Modeling of Intermediate Structures and Chain Conformation in Silica-Latex Nanocomposites Observed by SANS During Annealing

The evolution of the polymer structure during nanocomposite formation and annealing of silica-latex nanocomposites is studied using contrast-variation small angle neutron scattering. The experimental system is made of silica nanoparticles (Rsi \approx 8 nm) and a mixture of purpose-synthesized hydrogenated and deuterated nanolatex (Rlatex \approx 12.5 nm). The progressive disappearance of the latex beads by chain interdiffusion and release in the nanocomposites is analyzed quantitatively with a model for the scattered intensity of hairy latex beads and an RPA description of the free chains. In silica-free matrices and nanocomposites of low silica content (7%v), the annealing procedure over weeks at up to Tg + 85 K results in a molecular dispersion of chains, the radius of gyration of which is reported. At higher silica content (20%v), chain interdiffusion seems to be slowed down on time-scales of weeks, reaching a molecular dispersion only at the strongest annealing. Chain radii of gyration are found to be unaffected by the presence of the silica filler

CONFORMATIONAL SOLID-SOLID PHASE-TRANSITIONS IN LONG-CHAIN ALKYLAMMONIUM TETRACHLOROMERCURATES(II)

Long-chain alkylamine tetrachloromercurates(II) ((CnH2n+1NH3)2HgCl4, with n = 8-16) show high-enthalpy solid-solid phase transitions at 293-360 K. These are assocd. with the melting of the hydrocarbon parts of the crystal structure while the inorg. layers remain practically unchanged. The behavior of these salts, as compared with that of analogous compds. with different metals, is discussed in terms of the structural parameters of the inorg. layers

Melting behaviour of a series of diamides

The melting behaviour of diamides of general formula (n - C pH 2p+1)CONH-(CH 2) qNHCO(n - C pH 2p+1) has been investigated by calorimetric, dilatometric and IR techniques. The conformational contribution to the melting entropy, calculated from the hypothesis of complete conformational freedom of the molecules at the melting point, has been compared with the experimental data. The higher melting points of the diamides, as compared with those of the linear hydrocarbons having the same number of conformationally flexible chain bonds, are attributed to a reduction of conformational freedom of the chain segments in the liquid state (caused by the large fraction of hydrogen bonds maintained in the melt)