chimisical

title-2475963

Mon, 18 Jun 2007 18:35:44 +0200

Applications of conductive polymers
The commercialisation exemplified by the following list of materials illustrates the effects of Heeger’s,
McDiarmid’s and Shirakawa’s work on the later development of conductive polymers. The principal interest
in the use of polymers is in low-cost manufacturing using solution-processing of film-forming polymers. Light
displays and integrated circuits, for example, could theoretically be manufactured using simple inkjet printer
techniques. 6-10
Doped polyaniline is used as a conductor and for electromagnetic shielding of electronic circuits. Polyaniline
is also manufactured as a corrosion inhibitor.
Poly(ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid is manufactured as an antistatic
coating material to prevent electrical discharge exposure on photographic emulsions and also serves as
a hole injecting electrode material in polymer light-emitting devices.
Poly(phenylene vinylidene) derivatives have been major candidates for the active layer in pilot production of
electroluminescent displays (mobile telephone displays).
Poly(dialkylfluorene) derivatives are used as the emissive layer in full-colour video matrix displays.
Poly(thiophene) derivatives are promising for field-effect transistors: They may possibly find a use in
supermarket checkouts.
Poly(pyrrole) has been tested as microwave-absorbing “stealth” (radar-invisible) screen coatings and also as
the active thin layer of various sensing devices.
Other possible applications of conductive polymers include supercapacitors and electrolytic-type capacitors.
Some conductive polymers such as polyaniline show a whole range of colours as a result of their many
protonation and oxidation forms. Their electrochromic properties can be used to produce, e.g. “smart
windows” that absorb sunlight in summer. An advantage over liquid crystals is that polymers can be
fabricated in large sheets and unlimited visual angles. They do not generally respond as fast as in electron-gun
displays, because the dopant needs time to migrate into or out from the polymer - but still fast enough for
many applications. We shall return to electroluminescent polymers below.

Synthesis and processing
There is often a big step between the first chemical synthesis of a molecular substance and the development of
processing methods for practical applications. The first polyacetylenes were obtained from acetylene which
polymerized in the presence of a catalyst.
Of the two polyacetylene conformations, cis and trans, the trans form is thermodynamically more stable.
Shirakawa’s polyacetylene had mainly the cis form and was a copper-coloured flexible film which could be
converted to the silvery trans form by heating above 150° C. X-ray diffraction and scanning electron
microscopy showed that such films were polycrystalline matted fibrils. These materials were semiconductors,
the trans isomer with higher conductivity (4.4 x 10–3 S m–1) than the cis (1.7 x 10–7 S m–1). Shirakawa and
Ikeda had noticed that when (CH)x films were exposed to bromine or chlorine at room temperature for a few
minutes, there was a dramatic decrease in the infrared spectrum (decrease in transmission between 4000 and
400 cm–1). By contrast, complete halogenation, resulting in (CHBr)x, gave high IR transmission and a white
film. However, they did not investigate the corresponding conductivity, so it remained for Heeger and
McDiarmid, in collaboration, to discover the effect of doping.
The halogen doping that transforms polyacetylene to a good conductor of electricity is oxidation (or pdoping).
Reductive doping (called n-doping) is also possible using, e.g., an alkali metal.
[CH]n + 3x/2 I 2 [CH]n x+ +xI3
– oxidative doping
[CH] n + xNa [CH]n
x– + xNa + reductive doping
The doped polymer is thus a salt. However, it is not the counter ions, I3
– or Na+, but the charges on the
polymer that are the mobile charge carriers (see Mechanism of polymer conductivity, below).
By applying an electric field perpendicular to the film, the counter ions can be made to diffuse from or into
the structure, causing the doping reaction to proceed backwards or forwards. In this way the conductivity can
be switched off or on.
Processing polyacetylene and many other polymers such as polypyrrole and polythiophene was for a time
ruled out because of their failure to melt or to dissolve in any solvent. Ingenious methods developed over the
years have, however, made processing possible. In 1980, James W. Feast and co-workers at the University of
Durham synthesised polyacetylene from a soluble precursor polymer, poly(7,8-bis(trifluoromethyl)-
tricyclo[4.2.2.0]deca(3,7,9-triene). Upon heating, the dissociation product bis-trifluoromethylbenzene
evaporates to leave a polyacetylene film which is much denser than Shirakawa’s material. Another important
invention was Caltech researchers Robert H. Grubbs’ and co-workers’ production of polyacetylene by
metathesis polymerisation of cyclooctatetraene in the presence of a titanium alkylidene complex as catalyst.
Grubbs’ polyacetylene reportedly had a conductivity of about 35,000 S m–1, but was as intractable and
unstable as other polyacetylenes. However, by attaching alkyl substituents to the cyclooctatetraene molecule,
Grubbs and his group managed to prepare a soluble substituted polyacetylene that could be cast in any form
desired, although the alkyl substituents seemed to lower the conductivity considerably.
Another advance in electrical properties, but unfortunately not in processing, came in 1987 when BASF
(Badishe Anilinen und Soda Fabrik) scientists Herbert Naarman and Nicholas Theophilou in West Germany
developed a polymerisation method based on Shirakawa’s method, at 150°C. When doped, their material was
claimed to have a conductivity of more than 107 Sm–1, i.e., of the same order as that of copper’s. This
polyacetylene may have a higher conductivity because of its greater order and fewer defects than previous
preparations.
Other polymers with interesting properties have been developed: added to those already listed are
polyparaphenylene, polyparaphenylenevinylene, polypyrrole, polythiophene and polyaniline and their
derivatives. These materials generally show much lower conductivity than polyacetylene, ca 102–104 Sm–1,
which is more than enough for many purposes. These polymers have the advantage of relatively high stability
and processibility, e.g. poly(3-dodecylthiophene), can be prepared as a melt-spun, strong film in the undoped
state and then doped to a conductivity of 105 Sm–1.
Mechanism of polymer conductivity – role of doping
In a metal there is a high density of electronic states with electrons with relatively low binding energy, and
”free electrons” move easily from atom to atom under an applied electric field. The conductivity of the
material can be measured with standard procedures, a value for metallic copper around 108 S m–1 having been
measured.

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Geochemistry

Mon, 18 Jun 2007 17:50:46 +0200

OBSERVATIONS
All the descriptions to follow refer to the secretory epithelium alone. In general,
regions A, B, and D showed reactions in common while regions C and E responded
differently but like each other.

The entire secretory portion of the oviduct stained intensely with the PAS
technique. The ostial region, which presumably is relatively non-secretory, and is
characterized by very low epithelium, stained pink. The A region stained a bright
purplish red, whereas regions B, C, D, and E stained a distinctly different shade
which might be called reddish purple. The staining of all portions remained un
changed after treatment with saliva or malt diastase.
There was a marked difference in the response of the several regions to
toluidine blue. The staining of the ostial region was orthochromatic. Region A
showed violet to purple metachromasia in all cases. This region in the one post
breeding animal also showed rnetachromasia after all fixatives ; however, the color
produced in lead acetate-fixed material was chiefly blue. The metachromasia of
region A is alcohol-fast. After destaining for periods up to one and one-half hours
in 70% alcohol, the major part of the stain was removed, yet the violet meta
chromasia persisted. Region B usually stained an orthochromatic dark blue, but
in some cases strong tinges of purple were seen. There was, however, no difficulty
in distinguishing between regions A and B following this stain. Sections from
region C showed little or no cytoplasmic stain, and that which was present was
usually a very light blue. In a few cases there were traces of metachromasia. The
staining reaction of region C, then, was a striking contrast to that of either A or B.
Preparations from region D were variable in their response to toluidine blue, but,
for the most part, the cytoplasm stained a pale blue, and nearly all preparations
showed at least some violet rnetachromasia. The cytoplasm in cells of region E
stained a pale blue, with no trace of metachromasia.
The reaction of the several regions to alcian blue was also varied. The cyto
plasm of the secretory cells of region A stained a bright sky blue, as did that of
region B. The cells of region C, however, stained only lightly. In many cases the
stain in this region was so light as to be only barely detectable. The cytoplasm of
the cells of region D stained sky blue, similar to the reaction of regions A and B,
while that of region E was extremely lightly stained, similar to the reaction of the
cells of region C.
Although only one slide from each region was used, it may be worthwhile to
mention that results with Hale's technique were essentially the same as@those with
alcian blue, but gave promise of less clear differentiation between the regions.
Treatment with hyaluronidase failed to alter the strong violet metachromasia of
region A, or, in the few tests run, the staining reactions of regions B, C, or D.
Similarly, treatment with ribonuclease failed to alter the staining reaction of the
cytoplasm of the cells of either region A or region B. No other regions were tested.
DIscussIoN
These resultshow the secretingepitheliumof the newt oviductto be richin
polysaccharide, apparently distributed qualitatively among the several regions. The
histochemical differences follow the zonation which is anatomically demonstrable.
It is clear that the epithelium contains polysaccharide other than glycogen, since the
PAS reaction of all regions remains unchanged after glycogen digestion. The
PAS technique allows but little differentiation between the regions, however, since
region A is the only one which stains in a fashion distinctly different from the
others.

A striking parallelism between metachromatic staining with toluidine blue and a
positive reaction with alcian blue has been previously shown (Vialli, 195 1 ; Wagner
and Shapiro, 1957) . This finding was clearly borne out in our material. Un
fortunately, the metachromatic staining reaction has had a long history of confusion
as to application and interpretation, but â€oe¿_trumeâe€t•achromasia, in the sense of Lison
( 1953) or Kramer and Windrum (1955) , generally is taken to indicate the presence
of sulphated mucopolysaccharides, though nucleoprotein has also been reported to
stain metachromatically at times (Wiame, 1946 ; Penney and Balfour, 1949 ; Kramer
and Windrum, 1955). The occurrence of alcohol-resistant beta (violet) meta
chromasia. such as encountered in our material, is strong presumptive evidence of
nucleoprotein, according to Kramer and Windrum ( 1955 ) . However, we found no
change in staining reaction with toluidine blue or with pyronine following treatment
with ribonuclease. Results of several workers (especially Vialli, 1951 ; Lison,
1954 ; Mowry, 1956 ; and Wagner and Shapiro, 1957) indicate that alcian blue
positivity is good evidence for the presence of acidic carbohydrates. Combining the
evidence, then, the distinctive staining reactions of region A, in particular, and
probably those of regions B and D, would seem most likely attributable to the
presence of acid polysaccharide. The results with hyaluronidase seem to rule out
the possibility that the distinctive reactions, at least of region A, are due to hyalu
ronic acid or anything very closely related to it.
Similar findings with respect to the PAS reaction, toluidine blue metachro
masia, and hyaluronidase treatment have been reported for the Japanese newt,
Triturus pyrrhogaster, by Kambara (1956a, 1956b, 1957a, 1957b). Due to lack of
certainty as to corresponding regions in oviducts of the two species, it is not possible
to make more than a rough comparison of our results with those of Kambara, but
our results show strong general agreement with his.
The most probable conclusion to be drawn, at present, from the findings of
distinctive reactions along the oviduct is that the differential staining is due to the
presence of acid polysaccharide in regions A, B, and D only, with the positive PAS
reaction of regions C and E due perhaps to neutral polysaccharide. However,
quantitative differences alone might account for the results. Since PAS positivity
and strong metachromasia do not tend to coexist, it is worthwhile to note the sug
gestion of Hale (1957), that the combination may be caused by the presence of two
distinct substances. Our evidence, coupled with evidence from studies on the
chemistry and physiology of egg jellies themselves (Immers and Vasseur, 1949;
Vasseur, 1952; Kelly, 1954; Minganti, 1955; RunnstrÃ¶m and Immers, 1956),
leads to the conclusion that the metachromasia and alcian blue positivity of regions
A, B, and D are probably due to the presence of a heparin-like compound. If this
is the case, and if, as seems quite probable, the innermost layer secreted about the
egg contains the substance, it may very likely have significant effects upon the
physiology of the maturing oocyte. The effects of heparin and heparin-like com
pounds on the physiology of cells, especially egg cells, have been studied for years,
particularly by Heilbrunn and his co-workers (see Heilbrunn, 1956, for references).
In addition, one of us (Humphries, 1955, 1958) has obtained results which have
led to the hypothesis that the oviducal jelly plays an important role in the natural
blockage of the second meiotic division in the oocyte prior to fertilization. Oocytes
never exposed to oviducal jelly, such as coelomic eggs and eggs stopped experi

mentally in the ostial (non-secreting) part of the oviduct, are capable of completing
meiosis, while eggs exposed to jelly have in no case been seen to advance beyond
the normal stage of blockage, metaphase II. It is perhaps significant that as the
oocyte enters the first secreting portion of the oviduct it is completing the first
meiotic division or beginning the second (Humphries, 1956) . One of the possible
explanations of the meiotic blockage is that the oviduct secretes an antimitotic
substance. This possibility led to the present study of the histochemistry of the
oviduct, with the aim of gaining information concerning the secretions of particularly
the more anterior regions. Since heparin-like substances have been shown to act as
antimitotics (see especially Heilbrunn, 1956, and Heilbrunn et al., 1957) , the dis
covery that oviducal region A apparently produces a heparin-like compound is in
good agreement with the hypothesis. If this type of antimitotic is involved, how
ever, it is surprising that blockage of the division occurs at metaphase, rather than
prior to spindle formation.
SUMMARY
1. Application of some techniques of polysaccharide histochemistry to the oviduct
of the newt showed a histochemical differentiation of the secretory epithelium cor
responding to the grossly and histologically demonstrable zonation of the oviduct.
All regions responded positively to the PAS technique. No difference was detected
in sections previously exposed to glycogen digestion methods. Regions designated
A, B, and D were metachromatic with toluidine blue and reacted positively to alcian
blue.
2. The most probable explanation of the differences in staining reaction seems
to be the presence of an acid polysaccharide, probably a heparin-like compound, in
regions A, B, and D, and its absence (or much lower concentration) in regions C
and E.
3. The possible significance of the findings relative to the physiology of the
oocyte, particularly with regard to meiotic blockage, is discussed.
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