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Reduced and Surface-Modified Graphene Oxide with Non-Linear Resistivity
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.ORCID iD: 0000-0002-3310-9964
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.ORCID iD: 0000-0002-0236-5420
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.ORCID iD: 0000-0002-8194-0058
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Field-grading materials (FGMs) are used to reduce the probability for electrical breakdowns in critical regions of electrical components and are therefore of great importance. Usually, FGMs are heavily filled (40 vol.%) with semi-conducting and conducting particles. Here, the use of polymer-grafted reduced graphene oxide (rGO) as a filler to accomplish percolation networks is explored at very low filling ratios (<2 vol.%) in a semi-crystalline matrix (EBA). Various simulation models are used to predict the percolation threshold and the flake-to-flake distances, to complement the experimental results. A substantial increase in thermal stability of rGO is seen after surface modification, either by silanization or subsequent polymerizations. The non-linear DC resistivity of neat and silanized rGO and its trapping of charge-carriers in semi-crystalline EBA are demonstrated for the first time. It is shown that the polymer-grafted rGO improve the dispersibility in the EBA-matrix and that the graft length controls the inter-flake distances (i.e. hopping distance). By the appropriate selection of graft lengths, both highly resistive materials at 10 kV mm-1 and FGMs with large and distinct drops in resistivity (six decades) are obtained and followed by saturation. The nonlinear drop in resistivity is attributed narrow distributions of inter-flake distances of grafted rGO.

Keyword [en]
tuning of properties, non-linear resistivity, polymer-grafting, field-grading, rGO
National Category
Polymer Chemistry
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-204040OAI: oai:DiVA.org:kth-204040DiVA: diva2:1084018
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Note

Qc 20170323

Available from: 2017-03-23 Created: 2017-03-23 Last updated: 2017-03-23Bibliographically approved
In thesis
1. Controlled Polymer Grafting from Nanoparticles for the Design of Dielectric Nanocomposites
Open this publication in new window or tab >>Controlled Polymer Grafting from Nanoparticles for the Design of Dielectric Nanocomposites
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The interest for polymeric nanocomposites has rapidly grown during the last decades, fuelled by the great potential and superior properties of nanoparticles (NPs). The production volumes of commercial NPs have increased exponentially during the last ten years, and the quality has been significantly improved. The aim of this study was to design polymer grafted commercially available metal-oxide NPs, and graphene oxide (GO), to develop isotropic (homogeneous) and anisotropic (heterogeneous) polymer nanocomposites for dielectric applications. The motivation was to formulate functional insulation materials for compact components in future power-grid systems using high-voltage direct-current (HVDC) or high-voltage alternating-current (HVAC), and to fabricate responsive sensor materials for monitoring e.g. temperature and voltage fluctuations in so called “Smart Grids”.

Aluminium oxide (Al2O3), zinc oxide (ZnO) and reduced GO (rGO) NPs were modified with sparse polymer grafts via a controlled “covalent route” and were mixed with silicone (PDMS) or polyethylene matrices (EBA and LDPE) commonly used in HV-cable systems. The graft length and the graft-to-matrix compatibility were tailored to obtain nanocomposites with various self-assembled NP-morphologies, including well-dispersed, connected and phase-separated structures. The graft length was used to adjust the inter-particle distance of nanocomposites with continuous morphologies or connected (percolated) NPs. It was found that nanocomposites with percolated NPs and short inter-particle distances exhibited 10-100 times higher conductivity than the unfilled (neat) polymer, or displayed a rapid non-linear increase in conductivity (~1 million times) with increasingelectric field, while well-dispersed NPs with long inter-particle distances exhibited 10-100 times lower conductivity (i.e. higher resistivity) as an effect of their trapping of charge carriers. These tunable and functional properties are desirable for HV-insulation, field-grading applications, and flexible electronics.

In addition it was shown that GO modified with dense polymer grafts via a “physisorption route” formed suspensions with liquid crystals, or matrix-free GO-composites with well-dispersed GO in isotropic or nematic states. These materials were reinforced by the GO, and exhibited elevated glass transition temperatures and a rapid thermo-responsive shape-memory effect, and are thus proposed to have a great potential as sensor materials and responsive separation membranes.

Abstract [sv]

Intresset för polymera nanokompositer har snabbt ökat under de senaste decennierna, drivet av den stora potentialen och de överlägsna egenskaperna hos nanopartiklar (NPs). Produktionsvolymerna för kommersiella NP har ökat exponentiellt under de senaste tio åren, och kvaliteten har förbättrats avsevärt. Syftet med denna studie var att polymer-ympa kommersiellt tillgängliga metalloxid-NPs, och grafenoxid (GO), för att designa isotropa (homogena) och anisotropa (heterogena) polymera nanokompositer för dielektriska tillämpningar. Motiveringen var att formulera funktionella isoleringsmaterial för kompakta komponenter i framtida kraftnätssystem som använder högspänd likström (HVDC) eller högspänd växelström (HVAC), samt att tillverka responsiva sensormaterial för övervakning av t.ex. temperatur- and spänningsvariationer i så kallade "Smart Grids".

Aluminiumoxid (Al2O3), zinkoxid (ZnO) och reducerad GO (rGO) NPs modifierades med glesa polymerympar via en kontrollerad "kovalent väg" och blandades med silikon (PDMS) eller polyeten matriser (EBA och LDPE) som är vanliga i HV-kabelsystem. Ymplängden och ymp-till-matrix kompatibiliteten skräddarsyddes för att erhålla nanokompositer med olika självordnande NP-morfologier, inklusive väldispergerade, länkade och fasseparerade strukturer. Ymplängden användes för att justera partikelavståndet i nanokompositer med förbundna morfologier eller länkade NPs. Man fann att nanokompositer med länkade NPs och korta interpartikelavstånd uppvisade 10-100 gånger högre konduktivitet än den ofyllda (rena) polymeren, eller erhöll en snabb icke-linjär ökning i konduktivitet (~1 miljon gånger) med ökande elektriskt fält, medan väldispergerade NPs med långa interpartikelavstånd uppvisade 10-100 gånger lägre ledningsförmåga (dvs. högre resistivitet) som en effekt av deras infångande av laddningsbärare. Dessa inställbara och funktionella egenskaper är önskvärda för HV-isolering, fältstyrande applikationer och flexibel elektronik.

Dessutom visades att GO, som modifierats med täta polymerympar via en "fysisorptionsväg", bildade suspensioner med flytande kristaller, eller matrisfria GO-kompositer med väldispergerad GO i isotropa eller nematiska tillstånd. Dessa material armerades av GO och uppvisade förhöjda glastransitionstemperaturer och en snabb värmeresponsiv form-minneseffekt, och föreslås därigenom ha en stor potential som sensor-material och responsiva separationsmembran.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. 96 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2017:16
National Category
Polymer Chemistry
Research subject
Fibre and Polymer Science
Identifiers
urn:nbn:se:kth:diva-204036 (URN)
Public defence
2017-04-28, Kollegiesalen, Brinellvägen 8, KTH-huset, KTH Campus, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
SweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Note

QC 20170323

Available from: 2017-03-23 Created: 2017-03-23 Last updated: 2017-03-24Bibliographically approved

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