Environmental Engineering Reference
In-Depth Information
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Explosivity, lash point, and self-ignition temperature.
. The. high. surface.
area. of. very. small. particles. increases. their. tendency. to. combust. when.
suspended.in.air.in.the.presence.of.an.ignition.source.such.as.static.charge.
or.sparks..Readers.may.be.familiar.with.this.phenomenon.from.reports.of.
dust. explosions. in. grain. elevators.. The. potential. for. combustion. can. be. a.
safety.issue.for.some.nanomaterials.
Degree of agglomeration
..Van.der.Waals.forces,.which.are.weak,.transient.
intermolecular. forces. resulting. from. transient. polarity. related. to. shifts. in.
electron. density,. can. cause. nanoparticles. to. agglomerate.. Agglomeration.
increases.the.net.particle.size,.thereby.changing.the.size-dependent.charac-
teristics.and.behavior.of.the.original.nanomaterial..The.Hamaker.constant.
represents.the.net.van.der.Waals.attraction.
Surface charge.
.This.affects.dissolution,.suspension.in.water,.and.sorption,.
and. is. often. represented. by. the. zeta. potential.. A. positive. charge. on. the.
surface.of.a.colloid.(such. as.a.metal.oxide.nanoparticle).in.water.attracts.
negatively. charged. ions. in. the. luid.. These. negatively. charged. ions. form.
the. so-called. “Stern. layer”. around. the. colloid.. The. zeta. potential. is. the.
charge.measured.at.the.outermost.portion.of.the.Stern.layer..As.discussed.
further.in.Chapter.6,.the.stability.of.a.nanoparticle.suspension.relates.to.its.
zeta.potential..The.electrostatic.repulsion.resulting.from.surface.charge.can.
counter.the.tendency.toward.agglomeration.
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These.properties.affect.the.fate.and.transport.of.nanomaterials.in.the.environment,.their.
toxicity,.and.their.fate.in.wastewater.treatment,.as.discussed.in.subsequent.chapters.
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tYPes oF nanoMateRials and aPPliCations
New.applications.of.nanotechnology.appear.constantly..The.Nanotechnology.Con-
sumer.Products.Inventory.maintained.by.the.Woodrow.Wilson.Institute.listed.over.
500.consumer.products.containing.nanomaterials.as.of.June.2007.[1]..The.inventory.
grew.from.212.to.502.products.between.March.2006.and.June.2007,.demonstrating.
the. explosive. growth. of. this. market.. Those. products. represent. an. extraordinarily.
wide. range. of. applications.. The. list. of. products. below. demonstrates. the. range. by.
example.. (Characterizations. of. nanoscale. ingredients. in. the. materials. on. this. list,.
and.their.effects,.were.made.by.the.manufacturers.as.cited.by.the.Nanotechnology.
Consumer.Products.Inventory..The.information.provided.below.is.not.intended.as.an.
endorsement,.but.simply.to.illustrate.the.range.of.products.and.applications.)
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Cosmetics.and.personal.care.products:
RevitaLift®.Intense.Lift.Treatment.Mask.(L'Oreal®).—.uses.nanosomes,.
tiny. capsule-like. structures,. to. transport. active. ingredients. into. the.
skin's.outer.layer.and.then.release.them.
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.ASTM. International. distinguishes. between. agglomeration. and. aggregation. of. nanoparticles. as. fol-
lows.[2]..An.agglomerate.is.a.group.of.particles.held.together.by.relatively.weak.forces.(such.as.Van.
der.Waals.forces).that.can.be.broken.apart..An.aggregate.is.a.discrete.group.of.particles.composed.of.
individual.components.that.are.tightly.bonded.together.and.not.easily.broken.apart.
