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Structured and fluid
- Things that don’t hurt your hand when you hit them.
- Synonymous with “complex fluids”
- Examples: hair gel, mayonnaise, shaving cream, colloidal crystals, polymer solutions and blends
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Macosko Fig. 5-3-3
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Homberg Fig. 2.1
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Weitz Nature 339,60,1989.
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Comments on Figures: Elaborate HERE!
Properties of soft matter
- Viscoelasticity
- Turbidity/opacity
- Irreversible fragility
- Temperature sensitivity
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2500 years ago, South American Indians take sap from a hevea tree, cover their feet, wait about 20 minutes, and a pair of boots is created. The latex is crosslinked by oxidation only, so is weak. In 1830 Charles Goodyear decides to boil the hevea latex with sulfur (heaven only knows why), the crosslinking is much, much better, and eventually the radial tire is created. (de Gennes, 1996, p.4)
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Ink making for soft matter physicists
If you think this is primitive, check out how newpaper ink is make.
Soft matter - Ice cream!
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TEM of a typial ice-cream. (a) Ice crystals, average size 50 nm, (b) air cells, average size 100-200 mm, (c) unfrozen material. (W.S. Arbuckle, Ice Cream, 2nd ed., Avi Publishing, 1972. also, Hamley, Fig. 3.20)
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Plain frozen cream is as hard as rock, but the micro-scale structure of ice cream turns it into a wonderful dessert. Ice cream is a three phase mixture of pure water crystals, concentrated cream and sugar, and air pockets. The cream solution can remain liquid, since the sugar lowers the freezing point below 0 C. It coats each of the millions of ice crystals and lightly binds them together. The texture of ice cream is further improved by air pockets introduced during mixing. These air pockets are stabilized by fat molecules from the cream. The air weakens the network of crystals and cream, making the ice cream easier to serve and to eat.
Several variations of ice cream have evolved over the centuries. American ice cream traditionally uses a combination of milk and cream, whereas French ice cream uses lower-fat milk, with egg yolks as a stabilizer. Italian gelato also uses egg yolks, but contains less air, resulting in a denser product. Low-fat ice cream utilizes additives such as corn syrup, powdered milk, and vegetable gums. Indian kulfi is based on a recipe from the 16th century, in which milk is boiled down to concentrate the proteins and sugar, then frozen without stirring.
For more information about ice cream, see On Food and Cooking, 2nd ed., Scribner, 2004. by Harold McGee (pp. 39-45), from which this section is based.
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From great biology to great physics
Connect these scientists:
- Thomas Graham (1805-1869)
- Robert Brown (1773-1858)
- Michael Faraday (1791-1867)
- Ludwig Boltzmann (1844-1906)
- Albert Einstein (1897-1955)
- Jean Perrin (1870-1942)
Hint: Size dependence of diffusion
Length scales and order
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Polymers in solution
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Surfactant solutions
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Particle dispersions
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Comments:
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Structure and size, de Gennes, 1997, p.29
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Motion and size, de Gennes,1997, Fig I-1
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Structure and concentration, de Gennes, 1993, Fig. III-1
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Fractals
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Comments:
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