Sonochemical synthesis of latex
by Kathrin Hielscher, Hielscher Ultrasonics GmbH (www.hielscher.com)
Ultrasound induces and promotes the chemical reaction for the polymerization of latex. By
sonochemical forces, the latex synthesis occurs faster and more efficient. Even the handling of the
chemical reaction becomes easier.
Latex particles are widely used as additive for various materials. Common application fields include
the use as additives in paints and coatings, glues and cement.
Ultrasound is well-known as efficient and reliable method for dispersing and emulsifying. The high
potential of ultrasonics is the capability of creating dispersions and emulsions not only in the micronbut also in the nano-size range. For the synthesis of latex, an emulsion or dispersion of monomers,
e.g. polystyrene, in water (o/w = oil-in-water emulsion) is the basis of the reaction. Depending on the
emulsion type, a small amount of surfactant may be required, but often the ultrasonic energy
provides such a fine droplet distribution so that the surfactant is superfluous. If ultrasound with high
amplitudes is introduced into liquids, the phenomenon of so-called cavitation occurs. The liquid
bursts and vacuum bubbles are generated during the alternating high-pressure and low-pressure
cycles. When these small bubbles cannot absorb more energy, they implode during a high-pressure
cycle, so that pressures up to 1000 bar and shock waves as well as liquid jets of up to 400 km/h are
reached locally. [Suslick, 1998] These highly intense forces, caused by ultrasonic cavitation, take
effect to the enclosing droplets and particles. The free radicals formed under the ultrasonic
cavitation initiate the chain reaction polymerization of the monomers in the water. The polymer
chains grow and form primary particles with an approximate size of 10-20 nm. The primary particles
swell with monomers, and the initiation of polymer chains continues in the aqueous phase, growing
polymer radicals are trapped by the existing particles, and polymerization continues inside the
particles. After the primary particles have formed, all further polymerization increases the size but
not the number of particles. Growth continues until all of the monomer is consumed. The final
particle diameters typically are 50-500 nm.
200 watts powerful ultrasonic lab device UP200St for remote control and with various accessories
(©www.hielscher.com)
If polystyrene latex is synthesized via sonochemical route, latex particles with a small size of 50 nm
and a high molecular weight of more than 106 g/mol can be achieved. Due to the efficient ultrasonic
emulsification, only a small amount of surfactant will be needed. The continuous ultrasonication
applied to the monomer solution creates sufficient radicals around the monomer droplets, which
leads to the very small latex particles during the polymerization. Besides the ultrasonic
polymerization effects, further benefits of this method are the low reaction temperature, the faster
reaction sequence and the quality of the latex particles due to the high molecular weight of the
particles. The advantages of ultrasonic polymerization apply also for the ultrasonically-assisted
copolymerization. [Zhang et al. 2009]
A potential effect of latex is achieved by the synthesis of ZnO encapsulated nanolatex: The ZnO
encapsulated nanolatex shows high anticorrosive performance. In the study of Sonawane et al.
(2010), ZnO/poly(butyl methacrylate and ZnO−PBMA/polyaniline nanolatex composite particles of 50
nm have been synthesized by sonochemical emulsion polymerization.
Hielscher Ultrasonics high-power devices are reliable and efficient tools for sonochemical reaction. A
wide range of ultrasonic processors with different power capacities and setups makes sure to provide
the optimal configuration for the specific process and volume. All applications can be evaluated in
the lab and subsequently scaled up to the production size, linearly. Ultrasonic machinery for
continuous processing in the flow-through mode can be easily retrofitted into existing production
lines.
Ultrasonic industrial device UIP1500hd for high power applications (©www.hielscher.com)
References:
•
Ooi, S. K.; Biggs, S. (2000): Ultrasonic initiation of polystyrene latex synthesis. Ultrasonics Sonochemistry 7, 2000.
125-133.
•
Sonawane, S. H.; Teo, B. M.; Brotchie, A.; Grieser, F.; Ashokkumar, M. (2010): Sonochemical Synthesis of ZnO
Encapsulated Functional Nanolatex and its Anticorrosive Performance. Industrial & Engineering Chemistry
Research 19, 2010. 2200-2205.
•
Suslick, K. S. (1998): Kirk-Othmer Encyclopedia of Chemical Technology; 4th Ed. J. Wiley & Sons: New York, Vol. 26,
1998. 517-541.
•
Teo, B. M..; Ashokkumar, M.; Grieser, F. (2011): Sonochemical polymerization of miniemulsions in organic
liquids/water mixtures. Physical Chemistry Chemical Physics 13, 2011. 4095-4102.
•
Teo, B. M..; Chen, F.; Hatton, T. A.; Grieser, F.; Ashokkumar, M.; (2009): Novel one-pot synthesis of magnetite
latex nanoparticles by ultrasonic irradiation.
•
Zhang, K.; Park, B.J.; Fang, F.F.; Choi, H. J. (2009): Sonochemical Preparation of Polymer Nanocomposites.
Molecules 14, 2009. 2095-2110.
Hielscher Ultrasonics GmbH
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