Engineering and control of surfactant-laden flows: multi-scale analysis and experiments

Lead Research Organisation: Imperial College London
Department Name: Department of Chemical Engineering

Abstract

Over the past two decades, the use of surfactants as wetting agents has enjoyed considerable attention due to their importance and potential in a variety of industrial and biomedical applications (coating flows, detergency, enhanced-oil-recovery, treatment of respiratory distress syndrome). Despite the research in the area, numerous fundamental open problems remain, as no single approach (experiments, simulations or theory) in isolation is able to probe the formidable complexities of the fluid-solid behaviour of amphiphilic molecules in solution. This project will provide detailed understanding of how surfactants behave at contact lines and adsorb at interfaces, and how this ultimately affects the spreading and wetting of hydrophobic surfaces. In this context, even trivial-sounding problems are not fundamentally understood. For instance, although the equilibrium state of a surfactant-free droplet on a hydrophobic substrate is easily characterised using the Young equation, this is not the case when the droplet is laden with surfactant. How does the surfactant distribution equilibriate and the stresses induced by it balance with the forces at the contact line? How are the latter influenced by surfactant solubility, and the formation of surfactant aggregates at high surfactant concentrations? These questions underlie striking and technologically important, yet poorly eludicated effects, such as superspreading whereby aqueous droplets containing superspreader surfactants (e.g. trisiloxanes) spread rapidly to produce perfect wetting over hydrophobic substrates. The purpose of this proposal is to draw together three world-leading groupings to tackle these fundamental problems in a collaborative, systematic, multi-disciplinary and multi-scale manner. The chemistry and molecular interactions require detailed modelling on the molecular level: EAM brings this expertise. This must then be scaled up to the lengthscale of droplets and the application itself: RVC and OKM have considerable background in modelling surfactant-gradient (Marangoni) driven flows. The problem requires new physicochemical understanding of the phenomena and the developed models must be validated, and indeed informed by, detailed and careful experiments: VMS is a world-leader in both. The deep knowledge of surfactant-laden flows that will be achieved via the proposed, transformative research will be used not only to provide accurate and reliable predictions of these flows but also to rationally design bespoke surfactant molecular architectures for various applications ranging from agrochemicals to enhanced-oil-recovery.

Planned Impact

Motivated by a need to understand fundamental physio-chemical processes and deliver unprecedented physical insight into the behaviour of surface active additives near and on interfaces we propose a close-knit combination of experiments, modelling and theory. This will deliver highly reliable, accurate and efficient modelling tools to predict flow behaviour for given molecular architecture with wide applicability and impact; these tools will include the ability to design surfactants to control both interfacial and bulk (wettying/spreading) flows. This requirement is pressing, for instance, the most recent review paper on superspreading , written by a prominent industrial scientist, concludes that " ... the findings [of reseach in this area] should somehow relate to the molecular structure of the surfactants. This could help the synthetic chemist to design surfactants with improved properties. Moreover, the results should enable the practitioner to understand the phenomena observed in the application of trisiloxane surfactants" This is precisely what the unique combination of experiments/MD/continuum modelling described within this proposal will address.

Publications

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Avendaño C (2016) Assembly of porous smectic structures formed from interlocking high-symmetry planar nanorings. in Proceedings of the National Academy of Sciences of the United States of America

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Kovalchuk NM (2014) Fluoro- vs hydrocarbon surfactants: why do they differ in wetting performance? in Advances in colloid and interface science

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Theodorakis P (2014) Insights into surfactant-assisted superspreading in Current Opinion in Colloid & Interface Science

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Theodorakis PE (2015) Superspreading: mechanisms and molecular design. in Langmuir : the ACS journal of surfaces and colloids

 
Description Surfactants have enjoyed considerable attention due to their importance to coating flows, detergency, enhanced-oil-recovery, and treatment of respiratory distress syndrome. Numerous fundamental open problems remain, however: how do surfactants behave at contact lines and interfaces, and how does this ultimately affect spreading and wetting of hydrophobic surfaces at high concentrations in the presence of aggregate-formation? These questions underlie technologically-important, poorly-understood phenomena, such as superspreading whereby aqueous droplets containing superspreader surfactants spread rapidly to perfect wetting over hydrophobic substrates. Our workelucidates, for the first time, the mechanisms underlying superspreading and illustrates how superspreader molecules can be designed rationally.

The results of our work will impact the formulation of coatings in the agrochemicals industry for rapid spreading over leaves. The toxicity of available superspeaders makes them unsuitable for use in the pharmaceutical and personal care industries, and our approach, informed by fundamentals, will facilitate the development of analogous, yet bio-compatible surfactants. Another highly impactful application of our work is CO2 sequestration with enhanced oil recovery. Here, an initially oil-wet reservoir is flooded by gas following the introduction of aqueous surfactant solution into the fracture system. The ability to design bespoke surfactants will influence the economic feasibility of this process.
Exploitation Route The results of our work will impact the formulation of coatings in the agrochemicals industry for rapid spreading over leaves. The toxicity of available superspeaders makes them unsuitable for use in the pharmaceutical and personal care industries, and our approach, informed by fundamentals, will facilitate the development of analogous, yet bio-compatible surfactants. Another highly impactful application of our work is CO2 sequestration with enhanced oil recovery. Here, an initially oil-wet reservoir is flooded by gas following the introduction of aqueous surfactant solution into the fracture system. The ability to design bespoke surfactants will influence the economic feasibility of this process.
Sectors Chemicals,Education,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology

 
Description The knowledge accrued from this project has been used in order to design surfactants with bespoke molecular architecture for specific applications. We are working with oil-and-gas companies, as part of the Transient Multiphase Flows consortium, led by Omar Matar, to transfer the knowledge which is relevant to deploying surfactant in the field and for EOR applications.
First Year Of Impact 2013
Sector Chemicals,Energy,Environment
Impact Types Economic

 
Description Surfactant effects on vertical gas-liquid flows
Amount £146,000 (GBP)
Organisation Shell Global Solutions International BV 
Department Shell Global Solutions UK
Sector Private
Country Netherlands
Start 09/2014 
End 09/2016
 
Description Strategic partnership with Procter and Gamble 
Organisation Procter & Gamble
Country United States 
Sector Private 
PI Contribution Engaged with P&G researchers to provide solutions to problems in the area of multiphase flows.
Collaborator Contribution Engaged with the research group to provide a constant source of good problems to work on, secondment opportunities for our researchers, and cash contribution.
Impact Procter and Gamble have provided £100000 cash contribution which was instrumental in our winning an EPSRC Programme Grant.
Start Year 2012
 
Description Superspreading talk (Oxford invited) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Participants in your research and patient groups
Results and Impact Invited to present at the Surfactants Workshops, University of Oxford, 22 July, 2013. The talk on surfactant-driven superspreading generated a lot of interest and discussion.

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Year(s) Of Engagement Activity 2013