Convective instabilities in traveling fronts of addition polymerization

Craven, Richard; Khan, Akhtar M.; West, William W.

doi:10.1021/j100197a062

Cited by 130 publications

(127 citation statements)

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“…The first experiments were performed in capillary tubes and have addressed the influence of the radius of the tube or of the angle of orientation with respect to gravity on the onset of convection ͑characterized by one or two convection rolls͒ and on the speed of the front. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] More recently, experiments in Hele-Shaw cells [21][22][23][24][25][26][27][28][29][30] and in a three-dimensional tank 31 have allowed investigation of the dynamics of more extended systems and of the stability of a wider spectrum of instability modes.…”

Section: Classification Of Autocatalytic Reactionsmentioning

confidence: 99%

“…25,27,49 Free radical polymerizations are very exothermic and form polymer products that are more dense than the monomer ͑⌬ c Ͼ 0͒; they fall thus in the same antagonist category. 9,17,18 Various other examples of this family with ⌬ c Ͼ 0 and ⌬ T Ͻ 0 are quoted in Ref. 9.…”

Section: Classification Of Autocatalytic Reactionsmentioning

confidence: 99%

“…9,17,18 Various other examples of this family with ⌬ c Ͼ 0 and ⌬ T Ͻ 0 are quoted in Ref. 9. Finally, let us also mention combustion fronts 19,20 that fall generally in the cooperative family as the burned products are typically solutelighter and hotter than the fuel.…”

Section: Classification Of Autocatalytic Reactionsmentioning

confidence: 99%

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On the classification of buoyancy-driven chemo-hydrodynamic instabilities of chemical fronts

D’Hernoncourt

Zebib

Wit

2007

Chaos: An Interdisciplinary Journal of Nonlinear Science

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Exothermic autocatalytic fronts traveling in the gravity field can be deformed by buoyancy-driven convection due to solutal and thermal contributions to changes in the density of the product versus the reactant solutions. We classify the possible instability mechanisms, such as Rayleigh-Bénard, Rayleigh-Taylor, and double-diffusive mechanisms known to operate in such conditions in a parameter space spanned by the corresponding solutal and thermal Rayleigh numbers. We also discuss a counterintuitive instability leading to buoyancy-driven deformation of statically stable fronts across which a solute-light and hot solution lies on top of a solute-heavy and colder one. The mechanism of this chemically driven instability lies in the coupling of a localized reaction zone and of differential diffusion of heat and mass. Dispersion curves of the various cases are analyzed. A discussion of the possible candidates of autocatalytic reactions and experimental conditions necessary to observe the various instability scenarios is presented. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2405129͔It is common knowledge that light fluids rise while heavy fluids sink in the gravity field. Buoyant convection due to a hydrodynamic Rayleigh-Taylor instability can therefore be triggered if a heavy solution lies on top of a lighter one. Rayleigh-Bénard convection appears when a fluid is heated from below. Convection can also result from double-diffusive instabilities of a statically stable density stratification if solutal and thermal effects are in competition. However, it is expected that a stratification of a solute-light and hot fluid over a solute-heavy and cold one should always be stable. Here we show that chemical reactions can change this intuitive picture and trigger convection even in cases where concentration and heat both contribute to a stable density stratification. We find that the balance between intrinsic thermal and solutal density gradients initiated by a spatially localized reaction zone and double-diffusive mechanisms are at the origin of a new convective instability of stable density stratifications the mechanism of which is explained by a displaced particle argument. We also classify the stability properties and dispersion curves to be observed for various classes of exothermic chemical fronts depending whether they ascend or descend in the gravity field and whether their solutal and thermal contributions to the density jump across the front are cooperative or antagonistic.

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Section: Classification Of Autocatalytic Reactionsmentioning

confidence: 99%

Section: Classification Of Autocatalytic Reactionsmentioning

confidence: 99%

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On the classification of buoyancy-driven chemo-hydrodynamic instabilities of chemical fronts

D’Hernoncourt

Zebib

Wit

2007

Chaos: An Interdisciplinary Journal of Nonlinear Science

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“…When the reaction is exothermic, the combination of solutal and thermal density changes comes into play and has been noted to affect for instance the propagation of polymerization fronts in horizontal layers 42,43 and to result in new dynamical behaviors for the case of chemical fronts of the chlorite-tetrathionate (CT) reaction [44][45][46] and of the IAA reaction. 47 On the other hand, the opposite limit case of pure Marangoni flows affecting the propagation of chemical fronts in the absence of density changes has been relatively less investigated except for the case of surface reactions.…”

Section: Introductionmentioning

confidence: 99%

Marangoni-driven convection around exothermic autocatalytic chemical fronts in free-surface solution layers

Rongy

Assemat

Wit

2012

Chaos: An Interdisciplinary Journal of Nonlinear Science

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Segmented waves in a reaction-diffusion-convection system Chaos 22, 037109 (2012) Instability in evaporative binary mixtures. I. The effect of solutal Marangoni convection Phys. Fluids 24, 094101 (2012) Coalescence of surfactant covered drops in extensional flows: Effects of the interfacial diffusivity Phys. Fluids 24, 082101 (2012) Transient Rayleigh-Bénard-Marangoni solutal convection Phys. Fluids 24, 074108 (2012) Additional information on Chaos Gradients of concentration and temperature across exothermic chemical fronts propagating in free-surface solution layers can initiate Marangoni-driven convection. We investigate here the dynamics arising from such a coupling between exothermic autocatalytic reactions, diffusion, and Marangoni-driven flows. To this end, we numerically integrate the incompressible Navier-Stokes equations coupled through the tangential stress balance to evolution equations for the concentration of the autocatalytic product and for the temperature. A solutal and a thermal Marangoni numbers measure the coupling between reaction-diffusion processes and surface-driven convection. In the case of an isothermal system, the asymptotic dynamics is characterized by a steady fluid vortex traveling at a constant speed with the front, deforming and accelerating it [L. Rongy and A. De Wit, J. Chem. Phys. 124, 164705 (2006)]. We analyze here the influence of the reaction exothermicity on the dynamics of the system in both cases of cooperative and competitive solutal and thermal effects. We show that exothermic fronts can exhibit new unsteady spatio-temporal dynamics when the solutal and thermal effects are antagonistic. The influence of the solutal and thermal Marangoni numbers, of the Lewis number (ratio of thermal diffusivity over molecular diffusivity), and of the height of the liquid layer on the spatio-temporal front evolution are investigated. As a chemical reaction induces changes in the temperature and in the composition of the reactive medium, it can modify the properties of the solution (density, viscosity, surface tension) and thereby trigger convective motions, which in turn affect the reaction. Such a coupling can typically be observed around reactive interfaces in liquid solutions. Two classes of convective flows are then commonly developing in solutions open to air, namely Marangoni flows arising from surface tension gradients and buoyancy flows driven by density gradients. As both flows can be induced by compositional changes as well as thermal changes and in turn modify them, the resulting experimental dynamics are often complex. The purpose of our study is to gain insight into these intricate dynamics thanks to the theoretical analysis of model systems where only one type of convective flow is present. We address here the dynamics of an exothermic autocatalytic front propagating in the presence of Marangoni flows, when the density remains uniform. The surface tension gradient across the front has both a thermal component linked to the exothermicity of the reaction and a s...

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“…The non-dimensional control parameter is the Péclet number (Pe), which measured the relative importance of molecular advection and diffusion. Such phenomena have been observed in the flame propagation through other condensed phase media [160][161][162].…”

Section: Ii321 Gaseous Oxidizersmentioning

confidence: 68%

Nano Engineered Energetic Materials (NEEM)

Dlott¹,

Eden²,

Girolami³

et al. 2011

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The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. The ARO Nano Engineered Energetic Materials (NEEM) MURI program has been exploring new methodologies for developing energetic material formulations with control of all constituents over a wide range of length scales from 1 nm to 1 mm and larger and employing the latest techniques in molecular self-assembly and supramolecular chemistry for synthesizing and assembling NEEMs. The synthetic efforts have been guided by theoretical calculations and dynamic performance testing methodologies that also operate on all length scales. This final report ABSTRACTThe ARO Nano Engineered Energetic Materials (NEEM) MURI program has been exploring new methodologies for developing energetic material formulations with control of all constituents over a wide range of length scales from 1 nm to 1 mm and larger and employing the latest techniques in molecular self-assembly and supramolecular chemistry for synthesizing and assembling NEEMs. The synthetic efforts have been guided by theoretical calculations and dynamic performance testing methodologies that also operate on all length scales. This final report provides a summary of the accomplishments. In particular, new methods to generate metal nanoclusters were developed that are stabilized against environmental degradation while preserving their high energy content. Rapid expansion supercritical solution processes were developed and applied to synthesize nanosized particulate oxidizers and energetic oxidizer shell/fuel core composites. Surface science and experimental chemistry methods were applied to study the structures and energy releasing reaction pathways of NEEMs. Unique diagnostic capabilities were developed and applied to study the fundamental mechanisms that underlie NEEM dynamic performance. Combustion mechanisms of various NEEMs, including nanothermites and nanoparticulate fuel/liquid oxidizer systems, were experimentally analyzed. The reactive and thermal characteristics of NEEMs were studied using large (billion atoms) multiscale simulations that couple quantum-mechanical calculations to molecular dynamics calculations. In particular, the stability, structure and energetics of metallic nanoparticles with a special focus on the relationships between particle size, shape and excess surface free energy were studied. A unified theory of ignition and combustion of aluminum particles for a wide range of sizes, from nano to meso scales was established. . 12, 777-787 (2010 (b) Papers published in non-peer-reviewed journals or in conference proceedings (N/A for none)18.00 Number of Papers published in peer-reviewed journals:Number of Papers published in non peer-reviewed journals:1. USC group, "Multibillion-atom simulations of nano-mechano-chemistry on petaflops computers," First

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Convective instabilities in traveling fronts of addition polymerization

Cited by 130 publications

References 5 publications

On the classification of buoyancy-driven chemo-hydrodynamic instabilities of chemical fronts

On the classification of buoyancy-driven chemo-hydrodynamic instabilities of chemical fronts

Marangoni-driven convection around exothermic autocatalytic chemical fronts in free-surface solution layers

Nano Engineered Energetic Materials (NEEM)

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