Mixed micellization and surface properties of non-ionic/cationic surfactants

We investigate the surface properties of aqueous binary mixtures of our cationic surfactant O-dodecyl-N,N′-diisopropylisourea hydrochloride (ISO-DIC C₁₂) with commercially available nonionic surfactant polyoxyethylene p-(1,1,3,3-tetramethylbutyl)phenyl ether (TritonX-100) at different temperatures (288 to 303?K). The micellization behavior of the binary systems is studied by determining the surface tension and other important physicochemical parameters, such as the critical micelle concentration (CMC), surface tension at the CMC(γ_cmc), Krafft Temperature (T_K), maximum excess concentration (Γ_max), minimum surface area per molecule (A_min), surface pressure at the CMC (П_cmc), and the adsorption efficiency (pC20) at the air/water interface. The study has additionally covered the calculation of thermodynamic parameters of micellization, including the standard Gibbs free energy, the standard enthalpy, the standard entropy, the free energy, and the Gibbs free energy of adsorption at air/water interface. The CMC values of the binary systems determined by experimental data are used to evaluate the micellar composition in the mixed micelle, the interaction parameter β and the activity coefficients f₁(ISO-DIC C₁₂) and f₂ (polyoxyethylene p-(1,1,3,3-tetramethylbutyl)phenyl ether) using the theoretical treatment proposed by Clint and Rubingh. Our results reveal that the proposed binary systems possess enhanced surface activity compared to those of the individual surfactants.     

Theoretical Approach of Bubble Entrapment Through Interconnected Pores: Supplying Principle

Fiber-reinforced composite materials are often composed of fibers collected in bundles that are stitched together. During the impregnation of a fibrous preform by a liquid resin, the multiscale porous medium leads to an heterogenous flow front, and therefore bubbles may be created and entrapped. Indeed, for a wetting system, capillary pressure is higher inside bundle, due to the microspace between fibers, than outside the bundles that represent the macrospace, thus, inducing an overflow between both pore scales. Motivated by the prediction of bubble formation during fiber fabric infiltration for composite materials, we attempt to determine the bubble rate in imbibition through a simple model network with two connected capillaries, called ??Pore Doublet Model?? (PDM). Our system is composed of two parts: a first part, continuously interconnected, in which the suppling mass to the microchannel from the macrochannel occurs, and a second part connected only by nodes. To quantify the leading flow front, a theoretical model based on the supplying principle and arranged Washburn equation is proposed. This approach has been conducted for wetting liquids, Newtonian flows, incompressible fluids and pores, no inertial and gravitational forces and no dynamic contact angle. The geometrical variability (channel radius and length) and the different configuration of connections (continuous and discrete) influence the entrapped bubble rate, leading to either microbubble in the microchannel or macrobubble in the macrochannel. The outcomes can contribute to the knowledge of void formation especially during the filling of fibrous preforms and may extend the previous works on the PDM in general.     

Kinetic theory of colloidal suspensions: morphology, rheology, and migration

Smoluchowski kinetic equation governing the time evolution of the pair correlation function of rigid sphericalparticles suspended in a Newtonian fluid is extended to include particle migration. The extended kinetic equation takes into account three types of forces acting on the suspended particles: a direct force generated by an interparticle potential, hydrodynamic force mediated by the host fluid, and the Faxén-type forces bringing about the across-the-streamline particle migration. For suspensions subjected to externally imposed flows, the kinetic equation is solved numerically by the proper generalized decomposition method. The imposed flow investigated inthe numerical illustrations is the Poiseuille flow. Numerical solutions provide the morphology (the pair correlation function), the rheology (the stress tensor), and the particle migration.     

Screening of Fish Tissue for Methyl Mercury Using the Enzyme Invertase in a Solvent Interface

This paper describes a simple and rapid screening system for the extraction and determination of methyl mercury in tissue samples from fish. A novel clean-up procedure based on the use of two immiscible phases, an organic one containing methyl mercury and an aqueous one containing invertase, was developed. Methyl mercury was selectively extracted from the organic into the aqueous phase by its irreversible reaction with thiol groups of invertase, and the resulting inhibition of enzymatic activity served as a measure of methyl mercury concentration. Enzyme activity was measured with a spectrophotometric method using 3,5-dinitrosalicylic acid as a reagent. After parameter optimisation including pH, substrate concentration, and enzyme reaction time, it was possible to determine methyl mercury in the ppb range with this technique. Concentrations as low as 10ppb of methyl mercury in the extract, corresponding to 0.2ppm of methyl mercury in fish, were detected. The proposed procedure was successfully demonstrated as a simple screening method for methyl mercury in fish samples.     

Existence, uniqueness and analyticity for periodic solutions of a non-linear convolution equation

We study existence, uniqueness and analyticity for periodic solutions ofu(x)=( _IR J(y)u(x–y)dy) forxIR.     

Occurrence of rare events in ergodic interacting spin systems

We give asymptotics for the occurrence time of rare events in infinite spin systems whose invariant measure satisfies a Logarithmic Sobolev inequality. We then describe the typical paths close to this occurrence time. Finally, in the case of non-interacting spins, we obtain sharper estimates for the expected value of the occurrence time.     

Dirichlet-to-Neumann semigroup acts as a magnifying glass

The first aim of this paper is to illustrate numerically that the Dirichlet-to-Neumann semigroup represented by P. Lax acts as a magnifying glass. In this perspective, we used the finite element method for discretizing of the correspondent boundary dynamical system using the implicit and explicit Euler schemes. We prove by using the Chernoff’s Theorem that the implicit and explicit Euler methods converge to the exact solution and we use the (P1)-finite elements to illustrate this convergence through a FreeFem++ implementation which provides a movie available online. In the Dirichlet-to-Neumann semigroup represented by P. Lax the conductivity \(\gamma \) is the identity matrix \(I_n\) , but for a different conductivity \(\gamma \) , the authors of Cornean et al. (J Inverse Ill-posed Prob 12:111–134, 2006) supplied an estimation of the operator norm of the difference between the Dirichlet-to-Neumann operator \(\Lambda _\gamma \) and \(\Lambda _1\) , when \(\gamma =\beta I_n\) and \(\beta =1\) near the boundary \(\partial \Omega \) (see Lemma 2.1). We will use this result to estimate the accuracy between the correspondent Dirichlet-to-Neumann semigroup and the Lax semigroup, for \(f\in H^{1/2}(\partial \Omega )\) .     

Scheduling with uncertainties on new computing platforms

New distributed computing platforms (grids) are based on interconnections of a large number of processing elements. A most important issue for their effective utilization is the optimal use of resources through proper task scheduling. It consists of allocating the tasks of a parallel program to processors on the platform and to determine at what time the tasks will start their execution. As data may be subject to uncertainties or disturbances, it is practically impossible to precisely predict the input parameters of the task scheduling problem.     

Adsorptive properties of X zeolites modified by transition metal cation exchange

The ionic exchange of the NaX zeolite by Ni²⁺ and Cr³⁺ cations was progressively driven and studied by adsorption of nitrogen and carbon dioxide. For each cation-exchanged X zeolite sample, the development of characteristics such as profile of isotherms, RI criterion, isosteric adsorption heat and microporous volume using both the Dubinin–Radushkevich (DR) equation and the t-plot, was followed through the nitrogen adsorption. Results show that the cationic exchange process, in the case of Cr³⁺ introduced at middle degree, is accompanied by a textural damage for Cr(x)X, in contrast to Ni²⁺-exchanged X zeolites. This degradation occurs without significant presence of mesopores, because the RI criterion values were found to be much lower than 2.2. The CO₂ adsorption isotherms were measured at intervals of 30 K from 273 K and the equilibrium pressures ranged from 0.5 to 600 Torr. The experimental data were correlated by the Toth model. The associated three adjustable parameters were estimated by nonlinear least-squares analysis. The effect of temperature on the model parameters and the Henry’s law slope, K _H , represented by the product of Toth parameters, are discussed.     

In Vitro Study of the Phytochemical Composition and Antioxidant,Immunostimulant, and Hemolytic Activities of Nigella sativa (Ranunculaceae) and Lepidium sativum Seeds

The Moroccan flora abounds and is an important reserve of medicinal plants. Nigella sativa and Lepidium sativum are plants that are widely used in traditional medicine for their multiple therapeutic properties. The current study aims to highlight the biological activities that can justify and valorize the use of these plants. Flavonoids, total phenols, condensed tannins, and sugars were determined. The biological activities tested were antioxidant by determining the IC₅₀ (defined as the concentration of an antioxidant required to decrease the initial concentration by 50%; inversely related to the antioxidant capacity), hemagglutination, and hemolytic activities. Phytochemical quantification of the seed extracts indicated that the total phenol content was largely similar for both plants and in the order of 10 mg GAE (Gallic acid equivalent)/g. On the other hand, L. sativum seeds registered a higher content of flavonoids (3.09 ± 0.04 mg QE (quercetin equivalent)/g) as compared to Nigella saliva (0.258 ± 0.058). Concerning condensed tannins, N. saliva seeds present a higher amount with a value of 7.2 ± 0.025 mg/g as compared to L. sativum (1.4 ± 0.22 mg/g). Concerning the total sugar content, L. sativum shows a higher content (67.86 ± 0.87 mg/g) as compared to N. sativa (58.17 ± 0.42 mg/g); it is also richer in mucilage with a content of 240 mg as compared to 8.2 mg for N. saliva. Examination of the antioxidant activity using a DPPH (2.2-diphenyl 1-pycrilhydrazyl) test revealed that the EButOH (n-butanol extract) and EAE (ethyl acetate extract) extracts were the most active, with IC₅₀ values of 48.7 and 50.65 μg/mL for the N. sativa extracts and 15.7 and 52.64 μg/mL for the L. sativum extracts, respectively. The results of the hemagglutination activity of the different extracts of the two plants prepared in the PBS (phosphate-buffered saline) medium showed significant agglutination for the L. sativum extract (1/50) compared to the N. sativa extract (1/20). An evaluation of the hemolytic effect of the crude extract of the studied seeds on erythrocytes isolated from rat blood incubated in PBS buffer compared to the total hemolysis induced by distilled water showed a hemolysis rate of 54% for Nigella sativa and 34% for L. sativum. In conclusion, the two plants studied in the current work exhibited high antioxidant potential, which could explain their beneficial properties.