High-Yield Synthesis of Monodisperse Dumbbell-Shaped Polymer Nanoparticles
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
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 control whether they stabilze water in oil or oil in water emulsions. Because they have continuously variable control over moiety size ratios, it might also be possible control finer details of the size or kind of emulsion structures formed by these particles.