| Fluids trapped in small spaces feature prominently in science and technology, and understanding their properties is critical to progress in fields that range from granular media to the engineering of nanoscale devices. Confined fluids behave differently than bulk samples. Properties strongly affected by confinement include (i) how the particles pack, (ii) how the system responds to "heating" or "squeezing" [the equation of state] and (iii) how rapidly the fluid relaxes, diffuses, conducts heat, or flows. In some cases, quantitatively accurate theories exist for the first two types of properties, but even a rule of thumb for qualitatively predicting the third has proven elusive. In this talk, we explain how accurate predictions of dynamics from first principles are still possible for some confined fluid systems, even in the absence of a theory, once one recognizes that certain relationships between static and dynamic properties are insensitive to confinement. These relationships not only provide insights into "what matters" for dynamics of these inhomogeneous fluids, but also provide a guide for how to passively tune the transport properties of a confined fluid by modifying the geometry or boundary-particle interactions of the confined space. |
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