Re: Adhesion: (was Re: Dots of gum?

Katharine wrote:

> Etiene Garbaux wrote:
>
>> On the topic of chemical tooth: chemical tooth is a molecular effect.
>> Very simply, good subs are molecules which have one end with an affinity
>> for the support and the other with an affinity for whatever you want to
>> adhere to the support. This can work excellently, and solves some thorny
>> industrial problems. However, because the chemical tooth is only a
>> molecule deep, I do not believe it could "reach through" the thickness of a
>> gum layer to adhere the hardened gum away from the support if there were
>> still soluble gum in between. So it might be a boon in conjunction with
>> either of my suggestions above, but probably won't be a viable solution for
>> any "support one surface and expose the other one" system.
>
> Well, I'm still trying to figure this out. I've finally got the part
> about the bonded layer being one molecule thick, although I'm still not
> sure how that would work in the case someone suggested, of mixing the
> silane with the gum and just coating and exposing. Sorry to be so dense;
> I've been on Vicodin all week and am a bit foggy.
>
> So okay, you would use the silane as a sub, and then you'd coat the gum
> on the dried silane and expose it?

The way silane works with gelatin [simplified] is that one end of the
silane molecules has an affinity for glass, and the other end has an
affinity for gelatin. If you coat the glass with silane, the glass-philic
ends all grab the glass and leave a nanoforest of gelatin-philic ends
sticking up to grab the gelatin when you coat that. If you mix silane with
gelatin and coat it on glass, some of the silane molecules will be touching
the glass. One end of these molecules will adhere to the glass as above,
and the other to the gelatin. The silane molecules that are not touching
the glass will basically do nothing. (One end will bind to nearby gelatin
molecules, but the other end won't bind to anything.)

Either way, the gelatin that is bound to the glass comprises the molecules
that are touching the silane molecules (i.e., a one molecule thick layer of
gelatin, more or less). The rest of the gelatin sticks simply because the
gelatin itself is cohesive.

If silane works with gum, I expect the mechanism will be analogous to the
silane/gum model. It will bind a one-molecule layer (more or less) of gum
to the glass. In order to survive development of the gum image, you will
need to harden the gum down to the bound layer. Among other things, this
may mean that silane won't provide a foundation for a full-scale image.
(If you expose the plate through the glass, it may work because the
hardened layer will be next to the bound layer. You would need to use a
point source light to avoid unsharpness due to the thickness of the glass.)

Best regards,

etienne
Received on Mon Feb 21 12:18:35 2005