C hapter 10 nanomaterial product Forms and Functions
442
through. Yet others are designed to prevent gases escaping from
containers. Other sealants are designed to prevent staining of materials. Some are intended to prevent the growth of bacteria within
the surface pores of the host material. The list is virtually endless.
Each application needs particular properties in a sealant. Generally,
the sealant in its solid state must be stable and not break down
or dissolve when subjected to the liquid or gas against which it
is intended to serve as a barrier. Thus a sealant might need to be
resistant to simple water, as is the case in many architectural applications. It might need to be resistant to specific kinds of chemicals,
as is the case in many sealants developed to prevent staining of the
host material. Corrosion resistance or resistance to UV rays might
be needed. The sealant needs to be able to bond securely to the
surface of the host material. If the sealant is solvent based, the
solvent must not be deleterious to the host material. Many sea lants need to have some degree of abrasion resistance, toughness,
or scratch resistance so that their sealing properties are not lost
during use. Depending on the application, the sealant might
need to change from a fluid to a hard solid film (as in common
paints) or have an initial state that is viscous enough to be applied
by squeezing and that remains highly flexible when hardened. The
rheology of the sealant is thus very important. Sealants that serve
joining or gap-filling functions often need to be flexible because
relative movements often occur in adjacent materials. Many current
sealants are made of silicones, polyurethanes, polysulfides, latexes,
or vinyl plastisols.
Particle sizes and distributions have long been known to affect the
rheology of sealants; hence the use of nanoparticles offers interesting opportunities to improve sealants. Most nanosealants now
developed take the form of nanocoatings, nanofilms, or nanopaints, each of which is discussed more extensively elsewhere in
this chapter. Many nanosealants take the form of polymer-matrix
nanocomposites. Polymers with embedded nanoclay particles
are common. Nanosized silicates are often used. Small amounts
(around 2% by volume) of silicate nanoparticles to a polyimide
resin can increase strengths considerably (around double). Resulting coating thickness can also be reduced in comparison with
traditional coatings, since the solids content of nanoadhesives is
lower and thinner. Thinner coatings can be produced that have
good coating uniformity. As with other nanocoatings (see previous section), nanosealants can also be made optically transparent
or translucent due to the small size of the particles relative to the
400–700 nm wavelengths of visible light.
442
through. Yet others are designed to prevent gases escaping from
containers. Other sealants are designed to prevent staining of materials. Some are intended to prevent the growth of bacteria within
the surface pores of the host material. The list is virtually endless.
Each application needs particular properties in a sealant. Generally,
the sealant in its solid state must be stable and not break down
or dissolve when subjected to the liquid or gas against which it
is intended to serve as a barrier. Thus a sealant might need to be
resistant to simple water, as is the case in many architectural applications. It might need to be resistant to specific kinds of chemicals,
as is the case in many sealants developed to prevent staining of the
host material. Corrosion resistance or resistance to UV rays might
be needed. The sealant needs to be able to bond securely to the
surface of the host material. If the sealant is solvent based, the
solvent must not be deleterious to the host material. Many sea lants need to have some degree of abrasion resistance, toughness,
or scratch resistance so that their sealing properties are not lost
during use. Depending on the application, the sealant might
need to change from a fluid to a hard solid film (as in common
paints) or have an initial state that is viscous enough to be applied
by squeezing and that remains highly flexible when hardened. The
rheology of the sealant is thus very important. Sealants that serve
joining or gap-filling functions often need to be flexible because
relative movements often occur in adjacent materials. Many current
sealants are made of silicones, polyurethanes, polysulfides, latexes,
or vinyl plastisols.
Particle sizes and distributions have long been known to affect the
rheology of sealants; hence the use of nanoparticles offers interesting opportunities to improve sealants. Most nanosealants now
developed take the form of nanocoatings, nanofilms, or nanopaints, each of which is discussed more extensively elsewhere in
this chapter. Many nanosealants take the form of polymer-matrix
nanocomposites. Polymers with embedded nanoclay particles
are common. Nanosized silicates are often used. Small amounts
(around 2% by volume) of silicate nanoparticles to a polyimide
resin can increase strengths considerably (around double). Resulting coating thickness can also be reduced in comparison with
traditional coatings, since the solids content of nanoadhesives is
lower and thinner. Thinner coatings can be produced that have
good coating uniformity. As with other nanocoatings (see previous section), nanosealants can also be made optically transparent
or translucent due to the small size of the particles relative to the
400–700 nm wavelengths of visible light.