Formation of micelles in model lattice surfactant systems was studied by a novel methodology based on grand-canonical Monte Carlo simulations. The methodology involves combining free-energy information from a series of simulations in small systems by histogram reweighting. The solution osmotic pressure as a function of overall volume fraction of surfactant shows a sharp break at the critical micelle concentration (cmc) at sufficiently low temperatures. Studies in larger systems at appropriate values of the surfactant chemical potential are used to investigate the size distribution of micellar aggregates. The methodology allows for a clear distiction between micellization and macroscopic phase separation. Two symmetric diblock surfactants have been considered in the present work. The cmc was found to increase with increasing temperature. The enthalpy change on micellization was determined to be proportional to the chain length of the surfactant. The mean micelle aggregation numbers were found to decrease at higher temperatures and increase with overall surfactant volume fraction for temperatures near the upper limit for micellar aggregation. These observations indicate that simple geometric packing concepts for micelle formation do not adequately describe temperature and composition effects in nonionic surfactant solutions.

Small-angle neutron scattering measurements have been carried out at 50 °C as a function of external contrast (different ratios of H20 to D20) on 0.12 M solutions of hexadecyltrimethylammonium bromide, with the methyls of the ammonium group protiated and deuterated. The results indicate that most of the surfactant hydrocarbon is in a micellar core penetrated by little, if any, solvent. The micelles are described adequately by a dispersion of monodisperse prolate ellipsoids. There is a significant effect on the size of the aggregates by the isotopic composition of the solvent.

SilicaePMMA nanocomposites with different silica quantities were prepared by a melt compounding\ud method. The effect of silica amount, in the range 1e5 wt.%, on the morphology, mechanical properties\ud and thermal degradation kinetics of PMMA was investigated by means of transmission electron\ud microscopy (TEM), X-ray diffractometry (XRD), dynamic mechanical analysis (DMA), thermogravimetric\ud analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), 13C cross-polarization magic-angle\ud spinning nuclear magnetic resonance spectroscopy (13C{1H} CP-MAS NMR) and measures of proton spinlattice\ud relaxation time in the rotating frame (T1r(H)), in the laboratory frame (T1(H)) and cross-polarization\ud times (TCH). Results showed that silica nanoparticles are well dispersed in the polymeric matrix\ud whose structure remains amorphous. The degradation of the polymer occurs at higher temperature in\ud the presence of silica because of the interaction between the two components

H and 19 F NMR measurements on aqueous solutions of sodium perfluorooctanoate (SPFO) and sodium dodecanoate (SD) mixtures are reported. The surfactant concentration ranged from ∼0.3 to 10 times the critical micelle concentration (cmc = 0.03 mol L -1 ). The cmc of the SD/SPFO/water mixed system obtained from NMR data was in good agreement with that previously obtained by conductivity measurements. Below the cmc, the experimental chemical shift (δ) was independent of the total concentration for both surfactants. Above the cmc, however, the δ values for 19 F varied linearly with concentration, whereas the values for the hydrogenated surfactant deviated from linearity. These observations indicate that below the cmc each monomer is not affected by the presence of the others. Above the cmc, on increasing the total concentration, the chemical shift trends indicate that the fluorinated chains begin to aggregate, forming islands among hydrocarbon chain domains. Since the extended chain of the fluorinated surfactant is shorter than the inner micelle radius, some methyl groups of the longer SD must be segregated within the micelle. This patchwork distribution, involving an intramicellar phase separation, prevents the computation of the micelle composition; however, NMR data give information complementary to that obtained by a previous SANS study indicating the existence of mixed micelles having the same composition. Information on the structure of micelles and on the mean distribution of the two components in the system are obtained by SANS, while the NMR technique suggests details on the chemical environment of a single monomer and on the structural organization of the molecules within a micelle. Thus, the patchwork model here proposed is able to explain apparently conflicting data obtained from different techniques.

A Ce:YAG-poly(methyl methacrylate) composite was prepared using in situ polymerization by embedding the Ce:YAG nanopowder in a blend of methyl methacrylate (MMA) and 2-methacrylic acid (MAA) monomers and activating the photopolymerization using a radical initiator. The obtained nanocomposite was yellow and transparent. Its characterization was performed using transmission electron microscopy, small angle X-ray scattering, (13)C cross-polarization magic-angle spinning nuclear magnetic resonance, and photoluminescence spectroscopy. Results showed that Ce:YAG nanoparticles are well dispersed in the polymeric matrix whose structure is organized in a lamellar shape. The luminescence properties of the nanocomposite do not show quenching or a significant spectral shift, indicating that the nanocomposite can be useful for advanced applications such as white LED construction.