Chemistry Reference
In-Depth Information
concentration was 10 mM. The surfactants used were polyoxyethylene-
23-lauryl ether (Brij 35) and sodium dodecyl sulfate (SDS) (Sigma-Aldrich,
Poole, UK). Droplet-size distribution measurements at the end of the exper-
iments showed no change from the initial values.
Droplet-size distributions of the emulsions were measured using a Coulter LS
230 laser diffraction particle sizer (Beckman Coulter, CA, USA). The data were
analysed using an optical model for a fluid with real and imaginary parts of the
complex refractive index set to 1.332 and 1.391, respectively. The zeta potential
of the emulsions was measured using a Zetasizer 3 (Malvern Instruments, UK)
calibrated using the
50 mV standards supplied by the manufacturer. All
samples were measured after dilution using the relevant continuous phase
(separated by centrifugation).
Microscopy images were acquired using a Biorad 1024 confocal microscope
based around a modified Nikon Optiphot microscope. Samples were placed in a
specially modified cuvette which had one side replaced with a cover glass.
Observations were made using a 60
oil immersion objective with a numerical
aperture of 1.4. Samples were stained using Nile Red, which was added to the
sample in powder form and allowed to stand for several days.
The interfacial tension between the aqueous phase of the emulsion and
n-hexadecane was measured using the pendant drop technique. Images were
acquired using a digital camera (Pulnix, USA) and frame grabber (Matrox,
USA) and analysed using in-house software.
The surface and bulk shear rheological measurements were made using a TA
Instruments AR2000 controlled stress rheometer (TA Instruments, Crawley,
UK) in controlled stress mode for creep and steady-state bulk measurements
and in controlled strain mode for oscillatory shear and surface shear measure-
ments. Creaming experiments used a modified cup and bob arrangement with a
cup of 150 mm depth and an inner cylinder of 40 mm height. With this
arrangement we could monitor the bulk rheology of a sample at a range of
heights within a creaming emulsion. A frequency of 1 Hz and a strain of 1%
were chosen as the measuring conditions, and samples were monitored over the
same time-scale as for the ultrasonic experiments. Rheological measurements of
the creamed phase were carried out in a cone-and-plate geometry using a 21
cone in either steady or dynamic mode, as required. Surface rheological
measurements at the air
water or oil
water interfaces were undertaken with
a polished aluminium biconical disc (61, 60 mm diameter) over a 2-h time
period, again with a strain of 1%, but a frequency of 0.5 Hz.
Oil volume fraction profiles were assessed from time-dependent measure-
ments of ultrasonic velocity through the sample as a function of height within
the sample. These data were related to disperse phase volume fraction via
the Urick equation. Creaming measurements were made at 201C using an
Acoustiscan system (University of Leeds, UK).
29
Readings were taken every
2mm over the entire height of the emulsion, to give a profile of the dispersed
phase volume throughout the emulsion. Measurements continued until the
majority of the oil was in the cream layer, and the distribution was approaching
equilibrium.
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