Abstract: A method for providing anisotropic polymer membranes from a binary polymer/solvent solution using a thermal inversion process. A homogeneous binary solution is cast onto a support and cooled in such a way as to provide a differential in cooling rate across the thickness of the resulting membrane sheet. Isotropic or anisotropic structures of selected porosities can be produced, depending on the initial concentration of polymer in the selected solvent and on the extent of the differential in cooling rate. This differential results in a corresponding gradation in pore size. The method may be modified to provide a working skin by applying a rapid, high-temperature pulse to redissolve a predetermined thickness of the membrane at one of its faces and then freezing the entire structure.

Abstract: A rheometer (10) is disclosed which includes a central cylinder (14) surrounded by a tube (24) having a cylindrical bore (26), the bore (26) being slightly larger than the cylinder (14). A loading cup (44) has an interior cylindrical opening (50) larger than the bore (26) which extends from a first end portion (46) thereof toward a second end portion (48) thereof. The first end portion (46) of the cup (44) is detachably attachable to the tube (24) with the cylindrical opening generally coaxial with the bore (26) of the tube (24). An axial moving structure (34) serves for controllably axially moving the tube (24) relative to the cylinder (14). A measuring device (84) serves for measuring the instantaneous force exerted on the cylinder (14) as the tube (24) moves axially.