When two nominally rigid objects collide, their velocities change in response to the compression force between them. The difference in the normal component of the velocities of the objects is thus generally eliminated or reversed. The nature of collisions for nonrigid objects is more subtle. Surprisingly, when a long chain moving lengthwise collides with a wall, the chain can be pulled into the wall ͑instead of pushed away͒ with the approach velocity between the wall and chain increasing in time rather than not changing or decreasing. We discuss theoretical limits on how much a chain can be pulled into an object with which it collides, some chain link designs that lead to these limits, and experimental results which show the pulling of one of these chain link designs into a wall.
The wetting properties of aqueous solutions of a commercially available surfactant at various concentrations on porous media are investigated using the KRUSS DSA100 shape analyzer and the ADVANCED software to process the data. Time evolution of both the contact angle and drop base diameter at each surfactant concentration after deposition were monitored. Three different porous substrates (sponges) were examined. The sponges used were a car sponge, dish sponge and audio sponge. The sponges were investigated both dry and at different degrees of saturation, that is, the amount of water absorbed into the sponge. It was found that pure distilled water droplets deposited on the dry porous media showed non-wetting. However, if droplets of surfactant solutions were deposited, then a change to a complete wetting case was found at all surfactant concentrations used. It has been observed that for all sponges, no matter the degree of saturation, they display a minimum contact angle after which the droplet is rapidly absorbed into the porous media.
A theory of foam drainage placed on thin porous layer is developed. The rate of foam drainage and imbibition inside the porous layer and the possibility of a build-up of a free liquid layer on the foam/porous layer interface are investigated.
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