The physical properties of small gas bubbles in soft elastic materials: theory and applications

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Soft elastic materials have a degree of rigidity, and consequently a degree of intrinsic shape. They have fundamentally different properties from ordinary liquids such as liquid water, which have no rigidity or intrinsic shape (liquids are said to "take the shape of their container"). Examples of such soft materials include magma, soft rubber, "Jello", and soft tissues in the body. Unlike ordinary liquids, soft elastic materials can partially stabilize small gas bubbles suspended in them, giving the bubbles a longer lifetime than they would otherwise have. Simple liquids stabilize only large bubbles, in order to minimize surface tension effects. The tendency of soft elastic materials to partially stabilize small gas bubbles is relevant to the problem of Decompression Sickness (DCS) that can occur in scuba diving, aviation, and space exploration. The subject of elasticity has been studied in engineering for well over a century, mainly because of its relevance to the strength of materials. However the physical chemistry of elastic materials is not at all well characterized and is poorly understood. The grantee has recently begun a series of fundamental studies on the physical chemistry of soft elastic materials, particularly when these materials contain embedded gas bubbles. The point to these studies is to understand the behavior of such systems from a fundamental perspective. An important application will be to the problem of DCS in scuba diving. The connection this has to elasticity is that soft tissues in the body can be approximated as soft elastic materials, and DCS is believed to occur when gas bubbles in soft tissues in the body expand. Defense R&D Canada is a major player in the search for a biomarker for DCS (which is analogous to the search for biomarkers for cancer, heart disease, etc). This biomarker work however requires, as one of its inputs, accurate modeling and prediction of decompression stress. The applicant, whose earlier work included the creation of improved biophysical models for predicting decompression stress, and the role of elasticity in DCS, has begun collaborating with Defense R&D Canada on this problem.