electronic supplementary information · to the recipes given in table s1 and the schematic diagram...

Electronic Supplementary Information

Jianan Zhang,* Qing Liu, Beibei Yang, Wenlong Yang, Bo Wu, Jizhi Lin, Mingyuan Wu, Qingyun Wu and Jianjun Yang

School of Chemistry and Chemical Engineering of Anhui University & AnHui Province Key Laboratory of

Environment–friendly Polymer Materials, Hefei 230039, China

*Corresponding author: Jianan Zhang, E–mail address: [email protected] (J.A. Zhang)

1 Experimental

1.1 Materials

Tetraethoxysilane (TEOS), divinyl benzene (total isomers >46%, DVB), and methyl methacrylate

(MMA) were purchased from Shanghai Chem. Reagent Co. (China) and was purified by passing

through a short basic Al2O3 column before use. 2, 2`–azobis (isobutyronitrile) (AIBN, Shanghai

Chem. Reagent Co.) was purified by recrystallization in absolute ethanol and kept refrigerated until

use. γ– (Trimethoxysilyl) propyl methacrylate (MPS, Aldrich) and hexadecane (HD, Fluka) were

used without purification. Sodium dodecyl sulfate (SDS) and ammonium hydroxide (28% by wt)

(Shanghai Chemical Reagent Co.) were purchased in their regent grade and used without further

purification. FeCl2·4H2O and FeCl3·6H2O were purchased from Shanghai Chem. Reagent Co.

(China). Polystyrene (PS) was synthesized by solution polymerization method in our laboratory,

and was used as co-stabilizer in the miniemulsion polymerization system. The average molecular

weight of PS was found to be 28700 g/mol with Mw/Mn = 1.31 determined by gel permeation

chromatography (GPC). Deionized water was used for all experiments.

Electronic Supplementary Material (ESI) for Polymer ChemistryThis journal is © The Royal Society of Chemistry 2012

1.2 Synthesis of MPS modified magnetic nanoparticles

The magnetic nanoparticles were prepared by co-precipitation of FeCl2/FeCl3 (ratio 1:2). An

aqueous solution (150 mL) containing 5.6 mM FeCl2 and 11.2 mM FeCl3 in a 250-mL flask was

heated to 50 °C under N2 bubbling. Then 12.5 mL ammonia solution was added under vigorous

stirring. After 30 min, the precipitate was collected by a magnet and washed three times with water.

Then the precipitate was re-dispersed in ethanol (150 mL) and a certain amount of MPS was added.

The dark suspension was stirred for 3 h at room temperature under N2 atmosphere. The black

precipitate was collected, washed three times with ethanol and then dried under vacuum in an oven

at 30 °C.

1.3 Synthesis of double–shelled hollow microspheres

The silica/polymer hollow microspheres were prepared by miniemulsion polymerization according

to the recipes given in Table S1 and the schematic diagram in Scheme 1. In a typical synthesis

(Sample 13 in Table S1), 0.8 g of hexadecane and 0.2 g of AIBN were first added in the monomer

mixture of 14.0 g of MMA, 1.4 g of DVB, 6.0 g of TEOS, 1.6 g of MPS, and 1.0 g of modified

magnetic nanoparticles to form an oil phase. A portion of 80 g of SDS aqueous solution was

employed as a water phase. The mixture of oil phase and water phase was first pre-emulsified by

mechanical stirring for 0.5 h and then the miniemulsion was prepared by high speed shearing via

Fluko® FM200 homogenizer (Fluko® Equipment Shanghai Co., Ltd, China) at ~18,000 rpm for 5

min in an ice bath and the polymerization was carried out at 70 °C in a 250–ml four–neck round

flask equipped with a reflux condenser and an agitator. After the polymerization was carried out

under N2 atmosphere for 0.5 h, the pH value of the dispersion was adjusted by ammonia to around


9.0. The polymerization was carried out for 8 h to obtain the silica/polymer latexes.

Table S1. Synthesis conditions of double–shelled hollow microspheres

Samples Oil phase Water phase

MMA (g)

DVB (g)

MPS (g)

TEOS (g)

AIBN(g)

PS(g)

HD (g)

Water (g)

SDS(g)

1 140 1.40 1.20 6.0 0.20 0 0.80 80 0.152 14.0 1.40 0.00 0 0.20 0.20 0.80 80 0.153 140 1.40 1.20 2.0 0.20 0.20 0.80 80 0.154 14.0 1.40 1.20 4.0 0.20 0.20 0.80 80 0.15

5 14.0 1.40 1.80 6.0 0.20 0.20 0.80 80 0.15 6 14.0 1.40 2.40 8.0 0.15 0.20 0.80 80 0.157 14.0 0 0.31 6.0 0.20 0 0.80 80 0.258 14.0 0 0.31 6.0 0.20 0 0.80 80 0.159 14.0 0 0.31 6.0 0.20 0 0.80 80 0.10

10 14.0 0 0 6.0 0.20 0 0.80 80 0.15 11 14.0 0 0.80 6.0 0.20 0 0.80 80 0.15 12 14.0 0 1.60 6.0 0.20 0 0.80 80 0.1513* 14.0 1.4 1.60 6.0 0.20 0.20 0.80 80 0.1514* 14.0 1.4 1.60 6.0 0.20 0.20 0.80 80 0.15

* Magnetic nanoparticles was added in oil phase before miniemulsification process; 1.0 g and 2.0 g of MPS

modified Fe3O4 nanoparticles were incorporated in Samples 13# and 14#, respectively.

1.4 Characterization

Samples of transmission electron microscopy (TEM) were prepared by drying a drop of dilute

nanocomposite dispersion onto a carbon–coated copper grid. Analysis was conducted using a

Hitachi H-800 electron microscope operating at 200 kV. Thermogravimetric tests (TG) were

conducted using thermoanalyzer STA449F3 from Netzsch Gerǎtebau, Selb. Samples were pre–dried

in an oven at 70 °C and then heated in air to 800 °C at a heating rate of 10 °C min–1. Samples of

FT–IR characterization were dried at 60 °C under vacuum for 24 h and measured in the

wavenumber range from 4000 to 400 cm–1 at a resolution of 4 cm–1 using a Nicolet Nexus–870

FTIR spectrophotometer.


2. Results and discussion

2.1 Effect of SDS on the microstructure and morphology of hybrid microspheres

We have investigated the effects of emulsifier content on the microsphere morphology at low

MPS content. Sample 7, 8, and 9 in Table S1 gave the detailed information about the influences of

emulsifier content from 0.10, 0.15 to 0.25. Hybrid microspheres with bowl morphology were

prepared at the emulsifier content of 0.15 g (Fig. S2).

As is well known, the emulsifier content has effect on the emulsion and then the polymerization

stability, especially in miniemulsion polymerization system. In miniemulsion polymerization, the

loci of polymerization become the monomer droplets. The droplet surface area in these systems is

very large, and most of the surfactant is adsorbed at the droplet surface. Particle nucleation is

primarily via radical (primary or oligomeric) entry into monomer droplets, since little surfactant is

present in the form of micelles, or as free surfactant available to stabilize particles formed in the

continuous phase. The important feature is that the reaction proceeds by polymerization of the

monomer in these small droplets. So when the emulsifier content exceeded the critical micelle

concentration (CMC), conventional emulsion polymerization occurred (Fig. S1). However when the

emulsifier content decreased to 0.1 g, the polymerization process became unstable and the resulted

polymer particles became polydisperse (Fig. S3).


Fig. S1 TEM images of silica/polymer hybrid microspheres (Samples 7 shown in Table S1).

Fig. S2 TEM image of silica/polymer hybrid hollow microspheres (Samples 8 shown in Table S1).

Fig. S3 TEM images of silica/polymer hybrid hollow microspheres. (Samples 9 shown in Table

S1).

2.2 Effect of PS (co-stabilizer) on the microstructure and morphology of hybrid microspheres


Fig. S4 TEM image of silica/polymer hybrid hollow microspheres. The weight ratio of

MMA/TEOS/DVB/MPS/HD/PSt is 14.0/6.0/1.4/0/1.20/0.8/0 (Samples 1 shown in Table S1).

2.3 Effect of MPS on the microstructure and morphology of hybrid microspheres

Fig. S5 TEM image of silica/polymer hybrid hollow microsphere. The weight ratio of

MMA/TEOS/MPS/HD/PSt is 14.0/6.0/0/0.8/0.2 (Samples 10 shown in Table S1).


Fig. S6 TEM image (a) and SEM images (b and c) of silica/polymer hybrid hollow microspheres

(Samples 11 shown in Table S1).

Fig. S7 TEM image of silica/polymer hybrid hollow microspheres (Samples 12 shown in Table S1).

2.4 FTIR characterization

FTIR is generally used to identify the chemical structure of silica/polymer nanocomposites and

widely used to prove the formation of nanocomposites.[S1] Fig. S8 shows the typical FT–IR spectra

of hybrid hollow microspheres. The C–O stretching peaks of PMMA appeared at 1272, 1240, 1193,

1147 cm–1, and the band at 1732 cm–1 were assigned to the C=O stretching peak of PMMA. Peaks

at 711, 1606, 1481, and 1452 cm–1 confirmed that MMA and DVB were chemically copolymerized.


The characteristic absorption band of Si–O–Si asymmetric stretching (1130 cm–1) were in the

broadened major peak in the range of 1000–1200 cm–1, which was attributed to the asymmetric

stretching vibrations of Si–O–Si bonds of silica in the SiO2/PMMA hybrid microspheres.[S2] The

peaks at 476, 752, 968, 1094, and 1632 cm-1 are the typical peaks demonstrating the formation of

SiO2. Absorption at 1635 cm–1, which was attributed to the stretching vibration of C=C groups of

MPS, disappeared completely after the formation of hollow microspheres. This means that MPS

was effectively copolymerized with vinyl monomers.[S3]

Fig. S8 Typical FT–IR spectra of hybrid hollow microspheres with mass ratio of

MMA/DVB/TEOS/MPS/PSt = 14.0/1.4/6.0/1.8/0.2 (Sample 5 in Table S1).

2.5 The formation mechanism of hybrid hollow microspheres

75℃× 0.5h

2) 75 ℃×5h

1) NH3·H2O

MMA+TEOS+MPS Polymer + Monomer TEOS SilicaPolymer

Scheme S1 Illustration for the formation of hybrid hollow microspheres by miniemulsion


polymerization

We illustrated the formation of silica/polymer microsphere via miniemulsion polymerization in

Scheme S1. After PMMA polymer was formed, MPS acted as the solubilizer and enhanced the

compatibility between TEOS and the PMMA/MMA solution. TEOS phase was compressed and

divided into small droplets. With the polymerization of MMA continued, more monomers (MMA)

turned into PMMA and the viscosity of polymer phase increased accordingly. Small droplets were

extruded out and settled on the shells of the growing polymer particles.[S4] TEOS nodules were

transformed into silica particles under basic conditions. The hybrid hollow microspheres with silica

nanoparticles on the shells were shown in Fig. S7.

2.6 Effect of TEOS content on the microstructure and morphology of hybrid microspheres

Fig. S9 shows the TEM images of silica/polymer hybrid hollow microspheres (typical

high–magnification shown in e). The weight ratio of MMA/DVB/TEOS/MPS/HD/PSt is

14.0/1.4/4.0/1.2/0.8/0.2 (Samples 4 shown in Table S1). Fig. S10 shows the TEM images of

silica/polymer hybrid hollow microspheres (typical high–magnification shown in e). The weight

ratio of MMA/DVB/TEOS/MPS/HD/PSt is 14.0/1.4/2.0/1.2/0.8/0.2 (Samples 3 shown in Table S1).

As shown in Fig. S9 and 10, composite microspheres have a nonspherical morphology. The

collapsed structure of hybrid microspheres may come from the contraction of polymer phase during

the polymerization.


Fig. S9 TEM images of silica/polymer hybrid hollow microspheres (typical high–magnification

shown in inset). The weight ratio of MMA/DVB/TEOS/MPS/HD/PSt is 14.0/1.4/4.0/1.2/0.8/0.2


Fig. S10 TEM images of silica/polymer hybrid hollow microspheres (typical high–magnification

shown in inset). The weight ratio of MMA/DVB/TEOS/MPS/HD/PSt is 14.0/1.4/2.0/1.2/0.8/0.2


2.7 Thermogravimetric analyses (TGA)


The inorganic component contents of hybrid hollow microspheres were investigated by

thermogravimetric analyses (TGA). Fig. S11 shows the TGA curves of the prepared hybrid hollow

microspheres (a) and magnetic hollow microsphere with various Fe3O4 contents. As shown in curve

a of Fig. S11, we could see that the silica content in the hybrid microspheres was 11.7 %. The silica

content of theoretic calculation in the hybrid microspheres was consistent with the value from the

TGA result. As shown in curves b and c of Fig. S11, we could determine the magnetic nanoparticles

content in the hybrid microspheres was 11.7 %. The Fe3O4 contents in the magnetic hollow

microspheres were 5.7 % and 11.9 %, respectively. The magnetic nanoparticles content from the

TGA result was consistent with the value of theoretic calculation in the hybrid microspheres.

Fig. S11 TGA curves for hybrid hollow microspheres (curve a, Sample 5 in Table S1) and magnetic

hollow microsphere with various Fe3O4 contents (curve b and c correspond to Sample 13 and 14 in

Table S1, respectively).

2.8 Morphology of hybrid hollow microspheres with the weight ratio of

MMA/DVB/TEOS/MPS/HD/PSt = 14.0/1.4/8.0/2.4/0.8/0.2


Fig. S12 TEM images of hybrid hollow microspheres. The weight ratio of MMA/DVB/TEOS/MPS/

HD/PSt is 14.0/1.4/2.0/1.2/0.8/0.2.

Fig. S12 gives the additional TEM images of hybrid hollow microspheres with mass ratio of

MMA/DVB/TEOS/MPS/PSt = 14.0/1.4/6.0/1.8/0.2 (Sample 5 in Table S1), which has been

supplied in the manuscript.

References

[S1] Zou, H.; Wu, S. S.; Shen, J. Chem.Rev.,2008, 108, 3893.

[S2] Shang, X. Y.; Zhu, Z. K.; Yin, J.; Ma, X. D. Chem. Mater., 2002, 14, 71.

[S3] a) Zhang, K.; Chen, H. T.; Chen, X.; Chen, Z. M.; Cui, Z. C.; Yang, B. Macromol. Mater. Eng.,

2003, 288, 380; b) Zhang, J. A.; Liu, N. N.; Wang, M. Z.; Ge, X. W.; Wu, M. Y.; Yang, J. J.;

Wu, Q. Y.; Jin Z. L. J. Polym. Sci., Part A: Polym. Chem., 2010, 48, 3128.


[S4] Lu, W.; Chen, M.; Wu, L. M. J. Colloid Interface Sci., 2008, 328, 98; Zhang, J. A.; Yang, J. J.;

Wu, Q. Y.; Wu, M. Y.; Liu, N. N.; Jin, Z. L.; Wang, Y. F. Macromolecules, 2010, 43, 1188.


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