Subphase Exchange Cell for Studying Fluid-Fluid Interfaces with Optical Microscopy.

A subphase exchange cell was designed to observe fluid-fluid interfaces with a conventional optical microscope while simultaneously changing the subphase chemistry. Materials including phospholipids, asphaltenes, and nanoparticles at fluid-fluid interfaces exhibit unique morphological changes as a function of the bulk-phase chemistry. These changes can affect their interfacial material properties and, ultimately, the emergent bulk material properties of the films, foams, and emulsions produced from such interfacial systems.

2D Colloids: Size- and Shape-Controlled 2D Materials at Fluid-Fluid Interfaces.

Advances in synthesis of model 3D colloidal particles with exotic shapes and physical properties have enabled discovery of new 3D colloidal phases not observed in atomic systems, and simulations and quasi-2D studies suggest 2D colloidal systems have an even richer phase behavior. However, a model 2D (one-atom-thick) colloidal system has yet to be experimentally realized because of limitations in solution-phase exfoliation of 2D materials and other 2D particle fabrication technologies. Herein, we use a photolithography-based methodology to fabricate size- and shape-controlled monolayer graphene particles, and then transfer the particles to an air-water interface to study their dynamics and self-assembly in real-time using interference reflection microscopy.

Deviation from Equilibrium Thermodynamics of an Asphaltene Model Compound during Compression-Expansion Experiments at Fluid-Fluid Interfaces.

Asphaltenes play a crucial role in crude oil behavior, and model compounds are often used to capture, mimic, and predict certain interfacial properties. In previous works, sorption of an asphaltene model compound (C5PeC11) was studied using surface pressure isotherms, where a deviation from the expected thermodynamic behavior of the interface during decane-water and air-water compression experiments was observed but not explained. In this work, the interfacial behavior of C5PeC11 was assessed at the decane-water and the air-water interfaces using a multiscale approach that includes: compression-expansion experiments on rectangular and radial Langmuir troughs, dynamic interfacial stress relaxation, and fluorescence microscopy imaging.

A miniaturized radial Langmuir trough for simultaneous dilatational deformation and interfacial microscopy.

Innovation: Interfacial rheological properties of complex fluid-fluid interfaces are strongly influenced by the film microstructure. Experimental investigations for correlating interfacial morphology and rheology are notoriously challenging. A miniaturized radial Langmuir trough was developed to study complex fluid-fluid interfaces under purely dilatational deformations that operates in tandem with a conventional inverted microscope for simultaneous interfacial visualization.

Interference Provides Clarity: Direct Observation of 2D Materials at Fluid-Fluid Interfaces.

Monolayer particles of two-dimensional (2D) materials represent a scientifically and technologically interesting class of anisotropic particles with colloidal-scale lateral sizes but sub-nanometer thicknesses. This atomic-scale thickness leads to interesting phenomena that can be exploited in next-generation thin-film technologies, and fluid-fluid interfaces provide a potentially scalable platform to confine, assemble, and deposit functional thin films of 2D materials. However, directly observing how these materials interact and assemble into a given film morphology is experimentally challenging because of their sub-nanometer thicknesses.

Platelets Drive Thrombus Propagation in a Hematocrit and Glycoprotein VI-Dependent Manner in an In Vitro Venous Thrombosis Model.

Objective: The objective of this study was to measure the role of platelets and red blood cells on thrombus propagation in an in vitro model of venous valvular stasis.

Approach And Results: A microfluidic model with dimensional similarity to human venous valves consists of a sinus distal to a sudden expansion, where for sufficiently high Reynolds numbers, 2 countercurrent vortices arise because of flow separation. The primary vortex is defined by the points of flow separation and reattachment.

Micro and macrorheology at fluid-fluid interfaces.

Interfacial transport phenomena play an important role in the dynamics of liquid interfaces found in emulsions, foams, and membranes. Both macroscopic and microscopic measurements of interfacial transport and rheology can be made, the former typically relying on the use of at least millimeter-scale probes, and the latter exploiting the motion of micrometer-scale probes. Recent publications have shown multiple orders of magnitude differences between experimentally observed diffusivities in passive microrheology, and the diffusivities expected based on macroscopic measurements of the surface rheology.

The effect of high intensity mixing on the enzymatic hydrolysis of concentrated cellulose fiber suspensions.

Enzymatic hydrolysis of lignocellulosic biomass in a high shear environment was examined. The conversion of cellulose to glucose in samples mixed in a torque rheometer producing shear flows similar to those found in twin screw extruders was greater than that of unmixed samples. In addition, there is a synergistic effect of mixing and enzymatic hydrolysis; mixing increases the rate of cellulose conversion while the increased conversion facilitates mixing.