Phase Behavior, Structure, and Properties of Colloidal Microsphere-Nanoparticle Mixtures
Tohver, Valeria
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https://hdl.handle.net/2142/82707
Description
Title
Phase Behavior, Structure, and Properties of Colloidal Microsphere-Nanoparticle Mixtures
Author(s)
Tohver, Valeria
Issue Date
2001
Doctoral Committee Chair(s)
Lewis, Jennifer A.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
The phase behavior, structure, and properties of binary mixtures of negligibly charged colloidal microspheres were studied for two size ratios of 95 and 197 at pH = 1.5. In the absence of nanoparticle additions, the system spontaneously assembled into a colloidal gel whose strength increased with microsphere volume fraction. Between a lower and upper critical nanoparticle volume fraction, such binary mixtures formed a stable fluid phase due to nanoparticle haloing. In this concentration regime, colloidal microsphere crystals could be assembled under gravity-driven sedimentation. Confocal microscopy revealed that such crystals exhibited a center-to-center microsphere separation distance of 2 amusphere, where amusphere is the microsphere radius. Above the upper critical nanoparticle volume fraction, depletion flocculation induced by the presence of highly charged nanoparticles in solution led to the reformation of a colloidal gel phase. The structure and strength of the colloidal gel phases observed below and above the homogeneous fluid phase could be tailored by varying the respective colloidal microsphere and nanoparticle volume fractions, as evidenced by optical microscopy, sedimentation and rheological measurements.
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