Crystals and Liquids in Gravitationally Confined Quasi-2-Dimensional Colloidal Systems Open Access

Abstract

We use bright field microscopy to observe the phase behavior of the base layer in a gravitationally confined colloidal system of silica particles. After injecting the colloidal particles into a chamber and giving the system sufficient amount of time for sedimentation, we observe those particles settling on the base of the chamber forming a static quasi-2D structure. We control two parameters of the system, namely the particle concentration and their P\'eclet number. The Peclet number measures the relative importance of the gravitational force over the thermal effects, and is positively related to the particle diameters. We find that the most ordered states are formed by the heavy particles (with large Peclet numbers) at moderately high concentrations. For the lighter particles with smaller Peclet numbers, we observe the 'glassy' phases in some sedimented quasi-2D colloidal systems, which do not exist in the ideal 2D hard disk fluids.

Table of Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

2 Relevent Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Diffusion, Sedimentation, and the Peclet Number . . . . . . . . . . . . . . 4

2.2 Quasi-2D Ordering of Heavy Colloidal Particles . . . . . . . . . . . . . . . . 5

3 Experimental Methods  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.1 Preparation of A Sedimented Colloidal System . . . . . . . . . . . . . . . . 8

3.2 Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.3 Particle Identication, Tracking, and Phase Analysis . . . . . . . . . . . .  10

4 Analysis Methods  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

4.1 Two-Dimensional Crystalline Packing . . . . . . . . . . . . . . . . . . . . . . 12

4.2 Diffusion and Caging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.1 Base Layer Ordering Behaviors . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5.2 Overlayer Particle Density and Classication . . . . . . . . . . . . . . . . . . 20

5.3 Base Layer Particle Mobility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

About this Honors Thesis

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School	Emory College
Department	Physics
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Physics, Condensed Matter
Keyword	sedimentation colloidal crystallization two-dimensional crystalline packing
Committee Chair / Thesis Advisor	Weeks, Eric, Emory University
Committee Members	Kindt, James, Emory University Seitaridou, Effrosyni, Emory University

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