This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Tiny, soft polymer particles—known as microgels—can help to stabilize extremely thin liquid jets. How this works is the finding of a study led by researchers at TU Darmstadt, which has been published in Nature Communications.
The findings could be of interest for the development of needle-free medical injection systems. Microgels are soft polymer particles less than one micrometer in size. They can adsorb at the interface between air and water, where they reduce the surface tension of the liquid.
In this respect, their effect is similar to that of conventional surface-active components—so-called surfactants—such as those often found in soap, dishwashing liquid or detergent. However, unlike many conventional surfactants, the microgels used in the study are nontoxic, and their interaction mechanism with the liquid differs significantly. For their experiments, the scientists generated extremely thin jets of water using surface acoustic waves.
A drop of water containing the microgels was used for this purpose. A specially manufactured chip generated the waves at a frequency of around 64 MHz, producing a liquid jet approximately 200 micrometers in diameter from the drop. A high-speed camera recorded the jet formation and extension.
"This revealed a surprising effect: Although the microgels themselves are only around 700 nanometers in size, their properties can determine the stability of a liquid jet extending over a centimeter," explains Dr. Amin Rahimzadeh from the Institute of Condensed Matter Physics at the Department of Physics, TU Darmstadt. "The softer the particles were, the longer the water jet remained stable." The decisive factor appears to be the extent to which the microgels can deform.
The researchers tailored the stiffness of the particles during their synthesis by modifying the cross-linking of the so-called polymer scaffold, the three-dimensional, porous structure formed by the polymer. A more cross-linked framework makes the microgels stiffer, while weaker cross-linking makes them softer. Computer simulations provided an explanation for the observation.
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