When liquids get up close and personal with powders

March 3, 2016

Every cook knows that dissolving powder into a liquid, such as semolina in milk or polenta in water, often creates lumps. What they most likely don't know is that physicists spend a lot of time attempting to understand what happens in those lumps. In a review paper published in EPJ E, scientists from the École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI), France, share their insights following ten years of research into the wetting of soluble polymer substrates by droplets of solvents like water.

In this article, the authors focus specifically on the first stage of powder dissolution, as water gets into every pore of the powder— a stage called imbibition—and not on the latter, dissolution stage. Typical experiments in the field involve studying the mechanisms of how a droplet of water spreads onto a water-soluble layer over time. As the droplet spreads, the solvent content in the substrate varies. The way the droplet spreads therefore varies according to the variations in the substrate composition on the edge of the droplet.

As a result, scientists now understand the two reasons why certain powders, like flour, which have very long polymer chains, are difficult to dissolve. At the microscopic level, spontaneous imbibition is stopped because of a change in the material softness as the solvent melts the polymer. Thus turning the substrate into a gel and slowing the droplet's spreading. In parallel, hydration results in high solvent affinity for the material to be wetted and the droplet's ability to spread. Hence, the more solvent reaches the , the more the tends to spread on it. Scientists have yet to identify the typical size of the grains and pores or the size distribution of grains and pores that need to be fine-tuned to accelerate the imbibition and, at a later stage, the subsequent dissolution.

Explore further: New insights into the evaporation patterns of coffee stains

More information: François Lequeux et al. Wetting of polymers by their solvents, The European Physical Journal E (2016). DOI: 10.1140/epje/i2016-16012-y

Related Stories

New insights into the evaporation patterns of coffee stains

March 3, 2016

Few of us pay attention to the minutiae of coffee stains' deposition patterns. However, physicists have previously explained the increased deposition of ground coffee particles near the edge of an evaporating droplet of liquid. ...

New water soluble polymer for water resistant coatings

January 12, 2016

A new polymer on the basis of a trick used by mussels has been developed by the Wageningen PhD student Juan Yang. The polymer should be able to let water-based paint flow better and produce water resistant coatings. Yang ...

Researchers identify movement of droplets on soft surfaces

August 5, 2015

Researchers from the University of Twente have succeeded in clearly identifying why droplets on soft, squishy surfaces react differently than on hard surfaces. A water droplet, for example, moves very differently over jelly ...

Recommended for you

Making silicon-germanium core fibers a reality

October 25, 2016

Glass fibres do everything from connecting us to the internet to enabling keyhole surgery by delivering light through medical devices such as endoscopes. But as versatile as today's fiber optics are, scientists around the ...

Controlling ultrasound with 3-D printed devices

October 25, 2016

Ultrasound is more than sound. Obstetricians use it to peer inside a woman's uterus and observe a growing baby. Surgeons use powerful beams of ultrasound to destroy cancer cells. Researchers fire ultrasound into materials ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.