Re: dichromated colloids

"In short, I think the purity of PVA, especially in terms of per cent
-COOH in the long alcohol, kinda like mixed poly(vinyl alcohol/acrylic
acid) is the source of disagreeing results. Another possible impurity
might be a redox catalyst, like some transition metals. I think
Mannivanan, Lafond, and those groups pay some attention to the purity
of PVA, and some other studies were done with PVA containing some
impurities. One of their study says Cr(V) is stable in PVA. Then, it's
natural not to see Cr(III) absorptions right away."

I see. I guess purity may always be an issue - even more so where gelatin
and gum are involved...

"I'm not attached to gum in any way, but I think this is about time for
someone to run a series of analogous experiments with gum. I don't
know if holography community studies gum, but if not, I don't think
anyone is really interested in doing (or funding) it anyway."

To the best of my knowledge very little attention has been paid to
dichromated gum. I am not aware of any papers specifically dealing with gum.
Compared to gelatin, gum is said to require extensive pre-hardening. It's
likely to provide less index modulation than gelatin. So far it seems to
resemble PVA. I ignore wether gum shows equally good real-time efficiency
though.

Martin

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@sask.usask.ca>; <martinm@SoftHome.net>
Sent: Thursday, May 20, 2004 10:31 AM
Subject: Re: dichromated colloids

> From: MARTINM <martinm@SoftHome.net>
> Subject: Re: dichromated colloids
> Date: Thu, 20 May 2004 09:17:25 +0200
>
> > Looking forward to hearing about that.
>
> In short, I think the purity of PVA, especially in terms of per cent
> -COOH in the long alcohol, kinda like mixed poly(vinyl alcohol/acrylic
> acid) is the source of disagreeing results. Another possible impurity
> might be a redox catalyst, like some transition metals. I think
> Mannivanan, Lafond, and those groups pay some attention to the purity
> of PVA, and some other studies were done with PVA containing some
> impurities. One of their study says Cr(V) is stable in PVA. Then, it's
> natural not to see Cr(III) absorptions right away.
>
> > Do you see how those "-CHO aldehyde bits" contribute to Cr(III)
formation?
>
> Now you are talking about gelatin. In the case of gelatin, Cr(III)
> bridge crosslinking is well documented. Aldehyde may be reduced by
> other Cr(VI) as well, and I don't think it can be a major factor.
>
> I'm not attached to gum in any way, but I think this is about time for
> someone to run a series of analogous experiments with gum. I don't
> know if holography community studies gum, but if not, I don't think
> anyone is really interested in doing (or funding) it anyway.
>
> --
> Ryuji Suzuki
> "You have to realize that junk is not the problem in and of itself.
> Junk is the symptom, not the problem."
> (Bob Dylan 1971; source: No Direction Home by Robert Shelton)
Received on Thu May 20 21:35:25 2004