ISSN 1744-683X

www.rsc.org/softmatter Volume 8 | Number 30 | 14 August 2012 | Pages 7729–7990

1744-683X(2012)8:30;1-B

PAPERHale Ocak et al.Eff ects of molecular chirality on superstructural chirality in liquid crystalline dark conglomerate phases

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Highlighting research from the Whitby lab, Ian Wark Research Institute, University of South Australia.

Title: Structure of concentrated oil-in-water Pickering emulsions

In this study confocal microscopy was used to characterise

the structural changes inside aqueous emulsions of

nanoparticle-coated oil drops as they break under

compressive stress.

As featured in:

See Catherine P. Whitby et al.,

Soft Matter, 2012, 8, 7784.

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Structure of concentrated oil-in-water Pickering emulsions

Catherine P. Whitby,* Lisa Lotte and Chloe Lang

Received 1st May 2012, Accepted 18th June 2012

DOI: 10.1039/c2sm26014j

Following the structural changes in unstable Pickering emulsions is difficult due to the emulsion

turbidity. We studied droplet packing in concentrated oil-in-water emulsions stabilized by silanised

silica particles using confocal fluorescence microscopy to image thin sections of the emulsions. As the

volume fraction of the drops approaches close packing, they deform into polyhedral shapes and

flattened areas of contact between droplets appear. We show that the increase in the average number of

nearest neighbours of a drop is a power law function of the drop volume fraction, consistent with

theoretical predictions. At the volume fraction where the emulsions start to break down, f¼ 0.88, there

is a jump in drop elongation and thus in the number of drops in contact with each other. Drops increase

in size, with some forming shapes that resemble an intermediate stage of the coalescence process. A few

large drops grow more than most. A key finding is that the rigidity of the droplet surfaces controls the

destabilization mechanism.

Fig. 1 (a) Schematic of cream and water layers in a concentrated

emulsion. (b) Confocal fluorescence images of close packed drops in an

emulsion cream at different drop volume fractions (f). The drops are

compressed as their height in the cream layer increases. The maximum

volume fraction at which drops hexagonally close pack without being

distorted (fm ¼ 74%) is indicated. The drops merge together if the drop

volume fraction increases above the critical volume fraction (fc ¼ 88%).

1. Introduction

Packing spherical particles so closely together that they touch all

their neighbours and resist flow produces many useful materials.

Mayonnaise, emulsion explosives and moisturizer creams, for

example, consist of emulsion drops randomly packed into a

dense suspension. Concentrated emulsions possess a striking

rigidity, behaving like elastic solids. The shear elasticity is due to

the droplets being compressed by an osmotic pressure greater

than their Laplace pressure.1 Creating excess surface permits the

storage of interfacial shear energy.2 Despite their practical

importance, there are few reliable methods for visualising the

arrangement of droplets inside dense emulsions. Jammed matter

is opaque, making it difficult to optically probe its internal

structure in situ. Without dilution, multiple scattering effects

convolute light scattering patterns from concentrated systems.

Brujic and co-workers3,4 recently used confocal fluorescence

microscopy to map the network of droplet contacts inside

concentrated, surfactant-stabilised emulsions. In this work, we

investigate the microstructure of emulsions stabilized by particles

alone (Pickering emulsions5–12). The aim is to monitor droplet

packing as a Pickering emulsion is compressed. The conditions

leading to coalescence and therefore limiting emulsion lifetime

are of particular interest.

The volume fraction of drops in an emulsion can be increased

up to a certain critical value (fc) before the drops coalesce

together. The progress of coalescence in an oil-in-water emulsion

can be monitored as the drops move together under gravity to

form a concentrated layer (cream) at the top of the emulsion. The

Ian Wark Research Institute, University of South Australia, MawsonLakes, South Australia, 5095, Australia. E-mail: catherine.whitby@unisa.edu.au

7784 | Soft Matter, 2012, 8, 7784–7789

local drop volume fraction in the cream varies with the height, as

shown in Fig. 1a and b.

In monodisperse emulsions, the maximum volume fraction at

which drops hexagonally close pack without being distorted13 is

fm ¼ 74%. At fm the average number of contacts per drop (Z)

(c) Confocal fluorescence images of the particle shells show that the

circular drops deform into polyhedral shapes with sides of length, L, as

the drop volume fraction increases. The elongation of the deformed drop

is given by the ratio of the height, d1, and the width, d2.

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jumps from zero to a finite value, Zm.14 The drop volume fraction

is so high that they can support their own weight and resist

mechanical shear. The drops have enough contacts between them

so that they do not move around freely.15 In a two dimensional

system of frictionless spherical particles, the predicted minimum

average coordination number for mechanical stability is 4.16

Emulsions can be compressed considerably, yet remain

mechanically stable. Above fm, the coordination number

increases continuously.14 The droplets deform into polyhedral

shapes with flattened areas of contact and rounded edges and

corners (Fig. 1c).13 In a two dimensional system, assuming the

compression is uniform, the degree of compression, x, can be

approximated17 by the increase in the drop volume fraction.

x ¼ f � fm (1)

An emulsion cream is effectively separated from the water

layer underneath by a freely moving membrane that is permeable

to all the components in the water, except for the drops.18 Pres-

sure must be applied to the membrane to prevent water from

flowing into the cream and restoring the drops to spherical

shapes. Compression above fm therefore requires work against a

finite pressure (P, the osmotic or compressive pressure), reflect-

ing the increase in the total interfacial area as drops are

deformed. S/S0 is the ratio of the surface area of the deformed

drops to the surface area of the spherical drops (at f # 74%). P

increases from zero to infinity as f increases from 74 to 100%.

Assuming the total volume does not change, it is given by19

2P

g.D

¼ 3f2

d

�S.S0

�

df(2)

where g is the oil–water interfacial tension and D is the diameter

of the undeformed drops.

Considering the change from a sphere to a polyhedron of the

same volume, S/S0 is expected to approach a value of 1.10 as f

/ 100%.19 At relatively low volume fractions (74% < f < 90%),

an empirical equation19 is used to predict this ratio.

S.S0 ¼ 1þ 1

3

�0:084

f� 0:068

flnð1� fÞ � 0:237

�(3)

The compressive pressure on the thin flat films is counteracted

by a disjoining pressure which develops due to electrostatic, steric

or other repulsive forces between the drops.13 Presumably, the

maximum disjoining pressure is reached as the drop concentra-

tion increases up to fc. Emulsions are expected to break or invert

with the application of more stress.

The stability of Pickering emulsion droplets is due to the dense

packing of strongly bound colloidal particles at the liquid

interface.20,21 Based on studies of colloidal monolayers at planar

and curved interfaces, this particle layer is proposed to be a 2-

dimensional solid and provide a mechanical barrier to droplet

coarsening.22,23 Aveyard and co-workers24,25 demonstrated that

when a layer of particles at a planar fluid interface is compressed,

it bends and forms an undulating surface with a characteristic

wavelength. By measuring the pressure in particle-coated (single)

droplets as they were deflated, Xu et al.26 showed that there is a

fluid to solid transition in the particle shell. Tan et al.27 found

This journal is ª The Royal Society of Chemistry 2012

that individual oil droplets coated with kaolinite particles and

compressed by a cantilever tip are mechanically robust and

recover their spherical shapes after large deformations. Russell

and co-workers28,29 demonstrated that covalently cross-linking

interfacial assemblies of virus particles to form membranes

increases droplet stiffness. They found that cross-linked drops

deform irreversibly. While the elasticity of unmodified capsules

reflected a constant interfacial tension, the elastic response of the

cross-linked capsules changed as the strain increased, suggesting

the membranes had fractured.28 Ata30,31 studied the coalescence

dynamics between pairs of bubbles and found that nanoparticle-

coated bubbles show elastic behaviour compared to the relatively

rigid bubbles coated with micrometre-sized beads. Pawar et al.32

found that the coalescence of two oil drops could be halted at

some intermediate stage if micrometre-sized silica particles at the

drop surfaces form a close-packed, jammed layer. Direct exper-

imental evidence of the solid-like nature of the droplet surfaces in

bulk Pickering emulsions is, however, lacking.

In this work we study drops in the cream layer of almost fully

drained Pickering emulsions. By using confocal fluorescence

microscopy to examine the internal structure of the cream, we

characterise the shapes of drops and their network of contacts as

function of drop volume fraction. We show that the average

length of the interface between two drops in contact increases as

a linear function of the drop volume fraction in kinetically stable

emulsions. There is a dramatic increase in droplet deformation

and coordination number above a critical volume fraction of

88 vol%. From images of the interfacial particle layer we deduce

the likely causes of destabilization.

2. Experimental section

Dispersion and emulsion preparation

Silica nanoparticles modified by reaction with hexadecylsilane

were supplied by Degussa (Aerosil R816). Dispersions of nano-

particles in 0.1 M NaCl (Chem Supply, 99%) in water (resistivity

�18.2 MU cm, pH 5.3–5.8) were sonicated in an ultrasound bath

(Soniclean 160T, 70 W power, �44 kHz operating frequency) for

20 minutes. TEM images revealed that the approximately

spherical nanoparticles had radii between 10 and 30 nm.

Emulsions were prepared by homogenising equal volumes of

dodecane (Sigma Aldrich, 99%, passed through chromato-

graphic alumina twice to remove polar impurities) with the

aqueous silica dispersions (3 wt% in 0.1 M NaCl) using a

X1030D homogenizer with a 10 mm diameter shaft (Ingen-

ieurbuero CAT, M. Zipper GmbH) operated at 13 000 rpm for

1 min. The oil volume fraction in the (whole) emulsion (fo) was

then increased in small steps (10 vol%), rehomogenising for 30 s

after each addition of oil. The emulsion drop size distributions

were determined by static light scattering using a Malvern

Mastersizer 2000 (assuming a relative refractive index of 1.1 and

a particle absorption coefficient of 0). At 0.55 # fo # 0.70, the

volume weighted mean drop diameter (D(4,3)) was 95 mm and the

polydispersity was 30%. SEM images showed that the drops were

coated with layers consisting of particle aggregates about 50 nm

in size.

The emulsions were stored in screw-cap vials at 25 �C and left

standing prior to microscopy measurements. A volume fraction

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gradient of drops developed in the vertical direction, followed by

the appearance of a distinct boundary between an upper layer of

concentrated drops (cream) and a lower depleted layer (Fig. 1a).

The drops at a given height in the upper layer did not coalesce for

several weeks providing the drop volume fraction at that height

(the local drop volume fraction, f) was less than 88%.

Fig. 2 (a) Confocal fluorescence image highlighting the locations of the

particles in an oil-in-water emulsion at f ¼ 85%. (b) Line profiles of the

fluorescence intensity extracted along the solid, dashed or dotted paths

shown in (a). Drops are in contact (solid or dashed lines) or out of contact

when two separate particle layers are detected (dotted line). (c) Drop

volume fraction (f) dependence of the average distance over which the

drops are in contact, L. The interface distance L is scaled by the average

drop diameter, D. fm is the volume fraction corresponding to hexago-

nally close packed, undistorted drops. fc is the volume fraction above

which drops coalesce together. The line is the fitted variation in L

obtained assuming that it is a linear function of the increase in volume

fraction above fm.

Confocal fluorescence microscopy

Confocal fluorescence microscopy (CFM, Leica SP5 spectra

scanning confocal microscope) was used to visualise the micro-

structure in emulsion cream samples. An o-ring fixed on a glass

cover slip was filled with emulsion. A second cover slip placed on

top of the o-ring sealed the cell.

The particles were stained with Nile Blue (1 mM in 0.1 M

NaCl) and excited at 633 nm. Nile Red (1 mM in dodecane) was

used for staining the oil and the sample was excited at 496 nm.

Preliminary studies confirmed that the presence of the dyes did

not alter emulsion structure or stability. Fluorescence intensity

data for Nile Blue and Nile Red were collected in two separate

channels corresponding to 520–570 and 653–750 nm, respec-

tively. Each line of pixels in an image was scanned sequentially

for Nile Red and Nile Blue fluorescence to avoid interference due

to cross-fluorescence.

The two-dimensional confocal images were analysed using the

ImageJ software. Each image contained 1024 � 1024 pixels, with

a grey value ranging from 0 to 255. The images were processed by

converting them to a binary form and then segmented by

‘thresholding’ using an iterative selection procedure based on the

composite average of the averages of the background and object

pixels. The areas of all the drops in the Nile Red images were

calculated to determine the drop area fraction and hence the local

volume fraction of drops (f). The diameter of a circle with the

same area as each drop was calculated. The size distributions in

the compressed emulsions at f ¼ 85, 90 and 94% were estimated

by deriving frequency distributions of the drop areas from

images of several hundred drops.33

The perimeters of the drops in the Nile Blue images were

calculated to determine the total surface area and hence the ratio

of the surface area at f to the surface area at f < 74% (S/S0).

Fig. 1c shows how the compressed droplet shapes were charac-

terized using the ratio of their length (d1) and breadth (d2). This

parameter is sensitive to the large deformations observed near

destabilization (discussed later). The length of the flattened area

between drops in close contact was determined from the Nile

Blue images. The degree of drop compression was estimated by

calculating the ratio of the length of the flattened area to the

equivalent circular diameter. Line profiles of the fluorescence

intensity in the shells between neighbouring drops as in Fig. 2a

were extracted. The drops were identified as being in contact

where the shell profile consisted of a single peak due to over-

lapping shells (Fig. 2a and b) and not in contact when the profile

consisted of several peaks. The number of contacts for each drop

was counted. For emulsions at f < 0.88, averages of the equiv-

alent circular diameter, aspect ratio, number of contacts and

contact length for at least 300 drops were calculated to giveD, d1/

d2, Z and L respectively. In emulsions that were not stable to

droplet coalescence, the average values were calculated from

measurements of between 50 and 100 drops.

7786 | Soft Matter, 2012, 8, 7784–7789

3. Results and discussion

The multiphase nature of Pickering emulsions gives rise to a rich

morphology. Fig. 1b shows how emulsion microstructure is

tuned by increasing the volume fraction of drops (f) of a fixed

diameter (D). The volume fraction of particles (fp¼ 1.4%) is also

fixed. The oil is stained with fluorescent dye to reveal the droplet

shapes. Drop surfaces were rendered visible by staining the

particles covering them. High magnification images of the inte-

rior of the cream show drops packed closely together. As f

increases the drops deform into polyhedral shapes. Flat droplet

boundaries between drops in close contact are observed. The

increase in surface area per unit volume of drops (S) means that

the same number of particles is stabilizing a larger interfacial

area. Above a certain limit there is insufficient coverage to

stabilize the drops and they merge together.

Experiments revealed that kinetically stable emulsions were

obtained at drop volume fractions of up to 88% (fc). Droplet

creaming occurs during the first day after emulsion preparation.

The volume fractions and deformation of the drops in the

concentrated layer are reproducible after about 24 hours and do

not change for at least one week, providing that f < 88%. The

This journal is ª The Royal Society of Chemistry 2012

Fig. 4 Drop volume fraction (f) dependence of the average coordina-

tion number Z. The volume fraction where drops are first deformed (fm)

and the coordination number is at its minimum value (Zm) is identified.

Data is shown for kinetically stable (f < fc ¼ 88%) and unstable emul-

sions (f > fc). The solid line is the fitted variation in Z with f obtained

assuming that the increase in number of drop contacts is a power law

function of the increase in volume fraction.

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drop volume fraction dependent structure of this cream was

characterised before the structure in less stable emulsions (f> fc)

was investigated.

Estimates of S/S0 derived from images of kinetically stable

concentrated Pickering emulsions are slightly higher than the

values predicted using eqn (3). This indicates almost complete

drainage of liquid from the cream. Although initially fast,

drainage becomes extremely slow once the drops concentrate and

the drainage paths (the plateau borders) become extremely small.

Since drainage is almost complete, deformation of the drop

shapes is a measure of the response of the droplet surfaces to the

applied stress.

Below fm the drops are circular in shape and have little contact

with other drops. Deformation is observed at f> fm¼ 74%. This

is the maximum volume fraction for hexagonally close packed

drops (fm).13,17 Droplet compression above fm was estimated

using the ratio L/D. Fig. 2c shows that the drop compression is a

linear function of the drop volume fraction, consistent with eqn

(1). The degree of compression is small (x < 0.4) in the kinetically

stable emulsions.

The drop shapes are slightly elongated in response to the weak

compression. The droplet elongation (d1/d2) is a linear function of

f, as shown by Fig. 3. Drops deform by about 10% as the degree

of compression increases by about 10%. The variation in elon-

gation with is relatively uniform across the drop size distribution

(not shown). The drop size distribution remains narrow at f < fc.

At fm, the drops have an average number of close neighbours

ofZm¼ 4. Fig. 4 shows that the average number of close contacts

between drops (Z) increases with f at f > fm. The average

coordination number was determined from the number of flat

droplet boundaries. The increase in S with droplet deformation

causes a repulsive force on the facets that is proportional to g.

Since the deformation is relatively small in the kinetically stable

emulsions (Fig. 3) the average drop sizeD, and hence the Laplace

pressure, do not change. So the force is approximated34 using the

expression (2g/D)dS, where dS is the area of the flattened facet. If

we assume that the droplet interactions are dominated by this

repulsive interaction, then the interaction energy that controls

the structure formed by drops compressed to a large volume

fraction depends on Z.

Fig. 3 Average droplet elongation (d1/d2) as a function of drop volume

fraction (f). fm is the volume fraction corresponding to hexagonally close

packed, undistorted drops. Data is shown for kinetically stable (f < fc ¼88%) and unstable emulsions (f > fc). Shown are the fitted variations in

elongation for kinetically stable (solid line) and unstable emulsions

(dotted line) obtained assuming that the deformation is a linear function

of the increase in volume fraction above fm.

This journal is ª The Royal Society of Chemistry 2012

The line drawn in Fig. 4 shows that the increase in the coor-

dination number is a power law function of the increase in f,

Z � Zm f (f � fm)p (4)

with the coefficient, p, derived to be �0.6. This function has the

same form as that obtained in computer simulations35 of the

microscopic structure and dynamics of compressed bubbles.

Durian35 constructed two dimensional models of aqueous foams

by adding up the interactions between pairs of bubbles to

develop equations of motion for the bubbles. Durian35 found

that random packing effects play an essential role in the response

of foam to an external force and this could be understood in

terms of the average number of contacts per bubble. The

macroscopic behaviour of concentrated oil-in-water emulsions is

governed by the same interaction forces and random packing

effects.

As f increases, the length of the droplet interfaces and hence

the degree of compression increases, as shown in Fig. 2c. The

emulsion starts to break down at f $ 88%, indicating the dis-

joining pressure no longer balances the compressive forces being

exerted. Assuming that all the particles (50 nm in diameter)

attach to form hexagonally close packed layers around the drops

(95 mm in diameter) it can be calculated that the interfacial area

in emulsions at f $ 88% exceeds the total area that can be

occupied by the particles.

Droplet coalescence causes the drop size to increase (Fig. 1b).

This reduces the compressive pressure below the maximum dis-

joining pressure (at a given f, the compressive pressure is

inversely proportional to D). The volume fractions and defor-

mation of the drops in the concentrated unstable layer (f > fc �88%) are reproducible when measured within 48 hours of prep-

aration. The distribution of drop sizes is, however, significantly

broader than in stable emulsions (Fig. 1b). This increases the

uncertainty associated with calculations of the average droplet

size, deformation and coordination number. It also should be

noted that low magnification images showed that a few giant

(centimetre-sized) drops could also be present in the cream, as

shown in Fig. 5a.

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There is a jump in droplet deformation from about 10% at f¼fm to about 25% just above fc (Fig. 3). There is also a dramatic

increase in drop deformation with further increases in the drop

volume fraction at f > fc (Fig. 3). The variation in elongation

with D is no longer uniform across the drop size distribution.

Large coalesced drops tend to be less spherical in shape.

The coalesced drops have more close neighbours than is pre-

dicted in the model by Durian35 (Fig. 4). In fact the model no

longer applies, since it does not allow for changes in drop size

over time. Coalesced drops are often surrounded by a halo of

small drops which leads to a large variation in coordination

numbers at a given volume fraction. The elongated shape of the

coalesced drops means there is an increase in the average distance

over which drops are in contact and a broader distribution of

contact lengths (Fig. 2c).

The larger coalesced drops tend to have shapes that resemble

an intermediate stage of the coalescence process, as shown in

Fig. 5b. This means that coalescence was arrested before fusion

into a single spherical drop. It indicates there is a force opposing

relaxation into a spherical shape (which is driven by the surface

tension). The static nature of the distorted drops shows that the

interface is solid-like. So the attached particle layers on the

merging drops make their surfaces sufficiently viscoelastic to

cause a significant increase in the characteristic time for shape

relaxation.

Cracks were observed in the particle layer attached to other

drops (Fig. 5c). This indicates that the layer is rigid enough to

fracture as the degree of drop compression increases. This is

further evidence of the solid-like nature of the interfacial layer in

these concentrated Pickering emulsions.

Fig. 5 Confocal fluorescence images of an unstable emulsion with an oil

volume fraction (f) of 95%. (a) The drops are polydisperse in size and

shape. There are a small number of very large drops. Some intermediate-

sized drops are trapped in an intermediate stage of coalescence. There is a

large population of smaller drops. Small compressed drops have cracks in

their surfaces. (b) Profile of the particle shell coating a droplet fused into a

doublet shape. (c) Greyscale image showing a fracture in the particle shell

coating the end face of a droplet.

7788 | Soft Matter, 2012, 8, 7784–7789

Cracks in the attached particle layer on a drop will favour

coalescence with nearby drops in the emulsion. This could

explain the increase in the drop size distribution polydispersity in

the unstable emulsions. Previously, one of us observed homo-

geneous growth during the formation of dense particle-stabilised

emulsions. Limited coalescence36 occurs when the solid content is

initially insufficient to fully cover the oil–water interfacial area

created during emulsion formation. Narrow distributions of

drop sizes form, since the frequency of (limited) coalescence

events is a decreasing function of the droplet diameter.

The coalescence scenario is different here. The slow shape

relaxation process dominated drop coarsening. This meant that

the observed emulsion microstructure was typically already

arrested or coalesced. At 88 < f# 94% the polydisperse drop size

distributions consisted of a large population of drops centred at

sizes that are double the mean drop size in the stable emulsions

(the primary drop size) and a small population (<4%) of large

drops. The larger drops increased in size, from about four to nine

times the primary drop size, as the drop volume fraction

increased from 90 to 94%. This suggests that coalescence

proceeds by the growth of a small number of large droplets.

Assuming that the evolution of the drop size distribution in the

bulk emulsion is linked to microscopic properties of the inter-

facial particle layers, then there must be some spatial variation in

the interfacial properties. Fracturing would account for the

presence of a few macroscopic drops growing faster than the

drops of average size. Future experiments will investigate

whether changes in the elastic behaviour of concentrated Pick-

ering emulsions correlate with changes in the coalescence

stability of the emulsions.

4. Conclusions

We have presented confocal fluorescence microscopy images of

the droplet packing in compressed aqueous emulsions of oil

drops stabilized by silanised silica particles. Close packed drops

have hexagonal polyhedral shapes. The length of the polyhedral

sides increase with compression until no more area can be

encapsulated by the particle layer profile in the available space.

There is a sharp increase in droplet deformation due to the

attached particle layer making the coalesced droplet surfaces

solid-like in their response to stress. Complete fusion of merging

droplets into a single spherical drop is sometimes arrested.

Further increases in the degree of compression cause fracturing

in the particle layer and hence destruction of the emulsions.

Acknowledgements

The particles were kindly supplied by Evonik. We thank L.

Waterhouse (Adelaide Microscopy, The University of Adelaide)

for help with the confocal fluorescence microscopy experiments.

CPW acknowledges receipt of an Australian Research Council

Future Fellowship. We thank R. Sedev (University of South

Australia) for his useful suggestions.

References

1 H. M. Princen, J. Colloid Interface Sci., 1983, 91, 160.2 T. G. Mason, J. Bibette and D. A. Weitz, Phys. Rev. Lett., 1995, 75,2051.

This journal is ª The Royal Society of Chemistry 2012

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3 J. Brujic, S. F. Edwards, I. Hopkinson and H. A. Makse, Phys. A,2003, 327, 201.

4 J. Brujic, C. Song, P. Wang, C. Briscoe, G. Marty and H. A. Makse,Phys. Rev. Lett., 2007, 98, 248001.

5 R. Aveyard, B. P. Binks and J. H. Clint, Adv. Colloid Interface Sci.,2003, 100, 503.

6 S. Fujii, M. Okada, H. Sawa, T. Furuzono and Y. Nakamura,Langmuir, 2009, 25, 9759.

7 E. Dickinson, Curr. Opin. Colloid Interface Sci., 2010, 15, 40.8 S. Limage, J. Kragel, M. Schmitt, C. Dominici, R. Miller andM. Antoni, Langmuir, 2010, 26, 16754.

9 S. Simovic, N. Ghouchi-Eskandar and C. A. Prestidge, J. DrugDelivery Sci. Technol., 2011, 21, 123.

10 I. Kralova, J. Sjoblom, G. Oye, S. Simon, B. A. Grimes and K. Paso,Adv. Colloid Interface Sci., 2011, 169, 106.

11 O. J. Cayre, J. Hitchcock, M. S. Manga, S. Fincham, A. Simoes,R. A. Williams and S. Biggs, Soft Matter, 2012, 8, 4717.

12 P. Corbi Garcia and C. P. Whitby, Soft Matter, 2012, 8, 1609.13 H. M. Princen, J. Colloid Interface Sci., 1979, 71, 55.14 C. Heussinger and J.-L. Barrat, Phys. Rev. Lett., 2009, 102, 218303.15 S. F. Edwards and D. V. Grinev, Phys. Rev. Lett., 1999, 82, 5397.16 S. Alexander, Phys. Rep., 1998, 296, 65.17 T. G. Mason, M. D. Lacasse, G. S. Grest, D. Levine, J. Bibette and

D. A. Weitz, Phys. Rev. E: Stat. Phys., Plasmas, Fluids, Relat.Interdiscip. Top., 1997, 56, 3150.

18 H. M. Princen, Langmuir, 1986, 2, 519.19 H. M. Princen and A. D. Kiss, Langmuir, 1987, 3, 36.20 S. Arditty, V. Schmitt, J. Giermanska-Kahn and F. Leal-Calderon,

J. Colloid Interface Sci., 2004, 275, 659.21 D. Tambe, J. Paulis and M. M. Sharma, J. Colloid Interface Sci.,

1995, 171, 463.

This journal is ª The Royal Society of Chemistry 2012

22 P. S. Clegg, E. M. Herzig, A. B. Schofield, T. S. Horozov, B. P. Binks,M. E. Cates and W. C. K. Poon, J. Phys.: Condens. Matter, 2005, 17,S3433.

23 H. Firoozmand, B. S. Murray and E. Dickinson, Langmuir, 2009, 25,1300.

24 R. Aveyard, J. H. Clint, D. Nees and V. N. Paunov, Langmuir, 2000,16, 1969.

25 R. Aveyard, J. H. Clint, D. Nees and N. Quirke, Langmuir, 2000, 16,8820.

26 H. Xu, S. Melle, K. Golemanov and G. Fuller, Langmuir, 2005, 21,10016.

27 S.-Y. Tan, R. F. Tabor, L. Ong, G. W. Stevens and R. R. Dagastine,Soft Matter, 2012, 8, 3112.

28 J. K. Ferri, P. Carl, N. Gorevski, T. P. Russell, Q. Wang, A. Boekerand A. Fery, Soft Matter, 2008, 4, 2259.

29 J. T. Russell, Y. Lin, A. Boker, L. Su, P. Carl, H. Zettl, J. B. He,K. Sill, R. Tangirala, T. Emrick, K. Littrell, P. Thiyagarajan,D. Cookson, A. Fery, Q. Wang and T. P. Russell, Angew. Chem.,Int. Ed., 2005, 44, 2420.

30 S. Ata, Langmuir, 2008, 24, 6085.31 S. Ata, E. S. Davis, D. Dupin, S. P. Armes and E. J. Wanless,

Langmuir, 2010, 26, 7865.32 A. B. Pawar, M. Caggioni, R. Ergun, R. W. Hartel and P. T. Spicer,

Soft Matter, 2011, 7, 7710.33 J. C. Russ, Image Analysis of Food Microstructure, CRC Press LLC,

New York, 2005.34 M. D. Lacasse, G. S. Grest, D. Levine, T. G. Mason and D. A. Weitz,

Phys. Rev. Lett., 1996, 76, 3448.35 D. J. Durian, Phys. Rev. Lett., 1995, 75, 4780.36 S. Arditty, C. P. Whitby, B. P. Binks, V. Schmitt and F. Leal-

Calderon, Eur. Phys. J. E: Soft Matter Biol. Phys., 2003, 11, 273.

Soft Matter, 2012, 8, 7784–7789 | 7789

Addition and correction Note from RSC Publishing This article was originally published with incorrect page numbers. This is the corrected, final version.

The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.

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