Conclusions and Outlook on Future Fundamental Developments

Based on the present review, a few future trends or fields of development with great potential may be discerned  

Better control over morphological aspects also remains a matter of concern. The formation of ordered gels and the use of templating additives during gel 

A development of numerical or analytical modeling of sol-gel encapsulation and of the host- est relationships inside a sol-gel-encapsulated medium is urgently needed. This will lead to improved understanding of the kinetics encountered. 

Apart from controlhng the pores and their distribution, much research remains to be conducted to asses the possibilities of covalent grafting of spacer molecules or ionic bonding of exchange-controlling species inside the cavities. 

The authors are very grateful to their former co-worker. Dr. Greet Penneman, for her efforts and scientific contribution in the framework of her PhD thesis. They also thank their co-workers and students Dr. Els Bruneel, Dr. David Van de Vyver, Dr. Bart Schoofs, Dr. Klaartje De Buysser, Dr. Tran Thi Thuy, Veerle Cloet, Pieter Ver-meir and Nigel van de Velde for fruitful discussions. 

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