About membranes, phase separation and perspective

Phase separation is involved in many processes, and although we don’t realize that, some of them are in front of us every moment. For instance our body can function thanks to phase separation and in some specific case develops diseases because of that. A positive example of phase separation which can be found in every living being are membranes, which have the role of creating “compartments”.

Membranes are very complex aggregates which are not soluble into the surrounding environment. In few words, membranes wouldn’t exist without phase separation and therefore biological life exists because of phase separation. Industry, the living and pulsating hearth of our economy isn’t different. Many of the processes operated in companies are based on phase separations. In metallurgical industry for example, phase separation is constantly used.

The few lines above, even though sloppy and partially inaccurate, are meant to give an idea of the impact that phase separation has on our lives and therefore why studying these processes will always be of paramount importance. Of course one cannot focus on phase separation in such general terms and a narrowing of the focus is needed. In my case the focus are solvometallurgical processes.

Solvometallurgy implies processes that are similar to those of hydrometallurgy, but not involving aqueous phases. In hydrometallurgy, conventional solvent extraction is commonly used. In this case, different metals are distributed between an aqueous phase and an immiscible organic phase, making the extraction possible. As mentioned above, the new paradigm of solvometallurgy replaces the aqueous phase by a nonaqueous solvent. Several conditions have to be fulfilled and among them:

(1) the process should involve two mutually immiscible liquid phases,

(2) phase separation should be fast.

While studying how to match this conditions I realized how perspective sometime can lead to flaws in how we interpret what is in front us of. Since our childhood, we have been used to think that two immiscible liquids are repelling each other. The most intuitive example are oil and water: no matter how hard we try, we can not mix them together. The misconception coming from this is that water and oil have a repulsive interaction, in few words “they push each other away”.

And here comes the moral about perception: the truth is that water and oil molecules have no repulsive interaction, and the reason for such observed behavior is simple but hidden behind  the first impression. Water molecules interact through the so called hydrogen bond.

Relatively to this example such interaction can be considered very strong, way stronger that the interaction that can occur between water and oil molecules. And here it lies the truth! Water molecules are not “pushing” away oil molecules, this is just the resulting effect of water molecules “sticking” to each other very hard.
If we wanted to make another more intuitive example, it is like if water molecules were people who really love each other, and oil molecules people who would like to join the group, but for some reason they can’t really blend and finally they leave. Fun fact is that not even oil molecules love each other, they stick together just because they can’t find anyone else to go with.

As in science, perspective plays a huge role in every aspect of our life and this short story only intention is to make all of us think about that. Related to that there is a very famous citation of Socrates: “I know that I know nothing”. Which I suggest to translate into “There is usually more than what I see”.


Hope you enjoyed,



About the author:

My name is Roberto Macchieraldo and I am ESR 9. I am Italian and I was born in Biella, a small town close to Turin, in the north of Italy. Although right now I am a researcher (or I pretend to be at least), in my life I had several experiences, in Italy and abroad as well. I had the opportunity to work for GSK, a pharmaceutical company, in the field of the Quality Assurance. And here I am now, working in Germany as a researcher, seeking my PhD, which is onto the “miscibility of solvent systems that are relevant for metal extraction by theoretical methods”.


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