Environmental Engineering Reference
In-Depth Information
through.the.use.of.catalyst.particles,.template.materials.(e.g.,.to.control.nucleation.
and.precipitation.behavior),.and.controlled-size.droplets.or.aerosols.
The.six.nanomaterials.that.are.the.focus.of.this.topic.—.carbon.black,.carbon.
nanotubes,.fullerenes.(also.known.as.C60.or.buckyballs),.nano.silver,.nano.titanium.
dioxide,. and. nano. zero-valent. iron. —. can. all. be. fabricated. using. many. methods,.
and.with.the.interest.in.nanomaterials,.new.methods.are.being.discovered.rapidly..A.
quick.search.in.the.U.S..Patent.and.Trademark.Ofice.database.[8].brings.up.roughly.
50.patents.issued.in.the.past.two.years.with.“nanoparticle”.in.the.title..These.patents.
include. methods. of. making. nanoparticles,. modifying. nanoparticles,. and. products.
incorporating. nanoparticles.. Table.3.1. provides. a. few. examples. of. manufacturing.
techniques.for.the.six.target.materials.
3.3.3
i
ntegrating
n
anOpartiCles
intO
n
anOprOduCts
In.some.processes,.the.synthesis.of.the.nanoparticle.and.subsequent.deposition.onto.
a.substrate.occurs.in.one.continuous.process..In.others,.however,.the.nanomaterial.
must.be.collected.and.stored.until.needed.for.later.processing..Some.earlier.nanopar-
ticle.synthesis.approaches.resulted.in.the.nanomaterial.adhering.to.the.walls.of.the.
reactor,.requiring.physical.removal.equivalent.to.“scraping.the.soot.from.the.walls.”.
Needless. to. say,. such. direct. contact. with. the. materials. leads. to. worker. exposure.
issues.. Newer. methods. emphasize. limiting. human. contact. with. the. nanoparticles,.
partially.for.worker.safety,.but.also.for.economic.reasons:.reducing.contamination.
and.increasing.yield.
Once.the.nanomaterial.is.manufactured.and.sold.as.a.raw.material.to.multiple.
customers,.the.next.stage.of.exposure.is.handling.during.incorporation.into.a.prod-
uct.. Dispersion. is. often. the. key. process. in. incorporating. nanomaterials. into. bulk.
materials..This.often.involves.some.chemical.modiication.of.the.surface.to.cause.
the.nanomaterials.to.be.less.likely.to.agglomerate.with.each.other.and.more.likely.to.
bond.to.the.bulk.material..Again,.once.in.a.solvent.or.suspension.or.melt,.the.nano-
materials.are.very.unlikely.to.be.inhaled,.but.dermal.contact.may.still.be.a.concern..
Thus,.the.step.of.introducing.the.nanoparticles.or.nanotubes.into.the.solution.or.melt.
is. the. potential. hazard. point.. Beyond. this. point,. the. material. remains. in. a. closed.
environment.(e.g.,.in.a.melt.being.mixed.in.a.twin-screw.extruder).
For.future.generations.of.products,.the.vision.is.that.of.three-dimensional.multi-
material,.directed.self-assembly.manufacturing.processes..Simple.two-dimensional.
examples. include. the. organization. of. nanoparticles. and. other. nanomaterials. using.
conductive.vs..nonconductive.patterns.(Figure.3.5).and.the.alignment.of.nanotubes.
in. narrow. trenches.. In. directed. assembly,. the. material. to. be. assembled. (e.g.,. con-
ductive. polymer,. nanoparticles,. nanotubes). is. exposed. to. the. template.. Then,. with.
the.help.of.some.driving.force.such.as.an.electric.ield,.magnetic.ield,.or.chemical.
attraction,.the.nanomaterials.assemble.into.a.desired.pattern.over.a.large.area.within.
a.short.time..The.beneit.of.these.directed.assembly.processes.is.that.the.amount.of.
handling.will.further.decrease.and.the.raw.material.is.often.in.solution.(e.g.,.not.sub-
ject.to.inhalation)..This.is.an.advantage.not.only.for.repeatability,.but.also.for.worker.
exposure.. The. environmental. question. that. then. arises. is. the. capture. and. reuse. of.
