The researchers were puzzled: How does a gel particle understand how huge its neighbor is without touching it? Is there some sort of “telepathy” going on in between microgels?
Hypothesis of 2016 verified
” Of course not,” smiles Urs Gasser. The physicist has actually been studying the amazing shrinking of microgels in colloids for the past 10 years.
Together with a team of researchers, he released a paper in 2016 describing the phenomenon. Briefly, in this situation, the polymer particles include long carbon chains. These bring a weak negative charge at one end. These chains form a ball, the microgel. This can be thought of as looking like a ball of wool, with the residential or commercial properties of a sponge.
This three-dimensional tangle therefore contains unfavorable point charges that attract favorably charged ions in the liquid. These so-called counterions organize themselves around the negative charges in the ball, forming a positively charged cloud on the surface area of the microgel. When the microgels come close together, their charge clouds overlap (see image). This in turn increases the pressure inside the liquid, which compresses the microgel particles until a new stability is reached.
At the time, nevertheless, the research team was not able to supply experimental evidence of the cloud of counterions. Together with his Ph.D. trainees Boyang Zhou and Alberto Fernandez-Nieves of the University of Barcelona, Gasser has actually now provided that proof– and it impressively supports the 2016 hypothesis. The outcomes have been published in the journal Nature Communications.
SINQ neutron source crucial to resolving the puzzle
This was possible thanks to the neutrons from PSIs spallation source SINQ– in addition to a speculative trick. Since the cloud of counterions in the colloid is so rarefied that it is not actually visible in the image of the spread neutrons. The counterions represent no more than one percent of the mass of a microgel.
So Gasser, Zhou, and Fernandez-Nieves examined 2 samples: one colloid in which all the counterions were salt ions and another in which they were ammonium ions (NH4). Both these ions likewise occur naturally in microgels– and they spread neutrons differently. Subtracting one image from the other leaves the signals of the counterions. Boyang Zhou: “This seemingly basic service needs the utmost care in preparing the colloids so as to make the ion clouds visible. Nobody has ever measured such a rarefied ion cloud before.”
Applications in pharmaceuticals and cosmetics
Knowing how soft microgels act in colloids implies that they can be tailored to fit various applications. In the oil industry, they are pumped into underground tanks to change the viscosity of the oil in the well and facilitate its extraction. In cosmetics, they offer creams the preferred consistency.
Smart microgels are also conceivable, which could be filled with medications. The particles could respond to stomach acid, for example, and launch the drug by diminishing. Or else a microgel might shrink into a little, largely loaded polymer ball when the temperature level increases, one that reflects light in a different way than in its swollen state. This could be utilized as a temperature level sensing unit in narrow fluid channels. Other sensors might be designed to react to changes in pressure or contamination. “There are no limitations to the creativity,” states Urs Gasser.
Recommendation: “Measuring the counterion cloud of soft microgels using SANS with contrast variation” by Boyang Zhou, Urs Gasser and Alberto Fernandez-Nieves, 7 July 2023, Nature Communications.DOI: 10.1038/ s41467-023-39378-5.
An experiment carried out 15 years earlier revealed that soft particles made of polymers– so-called microgels– diminish quickly when their concentration in a solvent is increased above a certain threshold. These so-called counterions arrange themselves around the unfavorable charges in the ball, forming a favorably charged cloud on the surface of the microgel. When the microgels come close together, their charge clouds overlap (see image). Both these ions likewise happen naturally in microgels– and they spread neutrons differently. Understanding how soft microgels behave in colloids indicates that they can be tailored to fit lots of various applications.
This graphical simulation shows the microgel particles (green) arranging themselves in the liquid, with their overlapping ion clouds (red) on their surface. Credit: Urs Gasser
Researchers from PSI and the University of Barcelona have managed to describe the odd behavior of microgels. Their try outs neutron beams have stretched the abilities of this measurement technique to its limits. This breakthrough holds appealing potential for new applications in the fields of products science and pharmaceutical research study.
They flow through our arteries, add color to our walls, or make milk yummy: small particles or droplets that are really finely dispersed in a solvent. Together they form a colloid. Whereas the physics of colloids including hard particles– such as color pigments in emulsion paint– is comprehended well, colloids involving soft particles– such as hemoglobin, the red pigment in blood, or beads of fat in milk– hold some stunning surprises.
An experiment performed 15 years back revealed that soft particles made of polymers– so-called microgels– shrink abruptly when their concentration in a solvent is increased above a certain limit. Big particles contract until they are the size of their smaller neighbors when this occurs. Surprisingly, this takes place even when the particles are not actually in contact with each other.