Analysis of small-angle scattering of suspensions of organically modified montmorillonite: Implications to phase behavior of polymer nanocomposites

A generalized model for scattering from a collection of independent (isolated) stacks of layers enabled predictions of and parameterized fits to small-angle X-ray scattering from layered silicate dispersions. From this fundamental development, example investigations that use small-angle scattering to examine the structure of organically modified montmorillonite dispersions in toluene and toluene–acetone blends provided detailed information on the distribution of the stacks (relative concentrations, K and fraction of individual layers, χ) and characteristics of the intercalated crystallite (mean number of layers per stack, 〈N〉; layer repeat distance, D; and fractional stack disorder, δ). The analysis initially supported correlations with discotic phase behavior, which provides concise definitions for various morphologies (exfoliated, intercalated, and mixed). Finally, examination of the deviations between the scattering model and the experiment provided insights for improved experimental technique, more complete utilization of the scattering data, a sound basis for real-time observations, insight into inconsistencies between scattering and microscopy, and minimization of incorrect or overinterpretation of data. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3214–3236, 2003     

Reflection of Waves from a Ridged Surface and the Zeno Effect

Reflection of waves from a ridged surface is interpreted as the spatial Zeno effect. This interpretation leads to a simple estimate for the coefficient of reflection. This estimate shows good agreement with experimental data of scattering of cold atoms from ridged surfaces.     

On the equivalence of spectral theory and bayesian analysis in minimax linear estimation

The Bayesian point of view of the linear regression model is used to deal with some minimax problems. New tools for spectral theory make it possible to give an alternative equivalence of the Bayesian and the minimax approach.     

MP2 and DFT calculations on circulenes and an attempt to prepare the second lowest benzolog, [4]circulene

MP2 and DFT calculations have been carried out for [n]circulenes for n=3 to 20 in order to predict the strain energy and topology of these cyclically condensed aromatic systems. To synthesise [4]circulene (2), 1,5,7,8-tetrakis(bromomethyl)biphenylene (14) was prepared from the corresponding tetramethyl derivative (8) and subjected to various dehalogenation reactions; all attempts to obtain [2.2]biphenylenophane (7) as a precursor for 2 by this route failed. Treatment of 14 with sodium sulfide furnished the thiaphanes 16 and 17, thermal and photochemical desulfurization of which also failed to provide 7. In a second approach [2.2]paracyclophane was converted to the pseudo-geminal dithiol 23, which was subsequently bridged to the thiaphanes 22 and 24. On flash vacuum pyrolysis at 800 degrees C these were converted exclusively into phenanthrene (30). An approach to dehydrochlorinate the commercial product PARYLENE C to the tetrahydro[4]circulene 7 led only to polymerisation. The X-ray structures of the intermediates 8, 14, 17, 23, 24, 26, and 35 are reported.