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Photopatternable Electrolytes for Conducting Polymer Actuators
Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electroactive polymers (EAPs) are materials that can change their dimensions or shape in response to electric stimulation. They have attracted considerable interests for their applications as soft, lightweight and silently operating polymer actuators. One significant group of EAPs is conducting polymers. Conducting polymer actuators are driven by the volume variations of the conducting polymers, which is a result of the ion diffusion into/out of the conducting polymer matrix during an electrochemical redox process in the presence of an electrolyte. Over other actuation mechanisms, conducting polymers have many attractive features such as being electrically controlled, low activation voltage of 1V or less, large generated strain and high stress, and good biocompatibility. To miniaturize or fabricate microarrays of these electrochemical actuators that can operate in open air, micropatterns and microstructures of polymer gel electrolyte are desired. In this thesis, we develop photopatternable polymer gel electrolytes based on different routes of polymerization network formation and present their application in conducting polymer (micro)actuators.

First, photopatternable electrolyte patterns were developed through free radical photopolymerization of methacrylate monomers as conductive photoresist by a conventional photolithographic process. By immobilizing those electrolyte micropatterns on top of the electroactive polypyrrole layer, solid-state microactuator was achieved although with reduced movement as compared to microactuators operating in liquid electrolytes. The result shows a reliable and scalable microfabrication method for soft, on-chip polymer based microactuators operating in air using standard photolithography to broaden the microfabrication toolbox. It also shows the possibility to batch fabricate complex microsystems such as microrobotics and micromanipulators based on these solid state on-chip microactuators.

Second, a thiol acrylate mixed mode photopolymerization was used to prepare a novel soft and flexible ionogel with a reactive surface and a high ionic conductivity. The developed ionogel materials are well suited to be used with conventional photolithography as a negative-toned ionically conducting photoresist. Lithographic capabilities of the material enable direct fabrication of ionic conductive micropatterns and 3D microstructures using conventional photolithography. It has also been successfully utilized in a high-resolution soft imprint lithography process to pattern the surface of the ionogel film. This new type of ionogel has been demonstrated in the application of micro electrochromic micropatterns and twisting actuators. A Double Diaphragm Active Polymer Actuator (DDAPA) was also constructed using this novel ionogel to demonstrate its application as a microinjection tool, a flow regulator, and as a fully disposable unidirectional hybrid pump for active microfluidic components.

Finally, a novel platform to develop micropatternable ionogels with tunable mechanical and surface properties was established using the Michael addition reaction. Polymerization kinetic studies showed that the ionic liquid not only acts as an ion source but also a co-catalyst in the polymerization. Ionogels with tailorable surface and mechanical properties were prepared using three approaches: offstoichiometry, methacrylate addition, and dithiol chain extender addition. 3-dimensional ion conducting structures were constructed by bonding the flexible ionogel film together using the ionogel solution as an ionic adhesive. In addition, micro-patterns of the ionogels were obtained by photolithography and soft imprinting lithography. To illustrate the potential of the reactive surfaces, two 3-dimensional devices were created from a flat structure: a tube actuator with two embedded actuator pairs and a box with a flexible electrode forming a taxel. These interesting results demonstrate that thiol acrylate Michael chemistry provides a platform to prepare various forms (films, micro-patterns, 3-dimensional structures, and adhesive) of ionogels for the next generation of flexible electrochemical devices.

Abstract [sv]

Elektroaktiva polymerer (EAP) är material som kan ändra sin storlek eller form som svar på elektrisk stimulering. De är mycket intressanta för applikationer som mjuka och lätta polymeraktuator och är dessutom tysta. En viktig grupp inom EAP är ledande polymerer. Dessa aktuatorer drivs av volymförändringen hos de ledande polymererna, vilken är ett resultat av jondiffusionen in i och ut ur den ledande polymermatrisen under en elektrokemisk redoxprocess i närvaro av en elektrolyt. I jämförelse med andra aktuatorer har dessa aktuatorer av ledande polymerer många attraktiva egenskaper såsom att vara elektriskt styrd, ha en låg aktiveringsspänning på 1 V eller mindre, ge en stor genererad töjning och hög spänning samt god biokompatibilitet. För att miniatyrisera eller tillverka mikroarrayer av dessa aktuatorer i fast tillstånd behövs mikromönster och mikrostrukturer av en polymergelelektrolyt. I denna avhandling utvecklar vi fotomönsterbara polymergelelektrolyter baserade på olika syntesvägar för att bilda polymernätverk och presenterar deras tillämpning i ledande polymer (mikro-)aktuatorer.

Till att börja med utvecklades fotomönsterbara elektrolytmönster genom friradikalfotopolymerisering av metakrylat monomerer som jonisk ledande fotoresist genom konventionell fotolitografisk process. Genom att immobilisera elektrolytmikromönster ovanpå det elektroaktiva polypyrrolskiktet uppnåddes fasta-tillstånd-mikroaktuatorer, dock på bekostnad av den möjliga rörelsen jämförd med mikroaktuatorer som rör sig i flytande elektrolyter. Resultatet visar en pålitlig och skalbar mikrofabriceringsmetod för mjuka polymerbaserade mikroaktuatorer med standardfotolitografi för att bredda mikrofabriceringsverktygslådan. Det visar också möjligheten att satsa på komplexa mikrosystem, såsom mikrorobotik och mikromanipulatorer baserat på dessa fasta-tillstånd-mikroaktuatorer.

I den andra delen av arbetet användes en fotopolymerisering av en tiolakrylatblandning för att framställa en ny mjuk och flexibel jongel med en reaktiv yta och en hög jonledningsförmåga. De utvecklade jongelmaterialen är väl lämpade att användas med konventionell fotolitografi som en jonisk ledande negativ fotoresist. Litografiska egenskaper hos materialet möjliggör direkt tillverkning av jonledande mikromönster och 3D-mikrostrukturer med användning av konventionell fotolitografi. Det har också framgångsrikt utnyttjats i en högupplösande mjuklitografiprocess för att mönstra ytan av jongelfilmen. Tillämpning av denna nya typ av jongel har visats i elektrokroma mikromönster och böjbara mjuka aktuatorer. Denna nya jongel användes också för att konstruera en dubbel diafragma aktiv-polymer-aktuator (DDAPA) för att demonstrera dess tillämpning som ett mikroinjektionsverktyg, en flödesregulator och som en enkelriktad hybridpump för aktiva komponenter inom mikrofluidik.

Slutligen etablerades en ny plattform för att utveckla mikromönsterbara jongeler med justerbara mekaniska och ytegenskaper med hjälp av en Michael additionsreaktion. Polymeriseringskinetiska studier visade att jonvätskan inte bara fungerar som jonkälla utan också som en katalysator i polymerisationen. Jongeler med skräddarsydda ytor och mekaniska egenskaper framställdes med tre metoder: ej stökiometrisk reaktion, metakrylattillsats och tillsättning av ditiolkedjeförlängning. Några 3-dimensionella jonledande strukturer konstruerades genom att binda den flexibla jongelfilmen tillsammans med jongel-lösningen som ett jonbindemedel. Dessutom erhölls mikromönster av jongelerna genom fotolitografi och så kallad mjuk avtryckslitografi. För att illustrera potentialen hos de reaktiva ytorna skapades två tredimensionella anordningar från en platt struktur: en rörformig aktuator och en låda med en flexibel elektrod som bildar en ”taxel”. Dessa intressanta resultat visar att tiolakrylat-baserad Michael-kemi ger en plattform för att tillverka olika former (filmer, mikromönster, tredimensionella strukturer och lim) av jongeler för nästa generation av flexibla elektrokemiska anordningar.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. , p. 62
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2025
National Category
Textile, Rubber and Polymeric Materials
Identifiers
URN: urn:nbn:se:liu:diva-161360DOI: 10.3384/diss.diva-161360ISBN: 9789179299781 (print)OAI: oai:DiVA.org:liu-161360DiVA, id: diva2:1366762
Public defence
2019-11-19, Hörsal Planck, Fysikhuset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2019-10-30 Created: 2019-10-30 Last updated: 2019-10-30Bibliographically approved
List of papers
1. Development of polypyrrole based solid state on-chip microactuators using photolithography
Open this publication in new window or tab >>Development of polypyrrole based solid state on-chip microactuators using photolithography
2018 (English)In: Smart materials and structures (Print), ISSN 0964-1726, E-ISSN 1361-665X, Vol. 27, no 7, article id 074006Article in journal (Refereed) Published
Abstract [en]

There is a need for soft microactuators, especially for biomedical applications. We have developed a microfabrication process to create such soft, on-chip polymer-based microactuators that can operate in air. The on-chip microactuators were fabricated using standard photolithographic techniques and wet etching, combined with special designed process to micropattern the electroactive polymer polypyrrole that drives the microactuators. By immobilizing a UV-patternable gel containing a liquid electrolyte on top of the electroactive polypyrrole layer, actuation in air was achieved although with reduced movement. Further optimization of the processing is currently on-going. The result shows the possibility to batch fabricate complex microsystems such as microrobotics and micromanipulators based on these solid state on-chip microactuators using microfabrication methods including standard photolithographic processes.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-147342 (URN)10.1088/1361-665X/aabe42 (DOI)000434378700006 ()
Note

Funding agencies: European Union [641822]; SSF; VINNOVA (OBOE-Center for Organic Bioelectronics); Swedish Research Council [VR-2014-3079]

Available from: 2018-04-19 Created: 2018-04-19 Last updated: 2019-10-30Bibliographically approved
2. Highly Conductive, Photolithographically Patternable Ionogels for Flexible and Stretchable Electrochemical Devices
Open this publication in new window or tab >>Highly Conductive, Photolithographically Patternable Ionogels for Flexible and Stretchable Electrochemical Devices
Show others...
2018 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 25, p. 21601-21611Article in journal (Refereed) Published
Abstract [en]

An ionic conducting membrane is an essential part in various electrochemical devices including ionic actuators. To miniaturize these devices, micropatterns of ionic conducting membrane are desired. Here, we present a novel type of ionogel that can be patterned using standard photolithography and soft imprinting lithography. The ionogel is prepared in situ by UV-initiated free-radical polymerization of thiol acrylate precursors in the presence of ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The resultant ionogel is very flexible with a low Youngs modulus (as low as 0.23 MPa) and shows a very high ionic conductivity (up to 2.4 X 10(-3) S/cm with 75 wt % ionic liquid incorporated) and has a reactive surface due to the excess thiol groups. Micropatterns of ionogel are obtained by using the thiol acrylate ionogel solution as an ionic conducting photoresist with standard photolithography. Water, a solvent immiscible with ionic liquid, is used as the photoresist developer to avoid complete removal of ionic liquid from thin micropatterns of the ionogel. By taking advantage of the reactive surface of ionogels and the photopatternability, ionogels with complex three-dimensional microstructure are developed. The surface of the ionogels can also be easily patterned using UV-assisted soft imprinting lithography. This new type of ionogels may open up for building high-performance flexible electrochemical microdevices.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
Keywords
micropatterning; ionogel; reactive surface; thiol acrylate photochemistry; electrochemical devices; photolithography
National Category
Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:liu:diva-149873 (URN)10.1021/acsami.8b03537 (DOI)000437811400064 ()29856596 (PubMedID)
Note

Funding Agencies|European Unions Horizon 2020 research and innovation program under the Marie Sklodowska Curie grant [641822]; Swedish Research Council [VR-2014-3079]

Available from: 2018-08-02 Created: 2018-08-02 Last updated: 2019-10-30
3. Tailorable, 3D structured and micro-patternable ionogels for flexible and stretchable electrochemical devices
Open this publication in new window or tab >>Tailorable, 3D structured and micro-patternable ionogels for flexible and stretchable electrochemical devices
Show others...
2019 (English)In: Journal of Materials Chemistry C, ISSN 2050-7526, E-ISSN 2050-7534, Vol. 7, no 2, p. 256-266Article in journal (Refereed) Published
Abstract [en]

A new family of ionogels for electrochemical devices was developed from a mixture of multifunctional thiols, diacrylate and triethylamine in the presence of ionic liquid using Michael addition chemistry. Polymerization kinetic studies show that the ionic liquid not only acts as an ion source but also a co-catalyst in the polymerization. Ionogels with tailorable surface and mechanical properties were prepared using three approaches: off-stoichiometry, methacrylate addition, and dithiol chain extender addition. 3-Dimensional ionogels were constructed by bonding the flexible ionogel film together using the ionogel solution as an ionic adhesive. A tube actuator with PEDOT-PSS patterned on inner and outer wall was prepared to illustrate the potential of these ionogels with reactive surfaces. In addition, micro-patterns of the ionogels were obtained by photolithography and soft imprinting lithography. All in all, this thiol acrylate Michael chemistry provides a platform to prepare various forms (films, micro-patterns, 3-dimensional structures, and adhesive) of ionogels for the next generation of flexible electrochemical devices.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:liu:diva-154097 (URN)10.1039/c8tc04368j (DOI)000455001000003 ()
Note

Funding Agencies|European Unions Horizon 2020 research and innovation program under the Marie Sklodowska Curie grant [641822]; Swedish Research Council [VR 2014-3079]

Available from: 2019-01-29 Created: 2019-01-29 Last updated: 2019-10-30

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