Kinetic pathways of the Nematic-Isotropic phase transition as studied by confocal microscopy on rod-like viruses

We investigate the kinetics of phase separation for a mixture of rodlike viruses (fd) and polymer (dextran), which effectively constitutes a system of attractive rods. This dispersion is quenched from a flow-induced fully nematic state into the region where the nematic and the isotropic phase coexist. We show experimental evidence that the kinetic pathway depends on the overall concentration. When the quench is made at high concentrations, the system is meta-stable and we observe typical nucleation-and-growth. For quenches at low concentration the system is unstable and the system undergoes a spinodal decomposition. At intermediate concentrations we see the transition between both demixing processes, where we locate the spinodal point.Comment: 11 pages, 6 figures, accepted in J. Phys.: Condens. Matter as symposium paper for the 6th Liquid Matter Conference in Utrech

A stability criterion for the non-linear wave equation with spatial inhomogeneity

In this paper the non-linear wave equation with a spatial inhomogeneity is considered. The inhomogeneity splits the unbounded spatial domain into three or more intervals, on each of which the non-linear wave equation is homogeneous. In such setting, there often exist multiple stationary fronts. In this paper we present a necessary and sufficient stability criterion in terms of the length of the middle interval(s) and the energy associated with the front in these interval(s). To prove this criterion, it is shown that critical points of the length function and zeros of the linearisation have the same order. Furthermore, the Evans function is used to identify the stable branch. The criterion is illustrated with an example which shows the existence of bi-stability: two stable fronts, one of which is non-monotonic. The Evans function also give a sufficient instability criterion in terms of the derivative of the length function

Airborne particle deposition in cleanrooms: deposition mechanisms

This article discusses the mechanisms of particle deposition onto cleanroom surfaces. The main mechanism for particles above about 0.5μm is gravitational settling. Turbulent deposition and electrostatic attraction can also occur at all particle sizes, and for particles below 0.5μm Brownian diffusion is important. Measurements of particle deposition rates (PDRs) were made of particles ≥ 0μm on witness plates orientated in different directions and exposed in different ventilation conditions, and it was concluded that over 80% of particles were deposited by gravitational sedimentation, and probably more than half of the remainder by turbulent deposition

Airborne particle deposition in cleanrooms: relationship between deposition rate and airborne concentration

This article is the second of a series that discusses the deposition of airborne particles onto cleanroom surfaces. It investigates the relationship between the airborne concentration of a range of cumulative sizes of particles and the particle deposition rate (PDR) onto cleanroom surfaces, through knowledge of the deposition velocity of particles in air. The deposition velocity of a range of cumulative particle sizes was obtained by means of experiments, theoretical calculations, and literature search and the influence of a number of variables found in cleanrooms on the deposition velocity was investigated. The use of the deposition velocity to calculate the amount of deposition on cleanroom surfaces, such as manufactured products, is discussed, along with its use in deciding the required ISO 14644-1 class of cleanroom; these subjects will be discussed in more depth in the final article of this series

Airborne particle deposition in cleanrooms: calculation of product contamination and required cleanroom class

This is the third and final article in a series that discusses the deposition of airborne particles onto critical surfaces in cleanrooms. This article explains a method for calculating the amount of particle or microbe-carrying particle deposition onto critical cleanroom surfaces, such as product, and a method for calculating the airborne particle cleanliness class, or airborne microbial concentration that is required to obtain a specified and acceptable amount of product contamination

Nematic-Isotropic Spinodal Decomposition Kinetics of Rod-like Viruses

We investigate spinodal decomposition kinetics of an initially nematic dispersion of rod-like viruses (fd virus). Quench experiments are performed from a flow-stabilized homogeneous nematic state at high shear rate into the two-phase isotropic-nematic coexistence region at zero shear rate. We present experimental evidence that spinodal decomposition is driven by orientational diffusion, in accordance with a very recent theory.Comment: 17 pages, 6 figures, accepted in Phys. Rev.