Polymer International Polym Int 52:1095–1107 (2003) DOI: 10.1002/pi.1186 Mechanism of solvent entrapment within the network scaffolding in organogels: thermodynamic and kinetic investigations Nov Markovic, Milena Ginic-Markovic and Naba K Dutta ∗ Ian Wark Research Institute, ARC Special Research Centre, University of South Australia, Mawson Lakes Boulevard, Mawson Lakes, SA 5095, Australia Abstract: A detailed investigation on the thermodynamic behaviour of the physical and chemical organogels, using differential scanning calorimetry (DSC) and modulated thermogravimetric analy- sis (MTGA), is presented. Aluminium soap of fatty acid was used as the physical gelator and in situ crosslinking of siloxane copolymer was used for chemical gelation. The effects of the type and concen- tration of the gelators and the corresponding mesh-size distribution of the gel network scaffolding on the trapped-solvent crystallization, melting and evaporation mechanism, and kinetics are examined. It appears that the kinetics of crystallization of the trapped-solvent are significantly affected by the quality of the gel network scaffolding and can be treated successfully by the Avrami equation of crystallization. From the melting behaviour of the entrapped-solvent crystallites, quantitative information about the number of solvent molecules bound per molecule of the gelator has been extracted. The effect of gelation network structure on the kinetics of evaporation of the solvent from the gel network scaffolding has been evaluated. DSC appears to be the reliable technique to evaluate the population distribution of solvent molecules trapped in the gel network scaffolding.  2003 Society of Chemical Industry Keywords: physical gel; chemical gel; gel network scaffolding; DSC; MTGA; crystallization; melting; activation energy INTRODUCTION The hierarchical self-assembly and gelation is an area of increasing interest due to its importance in polymer technology, biotechnology, food technology, pharmacology, controlled-release applications, and in surfactant industries. Significant research effort has been dedicated to the hydrogel-networks that are hydrophilic and can be swollen by water, particularly for biopolymers in food, pharmaceutical, agricultural, medicinal and similar industries. 1–3 By considering the structural features of proteins and their functions, various amphiphilic copolymers have been designed and synthesized to develop a self-assembly sys- tem, especially in water. 4 Hydrophobically modified water-soluble associative polymers and amphiphilic polyelectrolytes, such as hydrophobically modified N- isopropylacrylamide (NIPAM) copolymers, 5 deoxy- cholic acid-modified chitosan, 6 bile-acid-bearing dextran, 7 cholesteryl-bearing poly(amino-acids), 8 etc., have extensively been studied; not only because of their biological relevance (such as enzyme models) but also because of the industrial applications such as surfactants, paints, coatings, viscosity improvers, thickeners and drug delivery systems. 9 Their inter- macromolecular self-associations, nanoparticle forma- tion, pH-and temperature-sensitivity, and rheological behaviour have been investigated in detail. However, very little attention has been focused on network gela- tion of hydrophobic liquids, and in particular, the in situ formation of a network that is specifically designed to trap the surrounding solvent, although this class of gel has significant importance in industry, military and environmental applications. Over many decades, industries have had to face the considerable risks associated with the storage and transportation of dangerous or unwanted liquids, such as commercial fuels, crude oil, disposed vegetable oils, organic and inorganic solvents, etc. The risks include, risk of explosion or fire, as well as large-scale spillage of noxious and potentially toxic substances. An indication that use of gels could be a solution emerged when it was realized that application of small quantities of suitable gelling agents have the ability to gel a vast quantity of solvent. 10 – 13 Such gels ∗ Correspondence to: Naba K Dutta, Ian Wark Research Institute, ARC Special Research Centre, University of South Australia, Mawson Lakes Boulevard, Mawson Lakes, SA 5095, Australia E-mail: Naba.Dutta@unisa.edu.au Contract/grant sponsor: University of South Australia, USPRA fellowship Contract/grant sponsor: DSTO, Melbourne (Received 30 August 2002; revised version received 7 November 2002; accepted 26 November 2002)  2003 Society of Chemical Industry. Polym Int 0959–8103/2003/$30.00 1095