Mobility of water and alcohols in a silica reinforced siloxane network

The water vapour permeability coefficient (P) of a silica reinforced siloxa ne network has been measured in the temperature range 5-45 degreesC. P is i ndependent of humidity and stretching of the material, but a plot of log P against reciprocal absolute temperature is non-linear. showing that the hea t of permeation is negative and varies with temperature. This can be explai ned by the formation of water clusters. The transport of some alcohols has been studied in gravimetric sorption experiments. Amounts absorbed at equil ibrium increase in the order methanol < 2-propanol < t-butanol, but diffusi on coefficients decrease with molecular size. When the network is formed wa ter is absorbed and alcohols are released. Gravimetric monitoring of the cu re process yields a value of D which equals that of methanol in the network , showing that it is the removal of this alcohol which controls weight loss . (C) 2001 Elsevier Science Ltd. All rights reserved.