SWELLING PROPERTIES OF AGAROSE GELS

Agarose hydrogels, which are composed of electrically neutral rigid ro ds, can deswell over a wide range of concentration. On being replaced in excess water, subsequent recovery both of their volume and their el astic modulus is, within experimental error, reversible. Here we descr ibe some of the properties that the gels dispay upon deswelling: 1 In conditions of uniaxial deswelling the gel undergoes a phase transition , which can be followed by analysing the concentration gradient genera ted in the sample. 2 The mechanical properties of the deswollen gel ar e strongly anisotropic. 3 The effective osmotic Poisson ratio sigma(os ) = - (Delta lambda(perpendicular to)/Delta lambda(parallel to)) is ne gative, where Delta lambda(perpendicular to) and Delta lambda(parallel to) are the relative compressions of the sample in the directions per pendicular and parallel to the applied stress. 4 With polarised incide nt light, the light scattered at 90 degrees displays a fringe pattern, the period of which provides a measure of the birefringence.