Joan Rosell-Llompart

Growth dynamics of granular films produced by electrospray

Particulate coatings produced by electrospray deposition (ESD) of ethyl cellulose particles are found to widen over time. We hypothesize that during the ESD process, the electrospray expands due to repulsion caused by accumulated electrostatic charge in the film. The radial profiles of film thickness, mass density (per unit area), and porosity (gas volume fraction) have been determined as a function of several factors which influence electrostatic charging, namely, collection time, relative humidity, and deposition flux. The mass density has been determined from the local film thickness attained upon thermal annealing, which is largest near the center of the spray. The local porosity is lowest at the film center (at between 0.5 and 0.6), whereas across the film, it is roughly uniform (between 0.6 and 0.7) for deposition in a dry ambient, and slightly higher and more variable for humid ambient deposition. The granular films are compact (with low fractality) as expected for ballistic deposition (large Peclet number).

A Comprehensive Framework for the Numerical Simulation of Evaporating Electrosprays

A framework for simulating the coupled physical phenomena that occur in evaporating electrosprays has been developed. This framework comprises a 3D Lagrangian model for droplets dynamics, evaporation, and Coulomb explosions, as well as steady-state 2D Eulerian models for gas flow induced by the droplets motions, the transports of vapor and heat in the gas phase, and the transport of the charged residues left behind by the fully evaporated droplets (residual-charge). To couple these different physics, the Lagrangian code and the four Eulerian ones are solved sequentially in order to attain a fully coupled solution of the global steady-state. This methodology has been applied to three electrospray systems made from solvents of different volatility (acetone, methanol, and n-heptane), with identical droplet size distribution at injection (a lognormal with mean diameter of 8 μm and CV = 10%). All fields converged after just a few (five) sequences of simulation. In the two systems in which the droplets travel fastest (acetone and methanol), conical fringes develop in the contour maps of volumetric rate of generation of residual-charge, which correspond to the first few Coulomb explosions. In the system in which the droplets moved slowest (n-heptane), such contour maps show an unstructured region, instead. Copyright 2015 American Association for Aerosol Research

Oriented Single-Walled Carbon Nanotubes as Saturable Absorber for Passive Q-Switching of a Tm:KLuW Microchip Laser

A Tm:KLuW laser is Q-switched with a saturable absorber based on aligned SWCNTs, generating a maximum average output power of 260 mW with a slope efficiency of 12%. The shortest pulse duration is 97 ns.