Abstract
Liquid foams are classified into a dry foam and a wet foam, empirically judging from the liquid fraction or the shape of the gas bubbles. It is known that physical properties such as elasticity and diffusion are different between the dry foam and the wet foam. Nevertheless, definitions of those states have been vague and the dry-wet transition of foams has not been clarified yet. Here we show that the dry-wet transition is closely related to rearrangement of the gas bubbles, by simultaneously analysing the shape change of the bubbles and that of the entire foam in two dimensional foam. In addition, we also find a new state in quite low liquid fraction, which is named “superdry foam”. Whereas the shape change of the bubbles strongly depends on the change of the liquid fraction in the superdry foam, the shape of the bubbles does not change with changing the liquid fraction in the dry foam. Our results elucidate the relationship between the transitions and the macroscopic mechanical properties.
Highlights
It is found that those states can be detected by analysing the change of the bubble shapes
It is indicated that those transitions alter the mechanical properties of the foam such as the rearrangement of the bubbles and the propagation of the external force
The dry-wet transition is characterized by the rearrangement of the bubbles, and the propagation of the external force is different between the superdry foam and the dry foam
Summary
Preparation of LG foams.We used a solution in which TTAB(Tetradecyl Trimethyl ammonium Bromide)14% and glycerol 17% were mixed with deionized water. We adjusted the solution to control the interval time of the bubble collapse events so that the foam is a quasi-static state. A silicon sheet of 1 mm thick was used as a spacer to control the thickness of the sample chamber. The size of the entire foam was about 60 mm in diameter. Since the bubble size is 4 times larger than the chamber thickness, the foam can be regarded as quasi two-dimensional. The sample chamber was sealed with silicon grease in order to prevent an evaporation. The number of the bubbles is more than 200 in small foam or 1200 in large foam at t = 0 and it decreases with time due to the collapse. We use a solution in which a household detergent (Biore, Kao co.) 50% was diluted by deionized water. The temperature was controlled by air conditioner around 16 °C
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