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Re: I'm back! Hi to all + Silane?



From: Loris Medici <mail@loris.medici.name>
Subject: Re: I'm back! Hi to all + Silane?
Date: Mon, 16 Jun 2008 10:23:59 +0300 (EEST)

> Don't you think plain high bloom gelatin may adhere to
> alkali cleaned / silanized glass better?

Short answer: that may be adequate, but if not,
trimellitiating or phthalating the gelatin is a very well
known way to improve adhesion.

Adhesion is determined by the chemical and electrical property
of the material, and treating gelatin with trimellitic
anhydride at pH of about 10 will increase the amount of
carboxyl groups in the gelatin, which is positively correlated
with the adhesion of gelatin.

On the other hand, bloom strength is a mechanical property of
bulk gel and not necessarily related to the fine chemical
nature of the gelatin. In very general terms, higher bloom
strength, high viscosity and larger average molecular weight
are correlated, but there is no definitive rule about this.

As a side note, gelatin is usually extracted from bone or skin
in batches. The first batch extracts larger gelatin molecules
(higher bloom) and the subsequent extractions use elevated
temperatures and smaller molecules and therefore lower bloom
strength. Food gelatin has generally lower end of molecular
sizes, because stiff gelatin gives poor mouthfeel.

Acid treated gelatin is generally not used in silver halide
emulsion making due to higher impurity content, but it is a
useful trick to enhance the membrane property of the coating
in various applications. Acid treated gelatin has a rather
different chemical components in the gelatin, compared to lime
treated gelatin, and they contribute to higher wet strength of
the membrane (that is, the coated layer is mechanically more
robust when swollen in water).

--
Ryuji Suzuki
"The truth that I am seeking is in your missing file."
(Bob Dylan, Something's Burning Baby, 1985)