SPI-Chem™ Victawet® Surface Release Compound for Electron Microscopy Applications
Instructions for use (electron microscopy applications)
There are several different "grades" of Victawet® and these instructions
apply strictly for those involved with electron microscopy or related
surface release applications.
Introduction
Victawet when used according to these instructions, will produce a thin,
water soluble parting film between any surface (so long as it is not water
soluble or otherwise affected by water) and a replica (such as
platinum/carbon). Victawet has been successfully used on surfaces of metal,
glass, ceramics, polymer molded surfaces, spun fibers, and films, just to
name a few.
The kinds of surfaces fall into three categories, when making replica films:
a) Very flat surfaces but because of extraordinary adhesion between the
surface and the evaporated replica film, water alone is not enough to bring
about the "lifting off" of the replica.
b) Rough, cragy surfaces, such as what one would expect for a metallurgical
fracture surface, where again, the presence of the film enables a more
complete lift off of the replica film from a convoluted surface. There are
limits of course to just how convoluted the surface might be and the
Victawet still "work" and do what it is expected to do, however for most
metallurgical surfaces, for example, it works just fine.
c) Surfaces easily damaged or altered by the normal lift off of a replica
from a surface, for example, a surface of "sintered" PTFE such as
DuPont Teflon®.
Note that in some instances, a "stripping agent" such as polyacrylic acid
(soon to be added to the SPI product line) is needed to enable replica
removal instead of by water flotation. This would be particularly true in
the case of metal surfaces or surfaces generally where water would not be
permitted. For example, Victawet used in conjunction with a non-water
soluble "stripping agent", such as
cellulose acetate can replicate surfaces of ionic salts such as NaCl
with introducing artifacts from the stripping film.
Chemical details
Victawet is a sodium salt of 2-ethylhexyl acid phosphate. When this
material is heated, in a vacuum (1 x 10-5 torr, there is evolved
a number of low temperature volatiles. The actual parting layer is believed
to be sodium metaphosphate.
Step-by-step Use Instructions
To use, place a small amount, literally no more than a grain of rice in
size, into a tungsten basket (or boat, but we
recommend the use of a basket). Heat slowly to a temperature between 500 and
600°C, which is generally at the point where the basket is between
cherry red and bright orange, and this is where the Victawet will evaporate
that is, under go the changes described above when heated. Continue
evaporation until the material is completely evaporated and then proceed
with subsequent evaporations to produce the replica, which can be "floated"
off on water or stripped off using one of the stripping methods. For best
results, the replication should be done immediately after the application of
the Victwet in order to avoid unnecessary moisture absorption by the
Victawet layer, however we have found it is not necessary for it to be done
in one vacuum evaporation step, with multiple posts, but without any
intermediate atmospheric exposure. We know that this concept is often
times promoted by manufacturers of vacuum evaporation equipment but we do
not believe the evidence suggests there is any benefit to doing it that way.
We have also been told of a variation of the above procedure. We do not
know for a fact that it really is any better, but some users would
swear by their "refinement" of the method. In this case, some investigators
prefer to proceed with their Victawet evaporation but without the sample
being present, to the point that just a small residue of the Victawet
remains in the tungsten basket. Then the bell jar is removed, and the other
evaporating materials inserted into the basket which typically might be
Pt/carbon pellets, the system is again pumped down, the Victawet is then
heated to incandescence for approximately 5 seconds and evaporated and then
the basket is taken to even higher temperatures where the Pt and carbon
evaporate simultaneously. We are not aware of any real documented proof
this this method is any better, but at least on the basis of first
principles, one could easily argue that it is indeed better.
The SPI-Chem version of Victawet, if you are experienced in the use of
Victawet from other sources, produces for the users a noticable reduction in
the "sputtering" or what is some times called the "sparking" of the material.
This is because all Victawet products are not created equal. The SPI
Victawet supplied for electron microscopy has been specially modified for
optimum use for evaporation purposes and is completely unlike either
commerical Victawet products, Victawet 12 or Victawet 35B. This would be
immediately obvious just by looking at it visually.
We invite your comments and suggestions
regarding our efforts to bring to the microscopy market a truly improved
product over what had been available previously and from other vendors of
supplies and consumables for use in the electron microscope laboratory.
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