光ピンセットを用いたコロイド結晶およびコロイド粒子間相互作用の研究

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Our main results can be separated into 3 parts.1) Study of the Colloid Polymer mixture:The effects of the existence of the polymers in the colloidal fluid can be observed as the depletion force as well as bridging interaction between the colloidal particles and both of these interaction result in the attractive interaction between colloidal particles. We have studied these attractive forces by the laser tweezers technique and have demonstrated that the bridging interaction can be eliminated by the addition of large amount of detergent. Thus we were able to measure the net strength of the depletion force as well as the bridging interaction that appears as the excess attractive force in detergent free system. Our result of the depletion force was in good agreement with the theoretical calculation.2) Determination of the weak repulsive interaction between charged Colloid particles:We have developed the 2 beam laser tweezers system and applied it to study the repulsive interaction between charged colloidal particles in de-ionized solution. Change of the potential felt by the colloidal particle with or without interacting particle in the second laser focus was carefully observed and the net potential between two interacting colloidal particles were deduced. Obtained result was in good agreement with DLVO theory.3) Dynamics of the colloidal crystal:Dynamics of each particle in colloidal crystal was studied using time sequence of digitized images of the crystal particles. Using the time sequence of the position of each particle, we have calculated the self and cross correlation function of the position of the particles. The results was in good agreement with our theory that treat the system as the real crystal immersed in viscous fluid. The cross correlation function of the nearest neighbor was, however, much larger than our theoretical prediction and the agreement was only qualitative.