(142bd) Controllable Microfluidic Production of Gas-in-Oil-in-Water Emulsions for Hollow Microspheres with Thin Polymer Shells

Controllable Microfluidic production of
Gas-in-Oil-in-Water emulsions for hollow microspheres with thin polymer shells

Jian-Hong Xu,* Ran Chen, Peng-Fei
Dong, Yun-Dong Wang, and Guang-Sheng Luo

(The State Key Laboratory
of Chemical Engineering, Department of Chemical Engineering, Tsinghua
University, Beijing, 100084, China)

* Corresponding
author. Tel.: +861062783870; Fax: +861062770304.

E-mail address: xujianhong@tsinghua.edu.cn

Encapsulation of microbubbles
can be very useful. It helps eliminate the bubble dissolution and coarsening by
separating the inner gas compartment from the outer fluid, ensuring the various
potential applications of microbubbles in lightweight
materials, aerated food products, waste water treatment3, ultrasound contrast
agents and pharmaceuticals. Moreover, such a method can also be applied in the
preparation of hollow particles, which are of great interest in areas such as
energy-storage materials, catalyst supports and drug delivery carriers.
Traditional ultrasonic approach provides an effective way in the encapsulation
of the microbubbles, but it lacks control over the
size and size distribution of the particles and the shell thickness. Here we
introduce a simple and novel capillary microfluidic device by injecting a
smaller capillary into another capillary and making sure that the tapered
orifices align where the single-step emulsification carries on (Fig. 1). This
simple microfluidic device ensures the flowing independency of the inner and
middle phases and finally eliminates the defects. In this communication, we
mainly introduce the application of such microfluidic device in the
controllable fabrication of hollow microspheres with thin shells using G/L/L
emulsion as templates.

Fig.1 The sketch of the microfluidic capillary device and the microscope
images of G/O/W droplets with different thickness of the oil layer, synthesized
by tuning the flow rates of the middle phase.

We successfully produced Gas-in-Oil-in-Water double
emulsions with high gas volume fraction using the simple and novel capillary
microfluidic device. The size of the encapsulated microbubbles
and the thickness of the oil layer can be easily controlled by adjusting the
flow rates of oil and water phases. Such emulsions were used as the template
for preparation of hollow core-shell microspheres with thin shells, as shown in
Fig. 2.

Fig. 2 The LSCM and SEM photograph of
the hollow microspheres after polymerization.

The hollow core-shell microspheres may find many
applications in areas such as industrial catalysis, pharmaceuticals and
delivery of cosmetics and nutrients. We believe that the approach we have
demonstrated here is promising because it is suitable for the preparation of
G/L/L emulsions with controllable structures, and it is a purely
flow-controlled method, which is very simple to adjust the size and structure
of G/L/L emulsions and hollow microspheres. Additionally, our approach is a
one-step technology to realize microbubble
encapsulation and hollow microspheres preparation. In the future work, we will try to explore the applications of the G/L/L emulsions in the area
of the enhancement of Liquid/Liquid
extraction, gas-liquid-liquid mass transfer and
heterogeneous reactions.

Key words: G/L/L emulsion;
microfluidic; hollow microsphere

Acknowledgement

The authors gratefully acknowledge the supports of the National Natural
Science Foundation of China (21036002, 21136006), A Foundation for the Author
of National Excellent Doctoral Dissertation of PR China (FANEDD 201053) and
National Basic Research Program of China (2012CBA01203).