In this dissertation, we describe a novel method that we call Diffusing Colloidal
Probe Microscopy (DCPM), which integrates Total Internal Reflection Microscopy
(TIRM) and Video Microscopy (VM) methods to monitor three dimensional trajectories
in colloidal ensembles levitated above macroscopic surfaces. TIRM and VM are well
established optical microscopy techniques for measuring normal and lateral colloidal
excursions near macroscopic planar surfaces. The interactions between particle-particle
and particle-substrate in colloidal interfacial systems are interpreted by statistical
analyses from distributions of colloidal particles; dynamic properties of colloidal
assembly are also determined from particle trajectories.
Our studies show that DCPM is able to detect many particle-surface interactions
simultaneously and provides an ensemble average measurement of particle-surface
interactions on a homogeneous surface to allow direct comparison of distributed and
average properties. A benefit of ensemble averaging of many particles is the diminished
need for time averaging, which can produce orders of magnitude faster measurement
times at higher interfacial particle concentrations. The statistical analyses (Ornstein-
Zernike and three dimensional Monte Carlo analyses) are used to obtain particle-particle
interactions from lateral distribution functions and to understand the role of nonuniformities
in interfacial colloidal systems. An inconsistent finding is the observation of
an anomalous long range particle-particle attraction and recovery of the expected DLVO
particle-wall interactions for all concentrations examined. The possible influence of
charge heterogeneity and particle size polydispersity on measured distribution functions
is discussed in regard to inconsistent particle-wall and particle-particle potentials. In the final part of this research, the ability of DCPM is demonstrated to map potential energy
landscapes on patterned surfaces by monitoring interactions between diffusing colloidal
probes with Au pattern features. Absolute separation is obtained from theoretical fits to
measured potential energy profiles and direct measurement by sticking silica colloids to
Au surfaces via electrophoretic deposition. Initial results indicate that, as colloidal probe
and pattern feature dimensions become comparable, measured potential energy profiles
suffer some distortion due to the increased probability of probes interacting with
surfaces at the edges of adjacent pattern features. Measurements of lateral diffusion via
analysis of mean square displacements also indicated lateral diffusion coefficients in
excellent agreement with rigorous theoretical predictions.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/3747 |
| Date | 16 August 2006 |
| Creators | Wu, Hung-Jen |
| Contributors | Bevan, Michael A. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 2663400 bytes, electronic, application/pdf, born digital |
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