Interpenetrating network formation in agarose-sodium gellan gel composites

Aqueous cold-set gels from mixtures of agarose and sodium gellan have been characterised structurally and mechanically using optical and electron micr oscopy, turbidity measurements, differential scanning calorimetry, mechanic al spectroscopy and compression testing. Consistent with expectations for c harged-uncharged polymer combinations at low ionic strength there is no liq uid-liquid demixing in sols prior to gelation, and although transmission el ectron microscopy reveals heterogeneities in gel microstructures at the hig her polymer concentrations, these are small in extent, and are unlikely to arise from normal segregative demixing. Overall, 'molecularly' interpenetra ting networks (IPNs) are indicated, in which the gellan and agarose archite ctures pass through one another on a distance scale comparable to their por e sizes. At concentrations greater than 2% w/w gellan, where gellan is the first gelling species, and when the agarose concentration is greater than 0 .5% w/w, the composite modulus falls below that expected for the agarose al one. At 0.5% w/w agarose, on the other hand, modulus contributions from the components are much closer to additive. These findings are reflected in th e results of large deformation compression testing where breaking stresses show similar trends. (C) 2001 Elsevier Science Ltd. All rights reserved.