Water forms droplets on the surface of a leaf but it spreads and completely wets the skin of a snail. Why does water behave so differently on the two surfaces? In this video, we introduce the fundamental concepts of surface tension, contact angle and the difference between hydrophobic and hydrophilic materials. Also, we illustrate with examples how the physics of wetting helps understand biological features in cells!

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.

Protein condensates are dense droplets of proteins that organise the interior of the cell. Curiously, they age, meaning their physical properties such as viscosity change over time. In our paper “Theory of rheology and aging of protein condensates” published in PRX Life, we study how protein condensates become very viscous with time reflecting its glassy nature. We formulate a theory to understand this intriguing phenomenon.

Check out the paper for more info! https://journals.aps.org/prxlife/abstract/10.1103/PRXLife.1.013006

Get ready to dive into the Free Energy!

Cells can be described as systems made of different phases. For instance, biomolecular condensates are dense droplets of proteins that coexist with the rest of the cytoplasm. Thermodynamics is a helpful theoretical framework to understand phases in cells. In this video, we explain the concept of Free Energy of a mixture and we see how can we predict the equilibrium state of the system from the Free Energy.

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.

Get ready to dive into the Free Energy!

If we want to understand phases in cells we need to talk about the Free Energy of a thermodynamic system. This is the second part of the video “Diving into the Free Energy”. In this video, we will understand how thermodynamic mixtures reach equilibrium by minimising the Free Energy. We will see that asking if a mixture will phase-separate or not is the same as asking what is the minimum energy allowed for the mixture. Not only that, but we will also show how the Binodal line on the Phase Diagram directly emerges from the Free Energy!

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.

Cells organize their interior into functional compartments, some without an enclosing membrane. These dense liquid droplets of biomolecules coexist with the surrounding environment like oil drops in water constantly exchanging material with it.

How is the random movement of single biomolecules influenced by the presence of these droplets?

In this video, we explain our recent work published in Phys. Rev. Research, answering this question. 

Check out the paper for more info https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.3.043150

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.

The Earth, which once was a messy ball of melted rock, is now teeming with complex living creatures extraordinarily adapted to their ecosystem. But the second law of thermodynamics tells us that systems spontaneously tend towards disorder and structures states, just like milk tends to mix with coffee. Then, where does complexity come from? Watch this quick intro to Complexity to understand how Nature creates complexity!

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.

Have you ever seen a movie backwards in time? How did you figure out that the time was flowing backwards? This could seem a silly question. But think about it. It strongly depends on the what process the movie was showing! If you see many pieces of broken glass coming together from different directions to build a bottle that moves against gravity, you’ll immediately know that the movie is reversed. You know that because breaking a bottle is a very irreversible process. But how would you know it if the movie shows a pendulum? Or two billiard balls colliding? Or a planet orbiting a star? The way we guess the arrow of time on irreversible processes has to do with the Second Law of Thermodynamics! Watch this quick intro to Irreversibility!

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.

Cells assemble structures that have lots of molecules. How can such complicated structures be reliably assembled? We propose that cells could be organizing an assembly line process for the construction. We show how this could be organized inside droplets. In this video we explain our recent work published in PRL. Check out the paper for more info: https://journals.aps.org/prl/abstract…

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.

Phase Diagrams are graphic representations that help understand many physical systems such as magnets and pure substances like water. These diagrams also help us understand how dense droplets of biomolecules, called Biomolecular Condensates, form inside cells. Phase Diagrams predict under which conditions these condensates can form and also what will be their molecular concentration. Watch this quick intro to learn more! References: -Video C. Elegans: Fritsch, Diaz-Delgadillo, Adame-Arana et al., PNAS (2021) https://www.pnas.org/doi/10.1073/pnas… -Multicomponent Phase Diagram: Bauerman, Laha, McCall, and Weber JACS (2022) https://pubs.acs.org/doi/pdf/10.1021/…

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.

Have you ever seen a tepid cup of coffee getting hot? Or a pile of sand grains organizing themselves into a sand castle? It would be strange, right? But why? The reason is behind one of the most fundamental and general laws of physics: The Second Law of Thermodynamics.

Prepared by Mariona Esquerda Ciutat from the Hyman and Jülicher labs in Dresden.