New methods for the determination of the parameters of a concentration‐dependent diffusion law for molecular penetrants from transient permeation or sorption data

New methods were developed for the determination of the plasticization parameters and the limit diffusion coefficient of a penetrant whose diffusivity varies exponentially with its concentration. No specific computer softwares is required for their use and they are user friendly. The method using differential permeation data is based on the correlations between the slope of the reduced permeation flux versus time plot at the inflexion point, and the two key parameters of the concentration‐dependent diffusivity laws. For the transient sorption method, the slope of the penetrant mass uptake versus square‐root of time curve leads to the same parameters of the diffusion law via similar correlations.     

Wettability of acrylate copolymer surfaces after ageing in water

Contact angle measurements (captive bubble and sessile drop techniques) were used to determine the surface energy of several acrylic based polymers at the early stage of immersion (t₀) in pure and salt water or after several days (t_x). The sessile drop technique using various liquid probes allows the calculation of the dispersive, acid and basic components of the surface energy. Significant differences of wettability are observed between the polymers at t₀ which tend to remain after immersion along with a general increase of the surface hydrophilicity. The same trend is observed by the “in-situ” captive bubble technique. The surfaces become more hydrophilic with a final contact angle, θ, ranging from 110 to 150 ± 3° in pure water and 130 to 150 ± 4° in 0,51 M salt water. The modifications of surface energy between t₀ and t_x are not only dependent on water diffusion. One assumption is that the degree of swelling of the immersed surface layer along with the particular dynamics resulting from a surface gel-like structure are significant factors in the measured surface thermodynamics.     

A regularized nonnegative canonical polyadic decomposition algorithm with preprocessing for 3D fluorescence spectroscopy

We consider blind source separation in chemical analysis focussing on the 3D fluorescence spectroscopy framework. We present an alternative method to process the Fluorescence Excitation‐Emission Matrices (FEEM): first, a preprocessing is applied to eliminate the Raman and Rayleigh scattering peaks that clutter the FEEM. To improve its robustness versus possible improper settings, we suggest to associate the classical Zepp's method with a morphological image filtering technique. Then, in the second stage, the Canonical Polyadic (CP or Candecomp/Parafac) decomposition of a nonnegative three‐way array has to be computed. In the fluorescence spectroscopy context, the constituent vectors of the loading matrices should be nonnegative (since standing for spectra and concentrations). Thus, we suggest a new nonnegative third order CP decomposition algorithm (NNCP) based on a nonlinear conjugate gradient optimization algorithm with regularization terms and periodic restarts. Computer simulations performed on real experimental data are provided to enlighten the effectiveness and robustness of the whole processing chain and to validate the approach. Copyright © 2015 John Wiley & Sons, Ltd.     

Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and Dienes

The influence of MgR₂ and AlR₃ additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s-Bu₂Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4- to 1,2- chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R₃Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed. Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators.