21 research outputs found
Particle-stabilized oscillating diver: a self-assembled responsive capsule
We report the experimental discovery of a self-assembled capsule, with
density set by interfacial glass beads and an internal bubble, that
automatically performs regular oscillations up and down a vial in response to a
temperature gradient. Similar composites featuring interfacial particles and
multiple internal compartments could be the solution to a variety of
application challenges.Comment: 7 pages, 3 figure
Bicontinuous Soft Solids with a Gradient in Channel Size
We present examples of bicontinuous interfacially jammed emulsion gels
("bijels") with a designed gradient in the channel size along the sample. These
samples are created by quenching binary fluids which have a gradient in
particle concentration along the sample, since the channel size is determined
by the local particle concentration. A gradient in local particle concentration
is achieved using a two-stage loading process, with different particle volume
fractions in each stage. Confocal microscopy and image analysis were used to
quantitatively measure the channel size of the bijels. Bijels with a gradient
in channel size of up to 2.8%/mm have been created. Such tailored soft
materials could act as templates for energy materials optimised for both high
ionic transport rates (high power) and high interfacial area (high energy
density), potentially making them useful in novel energy applications.Comment: 9 pages, 5 figure
Emulsification in binary liquids containing colloidal particles: a structure-factor analysis
We present a quantitative confocal-microscopy study of the transient and
final microstructure of particle-stabilised emulsions formed via demixing in a
binary liquid. To this end, we have developed an image-analysis method that
relies on structure factors obtained from discrete Fourier transforms of
individual frames in confocal image sequences. Radially averaging the squared
modulus of these Fourier transforms before peak fitting allows extraction of
dominant length scales over the entire temperature range of the quench. Our
procedure even yields information just after droplet nucleation, when the
(fluorescence) contrast between the two separating phases is scarcely
discernable in the images. We find that our emulsions are stabilised on
experimental time scales by interfacial particles and that they are likely to
have bimodal droplet-size distributions. We attribute the latter to coalescence
together with creaming being the main coarsening mechanism during the late
stages of emulsification and we support this claim with (direct)
confocal-microscopy observations. In addition, our results imply that the
observed droplets emerge from particle-promoted nucleation, possibly followed
by a free-growth regime. Finally, we argue that creaming strongly affects
droplet growth during the early stages of emulsification. Future investigations
could clarify the link between quench conditions and resulting microstructure,
paving the way for tailor-made particle-stabilised emulsions from binary
liquids.Comment: http://iopscience.iop.org/0953-8984/22/45/455102
Contactless Interfacial Rheology: Probing Shear at Liquid-Liquid Interfaces without an Interfacial Geometry via Fluorescence Microscopy
Interfacial rheology is important for understanding properties such as
Pickering emulsion or foam stability. Currently, the response is measured using
a probe directly attached to the interface. This can both disturb the interface
and is coupled to flow in the bulk phase, limiting its sensitivity. We have
developed a contactless interfacial method to perform interfacial shear
rheology on liquid/liquid interfaces with no tool attached directly to the
interface. This is achieved by shearing one of the liquid phases and measuring
the interfacial response via confocal microscopy. Using this method we have
measured steady shear material parameters such as interfacial elastic moduli
for interfaces with solid-like behaviour and interfacial viscosities for
fluid-like interfaces. The accuracy of this method has been verified relative
to a double-wall ring geometry. Moreover, using our contactless method we are
able to measure lower interfacial viscosities than those that have previously
been reported using a double-wall ring geometry. A further advantage is the
simultaneous combination of macroscopic rheological analysis with microscopic
structural analysis. Our analysis directly visualizes how the interfacial
response is strongly correlated to the particle surface coverage and their
interfacial assembly. Furthermore, we capture the evolution and irreversible
changes in the particle assembly that correspond with the rheological response
to steady shear.Comment: 14 pages, 11 figure
Interaction between Nearly Hard Colloidal Spheres at an Oil-Water Interface
We show that the interaction potential between sterically stabilized, nearly
hard-sphere [poly(methylmethacrylate)-poly(lauryl methacrylate) (PMMA-PLMA)]
colloids at a water-oil interface has a negligible unscreened-dipole
contribution, suggesting that models previously developed for charged particles
at liquid interfaces are not necessarily applicable to sterically stabilized
particles. Interparticle potentials, , are extracted from radial
distribution functions [, measured by fluorescence microscopy] via
Ornstein-Zernike inversion and via a reverse Monte Carlo scheme. The results
are then validated by particle tracking in a blinking optical trap. Using a
Bayesian model comparison, we find that our PMMA-PLMA data is better described
by a screened monopole only rather than a functional form having a screened
monopole plus an unscreened dipole term. We postulate that the long range
repulsion we observe arises mainly through interactions between neutral holes
on a charged interface, i.e., the charge of the liquid interface cannot, in
general, be ignored. In agreement with this interpretation, we find that the
interaction can be tuned by varying salt concentration in the aqueous phase.
Inspired by recent theoretical work on point charges at dielectric interfaces,
which we explain is relevant here, we show that a screened term
can also be used to fit our data. Finally, we present measurements for
poly(methyl methacrylate)-poly(12-hydroxystearic acid) (PMMA-PHSA) particles at
a water-oil interface. These suggest that, for PMMA-PHSA particles, there is an
additional contribution to the interaction potential. This is in line with our
optical-tweezer measurements for PMMA-PHSA colloids in bulk oil, which indicate
that they are slightly charged.Comment: 8 pages, 8 figure