High-Yield Synthesis of Monodisperse Dumbbell-Shaped Polymer Nanoparticles

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Original Entry: Tom Dimiduk APPHY 225 Fall 2010

[High-Yield Synthesis of Monodisperse Dumbbell-Shaped Polymer Nanoparticles http://pubs.acs.org.ezp-prod1.hul.harvard.edu/doi/pdf/10.1021/ja101760q]


Surface Tension, Janus Colloid, Polymerization, Asymmetry, Core-shell Particle


Figure 1: The authors' synthesis process, (a) schematic representation showing particle, adding the core, swelling, and then new polymerization to form the dumbell. (b) Electron micrograph of the polystyrene nanoparticles, (c) the core shell nanoparticles, (d) the symmetric dumbell particles.
Figure 2: Demonstration of the effects of toluene on the core shell particles. (a) the polystryene particles take up toluene and cream at the top when centrifuged, the copolymer and core shells do not take up enough toluene to rise. (b) electron micrograph showing deformation caused by toluene swelling in the core shell particles.
Figure 3: Changing the relative size of the two dumbell portions by varying ratio of swelling monemer to seed particles. (a) 1.3, (b) 1.6, (c) 2.0, and (d) 3.0. (e) shows where the measurments plotted in (f) are taken.
File:Dufresne dumbell fig4.png
Figure 4: Electron micrographs of the structures these particles assemble into. Scale bar in (a) is 5 micron, others are 1 micron

The authors present a high yield, scalable method for synthesis of asymmetric nanoparticles with aspect ratios of up to 1.8. They use core shell particle consisting of a polystyrene core with a random copolymer of styrene and trimethoxysilylpropylacrylate (TMSPA) grown on the outside as a shell. The polystyrene can be swelled with toluene or styrene monomer. At sufficiently high swelling, the core will breach through the copolymer shell (see figure 1 and 2). They then polymerize on more polystyrene, it preferentially adds to the polystyrene numb protruding from the core-shell particle. By controlling ammount of monomer added, they can control the aspect ratio of the particles. These particles self assemble into interesting structures which the authors believe may be useful for photonic crystal applications.

Soft Matter Discussion

Surface tension is both the cause of the problem the authors aim to address and one of their main tool is doing so. Non-spherical particles do not form naturally because their higher surface area to volume ratio makes them energetically disfavored. The authors manipulate surface tension to their advantage by using a shell which is more hydrophilic than the polystyrene core. This way when polystyrene leaks out it forms a small glob minimizing its area, rather than coating the shell to minimize total area.

These particles add an extra phase transition compared to plain spheres, between vertical and horizontal orientations of the dumbells.

These particles could serve as effective stabilizers for pickering emulsions since they possess hydrophobic and hydrophilic ends. The author's ability to control the relative sizes of these two ends should allow them to be engineered to stabilze water in oil or oil in water emulsions.