Thermodynamic properties of triangle-well fluids in two dimensions: MC and MD simulations.

With the aim of providing complementary data of the thermodynamics properties of the triangular well potential, the vapor/liquid phase diagrams for such potential with different interaction ranges were calculated in two dimensions by Monte Carlo and molecular dynamics simulations; also, the vapor/liquid interfacial tension was calculated. As reported for other interaction potentials, it was observed that the reduction of the dimensionality makes the phase diagram to shrink. Finally, with the aid of reported data for the same potential in three dimensions, it was observed that this potential does not follow the principle of corresponding states.

Cationic 1,2,3-Triazolium Alkynes: Components To Enhance 1,4-Regioselective Azide-Alkyne Cycloaddition Reactions.

4-Alkynyl-1,2,3-triazolium cations undergo thermal [3 + 2] cycloaddition reactions with azides roughly 50- to 100-fold faster than comparable noncharged alkynes. Further, the reaction is highly 1,4-regioselective (dr up to 99:1) owing to the selective stabilization of 1,4-TS transition states via conjugative π-acceptor assistance of the alkyne triazolium ring. The novel cationic triazolium alkynes also accelerate the CuAAC reaction to provide bis(1,2,3-triazoles) in an "ultrafast" way (<5 min).

Common behavior of the critical properties of the 2D and 3D square-well fluids.

We have analyzed the behavior of the critical properties and second virial coefficient of the square well fluids in two (2D) and three dimensions (3D) as a function of the interaction range. In both systems, the critical density shows an oscillating-like behavior as the interaction range increases. The second virial coefficient evaluated at the critical temperature as a function of the interaction range shows a general behavior for both cases, and quite surprisingly, there is a minimum of this parameter, for the 2D and 3D fluids, located approximately at the same interaction range. These findings are discussed in terms of the structure of the fluids, via the analysis of the radial distribution function evaluated at the critical point.

Encapsulation of clay within polymer particles in a high-solids content aqueous dispersion.

By using a two-step polymerization process, it was possible to encapsulate clay platelets within polymer particles dispersed in water. First, seed polymer particles with chemically bonded clay were obtained by batch miniemulsion polymerization. Then, the clay was buried within the particles by the addition of neat monomer in a second step. The final stable dispersions can have a solids content of up to 50 wt %. Transmission electron microscopy images clearly show the presence of clay platelets inside the polymer colloids, although they are not totally exfoliated. The obtained nanocomposites showed an increase in both the storage modulus in the rubbery state and the water resistance as the clay content increases. The approach presented here might be useful for encapsulating other high-aspect ratio nanofillers.

Revisiting chain transfer to polymer and branching in controlled radical polymerization of butyl acrylate.

Acrylic monomers undergo chain transfer to polymer during polymerization leading to branched and even gelled polymers. It has been experimentally demonstrated that the extent of branching is higher for conventional free radical polymerization than for controlled radical polymerization (ATRP, RAFT, NMP) and this has been qualitatively explained in terms of the differences in the concentrations of highly reactive short-chain radicals between controlled and conventional radical polymerizations. Contrary to this explanation, in this work, it is quantitatively demonstrated that the short transient lifetime of the radicals, i.e., the time between activation and deactivation of the radical in controlled radical polymerization, is the cause for the low level of branching in these polymerizations.

Modeling the equilibrium morphology of nanodroplets in the presence of nanofillers.

Waterborne polymer nanocomposites containing carbon nanotubes, clay platelets, laponite disks and other spherical/nonspherical nanofillers have been the focus of many recent investigations. The miniemulsion polymerization has proved to be a powerful technique to create new hybrid waterborne nanocomposites with enhanced properties. It is necessary to understand how the nanofiller shape/size and its compatibility with the phases affects the equilibrium morphology of the polymer nanoparticle to control the morphology and the properties of the resulting polymeric dispersions. With the aid of Monte Carlo simulations, the equilibrium morphology of hybrid monomer nanodroplets in the presence of nanofillers with different characteristics was obtained. A series of morphology maps depending on the nanofiller compatibility with the monomer and water phases and its shape have been obtained. These new maps may help to design and determine the required conditions to synthesize innovative waterborne polymer nanocomposites with specific morphologies through miniemulsion polymerization.

Modeling of drying in films of colloidal particles.

The process of film formation on a solid substrate from polymer colloid dispersion during solvent evaporation has been investigated by means of the Monte Carlo simulation method. Colloid particles are modeled as hard spheres. Time evolution of the colloid density distribution and coverage of the solid substrate are studied. Both density and structure of colloid film is shown to depend strongly on the evaporation rate. At a low evaporation rate, the coexistence of hexagonal and tetragonal domains of dried colloid monolayer has been observed. The results of monolayer structure are in good agreement with the confocal scanning laser microscopy observations of Dullens et al. (2004).