Title Page
Abstract
Contents
List of Abbreviation 11
Chapter 1. Introduction 12
1.1. Brownian motion in the nature 12
1.2. Colloidal particles in the active bath 12
1.2.1. Active bath 12
1.2.2. Effect of active bath on the colloidal particles 12
1.3. Scope and objectives of the thesis 13
Chapter 2. Passive particles with repulsive interactions 14
2.1. Introduction 14
2.2. Materials and Methods 14
2.2.1. Magnetic colloidal self-assembly in the 2D 14
2.2.2. Experimental setup: 2D colloidal dispersion sandwich cell. 15
2.3. Results and Discussion 16
2.3.1. Structures of passive particles 16
2.3.2. Dynamics of passive particle 18
2.3.3. Dynamics of passive particles in confinement 20
2.4. Conclusions 23
Chapter 3. Passive particles with repulsive interactions in the active bath 24
3.1. Introduction 24
3.2. Materials and Methods 24
3.2.1. Sample preparation: Bacteria culture and solution 24
3.3. Results and Discussion 25
3.3.1. Dynamics of passive particles in the active bath 25
3.3.2. Structures of the passive particles in active particles 27
3.3.3. Colloidal Crustal in the active bath 28
3.4. Conclusions 29
Chapter 4. Bacterial lane in active bath 30
4.1. Introduction 30
4.2. Results and Discussion 30
4.2.1. Fast Fourier Transform 30
4.2.2. Density fluctuation 31
4.3. Conclusion 32
Appendix 33
A. The method of MSD calculation 33
B. Steady-state condition in a repulsive interaction system 34
Reference 36
Figure 2.2.1. The schematic of two cases about formation chain (upper row) and colloidal crystal (below row) and represented process in (a) freely mono disperse, (b) two kinds of interaction for the attraction (Red), or repulsion (Blue).... 14
Figure 2.2.2. The schematic of the sandwich cell for 2D colloidal suspension on a plane (a). The schematic and experimental results for the oil confinement (b). 15
Figure 2.3.1. The experimental results for representative cases, no field (a), and repulsive interaction system (b). The schematic of calculating radial distribution function on experimental results. The detected particles are marked by a... 16
Figure 2.3.2. Six-fold orientational bond order parameter with Voronoi diagram(a). Each polygon indicates the number of neighboring particles and colored are local bond order parameters. The global bond order parameter averaging in... 17
Figure 2.3.3. The 2D trajectories of the passive particles for each case, free dispersion (0 mT), and repulsive interactions system (0.9 mT) in (a). The grey solid lines indicate all MSD data for each particle and the red (or blue) is the average... 18
Figure 2.3.4. (a) The probability distribution function(PDF) of MSD exponents, α. (b) The average value of the slope and their standard deviation with error bar 19
Figure 2.3.5. (a) The schematic of a sandwich cell with PDMS microarray substrate and glass coverslip were plasma treated and the solution placed between them. The height of the microarray is 10μm. (b) the image of the silicon wafer... 20
Figure 2.3.6. (a) The experimental results in the 40μm diameter hexagonal array with a few numbers of the bead. The scale bar is 20μm. (b) The power of time interval,α, (c) the calculated diffusion depends on number density. 21
Figure 2.3.7. The experimental result of the first frame after relaxation under 4mT, (b) is the last frame after 985 seconds. Each color means the individual trajectory for detecting time. The scale bar is 20μm. Results of the MSD calculation... 22
Figure 3.3.1. The trajectories for the passive particles in an active bath. the upper row is free dispersion and the other is a repulsive interaction system. (b), (c) is the individual MSD graph and average for comparing each case. 25
Figure 3.3.2. The probability distribution function for MSD exponent as increasing |B|. And the average values with standard deviation error bar(b). Black empty squares indicate the passive bath and red filled triangles are an active bath. 26
Figure 3.3.3. The spatial pair correlation function in the active bath depending on |B|. And the comparison with passive bath. Filled symbols indicate active baths and black symbols are passive baths. 27
Figure 3.3.4. Voronoi diagram with local 6-fold orientational bond order parameters, red is 1. The global parameter depends on |B|. 27
Figure 3.3.5. Experimental results of the colloidal crystal, (a) Low density, inset: frequency domain by FFT, (b) high density in passive bath, and (c) with active noise. 28
Figure 3.3.6. (a) MSD exponent distribution of colloidal crystal, comparing passive(red) and active bath(green). (b) The pair correlation function, g(r) and (c) Voronoi diagram with local bond order parameter. 29
Figure 4.1.1. The "Bacterial lane" appearance in a bacterial active bath with phase contrast microscopy. Low bacterial density and a yellow solid line indicate an expected empty line (a) and high bacterial density (b). 30
Figure 4.2.1. Bacterial lane results for two densities of bacteria. The yellow circles are a guide for the width from the FFT analysis. (c) is the frequency space of the (a) and their radial intensity profile (d). 31
Figure 4.2.2. Area fraction map for low and high density of bacteria. The spatial correlation function was calculated on the area fraction map. 32
Figure A.1. (a) The simple image for calculating MSD. (b) Simulated random walk in 2D with Gaussian noise for 300 steps. (c) Results of MSD calculation in log-log scale. The slope means the power of time interval, the y-intercept is... 33
Figure B.1. Table of the pair correlation function for each condition, passive bath(upper) and active bath(below), column rightward as increasing |B|. 34
Figure B.2. The global bond order parameter for various weak magnitudes of a magnetic field in a passive and active bath. (Inset), the local bond order parameter of the representative frame. 35