Environmental Engineering Reference
In-Depth Information
Once. in. use,. these. commercial. products. containing. ixed. nanoparticles. are.
unlikely. to. release. nanomaterials. to. the. environment.. Therefore,. the. potential. for.
human.or.ecological.exposure.to.ixed.nanoparticles.is.limited.after.their.incorpora-
tion.into.the.inal.manufactured.materials.
.
PRoPeRties oF nanosCale MateRials
2.3.1 O
verview
The.properties.of.nanoscale.materials.generally.differ.from.those.of.the.same.mate-
rials.in.bulk.size..This.effect.results.from.two.aspects.of.the.small.size.of.nanopar-
ticles:.(1).the.increased.relative.surface.area.per.unit.mass,.and.(2).the.inluence.of.
quantum.effects..Each.of.these.points.is.discussed.below.
...
effect of increased surface area
Reducing.the.size.of.a.particle.increases.the.ratio.of.surface.area.to.mass..Because.
the. reactive. portion. of. the. particle. is. at. its. surface,. increasing. the. relative. surface.
area.will.increase.reactivity.for.a.given.amount.of.material..To.illustrate,.consider.a.
spherical.particle.0.1.millimeter.(mm).in.diameter..Its.surface.area.is.3.×.10
−8
.m
2
..If.
technicians.mill.the.same.mass.of.material.into.100-nm-sized.spheres,.then.the.total.
surface.area.increases.to.3.×.10
−5
.m
2
..Decreasing.the.diameter.of.the.particle.by.a.
factor.of.1000.increases.the.surface.area.by.a.factor.of.1000..If.reactive.sites.cover.
the.surface.of.the.particle,.then.—.all.else.being.equal.—.this.decrease.in.particle.
size. would. increase. reactivity.substantially.. This. effect. accounts. for. the. increased.
eficiency.of.nanoscale.catalysts.compared.to.their.bulk.counterparts.
...
inluence of Quantum effects
At.the.nanoscale,.both.classical.physics.and.quantum.physics.can.govern.the.behav-
ior. of. a. particle.. The. inluence. of. quantum. effects. can. change. essential. material.
characteristics. such. as. optical,. magnetic,. and. electrical. properties.. An. in-depth.
explanation.of.the.relevant.physics.is.beyond.the.scope.of.this.topic,.which.focuses.
on.the.implications.of.nanotechnology.for.the.environment..In.lieu.of.pages.of.theo-
retical.explanation.and.equations,.consider.the.following.examples.
In.our.everyday,.visible.world,.objects.move.according.to.Newton's.models.of.
velocity,.acceleration,.inertia,.and.momentum..For.example,.one.can.predict.the.tra-
jectory.of.a.lacrosse.ball.based.on.its.mass.and.velocity,.the.pull.of.gravity,.and.the.
resistance.of.the.air..If.the.lacrosse.ball.splashes.into.a.pond,.its.inal.trajectory.also.
will.relect.the.buoyancy.of.the.water.
Other. factors,. however,. can. inluence. the. movement. of. a. molecule. or. certain.
nanoparticles.. Even. nonpolar. molecules. exhibit. slight,. transient. polarity. of. charge.
because. of. instantaneous. shifts. in. electron. density.. (Quantum. mechanics. projects.
this. electron. density. probabilistically.). A. slight. negative. charge. on. a. portion. of. a.
molecule.or.nanoparticle.due.to.this.transient.polarity.will.be.attracted.to.a.positive.
charge. or. repelled. by. a. negative. charge.. These. weak. and. transient. intermolecular.
forces.are.called.Van.der.Waals.forces..For.many.nanoparticles.—.unlike.the.lacrosse.
