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Sustained Superhydrophobic Friction Reduction at High Liquid Pressures and Large Flows
KTH, School of Electrical Engineering (EES), Microsystem Technology.
KTH, School of Electrical Engineering (EES), Microsystem Technology.ORCID iD: 0000-0001-8248-6670
2011 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 1, 487-493 p.Article in journal (Refereed) Published
Abstract [en]

This Article introduces and experimentally explores a novel self-regulating method for reducing the friction losses in large microchannels at high liquid pressures and large liquid flows, overcoming previous limitations with regard to sustainable liquid pressure on a superhydrophobic surface. Our design of the superhydrophobic channel automatically adjusts the gas pressure in the lubricating air layer to the local liquid pressure in the channel. This is achieved by pneumatically connecting the liquid in the microchannel to the gas-pockets trapped at the channel wall through a pressure feedback channel. When liquid enters the feedback channel, it compresses the air and increases the pressure in the gas-pocket. This reduces the pressure drop over the gas liquid interface and increases the maximum sustainable liquid pressure. We define a dimensionless figure of merit for superhydropbic flows, W-F = PLD/gamma cos(theta(c)), which expresses the fluidic energy carrying capacity of a superhydrophobic microchannel. We experimentally verify that our geometry can sustain three times higher liquid pressure before collapsing, and we measured better friction-reducing properties at higher W-F values than in previous works. The design is ultimately limited in time by the gas-exchange over the gas-liquid interface at pressures exceeding the Laplace pressure. This method could be applicable for reducing near-wall laminar friction in both micro and macro scale flows.

Place, publisher, year, edition, pages
2011. Vol. 27, no 1, 487-493 p.
National Category
Chemical Sciences Atom and Molecular Physics and Optics Materials Engineering
URN: urn:nbn:se:kth:diva-29363DOI: 10.1021/la103624dISI: 000285560400066OAI: diva2:395141
QC 20110204Available from: 2011-02-04 Created: 2011-02-01 Last updated: 2011-09-02Bibliographically approved
In thesis
1. Development of materials, surfaces and manufacturing methods for microfluidic applications
Open this publication in new window or tab >>Development of materials, surfaces and manufacturing methods for microfluidic applications
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents technological advancements in microfluidics. The overall goals of the work are to develop new miniaturized tests for point-of-care diagnostics and robust super-lubricating surfaces for friction reduction. To achieve these goals, novel materials, surfaces and manufacturing methods in microfluidics have been developed.

Point-of-care diagnostic tests are portable miniaturized instruments that downscale and automate medical tests previously performed in the central laboratories of hospitals. The instruments are used in the doctor’s office, in the emergency room or at home as self-tests. By bringing the analysis closer to the patient, the likelihood of an accurate diagnosis, or a quick therapy adjustment is increased. Already today, there are point-of-care tests available on the market, for example blood glucose tests, rapid streptococcus tests and pregnancy tests. However, for more advanced diagnostic tests, such as DNA-tests or antibody analysis, integration of microfluidic functions for mass transport and sample preparation is required. The problem is that the polymer materials used in academic development are not always suited for prototyping microfluidic components for sensitive biosensors. Despite the enormous work that has gone into the field, very few technical solutions have been implemented commercially.

The first part of the work deals with the development of prototype point of-care tests. The research has focused on two major areas: developing new manufacturing methods to leverage the performance of existing materials and developing a novel polymer material platform, adapted for the extreme demands on surfaces and materials in miniaturized laboratories. The novel manufacturing methods allow complex 3D channel networks and the integration of materials with different surface properties. The novel material platform is based on a novel off-stoichiometry formulation of thiol-enes (OSTE) and has very attractive material and manufacturing properties from a lab-on-chip perspective, such as, chemically stable surfaces, low absorption of small molecules, facile and inexpensive manufacturing process and a biocompatible bonding method. As the OSTE-platform can mirror many of the properties of commercially used polymers, while at the same time having an inexpensive and facile manufacturing method, it has potential to bridge the gap between research and commercial production.

Friction in liquid flows is a critical limiting factor in microfluidics, where friction is the dominant force, but also in marine applications where frictional losses are responsible for a large part of the total energy consumption of sea vessels. Microstructured surfaces can drastically reduce the frictional losses by trapping a layer of air bubbles on the surface that can act as an air bearing for the liquid flow. The problem is that these trapped air bubbles collapse at the liquid pressures encountered in practical applications.

The last part of the thesis is devoted to the development of novel low fluidfriction surfaces with increased robustness but also with active control of the surface friction. The results show that the novel surfaces can resist up to three times higher liquid pressure than previous designs, while keeping the same friction reducing capacity. The novel designs represent the first step towards practical implementation of micro-structured surfaces for friction reduction.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xiii, 87 p.
Trita-EE, ISSN 1653-5146 ; 2011:058
microsystem technology, MEMS, microfluidics, polymers, off-stoichiometry thiol-ene, point-of-care, lab-on-chip
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:kth:diva-38605 (URN)978-91-7501-086-1 (ISBN)
Public defence
2011-09-23, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)

QC 20110907

Available from: 2011-09-02 Created: 2011-08-30 Last updated: 2012-09-03Bibliographically approved

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