Chemistry Reference
In-Depth Information
systems have recently been shown to be ideal candidates for various industrial
applications because they have excellent stiffness and strength, high heat distortion
temperature, and good scratch resistance
[35
37]
. Polymer nanocomposite thin
films have also demonstrated improved adhesive properties. As a result, polymer
nanocomposites have started to gain commercial acceptance in practical applica-
tions recently: for example, used in materials designing for microelectronics,
optics, and coatings. In view of the strong industrial-application potential, consider-
able research and development interests have been generated, in both academic and
industrial communities, to study polymer nanocomposites in relation to the selec-
tion and modification of nano-sized inorganic fillers for various polymer matrices
of interest and to the determination of the optimum conditions for processing such
materials
[38
40]
. The two classes of nano-sized inorganic fillers that have been
extensively used and studied are clays and carbon nanotubes. Clays belong to the
platelet type of fillers that have nanometer thickness and can be exfoliated, while
carbon nanotubes have diameter in the nanometer range. Since such fillers possess
high surface to volume ratios, they would greatly enhance the mechanical proper-
ties even though a low dosage of such fillers is used. This is because nano-sized fil-
lers, either in the platelet or tube form, have a geometrical length scale comparable
to the size of polymer molecules. As a result, this produces, for example, an
excluded volume interaction with a flexible polymer that strongly reshapes the
overall polymer conformation (Section 1.14). The entropy loss of the flexible
chains in the vicinity of the nano-sized fillers is one of the physical reasons to drive
the phase separation. The free volume available to nano-sized particles and the con-
formational change of the interacting polymer molecules, especially in the interfa-
cial region, are the critical controlling factors for the surface modification, leading
to enhanced mechanical properties
[20,41,42]
.
PROBLEMS
5-1 Toluene (molecular weight
0.87 g/cm
3
) boils at 110.6
C
at 1 atm pressure. Calculate its solubility parameter at 25
C. [The
enthalpy of vaporization can be approximated from the normal boiling
point T
b
(K) of a solvent from
5
92, density
5
Δ
:
:
020T
b
2
2950 cal/
mol (J. Hildebrand and R. Scott, The Solubility of Nonelectrolytes, 3rd ed,
Van Nostrand Reinhold, New York, 1949).]
H
ð
25
C
Þ
5
23
7T
b
1
0
5-2 Calculate the solubility parameter for a methyl methacrylate
butadiene
copolymer containing 25 mol% methyl methacrylate.
5-3 Calculate the solubility parameter for poly(vinyl butyl ether). Take the
polymer density as 1.0 g/cm
3
.
5-4
(a) A vinyl acetate/ethylene copolymer is reported to be soluble only in
poorly hydrogen-bonded solvents with solubility parameters between 8.5
