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Colloidal particle deposition onto charge-heterogeneous substrates Open Access


Other title
atomic force microscopy
colloid deposition
random sequential adsorption
patterned substrate
deposit morphology
membrane fouling
Type of item
Degree grantor
University of Alberta
Author or creator
Rizwan, Tania
Supervisor and department
Bhattacharjee, Subir (Mechanical Engineering)
Examining committee member and department
Mitra, Sushanta (Mechanical Engineering)
Amirfazli, Alidad (Mechanical Engineering)
Ghoshal, Subhasis (Civil Engineering, McGill University)
Raboud, Don (Mechanical Engineering)
Yeung, Anthony (Chemical and Materials Engineering)
Department of Mechanical Engineering

Date accepted
Graduation date
Doctor of Philosophy
Degree level
This dissertation investigates the influence of surface heterogeneities on colloid deposition. First, deposition of colloidal particles on a nanofiltration membrane during cross flow membrane filtration was studied under different operating pressures and solution chemistries. An atomic force microscope (AFM) was then used to observe the deposit morphology formed on the membrane. At the initial stages of fouling, more particles preferentially accumulate near the ‘peaks’ than in the ‘valleys’ of the rough nanofiltration membrane surface. This study demonstrates that it is difficult to isolate, correlate and assess the effects that physical (roughness) heterogeneity and chemical heterogeneity has on colloid deposition based on experiments involving surfaces where the physical and chemical heterogeneities are uncorrelated or ‘randomly distributed’. In the second phase of the study, the deposition of model colloidal particles onto patterned charge-heterogeneous surfaces was studied both experimentally and theoretically. Controlled charge heterogeneity was created experimentally employing self assembled monolayers of alkanethiols patterned onto gold substrates using a soft lithographic technique. Model colloidal particles and fluorescent nanoparticles were sequentially deposited onto the patterned substrate under no flow (quiescent) conditions, and the deposited structures and the micro-patterns were imaged in situ using a combination of phase contrast and fluorescence microscopy. This study indicates that particles tend to preferentially deposit at the edges of the chemically favourable stripes. The theoretical investigation involved the formulation of a mathematical model based on Random Sequential Adsorption (RSA). This study showed that a simple binary probability distribution assumed in the model is able to predict the experimental deposit morphology adequately, particularly the periodicity of the underlying patterns on the substrate. Furthermore, the effect of charge heterogeneity on the electrostatic double layer interaction between a particle and a charge heterogeneous planar surface was studied numerically employing a 3D finite element model. In this system, significant lateral forces at close separation distances were observed, and found to be appreciably higher when the particle is near the edge of a heterogeneous region of the substrate. From the above studies, it can be concluded that by altering/controlling the chemical heterogeneity of the substrate, it is possible to achieve significant control on the resulting deposit morphology.
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