Environmental Engineering Reference
In-Depth Information
well-dispersed.nanoiller.[5]..As.greater.understanding.is.achieved,.more.advanced.
processes.and.products.are.developed.
The. following. generational. designations.have. been. described. on. several. occa-
sions.by.M.C..Roco,.who.is.recognized.as.one.of.the.key.architects.of.the.National.
Nanotechnology. Initiative. (NNI).. A. more. detailed. presentation. can. be. found. in. a.
chapter.by.Roco.reviewing.the.history.of.the.NNI,.its.evolution.over.the.past.decade,.
and.the.future.prospects.for.this.technology.and.its.impact.on.society.[6]..Additional.
information.emphasizing.aspects.related.to.manufacturing.at.the.nanoscale.appears.
in.a.report.issued.by.the.National.Nanotechnology.Coordination.Ofice.[7].
•
The “1st generation” products (2000+): represented primarily by passive
nanostructures.
. The. majority. of. products. that. are. already. commercial-
ized.fall.into.this.category,.where.the.nanoscale.element.(e.g.,.nanoparticle,.
nanoclay.platelet,.nanotube).is.incorporated.into.a.matrix.material.for.coat-
ings,. ilms,. and. composites,. or. is. part. of. a. bulk. nanostructured. material..
The. processes. for. fabricating. the. target. nanomaterials. discussed. in. this.
topic,. as. well. as. the. products. incorporating. these. nanoparticles. represent.
the.irst.generation.of.nanoproducts.
The “2nd generation” products (2005+): represented by active nanostruc-
tures.
In. these. structures,. the. nanoscale. element. is. the. functional. struc-
ture,.as.in.the.case.of.nanospheres.and.nanostructured.materials.for.drug.
delivery..The.materials.are.functional.in.that.they.respond.to.some.external.
stimuli.such.as.pH.or.temperature.to.release.the.stored.drug.at.a.controlled.
rate..Other. examples. include. sensors.and. actuators,.transistors,.and. other.
electronics,.where.individual.nanowires.serve.to.provide.the.switching.or.
amplifying.mechanism.
The “3rd generation” products (2010+): represented by three-dimensional
nanosystems and multi-scale architectures, expanding beyond the two-
dimensional layer-by-layer approach currently used in microelectronics.
.
These.systems.will.be.manufactured.using.various.directed.self-assembly.
methods.such.as.bio-assembly.(e.g.,.using.DNA.and.viruses.as.templates),.
electrical.and.chemical.template-guided.assembly.
The “4th generation” products (2015+): represented by truly heteroge-
neous molecular nanosystems.
In. these. products,. multi-functionality. and.
control.of.function.will.be.achieved.at.the.molecular.level.
•
•
•
Common.to.all.four.generations.of.product.development.are.three.stages.where.
exposure. to. nanomaterials. is. the. most. signiicant.. In. general,. nanomaterials. such.
as. carbon. nanotubes. and. silver. nanoparticles. can. be. relatively. expensive,. so. com-
panies.will.want.to.reduce.waste.as.much.as.possible..Nevertheless,.exposure.and.
entry.into.the.waste.stream.can.occur:.(1).during.fabrication.of.the.nanomaterial;.(2).
during.storage.and.handling.of.the.nanomaterial,.including.during.incorporation.of.
the. nanomaterial. into. another. material,. structure,. or. device;. and. (3). during. mate-
rial.removal.or.failure.upon.further.processing.or.disposal.of.the.product..Once.the.
nanomaterial.is.incorporated.into.a.bulk.material.(e.g.,.a.carbon.nanotube.bonded.
within.a.polymer.matrix),.the.concern.is.the.same.as.that.for.the.bulk.material.and.
