Effect of Aging fa and Washing fw Periods

For any washing or solvent exchange step, there are two distinctly different modes of operation  

In the diffusion-limited case, the exchange time is limited by the diffusion coefficient of the solvent(s) and the pore size and structure of the gel. Diffusive processes are strongly temperature dependent. This is the reason why washing and exchange steps during APD processes are often carried out at moderate temperatures in the 40-70°C range. 

For the gels studied here, a washing time of 18 h is needed. After that, no significant change in the properties is observed. This is because the gel and water phases reach equilibrium. K the gel is washed once with the same volume of pure water, the equiUbrium composition will come to lay around half of the initial Na concentration. Hence, for a complete removal, multiple washings are required [40]. In addition, the use of larger volume equivalents of the washing fluid or a continuous process with a countercurrent flow can help 

Water washing time [h] Density [g/cm ] Na content [%] Optical transmission [%] 

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