Microcellular foams were prepared by the thermally induced phase-separation technique, which yields materials having very small cell dimensions (0.1-20 pm) . The polymers employed were isotactic polystyrene, polyacrylonitrile, poly (4-methyl-l-pentene), polyurethane, and Lycram and the resulting foams all had densities in the range 0.04-0.27 g ~m -~. Values of Young's modulus and the collapse stress for these foams were measured and compared with predictions for conventional foams containing defects. Also investigated were plastic deformations, some time-dependent behavior, and Poisson's ratio. 0 1993 John Wiley & Sons, Inc.
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Microcellular foams are those having open cells with dimensions of 0.1-20 pm, which makes these cells about 10-100 times smaller than those of conventional foams. Such foams can be prepared by a thermally induced phase-separation technique that is explained in detail elsewhere.* Such microcellular foams have been used, e.g., in physics laboratories for targets in inertial confinement fusion because of their small-pore dimensions.' However, more recent investigations have explored the possibility of using these foams in new areas such as biomedical applications, controlled release of drugs, and preparation of composite material^.^ In some parallel investigations, the mechanical behavior of these foams has also received considerable attention. Such investigations of mechanical properties 5-7 have generally compared the experimentally measured moduli with the predictions of current theory for conventional foams.' According to such theory, the relative mechanical property of a foam can be related to its relative density by the formula * To whom correspondence should be addressed.