Investigations on some selected conducting polymers and polymer ...

Chapter-L
polymeristaion, isomerization, Durham method, dehydrochlorination and
dehydration are used [9].
A variety of techniques can be employed to get conducting
polymers in thin film form. Solution casting, spin coating, plasma
polymerization and electro chemical polymerization are some of the
commonly used polymer thin film deposition techniques [9,34-37].
Solution cast films are prepared by dissolving definite amounts of the
polymer in a selected suitable solvent. The mixture is stirred for several
hours. The resulting solution is poured onto ultrasonically cleaned glass
plates and spread uniformly using doctor's blade technique. The film is
left to dry in a hot air/vacuum oven at about 70° C for one or two days.
Commonly used solvents are meta-cresol (m-cresol), N-Methyl
Pyrrolidinone (NMP), Para-cresol (p-cresol), Cyclohexanol and Xylene
[9,36-37]. Metacresol is preferred over the rest because of its better
solvation properties. Also the polymer-solvent interactions are greater
for the m-cresol solution compared to others[9,38].Still the solubility of
conducting polymers in organic solvents remains a lot to be improved,
the main reason being the rigid polymer back bone. The n conjugation
imparts stiffness to the polymer back bone which makes the polymer
intractable. The Il electron delocalization leads to large electronic
polarizability, giving rise to Il- Il interchain attraction. This favours
polymer aggregation rather than solvation. Also the rigidity of the
polymer back bone thus formed creates an unfavourable entropy for
solution. The polymer chains complexed with ionic dopants also
contain hydrophobic organic segments. It is very difficult to find