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Vapor condensation onto a non-volatile liquid drop  [PDF]
Levent Inci,Richard. K. Bowles
Physics , 2013, DOI: 10.1063/1.4834676
Abstract: Molecular dynamics simulations of miscible and partially miscible binary Lennard--Jones mixtures are used to study the dynamics and thermodynamics of vapor condensation onto a non-volatile liquid drop in the canonical ensemble. When the system volume is large, the driving force for condensation is low and only a submonolayer of the solvent is adsorbed onto the liquid drop. A small degree of mixing of the solvent phase into the core of the particles occurs for the miscible system. At smaller volumes complete film formation is observed and the dynamics of film growth are dominated by cluster-cluster coalescence. Mixing into the core of the droplet is also observed for partially miscible systems below an onset volume suggesting, the presence of a solubility transition. We also develop a non-volatile liquid drop model, based on the capillarity approximations, that exhibits a solubility transition between small and large drops for partially miscible mixtures and has a hysteresis loop similar to the one observed in the deliquescence of small soluble salt particles. The properties of the model are compared to our simulation results and the model is used to study the formulation of classical nucleation theory for systems with low free energy barriers.
Mathematical modeling at the calculation of the vapor-liquid equilibrium of multicomponent systems  [PDF]
Komissarov Yuriy Alekseevich,Dam Quang Sang
Vestnik Astrahanskogo Gosudarstvennogo Tehni?eskogo Universiteta. Seria: Upravlenie, Vy?islitel?naa Tehnika i Informatika , 2011,
Abstract: A mathematical description of equilibrium conditions in vapor-liquid mix-tures with the use of the equations of Wilson, NRTL, Soave – Redlich – Kwong, Peng – Robinson and others is given in the paper. Software is developed in order to calculate and analyze the vapor-liquid equilibrium of multicomponent systems when input parameters (temperature, pressure, composition of the liquid and vapor phases) are changed. A database is created that contains important thermodynamic properties of more than 600 components for gas and liquid, parameters of the binary interaction (more than 300 pairs) in the above mentioned equa-tions. This database was used in calculating the vapor-liquid equilibrium of mul-ticomponent systems.
Multivariable theory of droplet nucleation in a single-component vapor  [PDF]
Nikolay V. Alekseechkin
Physics , 2014, DOI: 10.1016/j.physa.2014.06.050
Abstract: The multivariable theory of nucleation [N. V. Alekseechkin, J. Chem. Phys. 124, 124512 (2006)] is applied to the droplet nucleation in a supersaturated single-component vapor; the droplet volume V, temperature T, and volume change rate U=V_dot are the variables of the theory. A new approach based on macroscopic kinetics is developed for the droplet evolution and results in the derived equations for U_dot, V_dot, and T_dot. It is shown that there is no the viscosity effect in the employed ideal gas approximation, so the variable U can be omitted. The nonisothermal effect (the discrepancy between the actual and isothermal nucleation rates) earlier studied numerically is analytically examined here. The calculated steady state distribution function of droplets shows their average overheating relatively the vapor temperature. An inert background gas is shown to diminish the nonisothermal effect in comparison with a pure vapor case.
New Phase Transition in Polymer Solutions with Multicomponent Solvent  [PDF]
Zh. S. Gevorkian,Chin-Kun Hu
Physics , 2002,
Abstract: Considering the density-density correlation function of a concentrated polymer solution with multicomponent solvent we find a phase transition due to the heterogeneity of excluded volume constant. This new phase transition implies a strong enhancement of the scattered light intensity in the critical region, which can explain a recent experiment showing strong light scattering from a ternary polymer system consisting of polyethylene oxide (PEO) dissolved in nitroethane and 3methyl-pentane.
Power-law setting of steady concentration in a binary solution within a droplet at diffusion-controlled or free-molecular regimes of the droplet binary growth in the vapor-gas environment  [PDF]
Fedor M. Kuni,Alexandra A. Lezova,Alexander K. Shchekin
Physics , 2009,
Abstract: The times required for reaching the power-law-in-time growth of the droplet radius after nucleation of a markedly supercritical binary droplet, are found analytically and estimated at diffusion-controlled or free-molecular regimes of isothermal binary vapor condensation. The process of setting steady concentration in the binary solution within the growing droplet at the same regimes of binary condensation has been analyzed. It has been shown that setting the steady droplet concentration has also a power-law character in time. The parameters of the power law are specified for each regime of binary condensation and are linked to thermodynamic and kinetic characteristics of condensing vapors and to the steady concentration established in a binary droplet.
Droplet Formation via Solvent Shifting in a Microfluidic Device  [PDF]
Ramin Hajian,Steffen Hardt
Physics , 2014,
Abstract: Solvent shifting is a process in which a non-solvent is added to a solvent/solute mixture and extracts the solvent. The solvent and the non-solvent are miscible. Because of solution supersaturation a portion of the solute transforms to droplets. In this paper, based on this process, we present an investigation on droplet formation and their radial motion in a microfluidic device in which a jet is injected in a co-flowing liquid stream. Thanks to the laminar flow, the microfluidic setup enables studying diffusion mass transfer in radial direction and obtaining well-defined concentration distributions. Such profiles together with Ternary Phase Diagram (TPD) give detailed information about the conditions for droplet formation condition as well as their radial migration in the channel. The ternary system is composed of ethanol (solvent), de-ionized water (non-solvent) and divinyle benzene (solute). We employ analytical/numerical solutions of the diffusion equation to obtain concentration profiles of the components. We show that in the system under study droplets are formed in a region of the phase diagram between the binodal and the spinodal, i.e. via a thermally activated process. The droplets are driven to the channel centerline by the solutal Marangoni effect but are not able to significantly penetrate into the single-phase region, where they get rapidly dissolved. Therefore, the radial motion of the binodal surface carries the droplets to the centerline where they get collected.
Instabilities during the evaporation of a film: non glassy polymer + volatile solvent  [PDF]
Pierre-Gilles de Gennes
Physics , 2001,
Abstract: We consider solutions where the surface tension of the solvent is smaller than the surface tension of the polymer. In an evaporating film, a plume of solvent rich fluid, then induces a local depression in surface tension, and the surface forces tend to strengthen the plume. We give an estimate (at the level of scaling laws) for the minimum thickness required to obtain this instability. We predict that the thickness a) is a decreasing function of the solvent vapor pressure b) should be very small (<1 micron) provided that the initial solution is rather dilute. The overall evaporation time for the film should be much longer than the growth time of the instability. The instability should lead to distortions of the free surface and may be optically observable. It should dominate over the classical Bernard-Marangoni instability induced by cooling.
Comparison of gel swelling under organic vapor and in organic solvent  [PDF]
M. Erdo an, . Pekcan
International Journal of Photoenergy , 2005, DOI: 10.1155/s1110662x05000061
Abstract: A Fast Transient Fluorescence Technique (FTRF) was employed for studying swelling of disc shaped poly (methyl methacrylate) (PMMA) gels, which were prepared by free radical copolymerization of methyl (methacrylate) (MMA) using various ethylene glycol dimethacrylate (EGDM) contents at 60 ∘C. Pyrene (P) was introduced as a fluorescence probe during polymerization. Swelling experiments were performed by using P doped PMMA gels under chloroform vapor and in chloroform at room temperature. P lifetimes in and out of the gel were measured from fluorescence decay traces during in-situ swelling experiments. It was observed that P lifetimes in the gel decreased as swelling proceeds. An equation is derived for low quenching efficiencies to interpret the behavior of P lifetimes during swelling. The Li-Tanaka equation was used to determine the cooperative, Dc diffusion coefficients for the gels made at various crosslinker contents. It is observed that Dc values decrease as the crosslinker content is increased both in chloroform vapor and in chloroform.
Tight coupling of particle size, number and composition in atmospheric cloud droplet activation
D. O. Topping,G. McFiggans
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012,
Abstract: The substantial uncertainty in the indirect effect of aerosol particles on radiative forcing in large part arises from the influences of atmospheric aerosol particles on (i) the brightness of clouds, exerting significant shortwave cooling with no appreciable compensation in the long wave, and on (ii) their ability to precipitate, with implications for cloud cover and lifetime. Predicting the ambient conditions at which aerosol particles may become cloud droplets is largely reliant on an equilibrium relationship derived by K hler (1936). However, the theoretical basis of the relationship restricts its application to particles solely comprising involatile compounds and water, whereas a substantial fraction of particles in the real atmosphere will contain potentially thousands of semi-volatile organic compounds in addition to containing semi-volatile inorganic components such as ammonium nitrate. We show that equilibration of atmospherically reasonable concentrations of organic compounds with a growing particle as the ambient humidity increases has potentially larger implications on cloud droplet formation than any other equilibrium compositional dependence, owing to inextricable linkage between the aerosol composition, a particles size and concentration under ambient conditions. Whilst previous attempts to account for co-condensation of gases other than water vapour have been restricted to one inorganic condensate, our method demonstrates that accounting for the co-condensation of any number of organic compounds substantially decreases the saturation ratio of water vapour required for droplet activation. This effect is far greater than any other compositional dependence; more so even than the unphysical effect of surface tension reduction in aqueous organic mixtures, ignoring differences in bulk and surface surfactant concentrations.
Parameterization of cloud droplet formation for global and regional models: including adsorption activation from insoluble CCN
P. Kumar, I. N. Sokolik,A. Nenes
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2009,
Abstract: Dust and black carbon aerosol have long been known to exert potentially important and diverse impacts on cloud droplet formation. Most studies to date focus on the soluble fraction of these particles, and overlook interactions of the insoluble fraction with water vapor (even if known to be hydrophilic). To address this gap, we developed a new parameterization that considers cloud droplet formation within an ascending air parcel containing insoluble (but wettable) particles externally mixed with aerosol containing an appreciable soluble fraction. Activation of particles with a soluble fraction is described through well-established K hler theory, while the activation of hydrophilic insoluble particles is treated by "adsorption-activation" theory. In the latter, water vapor is adsorbed onto insoluble particles, the activity of which is described by a multilayer Frenkel-Halsey-Hill (FHH) adsorption isotherm modified to account for particle curvature. We further develop FHH activation theory to i) find combinations of the adsorption parameters AFHH, BFHH which yield atmospherically-relevant behavior, and, ii) express activation properties (critical supersaturation) that follow a simple power law with respect to dry particle diameter. The new parameterization is tested by comparing the parameterized cloud droplet number concentration against predictions with a detailed numerical cloud model, considering a wide range of particle populations, cloud updraft conditions, water vapor condensation coefficient and FHH adsorption isotherm characteristics. The agreement between parameterization and parcel model is excellent, with an average error of 10% and R2~0.98. A preliminary sensitivity study suggests that the sublinear response of droplet number to K hler particle concentration is not as strong for FHH particles.
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