Movies; seeing science

Below you will find a series of movies that have been taken at different times over a period of some forty years. If you want to know more about the scientific content of each movie click on the “more info” top right hand corner marker for each movie. Below the movie in most cases you will find the scientific reference that relates to the work.  

The Cold Extrusion of Chocolate

In the 1990s I discovered that chocolate could be “cold extruded” and there was an exciting period at Cambridge where we pursued the science behind the concept and Nestle explored the commercial potential. The movie below shows how chocolate can be “cold extruded” below its normal melting point using reasonably high pressure ( 200bar) ram extrusion,  


Chocolate Cold  Extrusion.  Yu Wen Chen. 2000s


  Flexible chocolate.

Cold extruded Flexible chocolate being tied in knots. Yu Wen Chen 2000s

Flexible chocolate.

Injection moulding of cold extruded  chocolate 1990s 

Flexible chocolate.

The “Ovaci Necklace ” chocolate extrusion instability 2000s  “Expect the unexpected”.  This movies shows a quite remarkable chocolate cold extrusion condition where a “necklace” of extruded chocolate was formed. There is an explanation given in the paper below for this “incredibly unexpected” experimental set of conditions.



The experimental observation and modelling of an “Ovaici”necklace and stick-spurt instability arising during the cold extrusion of chocolate.

Tomorrows World”, Flexible chocolate 1996

They say people generally  enjoy “15 minutes of fame” in their life and the discovery of chocolate cold extrusion was one of those for me. At the time, “chocolate” was considered a very “un Cambridge” area to work in and my work and its notoriety received a very mixed response from some Cambridge academic colleagues.


Linkam Cambridge Shear Cell

The Linkam Cambridge Shear cell was originally designed to study the effect of shear on thermotropic Liquid Crystal Polymers (LCPs), and  it has found application for a range of different structured complex fluids.

Carbon Nanotubes (CNTs)

Carbon Nanotubes (CNTs) were all the rage in the 2000s and now have found niche rather than widespread application. This remarkable movie taken by Anson Ma shows how CNTs can aggregate during shear to form helical banding. The Movie was taken using a Linkam Cambridge Shear Cell and is an example of “expect the unexpected”, but seeing is believing!

Carbon Nanotube (CNT) aggregate Helical banding. Anson Ma


Experimental observation on the flow-induced assembly of Carbon nanotube suspensions to form helical bands

Carbon Black

The video below shows the effect of a carbon black suspension when sheared under increasing shear conditions.

The effect of shear on carbon black aggregates. Kat Yearsley 2009



The rheology of multi-walled carbon nanotube and carbon black suspensions  

Multipass Rheometer (MPR) Flow Birefringence.

One of the application areas of the  Cambridge Multipass Rheometer (MPR) was  to study optical stress fields (Flow Birefringence) of molten polymers in complex flow geometries. This involved providing a  “test section” with optical windows that were able to withstand 100 bar pressure and using the piston control to provide precise polymer flow. One geometry tested was the so called “Cross Slot” and the video below shows the evolution of stress fringences during flow.

Flow birefringence within a Cross Slot geometry. David Hassell 2005



Cross-slot extensional flow birefringence observations of polymer melts using a multi-pass rheometer

Flow birefringence within a slot.

This video sequence shows the way molten polyethylene flows within an MPR flow constriction. The black fringes correspond to different levels of stress in the melt. I first observed flow birefringence pictures similar to this in the 1970s and it has taken some 40 years before others were able to model the time dependant stress fields.

DOW150R DGH3 160C 1mms 30 450



Oscillatory Flow Mixing 

Oscillatory flow mixing formed an important element in our Cambridge work on innovative processing. We discovered that fluid oscillation in a tube in the presence of sharp edged periodic baffles could produce very effective  “chaotic mixing” and the  video sequence below is an excellent example of the type of mixing that could be achieved. 

Oscillatory flow mixing in a baffled tube.

Osc Flow Adam Harvey 1995

Oscillatory flow mixing in a multi baffled tube

This video sequence below shows the mixing of air bubbles that can be achieved by fluid oscillation in a baffled column. In order to visualize the flow the frame rate has been greatly reduced.

8hz 3mm 01Lmin


Numerical simulation of Oscillatory flow mixing (OFM).

From the 1980s onwards numerical simulation of complex flows became possible and OFM was an excellent candidate to work on as the flow is complex but not as “complex” as what most people call turbulence. The videos below are examples of OFM numerical simulations of fluid motion in the smaller smooth constriction OFM mesotubes.

Simulation of oscillatory flow mixing in a smooth constriction mesotube

F10A1 ave vm f2

Simulation of fluid mechanics and actual experimental particle motion in a smooth constriction mesootube.

F10A2 resize 5

Simulation of oscillatory flow fluid mixing in a smooth constriction mesotube.

Minghzi LES


MIcro Capillary Flow

The invention of plastic microcapillary films enabled use to optically interrogate flow in microchannels and the videos below show a series of experiments that were carried out. Most of the background to work is given in the publication below.

The separation of immiscible liquid slugs within plastic microchannels using a metallic hydrophilic sidestream

Slug flow in plastic microcapillary films

Plastic Microcapillary films have flat outer surfaces and the refractive index match of fluid within the capillaries is a close match to the transparent plastic thereby enabling easy optical interrogation of the 150 micron diameter channels. This video shows the movement of aqueous slugs in an oil matrix for  the micro channels. multi slugs



Downstream flow splitting within a microcapillary film.

A way of separating water from oil!

This video sequence is special and unique! It shows how “under the right conditions” aqueous slugs can be separated from a mineral oil stream within a capillary channel. Flow splitting attempt Mineral oil water with 0 8mm needle

Upstream slug generation in a microcapillary film

This video shows the well known effect where aqueous slugs are created in a mineral oil stream by the continuous injection of water from a side stream. slug generation upstream


Fast Filament stretching.  

Dr Simon Butler at Cambridge and Prof Rudy Valette and his team at CEMEF Sophia Antipolis have, over the last few years, been working on fast filament stretching and a paper on the subject is given below.

Valette et al JNNFM 2019

The video below  shows the  way watery Newtonian fluid deform and form drops by an end pinching mechanism. The process is complex but has been very well captured by the CEMEF modelling.


                                       Buffer 1-0 18k avi

The video below shows the way a higher Newtonian viscosity fluid (silicon oil) responds to the same deformation as above. In this case a longer lasting thinning thread is formed without the formation of a drop. Again the CEMEF modelling captures this behaviour.


                              SiOil500 1-0 18k avi

The next video shows the way a high yield stress fluid (A skin cream) deforms and forms asymptotic cones on each of the pistons. It should be clear from these examples that the rheology (and surface tension) of the fluids play a very important part in the shape and form of break up behaviour.


Nivea 1-00 b 18k avi

The presentation below also contains background and videos of fast filament stretching and breakup and shows how effectively the CEMEF modelling is able to capture experimentally observed events..