O o d h e a d p u b L i s h I n g L i m I t e d

particle (Jiang et al., 2006), giving a decrease in melting point. Buffat and
Borel (1976) reported melting points for gold nanoparticles as low as 600 K
for a 2 nm particle compared with the bulk melting point of 1336 K. Similarly
catalytic activity of gold, normally considered an inert metal, has been reported
for nanoparticles (Grisel et al., 2002; Hurata, 2004) supported on metal
oxide or activated carbon surfaces.
An emerging technology that may have application to wool is the nano-
emulsion (Mason et al., 2006). Nano-emulsions are conventional emulsions
on the nano-scale, that is with radii in the range 1–100 nm. Nano-emulsions
differ from micro-emulsions, which can have similar dimensions, in a number
Table 10.2 Calculated shape factors and percentage surface atoms for
nanoparticles of different shapes with nominal diameters in the range 5 to 100 nm,
assuming an atom diameter is 0.32 nm (silver)
Shape
α
N/n (%) for nominal diameter (nm)
5
10
20
50
100
Sphere
1
26
13
6
3
1
Rod
1.167
30
15
7
3
1
Tetrahedron
1.49
38
19
10
4
2
Disc*
2
37
18
9
4
2
*Radius to height ratio 2.
Sphere
Rod
Disc
Tetrahedron
0
5
10
15
20
D (nm)
N
/n
 (%)
100
80
60
40
20
0
10.2
 The percentage surface atoms of nanoparticles of different
shapes calculated using equation 10.1 where 
D
 is the nominal
diameter of the particle and 
d
 is the diameter of silver.
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252
of important characteristics outlined in 
Table 10.3.
 Formation of nano-emulsions
is usually by shear-induced rupture of conventional emulsions. Very high
shear is applied to an emulsion containing excess surfactant. As the droplets
rupture, they are stabilised by a coating of surfactant. As droplets approach
each other in the emulsion, the surfactant films repel each other, preventing
contact and coalescence. To achieve stable films, an equilibrium surface
density of surfactant is needed. Given the very high surface area to bulk ratio
of nanoparticles, surfactant concentrations are usually in excess of the critical
micelle concentration. Nano-emulsions are therefore mixtures of emulsion
droplets and surfactant micelles.
10.1.3 Introduction to nanostructured films
Nanostructured films are a new technology based on self-assembled monolayers
(SAMs) where a single layer of a chemical or molecule is absorbed onto the
surface of the fibre. These films differ from traditional textile coatings in
that their thickness is in the nanometre range, they are often more even and
develop higher film densities. Films can be built in multi-layers, each a
mono-layer of the materials being applied as represented by 
Fig. 10.3.
 Often
the layers contain different materials to achieve the final desired textile
property.
The production of SAMs on textiles usually required a pre-treatment of
the fibre to produce a surface suitable for self-assembly. For example to
achieve a continuous monolayer of a charged molecule, an evenly distributed,
dense, opposite ionic charge is needed on the textile fibre surface. Electrostatic
interactions then build the monolayer on the surface. Techniques that have
been used to produce the charge in the fibre surface include plasma, ion
beam or chemical treatment such as oxidation or reduction.
Table 10.3 Comparison of nano-emulsion and micro-emulsion properties
Property
Nano-emulsion
Micro-emulsion
Droplet radius
2–100
 
nm
2–300
 
nm
Formation
Mechanical dispersion
Self-assembled thermodynamic
phases
Shape
Spherical
Various including spherical, laminar
sheet, hexagonal packed columns
Surfactant
Soluble in bulk phase
Soluble in both phases
Lower concentration
High concentration
Solubility of
Low
Relatively high
dispersed phase
in bulk phase
Surface tension
High
Low
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Nanostructured films can be made self-repairable by engineering a storage
source within the nanolayers. When material in the top layer is removed by,
for example, abrasion, electrostatic interactions will try to neutralise the
charge on the surface where the material was removed. These interactions
will result in material moving from the storage source to cover the exposed
charge. Unlike traditional coating that loose their effectiveness as the coating
material is removed, the self-repair effect of SAMs can extend the life of the
coating and maintain the finish properties throughout the garment life.
10.1.4 Advantages of nanotechnology on textiles
Nanotechnology has been applied to textiles at all stages from fibre production
to consumer products. This section will summarise general applications of
nanotechnology to textiles. The next section will describe specific applications
to wool.
Fillers have been used for some time to produce composite fibres with
improved properties such as increased strength. The high surface area and
strong interactions of nanoparticles with polymers can be used to further
enhance composite fibre properties. In particular, nanoparticles have been
used to significantly improve fibre strength, stiffness and solvent resistance
and reduce shrinkage and flammability.
The most common nanoparticle in use is clay. Clay nanoparticles are
sheets of hydrous aluminosilicate that typically have a negative charge on
Fibre surface
10.3
 Representation of a two-layered self-assembled monolayer fibre
coating.
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Advances in wool technology
254
the face and positive charge on the edge. Clay has been used to introduce dye
sites into polypropylene (Fan et al., 2003), to improve the flame resistance
of nylon and to improve the heat resistance of polyester and nylon fibres.
The use of nanoparticles in these applications reduced the mass of clay
required to achieve the effect when compared to larger filler particles.
Self-cleaning cotton fabrics have been developed using titanium dioxide
nanoparticles bound to the surface of the fibres (Bozzi et al., 2005a; Meilert
et al., 2005). When titanium dioxide is exposed to light in the presence of
oxygen and water vapour highly oxidative radical species such as 
HO
2
–