Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session T10: Experimental Techniques: Microscale (8:00am - 8:45am CST)Interactive On Demand
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T10.00001: Simultaneous measurement of flow, rheology and structures of shear resistant biofilms in shear flows Jian Sheng, Maryam Jalali, Wei Xu Recent studies reveal that flow shear plays significant role in shaping 3D architecture of biofilms formed in flows. They include physiological (phenotype composition), topological and rheological (viscoelasticity) structures enable the biofilm's adaption to high shear environment. To elucidate key mechanisms among cells, films, and flows that allow them to resist flow-induced shear-erosion, we have developed a close-loop \textit{Ecology-on-a-chip} (\textit{eChip}) microfluidic platform including a chemostat, two peristaltic pumps, and a microchannel, which allows in-situ inoculation, growth and maturation of biofilms under realistic flow shear (U$_{\mathrm{c}}=$0.5 m/s) and long-term (\textgreater weeks) observations at film-relevant scales. The platform integrated with an inverted microscope lasers and cameras allows us to perform high-speed microscopy to quantify instantaneous film viscoelasticity, time-lapsed scanning epi-fluorescent microscopy to resolve 3D film topology and composition, and digital holographic microscope to measure near film flow shear and cell motility. Biofilms by GFP-labeled \textit{Pseudomonas} \textit{aeruginosa} (PAO1) are grown under three different flow shear, while film and flow characteristics are measured at every 20 min. The correlative relations between biofilm structure and shear will be established and presented in the talk. Funded by ONR, ARO [Preview Abstract] |
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T10.00002: Particle Image Rheometry (PIR) Adib Ahmadzadegan, Pavlos P Vlachos, Arezoo M Ardekani We will be presenting a method utilizing \textmu PIV to determine the rheological properties of the surrounding fluid. Passive microrheology methods use particle tracking to find the mean squared displacement (MSD) of the trajectories. Particle tracking methods face localization error and cannot be used for high concentration particle suspensions. Our method eliminates the use of tracking in micro-rheology and finds the MSD directly from the images using cross-correlation techniques. This novel method allows us to resolve the spatial and temporal rheological properties of the sample of interest. We will compare the results of our method with the existing methods and show validations using both synthetic images and experimental datasets. [Preview Abstract] |
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T10.00003: Characteristics of structured-illumination microscale particle tracking velocimetry Michael Spadaro, Minami Yoda In microscale particle tracking velocimetry ($\mu $PTV) images, the tracer particles beyond the focal plane can degrade contrast and introduce measurement errors. Structured-illumination microscale particle tracking velocimetry (SI$\mu $PTV) is an imaging technique that adapts structured-illumination microscopy (SIM) for use in enhancing the axial spatial resolution of images of tracer particles in a flow. SI$\mu $PTV takes two ``raw'' images modulated with a sinusoidally varying intensity profile ($i.e.$, acquired with ``structured'' illumination) with a phase shift between the images, and reconstructs the signal from the focal plane using a Hilbert transform-based approach. The technique was analyzed using artificial images to determine the origins of the anisotropy of the reconstructed tracer particle images observed in previous work and determine how parameters such as the number of ``raw'' images, the spatial frequency and phase shift of the illumination, and image contrast and background noise affect the accuracy of SI$\mu $PTV measurements. These results are demonstrated with experimental data that expand the applicability of the technique to a broader range of flows. [Preview Abstract] |
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T10.00004: Droplet microfluidics for phase transitions as functions of temperature and relative humidity Priyatanu Roy, Cari Dutcher Phase state of complex multiphase liquid droplets such as atmospheric aerosols, spray coatings or biological fluids are dependent on the temperature and relative humidity (RH) of the surrounding environment, with large implications in climate modeling, coating processes or biomedical applications. We present droplet microfluidic platforms for studying phase transitions as functions of these parameters for phase separation and crystallization at above and below freezing point for multiphase liquid droplets. Some ternary droplets showed temperature, droplet solute concentration and organic to inorganic solute ratio dependence of phase transition at temperatures down to -20\textdegree C in static traps. Equilibrium thermodynamic models were used to translate the droplet solute concentration to RH relevant to control systems. Droplet freezing experiments were conducted on a platform with a controllable temperature gradient and a flow-through microfluidic channel. Rapid detection of freezing was attempted with polarized optics utilizing birefringence of droplets ice crystals, and a deep neural network to classify frozen vs. liquid droplets with high accuracy. These platforms will enable phase transitions studies of environmental droplet samples in the future. [Preview Abstract] |
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