Performing chemical reactions inside tiny droplets can help manufacturers develop greener processes for coating drugs.
A discovery led by Singapore's Agency for Science, Technology and Research (A*STAR) could lead to improvements in the way drugs are delivered to the right parts of the body by uncovering the mechanisms that help oil, water, and free radicals mix in tiny droplets .
Understanding how radical fragments (red spheres) react with surrounding water molecules to create hydroxyl radicals, while leaving behind hydrophobic residues (black), can help green chemistry researchers. © 2016 A*STAR Institute of Chemical and Engineering Sciences
Emulsion polymerization is an emerging technology used to produce enormous chain-like molecules called polymers inside oil-filled drops suspended in water. This approach enables producers of goods such as latex paints to do away with traditional oil-based solvents, which helps them meet stricter environmental controls. Recently, researchers have discovered that ‘mini-emulsions’, in which droplets are shrunk to nanoscale sizes using powerful blenders and stabilized with fatty molecules, can produce nanoparticles for applications including controlled drug release.
Alex van Herk from the A*STAR Institute of Chemical and Engineering Sciences explains that in mini-emulsions, each droplet can be regarded as a ‘nanoreactor’ — a segregated system where all the ingredients for polymerization are present in one spot. Once a highly reactive free radical enters the drop, the small molecules inside link into chains. “The nanoreactors grow completely independently, and we can achieve very high reaction rates,” he says.
This polymerization only works when one free radical enters a nanoreactor. However, the molecules that generate free radicals, known as initiators, generally produce them in pairs. To better understand these radical movements, van Herk and colleagues from the Netherlands and the United Kingdom investigated the effects of using initiators that either repelled or attracted water molecules.
Typical initiators are water-soluble and researchers propose that they create pairs of free radicals in water where one of the free radicals enters the nanoreactor and starts the polymerization. However, when the initiator is a water-repelling molecule, such as lauroyl peroxide, theory predicts the chemical reaction will be hindered because the two radicals in a confined space would easily recombine and the polymerization process would not start.
Surprisingly, the A*STAR-led team found mini-emulsion polymerization proceeded rapidly and completely using lauroyl peroxide initiators. To explain this discrepancy, the team deduced that a free radical must leave by an alternative mechanism, known as chain transfer, which transforms one of the water molecules surrounding the nanoreactor into a hydroxyl radical compound. The remaining radical produces latex nanoparticles that correspond one-to-one with the initial droplet size — a benefit for manufacturers seeking to predict morphologies with exact specifications.
“Industry is only modestly adopting mini-emulsion polymerization, partly because its mechanism is not fully understood and controllable yet,” says van Herk. “These findings give us a better edge to design and produce special nanoparticle morphologies such as low-cost nanocapsules.”
The A*STAR-affiliated researchers contributing to this research are from the Institute of Chemical and Engineering Sciences. For more information about the team’s research, please visit the Polymer Engineering & Characterisation group webpage.
 Jansen, T. G. T., Meuldijk, J., Lovell, P. A. & van Herk, A. M. On the miniemulsion polymerization of very hydrophobic monomers initiated by a completely water-insoluble initiator: thermodynamics, kinetics, and mechanism. Journal of Polymer Science Part A: Polymer Chemistry 54, 2731–2745 (2016).
 Jansen, T. G. T., Meuldijk, J., Lovell, P. A. & van Herk, A. M. On the reaction characteristics of miniemulsion polymerization with aqueous phase initiation — Experiments and modeling. Macromolecular Reaction Engineering 9, 19–31 (2015).
A*STAR Research | Research SEA
World’s Largest Study on Allergic Rhinitis Reveals new Risk Genes
17.07.2018 | Helmholtz Zentrum München - Deutsches Forschungszentrum für Gesundheit und Umwelt
Plant mothers talk to their embryos via the hormone auxin
17.07.2018 | Institute of Science and Technology Austria
For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.
To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...
For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.
Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...
Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.
A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...
Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.
"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....
Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.
Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...
13.07.2018 | Event News
12.07.2018 | Event News
03.07.2018 | Event News
17.07.2018 | Power and Electrical Engineering
17.07.2018 | Life Sciences
16.07.2018 | Physics and Astronomy