Hydrophobic and hydrophilic fumed silica

Barbara Appelbaum <aandh<-a t->idt< . >net> writes

>Various bits of conservation literature refer to hydrophobic and
>hydrophilic fumed silica.  Are both used as additives to resins?  Is
>it correct to assume that the one commonly used in the hydrophilic?
>Is it possible that the hydrophobic kind would make a resin into a
>better moisture barrier?

Both hydrophilic and hydrophobic fumed silicas (or fumed "colloidal"
silica) can be added to resins dissolved in a solvent system.  Greg
Byrne's article in the 1984 Adhesives and Consolidants IIC Paris
Preprints (pp.78-80) provides a comprehensive introduction to these
amorphous silicas.  The choice of fumed silica type and grade will
affect the rheological and surface characteristics of the (resin)
polymer system, so you will certainly be able to modify application
properties and have differing rates of water absorption in the
resulting film or adhesive.

In addition to Byrne's bibliography, you might want to obtain
product information from Degussa Corporation, Pigments Division, 65
Challenger Road, Ridgefield Park, NJ 07660  (201-641-6100).  In the
1989 brochure they list 27 publications "from the Series 'Basic
Characteristics and Applications of AEROSIL (Degussa Trademark)'."

One final note: either hydrophilic or hydrophobic can be used for
solvent systems, but you cannot use hydrophobic in water. It's a
good way to test what you have, if you don't know.  A hydrophobic
fumed silica will float on the water, while a hydrophilic one will
sink and mix in.

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                  Conservation DistList Instance 11:46
               Distributed: Wednesday, November 19, 1997
                       Message Id: cdl-11-46-002
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