Chemistry Reference
In-Depth Information
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Figure 7.5
Schematic diagram of the batch ultrafiltration system: 1, nitrogen flask; 2,
pressure transducer; 3, filtration cell; 4, water jacket; 5, magnetic stirrer; 6, electronic bal-
ance; and 7, personal computer.
These derivatives also enable the voidage,
, of the nano-particles at the mem-
brane surface at any given time to be calculated by a simple interpolation proce-
dure [113]. The concentration of the particles corresponding to a given osmotic
pressure can then be established as voidage is simply related to the nano-particle
concentration.
In order to obtain a full osmotic pressure curve, frontal ultrafiltration exper-
iments need to be carried out at several different pressures. This is due to the
nature of numerical differentials taken from experimental data. Differentiation of
numerical data may be an unstable process, i.e. any fluctuations in the original
data will be amplified [112]; therefore, as the filtration proceeds with time, the
smaller changes in volume with respect to time result in greater errors for the cal-
culated flux. It is therefore best to use only the initial data from the first 5 minutes
of filtration (approximately five to six points) to evaluate the osmotic pressure
and concentration values, for after this instability may arise due to the numerical
errors from the numerical differentiation. This method for measuring the osmotic
pressure has the following advantages over conventional membrane osmometer
measurements: (a) only very simple apparatus is required, (b) results are obtained
quickly, (c) only small sample quantities are required and (d) only dilute initial
samples are needed, as the ultrafiltration process creates a concentrated solution
at the membrane, making sample preparation a simple task. However, this mea-
surement is not a direct measurement and some calculations have to be performed
in order to obtain the required data.
ε
7.3.1.3 Results
Figures 7.6 to 7.8 show experimental results for the osmotic pressures of several
different nano-fluids. The osmotic pressures were determined using the various
different methods for measuring the osmotic pressure. The data for BSA were
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