Non‐UV‐Induced Radical Reactions at the Surface of TiO2 Nanoparticles That May Trigger Toxic Responses

Kept in the dark : The non‐photocatalytic generation of free radicals from fine and ultrafine TiO₂ particles has been studied by means of a spin‐trapping/ESR spectroscopy technique (see figure). The amount and kind of free radicals generated depends on the crystalline structure, but not on the particle dimensions.

     

An implicit strong $$mathrm {G}^{1}$$ G 1 -conforming formulation for the analysis of the Kirchhoff plate model

Continuum Mechanics and Thermodynamics - In this work, we present a quadrilateral plate element for the Kirchhoff plate bending model that satisfies the continuity requirements in implicit way. The...     

Rheo-optical determination of the interfacial tension in a dispersed blend

In this work, we present two novel methods to determine the interfacial tension of a disperse polymer blend through rheo-optical measurements of flow-induced single drop distortions. A counter-rotating shearing device with transparent plates is used to measure drop distortions. The cell geometry allows for a top view of the deforming drop, i.e., along the velocity gradient direction. Such a view is the only possible option for all currently available commercial rheo-optical instruments. Two different quantities are monitored, namely, the drop axis along the vorticity direction, and the rotation period of the drop surface. We use drops of a polyacrilamide aqueous solution (a shear thinning liquid) immersed in a polyisobutene matrix. Experimental results are interpreted in terms of theories for Newtonian liquids, where the relevant parameter is the Capillary number. If an appropriate viscosity ratio is chosen, that accounts for the shear thinning behaviour of the drop phase, good agreement is found between measurements and theoretical predictions. As a result, a robust estimate of the blend interfacial tension, that makes use only of the information acquired from top view experiments, is obtained.     

On the determination of the average molecular weight,radius of gyration,and mass/length ratio of polydisperse solutions of polymerizing rod‐like macromolecular monomers by multi‐angle static light scattering

The angular dependence of the light scattered from polydisperse solutions of rod‐like or worm‐like linear polymers formed by the polymerization of rod‐like macromolecular monomers was studied with the aid of computer simulations. Except at very low conversion degrees, these ensembles are characterized by curved Zimm‐like plots. An appraisal of the use of polynomial fittings for the derivation of the weight‐average molecular weight (M_w) and of the z‐average square radius of gyration (<R_g²>_z) from such plots is presented and discussed. Depending on the average size and shape distribution, the use of polynomial fittings allows the applicability of the Zimm method well beyond the standard condition q²<R_g²>_z<<1, q being the scattering wavevector. In addition, the derivation of the w/z‐average mass/length ratio M_L of the polymers from only partially linear Casassa plots, from which large errors in the derived M_L values can be made, is analyzed. By combining the Casassa method with the complementary Holtzer plots, it is usually possible to assess the reliability of the results and give an estimate of their accuracy. However, it was also found that apparently linear Casassa plots, allowing a good estimate of the M_L value, may arise in particular situations even when the Holtzer plot would indicate otherwise.     

Possible role of force balance on entanglements

The usual assumption of affine deformation of the strands of a polymeric network appears not to fulfil force balance over the nodes of the network in case such nodes are entanglements. In an effort to improve over the classical theory of Doi and Edwards for entangled polymers, a simple model is here proposed which is so constructed as to obey force balance. Explicit predictions for step strains are here obtained which compare very favourably with data, not only of damping function, but also of normal stress ratio.