Charged fine particles are confined in a high-frequency argon plasma and their mo- tions are observed. They show perturbed motions and several particles undergo circular motions. When charged short rods are confined, they stand vertically and shorter rods spin around their vertical axis. For mono-dispersed silica particles, they also form a cloud. Moreover, it is commonly observed that a portion of the particles move in pairs. They fluctuate all the time; however, particles in a pair do not separate nor collide with each other. The mechanism of the motions of paired particles is discussed in relation to local potential structures.

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For more than a century, Classical Nucleation Theory (CNT) has been used to explain the process of crystallization in supersaturated solutions. According to CNT, nucleation is a single-step process that occurs via monomer-by-monomer addition. However, recent findings from experiments and numerical simulations have shown that nucleation is a multi-step process that occurs via more complex pathways that involve intermediate species such as ion complexes, dense liquid precursors, or even nanocrystals. Such non-classical pathways observed in protein solutions, colloidal suspensions and electrolytes are reviewed in this paper. The formation of stable Pre-nucleation Clusters (PNCs) in the crystallization of biominerals is also discussed. In spite of the mounting evidence for non-classical nucleation behaviors, the knowledge about the structural evolution of the intermediate phases and their role in polymorph selection is still limited. It has also been observed that gravitational force interferes with the crystallization behavior of materials thereby posing limitation to ground-based experiments. Microgravity conditions, coupled with containerless processing techniques provide a suitable alternative to overcome these limitations.

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An ignition device that can induce a cool flame around a hydrocarbon droplet and simultaneously detect the ignition occurrence was developed for microgravity experiments of cool-flame spread along a fuel droplet array. The ignition system circuit was designed based on the principle of a hot wire anemometer to ignite droplet without inducing hot-flame ignition. The ignition wire senses the heat generated by the cool flame and decreases the output power. Thus, one can detect the cool-flame ignition by measuring the current passing through the ignition wire. As a result of the preliminary experiments at normal gravity, the cool-flame ignition of a fuel droplet was successfully induced, and, from the histories of current passing through the ignition wire, the cool-flame ignition, the two-stage ignition (cool flame to hot flame transition), and pure evaporation were distinguished respectively. The cool-flame ignition delay time for various droplet diameters and fuels was also measured. It was found that the tendency of the cool-flame ignition delay time to the initial droplet diameter and fuel type is the same as that of the hot-flame ignition delay time in high temperature environments.

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