Reports: ND551803-ND5: Role of Drainage Channels on Lubrication Forces
Joelle Frechette, Johns Hopkins University
Overview:
The ACS-PRF grant (type
ND) has helped support two separate projects over the last year. The focus of
the first project is to understand the adsorption of nanoparticles to the
oil-water interface. The goal of the second project was to understand the role
of interconnected vertical channels on the fluid pressure necessary to separate
(move) two surfaces. Both projects are relevant to the petroleum industry. For
the first one, nanoparticles at fluid interfaces are important for oil recovery
and, more generally, for transport in porous media. The second project has
direct implications to hydrofracturing. The
ACS-PRF-supported work has led to additional funding from the Office of Naval
Research, and the National Science Foundation, as well as a long-term
collaboration with another faculty. Additionally, three additional manuscripts
are will soon be submitted reporting on the finding of the work supported by
this grant.
Summary of Activities:
Project 1) Nanoparticles at interfaces
Pickering
emulsions are oil-water emulsions kinetically stabilized by solid particles[1]. They are important in flotation, oil recovery,
and catalysis. As with all emulsions, Pickering emulsions are only kinetically
stable due to the energetic cost associated with the creation of oil-water
interfacial area. In contrast to larger colloids, the attachment of
nanoparticles (< 10 nm) at an oil-water interface is often comparable to
thermal energy (kT), the
inherent energy scale of any reversible phenomena[2-3].
The weaker energy can make nanoparticle adsorption at fluid interfaces dynamic
and reversible, a necessary criteria for thermodynamic equilibrium. This regime
of interactions also provides the capability to develop reversible Pickering
emulsions, which could enable reconfigurable, and adaptive multiphase
fluid-based materials and devices. Nanoparticles provide access to unique
optical and electrical properties as well as the possibility to create much
smaller droplets with increased surface area with advantages for catalysis and
mass transport.
Achievements. We previously demonstrated the
mechanisms driving the interfacial adsorption of 5 nm ion-pair functionalized
gold nanoparticles to the toluene-water interface.[4] In the last year we
performed extensive characterization of the equilibrium and dynamic of
nanoparticle adsorption to a fluid interface using pendant drop tensiometry (Fig 1A-B). We combined the interfacial tension
measurements with UV-Vis absorption spectroscopy to determine the partitioning
of the particles between the interface and bulk phases (Fig. 1C). When then
used 2D equations of state to relate the relationship between the surface
pressure and bulk nanoparticle concentrations to the adsorbed amount at the
interface. Using the Singer 2D equation of state we found good agreement
between the tensiometry measurements and the
adsorption obtained from UV-Vis (Fig. 1B-C).
Finally we developed an electrochemical method to modulate externally
the adsorption of the particles to the interface (see Fig. 1D). Currently we are working on developing a
rigorous thermodynamic model for the reversible nanoparticle adsorption. We
also aim to investigate how nanoparticles adsorption is altered by dynamic
transport, as what is observed in unsaturated porous media.
Fig. 1. A. Dynamic of adsorption of nanoparticles to a fluid interface measured via pendant drop tensiometry. B. Decrease in interfacial tension due to the adsorption of nanoparticles. C. Comparison between adsorbed amount calculated from the Singer 2D equation of state and analysis of the UV-Vis absorption spectra. D. Demonstration of electrochemical modulation of nanoparticle adsorption at a fluid interface.
Project 2) Role of interconnected
vertical channels.
Rock masses contain
complex and interconnected fracture networks, which are important for oil recovery,
groundwater resources, and the generation of power from geothermal sources.[5] Hydrofracture is a practice
in which fluid pressure causes the initiation or propagation of a crack in a
reservoir.This practice is commonly
employed for secondary and tertiary oil recovery where water at high pressure
is inserted into a well to increase its productivity. Important fundamental
questions relevant to hydraulic fracturing are 1) What
is the necessary fluid pressure to initiate or propagate a fracture? 2) What is
the timescale for this process? and 3) How to ensure that the fluid injected
will not only open the pore space but will also allow for oil recovery in all
the interconnected channels forming the porous material?
Achievements. We performed direct force
measurement of the peeling hydrodynamic force during the peeling of a
semi-rigid structured surface from a flat surface in a viscous fluid environement using a custom-built apparatus (Fig 2A-B). The
structured surface consist of a hexagonal array of cylindrical posts to
represent the network of interconnected channels (Fig. 2C). The measured
hydrodynamic work of separation shows a strong dependence on the surface
structure, which can be explained based on porous media formalism. We highlight
the interplay between the initial loading and the work of separation (Fig 2D).
Fig. 2. Reduction in hydrodynamic work of separation forces caused by the presence of an interconnected network of channels. A. Peeling measurements in viscous fluid showing the resulting force curve. B. Custom-built apparatus for the measurement of peeling forces. C. Structured surfaces investigated. D. Work of separation for different loading conditions highlighting the different fluid flow regimes.
[1]a) Ramsden,
Proceedings of the Royal Society of London 1903, 72, 156; b) Pickering, Journal
of the Chemical Society 1907, 91, 2001; c) Binks, Lumsdon,
Langmuir 2001, 17, 4540.
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