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7V,IV-Diethylacrylamide and IV-isopropylacrylamide gels having ionizable groups were found to undergo a reentrant volume transition between swollen and collapsed states when the ratio of water to dimethyl sulfoxide in the solvent was monotonically varied. The behavior of the gels was interpreted by assuming the free energy of contact between polymer segments was not a linear function of the solvent composition.

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In laser and electron-beam welding, a deep cavity called a keyhole or beam hole is formed in the weld pool due to the intense recoil pressure of evaporation. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. However, a hole drilled in a liquid is primarily unstable by its nature and the instability of the keyhole also causes the formation of porosity or cavities in the weld metal. In particular, the porosity formation is one of the serious problems in very high-power laser welding, but its mechanism has not been well understood. The authors have conducted systematic studies on observation of keyhole as well as weld pool dynamics and their related phenomena to reveal the mechanism of porosity formation and its suppression methods. The article will describe the real-time observation of keyhole and plume behaviors in the pulsed and continuous-wave laser welding by high-speed optical and x-ray transmission methods, the cavity formation process and its suppression measures.

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In recent years, coating processes based on the impact of high-velocity solid particles such as cold spraying and aerosol deposition have been developed and attracting much industrial attention. A novel coating process called 'warm spraying' has been developed, in which coatings are formed by the high-velocity impact of solid powder particles heated to appropriate temperatures below the melting point of the powder material. The advantages of such process are as follows: (1) the critical velocity needed to form a coating can be significantly lowered by heating, (2) the degradation of feedstock powder such as oxidation can be significantly controlled compared with conventional thermal spraying where powder is molten, and (3) various coating structures can be realized from porous to dense ones by controlling the temperature and velocity of the particles. The principles and characteristics of this new process are discussed in light of other existing spray processes such as high-velocity oxy-fuel spraying and cold spraying. The gas dynamics of particle heating and acceleration by the spraying apparatus as well as the high-velocity impact phenomena of powder particles are discussed in detail. Several examples of depositing heat sensitive materials such as titanium, metallic glass, WC-Co cermet and polymers are described with potential industrial applications.