Preparation and characterization of the nano-promoters
The nano-promoters were prepared
through soap-free emulsion polymerization with St as the hydrophobic
monomer, while polymerizable monomers and KPS were applied as the
hydrophilic monomers and initiators, respectively. Two polymerizable
monomers with different hydrophilic groups
(-SO3- and -COO-)
were used to give rise to two kinds of nano-promoters, which were
defined as -SO3-@PSNS and
-COO-@PSNS separately. A 250 mL flask equipped with an
agitator was used to synthesize the nano-promoters in nitrogen
environment, and a reflux condenser was employed. Firstly, the
appropriate amount of deionized water, St and hydrophilic monomers were
added into the flask in sequence, while the agitation was turned on at a
speed of 300 rpm. Then, when the temperature was reached set value, the
initiator solution was dropped into the flask at a rate of 1 drop per
second, and subsequently the system was kept for 5 h until the end of
polymerization. The recipe of the soap emulsion polymerization is given
in Table S1, and the reaction temperature was set as 353.15 K, which was
controlled by constant temperature oil-bath pans
The morphologies of the nano-promoters were observed by a transmission
electron microscope (TEM, JEM-1200EX, Japan Electronics Co., Ltd.,
Japan), and it is clear from Figure 1 that both of the nano-promoters
are uniform nanospheres. The hydrophilic group on the surface of the
nano-promoters was determined with an infrared spectrometer (Nicolet iN
10, Thermo Fisher, USA), the adsorption peaks corresponding to the S=O
and C=O confirm the existence of -SO3-and -COO‑ groups on the surface of
-SO3-@PSNS and
-COO-@PSNS, respectively. The size distribution and
zeta potential of the nano-promoters were determined by a Laser Particle
Size Analyzer (Malvern Nano-s90, UK), and
-SO3-@PSNS and
-COO-@PSNS produce the zeta potential of -31.8 mV and
-20.36 mV separately. This confirms the existence of corresponding
hydrophilic groups on the nano-promoters, and excellent stability is
also anticipated through the electrostatic force between the
nano-promoters.