CycleBanter.com - View Single Post - Elmer's Rubber Cement is not the vulcanizing kind!

**jim beam[_4_]** · April 29th 09, 04:57 AM posted to rec.bicycles.misc,rec.bicycles.tech

Michael Press wrote:
In article ,
(Tom Keats) wrote:

In article ,
Michael Press writes:
In article ,
(Tom Keats) wrote:

In article ,
Michael Press writes:
In article ,
(Tom Keats) wrote:

Now I'm wondering
how those long polymers find their ways into their holes
or ruts or whatever allows them to interdigitate -- do
they just fall in when a hole opens up beneath them,
or do they just randomly flow around until they drop
into a hole/rut/whatever? If they're electrically drawn
in, could that arguably be a chemical process?
Physically it is similar to interleaving the pages of
two books.
Interleaving the pages of two books requires thought
and intention and maybe a little cleverness, if the
job is to be done neatly, without collisions.

What forces are at work with this interdigitation/
interleaving? What downright ~makes~ polymers
first agree to interdigitate, and then move around
to align themselves accordingly? Or is this just
another one of those axiomatic things?

Adjacent books don't suddenly decide to interleave
their pages, neither does a jumbled pile of bricks
decide to form a chimney. So I'm having difficulty
with the concept of molecular chains somehow elegantly
and neatly (but non-chemically) organizing themselves
by dint of their proximity to each other.

We're being told one substance somehow molecularly
intimates and intermingles itself with another
similar substance, and yet the process is not
chemical.

BTW, as a preemptive afterthought: Jim Beam and the
horse he rode into town on can both enjoy precious
moments with their respective selves.

Or each other, if they're into that.
The interleaved page analogy is to illustrate
the scale of the forces at work. You did not know that?
^^^^^^^^^^^^^^^^^^

But exactly ~what~ forces are at work?
That is my question.

Induced electric dipole interaction.

We stick a patch on a tube, maybe press it on
a little, leave it overnight, and when we look
at it the next day, the patch is pancaked right
on there as if it had been in a clamp.

The loss of volatile solvent is so rapid you see
the patch move closer to the tube as the glue volume decreases.

I realize the patch isn't chemically integrated
with the inner tube rubber. But it does seem to
be more mechanically squashed onto the tube than
by the thumb pressure that initially installed it
into place. I'm just curious as to what does that.

I'm guessing that as the more volatile stuff in
the cement evaporates, the remaining cement
somehow shrinks, thereby pulling interdigitated
patch & inner tube together. But that's just a
guess on my part, and guessing ain't knowing.
Shrinkage of the cement at least provides an
explanation for the movement necessary for the
process.

Yes.

I think wet newspaper pages are stuck together by
air pressure and maybe a li'l static electricity
largely introduced by foreign material and dust on
the paper. But I'm probably wrong about that, too.
It would be nice to know what's really going on.

Electrical forces are what constitute the London and
van der Waals forces previously mentioned. To know
what is really going on do a year of physics; a year
of chemistry; a year of electrodynamics; a year of
thermodynamics and statistical physics---alternatively
a year of physical chemistry; and a couple years of
calculus. MIT puts all their courses complete with
problem sets on the web.

that's not the point - the point is that it's been explained in this
thread. if you want to get into detail, read up on the above, but you
don't need to do that to simply accept the concept of molecular interaction.