Change search
ReferencesLink to record
Permanent link

Direct link
Loss and recovery of hydrophobicity of polydimethylsiloxane after exposure to electrical discharges
KTH, Superseded Departments, Polymer Technology.
2001 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Silicone rubber based on polydimethylsiloxane is used ashigh voltage outdoor insulation, due to its ability to preservethe hydrophobic surface properties during service and evenregain hydrophobicity after exposure to electrical discharges.The underlying processes for the hydrophobic recovery arediffusion of low molar mass siloxanes from the bulk to thesurface and reorientation by conformational changes ofmolecules in the surface region. Only little is known of whichfactors are responsible for the long-term stability of thishydrophobic recovery. It is therefore important to increase theknowledge about the fundamental mechanisms for the loss andrecovery of hydrophobicity of silicone rubbers, exposed toelectrical discharges. Addition-cured polydimethylsiloxanenetworks, with known crosslink densities, were exposed tocorona discharges and air/oxygen-plasma and the loss andrecovery of hydrophobicity was characterised by contact anglemeasurements. The degree of surface oxidation increased withincreasing exposure time with a limiting depth of 100- 150 nm,as assessed by neutron reflectivity measurements. The oxidationrate increased with increasing crosslink density of the polymernetwork, according to X-ray photoelectron spectroscopy. Withinthe oxidised layer, a brittle, silica-like layer was graduallydeveloped with increasing exposure time. The hydrophobicrecovery following the corona or air/oxygen- plasma exposuresoccurred at a slow pace by diffusion of cyclic oligomericdimethylsiloxanes through the micro-porous but uncrackedsilica-like surface layer or at a much higher pace by transportof the oligomers through cracks in the silica-like layer. Theoligomers were present in the bulk, but additional amounts wereformed during exposure to corona discharges. High-temperaturevulcanised silicone rubber specimens were aged in a coastalenvironment under high electrical stress levels (100 V/mm). Thechanges in surface structure and properties were compared tothe data obtained from specimens exposed to coronadischarges/plasma. The dominating degradation mechanism wasthermal depolymerisation, initiated by hot discharges. Thisresulted in the formation of mobile siloxanes, of which the lowmolar mass fraction consisted of cyclic oligomericdimethylsiloxanes. Oxidative crosslinking resulting insilica-like surface layers was not observed during theseconditions.

Keywords:silicone rubber, polydimethylsiloxane,hydrophobicity, corona, air-plasma, oxygen-plasma, surfacecharacterisation, degradation products, crosslink density.

Place, publisher, year, edition, pages
Institutionen för polymerteknologi , 2001. , ii, 71 p.
Keyword [en]
silicone rubber, polydimethysiloxane, dydrophobicity, corona, air-plasma, oxygen-plasma, surface characterisation
URN: urn:nbn:se:kth:diva-3082ISBN: 91-7283-029-8OAI: diva2:8835
Public defence
NR 20140805Available from: 2001-01-31 Created: 2001-01-31Bibliographically approved

Open Access in DiVA

fulltext(2707 kB)5754 downloads
File information
File name FULLTEXT01.pdfFile size 2707 kBChecksum SHA-1
Type fulltextMimetype application/pdf

By organisation
Polymer Technology

Search outside of DiVA

GoogleGoogle Scholar
Total: 5757 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

Total: 615 hits
ReferencesLink to record
Permanent link

Direct link