Papers by mabrouk benhamou
Plasmonics
The current COVID-19 pandemic has resulted in an urgent need for methods to decontaminate respira... more The current COVID-19 pandemic has resulted in an urgent need for methods to decontaminate respirators masks for reuse while keeping them intact and functional. The severe shortage of professional masks such as N95 and FFP2 has necessitated their reuse over long periods. A very promising method is the pasteurization of these masks by thermoplasmonic heat generated by plasmonics nanoparticles when they are irradiated by light. Under illumination at its plasmonic resonance, a metal nanoparticle features enhanced light absorption, turning it into an ideal nano-source of heat, remotely controllable using light. In this work, we propose a numerical study based on the finite element method (FEM) of the thermoplasmonic properties of silver nanoparticles (AgNPs) decorating polypropylene (PP) fibers which is a basic material for the manufacture of these masks. The surface plasmon resonance (SPR) of these nanostructures was investigated through the computation of the complex effective dielectric permittivity and the absorption cross section in the near UV-visible (NUV-Vis) range. First, the SPR characteristics of AgNPs for different morphologies are determined from the absorption spectra, including the SPR-peak position λ max and the electric field enhancement. Second, we determine the power absorbed by an individual AgNP of different morphologies. From this, we calculate the internal temperature increase of the particle at the plasmonic resonance. The last step is devoted to the determination of the temperature profile in the surrounding medium in order to better understand and design the plasmon-assisted heating processes at the nanometric scale.
Journal of Thermal Analysis and Calorimetry
Polymer/clay-based composites were prepared via solution intercalation method using natural clay ... more Polymer/clay-based composites were prepared via solution intercalation method using natural clay and poly (ethylene) glycol (PEG4000) as organic dispersed phase. The present work consists of studying the effect of PEG content on the hybrids surface morphology, thermal stability and thermophysical properties. On the other hand, the TGA data and the measured thermophysical properties are, respectively, fitted with a logistic-like laws and virial expansions for different polymer contents. The results showed that the experimental data agree with the proposed theoretical models. Furthermore, the incorporation of the PEG chains into the clay matrix improves both the thermal stability and thermal characteristics of the raw clay. The thermophysical properties data showed that the elaborated hybrid acts as good thermal insulator for polymer contents higher than 2.5%\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$2.5\%$$\end{document}. Finally, the resulting clay-based composite showed not only interesting characteristics in terms of insulation, but also satisfies both economic and environmental requirements.
Plasmonics
In this paper, the optical and thermoplasmonics properties of nanocomposites consisting of spheri... more In this paper, the optical and thermoplasmonics properties of nanocomposites consisting of spherical gold nanoparticles (AuNPs) integrated in Al 2 O 3 matrix are determined using the Finite Element Method (FEM). Firstly, the refractive index (n) , extinction coefficient () , absorption coefficient (a) , and optical conductivity () are calculated from the effective complex permittivity obtained by solving the Laplace's equation for different size and concentration of nanoparticles. The surface plasmon resonance (SPR) properties of AuNPs are optimized from the peak presented in the absorption coefficient spectrum. The results show that the optical parameters n, , a , and undergo a strong variation around the wavelength max corresponding to the SPR phenomenon. The value of max increases from 560 to 600nm when the radius of the particles varies between r = 5 and r = 30nm. The effect of the AuNP concentration on the band gap energy E g (eV) of Au-Al 2 O 3 nanocomposites is also studied, a shift from Eg = 5.34 to Eg = 5.49eV is observed when the concentration of the AuNPs increases from 0 to 0.82%. The electric field enhancement induced by the AuNPs at plasmonic resonance is also determined depending to the particle size; the results show that the enhancement factor increases from g = 4.71 to g = 6.95 when the radius of the AuNPs increases from r = 5 to 30nm. The thermal dissipation of the plasmonic energy of spherical of our system dispersed in the Al 2 O 3 matrix is determined considering the Joule effect which occurs by the oscillation of the charges at the plasmonic resonance. The generated thermal power by particles is calculated for different sizes, which allows to calculate the thermal power per gram of particles depending on the intensity of the incident electric field. The results show that the plasmonic thermal power is almost identical for small particles when the radius is less than r = 15nm and increases considerably when the size increases from r = 15 to 30nm. For a fixed size and incident field amplitude, we calculated the temperature change in the nanocomposites Au-Al 2 O 3 depending of time for different particle concentrations; the temperature variation curves obtained are linear as a function of time.
IOP Conference Series: Materials Science and Engineering, 2017
In this work, we propose a model to study the Statistical Mechanics of a confined bilayer-membran... more In this work, we propose a model to study the Statistical Mechanics of a confined bilayer-membrane that fluctuates between two interactive flat substrates. From the scaling laws point of view, the bilayer-membranes and strings are very similar. Therefore, it is sufficient to consider only the problem of a string. We assume that the bilayer-membrane (or string) interact with the substrate via a Double Morse potential that reproduces well the characteristics of the real interaction. We show that the Statistical Mechanic of the string can be adequately described by the Schrödinger equation approach that we solve exactly using the Bethe method. Finally, from the exact value of the energy of the ground state, we extract the expression of the free energy density as well as the specific heat.
International Journal of Academic Research, 2013
Physical Review E, 2004
Surface effects are generally prevailing in confined colloidal systems. Here we report on dispers... more Surface effects are generally prevailing in confined colloidal systems. Here we report on dispersed nanoparticles close to a fluid membrane. Exact results regarding the static organization are derived for a dilute solution of non-adhesive colloids. It is shown that thermal fluctuations of the membrane broaden the density profile, but on average colloids are neither accumulated nor depleted near the surface. The radial correlation function is also evaluated, from which we obtain the effective pairpotential between colloids. This entropically-driven interaction shares many similarities with the familiar depletion interaction. It is shown to be always attractive with range controlled by the membrane correlation length. The depth of the potential well is comparable to the thermal energy, but depends only indirectly upon membrane rigidity. Consequenses for stability of the suspension are also discussed.
Creating a new energetic indicator for the measurement of a serie of plastification of materials.... more Creating a new energetic indicator for the measurement of a serie of plastification of materials. Applciation on clay polymer micro composites.
The system that we consider the position fluctuations of a fluid membrane confined to a substrate... more The system that we consider the position fluctuations of a fluid membrane confined to a substrate in an external potential and at finite temperature. We took in first time a quasi-flat membrane subjected to a kind of potential van der Waals -Helfrich where it appears the temperature setting. The analytical study shows that as the temperature increases phospholipids pass a crystalline phase at very low temperature, a gel phase in an intermediate area at a high temperature fluid phase, and in second time, we interested in studying lipid bilayers where van der Waals attractions are balanced by hydration repulsion associated with a hard wall. Careful study shows that the decrease in pressure causes an increase in the depth that is to say, the membrane becomes more stable.
The system that we consider the position fluctuations of a fluid membrane confined to a substrate... more The system that we consider the position fluctuations of a fluid membrane confined to a substrate in an external potential and at finite temperature. We took in first time a quasi-flat membrane subjected to a kind of potential van der Waals -Helfrich where it appears the temperature setting. The analytical study shows that as the temperature increases phospholipids pass a crystalline phase at very low temperature, a gel phase in an intermediate area at a high temperature fluid phase, and in second time, we interested in studying lipid bilayers where van der Waals attractions are balanced by hydration repulsion associated with a hard wall. Careful study shows that the decrease in pressure causes an increase in the depth that is to say, the membrane becomes more stable.
Dans cette these nous demontrons la conjecture de J. Des Cloizeaux, selon laquelle les theories s... more Dans cette these nous demontrons la conjecture de J. Des Cloizeaux, selon laquelle les theories standard de polymeres en solution se renormalisent multiplicativement jusqu'aux dimensions critiques. Nous utilisons pour cela l'equivalence de ces theories avec les theories du champ scalaire a zero composante, equivalence realisee par la transformation de Laplace-de Gennes. Nous montrons que la renormalisation dimensionnelle avec la prescription minimale de 't Hooft et Veltman, est particulierement bien adaptee au probleme, car elle commute avec la transformation de Laplace-de Gennes. 1 Ce resultat est etendu ensuite aux theories de polymeres en solution en presence d'une paroi plane, qui exerce sur ces polymeres des forces suffisamment attractives pour induire des phenomenes d'adsorption. Nous montrons dans quelles conditions ces theories sont equivalentes a des theories du champ scalaire a zero composante, avec une interaction de surface quadratique, generalisant a...
Condensed Matter Physics, 2004
Here, of great interest to us is a quantitative study of the scattering properties from ramified ... more Here, of great interest to us is a quantitative study of the scattering properties from ramified polymeric systems of arbitrary topology. We consider three types of systems, namely ramified polymers in solution, ramified polymer blends, or ternary mixtures made of two ramified polymers of different chemical nature immersed in a good solvent. To achieve the goal of the study, use is made of the Random Phase Approximation. First we determine the exact expression of the form factor of an ideal ramified polymer of any topology, from which we extract the exact expression of its gyration radius. Using the classical Zimm's formulae and the exact form factor, we determine all scattering properties of these three types of ramified polymeric systems. The main conclusion is that ramification of the chains induces drastic changes of the scattering properties.
Macromolecular Theory and Simulations, 1995
Macromolecular Theory and Simulations, 1994
The phase behavior and scattering properties of crosslinked charged polymer blends in solution ar... more The phase behavior and scattering properties of crosslinked charged polymer blends in solution are examined. De Gennes' analogy between the effects of crosslinks in a network and electrostatic charges in a dielectric medium on the scattering properties and the phase behavior of crosslinked polymer blends is used. This analogy is extended to include the effects of screening in order to improve its agreement with the experimental data in the small q range. The excluded volume interactions are explicitely introduced through the blob model. The enhancement of compatibility of the mixture and the increase of its rigidity constant are evaluated in certain cases. The limit of neutral polymers is discussed because it corresponds to the case of charged mixtures in the presence of excess salt. The kinetics of the microphase separation transition is briefly discussed. A dynamical model including the long range hydrodynamic interaction is presented. The relaxation frequency of the stable modes and the growth rate of unstable ones are also considered.
Journal of Magnetism and Magnetic Materials, 2001
The purpose of the present work is a quantitative investigation of the biquadratic exchange inter... more The purpose of the present work is a quantitative investigation of the biquadratic exchange interaction effects on the paramagnetic-ferrimagnetic transition arising from two strongly coupled paramagnetic (1-spin) sublattices, of respective moments m and M. The free energy describing the physics of the system is of Landau type. In addition to the quadratic and quartic terms, in both m and M, this free energy involves two mixing interaction terms. The first is a lowest order coupling ÀCmM, where C50 stands for the coupling constant measuring the interaction between the two sublattices. While the second, which is relevant for 1-spin systems and which traduces the dipole-dipole (or biquadratic) interaction, is of type wm 2 M 2 , where w > 0 is the new coupling constant. These two interactions enter in competition, and then, they induce drastic changes of the magnetic behavior of the material. The main change is that, the presence of this high order coupling tends to destroy the ferrimagnetic order of the system. We first show that the introduction of this biquadratic interaction does not affect the values of critical exponents. Also, we find that the compensation temperature (when it exists) and the compensation magnetic field are shifted to their lowest values, in comparison with the w ¼ 0 case. The Arrott-phase-diagram shape is also investigated quantitatively. We show the existence of three regimes depending on the values of w. When the latter is small, we find that the region of competition between the coupling C and the applied magnetic field H becomes more narrow under the effect of w (by competition, we mean the passage from the antiparallel state to the parallel one). While for higher values of w, this competition disappears completely, and then, the system loses its ferrimagnetic character. Kinetics of the phase transition is also examined, when the temperature is lowered from an initial value T i to a final one T f very close to the critical temperature T c. As in the w ¼ 0 case, we find that kinetics is controlled by two kinds of relaxation times t 1 and t 2. The former is the relevant time, and is associated to long-wavelength fluctuations driving the system to undergo a phase transition. The second is a short time, which controls local dynamics. Near T c , we show that, in particular, the longest relaxation time t 1 becomes less important in comparison with that relative to the w ¼ 0 case. Finally, we note that the existence of two relaxation times is consistent with the predictions of a recent experiment, which was concerned with the 1/2-spin compounds Li x Ni 2Àx O 2 , where the composition x is close to 1.
The Journal of Chemical Physics, 1997
ABSTRACT We consider here a polymer blend made of two crosslinked polymers A and B of different c... more ABSTRACT We consider here a polymer blend made of two crosslinked polymers A and B of different chemical nature, in the presence of a common solvent assumed to be good for both species. To study the solvent effects on the microphase separation of the mixture, we first apply the so-called blob model which is a direct consequence of the renormalization theory. In this model and at large scales compared with the screening length ξ of the semidilute regime, polymer chains A and B are viewed as sequences having blobs of size ξ as subunits. Within this model, we calculate the structure factor enabling us to derive all microphase critical properties. The main result is that, the swelling effects simply lead to a renormalization of these properties, and that the renormalization factors are powers of the monomer concentration. Quantitatively, such a renormalization is in agreement with the fact that, in presence of a good solvent, the mixture is more compatible. The blobs picture is a mean-field approximation, to go beyond this approach which neglects the strong fluctuations of the density near the critical point, we reconsider the problem using the renormalization-group techniques. We show that these strong fluctuations lead to a microphase critical behavior characterized by nonclassical exponents, which are found to be identical to those of the Ising-type system. © 1997 American Institute of Physics.
The Journal of Chemical Physics, 2002
Colloid & Polymer Science, 2001
Brazilian Journal of Physics, 2006
This paper is devoted to a review of recent progresses concerning the computation of the Casimir ... more This paper is devoted to a review of recent progresses concerning the computation of the Casimir force between two parallel plates delimitating a polymer blend or a ternary polymer solution (with a good solvent). We assume that, close to the consolute point, one or the two polymers of the mixture are strongly attracted by the plates (critical adsorption). For both systems, the induced force originates from the fluctuations of composition near the consolute point. In polymer blends case, it was found that the force decreases with separation L between the two plates as L −4 , with a known universal amplitude. For ternary polymer solutions, however, it has been shown that the interaction force decays rather as L −3. This drastic change of the force expression is due to the presence of the good solvent, which gives rise to additional fluctuations of polymer concentration. To do calculations, for the two systems, use is made of the standard ϕ 4-theory, where the field ϕ is the order parameter or composition fluctuation.
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Papers by mabrouk benhamou