Osmosis? Isn’t that the very well known, but also poorly understood subject from biology class in secondary school? The 'emergency exit' for every question asked during the biology lesson?



what is osmosis?


Osmosis is the diffusion of water through a so-called semipermeable membrane. More specifically, it is the movement of water across a semipermeable membrane from the side with the high water concentration or potential (i.e. the low solute concentration) to the side with the low water concentration or potential (i.e. the high solute concentration). Normally one does not regard, or think about the concentration of water in a solution as water is often the solvent and the focus is on the concentration of the solutes. But water itself has a concentration in any solution! Pure water has a molecular weight of 18 grams per mole, so its concentration is approximately 55 Molar. Thus the more dissolved chemicals or solutes in a solution the lower the water concentration or potential is of that solution.
Osmosis is a physical process in which the water or solvent moves, without any input of energy, across the semipermeable membrane as a result of different concentrations.



osmosis and earth sciences?


What has osmosis to do with earth sciences, I did after all get my degree in Geology ... Both biology and earth sciences include the study of materials capable of separating the transport of solutes from the transport of solvents. These materials are the above mentioned semipermeable membranes. Biology shows that the membrane walls of plant and animal cells are capable of restricting the passage of salts —or sugar in biology class— but allow water to pass in or out of the cell depending on the solution in which the cells are placed. A famous example of a semipermeable membrane is the pig bladder which served as an example of semipermeability for countless generations of scientists in several scientific disciplines. Earth sciences show that clays or sediments with high clay content are also capable to act as a semipermeable membrane under the right conditions. A more detailed description of why and how this works is given on the theory page.



research at Utrecht University


My research work at Utrecht Universiteit started in 1995 and ended 1999 with the Ph.D.-defence in 2000. The research dealt with the semipermeability of clays and clayey natural materials. Why? Take a waste disposal site. According to Dutch legislation a low permeable clay liner must be present as a barrier to prevent the dispersion of contamination into the groundwater. Transport of contaminants across these clay barriers is often said to be only diffusion controlled. However, the concentration gradient that drives diffusion is also capable of driving water transport whenever the clay layer exhibits semipermeable properties! Thus, the transport of contaminants can be facilitated by osmotically driven water transport. Main goal of the research was to demonstrate the semipermeable behaviour of clays and clayey natural materials and the effect on contaminant transport across these natural semipermeable membranes.

For a more detailed description of the research please refer to the
research page. A pdf-copy of my thesis can be obtained via the download page.



these pages


Intrigingly osmosis has recently gained renewed interest as it can help explain anomalies in groundwater pressues in deeper groundwater systems, it offers an explaination for the formation of certain ores, and is capable of generating electricity. Reasons enough to dust off some 'old' research and make the results available for everyone who is interested in this process. I also added links to other,
related research and their results.



Wordle summary


For the lazy I have included a
WordleIcon_External_Link summary of the theory behind chemical osmosis. Sub & sup are a clear indication that the text contains a lot sub and super scripts and are thus a clear indication for its scientific content ;)

Wordle summary