Effects of addition of polar organic solvents on micellization

Micellization of several surfactants in water-organic solvent mixtures has been investigated. Only solvents localized mainly in the bulk phase of the micellar solutions (they do not incorporate into the micelles) were studied, with either higher or lower permittivity than that of pure water. Results show that the influence of organic solvent addition on the aggregation process can be approximately accounted for by considering the changes in the bulk phase cohesive energy density, described by the Gordon parameter, G. To our knowledge, this is the first time that, for a given surfactant, the Gibbs energies of micellization, Delta G M degrees , obtained in several water-organic solvent mixtures have been fitted together. It is worth noting that data from different research groups have been considered. The Delta G M degrees versus G correlation will permit the estimation of the variations in the Gibbs energy of micellization upon addition of known quantities of a given polar organic solvent. Speaking in a general way, organic solvent addition results in the bulk phase becoming a better solvent for the surfactant molecules. This would make the hydrophobic tail transfer from the bulk phase into the micelles less favorable and, as a consequence, Delta G M degrees increases (becomes less negative), making the aggregation process less spontaneous.     

Simultaneous measurement with one-capture of the two in-plane components of displacement by electronic speckle pattern interferometry

We present the simultaneous measurement of the two in-plane displacement components by electronic speckle pattern interferometry with three object beams and without an in-line reference beam. Three interference fringe patterns, corresponding to three different sensitivity vectors, are recorded in a single interferogram and separated by means of the Fourier transform method. Then, two interference fringe patterns are selected to obtain the in-plane displacement components.     

Strain maps obtained by phase-shifting interferometry: An uncertainty analysis

We used Moiré interferometry to evaluate the strains induced on a specimen subjected to a steady tensile load. The strains were evaluated by differentiating the whole-field phase values obtained by a phase-shifting algorithm. Because the direct differentiation of even slightly noisy data may lead to unacceptable derivative errors, the strain evaluation procedure included the application of a low-pass filter, which allowed us to smooth out local fluctuations in the phase data. In addition to the noise, the strain values were also affected by systematic errors in the phase values rendered by the phase-shifting algorithm as well as uncertainties in the determination of both the interferometer sensitivity and the magnification of the imaging system. In this paper, the influence of these error sources was assessed by applying a Monte Carlo-based uncertainty propagation technique; the strain uncertainty evaluation was based on simulating a large number of times, both the phase-shifting procedure and the post-image processing (which included the filter application). We found that the strain uncertainty strongly depends on the low-pass filter used to counteract the noise effect. Although we obtained the phase data from a Moiré pattern, the procedure presented to evaluate the strain uncertainty is valid independently of the techniques used to generate the fringe pattern or the algorithm applied to exploit the phase-shifting procedure.     

Transition events fluctuations in jump markovian dynamics. A general approach to Šolc's problem

We introduce a new formalism for computing the moments of transition events for nonhomogeneous Markov jump processes. Our method is applied directly to the master equation and does not involve the use of diffusion approximation. The general theory is applied to produce exact expressions for means and dispersions. For time homogeneous Markov processes with a finite number of connected states we are able to prove that both means and dispersions asymptotically increase linearly in time.     

Spectrophotometric micro-method for the determination of ethanol in commercial beverages

 A sensitive spectrophotometric method for the determination of ethanol with potassium dichromate was developed. Chromium(VI), in 7 mol L^-1 perchloric acid, reacts quantitatively with ethanol to form chromium(III) and acetic acid. The reaction is complete in about 15 min at room temperature and the chromium(VI) consumed may be determined by the decrease of the absorbance at 267 nm. The analytical working parameters (such as acidity and ionic strength of the solution, temperature and time of the reaction, chromium(VI) concentration, matrix interferences) were optimized. The apparent molar absorptivities of chromium(VI), in the monomer and dimer form, and the equilibrium quotient for the dimerization reaction were determined in 3 mol L^-1 perchloric acid solution. The method was applied to the analysis of micro samples of commercial beverages (beers, wines and spirits) without the previous distillation of ethanol. Received: 9 April 1996/Revised: 3 June 1996/Accepted: 11 June 1996     

B?H,C?H,and B?C Bond Activation: The Role of Two Adjacent Agostic Interactions

Tuning the nature of the linker in a L∼BHR phosphinoborane compound led to the isolation of a ruthenium complex stabilized by two adjacent, δ‐C H and ε‐B_sp2 H, agostic interactions. Such a unique coordination mode stabilizes a 14‐electron “RuH₂P₂” fragment through connected σ‐bonds of different polarity, and affords selective B H, C H, and B C bond activation as illustrated by reactivity studies with H₂ and boranes.