From:   GORDON::COCKCROFT    "Jeremy Karl Cockcroft (Tel. 0171-631-6800)" 21-JAN-2000 18:05:24.33
To:     SMTP%"KMiller@brand-rex.com"
CC:     COCKCROFT
Subj:   RE: PTFE sample prep

Dear Kennedy,

In answer to your recent email:

>Apologies for not attending the MUD session on the powder diffraction course
>but is difficult to get timeout from work to attend.  The course is going
>well and I expect to try and send my first html at the week-end.  My home
>email is Rimell@miller78.freeserve.co.uk
><mailto:Rimell@miller78.freeserve.co.uk>  but continue to use my work
>address for correspondance.

We realize that the timing may not have suited everyone - we will try and
vary it. On the other courses, we also offer evening sessions - we can do
MUD sessions from home as well so it is not a problem for us if students
prefer that.

>On a different issue, we are trying to do some work on PTFE samples at
>Edinburgh University but the samples are proving extremely difficult to
>grind up.  I don't think Edinburgh have a mill, but they have been
>attempting Liquid N2 and grinding.  Do you have any alternative ideas about
>preparing PTFE samples?

>They (Edinburgh Uni) have resorted to cutting the samples into strips and
>laying them in the sample holder but the pattern is quite amorphous.

Although I have looked at polymer samples briefly by powder diffraction,
I have not huge experience in this area. My only experience with PTFE
was collecting neutron powder patterns of 1 cm diameter solid rod! This had
just a single very intense Bragg peak and not much else. I have also studied
deuterated polyethylene, again by powder neutron diffraction, and I
could refine the crystal structure from the powder data without too many
problems.

Also, I have a lot of experience of grinding things up in liquid N2 having
determined the crystal structures by powder methods of many of the freon
and related gases. This is difficult to do when the materials are hard, and
has the added danger of getting cold burns on ones fingers! I cannot imagine
that it would work well with polymers. Cutting the polymer into strips
should work OK, but if the polymer is extruded in some way, then any
crystalline component may have a preferred orientation within the solid
(non-powdered) sample.

One of the difficulties I have had with polymers is that what
is considered to be, say, 80% crystalline by e.g. thermal measurements,
may turn out to be only 10-80% semi-crystalline by diffraction methods,
or even completely amorphous.

I don't know how useful these comments are, but I hope they help. Please
feel free to come back to be with more queries if you have them.

Best regards,

Jeremy Karl Cockcroft.

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