Magazine article Science News

Another Face of Entropy: Particles Self-Organize to Make Room for Randomness

Magazine article Science News

Another Face of Entropy: Particles Self-Organize to Make Room for Randomness

Article excerpt

Particles self-organize to make room for randomness

There's a flip side to the doom and gloom of entropy. The steady march to disorder is not all degradation and the ultimate, bland sameness found so depressing by thinkers from philosopher Bertrand Russell to novelist Thomas Pynchon.

Entropy measures the amount of disorder in any patch of the universe, be it the dust, gas, stars, and planets of a galaxy, a belching steam engine, or the cells of a living organism. The laws of thermodynamics require that entropy must always increase. Rudolf Clausius, the 19th century German physicist, imagined that the relentless increase of entropy would ultimately degrade the universe to a disordered, stagnant confusion--a fate he called the heat-death.

As Russell sadly put it, "all the labors of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction.' And, Pynchon's character Callisto in the story "Entropy, bemoaned a heat-death of culture as well, "in which ideas, like heat-energy, would no longer be transferred."

Scientists, however, are discovering with apparent glee how often the road to disorder is paved with a little useful order. "Even though it's been known for a long time that entropy can produce order, it's still not fully realized how general that phenomenon is and how rich in potential," says Seth Fraden of Brandeis University in Waltham, Mass.

That potential holds in particular for a submerged realm of objects that are much bigger than atoms but too small to be seen without a microscope. There, remarkable feats of self-assembly take place. Such processes can create intricate molecular structures that, despite appearances, represent an increase of entropy over their ingredients.

It's a realm of special importance to humankind because it encompasses the contents of biological cells. In optics, it's the arena where researchers strive to make the photonic crystals that have been touted as the silicon of future, light-based computing. It's also where scientists grapple with problems of protein crystallization--a vital step toward understanding the functions of many new-found genes.

Although scientists have known since at least the 1940s that entropy can act as an unseen hand to create order, only in the last few years have they begun to suspect--and to demonstrate--how elaborate its handiwork can be. They have found that simply blending microscopic particles of different shapes or sizes in liquids sometimes causes crystalline structures of remarkable complexity to appear. The aimless interactions of the particles creates these structures, even while maximizing entropy as thermodynamics demands.

In entropy's most virtuoso laboratory performance to date, Fraden and his colleagues at Brandeis University blended plastic spheres and rods in water. The spheres, each no larger than a micron in diameter, were combined with micron-long rods--actually genetically engineered viruses--about 10 nanometers in diameter.

In experiments reported in the May 28 Nature, the suspended mixtures spontaneously solidified into two types of highly ordered, complex, permanent structures. One is a cake in which layers of vertical rods alternate with a thin frosting of balls--a stacked, or lamellar, arrangement. This pattern reflects the arrangement of phospholipids in cell membranes and the alignment of soap molecules in the surfaces of bubbles.

The other structure, known as columnar, features a regular, crystal lattice of vertical columns of clustered spheres embedded in a horizontal sea of rods all pointing roughly the same way.

Polymers used as glues and soaps commonly take on such structure, a phenomenon that materials scientists have long attributed to an incompatibility between the ends of the polymer molecules. The rods used by Fraden and his colleagues, however, don't have antagonistic ends. …

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