Chemistry Reference
In-Depth Information
of calculating the area of the image. Since the magnitude of the area/molecule of the
cholesterol molecule is known (40 Å
2
), this analysis can be carried out. In compari-
son to macro domains, molecular domains are measured as three-dimensional by
AFM. This indicates that such nanostructures can be investigated by using AFM.
Thus, in the future, any nanosurface analysis will be useful in understanding these
new technologies.
As compared to ordinary microscopes, SPM provides two- and three-dimen-
sional images. The 3D images allow one to see molecules with different diameters
(Birdi, 2002a).
10.3 druG delIvery deSIGn (ddd)
In pharmaceutics, a medicine is prescribed in a quantity that can be present in the
blood at a particular and sufficient concentration. If one considers some examples,
the range of concentration per doses (i.e., per tablet) may range from microgram to
1000 mg. Since many of medicinal molecules decompose in the body before reach-
ing the target (such as the liver, heart, or lungs), one uses a higher concentration (10
to 1000 times) than needed at the target. During the past decades, investigations
have been reported on designing drug delivery techniques that can reduce the initial
excess concentration.
10.4 SurFace and colloIdal aSPectS oF cement InduStry
Mankind has used some form of cement for thousands of years to build houses and
monuments. Some examples are the pyramids (3000 BC) and the Colosseum (2000
BC), indicating an early awareness of the role of surface and colloidal chemistry. In
modern times, besides small structures such as houses, the use of cement has been
widened to include very large constructions such as dams. The main aim of using
cement is to bind two bricks with a material consisting of very fine particles, and
which hardens after water has evaporated.
In general, there are two main
classes of constructional cements: nonhydraulic,
which do not set under water, and
hydraulic. Their composition can be indicated by
the following two examples:
(i) Plaster of Paris (CaSO
4
.
1
/2 H
2
O)
CaSO
4
.
1
/2 H
2
O + 1
1
/2 H
2
O ⇒ CaSO
4
.2H
2
O (gypsum)
(ii) Lime-based cement (CaO)
CaO + H
2
O ⇒ Ca(OH)
2
+ CO
2
→ CaCO
3
(calcite)
Nonhydraulic cements were among the most common of the ancient cements.
The relatively high solubilities of portlandite (Ca[OH]
2
) and gypsum means that they
deteriorate rapidly in moist or wet environments. Many decades ago, the Romans
used lime-based cements and mortars (cement plus sand) by ramming the wet pastes
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