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"We are opening the new world of active particle"
Name관리자| Date2017-08-24 13:38| Hit79
- Granick's research team suggested the blueprint of active colloid research field
- Development of the active particle... will make micro-robot in vivo possible 

Jie Zhang(1st author) and Steve Granick
 
"If we have a tiny robot that runs without a battery, it could cure inside a body. It's possible if we motivate the colloid particles as we want". Steve Granick, a professor of the Department of Natural Sciences, UNIST, who is the director of the Center for Soft and Living Matter in IBS(Institute of Basic Science, Korea) at the same time, recently presented the prospect of the new field, 'collective mobility of active colloid particles'. This article, which has been published in the current issue of the world-renowned journal Chemical Society Review (IF = 38.618), is taking center stage.
 
A colloid is a mixture of particles, such as milk, ink, blood, fog, and mayonnaise, in which the particles float uniformly in the solvent. Milk, for example, is a state which fat, protein, calcium, and so on spread evenly in transparent water (solvent). The particle size of protein, calcium and the like is larger than 1 nm (nanometer, 1 billionth of a meter) and smaller than 1 ㎛ (micrometer, 1 millionth of a meter). 
 
"Colloidal particle is the minimum scale of living organisms, and our bodies work by moving a myriad of colloidal particles, such as enzymes and proteins," he said. "Colloidal particles are used in many industries such as food, air purification, but the scientific research couldn't offer the understanding on it".

Because colloidal particles are much cheaper than nanoparticles, they can be used widely. Especially, 'active colloid particles', which have spontaneous propulsion, don't need extra energy. For example, micro-robots move without batteries in the body, and synthetic particles generate power from chemical reactions occurring on the surface of the particles.
 
Collective self-assembly of active colloids as the electric charge changing.
 
Because this small particle can move by themselves, the 'active colloid particle' is considered a promising technology in nano medical engineering. Particularly, when active colloidal particles are collected in a group, they show completely different form, assembling regularly with some rule. But it is not clear why this happens. 
 
"The active colloidal particle is a new field that has been pioneered over the past decade. It gets energy from environmental factors such as electric field, magnetic field, heat, light, change of chemical concentration," Prof. Granick said. "By moving the active colloid particles freely, we can change the properties of the usual materials made of colloid particles. We are still in its infancy." 
 
In 2006, Prof. Granick's team created an active colloidal particle called 'Janus particle' and reveals interesting phenomena. Janus particles are spherical particles about 1 μm-diameter, but only half sphere the surface is coated with a specific material. Therefore,t, half of the particles have different electrical and chemical characteristics. Various behaviors are observed in the particles in a liquid solvent.
 
Collective mobility of active colloids distinguished by its solvent, particle shape, and external energy source.
 
The researchers are further studying the behavior of 'collective' colloid particles. It is noted how the colloid group behavior changes with the particle shape and the material, the effect of the solvent, and the interaction between particles. As a result, in 2016, they revealed that 'the balance breaking of magnetic field' re-assemble active particles, and published in Nature Materials.
 
"There are so many colloidal particles, not just one or two, so we should know the collective mobility to handle the colloids in real life," Granick said. "It's like you can not identify a society or a country though you know one or two people". "We do not think humans will spend the next 500 years improving their smartphones or engines," he said continuously. "Our technology makes only static paint and static food. Bringing the 'voluntary movement' of active colloids to our lives will open up a future we couldn't have imagined." 

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