4.1 Brownian motion  (Page 2/5)

Objectives

By the end of this module, the student should be able to address the following critical questions.

- Robert Brown is generally credited to have discovered Brownian motion, but a number of individuals wereinvolved in the actual development of a theory to explain the phenomenon. Who were these individuals, and how are theircontributions to the theory of Brownian motion important to the history of science?

- Mathematically, what is Brownian motion? Can it be described by means of a mathematical model? Can themathematical theory of Brownian motion be applied in a context broader than that of simply the movement of particles influid?

- What is kinetic-molecular theory, and how is it related to Brownian motion? Physically, what does Brownianmotion tell us about atoms?

- How is Brownian motion involved in cellular activity, and what are the biological implications of Brownianmotion theory?

- What is the significance of Brownian motion in nanotechnology? What are the challenges posed by Brownianmotion, and can properties of Brownian motion be harnessed in a way such as to advance research in nanotechnology?

A brief history of brownian motion

Adolphe Brongniart made similar observations in 1827, but the discovery of Brownian motion is generallyaccredited to Scottish-born botanist Robert Brown, even though the manuscript regarding his aforementioned experiment with primrosepollen was not published until nearly thirty years after Ingenhousz’ death.

At first, he attributed the movement of pollen granules in water to the factthat the pollen was “alive.” However, he soon observed the same results when he repeated his experiment with tiny shards of windowglass and again with crystals of quartz. Thus, he was forced to conclude that these properties were independent of vitality.Puzzled, Brown was in the end never able to adequately explain thenature of his findings.

The first person to put forward an actual theory behind Brownian motion was Louis Bachelier, a Frenchmathematician who proposed a model for Brownian motion as part of his PhD thesis in 1900.

Five years later in 1905, Albert Einstein completed his doctoral thesis on osmotic pressure, in which hediscussed a statistical theory of liquid behavior based on the existence of molecules. He later applied his liquidkinetic-molecular theory of heat to explain the same phenomenon observed by Brown in his paper Investigations on the Theory of theBrownian Movement. In particular, Einstein suggested that the random movements of particles suspended in liquid could beexplained as being a result of the random thermal agitation of the molecules that compose the surrounding liquid.