Bijels by STRIPS: A complex new form of liquid matterMartin F. Haase, Kathleen J. Stebe, Daeyeon Lee

Chemical and Biomolecular Engineering, University of Pennsylvania

1. Bicontinuous interfacially jammed emulsion (Bijel)

3. Fiber or Membrane formation

2. Solvent Transfer Induced Phase Separation (STRIPS)

1 cm

DEP reservoir 1

DEP reservoir 2

a)

0’ 74’ 186’b)

c)

50 µm

z = 0 µm z = 32 µmz = 8 µm z = 20 µm

Diffusion fluorescent dye in oil

Diffusion fluorescent dye in water

Ternary phase separation

0.2 0.4 0.6 0.80 1water

ternary mixture water solvent transfer

silica 20nm CTAB surface active

Particles with surfactants

tim

e

alumina 30nm

OO

O O

AOT surface active

Instead of binary, we use ternary phase separation (a): This approach facilitates the combination

of many different pairs of immiscible liquids that cannot be mixed by raising the temperature. We

inject a homogeneous mixture of oil, water and a solvent into a water stream (b). Phase

separation occurs in the so formed droplets because the solvent diffuses into the water stream,

leaving immiscible water and oil behind. The spinodal patterns are clearly visible under the

microscope (c). Introducing surface active nanoparticles to the ternary mixture allows for the

formation of bijel droplets (d). To this end we make the nanoparticles surface active by

combining oppositely charged particles and surfactants (e). The surfactants adsorb on the

particles and make them partially hydrophobic. With the nanoparticles the droplet pinch off looks

very different (f). The droplet are viscoelastic (like toothpaste) and pinch off as irregularly shaped

objects. Interfacial particle jamming causes the liquid mixture to have mechanical properties.

ternary mixture + nanoparticles

water solvent diffusion

5 µm

500 nm

200 nm

0.2 0.4 0.6 0.8 1.0

20

33

38

43

Te

mp

era

ture

, °C

binary vol. fraction

1

Binary phase separation(a)

Spinodal phase separation

Complete

phase

separation

4.6 4.6

72 10836363636 CTAB mM

silica %6.54.62.30.9

5 µm 15 µm 50 µm25 µm

10

8 m

M C

TA

B3

6 m

M C

TA

B

z =a)

d)

4. 3D-analysis of STRIPS-Bijel Fibers, Membranes and Particles

Simulation in 20052

3Experiment in 2007

100µm

Bijels are a new class of soft materials that are formed by

phase separation of immiscible liquids. The binary phase

diagram in (a) shows the temperature dependent mis-

cibility of 2 liquids. Above 40°C the two liquids can be

mixed. Rapidly cooling this warm mixture along the blue

arrow induces a spinodal phase separation as shown in

(b). An interconnected liquid-liquid channel network forms,

which coarsens into 2 completely separated phases. To

make a bijel the phase separation has to be arrested with

colloidal particles in the mixture, as was first demonstrated

in computer simulations in the year 2005 (c).

The particles attach strongly to the interface

between the 2 liquids and form a densely

packed layer. This layer is interfacially

jammed an stabilizes a bicontinuous fluid

network (first demonstrated experimentally in

2007). This poster describes an advanced

method of making bijels introduced by me in

2015.

6. Mass-transfer in bicontinuous channel system

Instead of irregularly shaped droplets a uniform fiber can be

extruded (a). You can see the coarsening of the oil/water

structures within the fiber over its trajectory under the microscope.

At the end a liquid fiber stabilized by nanoparticles is formed.

Alternatively, a thin film of the ternary mixture coated onto a plate

can be immersed into a water bath and the same process takes

place in a planar geometry (b).

5. Surface area and pore size

With the 3D structure data we can analyze the surface area and

pore size in dependence of the surfactant and nanoparticle

concentration. The general trends are increasing both

concentrations leads to smaller pores and higher surface areas.

7. Outlook and Future applications

Aligning the fibers as parallel bundles and connecting those to oil reservoirs allows us

to study their application as porous transport pipes (a). In (b) you see the transport of a

green dye over time through diffusion in the oil channels of the fiber. Moreover, when

we inject a blue dye into the surrounding water we can see that the blue color

penetrates into the water pores of the STRIPS-bijel fiber. This openness and channel

interconnectivity of the fibers shows great potentials for applications as outlined in 7.

Special Thanks to:

M. Pera-Titus, Angewandte Chemie Int.

Ed., 2015, 54, 2006

500µm

Mass transfer and catalysis Separation membranes

Edible Bijels Cosmetics

M.N. Lee, A. Mohraz, Advanced Materials,

2010, 22, 4836

50µm

Sensors Tissue

Engineering

1 2 3

4 5 6

time

time

Publication

Haase et al. 2015

77 µm 103 µm

74 µm84 µm

10 µm

xy

z

b)

30 µm

c)

e)

(b) (c)

(a)

(b)

(c) (f)

(d) Interfacial jamming (e)

(a)

(b)

The structure of the oil/water channels within these fibers can be analyzed by confocal laser

scanning microscopy. In (a) tomographic visualization (slice-by-slice) of two different fibers

fabricated at different surfactant concentrations is shown. Using this technique we can obtain

3D-reconstructions of STRIPS-bijel fibers, membranes and particles (b, c, d). As you can see in

(c), the fibers can have remarkably different internal structures. Moreover, (d) shows that the

surface pore size strongly depends on the concentration of the surfactants and the nano-

particles. These different structures suggest different applications for the STRIPS-bijels, for

instance hollow fiber membranes are very useful as separation membranes.

Scanning electron microscopy allows us to magnify the surface of the fibers further (e). At

magnifications as high as 150,000x we can see the interfacially jammed nanoparticle film. The

nanoparticles can be quite useful in applications of the STRIPS-bijels, for instance they can act

as catalysts to promote reactions for the synthesis of manifold chemical products.