Carbon Pastes and Carbon Paste Electrodes - Electroanalysis with Carbon Paste Electrodes - page 18

The.most.popular.product.of.this.kind.is.Nujol ® .(oil.or.mull,.respectively;.originally.solvent.for.
IR-spectroscopy).obtainable.from.every.renowned.dealer;.see,.for.example,.[212]..Very.similar.in.
nature,. as. well. as. in. the. basic. properties,. are. mineral. oils. used. as. solvents. in. UV-spectroscopy,.
for.example,.the.product.supplied.by. Merck .being.well.known.and.declared.as.the.mineral.oil.of.
Uvasol ® .purity.grade.[213]..(Perhaps,.under.the.inluence.of.the.name.“Nujol,”.some.authors.call.
this.product.“Uvasol.oil”.being.unaware.of.the.original.meaning.)
Despite.some.classiications.as.heavy.mineral.oils,.both.Nujol.and.the.solvent.for.UV-spectroscopy.
are.liquids.with.distinctly.liquid.consistency.(almost.like.water),.completely.transparent,.odorless,.
and—if.coming.into.a.short.contact.with.skin—essentially.harmless..These.features.are.not.so.obvi-
ous.(see.the.following.Note.).and.surely.belong.among.good.reasons.for.their.constant.popularity.
and.widespread.global.use.[7,83]..Their.drawback.may.be.a.potential.lammability.and,.especially,.
their.capability.to.act.as.solvent.of.some.less.resistant.materials—potentially.vulnerable.compart-
ments.of.measuring.cells.or.of.the.electrode.itself.
2.1.3.2 Aliphatic and Aromatic Hydrocarbons
The. dominance. of. commercial. POs. with. often. anonymous. composition. has. also. resolved. the.
previous.dilemmas.on.which.particular.hydrocarbon.would.be.the.best.as.the.binder.for.carbon.
pastes.. As. documented. in. studies. with. a. series. of. either. aliphatic. or. aromatic. hydrocarbons,.
even.a.very.thorough.testing.did.not.lead.to.any.conclusive.answer..In.this.context,.for.example,.
one. can. remember. the. comparative. studies. with. homologues. of. aliphatic. hydrocarbons. C 8 -C 20 .
[8,9,11,34,60,68]. or. various. derivatives. of. benzene,. naphthalene,. and. phenanthrene. [8,9,40]..
Occasionally,. some. of. these. compounds. have. been. used. again. in. later. electroanalytically. ori-
ented.measurements,.such.as.hexadecane.[60,214,215].or.selected.items.of.shorter.chain.aliphatic.
hydrocarbons.(C 10 -C 14 ;.[216]).
2.1.3.3 Silicone Oils and Greases
The. binders. of. this. kind. belong. among. polymerized. siloxanes. with. organic. side. chains.. If. the.
substance.of.interest.is.still.being.luid,.it.is.usually.called.silicone.oil.(SO),.whereas.a.thicker.and.
already. gelatin-like. derivative. is. silicone. grease. (SG).. The. latter. may. either. be. a. representative.
of.polysiloxanes.with.high.molecular.weight.or.even.silicon.oil.combined.with.a.thickener.(e.g.,.
fumed.silica).
In.general,.both.SO.and.SG.share.numerous.valuable.properties.of.POs,.such.as.chemical.inert-
ness,.insulating.character,.and.health.harmlessness..Moreover,.unlike.these.carbon.analogues,.sili-
cones.are.nonlammable.and.friendlier.to.some.plastic.materials..And.compared.to.Nujol.or.the.oil.
of. Uvasol .grade,.typical.SOs.are.often.more.viscous.and.usually.forming.denser.and.more.compact.
carbon.paste.mixtures.[175].
Both.SO.and.SG.represent.the.second.major.group.of.binders.used.for.traditional.carbon.pastes..
The. pioneering. reports. on. their. use. can. be. traced. up. as. early. as. in. 1960s. [20,28,217],. including.
some.capacitance.testing.measurements.in.Adams's.laboratories.[2],.and.various.SO-based.carbon.
pastes.appear.regularly.over.the.upcoming.decades.(see,.e.g.,.[41,60,61,202,209,218,219,224,225]),.
when.the.functioning.of.numerous.SOs.or.greases.was.also.the.subject.of.extensive.comparative.
studies.[2,40,192,218,220-222].
In. general,. silicone. luids. form. carbon. pastes. with. properties. very. close. to. those. of. mixtures.
from.mineral.oils;.nevertheless,.there.are.also.some.differences.in.behavior.of.these.two.fundamen-
tal.types..Besides.the.already.mentioned.consistency,.the.most.evident.dissimilarity.can.be.seen.in.
resistivity.of.both.types.of.pastes.in.media.with.organic.solvents,.where.silicone.luid-based.mix-
tures.exhibited.better.stability.compared.to.the.counterparts.made.of.mineral.oils.[211].
Note: . For.instance,.a.CPE.of.the.C/SO.type.could.be.reliably.operated.in.a.solution.of.2.M.H 2 SO 4 .
containing.25%.(v/v).MeOH,.when.the.C/Nj.counterpart.at.identical.experimental.conditions.had.
already.exhibited.the.extremely.high.background..And,.after.increasing.the.content.of.solvent.up.to.