SPI Replicating Tapes and Sheets
Instructions for use
All SPI Replicating Tapes and Sheets products are made from the same high
purity, highly homogeneous cellulose acetate, specially selected for high
performance applications in science and technology. Our greatest concern
about generic cellulose acetate is the presence of gel particles but we
have never found, in the special SPI Replicating Tapes and Sheets any
evidence for even the small gel particle.
Over the years, there have been a number of different protocols
and procedures for the use of these product, and for illustrative
purposes, we will present the two extremes:
Application from dilute solution:
We would recommend making a "stock" solution of 3% in acetone.
Simply weigh out a quantity of the tape or sheet, and dissolve in
acetone to make a 3% solution.
With an ordinary eye dropper or pipette tube, extract some of the
liquid and deposit the solution on the surface to be replicated.
Obviously, that surface can not be soluble in acetone, so this would
rule out most polymers and other plastic systems. This system was
designed primarily for use on metals, ceramics, refractories, and other
surfaces that would not be changed or swollen by the application of acetone.
Most surfaces are not readily "wet" buy acetone, therefore the liquid
will tend to "bead up" on the surface. After a few hours, the acetone
will have evaporated, leaving a thin cellulose acetate film behind on the
surface.
One the film is completely dry, and we like to recommend a short exposure
to the hot air from a hair dryer, it is quite brittle, but not too brittle
to be stripped off of the surface, taking with it a perfect "impression"
or negative replica of that particular surface.
Now, this stripped off replica at this point can be examined several
different ways:
a) It can be platinum/carbon shadowed, using established platinum carbon
shadowing techniques, the cellulose acetate dissolved away, with the
"replica" being picked up on TEM grids and photographed by TEM, or
b) It can be gold coated, after mounting onto an SEM mount, and
examined by SEM.
Clearly the two views will be somewhat different, with the TEM giving
the highest resolution, of course, but when viewed by both methods,
one does have the potential for gaining a far better understanding of
the surface morphology.
Application from swollen solid
Some surfaces are of a nature that one must minimize either
a) exposure to acetone or
b) degree of penetration into a porous
structure.
For example, if the surface to be replicated is a plastic
material itself, sometimes a better result is obtained by squirting
some acetone onto the sheet or tape, thereby "softening" it and then
after this has been done, the softened surface is literally pressed
onto the surface. This approach generally requires a longer time for
solvent evaporation and the use of the hot air dryer might even be more
important because of that added thickness. But one can get to the point
where they have a dry and brittle film on the surface of interest, and
it can be stripped off exactly as indicated previously.
And then the protocol can be continued as indicated above.
There is another possible variation on the technique and that is, for TEM
examination only, the surface to be studied is first
Pt/C shadowed, and then the cellulose acetate is applied
using either of the methods described above.
Absent any reason other wise, we would recommend the dilute solution
approach in this instance in order to get the best stripping off of the
replica.
Now some polymers like PTFE
and probably other materials as well, exhibit peculiar surface properties
that cause an anomalous agglomeration of the Pt/C shadowing grain, hence
this variation is discourage.
For purely SEM work, since the cellulose acetate replica is not known
for its beam insensitivity, and if only lower magnification views are
contemplated (e.g. less than 700X), then one should consider as an
alternative, the
SPI Wet Replica Kit.
However, we do want to stress that one should not attempt to use this kit
for magnifications higher than 700X or structure from the replicating
system, instead of from the surface being replicated, will be seen.
But when the researcher is interested in lower magnifications,
the resulting positive replica becomes the ideal sample for SEM
examination.
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Thursday March 18, 2010
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