3.2. Morphology of NaHA before and after coupling reaction
The effect of coupling reaction can be confirmed by means of
the morphological observation by AFM. Figs. 3 and 4 show AFM
images of spin-coated films prepared from aqueous NaHA solutions
at 0.004 and 0.04 wt%, respectively, by comparison between complexes
without and with coupling reaction.NaHAmolecules formed
network domains with monomolecular and multimolecular thicknesses
for solutions at 0.004 and 0.04 wt%, respectively, according
to their section analyses. Because of intermolecular hydrogen bonding,
NaHA molecules attract each other to form domains, which
were dispersed as network films on a substrate, if the solution
is dilute. Larger amount of residues in NaHA molecules were
intermolecularly hydrogen-bonded in a concentrated solution, producing
larger network domains in comparison with those in a dilute
solution.