Movement of a secondary immiscible liquid in a suspension using a non-invasive technique

In this paper, the movement of a secondary immiscible liquid when added to a suspension of hydrophilic particles in a continuous hydrophobic phase is investigated. This was achieved through an approach using high speed camera and X-ray computer tomography. These non-invasive approaches allowed the secondary liquid displacement within the suspension to be monitored on the surface level and within the suspension through a time lapse of scans. The addition of a small amount of secondary liquid to suspensions, can lead to a transition from a fluid-like to paste-like structure. The kinetics taking place and responsible for this, during both short and long term storage were investigated to better understand the mechanisms taking place. Water was added as the secondary immiscible liquid to suspensions composed of sucrose (icing sugar) and sunflower oil. Different volumes of secondary liquid were added to the suspensions. The rate of movement as well as the spreading of the secondary liquid into the suspension was calculated from the scans taken. The surface area to volume ratio was proposed as a reason for the spreading of the liquid for the smaller volume droplet being greater in comparison to the larger volume droplet

Electrical and optical behavior of tungsten oxide based electrochromic devices.

A broad set of phenomenological analysis tools, aimed at isolating generic characteristics of electrochromic (EC) device behavior from measured data with minimal reference to specific models, have been developed. The tools, which involve both directly-measured and derivative parameters, are applied in a demonstrative manner to specific EC devices; step-potential and step-current excitations are considered, along with variations in applied potential, imposed current, film thickness, insertion species, and series resistance. The step-current methods are extended and applied in appreciable detail to EC devices involving both H- and Li-electrolytes. In the H-based devices, a spontaneous (open-circuit) deintercalation process has been observed; this process is absent in the Li-based devices. In both types of devices, the present work exposes an inherent asymmetry between bleaching (deintercalation) and coloring (intercalation), most prominent at the onset of deintercalation. This asymmetry, and the resulting hysteresis, are explained in terms of a two-phase model. From a corresponding equivalent circuit, it is shown that the bleaching behavior may be well-predicted from the coloring behavior with essentially a single adjustable parameter. Behavior, in terms of measured and derived parameters, of devices using an aqueous H-electrolyte are compared with that of devices using a non-aqueous Li-electrolyte. The curves representing the various aspects of behavior for each device are generally similar in shape and may be made approximately to coincide through a linear scaling relation, suggesting that similar fundamental processes govern behavior in both types of devices. Preliminary work towards a model to predict the effect of the size of the insertion species on the intercalation/deintercalation behavior is performed. Additionally, a phenomenological site-saturation model for the optical efficiency is proposed and shown to predict well the observed behavior with no adjustable parameters. The tungsten-oxide films used in the present study, prepared through a novel wet-chemical synthesis and processing procedure involving the use of a transient additive, have been characterized in terms of their resulting microstructures, stoichiometries, and EC behavior. Additionally, the effect of the additive on these properties has been assessed. Finally, identification of particularly fertile avenues for investigation of the means to construct made-to-order devices of the future is also attempted

Modelling of dynamic wetting phenomena

A general dynamic wetting model is presented in which surface and gravitational driving energies are balanced against energy lost through bulk viscous dissipation. Behavior is described in terms only of independently measurable quantities, with no adjustable parameters. Additionally, the model can be expressed so as to predict liquid viscosity as a function of dynamic wetting behavior. Application of the model to a lead-silicate liquid on a gold substrate demonstrate excellent agreement of the model with experiment. The general framework of the model is especially amenable to the incorporation of other physico-chemical processes which may impact dynamic wetting phenomena. Examples are given which extend the model to specific cases where substrate roughness and/or substrate dissolution are important. Additionally, the dynamic wetting model is extended to porous substrates, accounting for the effects of composite interface formation and depletion of the liquid via capillary flow

Rewetting effects and droplet motion on partially wetted powder surfaces

In high shear mixer granulation, the powder is agitated in a vessel while liquid is sprayed onto the powder. Formation of “nuclei” can be predicted using a nucleation regime map. However, this approach assumes that only dry powder enters the spray zone. Industrial granulation processes commonly add 20–50 wt % fluid, and the partially wetted powder recirculates many times through the spray zone. The effect of partially wetted powder re-entering the spray zone is not currently known. To investigate, droplets were added to a powder bed at controlled separation distances and time intervals. A strong correlation between drop penetration time and droplet motion on the powder bed surface was observed. For fast penetrating systems, nucleation was only slightly affected by the presence of the previous droplet. However, systems with long penetration times showed lateral droplet motion due to Laplace pressure differences. Implications for the nucleation regime map are discussed