A short project to find out Critical Micellar Concentration of reverse micelle in non-polar environment. the instrument used is obviously Dynamic Light Scattering Machine.

1. CH-222
FOURTH SEMESTER CHEMISTRY PROJECT
Determination of Critical Micellar Concentration(CMC) of
Sodium Dodecyl Sulphate in Hexane using
Dyanamic Light Scattering (DLS) Method.
Done By:
Hemanta Sarmah (09MS001)
Soumalya Sinha (09MS006)
Ankan Bag (09MS030)
Debtanu Chakraborty (09MS031)

2. INTRODUCTION:
Dynamic light scattering (also known as photon correlation spectroscopy or quasi-elastic
light scattering) is a technique in physics, which can be used to determine the size
distribution profile of small particles in suspension or polymers in solution. It can also
be used to probe the behavior of complex fluids such as concentrated polymer solutions.
When light hits small particles the
light scatters in all directions
(Rayleigh scattering) so long as the
particles are small compared to the
wavelength (below 250 nm). If the
light source is a laser, and thus is
monochromatic and coherent, then
one observes a time-dependent
fluctuation in the scattering intensity.
These fluctuations are due to the fact
that the small molecules in solutions
are undergoing Brownian motion and
so the distance between the scatterers
in the solution is constantly changing
with time. This scattered light then
undergoes either constructive or destructive interference by the surrounding particles
and within this intensity fluctuation, information is contained about the time scale of
movement of the scatterers.
The sample that we are going to analyze is Sodium Dodecyl Sulphate (C12H25SO4Na).
Our solvent is n- Hexane (99.9 % pure) . Now since the solvent is non-polar so, there
will be a reverse micelle formed, with the polar head groups pointing inwards and the
non-polar tail protruding outwards. In such a system we cannot apply the normal
conductometric method of determining the critical micelle concentration . So we resort
to DLS method, that has already been described above.
OBJECTIVES:
1) To become familiar with the technique of Dynamic Light Scattering(DLS).
2) To compare the closeness of CMC values of SDS in reverse micelle condition to
that in micelle condition.

3. MATERIALS AND EQUIPMENT:
• n-Hexane
• 10 test-tubes
• tes-tube stand
• SDS (Molecular Weight = 288.5 g/mol)
• DLS machine
• quartz cubette
• dipso-van syringe
• Nylon filter
REAGENTS REQURED: (per 100 ml of solution)
1) Sodium Dodecyl Sulphate (SDS) (0.02885 x 36) gms = 1.0368 gms
2) n- Hexane 10 ml
Procedure:
1) We calculate the molar mass of SDS and find it to be 288.5 g/mol.
2) We measure 0.0288 gm of SDS using an electronic balance and then transfer it to
an empty test-tube. Add hexane in it to make the final volume to be = 10 ml.
3) In the next test-tube we add ( 2x0.0288 )
g i.e 0.0576 g of SDS in 10 ml hexane.
4) In the remaining 6 test-tubes, we now
keep adding 0.0288 g more than what
we added in the previous one.
5) We then seal the test-tubes. It is
necessary because hexane is volatile in
nature and can easily escape in room
temperature.
6) We then shake the test-tubes , such that
the entire amount of SDS gets dissolved.
7) The DLS machine is switched on and, left for 20 minutes and then the calibration
is done of n-hexane i.e our solvent.
8) Then we filter the individual solutions using a 45 μm nylon filter. For filtering we
place the filter over the cubette and then with the help of a dispo-van push the
solvent through the filter.
9) Parameters for DLS are set, viz: Room temp. = 250C, Equilibrating time= 60 secs.
10) Data (Diameter of the particles vs frequency) is taken from the graphs that
emerge on the computer screen.

4. Result Analysis :
Table 1: Concentration vs. Size of particle
Sl. No Concentration Size of the particle Size of the particle (I) Average Size of I and II
of solution (N) (I) (nm) (nm) (nm)
1 0.02885 0.3921 0.3764 0.38425
2 0.0577 0.399 0.387 0.393
3 0.0865 0.3597 0.3106 0.33515
4 0.1154 0.4825 0.3597 0.4211
5 0.1442 0.3597 0.4841 0.4219
6 0.1731 6.772 5.05 5.911
7 0.2019 5.765 5.007 5.386
8 0.2308 6.4825 5.3597 5.9211
From the graph the CMC value can be calculated to be 0.16 mol/lit i.e = 0.16 M.

5. SOURCES OF ERROR:
1) SDS is sparingly soluble in n-hexane. Even at low concentrations it is very
difficult to dissolve completely in solution, and as a result there might arise bulky
particles. If these were to be scanned over a large number of particles, then the
error will be very high.
2) No external dust should be falling after the filtration has been done
3) Once a nylon filter is used, it should be discarded, before re-use.
4) Solvent being volatile, will always try to escape away. So seal the test-tubes
before shaking.
CONCLUSION: The critical micelle concentration was found out to be = 0.16 M
ACKNOWLEDGEMENTS:
We are very grateful for Prof. Parna Gupta Bhattacharya and Prof. Priyadarshi De and
Prof. Mousumi Das for allowing us to do project titled “Determination of Critical
Micellar Concentration(CMC) of Sodium Dodecyl Sulphate in Hexane using Dyanamic
Light Scattering (DLS) Method.”. Their guidance came in a lot handy for doing the
project successfully.
We are also thankful to Dr. Srikanth and Mr. Saroj (Lab Assistant) who provided us
with chemicals and reagents.
Last but not the least we would like to thank Prof . Raja Shunmugam along with his Phd
student Mr. Santu Sarkar, Department of Chemical Sciences , IISER Kolkata for having
allowed us the space and equipment for working .
REFERENCES:
1. Physical Chemistry by Atkins.
2. www.wikipedia.org
3. http://pubs.acs.org/doi/abs/10.1021/la051447u
4. Dynamic Light scattering : with applications to chemistry,biology and physics.