Third Day Poster Session, 17 June 2010 - NanoTR-VI

Poster Session, Thursday, June 17
Theme F686 - N1123
Determination of Critical Micelle Concentration (cmc) of PB-b-PEO Diblock Copolymer by Two
Different Methods
Önder TOPEL*, Burçin ACAR, Leyla BUDAMA, Numan HODA
Akdeniz University Department of Chemistry, Antalya, Turkey
Abstract- Critical micelle concentration (cmc) was measured for PB 1800 -b-PEO 4000 amphiphilic diblock copolymer in aqueous solution by
two different methods. The fluorescent probe technique was utilized with pyrene as a probe molecule, and the intensity of the scattered light
was used in dynamic light scattering technique. The cmc values obtained by these two techniques are rather close each other.
Micellization of block copolymers is an important
research area of colloid science in the last few decades.
Block copolymers may have a soluble block which
constitutes corona, and an insoluble block which
constitutes core in selective solvents. In these solvents
micelles resemble different morphologies such as sphere,
warm-like and lamellar. The self-assembled micelles have
found many applications in many areas such as drug
delivery systems, surface modification and viscosity and
water purification.
Micelles are observed only above a certain concentration
which is the critical micelle concentration (cmc). The cmc
can, most conveniently, be defined as that concentration
below which only single chains are present but above
which both single chains and micellar aggregates can be
found. There are some methods to measure cmc such as
tensiometry, spectrofluorometry, and dye solubilization [1-
3]. DLS (Dynamic Light Scattering) method is a rather
new method to determine cmc of diblock copolymer
micelles [4]. In this study we report the cmc behavior of
PB 1800 -b-PEO 4000 (Polymer Sources, Canada) in aqueous
solution using two different methods, DLS and
fluorometry.
cmc
1,5
A series of block copolymer solutions ranging from
1.72x10 -5 -4.31x10 -8 mol/L were prepared from aqueous
stock solution of block copolymer PB-b-PEO (2%) which
was stirred for 24 h at room temperature. These aliquots
were filtered with 0.45μm filter to get rid of large
agglomerates and dusts. The dispersion was filtered
through a 0.45 mm filter. Size and distribution of the
micelles were analyzed by means of a DLS instrument
(Malvern Zetasizer Nano ZS) with a He-Ne laser beam at a
wavelength of 633 nm at 25°C and 173° of scattering
angle. The results of DLS measurements are expressed in
size distribution by intensity.
Intensity
300
250
200
150
100
50
cmc
0
0 5 10 15 20
concentration x 10 7 (mol/L)
Figure 2. Plot of concentration vs. DLS intensity
1
0,5
0
-10 -8 -6 -4 -2 0
log c
I1/I3
By plotting concentration vs. intensity data, the cmc
value is obtained from the intersection of the two curves
(Figure 2). According to DLS results the cmc is found to
be 3.07x10 -7 mol/L. The cmc values by two different
methods are rather close each other.
This work was supported by Akdeniz University The
Scientific Research Projects Coordination Unit under
Grant No. 2007.01.0105.007.
Figure 1. Plot of the fluorescence intensity ratio I 374 /I 385
(from pyrene emission spectra) vs. log c
First, the critical micelle concentration of copolymer in
aqueous solution was determined using pyrene as a
fluorescence probe. The excitation spectra (350-450 nm)
of the solutions were recorded with an emission
wavelength of 340 nm with the excitation and emission
bandwidths being set at 5 nm. The ratios of the peak
intensities at 374 and 385 nm (I 374 /I 385 ) of the excitation
spectra were recorded as a function of block copolymer
concentration. The cmc value was taken from the
intersection of the tangent to the curve at the inflection
with the horizontal tangent through the point at the low
concentrations (Figure 1). The cmc of PB-b-PEO diblock
copolymer in aqueous solution was estimated to be
2.94x10 -7 mol/L by fluorescence spectroscopy.
*Corresponding Author:ondertopel@akdeniz.edu.tr
[1] Birdi, K. S., 1997. Handbook of Surface and Colloid
Chemistry. CRC Press, Boca Raton, FL.
[2] Dominguez, A., Fernandez, A., Gonzalez, N., Iglesias, E. and
Montenegro, L, 1997. Determination of critical micelle
concentration of some surfactants by three techniques. J. Chem.
Educ., 74 (10): 1227-1234.
[3] Nakahara, Y., Kida, T., Nakatsuji,Y. and Akashi, M., 2005.
New Fluorescence Method for the Determination of the Critical
Micelle Concentration by Photosensitive Monoazacryptand
Derivatives. Langmuir, 21; 6688-6695.
[4] App. Note: Surfactant micelle characterization using dynamic
light scattering
http://www.malvern.com/common/downloads/campaign/MRK80
9-01.pdf
6th Nanoscience and Nanotechnology Conference, zmir, 2010 673