Colloids with a tunable dipolar interaction: equations of state and order parameters via confocal microscopy

Li, Nigh and Newman, Hugh D. and Valera, Manuel and Saika-Voivod, Ivan and Yethiraj, Anand (2009) Colloids with a tunable dipolar interaction: equations of state and order parameters via confocal microscopy. Soft Matter, 6. pp. 876-880. ISSN 1744-6848

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Abstract

Laser scanning confocal microscopy studies were carried out on charged screened colloidal silica microspheres in sedimentation equilibrium in the presence of a tunable external alternating electric field. The external a.c. field controls the averaged dipolar interaction between the silica microspheres. From the equilibrium sedimentation profiles, equations of state were obtained as a function of the dipolar strength and volume fraction. The colloidal fluid at zero field follows the hard-sphere equation of state but with an effective larger hard-sphere diameter. At non-zero fields, the average colloidal fluid isothermal compressibility was obtained as a function of a dipolar strength parameter. We then investigated bond order parameters upon increasing the field, and monitored an orientational order parameter associated with the field dependence of the average orientation of dual-particle bonds. The orientational order parameters were found to be very sensitive measures of anisotropy. The field dependence strongly confirms the use of the point dipolar approximation in this system.

Item Type: Article
URI: http://research.library.mun.ca/id/eprint/8056
Item ID: 8056
Department(s): Science, Faculty of > Physics and Physical Oceanography
Date: 21 December 2009
Date Type: Publication
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