Véronique Pimienta

Véronique Pimienta
Université de Toulouse · IMRCP

PhD

About

88
Publications
8,093
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1,583
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Introduction
Véronique Pimienta currently works at the IMRCP, University of Toulouse. Véronique does research in Chemical Kinetics. Their current project is 'dropdyn'.

Publications

Publications (88)
Article
Hypothesis Switchable assemblies relevant for bio-applications may be accessed from water-soluble tetra-ortho-substituted azobenzenes that reversibly self-assemble and form complexes with β-cyclodextrin under visible light. Experiments Two azobenzenes bearing either four fluorines or two chlorines and two fluorines in the ortho positions were synt...
Article
Full-text available
Planar Laser Induced Fluorescence with Inhibition (PLIF-I) is a powerful technique for studying the local gas/liquid oxygen mass transfer from a single rising bubble. However, to track oxygen in the liquid phase, it is necessary to use an oxygen sensitive luminescent probe, which needs to be unreactive toward the liquid phase. This article presents...
Article
We report a series of experiments carried out with a dichloromethane drop deposited on the surface of an aqueous solution containing a surfactant, cetyltrimethylammonium bromide. After an induction stage during which the drop stays axisymmetric, oscillations occur along the contact line. These oscillations are succeeded by a spectacular spontaneous...
Article
The dynamics of radial A+B→C reaction fronts can be affected by buoyancy-driven convection. Motivated by recent advances in reaction-diffusion-advection (RDA) systems theory, we investigated experimentally a radial A+B→C RDA system under modulated gravity, using a Hele-Shaw cell setup onboard a parabolic flight. We evaluated characteristic properti...
Preprint
Full-text available
We report a series of experiments carried out with a dichloromethane drop deposited on the surface of an aqueous solution containing a surfactant, cetyltrimethylammonium bromide. After an induction stage during which the drop stays axisymmetric, oscillations occur along the contact line. These oscillations are succeeded by a spectacular spontaneous...
Article
We report various modes of synchrony observed for a population of two, three and four pentanol drops in a rectangular channel at the air-water interface. Initially, the autonomous oscillations of a single 1-pentanol drop were studied in a ferroin DI water solution pre-mixed with some volume of pentanol. A pentanol drop performs continuous motion on...
Article
Full-text available
This work is an experimental investigation of the effect of the nature of surfactants on oxygen mass transfer. The study focuses on three cationic surfactants with different hydrophobic chain lengths, and four nonionic surfactants with different hydrophilic chain lengths. Equilibrium adsorption isotherms are calculated for each surfactant from expe...
Article
Flow-driven precipitation experiments are performed in model porous media shaped within the confinement of a Hele-Shaw cell. Precipitation pattern formation and the yield of the reaction are investigated when borosilicate glass beads of different sizes are used in a mono-layer arrangement. The trend of the amount of precipitate produced in various...
Article
Full-text available
We present experiments on multiple pinned self-propelled camphor ribbons, which is a rectangular piece of paper with camphor infused in its matrix. Experiments were performed on three, four, and five ribbons placed in linear and polygonal geometries. The pinned ribbons rotate on the surface of water, due to the surface tension gradient introduced b...
Data
This pdf contains the supplementary material, which supports the published article Rotational synchronization of camphor ribbons in different geometries.
Article
Hydrophilic host-guest complexes, consisting in a water-soluble azobenzene and α-, β- or γ-cyclodextrins, have been proposed as a model to study supramolecular photoresponsive systems in aqueous environments through a full spectrometric approach combined to a simulation and data fitted methodology. Various essential and complementary spectroscopic...
Article
Full-text available
The use of nanocarriers for hydrophobic photosensitizers, in the context of photodynamic therapy (PDT) to improve pharmacokinetics and bio-distribution, is well-established. However, the mechanisms at play in the internalization of nanocarriers are not well-elucidated, despite its importance in nanocarrier design. In this study, we focus on the mec...
Article
Full-text available
This article explores the contrasting reactivity of cyclopropyl complexes of early transition metals. [Cp*W(NO)(CH2R)(c‐C3H5)] (R = SiMe3, Ph, t‐Bu) generated in THF solution from [Cp*W(NO)(CH2R)Cl] and [Mg(c‐C3H5)2(dioxane)x] readily rearrange to η³‐allyl derivatives [Cp*W(NO)(CH2R)(η³‐C3H5)] by an intramolecular ring opening reaction. Both direct...
Article
Full-text available
Experiments on interacting pinned self-propelled rotators are presented. The rotators are made from paper with camphor infused in its matrix. The ribbons rotate due to Marangoni effect driven forces arising by virtue of surface tension gradients. Two such self-rotating camphor ribbons are observed to experience a repulsive coupling via the camphor...
Data
We present the experimental study of a single camphor ribbon and have shown the decay in the angular frequency of the ribbon with time.
Chapter
Pattern formation and periodical regimes are generally observed for reactive nonlinear chemical systems. They are here obtained for a non-reactive system constituted by an oil (dichloromethane) drop deposited on a surfactant (cetyltrimethylammonium bromide) aqueous solution. The interplay between physicochemical processes (evaporation, solubilizati...
Article
Full-text available
Drop motility at liquid surfaces is attracting growing interest because of its potential applications in microfluidics and artificial cell design. Here we report the unique highly ordered pattern that sets in when a millimeter-size drop of dichloromethane spreads on an aqueous substrate under the influence of surface tension, both phases containing...
Article
We investigated the influence of the nature of the substituent on the 4′-position of terpyridine ligands and the geometry around the metal ion on the photosensitization of ruthenium nitrosyl complexes. This was achieved by synthesizing a series of [Ru(R-Phtpy)Cl2(NO)]⁺ complexes based on tridentate terpyridine ligands with a substituted phenyl ring...
Conference Paper
We investigate the dynamics of a dichloromethane droplet placed on the surface of an aqueous solutions of cetyltrimethylammonium bromide. By varying the surfactant concentration, we observe a rich variety of different shapes, ranging from pulsating over rotating to polygonal-like shaped drops, during the dissolution process. These remarkable shapes...
Article
In this Letter, we report on the first experimental evidence of a self-pinning liquid drop on a liquid surface. This particular regime is observed for a miscible heavier oil drop (dichloromethane) deposited on an aqueous solution laden by an ionic surfactant (hexadecyltrimethylammonium bromide). Experimental characterization of the drop shape evolu...
Article
Surface tension gradients are at the origin of the self-motion and deformation of millimeter-sized floating objects. For (quasi-)non-deformable systems, like solids and gels, the motion-mode is mainly controlled by the shape of the object and by the way the surface active propellant is released on the surrounding surface. Two situations are reviewe...
Article
Various polymeric micelles were formed from amphiphilic block copolymers, namely poly(ethyleneoxide-b--caprolactone), poly(ethyleneoxide-b-D,L-lactide) and poly(ethyleneoxide-b-styrene). The micelles have been characterized by static and dynamic light scattering, electron microscopy and asymmetrical flow field-flow fractionation. They all displaye...
Article
Self-pulsating sessile drops are a striking example of the richness of far-from-equilibrium liquid/liquid systems. The complex dynamics of such systems is still not fully understood and simple models are required to grasp the mechanisms at stake. In this paper, we present a simple mass-spring mechanical model of the highly regular drop pulsations o...
Article
Hydrodynamic instability arising in horizontally propagating vertical chemical fronts leading to the formation of a single stable convection roll is investigated experimentally in the iodate-arsenous acid reaction for various stoichiometry. In the presence of a free surface, the tilted reaction front becomes more elongated due to the evaporation of...
Article
Full-text available
A combined study devoted to chemo-Marangoni convection and the underlying kinetics is presented for a biphasic system in which surfactants are produced in situ by an interfacial reaction. The pattern formation studied in a Hele-Shaw cell in both microgravity and terrestrial environments initially shows an ensemble of chemo-Marangoni cells along a n...
Article
A system far from equilibrium, where the surfactant transfer from a small drop located in the aqueous bulk to the air-water interface results in spontaneous nonlinear oscillations of surface tension, is theoretically and experimentally considered. The oscillations in this system are the result of periodically arising and terminating Marangoni insta...
Article
Wir danken David Villa (SPI-FR BT) für die Gegenlicht-Fotografie (Abbildungen 2 e,f und S1) und Jean-Claude Micheau für Diskussionen. Wir danken außerdem dem CNES und der UFR PCA der Université Paul Sabatier für die finanzielle Unterstützung. O.S. wird unterstützt von der National Science Foundation (Fördernr. CHE-0910657 und DMR-1005861).
Article
Generation of cohesive motion was observed during the dissolution of mm-sized drops of dicholoromethane into aqueous surfactant solutions. This system shows pulsating drops, multi-armed rotors, and polygonal shapes. The sharp tips of these patterns eject much smaller droplets to form expanding halos or swirling chains. The daughter droplets also un...
Article
Equilibrium and transfer properties of two surfactants (a non-ionic one, Brij5, and a cationic one, CTAB) were studied in water/oil biphasic systems. Water/air surface tension measurements provide information on both the partition coefficient and also on the type of aggregates formed: classical micelles or swollen micelles (oil-in-water microemulsi...
Article
A spirobenzopyran containing 6-chloro and 8-diphenyloxazole substituents has been investigated in acetonitrile solution by nanosecond laser photolysis at room temperature. In degassed solution, a short-lived transient (5 μs) has been identified as the triplet state of the closed spiro form. The ratio between the singlet and triplet pathways of ring...
Article
We report the synthesis of a niobium cyclopropyl complex, Tp(Me2)NbMe(c-C(3)H(5))(MeCCMe), and show that thermal loss of methane from this compound generates an intermediate that is capable of activating both aliphatic and aromatic C-H bonds. Isotopic labeling, trapping studies, a detailed kinetic analysis, and density functional theory all suggest...
Article
Spontaneous non-linear oscillations were observed during the transfer of commercial non-ionic surfactants, oxyethylated alcohols C8EO4 and C8EO5 through the water/heptane interface. The oscillations appear in a certain range of initial surfactant concentrations in the water phase. The experimental results are discussed using numerical simulations o...
Article
The photochromic, thermochromic and metallochromic behaviour of a series of three spiro[indoline-8-(benzothiazol-2-yl)-benzopyrans] has been investigated. The thermodynamic and kinetic parameters of their thermal equilibrium between the ring-closed (spiro) and ring-opened (merocyanine) isomeric forms have been determined using UV-Vis absorption and...
Article
This review focuses on the results of the studies of metal ion complexation by spiropyrans published mostly in recent years. Introduction of ionophore substituents in the molecules of photochromic spiropyrans induces a reasonably strong bonding in the complexes of these compounds with metal ions. The degree of complexation depends on the state (ope...
Article
Adsorption isotherms have been determined at the water/oil interface for five biphasic systems involving surfactants (non-ionic and ionic) present in both phases at partition equilibrium. The systems studied were polyoxyethylene(23)lauryl ether (Brij35) in water/hexane and four ionic surfactants, hexadecyltrimethylammonium bromide (CTAB), and a ser...
Article
We consider a Hele-Shaw cell containing two immiscible liquids. A chemical species initially dissolved in an organic phase crosses the interface into the aqueous phase. In the aqueous phase this chemical reactant is involved in a reaction producing a surfactant which undergoes micellisation when the critical micelle concentration is reached. These...
Data
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and...
Data
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and...
Article
Several biphasic systems giving rise to periodical Marangoni instability have been analyzed from the point of view of the physicochemical properties of the involved compounds. In each case, the compound at the origin of the oscillatory behavior has been identified: the reactant cetyltrimethylammonium bromide (CTAB) for the CTAB/picric acid (PH) sys...
Article
By means of UV/Vis absorption spectroscopy, NMR measurements and kinetic modelling, two spironaphthoxazine compounds bearing 5-OAlk substituent have been investigated in neutral and acidified ethanol media. The kinetics of ring opening/ring closure and the equilibrium constant, the quantum yield of photocoloration, the molar absorption coefficients...
Article
A detailed comparative study of the structural and spectroscopic features and of the reactivity of ruthenium phosphinidene complexes (η6-Ar)(PCy3)Ru(PMes*) (2a, Ar = p-cymene; 2b, Ar = benzene) has been undertaken. The structures of complexes 2a and 2b have been determined by single-crystal X-ray diffraction and display similar features. Both compo...
Article
The macroscopic manifestation of hydrophobic interactions for amphiphilic organic ion pairs (tetraalkylammonium-anion) has been shown experimentally by measuring their association constants and their affinity with the organic phase. Beyond a certain size, there is a direct relation between association constants and chain lengths in tetraalkylammoni...
Article
Three new spirooxazines derivatives have been investigated in neutral and acidic ethanol solution. Besides, the classical photochromic and thermochromic properties of spirooxazines compounds, a strong reversible visible-light photobleaching of the protonated open form has been found. A global mechanism is proposed.
Article
The partition at equilibrium, in a two-phase liquid system, of a compound dissociated in one phase, or both, is expressed in terms of general equations and analyzed. Dissociation in the second phase, even weak, has a non-negligible influence. The distribution ratio depends strongly on the concentration and can even be reversed in certain cases. All...
Article
Association constants and adsorption parameters of tetraalkylammoniumdodecyl sulfate (TAADS) ion pairs in water were determined. We have analyzed water/air surface tension measurements obtained for mixtures of sodium dodecyl sulfate (SDS) and tetraalkylammonium bromide of increasing chain lengths (TMAB, TEAB, TPAB, and TBAB). To reproduce the exper...
Article
Full-text available
Hydrogen peroxide evolution during the vacuum-ultraviolet (V-UV, 172 nm) photolysis of water is considerably affected by the presence of oxalic acid (employed as a model water pollutant) and striking differences are observed in the absence and in the presence of dioxygen.
Article
Periodic Marangoni convective instability has been observed in a biphasic system during the mass transfer of cetyltrimethylammonium bromide (CTAB) from an aqueous to a dichloromethane organic phase. Visualization of the convective fluxes was possible thanks to the CTAB crystals that are formed in the aqueous phase at a temperature below the Krafft...
Article
In solution, the photochromic molecule 5-methoxyspiro[indole-phenanthrolinoxazine] (SPO) is in equilibrium with its corresponding merocyanine open isomer. In pure acetonitrile, there is about 22.5% of the open form, whereas in acetonitrile–water binary solvents this proportion increases to more than 60% when the water molar fraction χ(H2O) is aroun...
Article
Full-text available
For three 5-alkyloxyspiro[indolephenanthrolinoxazines], the open form possesses a low-polarity semi-quinoidal structure. In acetonitrile-water binary solvent, the merocyanine is stabilized by a specific interaction with a water molecule. At high water content, the hydrated open form gives rise to H-aggregates.
Article
Oscillations of the electric potential and of the interfacial tension were simultaneously recorded in a water−oil−water system (cetyltrimethylammonium bromide (CTAB) in water/picric acid in dichloromethane/water). Both types of oscillations were perfectly correlated in time and shape. In each oscillatory cycle, the fast jumps in the electric potent...
Article
The influence of oligothiophene substituents on five new [3H]naphtho[2,1-b]pyrans has been investigated using flash photolysis and continuous irradiation techniques. Photochromic properties strongly depend on the number and position of the thienyl units. Thienyl substitution increases the UV/visible absorbance of the lower energy transition of both...
Article
Computational kinetic analysis of a lately discovered homochiral peptide self-replicator is presented. A 6-step kinetic model was designed that addresses the main reactions and hydrophobic interactions involved in this template-directed, autocatalytic system and that gave rise to excellent fitting of 4 previously published independent experimental...
Article
A kinetic model has been designed to describe and to analyze the stereoselective behavior of a recently discovered heterochiral template-directed peptide self-replicator by Ghadiri and co-workers [Nature 409 (2001) 797-801]. It turned out that previous assumptions stating that exclusively homochiral species participate in a stereoselective and auto...
Article
Full-text available
The photochromic properties of three ferrocenyl-[2H]-benzopyrans were investigated under monochromatic irradiation and compared with those of their phenyl homologues. The UV/visible spectra of the closed and open forms are reported together with the quantum yields of photocoloration. It was shown that the ferrocenyl- substitution induces the format...
Article
The oscillatory picric acid/CTAB two-phase systemsas introduced by Yoshikawa and Matsubara [J. Am. Chem. Soc. 1984, 106, 4423-4427]shas been revisited. UV-vis spectroscopic studies were presented that provide a clearer and new insight into the possible kinetic mechanism for the oscillatory behavior. It was shown that the key process in the system i...
Article
The autocatalytic biphasic alkaline hydrolysis of C-4 to C-8 ethyl alkanoates was studied in a CSTR. In our experimental conditions, the two shorter esters (C-4 and C-5) showed monostable behavior while the longer ones (C-6 to C-8) showed bistability. Both the occurrence of bistability and the amplitude of the bistable domain in the CSTR can be rel...
Article
The kinetics of solubilization of ethyl hexanoate into an aqueous phase was investigated in the presence of various additives (NaCl, ethanol, and sodium hexanoate). The salting-out effect of NaCl and the solvent effect observed in the presence of ethanol were quantified. Solubilization by sodium hexanoate shows a dramatic enhancement when the criti...
Article
Autocatalytic kinetics are observed during the biphasic alkaline hydrolysis of C-4, C-6 and C-8 (butanoate, hexanoate and octanaoate) ethyl esters. Ethanol and alkanoate anions are the products of the reaction. A kinetic model including spontaneous dissolution of the organic phase into the aqueous phase, aqueous hydrolysis of the ester, formation o...
Article
Photoreversible photochromic systems can be analysed quantitatively even if the photoi-somers have not been isolated. Quantum yields of photocoloration and photodecoloration and UV / visible spectra of each photoisomer can be extracted simultaneously by numerical simulation and fitting of Abs vs time curves recorded under continuous monochromatic i...
Article
Chemical reactivity is generally taught by considering the chemical properties of the reacting entities (acid-base, oxidation-reduction, complexation, and precipitation) and the values of the corresponding equilibrium thermodynamic constants (K a, E 0K d, K s). This approach, however, is not well-suited to the dynamic chemical systems that are ofte...
Article
The photochromism of the 1,3,3-trimethylspiro[indoline-naphthoxazine] A has been studied under continuous monochromatic irradiation (313 and 365nm) in liquid toluene solution at 278K. The values of the main photochromic parameters (quantum yields and absorption coefficients) have been determined by kinetic modelling of absorbance (Abs) versus time...
Article
The biphasic alkaline hydrolysis of ethyl caprylate, which has attracted attention as a prototype reaction for the so-called self-reproduction of micelles (Bachmann, P. A.; et al. Nature 1992, 357, 57), was shown to give rise to kinetic bistability in a continuous flow stirred tank reactor. At higher flow rates, the stationary state composition was...
Article
The kinetics of spiropyran photochromic systems in solution in a stirred batch reactor continuously irradiated with monochromatic light was studied by UV/visible spectrophotometry. The plots of absorbance vs time were analyzed, and the desired parameters (quantum yields, UV/visible spectrum of the unstable photomerocyanine, ...) were extracted from...
Article
The mechanism of the reduction of permanganate by oxalic acid in sulfuric acid medium was completely described by a model incorporating the specific reactivities of permanganate and of various Mn(III) and Mn(IV) reaction intermediates. It involved 14 steps including 8 equilibria (dissociation of the two diacids and complexation of Mn(III) intermedi...
Article
In photochemistry, under continuous irradiation, kinetic non-linearity results from Beer-Lambert's law. In monophotonic or photoequilibrated systems, non-linearity is too weak in order to exhibit dynamic instabilities. On the other hand, when there is a biphotonic process, as in the so-called ABC system or a process of auto-inhibition, as in the se...
Article
UV/visible spectrophotometric analysis of the permanganate/oxalic acid reaction in sulfuric acid demonstrated the presence of two intermediates: bis(oxalato)manganate(III) and a soluble Mn(IV) compound. Their relative proportions were found to depend on the initial concentrations [H2C2O4](0) and [H2SO4](0). The proportion of bis(oxalato)manganate(I...
Article
We propose a general method for the computer analysis of the thermoreversible photochromism. By combining numerical integration of the photokinetic equations and least square adjustement of the quantum yield (φ) and absorption coefficients (ε), it is possible to fit accurately the experimental absorbance vs time curves recorded during continuous mo...
Article
Seven general kinetic schemes encompassing reversible, mixed first- and second-order and autocatalytic reactions were shown to be governed by a single integrated rate law involving two parameters a and m: Y(t) = (1 - m)/(exp(at) - m), where Y(t) is the normalized amplitude of the kinetics. This mathematical expression is derived by integration of a...
Article
If the rate equation of a chemical reaction can be expressed in terms of a single variable, the steady-state conditions in a CSTR can be predicted from the batch kinetics. This does not require detailed knowledge of the reaction mechanism. However, if the reaction comprises several elementary steps, deduction is not possible since the rate depends...
Article
The rate law of an elementary photochemical reaction: A → B (hv), contains 4 independent factors: the quantum yield, the photon flux, the concentration of the photosensitive substrate and the photokinetic factor. This type of reaction will always slow down. However, by increasing one of these 4 factors artificially, the reaction can be made to spee...
Article
If the rate equation of a chemical reaction can be expressed in terms of a single variable, the steady-state conditions in a CSTR can be predicted from the batch kinetics. This does not require detailed knowledge of the reaction mechanism. However, if the reaction comprises several elementary steps, deduction is not possible since the rate depends...

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