Primary surface measurement reported
Oil–water surface tension (Σ) is used to nondimensionalize yield stress as a function of volume fraction in the emulsion rheology chapter (Figure 4.7, panel b).
Client Citation Analysis
Glassy and Jammed Systems: Structures and Dynamics
This dissertation studies structure and dynamics across colloidal glasses, 3D rod packings, and oil-in-water emulsion rheology, with oil–water surface tension (Σ) used to nondimensionalize yield stress in the emulsion analysis.
At-a-Glance Summary
Dropometer attribution in the paper
Oil–water surface tension (Σ) appears as the interfacial normalization term in the yield-stress presentation described for Figure 4.7.
How the surface-tension / contact-angle data were used in the study
Surface tension (Σ) is used as a scaling quantity for yield stress versus volume fraction, presented alongside an alternative nondimensionalization by thermal energy (k_B T) in the same figure entry (Figure 4.7).
Paper Details
Title
Glassy and Jammed Systems: Structures and Dynamics
Authors
Cong Cao
Institution
Emory University (PhD dissertation)
Year
2020
License
Non-exclusive license granted to Emory University to archive, make accessible, and display the dissertation (Distribution Agreement).
What Was Measured
Primary surface / interfacial measurement
Oil–water surface tension (Σ) is used as a normalization factor for yield stress versus volume fraction in the emulsion rheology chapter’s figure descriptions (Figure 4.7, panel b).
Supporting measurements
The dissertation describes confocal microscopy measurements of colloidal-glass aging near rough versus smooth boundaries, x-ray tomography measurements of boundary effects in 3D rod packings, and rheometer-based shearing experiments on oil-in-water emulsions with yield-stress behavior analyzed versus volume fraction. Emulsion imaging is also described in figure entries using optical microscopy and SEM.
Colloidal glass aging near boundaries
Confocal microscopy
3D rod packing boundary effects
X-ray tomography
Emulsion imaging (silicone oil + water; polystyrene particles; swelled emulsions)
Leica DM IRB research microscope
TPM emulsion imaging after polymerization
SEM
Emulsion rheology (shearing; yield stress; model fits)
Rheometer
Role of the Dropometer
Oil–water surface tension (Σ) is used as the nondimensionalization term for yield stress plotted versus volume fraction in the emulsion rheology figure description (Figure 4.7, panel b), presented alongside a thermal-energy-based nondimensionalization (k_B T) in panel (a).
The Figure 4.7 entry notes that the legend identifies droplet diameter (d) and the source of the plotted data.
Bring This Measurement Into Your Lab
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Key Findings
Wall-induced layering tracks with slowed dynamics in colloidal glass
Near smooth boundaries, particles form layers and motion is dramatically slower near the boundary compared to the bulk; near rough boundaries, layers nearly vanish and particle motion is nearly identical to the bulk. The abstract links gradients in dynamics near boundaries to gradients in structure for both boundary types.
Rod packings show boundary-dependent volume fraction changes
Rod packings in smaller cylindrical containers have lower volume fractions than those in larger containers, and x-ray tomography results show boundary effects that depend on boundary orientation. The abstract states the boundary influence extends approximately half a particle length into the interior.
Emulsions exhibit yield-stress behavior and droplet-size-dependent transition signatures
For oil-in-water emulsions, the abstract describes solid-like behavior with a yield stress above a critical volume fraction (φ_c). It reports both glass and jamming transitions for smaller diameter droplets and only a jamming transition for larger diameter droplets, with the bidisperse sample behaving similarly to the small-droplet sample.
Yield stress is presented with interfacial and thermal normalizations
The List of Figures description for Figure 4.7 reports yield stress versus volume fraction plotted with nondimensionalization by thermal energy (k_B T) in panel (a) and by oil–water surface tension (Σ) in panel (b), with the legend indicating droplet diameter (d) and the source of the data.
Rheological model fitting is used to evaluate data collapse behavior
The abstract states the emulsion rheology data are fit using both the Herschel–Bulkley model and a Three-Component model, and that the raw rheological data would not collapse into a master curve based on the fitting parameters.
Figures & Visuals
What it shows
Shows yield stress as a function of volume fraction with panel (b) nondimensionalized by oil–water surface tension (Σ) and panel (a) nondimensionalized by thermal energy (k_B T), with droplet diameter (d) and data source identified in the legend.
What it shows
Plots shear stress (σ) versus strain rate (γ̇) for monodisperse (2.04 µm; 1.16 µm) and bidisperse (1.06/1.86 µm) emulsions, labeled by volume fraction (φ), with Herschel–Bulkley and TC model fits.
What it shows
Presents yield stress (σ_y) as a function of volume fraction (φ) for experimental data labeled by mean droplet diameter, with simulation results described in the panel (b) entry.
Why It Matters
In the emulsion rheology chapter, yield stress is presented as a function of volume fraction with a nondimensionalization using oil–water surface tension (Σ) (Figure 4.7b), alongside a thermal-energy-based nondimensionalization (k_B T) (Figure 4.7a). The figure entry also indicates that droplet diameter (d) and the data source are part of the figure legend.
Across the broader dissertation scope, the abstract connects structure–dynamics relationships near boundaries in colloidal glasses, boundary effects in rod packings, and droplet-size-dependent transition behavior in emulsions, and for the emulsions the author suggests that liquid–solid transitions may not be universal but may depend on particle type.
Practical Takeaways
Consider Σ-based normalization alongside k_B T when presenting emulsion yield stress
The emulsion chapter includes yield stress versus volume fraction presented in nondimensional form using oil–water surface tension (Σ) (Figure 4.7b).
Pair normalized yield-stress plots with droplet-size labeling
The Figure 4.7 entry states that droplet diameter (d) is indicated in the legend, along with the source of the data.
Track yield-stress onset using flow-curve families and fits
Flow curves (σ vs γ̇) are shown for multiple droplet sizes and volume fractions, with Herschel–Bulkley and TC model fits described for those datasets (Figure 4.4).
Droplet-size-dependent transition behavior in these emulsions
The abstract reports both glass and jamming transitions for smaller diameter droplets and only a jamming transition for larger diameter droplets, with the bidisperse sample behaving similarly to the small-droplet sample.
Frequently Asked Questions
Where does surface tension appear in this dissertation?
In the emulsion rheology chapter, Figure 4.7b plots yield stress against volume fraction with the yield stress nondimensionalized by the oil and water surface tension, Σ. Figure 4.7a shows the same quantity nondimensionalized by thermal energy, k_B T, and the legend gives the droplet diameter and the source of any data from other work.
What does the dissertation report about the emulsions?
The author sheared four oil in water emulsions with droplet diameters of about 1 to 2 µm, which show a yield stress above a critical volume fraction. The abstract reports both a glass and a jamming transition for the smaller droplets, only a jamming transition for the larger droplets, and behaviour similar to the small droplets for the bidisperse sample.
What does the author conclude?
The rheology data were fitted with both the Herschel–Bulkley model and a Three-Component model, and the author reports that the raw data would not collapse onto a master curve based on the fitting parameters. The author suggests that liquid to solid transitions may not be universal but may depend on particle type.
What were the main measurements in the dissertation?
The dissertation describes confocal microscopy of colloidal glass aging near rough and smooth boundaries, x-ray tomography of boundary effects in 3D rod packings, and rheometer shearing of oil in water emulsions. Surface tension enters the emulsion chapter as a scaling quantity for yield stress in Figure 4.7b.