Environmental Engineering Reference
In-Depth Information
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1.. Nanomaterials. must. be. internally. structured,. based. on. stable. covalent.
bonds,.and.will.not.be.immediately.soluble.in.environmental.luid.media.
.
2.. The. chemical. activity. of. the. particle. is. based. on. its. surface. chemistry,.
which.is.a.function.of.both.its.composition.and.its.structure.
.
3.. The.nanomaterials.will.tend.not.to.have.either.strong.nucleophilic.or.elec-
trophilic.afinities;.otherwise.they.would.not.be.stable.in.particulate.form..
Therefore,.in.the.absence.of.harsh.agents,.they.will.tend.to.interact.with.the.
environment.via.weaker.ionic.and.van.der.Waals.interactions.
Predicting.the.surface.behavior.of.nanomaterials.can.be.very.dificult.because.
the.architecture.of.the.particle.can.dramatically.affect.both.energy.transfer.and.elec-
tron. distribution.. This. can. be. particularly. true. for. heterogeneous. particles. where.
partial.charge.sharing.or.excitation.quenching.can.occur..However,.if.it.is.assumed.
that.the.initial.nanoparticle.is.indivisible,.then.the.potential.for.environmental.inter-
actions.is.limited.to.the.interactions.of.the.surface.layer..Therefore,.by.characterizing.
the.surface.chemistry,.it.would.be.possible.to.determine.the.types.of.interactions.that.
are.likely.to.occur.in.natural.air.or.water.environments..These.interactions.would.
determine.the.most.likely.physical/chemical.fate,.and.thereby.the.ultimate.disposi-
tion.of.the.material.once.released.
Surface.chemistry.interactions.can.be.deined.using.a.speciic.generalized.force.
ield.summation.for.colloidal.systems.developed.by.Derjaguin,.Landau,.Verwey,.and.
Overbeet.(DLVO).[2]..In.the.DLVO.summation,.the.total.force.ield.( F T ).includes.van.
der.Waals.forces.( F vdw ),.the.forces.of.solvency.( F s ),.and.electrostatic.repulsive.forces.
( F R ).as.follows:
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F T .=. F R .+. F vdw .+. F s .
(6.7)
These.forces,.while.typically.weak,.become.the.signiicant.driving.forces.for.nano-
materials.because.of.the.particles'.high.Brownian.velocity.and.low.inherent.inertia..
Each. of. these. forces,. and. their. implications. for. the. transport. of. nanoparticles,. is.
discussed.below.
... 
electrostatic or Coulomb Force
The.electrostatic.repulsive.or.Coulomb.force.( F R ).represents.a.speciic.point-to-point.
force.that.relates.directly.to.the.intermolecular.charge.balance.of.the.particle.or.moi-
ety.relative.to.its.environment..Charges.arise.from.two.speciic.types.of.interactions..
First,.the.valence.stability.of.an.atom.or.moiety.in.a.given.environment.may.favor.an.
unbalanced.charge.conformation..This.is.seen.with.ionizable.salts.where.the.electron.
afinity. of. a. given. anion. is. greater. than. the. electron. afinity. of. the. corresponding.
cation.. Hence,. the. lowest. energy. conformation. results. in. a. charge. separation.. The.
energy.change.between.the.neutral.and.the.charged.form.is.referred.to.as.the.ioniza-
tion.energy.
Coulomb. forces. also. can. arise. from. electron. stripping.. This. occurs. when. an.
external.force.causes.the.separation.of.a.charge.from.its.neutral.location..The.charge.
separation.actually.results.in.an.increase.in.the.energy.state.of.the.system..However,.
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