Polymerization contraction of light-cured composite resins containing silica/polymethylmethacrylate bonded microstructured networks

The adsorption of methylmethacrylate polymer at silica/methylmethacrylate interfaces was determined to provide microstructured networks whose structural characteristics were determined to be controlled by the amount of polymer initially supplied to the system. First, the microstructure was investigated by determining as a function of the amount of polymer (i) the shrinking rate due to evaporation of the methylmethacrylate monomer, (ii) the rate of sedimentation of the silica/polymer complexes in the methylmethacrylate monomer, and (iii) the height of the sediment in the long term. These different characteristics were found to be strongly correlated. Second, the sedimentation characteristics were determined as a function of the amount of polymer initially supplied to the dispersion of the same silica/polymer system in the ethylene glycol dimethacrylate monomer. Then the rate of the polymerization contraction during light-curing of the resin was determined for the sediment recovered after centrifugation. The slowest polymerization contraction and the smallest contraction were obtained with the filler/polymer/resin system composed of aggregates of medium porosity and size.     

Liquid-core capsules via interfacial polymerization: a free-radical analogy of the nylon rope trick

Liquid-core capsules have wide-ranging applications in the high-efficiency encapsulation and controlled release of drugs, dyes, enzymes, and other substrates. Their great utility has driven the rapid development of various preparation techniques. However, there remains no convenient technique for the preparation of submicrometer liquid-core capsules with shell thicknesses less than 100 nm. Here, we demonstrate a new interfacial free-radical polymerization approach for the straightforward preparation of liquid-core polymer capsules. Conceptually, this interfacial free-radical polymerization is analogous to the classical "nylon rope trick" wherein hydrophobic and hydrophilic monomers alternately copolymerize to constrain the polymerization at interfaces, but its free-radical mechanism allows precise control of initiation, which makes it possible to finely disperse the immiscible phases prior to polymerization.     

Vibrational spectra and structure of CH3Cl:NO complex: IR matrix isolation and DFT study

Infrared spectra of the CH(3)Cl:NO complex isolated in solid neon have been investigated. Most of the vibrational modes of the complex have been detected. The weak interaction between NO and CH(3)Cl in CH(3)Cl:NO is responsible for small shifts of the vibrational mode frequencies of both CH(3)Cl and NO molecules. The measured shifts range between -3.2 and + 3.8 cm(-1). On the basis of DFT calculations, different geometries have been explored for the complex, and it has been shown that the most stable structure is of C(1) symmetry. The calculated frequency shifts match well the experimental data.     

Asymptotic behavior for an almost periodic,strongly dissipative wave equation

This paper deals with asymptotic behavior for (weak) solutions of the equation $\text{u}{}_{\mathrm{tt}}\text{? Δu + β(u}{}_{\mathrm{t}}\text{) ? ?(t, x)}$, on $\text{R}$⁺ × Ω; u(t, x) = 0, on $\text{R}$⁺ × ?Ω. If $\text{?∈L∞(R}{}^{\mathrm{+}}\text{,L}{}^2\text{(Ω))}$ and β is coercive, we prove that the solutions are bounded in the energy space, under weaker assumptions than those used by G. Prouse in a previous work. If in addition $\text{?}{}_{\mathrm{t}}\text{∈S}{}^2\text{(R}{}^{\mathrm{+}}\text{,L}{}^2\text{(Ω))}$ and ? is srongly almost-periodic, we prove for strongly monotone β that all solutions are asymptotically almost-periodic in the energy space. The assumptions made on β are much less restrictive than those made by G. Prouse: mainly, we allow β to be multivalued, and in the one-dimensional case β need not be defined everywhere.     

Halato-telechelic polymers. VII. Viscoelastic behavior of α,ω-divalent cation dicarboxylato polybutadiene

Ba, Ca, Mg, and Zn short-length carboxylato-telechelic polybutadienes (M?_n = 4,600) exhibit thermorheological simplicity. A secondary relaxation characteristic of ionic aggregates obeys an Arrhenius type of activation, the energy of which is in inverse proportion to the ionic radius of the cation, whereas the mean size of the ionic aggregates is proportional to it. The glass transition of the carboxy-telechelic polybutadiene is quite independent of the degree of neutralization and of the subsequent phase separation by the metal cations. The increase in cation size favors the growth of the multiplets into layered structures. Two sets of relaxation times are reported for the smallest alkaline-earth cation (Be). They suggest the existence of small multiplets unable to grow except into clusters.