Bulk and surface characterization of the resultant nanocomposites
was carried out using a ThermoNicolet NEXUS 870 FTIR
spectrophotometer (Nicolet Instrument Corp., USA) integrated
with an IBM personal computer. The spectrophotometer was
equipped with a single reflection ATR accessory for reflection
mode. All the ATR spectra of PET/nano-silica nanocomposites
were normalized and were then subtracted from the spectra of
pure PET. Atomic force microscopy (AFM) was used to determine
surface topography and roughness of samples on a contact mode
SPM microscope (Park Scientific Instrument, Auto Probe CP
Model, Korea). Contact angle measurement and surface free
energy estimation of the nanocomposites were carried out at
room temperature on a Kruss G10 instrument of German origin.
Surface free energies of such nanocomposites were estimated by
the aid of Owens–Wendt method, utilizing the theory of adhesion work between solid and liquid phases from which
polar (gP
) and non-polar or dispersive (gD) surface free energies
could be derived. Water, diiodo-methane and benzyl alcohol were
used as probe liquids at 23 2 8C and 65% relative humidity. The
average contact angle from six different locations on each nanocomposite
was determined and the experimental uncertainty was within
28. Surface morphology analyses of the nanocomposite were carried
out by means of a scanning electron microscope (SEM, Philips, XL30,
The Netherlands). Samples were covered with an Au layer under
vacuum conditions prior to measurement. The presence of silica on
each nanocomposite surface was also determined by energy dispersive
X-ray microanalysis (EDX) attached to the SEM. The reflectance and
absorbance of each sample were recorded using a Cary 500 UV–Vis–NIR
spectrophotometer from Varian (USA) integrated with an IBM personal
computer.