2223242526272825 of 204
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Electrowetting diminishes contact line friction in dynamic wetting
KTH, Centres, SeRC - Swedish e-Science Research Centre.ORCID iD: 0000-0001-9160-2549
KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI).ORCID iD: 0000-0002-7498-7763
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We use large-scale molecular dynamics to study dynamics at the three-phase contact line in electrowetting of water and electrolytes on no-slip substrates. Under the applied electrostatic potential the line friction at the contact line is diminished. The effect is consistent for droplets of different sizes as well as for both pure water and electrolyte solution droplets. We analyze the electric field at the contact line to show how it assists ions and dipolar molecules to advance the contact line. Without an electric field, the interaction between a substrate and a liquid has a very short range, mostly affecting the bottom, immobilized layer of liquid molecules which leads to high friction since mobile molecules are not pulled towards the surface. In electrowetting, the electric field attractscharged and polar molecules over a longer range which diminishes the friction.

Keywords [en]
electrowetting, contact lines, computational physics, molecular dynamics
National Category
Other Physics Topics
Research subject
Biological Physics
Identifiers
URN: urn:nbn:se:kth:diva-271218OAI: oai:DiVA.org:kth-271218DiVA, id: diva2:1416079
Funder
Swedish Research Council, 2014-4505Swedish National Infrastructure for Computing (SNIC), 2018/1-22Swedish National Infrastructure for Computing (SNIC), 2019/1-22
Note

QC 20200324

Available from: 2020-03-20 Created: 2020-03-20 Last updated: 2020-03-24Bibliographically approved
In thesis
1. Molecular Processes in Dynamic Wetting
Open this publication in new window or tab >>Molecular Processes in Dynamic Wetting
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The spreading of liquids onto and over surfaces is a fundamental process in nature. It is present in all forms and sizes: From rivers carving through landscapes, to our blood stream transporting nutrients to cells, and even single water molecules moving through channels into these cells. We now have a good understanding of how fluid movement works inside the fluid itself. However, we do not fully understand the processes close to the contact line, where the liquid is spreading onto the surface. We are forced to make assumptions about this behaviour and none of these assumptions have yet proven to be universally valid.

As everything in nature, liquid spreading is a fundamentally molecular process. This thesis summarises my work on applying this lens to the process. By studying molecules we begin at the smallest combined building blocks of nature and do not have to make any prior assumptions of the involved processes. Instead, we simply observe their behaviour. This is accomplished through the use of molecular dynamics simulation, which are an atomistic form of computer experiments. We use a realistic model of water molecules as our base liquid, since this captures realistic effects such as hydrogen bonding which are not present when using simpler models. Combined with large-scale systems which minimise the influence of finite-size effects, we have a realistic treatment of complex liquid systems.

We find that the molecular processes of wetting have an important influence on large-scale wetting. Most importantly, the hydrogen bonding nature of water to realistic substrates yields the no-slip condition often used as a boundary condition for models of wetting. Furthermore, since molecular processes are thermal in nature they create energy barriers which impede contact line advancement. We show how these barriers are created and how they can be diminished, for example in the case of electrowetting. This highlights that understanding the molecular behaviour of fluids remains an important field of study.

Abstract [sv]

Hur vätskor breder ut sig över ytor är en grundläggande process i naturen. Den dyker upp i alla former och storleksgrader: från floder som skär genom berg, till vår blodström som levererar näring till våra celler, och till och med enstaka vattenmolekyler som rör sig genom de kanaler som celler tar in näringen från. Hur vätskor beter sig i stora flöden är sedan länge känt, men vi vet ännu inte hur de beter sig nära ytor. Istället gör vi antaganden, varav inga ännu är korrekta för alla tillämpningar.

Fundamentalt sett är en vätska som breder ut sig en molekylär process. Denna avhandling sammanfattar mitt arbete med att förstå den ur denna synvinkel. Genom att studera molekyler använder vi naturens minsta sammansatta byggstenar. Vi behöver inte göra antaganden om hur de beter sig, vi behöver bara titta. Det fönster som vi tittar igenom är molekylär dynamik-simuleringar, en atomistisk typ av datorexperiment. För att fånga verkliga effekter som vätebindningar, använder vi realistiska modeller av vattenmolekyler och ytor. Vi använder tillräckligt stora system för att se hur molekylära effekter påverkar större processer.

Vi visar med dessa metoder att molekylära processer har stor påverkan på hur vätskor flödar över ytor. En stor effekt är att vätebindningarna mellan vatten och realistiska ytor förhindrar vätskan från att glida över den, vilket är ett vanligt antagande i modeller. Vi visar också hur molekyler vid gränsen där vätskor sprider på ytor ger upphov till en energibarriär som förhindrar att vätskan enkelt sprider sig framåt. Denna barriär beskrivs i detalj och vi visar vilka effekter som kan förminska den. Detta genomlyser hur molekylära processer i vätning är en viktig ingrediens för ökad förståelse av vätskespridning i system.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2020. p. 58
Series
TRITA-SCI-FOU ; 2020:05
Keywords
contact lines, nanodroplets, computational physics, molecular dynamics, fluid dynamics, multi-phase flows, electrowetting
National Category
Other Physics Topics
Research subject
Biological Physics
Identifiers
urn:nbn:se:kth:diva-268935 (URN)978-91-7873-480-1 (ISBN)
Public defence
2020-04-16, F3, Lindstedtsvägen 26, Stockholm, 09:00 (English)
Opponent
Supervisors
Available from: 2020-03-23 Created: 2020-03-19 Last updated: 2020-03-23Bibliographically approved

Open Access in DiVA

fulltext(1386 kB)11 downloads
File information
File name FULLTEXT01.pdfFile size 1386 kBChecksum SHA-512
379908d776f97e6efdbe77f4df5c149441ace5819f65539c81f734ff57f6312cd5f2fa5c72839b032cc377421d11df55fd90bb7b90eaabb4dce66421582b7cac
Type fulltextMimetype application/pdf

Authority records BETA

Johansson, PetterHess, Berk

Search in DiVA

By author/editor
Johansson, PetterHess, Berk
By organisation
SeRC - Swedish e-Science Research CentreScience for Life Laboratory, SciLifeLabSchool of Engineering Sciences (SCI)
Other Physics Topics

Search outside of DiVA

GoogleGoogle Scholar
Total: 11 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

urn-nbn

Altmetric score

urn-nbn
Total: 38 hits
2223242526272825 of 204
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf