Experimental results indicate that the electric field governing retention in the electrical field-flow fractionation (FFF) experiment is very sensitive to experimental parameters such as the flow rate and carrier conductivity. In this paper, the first of a two-part study on the mechanics of electrical FFF, we present an electrical model of the channel and characterize the dependence of many of the system parameters. Understanding the nature of the electric field in the channel is essential for using electrical FFF as a separation tool as well as a physical characterization technique where electrophoretic mobility and particle size are estimated.

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Experimental work presented in this paper demonstrates that retention in electrical field-flow fractionation shows a very strong dependence on the amount of injected sample, even for very low concentrations. This concentration dependence on retention is shown to result from conductivity differences between the colloidal particles and the carrier fluid. As a result of this concentration dependence, the electric field is a function of position inside the channel. This fact is important when electrical FFF is used for determining electrophoretic mobilities and particle sizes because the analyst must be careful in interpreting the physical origin of retention changes. Furthermore, it is shown through experiment that residual salt in the injected sample buffer can affect retention. A transport model is developed that characterizes the relaxed zone profile; computation of these developed equations shows the extent of deviation from the standard transverse exponential concentration profile.

As inkjet printing technology is increasingly applied in a broader array of applications, careful characterization of its method of use is critical due to its inherent sensitivity. A common operational mode in inkjet technology known as drop-on-demand ejection is used as a way to deliver a controlled quantity of material to a precise location on a target. This method of operation allows ejection of individual or a sequence (burst) of drops based on a timed trigger event. This work presents an examination of sequences of drops as they are ejected, indicating a number of phenomena that must be considered when designing a drop-on-demand inkjet system. These phenomena appear to be driven by differences between the first ejected drop in a burst and those that follow it and result in a break-down of the linear relationship expected between driving amplitude and drop mass. This first drop, as quantified by high-speed videography and subsequent image analysis, can be different in morphology, trajectory, velocity, and volume from subsequent drops within a burst. These findings were confirmed orthogonally by both volume and mass measurement techniques which allowed quantitation down to single drops.

A finite difference time domain (FDTD) algorithm with nonstandard finite differences is used to compute light scattering by colloidal particles. The objective of this research is to simulate scattering for cases where multiparticle scattering is significant and where particle shape is arbitrary and not limited to regular geometries commonly illustrated in mathematical solutions such as the Mie theory. In this paper scattering characteristics computed using the FDTD method are compared with known analytical solutions for a number of cases for which a two-dimensional treatment is sufficient. These include scattering by a single infinite cylinder, a hollow cylinder, and two parallel cylinders. The numerical results were found to agree well with the analytical solutions. Results are also given for cases where multiparticle scattering is significant and analytical solutions are extremely difficult if not impossible to obtain.