C haptEr 9 design Environments and systems
398
It is a layered smectite clay mineral that has a platelet structure.
Platelets are very thin—for example, 1–2 nm—but have very large
surface dimensions, perhaps over 500 nm, that make them highly
effective providers of surface areas. These kinds of nanoparticles are
relatively inexpensive compared to other types of nanoparticles and
can be easily manufactured in bulk quantities. Section 8.8 describes
nanocomposites based on smectite materials in greater detail.
Nanoparticles can also come in varying levels of treatments. Various
nanoparticles can be obtained that, for example, already have
hydrophobic or hydrophilic properties (see Chapter 8) useful in a
wide range of applications. Typically, when obtained from a manufacturer, nanoparticle batches may need to be further processed
via application of surfactant coatings, ultrasonification, milling, or
other processes because of their inherent tendency to agglomerate
or attract moisture.
Carbon nanotubes for applications are available in a wide variety
of single-walled (SWNT) and multiwalled (MWNT) forms, including different lengths, diameters, and purities. A primary quality and
cost issue is purity. Depending on the synthesis process used, purified forms are characterized by descriptions such as “95 wt%” or
“60 wt%,” which simply refers to the actual percentage by weight
of nanotube content within a unit weight of a gram of nanotube
material. Other constituents might include ash, amorphous carbon,
residual catalyst, or other materials. Some SWNT formulations
can also include some percentage of MWNTs. Obviously, higher
purity forms have more effective properties. Cost-per-gram values,
however, are invariably higher than lower purity forms. Lower purity
and lower-cost forms, however, can be suitable for many bulk applications. Most commercialization has been with MWNTs. SWNTs
are available but often at higher unit prices. Typical diameters for
available SWNTs are on the order of 1–2 nm, and common lengths
are on the order of 10–50 um, although there is variation in these
numbers as well. Special short nanotube forms are also available
that are on the order of 0.3–5 um. Outer diameters of common
MWNTs are on the order of 5–15 nm, with inside diameters on the
order of 2–8 nm. Several walls are common. Short-form MWNTs
often have larger outer diameters (20–50 nm or so) and somewhat
larger inner diameters than longer forms.
Incorporating carbon nanotubes into other matrix materials to form
nanocomposites has often proven difficult because of the surface
chemistry of the carbon. Problems include achieving uniform dispersions and poor adhesion with the primary matrix. Many highly
398
It is a layered smectite clay mineral that has a platelet structure.
Platelets are very thin—for example, 1–2 nm—but have very large
surface dimensions, perhaps over 500 nm, that make them highly
effective providers of surface areas. These kinds of nanoparticles are
relatively inexpensive compared to other types of nanoparticles and
can be easily manufactured in bulk quantities. Section 8.8 describes
nanocomposites based on smectite materials in greater detail.
Nanoparticles can also come in varying levels of treatments. Various
nanoparticles can be obtained that, for example, already have
hydrophobic or hydrophilic properties (see Chapter 8) useful in a
wide range of applications. Typically, when obtained from a manufacturer, nanoparticle batches may need to be further processed
via application of surfactant coatings, ultrasonification, milling, or
other processes because of their inherent tendency to agglomerate
or attract moisture.
Carbon nanotubes for applications are available in a wide variety
of single-walled (SWNT) and multiwalled (MWNT) forms, including different lengths, diameters, and purities. A primary quality and
cost issue is purity. Depending on the synthesis process used, purified forms are characterized by descriptions such as “95 wt%” or
“60 wt%,” which simply refers to the actual percentage by weight
of nanotube content within a unit weight of a gram of nanotube
material. Other constituents might include ash, amorphous carbon,
residual catalyst, or other materials. Some SWNT formulations
can also include some percentage of MWNTs. Obviously, higher
purity forms have more effective properties. Cost-per-gram values,
however, are invariably higher than lower purity forms. Lower purity
and lower-cost forms, however, can be suitable for many bulk applications. Most commercialization has been with MWNTs. SWNTs
are available but often at higher unit prices. Typical diameters for
available SWNTs are on the order of 1–2 nm, and common lengths
are on the order of 10–50 um, although there is variation in these
numbers as well. Special short nanotube forms are also available
that are on the order of 0.3–5 um. Outer diameters of common
MWNTs are on the order of 5–15 nm, with inside diameters on the
order of 2–8 nm. Several walls are common. Short-form MWNTs
often have larger outer diameters (20–50 nm or so) and somewhat
larger inner diameters than longer forms.
Incorporating carbon nanotubes into other matrix materials to form
nanocomposites has often proven difficult because of the surface
chemistry of the carbon. Problems include achieving uniform dispersions and poor adhesion with the primary matrix. Many highly