with nanoscale dimension. Nanotoxicity is now a term describing the
negative health consequences of some toxic nanomaterials.
To put the nanoscale in perspective, consider the size of a hydrogen atom.
You may have learned from introductory physics or chemistry that the
Bohr radius (the distance from the 1s electron to the central proton in
hydrogen) is about 52.0 pm, or roughly 0.05 nm. This distance arguably
represents the lowest limit with respect to atomic distances. Atoms and
their ions vary in size between the Bohr radius and about 0.3 nm. This
range represents the atomic scale. The hydrogen molecule, H 2 , has a
proton-proton distance (bond length) of about 0.07 nm. The much larger
I 2 molecule has a bond length of about 0.3 nm, and the diameter of
the benzene ring is about 0.5 nm. The size of molecules increases rapidly
with structural complexity. The diameter of a DNA double helix is about
2 nm. The polyatomic molecule dodecanol, CH 3 (CH 2 ) 10 CH 2 OH, also has
a length approaching 2 nm. If 48 such molecules were stacked together
as shown in Figure 1.3, then it is conceivable that an aggregate of length
~10 nm and height ~10 nm could be formed. Nanostructures may be
comprised of thousands of molecules, resulting in aggregates on the
scale of tens to hundreds of nanometers. Furthermore, macromolecular
systems such as polymers and proteins have average sizes (hydrodynamic
radii) approaching 10 nm; the aggregation of such molecules may result
in structures on the scale of micrometers.
There is no clear boundary between what one considers the molecular
scale and the nanoscale that characterizes aggregates of molecules. The
distinction depends on the size of the smallest dimension of the discrete
units (molecules or aggregates thereof) within the system; a nanosystem
could consist of a large collection of small molecules or a few larger ones.
It is sufficient to say that the field of nanotechnology or nanoscience deals
with the manipulation and control of structures of a length scale with at
least one dimension that is 1000 nm or smaller. The same definition holds
for solid materials without a discrete covalent structure (e.g., metals and
inorganic crystals). The science is fascinating because physical and
chemical phenomena at these scales are markedly different from those
observed in bulk (macroscopic) matter. Sometimes the difference is just a
result of the much larger surface-area-to-volume ratio as particles shrink
in size.
Consider a soccer ball, which has a radius of 11 cm and a C 60 fullerene
(also known as a buckyball), a spherical molecule composed entirely of
sp
2 hybridized carbon atoms, which has a radius of 0.5 nm. Given that the
CHAPTER 1: A Brief Introduction to Nanoscience
6
negative health consequences of some toxic nanomaterials.
To put the nanoscale in perspective, consider the size of a hydrogen atom.
You may have learned from introductory physics or chemistry that the
Bohr radius (the distance from the 1s electron to the central proton in
hydrogen) is about 52.0 pm, or roughly 0.05 nm. This distance arguably
represents the lowest limit with respect to atomic distances. Atoms and
their ions vary in size between the Bohr radius and about 0.3 nm. This
range represents the atomic scale. The hydrogen molecule, H 2 , has a
proton-proton distance (bond length) of about 0.07 nm. The much larger
I 2 molecule has a bond length of about 0.3 nm, and the diameter of
the benzene ring is about 0.5 nm. The size of molecules increases rapidly
with structural complexity. The diameter of a DNA double helix is about
2 nm. The polyatomic molecule dodecanol, CH 3 (CH 2 ) 10 CH 2 OH, also has
a length approaching 2 nm. If 48 such molecules were stacked together
as shown in Figure 1.3, then it is conceivable that an aggregate of length
~10 nm and height ~10 nm could be formed. Nanostructures may be
comprised of thousands of molecules, resulting in aggregates on the
scale of tens to hundreds of nanometers. Furthermore, macromolecular
systems such as polymers and proteins have average sizes (hydrodynamic
radii) approaching 10 nm; the aggregation of such molecules may result
in structures on the scale of micrometers.
There is no clear boundary between what one considers the molecular
scale and the nanoscale that characterizes aggregates of molecules. The
distinction depends on the size of the smallest dimension of the discrete
units (molecules or aggregates thereof) within the system; a nanosystem
could consist of a large collection of small molecules or a few larger ones.
It is sufficient to say that the field of nanotechnology or nanoscience deals
with the manipulation and control of structures of a length scale with at
least one dimension that is 1000 nm or smaller. The same definition holds
for solid materials without a discrete covalent structure (e.g., metals and
inorganic crystals). The science is fascinating because physical and
chemical phenomena at these scales are markedly different from those
observed in bulk (macroscopic) matter. Sometimes the difference is just a
result of the much larger surface-area-to-volume ratio as particles shrink
in size.
Consider a soccer ball, which has a radius of 11 cm and a C 60 fullerene
(also known as a buckyball), a spherical molecule composed entirely of
sp
2 hybridized carbon atoms, which has a radius of 0.5 nm. Given that the
CHAPTER 1: A Brief Introduction to Nanoscience
6