Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Polydimethylsiloxane (PDMS) compounds are utilized in outdoor high voltage insulation
due to their low weight, vandalism resistance, better anti-contamination performance
and their superior hydrophobic nature. Under severe environmental conditions and over
prolonged service time, however, the hydrophobic surface can gradually become
hydrophilic and then recover with adequate resting period.
In this study, room temperature vulcanized (RTV) PDMS samples were prepared with
different formulations and then exposed to corona discharge to evaluate its effect. The
influence of different additives, such as different types and amount of fillers and
additionally added low molar mass silicone oils, on the hydrophobicity recovery of the
material was investigated. The effects of two types of corona treatment were also
evaluated.
Hydrophobicity recovery of corona and UV-C aged PDMS samples was evaluated by
means of static contact angle measurements.
Positron annihilation spectroscopy (PAS) gave important information on the micro
structural change after corona treatment of RTV PDMS as well as naturally aged high
temperature vulcanized (HTV) PDMS samples. The different formulations of the RTV
PDMS samples and the effect of the additives were studied with this technique. The
formation of a thin, highly crosslinked inorganic silica-like (SiOx) layer was confirmed
even at the early stage of degradation. It was also possible to estimate the thickness of
the silica-like layer formed during corona exposure that is responsible for the loss and
recovery of hydrophobicity.
The surface hardness and hydrophilicity change of PDMS samples due to corona
treatment were studied simultaneously with force distance measurements by atomic
force microscopy (AFM). The adhesive force calculated from the pull-off force-distance
curves showed that the adhesive force between the probe and the sample decreased
with increasing corona treatment time, indicating hydrophobicity recovery. In addition to
this, the increase in hardness after corona exposure provides indirect evidence of the
formation of a silica-like layer. In all cases the hydrophilicity and the surface hardness of
the PDMS samples increased directly after corona treatment and recovered with time.
Two types of FTIR spectroscopy were used to analyse the surface of the polymer. / AFRIKAANSE OPSOMMINGS: Polidimetielsiloksaan (PDMS) word in buitelug hoogspanninginsulasie gebruik as gevolg
van sy lae massa, weerstand teen vandalisme, verbeterde anti-kontaminasie
werkverrigting en superieure hidrofobiese karakter. Die hidrofobiese oppervlakte kan
egter gelydelik hidrofillies word onder uiterste omgewingsomstandighede en oor
langdurige dienstyd. PDMS materiaal herstel egter nadat dit genoeg rustyd toegelaat is.
Kamertemperatuur-gevulkaniseerde (KTV) PDMS met verskillende formulasies is in
hierdie studie voorberei, aan korona ontlading blootgestel, geëvalueer en vergelyk. Die
invloed van bymiddels soos verskillende tipes en hoeveelhede vuiler, asook addisionele
lae molekulêre massa silikoonolie, op die herstel van hidrofobisiteit van die materiaal is
ondersoek. Twee verskillende metodes van korona behandeling is ook geëvalueer.
Die herstel van hidrofobisiteit van korona en UV-C verouderde PDMS monsters is met
statiese kontakhoekmeting geëvalueer.
Positronvernietigingspektroskopie (PVS) is 'n kragtige tegniek wat belangrike inligting
oor die mikrostrukturele verandering van korona behandelde van KTV PDMS sowel as
natuurlik-verouderde hoë temperatuur gevulkaniseerde (HTV) PDMS monsters gee. Die
verskillende formulasies van die KTV PDMS monsters, sowel as die effek van die
vullers, is met behulp van hierdie tegniek ondersoek. Die vorming van 'n dun, hoogskruisgebinde,
anorganiese silika-agtige (SiOx) laag op die PDMS oppervlak, selfs
tydens die vroeë stadium van degradasie, is bevestig. Dit was ook moontlik om die dikte
van die silika-agtige laag wat gedurende die korona blootstelling gevorm het, en wat
verantwoordelik is vir die verlies aan hidrofobisiteit, te bepaal.
Die oppervlakhardheid en hidrofilisiteit verandering van PDMS monsters as gevolg van
korona behandeling, was gelyktydig met krag-afstand metings deur middel van
atoomkragmikroskopie (AKM) bestudeer. Die kleefkrag, soos bereken van aftrek kragafstandkurwes,
dui daarop dat kleefkragte tussen die taster en die monster afneem met
toenemende korona behandelingstyd, wat beduidend is op die herstel van
hidrofobisiteit. Daarbenewens is die toename van oppervlakhardheid na korona
blootstelling "n indirekte bewys van die formasie van 'n silika-agtige laag. In alle gevalle
het die hidrofilisiteit en die oppervlakhardheid van die PDMS monsters toegeneem direk
na afloop van korona behandeling en gevolglik herstel met tyd. Twee tipes IR spektroskopie metodes is gebruik vir die chemiese-oppervlak analises
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/49902 |
| Date | 12 1900 |
| Creators | Abraham Berhane, Teclesenbet |
| Contributors | Mallon, P. E., Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 130 p. : ill. (some col.) |
| Rights | Stellenbosch University |
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