18 August 2005 Force measurement in colloidal glasses using optical tweezers
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Abstract
Colloidal systems form the basis of many complex areas of academic and industrial research efforts. As well as contributing to the understanding of many industrially-produced substances such as paints and glues, they have also proved an excellent model thermodynamic system. Changing the properties of an ensemble of colloidal particles, chemically or otherwise, and observing the evolution of the many-body system gives insight into thermodynamic phenomena such as condensation and crystallisation. Some colloidal systems with a particle density that would place them around the dense end of the liquid-crystal coexistence region show a transition into an amorphous glassy state. Long range particle movement is prevented, while local diffusion is still allowed. Such systems are ideal candidates for exploration with optical force measurements, which allow the relatively non-intrusive manipulation of particles deep within colloidal suspensions. Careful use of refractive index matching has allowed an invisible colloidal suspension to be examined with probe particles of a similar size, but higher refractive index. The environment of particles in colloidal cages has been measured by studying the forces acting on a localised particle, as well as the forces needed to break one or more cages.
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Laurence Wilson, Rut Besseling, Jochen Arlt, Wilson C. K. Poon, "Force measurement in colloidal glasses using optical tweezers", Proc. SPIE 5930, Optical Trapping and Optical Micromanipulation II, 593016 (18 August 2005); doi: 10.1117/12.616450; https://doi.org/10.1117/12.616450
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