Depuis plus de trente années, des recherches en didactique de la physique ont montré dans un grand nombre de pays que les élèves rencontrent des difficultés d'apprentissage en électricité et ce, quel que soit le niveau scolaire. Ces difficultés s’expliquent notamment par un certain nombre de conceptions qui viennent entraver la compréhension des phénomènes électriques. Pour palier ces difficultés, les didacticiens, et de fait les enseignants, utilisent des analogies plus ou moins adaptées et performantes. Pour réaliser notre travail de recherche, nous étudions une analogie innovante entre les domaines mécanique (domaine source) et électrique (domaine cible), cette analogie a la particularité d'être instrumentée, ce qui permet d'expérimenter dans le domaine source. Notre travail de recherche s’intéresse aux conditions d’efficacité de cette analogie pour l'apprentissage des élèves. La revue bibliographique dans les domaines de la didactique de la physique, l'ergonomie et la cognition incarnée a permis, dans un premier temps, d'établir un ensemble de conditions auxquelles doit répondre l'analogie pour être efficace. Notre travail a permis de montrer que cette analogie possède les critères requis pour être considérée comme une analogie potentiellement efficace. Dans un second temps, nous avons vérifié l'impact de la mise en oeuvre de cette analogie avec des élèves de terminale scientifique. Pour cela nous avons réalisé des questionnaires et des entretiens avec les élèves. Les résultats aux questionnaires mettent en évidence une efficacité moindre que celle que laissait supposer l'étude sur le potentiel didactique de l'analogie. C'est par le biais d'entretiens auprès des enseignants et d'enregistrements de cours qu'une très grande disparité d'utilisation de l'analogie a été repérée. L'étude des données recueillies permet de mieux comprendre les raisons qui expliquent la faible utilisation de l'analogie. Ces résultats ont permis la conception d'une première version d'un guide d'utilisation à destination des enseignants. / For over thirty years, research in didactics of physics have shown in many countries that students encounter learning difficulties in electricity and that, regardless of the grade level. These difficulties can be especially explained by a number of misconceptions that prevent the understanding of electrical phenomena. To overcome these difficulties, researchers in didactics and teachers use analogies which are more or less adapted and powerful. To achieve our research, we study an innovative mechanical analogy between mechanical domain (source domain) and electrical domain (target domain). This analogy has the feature of being instrumented, which allows to experiment in the source domain. Our research focusses on the conditions of effectiveness of this analogy for student learning. The literature review in physics, science education, ergonomics and embodied cognition allowed, firstly, to establish a set of conditions to be met by the analogy to be effective. Our work has shown that this analogy has the necessary criteria to be considered an effective analogy. Secondly, we tested the impact of the implementation of this analogy with scientific 12th grade students. For this, we made tests and interviews with students. The test results show a lower efficiency than suggested by the study of the potential of the analogy. Through interviews with teachers and course records, we note a great disparity of use of the analogy. The study of collected data allows to better understand the reasons of the low use of the analogy. These results allowed to design a first version of a manual for teachers.

[pt] Solos residuais são geralmente pobres em nutrientes. Isto prejudica a aplicação da atenuação natural monitorada em sítios contaminados com compostos orgânicos no Brasil. Para que o processo de biodegradação obtenha sucesso torna-se necessário à adição de nutrientes inorgânicos essenciais, como o fosfato e o nitrato, na massa de solo. Contudo, este processo deve ser estritamente controlado buscando atingir o equilíbrio de carbono:nitrogênio -C/N- mais favorável. Em solos com baixa condutividade hidráulica a adição de compostos inorgânicos na amostra de solo pode ser alcançada através da eletrocinese. O programa experimental desenvolvido neste trabalho objetivou avaliar a viabilidade do transporte de nitrato de amônio em um solo residual maduro do Município de Duque de Caxias através da eletrocinese. O programa também buscou acessar a variação na microbiota em decorrência da exposição prolongada de um campo elétrico. Os resultados obtidos no programa experimental revelaram que o nitrato de amônio pode ser transportado facilmente através de solos residuais. Também foi observado que houve um aumento de uma ordem de magnitude na população microbiana dentro da amostra de solo após a aplicação do potencial elétrico. Resultados preliminares indicaram que a eletrocinese pode ser uma alternativa para estimular a biorremediação de contaminantes orgânicos em solos residuais. / [en] Residual soils are generally poor in nutrients. This minimizes potential application of monitored natural attenuation of sites contaminated with organic compounds in Brazil. In order to allow the biodegradation process it is necessary to add essential inorganic nutrients, such as phosphate and nitrate. However this process must be strictly controlled in order to attain the most favorable C/N balance. In soils with low hydraulic conductivity the addition of inorganic compounds through the soil mass could well be achieved by electrokinetics. An experimental programme was carried out on mature residual soil samples from Duque de Caxias aiming on assessing the feasibility of ammonium nitrate transport via electrokinetics. The programme also evaluated the change in microbiota due the prolonged exposure to an electrical field. Results have shown that ammonium nitrate can be easily transported through residual soils. It was also observed one-order magnitude microbial population increase within the soil mass after the application of DC current. Preliminary results indicated that electrokinetics could well be used to enhance bioremediation of organic contaminants in residual soils.

Microfluidic technology has been grown rapidly in the past decade. Microfluidics can find wide applications in multiple fields such as medicine, electronics, chemical and biology. Micro-pumping is an essential part of a microfluidic system. This thesis presents the optimization process of AC electro-thermal micropump with respect to the geometry of electrode array and channel height. The thesis first introduces the theories of AC electrokinetic including dielectrophoresis, AC electro-osmosis (ACEO) and AC electro-thermal (ACET). Also presented are the basic theory and governing equations of microfluidics, the continuity equation, the Navier-Stokes equation, and the conservation of energy equation. AC electro-thermal effect results from the interplays between electric field, temperature field and fluid mechanics. Since the governing equations are highly non-linear, numerical simulation is extensively used to understand the effects of factors such as the electrode dimensions and channel height. By interfacing finite element analysis software COMSOL Multiphysics with Matlab, to the simulation model is able to scan the geometry variables so as to find the optimal micropump design. The optimization has been performed with respect to flow rate and power efficiency of the micropump.

The objective of this research was to evaluate the treatment efficiency of a nitrate-contaminated soil by combined technologies of the injection of palladized nanoiron slurry and electrokinetic remediation process. First, nanoiron was prepared by two synthesis processes based on the same chemical reduction principle yielding products of NZVI-A and NZVI-B, respectively. Then they were characterized by various methods. Micrographs of scanning electron microscopy have shown that a majority of these nanoparticles were in the range of 50-80 nm and 30-40 nm, respectively. Results of nitrogen gas adsorption-desorption show that NZVI-A and NZVI-B are mesorporous (ca. 30-40 Å) with BET surface areas of 128 m2/g and 77 m2/g, respectively. Results of X-ray diffractometry have shown that both types of nanoiron were poor in crystallinity. Results of zeta-potential measurements indicated that NZVI-A and NZVI-B had the same isoelectric point at pH 6.0. Although NZVI-A and NZVI-B were found to be superparamagnetic, their magnetization values were low. Poly acrylic acid (PAA), an anionic dispersant, was employed for stabilizing various types of nanoiron. Then Palladium¡]ca. 1 wt% of iron¡^ was selected as catalysis to form palladized nanoiron¡]Pd/Fe¡^. Results have demonstrated that an addition of 1 vol. % of PAA during the nanoiron preparation process would result in a good stabilization of nanoiron and nanoscale Pd/Fe slurry. Batch tests were carried out to investigate the effects of pH variation on degradation of nitrate aqueous solutions. Experimental results have indicated that palladized nanoiron outperformed nanoiron in treatment of nitrate in this study. Apparently, an employment of catalyst would enhance the treatment efficiency. Further, an exponential increase of the reaction rate was found for the systems at low pH. The final stage of this study was to evaluate the treatment efficiency of combined technologies of the injection of palladized nanoiron¡]Pd/Fe¡^ slurry and electrokinetic remediation process in treating a nitrate-contaminated soil. Test conditions used were given as follows: (1) slurry injection to four different positions in the soil matrix; (2) electric potential gradient: 1 V/cm; (3) daily addition of 20 mL of palladized nanoiron (4 g/L) slurry to the injection position; and (4) reaction time: 6 days. Test results have shown that addition of palladized nanoiron slurry to the anode reservoir yielded the lowest residual nitrate concentration in soil. Namely, about 99.5% removal of nitrate from soil. On the other hand, the acidic condition of soil matrix around the anode reservoir would enhance the degradation of nitrate therein. Based on the above findings, the treatment method employed in this work was proven to be a novel and efficient one in treating nitrate contaminated soil.

The research presented in this thesis involves the application of chiral cationic and anionic surfactants for simultaneous enantioseparation of structurally similar compounds in capillary electrophoresis (CE) and CE coupled to mass spectrometry (CE-MS). The first chapter briefly introduces the fundamentals of CE and CE-MS, emphasizing the micellar electrokinetic chromatography (MEKC) and MEKC-MS techniques, as well as ionic liquids (ILs) and affinity CE (ACE). In chapter 2, a mixture of five racemic profen (PROF) drugs are simultaneously separated with the combined use of 2,3,6-tri-O-methyl-β-cyclodextrin (TM-β-CD) and IL-type surfactant, N-undecenoxycarbonyl-L-leucinol bromide (L-UCLB). Enantioseparations of these PROFs are optimized using a standard recipe containing 35.00 mM TM-β-CD, 5.00 mM sodium acetate at pH 5.0, and varying the concentration as well as chain length of the IL surfactants. The batch-to-batch reproducibility of L-UCLB is found to be acceptable in terms of enantiomeric resolution, and migration time. A competitive inhibition mechanism is proposed to investigate the ternary interactions among TM-β-CD, ILs, and PROFs. The apparent binding constant of TM-β-CD to L-UCLB is estimated by nonlinear and linear plotting methods. The binding constants of one representative PROF (e.g., fenoprofen) to TM-β-CD and to L-UCLB are estimated by a secondary plotting approach. The R- and S-fenoprofen having different binding constant values, resulting in the enantioseparation due to the synergistic effect of TM-β-CD and L-UCLB. The R- and S-configurations of barbiturates display differences in potency and biological activity. In Chapter 3, a multivariate MEKC-ESI-MS approach for the simultaneous analysis of the racemic mixture of three barbiturates is presented. The chiral selector employed is the polymeric surfactant polysodium N-undecenoxycarbonyl-L-isoleucinate. The central composite design is used to optimize the chiral resolution, decrease the total analysis time, and improve the ESI-MS signal-to-noise ratio for these barbiturates. In preliminary experiments, the ranges of the factors investigated in the multivariate approaches are determined. Then the multivariate optimizations are conducted to determine the best overall chiral resolution with shortest possible run times for barbiturates. The limit of detection of ESI-MS is several folds higher compared to the UV detection. The predicted optimum results are in good agreement with the experimental data.

Modeling electrophoresis of peptides, proteins, DNA, blood cells and colloids is based on classical electrokinetic theory. The coupled field equations-Poisson, Navier-Stokes or Brinkman, and ion transport equations are solved numerically to calculate the electrophoretic mobilities. First, free solution electrophoretic mobility expressions are derived for weakly charged rigid bead arrays. Variables include the number of beads (N), their size (radius), charge, distribution (configuration), salt type, and salt concentration. We apply these mobility expressions to rings, rigid rods, and wormlike chain models and then apply the approach to the electrophoretic mobilities and translational diffusion constants of weakly charged peptides. It is shown that our bead model can predict the electrophoretic mobilities accurately. In order to make the method applicable at higher salt concentrations and/or to models consisting of larger sized subunits, account is taken of the finite size of the beads making up the model structure. For highly charged particles, it is also necessary to account for ion relaxation. This ion relaxation effect is accounted for by correcting "unrelaxed" mobilities on the basis of model size and average electrostatic surface, or "zeta" potential. With these corrections our model can be applied to the system with absolute electrophoretic mobilities exceeding approximately 0.20 cm2/kV sec and also models involving larger subunits. This includes bead models of duplex DNA. Along somewhat different lines, we have investigated the electrophoresis of colloidal particles with an inner hard core and an outer diffusive layer ("hairy" particles). An electrokinetic gel layer model of a spherical, highly charged colloid particle developed previously, is extended in several ways. The charge of the particle is assumed to arise from the deprotonation of acidic groups that are uniformly distributed over a portion (or all) of the gel layer. Free energy considerations coupled with Poisson-Boltzmann theory is used to calculate the change of the local pKa of the acidic groups depending on the local electrostatic environment. Based on the modeling of electrophoresis and viscosity, we predict that the thickness of the gel layer decreases as the salt concentration increases. And only the outermost portion of the gel layer is charged.

Micellar electrokinetic chromatography (MEKC) and capillary electrochromatography (CEC) are two of the major capillary electrophoresis (CE) modes that have been interfaced to mass spectrometry (MS) for sensitive and selective analysis of chiral compounds. This research combines these two modes and expands their applications in chiral CE analysis. Chapter 1 is a review of amino acid based molecular micelles used in MEKC-MS for enantioselective analysis over the past five years. In this chapter, a typical MEKC-MS experiment setup as well as detailed standard operating procedure in synthesis of molecular micelles and running a typical MEKC-MS experiment using the molecular micelles is discussed. Chapter 2 described a multivariate MEKC-MS optimization for the simultaneous analysis of two negatively charged model chiral compounds in negative ion mode with molecular micelles. In this chapter, a central composite design (CCD) is used to first construct a series of experiments to optimize all the important MEKC-MS parameters. Next, response surface methodology (RSM) was used to analyze the interactions between the factors, picking up the best separation and detection conditions, predicting the result of the chiral separation/MS detection, and finally running the actual experiment and comparing the chromatographic results with the predicted parameters. Chapter 3 demonstrates a similar multivariate MEKC-MS optimization for analysis of a positively charged model chiral compound in a positive ion mode. The same CCD and RSM methods were used to optimize the separations and MS sensitivity. Chapter 4 describes a chiral analysis of four neutral benzoin derivatives (hydrobenzoin, benzoin, benzoin methyl ether, and benzoin ethyl ether) using MEKC coupled to atmospheric pressure photo-ionization mass spectrometry (APPI-MS). The same multivariate experimental design strategy was used to optimize the MEKC as well as APPI-MS parameters. Simultaneous chiral separation of all four benzoin derivatives was achieved with high detection sensitivity compared to UV-detection. Chapter 5 introduces a novel one-pot synthesis scheme for an acryloyl-terminated, carbamate-linked surfactant-bound monolith with leucine head group and different chain lengths. The method promises to open up the discovery of new amino acid based polymeric monoliths for chiral separations and enhanced chemoselectivity for simultaneous chiral separations and enhanced detection in CEC and CEC-MS. In Chapter 6, five amide-linked surfactant-bound monoliths with different chain lengths and head groups (leucine, valine, and phenylalanine) were synthesized and characterized. Enantioseparation of several test compounds was achieved by CEC using the monolithic columns. One of the chiral surfactant, sodium 11-acrylamidoundecanoyl-L-leucinate (SAAUL), was polymerized in aqueous solution under 60Co radiation to form molecular micelle poly-SAAUL. MEKC experiments were carried out with the poly-SAAUL molecular micelle to separate ten cationic chiral compounds. The result was compared with the CEC separation using the AAUL monolithic column. This study is the first comparison of chiral CEC and MEKC with the same surfactant monomer, which has the capability of forming both chiral stationary phase for CEC and chiral pseudophase for MEKC.

Abstract The object of this study was to investigate the synthesis of a nanoscale zero-valent iron slurry (NZVIS) for use in Fenton-like reactions, and to evaluate its efficiency for As(III) oxidation to As(V) in spiked deionized water and simulated groundwater containing humic acid. Furthermore, this study used injection of the nanoiron slurry combined with electrokinetic processes to remediate As(III) in soil. NZVI was prepared by a chemical reduction process. The efficiency of using 3 wt% soluble starch (SS) to stabilize NZVI was also studied. It was found that the SS could keep the nanoparticles dispersed for over one day. The NZVI was characterized by XRD, FE-SEM, ESEM-EDS, and EDS-mapping, to observe its morphology and crystal structure. In this research the iron species observed took non-crystalline forms. In water batch tests, studies in deionized water were compared with those in simulated groundwater with humic acid, and dissolved oxygen content was adjusted. Injection of NZVIS oxidized As(III) to As(V) in all cases. In both deionized water and simulated groundwater, it was found that when the dissolved oxygen(DO) content was not increased, the NZVIS generated non-selective oxidant OH¡E, thus reducing the As(V) production rate. When dissolved oxygen content was increased, the DO oxidized organic matter present in the simulated groundwater, allowing the OH¡E to react further with As(III) and increasing the As(V) production rate. Finally, a test was performed in actual groundwater under optimal reaction conditions, without increasing the dissolved oxygen content, for comparison of As(V) yield. The concentration of As(V) was found to be higher in this test (As(V) Conc. = 17.55 £gg/L) than when using simulated groundwater (As(V) Conc. = 4.63 £gg/L). This study further examined NZVIS injection combined with electrokinetic (EK) technology for the remediation of soil columns containing a low concentration (initial conc. = 100 mg/kg) and a high concentration (initial conc. = 500 mg/kg) of As(III). EK alone without injection of NZVIS (Test E-1) resulted in a residual soil As(V) concentration of 24 mg/kg in the low-concentration test group. In Test E-2, where NZVIS was injected into the anode reservoir, and Test E-3, where NZVIS was injected into the cathode reservoir, residual soil As(V) concentrations were 2.3 mg/kg and 3.4 mg/kg, respectively. The high-concentration test group was comprised of Test E-4 (EK alone without injection of NZVIS), Test E-5 (NZVIS injected into anode reservoir), and Test E-6 (NZVIS injected into cathode reservoir). In these tests, only soil sections 0.2 and 0.4 (normalized distance from anode reservoir) met soil regulation standards. Residual As(V) concentrations in soil sections 0.6, 0.8, and 1.0 are much higher than the regulatory standard. In soil section 1.0, the residual As(V) concentration was less in Test E-6 than in Test E-5 (116.6 mg/kg and 183.5 mg/kg, respectively). This may be because at high pH values, the iron surface does not corrode, instead arsenic adsorption prevails. Only a fraction of negatively charged As(V) species will migrate towards the anode resulting in a relatively low soil As(V) concentration near the cathode.

This research was aimed to investigate the enhancement of electrokinetic (EK) remediation arsenate-contaminated soil by permeable reaction barrier (PRB). All experiments, which experimental parameters included the position, materials, and quantity of PRB, processing fluid types, potential gradients, and treatment time, were conducted in two types of EK systems. One was Pyrex glass cylindrical cells with dimension of 4.2 cm (£r) ¡Ñ 12 cm (L) and the other was a small pilot-scale modulus with dimension of 36cm (L) ¡Ñ18cm (W) ¡Ñ18cm cm (H). The PRBs were composed of four kinds of reaction materials, which included commercial zero valent iron (Fe(0)C), manufactured zero valent iron (Fe(0)M), commercial hydrous ferric oxide (FeOOHC), and manufactured hydrous ferric oxide (FeOOHM), mixed with ottawa sand in a ratio of 1:2,respectively, and installed in the anode, middle, and cathode side of the EK systems. For 5-day EK cylindrical cell tests, the results showed that the PRB installation would result in a lower electroosmosis permeability (Ke) and a higher removal efficiency of arsenate. The arsenate removal efficiency of EK system with PRB was in the range of 43.89-70.25%, which was 1.5~2.6 times greater than that without PRB, and the value of Ke was in the range of 4.30-12.61¡Ñ10-6 cm2/V-s. The soil pH after EK/PRB treatment was much closer to natural and more arsenate was collected in the anode reservoir. Moreover, the remediation performance of FeOOHC as PRB materials was much better than other materials. For EK pilot-scale modulus tests, it was shown that the removal efficiency of arsenate was effectively enhanced as improved experimental parameters and, however, led to increase the treatment cost. In EK modulus without PRB, the removal efficiency of arsenate, elctroosmosis permeability, and energy consumption were 27.76%, 3.30-5.39¡Ñ10-6 cm2/V-s, and 1724.81 kWh/m3, respectively. Furthermore, the treatment cost was NT 9583/m3. As increasing treatment time, graphite electrode, potential gradient, and quantity of PRB materials, the removal efficiency of arsenate increased to as high as 45.11-71.22% and the treatment cost also increased up to NT 24,800-57,730/m3. As investigated the binding form of arsenate with soil after EK/PRB treatment, it was found that the arsenate ¡Vsoil binding forms of Fe-Mn oxide bound, organically bound, and residual in the soil section behind the PRB were much easier transformed to the forms of exchangeable and carbonate bound. The transformation rate reached as high as 72.5% and it increased with treatment time. However, the Fe-Mn oxide bound was still the main binding form, 61.6-81.6%, in the soil section prior to the PRB. The removal mechanism of arsenate contaminated soil remediation was dominated by electromigration, electrolysis, and electroosmosis in EK system without PRB. And, in EK/PRB system, the removal of arsenate from soil was mainly resulted from adsorption rather than redox reaction by PRB. To sum up, the PRB can effectively enhance the electrokinetic remediation of arsenate contaminated soil by choosing the right PRB materials and operation parameters.

Albite (Na-feldspar) and orthoclase (K-feldspar) are the major feldspar minerals used in the production of glass and ceramics. They are found together with impurities like biotite, muscovite, quartz and rutile which are not desired for ceramics and glass industries. Therefore, these have to be removed to make the ore available for industrial use. In order to shed light on the actual feldspar ores, in this study / the flotation characteristics of albite, biotite, muscovite, orthoclase, quartz and rutile were investigated separately in their pure forms. In the investigation, the electrokinetic potential measurements and micro-flotation studies have been carried out to get information about their flotation characteristics under the effect of three different collectors, Aero 704, Aero 3000C and Aero 825, and the pH of the medium. The flotation recoveries were found to be pH dependent and the effective between the pH range of 7.0 and 11.5 in the presence of Aero 704. In the case of flotation with Aero 3000C, the recoveries reached up to 95.0% at certain concentrations and pH values and decreased sharply below pH 3.0 and above pH 9.5 for all the minerals tested. In the presence of Aero 825, the flotation recoveries of the minerals except for rutile, were found to be insufficient even with its highest concentration. In order to evaluate the adsorption mechanism of the collectors, Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR) analyses were carried out. From the AFM results it might be deduced that the behavior of Aero 3000C and Aero 825 was found to be almost similar for biotite and muscovite as monolayer adsorption and for the remaining minerals, albite, orthoclase, quartz and rutile, as monolayer and bilayer adsorption together. In the case of Aero 704, for albite and orthoclase, the adsorption of the collector might be the reason for monolayer and bilayer formation on their surfaces. The strength of the interaction of the collectors on the mineral surfaces was followed by FTIR analyses before and after acetone washing. The interaction of all the collectors was found to be weak in the case of albite, orthoclase, quartz and rutile whereas the interaction of Aero 704 and Aero 3000C was found to be strong in the case of biotite and muscovite.