Future Trends - Polymers in a Marine Environment - page 181

luorescent dyes. The arrangement of microorganisms can be visualised by the optical
sectioning of the bioilm. This provides information regarding their interactions with
the substratum. CLSM can be used in real time and allows visualisation of both
adherent cells and the local polymer surface. CLSM does not require any sample
processing unlike SEM and can image both cells and the substrate [19]. The main
drawback of this technique is the cost, the use of dyes and the limitation in excitation
wavelengths produced with common lasers. The excitation wavelength range is
very narrow and is expensive to produce in the ultraviolet region and because of
this many of the traditional luorophore probes that are available have little use in
CLSM. Advances in luorophore probe design, and utilisation of low cost high power
diode laser systems that produce shorter wavelength spectrum lines will be the future
research in the CLSM technique. At present its use is limited to research laboratories.
Application of CLSM in the ield is not possible because sample preparation takes
a long time.
Chemical spectroscopy at the surface of a specimen provides qualitative and semi-
quantitative information on the nature of deterioration and the type of microorganisms
involved. Infrared (IR) absorption spectroscopy is a well-established method for
studying polymers and other materials. It is a sensitive and eficient technique to
examine the functional groups associated with oxygen [20]. Any elimination or
addition or changes in functional groups of the polymers because of deterioration can
be identiied using FTIR. Aerobic degradation of polyethylene leads to a number of
carbonyl groups with absorption bands in the region of 1,800−1,675 cm -1 . Absorption
bands because of hydroxyl species are seen at 3,600−3,200 cm -1 and change in vinyl
groups is observed as a pair of bands occurring at 990 and 910 cm -1 [20, 21].
In addition to transmission spectroscopy, attenuated total relection spectroscopy
(ATR), also referred to as internal relection spectroscopy, allows the study of the
surface of materials. ATR probes the surface layer between 0.3 and 5μm over the
range 4,000−400 cm -1 [20]. Raman spectroscopy provides higher lateral spatial
resolution than is achievable with FTIR spectroscopy. But it is costly and it generally
cannot compete with chromatographic techniques for quantitative analysis. Highly
pigmented or degraded samples often burn in the laser beam or luoresce. Moving the
excitation wavelength towards the deep red or near IR helps to reduce the problem,
but luorescence is still a problem. Determination of degradation and measurement
of thin (<<1 μm) surface coatings and treatments on bulk polymers are dificult [22].
Although IR spectroscopy is a superior tool in polymer analysis, its use is severely
restricted by the multi-component nature of polymer samples, presence of stabilisers
and degradation products and it becomes extremely dificult to interpret the spectra.
In such cases a combination of IR spectroscopy with chromatography can yield very
good results. This improved combined technology can help to determine the mass