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V Talanquer

Publications and source records attributed to V Talanquer.

9 recordsLinked to original sources
PubMed2006

Phase transitions in DNA-linked nanoparticle assemblies: a decorated-lattice model.

We use decorated-lattice models to explore the phase behavior of two types of DNA-linked colloidal mixtures: systems with identical nanoparticles functionalized with two different DNA strands (mixture Aab) and mixtures involving two types of particles each one functionalized with a different DNA strand (mixture Aa-Ab). The model allows us to derive the properties of the mixtures from the well-known behavior of underlying spin-n Ising models with temperature and activity dependent effective interactions. The predicted evolution of the dissolution profiles for the colloidal assemblies as a function of temperature and number of single DNA strands on a nanoparticle M is in qualitative agreement with that observed in real systems. According to our model, the temperature at which the assemblies dissolve can be expected to increase with increasing M only for concentrations of colloids below a certain threshold. For more concentrated solutions, the dissolution temperature is a decreasing function of M. Linker-mediated interactions between Aa and Ab particles in the Aa-Ab mixture render the phase separation involving disordered aggregates metastable with respect to a phase transition between a solvent-rich and an ordered phase. The stability of the DNA-linked assembly is enhanced by the ordering of the colloidal network and the ordered aggregates dissolve at higher temperatures. Our results may explain the contrasting evolution of the dissolution temperatures with increasing probe size in Aab and Aa-Ab mixtures as observed experimentally.

Colloids↗
PubMed2005

Nucleation on cylindrical plates: sharp transitions and double barriers.

We apply methods of density-functional theory in statistical mechanics to study the properties of droplets and bubbles formed on a single cylindrical plate or between two such disks immersed in a metastable fluid. Our approach allows us to analyze the properties of different types of aggregates and investigate the effect of disk size, disk separation, and solid-fluid interactions on the dynamics of a liquid-vapor phase transition. The finite size of disks induces nucleation phenomena that are not observed in the cases of either a planar wall or a slit pore. Heterogeneous nucleation on a single disk is characterized by the existence of two distinct types of critical nuclei that control the phase-transition dynamics at different supersaturations. Asymmetric droplets or bubbles formed on one side of the disk are the preferred nucleation path at high supersaturations. However, these types of aggregates become unstable close to the binodal, where they abruptly collapse into nuclei that engulf the cylindrical plates. Droplet or bubble nucleation in between two disks may occur through a free-energy barrier with one or two maxima depending on the value of the system parameters and the supersaturation. Metastable droplets or bubbles corresponding to local minima of the free energy are observed forming between two plates only after density fluctuations in the system achieve a critical size. These types of aggregates only exist for cylindrical plates larger than a minimum size given a fixed distance between the disks. The stability of these droplets and bubbles decreases when the plates are separated.

Journal Article↗
PubMed2005

Phase behavior of self-associating fluids with weaker dispersion interactions between bonded particles.

In this study, we explore the global phase behavior of a simple model for self-associating fluids where association reduces the strength of the dispersion interactions between bonded particles. Recent research shows that this type of behavior likely explains the thermodynamic properties of strongly polar fluids and certain micellar solutions. Based on Wertheim's theory of associating liquids [M. S. Wertheim, J. Stat. Phys. 42, 459 (1986); 42, 477 (1986)], our model takes into account the effect that dissimilar particle interactions have on the equilibrium constant for self-association in the system. We find that weaker interactions between bonded molecules tend to favor the dissociation of chains at any temperature and density. This effect stabilizes a monomeric liquid phase at high densities, enriching the global phase behavior of the system. In particular, for systems in which the energy of mixing between bonded and unbonded species is positive, we find a triple point involving a vapor, a dense phase of chain aggregates, and a monomeric liquid. Phase coexistence between the vapor and the monomeric fluid is always more stable at temperatures above the triple point, but a highly associated fluid may exist as a metastable phase under these conditions. The presence of this metastable phase may explain the characteristic nucleation behavior of the liquid phase in strongly dipolar fluids.

Journal Article↗
PubMed2005

Nucleation in a simple model for protein solutions with anisotropic interactions.

A lattice analog of density functional theory is used to explore the structural and thermodynamic properties of critical nuclei in mixtures of particles with attractive anisotropic interactions. Protein molecules are assumed to occupy the sites on a regular cubic lattice, with effective directional interactions that mimic hydrogen bonding and the solvation forces induced by water. Interaction parameters are chosen to qualitatively reproduce the phase behavior of protein solutions. Our model predicts that critical nuclei of the solidlike phase have nonspherical shapes, and that their specific geometry depends on the nature of the anisotropic interactions. Molecules tend to align in distinctive ways in the core and in the interfacial region of these critical clusters, and the width and structure of the interface are highly affected by the presence of a metastable fluid-fluid critical point. Close to the critical region, the height of the barrier to nucleation is strongly reduced; this effect is enhanced by increasing the anisotropy of the intermolecular interactions. Unlike systems with short-range isotropic interactions, nucleation in our model is initiated by highly ordered clusters in which the order-disorder transition is confined to the interfacial region.

Anisotropy↗
PubMed2004

Nucleation in cylindrical capillaries.

We use a local density functional theory in the square gradient approximation to explore the properties of critical nuclei for the liquid-vapor transition of van der Waals fluids in cylindrical capillaries. The proposed model allows us to investigate the effect of pore size, surface field, and supersaturation on the behavior of the system. Our calculations predict the existence of at least three different pathways for the nucleation of droplets and bubbles in these confined fluids: axisymmetric annular bumps and lenses, and asymmetric droplets. The morphological transition between these different structures is driven by the existence of states of zero compressibility in the capillary. We show that the classical capillarity theory provides surprisingly accurate predictions for the work of formation of critical nuclei in cylindrical pores when line tension contributions to the free energy are taken into account.

Journal Article↗