Stability Mechanisms of Pickering Emulsion Co-stabilized by Silica Nanoparticles and PEO†

doi:10.7503/cjcu20130905

Abstract

Abstract:

The Pickering emulsions with 65% water and 35% xylene system stabilized by silica nanoparticles or by both the particles and polyethylene oxide(PEO) additives were prepared. The emulsification was performed using a rotor-stator homogenizer under varied rotation speeds from 5000 r/min to 24000 r/min. The emulsion droplets were observed using an optical microscope, consequently, the droplet diameters vs. rotation speed and aging time were obtained. For most cases, W/O type emulsion was obtained. It is found that the mean diameter of water droplets decreases with increasing shear rate or shear duration. With the presence of PEO, the diameters of the droplets are significantly reduced and the phase inversion from W/O to W/O/W is prevented, which occurs in the system without PEO when prolong the shear duration. In addition, the coalescence of droplets is completely inhibited. To elucidate the ultrastability of the Pickering emulsion resulted from co-stabilization by silica nanoparticles and PEO, we study the rheological properties of the particle layers at the gas-liquid interface using the Langmuir trough equipped with a Wilhelmy plate. The silica nanoparticles were spreaded on the surface of either water or PEO water solution, consequently and the effect of PEO additives on particle layer properties was investigated. The results confirm that PEO additives can favor the trapping of particles at the water/xylene interface, due to the formation of larger size aggregates with the presence of PEO. Therefore, the particle layer has a higher compression modulus. The stronger mechanical property of the particle layer protects the water/xylene interface from rupture when exerted turbulent shearing, hence preventing the occurrence of phase inversion from W/O emulsion to the W/O/W one. Owing to the satisfaction of the Gibbs stability criterion, the coalescence of droplets is almost completely inhibited. The results demonstrate that the rheological properties of the liquid/liquid interface play an important role in the stability of Pickering emulsion.

Key words: Pickering emulsion, SiO2 nanoparticles, Interfacial tension, Phase inversion, Polythylene oxide(PEO)

CLC Number:

O647

TrendMD:

TAN Weiqiang, ZANG Duyang, LI Yunfei, ZHANG Yongjian, LU Chenjun, LI Zhiguang. Stability Mechanisms of Pickering Emulsion Co-stabilized by Silica Nanoparticles and PEO^†[J]. Chem. J. Chinese Universities, 2014, 35(1): 85.

Figures/Tables 9

Fig.1 Appearance of the systems containing 65% water, 35% xylene and 0.5% silica nanoparticles(A) Before shearing; (B) and (C) sheared at rotation speeds of 5000 and 9000 r/min, respectively, shearing time: 3 min;(D) Pickering emulsion obtained at 24000 r/min is solid-like.

Fig.2 Shear rheological properties of the emulsion sample obtained at 24000 r/min as shown in Fig.1(D)

Fig.3 Optical microscope images of Pickering emulsion droplets of type A(A—D) and type B(E—H) obtained at different rotation speeds Rotation speed/(r·min-1): (A, E) 5000; (B, F) 12000; (C, G) 20000; (D, H) 24000.

Fig.4 Variation of droplets diameter of Pickering emulsions of type A(a) and type B(b) with increasing shear rate

Fig.5 Droplet diameter of Pickering emulsions of type A(a) and type B(b) vs. shear duration with rotation speed of 24000 r/min

Fig.6 Formation of W/O/W multiple droplets(A) Non-sphered morphology of the multiple droplets; (B) a close view for a large droplet.

Fig.7 Coarsening of Pickering emulsions of type A(A—D) and type B(E—H) Coarsening time: (A, E) 15 min; (B, F) 1 d; (C, G) 2 d; (D, H) 7 d.

Fig.8 Variation of droplet diameter of Pickering emulsions of type A(a) and type B(b) with coarsening time

Fig.9 Rheological properties of silica nanoparticle layer at the air/water interface(A) Π-Γ isotherms; (b) comparison between compression modulus E and γ/2.

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