes of about 110 Å is sufficient to develop a tough, coherent film.     

Elastomeric and Mechanical Properties of Poly-m-carboranylenesiloxanes. III

Stress relaxation properties of SiB-2 and poly(dimethyl siloxane) were compared in air and pure nitrogen. The effect of a protective filler system was also investigated for these materials. In addition, stress relaxation experiments were conducted on unfilled SiB-1 and SiB-1.5 in air only.

The crystalline structure of a special SiB-2 was investigated by X-ray techniques (courtesy of Olin), and by force-temperature experiments. The thermodynamic melting point of SiB-2 was found to be 66°C, and qualitative information was obtained on the crystallite size distribution.

The physical and mechanical properties of SiB-1 and a series of random copolymers of SiB-1 and SiB-2 were investigated by modulus-temperature and weight-loss experiments. SiB-1 and all the copolymer compositions investigated were found to have well-developed crystallinity. Thermal stability increased from SiB-2 to SiB-1, as expected.     

Two-dimensional electronic spectra of symmetric dimers: Intermolecular coupling and conformational states

We study the information content of two-dimensional (2D) electronic photon-echo (PE) spectra, with special emphasis on their potential to distinguish, for waiting times T=0, between different conformations of electronically coupled symmetric dimers. The analysis is performed on the basis of an analytical formula for the frequency-domain 2D PE signal. The symmetric dimers are modeled in terms of two identical, energy-degenerate, excitonically coupled pairs of electronic states in the site representation. The spectra of conformationally weighted ensembles, composed of either two or four dimers, are compared with their one-dimensional linear absorption counterparts. In order to provide a realistic coupling pattern for the ensemble consisting of four dimers, excitonic couplings are estimated on the basis of optimized geometries and site-transition dipole moments, calculated by standard semiempirical methods for the bridged bithiophene structure 1,2-bithiophene-2-yl-ethane-1,2-dion (T2[CO]2). In the framework of our model, the highly readable 2D PE spectra can unambiguously identify spectral doublets, by relating peak heights and positions with mutual orientations of site-localized transition dipoles.     

Controlling the Shape of Evaporating Droplets by Ionic Strength: Formation of Highly Anisometric Silica Supraparticles

Anisometric silica supraparticles are produced by a simple process of evaporation of sessile droplets containing fumed silica deposited on a superhydrophobic substrate. The shape of the supraparticles is directly controlled by the salt (NaCl) concentration, becoming anisometric beyond a threshold concentration, as quantified by light microscopy. This process is easily extended to supraparticles containing further functional colloidal components.     

Vanadium in marine mussels and algae

A method is presented which is sensitive enough for the determination of vanadium (V) in marine organisms such as mussels and algae. It was sufficiently checked by a reference material and it was applied to V determination in blue mussels and brown algae from the German Bight. Received: 28 July 1999 / Revised: 1 November 1999 / Accepted: 1 November 1999     

Fractionation of the human plasma proteome for monoclonal antibody proteomics-based biomarker discovery

mAb proteomics, a reversed biomarker discovery approach, is a novel methodology to recognize the proteins of biomarker potential, but requires subsequent antigen identification steps. While in case of high-abundant proteins, it generally does not represent a problem, for medium or lower abundant proteins, the identification step requires a large amount of sample to assure the proper amount of antigen for the ID process. In this article, we report on the use of combined chromatographic and precipitation techniques to generate a large set of fractions representing the human plasma proteome, referred to as the Analyte Library, with the goal to use the relevant library fractions for antigen identification in conjunction with mAb proteomics. Starting from 500?mL normal pooled human plasma, this process resulted in 783 fractions with the average protein concentration of 1?mg/mL. First, the serum albumin and immunoglobulins were depleted followed by prefractionation by ammonium sulfate precipitation steps. Each precipitate was then separated by size exclusion chromatography, followed by cation and anion exchange chromatography. The 20 most concentrated ion exchange chromatography fractions were further separated by hydrophobic interaction chromatography. All chromatography and precipitation steps were carefully designed aiming to maintain the native forms of the intact proteins throughout the fractionation process. The separation route of vitamin D-binding protein (an antibody proteomics lead) was followed in all major fractionation levels by dot blot assay in order to identify the library fraction it accumulated in and the identity of the antigen was verified by Western blot.     

MR-visible brain water content in human acute stroke

Quantification of metabolite concentrations by proton magnetic resonance spectroscopy (1H-MRS) in the human brain using water as an internal standard is based on the assumption that water content does not change significantly in pathologic brain tissue. To test this, we used 1H-MRS to estimate brain water content during the course of cerebral infarction. Measurements were performed serially in the acute, subacute, and chronic phase of infarction. Fourteen patients with acute cerebral infarction were examined as well as 9 healthy controls. To correlate with regional cerebral blood flow (rCBF) SPECT-scanning using 99mTc-HMPAO as flow tracer was performed in the patients. Mean water content (SD) in the infarct area was 37.7 (5.1); 41.8 (4.8); 35.2 (5.4); and 39.3 (5.1) mol x [kg wet weight](-1) at 0-3; 4-7; 8-21; and >180 days after stroke, respectively. Water content increased between Day 0-3 and Day 4-7 (p = 0.034) and decreased from Day 0-3 to Day 8-21 (p = 0.028). Water content at Day 4-7 was significantly higher than in controls (p < or = 0.05). At the same time intervals, mean rCBF (SD) was 76 (23); 94 (31); 106 (35); and 64 (26)%, respectively. There was a significant increase in rCBF from Day 0-3 to Day 4-7 (p = 0.050) and from Day 0-3 to Day 8-21 (p = 0.028). No correlation between rCBF and water content was found. Water content in ischemic brain tissue increased significantly between Day 4-7 after stroke. This should be considered when performing quantitative 1H-MRS using water as an internal standard in stroke patients.     

Review of polystyrene diffusion studies in latex particles by small‐angle neutron scattering

This paper reviews small‐angle neutron scattering (SANS) and some results from direct nonradiative energy transfer (DET), for the observation of the diffusion coefficients of polystyrene chains at latex interfaces. To compare SANS with DET, doubly labeled polystyrene with deuterium and fluorescence groups were synthesized, showing that while SANS and DET produce comparable data in terms of diffusion coefficients, both results differ in detail, each having their own advantages. Chain confinement, ionic end groups, and short branch effects on interdiffusion were studied. Large polymer chains confined in small particles have non‐Gaussian shapes that store rubber elastic energy. Rapid, non‐diffusion relaxation is inhibited because the density would be required to become less than normal. Hence confinement effects on the diffusion rate are not significant. Using the DET method, ionic end‐groups were found to increase the early‐time apparent interdiffusion coefficients during film formation. The early‐time apparent diffusion coefficients of polystyrene with varying end‐groups were found to increase as follows: The higher apparent diffusion coefficients of the chains with ionic groups are presumably due to a surface segregation of the end‐groups caused by the polar, aqueous environment during latex synthesis. The interdiffusion behavior of sulfite‐ended polystyrene (M_n ? 300 000 g/mol) with H‐ends, one sulfite end, and two sulfite ends were compared via SANS and DET. The diffusion coefficients of polystyrene with one or two sulfite end groups were five times and ten times lower than that of polystyrene, respectively. The ionic end group effects on the reduced diffusion coefficients are interpreted as the competition between enhancement by the surface segregation of end groups and reduction by end group aggregation. Noting that sulfate end groups diffused faster, while sulfite end groups diffused slower, the effect is complex, and not yet fully resolved. Diffusion coefficients of polystyrene with branches were studied by DET. Short branches work to decrease the T_g and hence increase the diffusion coefficients. However, after the experimental temperature, T, is converted to a normalized temperature, T‐T_g, the diffusion coefficients are found to be almost independent upon the number of branches and the length of branches. The branch length ranged from one‐carbon to 40 carbons. Side chains of entanglement molecular weight or longer may be required to significantly reduce the diffusion coefficient. Copyright © 2002 John Wiley & Sons, Ltd.