Diverse Applications of Surface and Colloid Chemistry in Science and Industry - Surface and Colloid Chemistry: Principles and Applications - page 224

Another area of much interest is the adhesion of ice to solids. This system is
obviously of much interest in general everyday phenomena (tire friction on road
surfaces, ice on metal surfaces, ships, etc.). Especially of interest is the adhesion
of ice on ships sailing in the cold areas, and on wings of airplanes. Investigations
have shown that the adhesive bonds between clean metal surface and ice are very
strong. When the ice is removed by force, it breaks, leaving a thin layer of ice on
the solid layer.
Further, a large attraction exists between two smooth solid surfaces if a drop of
liquid (say, water and two glass plates). It is thus obvious that the peeling energy of
two plates in this system will increase if a glue or similar substance is used (instead
of water).
10.5.1.3 Surface coatings of Solids
The properties of solid surfaces can be changed by coating while the rest of the mate-
rial remains unchanged. Such coatings are numerous, and new applications are being
continuously developed.
A recent product called Sol-Gel (solution and gelling) coating has as its principle
the following:
A solid surface is coated with a metal alkyl-oxide solution.
The metal alkyl-oxide is hydrolyzed and forms a gel.
The gel forms a network on the solid surface.
The gel is exposed to high temperature, leaving behind a transparent coating.
The alkyl oxide (Si[RO] 4 ) n , is converted by a catalyst and, after dealkylation, it
forms a polymer of (Si[OH] 4 ) n . On heating and dehydration, a coating of (Si[O] 4 ) n
is obtained. The thickness of the coating on aluminum (or other metal surface) can
be 3 to 10 μm.
10.5.2 e m u l S I o n p o l y m e r I z a T I o n
Emulsion polymerization is one of the major examples where detergents are applied
to create microreactions. For instance, to polymerize styrene (which is insoluble in
water), an initiator is added to the aqueous phase. The polymer (polystyrene [PS]) is
formed, and the suspension is stabilized by using suitable emulsifiers. The latex thus
formed is used in various industrial applications.
Polystyrene can be prepared as follows: A mixture of styrene, detergent
(Na-dodecanoate), and water is agitated ultrasonically to produce a fine emulsion.
On the addition of hydrogen peroxide (initiator), PS is obtained as a polymer, which
can be extracted after filtration. The polymer molecular weight is determined by
various methods (such as light scattering and osmotic pressure).
10.5.2.1 Polymer colloidal Systems
Polymers play a important role in both biological and industrial systems. Recently,
there has been much interest in developing methods to apply polymer colloidals. The
principle is to employ polymer colloidal beads instead of using large solid particles.