AbstractIt was demonstrated that swelling of cross‐linked polymers can be monitored much more conveniently and reproducibly after that polymer has been comminuted to a fine powder, and then fabricated mechanically into a tough microporous composite film consisting of the particulate matter (>80) enmeshed in poly(tetrafluoroethylene) PTFE;<20. The latter component provides the physical integrity that affords ease of handling and ensures permanent entrapment of the particles even after 100 cycles of swelling and desiccation to the original dry state. The PTFE microfiber network, however, does not affect adversely either the physicochemical properties of the particles or the permeability to fluids. Kinetic studies in 10 replicates have shown that the void space (0.3 to 0.6 mL/g of composite) is filled by capillary action within the first few minutes of contact with the liquid, and that swelling to the equilibrium state (2 to 90 mL/g of composite) usually occurs within 0.5 to 2 hours thereafter, depending primarily upon the surface to volume ratio of the particles. The magnitude of swelling at equilibrium, however, is depended only on the thermodynamic state of the gelled polymer in excess liquid, and is reproducible usually within 0.2
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