The effect of pH on charge, swelling and desorption of the dispersant poly(methacrylic acid) from poly(methyl methacrylate) microcapsules

Poly(methyl methacrylate) microcapsules have been prepared using the solvent evaporation technique with poly(methacrylic acid) (PMAA) as dispersant. The charge, swelling and desorption of PMAA from the microcapsules after treating the suspension with base have been followed using microelectrophoresis, X-ray photoelectron spectroscopy and quartz crystal microbalance with dissipation monitoring on model PMMA surfaces. Basic treatment of the microcapsule suspension leads to temporary colloidal stability through the introduction of charges on the PMAA chain. However, the increase in charge causes a continuous desorption of PMAA from the microcapsule surface, eventually leading to aggregation. If instead poly(diallyldimethylammonium chloride) is added to the base treated microcapsule suspension, good colloidal stability is obtained.     

The importance of proper anchoring of an amphiphilic dispersant for colloidal stability

Highly stable poly(methyl methacrylate) (PMMA) based microcapsule suspensions without excess dispersant are obtained via the solvent evaporation route using poly(methyl methacrylate)-block-poly(sodium methacrylate) or poly(methyl methacrylate)-block-poly(sodium acrylate) diblock copolymers as dispersant. The stable suspension is characterized by a high ζ-potential that does not change with time or after washing steps. It is indirectly proven on model PMMA surfaces using quartz crystal microbalance with dissipation monitoring that the PMMA block of the copolymer is embedded in the underlying PMMA microcapsule. Such anchoring of the dispersant is key for the good colloidal stability.     

Determination of the proteins in mixtures of meat,soymeal and rind from their chromatographic amino-acid pattern by the partial least-squares method

The simultaneous determination of muscle protein and rind protein in mixtures of muscle, soymeal and rind is described. Hydrolysates are derivatized with dansyl chloride and separated by reversed-phase liquid chromatography. The chromatographic pattern is subjected to multivariate evaluation. An indirect calibration method, partial least-squares modelling in latent variables (p.l.s.), is used. The rind protein is determined accurately regardless of sample composition. The accuracy of muscle protein determinations is lower when high concentrations of soymeal are present in the samples, because of the similarity in amino acid composition between soy protein and muscle. The method not only predicts the concentrations of the constituents but also calculates a measure of the similarity between the calibration set and each unknown sample. This gives an indication of the reliability of the predicted concentrations.     

Minimal and maximal methods of interpolation

We show that several interpolation functors, including the widely used real and complex methods, are minimal or maximal extensions from a single couple of Banach spaces. Various consequences are drawn from this property.     

Invariance principles for stochastic area and related stochastic integrals

Given an antisymmetric kernel K (K(z, z′) = ?K(z′, z)) and i.i.d. random variates Z_n, n?1, such that EK²(Z₁, Z₂)<∞, set A_n = ∑₁?i?j?nK(Z_i,Z_j), n?1. If the Z_n's are two-dimensional and K is the determinant function, A_n is a discrete analogue of Paul Lévy's so-called stochastic area. Using a general functional central limit theorem for stochastic integrals, we obtain limit theorems for the A_n's which mirror the corresponding results for the symmetric kernels that figure in theory of U-statistics.     

Hole centers in γ-irradiated,oxidized Al2O3

ESR observations of centers with $\text{S =}\text{1}\text{2}\text{, g ? 2, S = 1, g ? 2}$ have been made at 77 K on oxidized Al₂O₃ after γ-irradiation at 30°C. From the radiation growth data, it is shown that the $\text{S =}\text{1}\text{2}$ centers are precursors of the S = 1 centers. In addition, when the S = 1 centers anneal out at about 110°C, the $\text{S =}\text{1}\text{2}$ centers reappear and eventually anneal out at about 260°C. Previously Gamble and Cox, respectively, observed $\text{S =}\text{1}\text{2}$ and S = 1 paramagnetic centers in electron-irradiated nominally pure Al₂O₃ and γ-irradiated, oxidized, titanium-doped Al₂O₃. The models proposed for these centers were one hole and two holes trapped on oxygen ions adjacent to Al³⁺ vacancies. Our results further substantiate these models.