Soft Matter Blog

From a 4kg cat to a 4000kg elephant, any animal takes only around 12 seconds to ‘do their business’. This is what a team of US scientists found after thoroughly studying the process of defecation in over 40 animal species. They then developed a theoretical fluid dynamics model that shows how viscosity changes in faecal mucus ease excretion.

Source: © RSC
The relationship between body mass and defecation time

Despite being extensively studied from a clinical and medical perspective, the physics of pooing has until now escaped extensive exploration.

Inspired by a slow motion video of a defecating elephant obtained during their previous work on urination, David Hu and his team from Georgia Institute of Technology acquired similar videos of other mammals ranging from dogs to giant pandas. They found that despite obvious differences in animals’ size and diet, defecation time averaged to around 12 (±7) seconds across all of the species they looked at.

Read the full story by Charlie Quigg in Chemistry World.

This article is free to access until 21 June 2017

P J Yang et al, Soft Matter, 2017, DOI: 10.1039/C6SM02795D

Researchers in Canada have shrunk bubbles to single-micrometre diameters, suitable for use in ultrasound.

Source: Royal Society of Chemistry
Bubbles shrink down to 1–7µm in diameter as they flow through the device’s serpentine microchannel

Microbubbles are commonly used in ultrasound imaging as they improve the visual distinction between blood and surrounding tissues. Bubbles are injected intravenously, and under ultrasound they are excited at their resonant frequency. This resonance means they scatter a much higher proportion of the ultrasound than the surrounding tissues, allowing clear imaging of blood vessels.

The bubbles needed for ultrasound are around 2µm in diameter. Current microfluidic techniques cannot produce bubbles this small, and the techniques used to generate these microbubbles generally use physical agitation or shearing. The bubbles produced often have a large size distribution, and filtration is needed to separate out those suitable for use.

Read the full story by Laura Fisher in Chemistry World.

This article is free to access until 24 May 2017

V Gnyawali et al, Soft Matter, 2017, DOI: 10.1039/C7SM00128B

Chinese scientists have used conducting carbon nanotubes and impact-responsive polymers to create a smart Kevlar composite with enhanced ballistic and stab resistance. Body armour made from this material could sense the force and location of impacts, and detect when it has been pierced.

Flexible, lightweight and durable, Kevlar has been a key component in personal armour for decades. It has excellent stab and cut resistance, making it the primary component in police stab vests, also offering limited protection against small arms fire.

Source: © Royal Society of Chemistry
Scanning electron microscopy images showing regular Kevlar (a, b) and the improved version with different shear-stiffening polymer/Kevlar ratios (c: 4.8 weight% polymer; f: 84 weight% polymer)

The problem with Kevlar’s flexibility is that when it stops a bullet, the energy is still transferred directly to the wearer at the point of impact, which causes trauma – imagine being punched at the speed of a bullet! For military applications, where Kevlar would not stand up to high-velocity rifle rounds, it is often combined with heavier steel or ceramic plates to spread the impact over a larger area.

Read the full story by Will Bergius in Chemistry World.

This article is free to access until 17 May 2017.

S Wang et al, Soft Matter, 2017, DOI: 10.1039/c7sm00095b

Study adds to understanding of droplet behaviour

New research by a scientist in the US can better explain how a droplet splash is dictated by the smoothness of a surface, as well as the surrounding air pressure.

Source: © Royal Society of Chemistry

Scientists already knew that two aspects were involved in this seemingly simple process; one related to the surrounding air, and the other to how the liquid spreads on the substrate. ‘If we were forced to guess, we’d probably assume that decreasing the ambient pressure around the drop would make the splash bigger. After all, we’re decreasing air resistance,’ explains Andrzej Latka, at the University of Chicago, who performed the new research.

Read the full story and watch the video showing the splash in Chemistry World.

This article is free to access until 28 February 2017.

Andrzej Latka, Soft Matter, 2017. DOI: 10.1039/C6SM02321E