experimental investigation of foam films stabiluzed

5
Nanoscience& NanotechnologY,
eds. E. Balabanova,l. Dragieva,Heron Press,Sofia,2006
OF FOAMFILMSSTABILUZEDWITH N-HEPTANOL
INVESTIGATION
EXPERIMENTAL
D. Arabadzhieva,P.Tchoukov,E. Mileva, D. Exerowa
Instituteof PhysicalChemistry,BulgarianAcademyof Sciences,l1l3 Sofia,Bulgaria
Abstract. The drainagepropertiesof foam films stabilizedwith
of electrolyte(KCl) are studied.The
n-heptanolin the presence
via the microinterferometric
obtained
are
film characteristics
method,which operateswith the measuringcell of ScheludkoExerowa.The experimentalsetup is additionally improvedby
imageanalysis.The
and consecutive
includingvideo-recording
the range of
covers
amphiphile
of
the
interval
concentration
arejudged
2.2 x 10-6-2.8 x 10-5 mol/I.Thekineticproperties
for the sameexagainstprevioussurfacetensionmeasurements
Theresultsarejuxtaposedto formersimiperimentalconditions.
solutionsof sodiumdodecylsulfate.
of aqueous
lar investigations
Thesestudiesare very importantfor understandingthe impact
in amnanostructures
of surfactanttype on the self-assembled
phiphilicsolutions.
self-assembly,thin liqKeywords: amphiphilicnanostructures,
uid films
1.
to be expectedat concentrationsone-two orders of magnitude lower than the critical micellar concentrations(CMC).
Although there are several other examples of surfactants displaying peculiarities in the static surface tension
measurements,no systematicfoam film studieshave been
performed for these intermediate concentration ranges.
One interesting example is n-heptanol [3]. It is nonionic
surfactantand no CMC has been observedfor it. The surface tension isotherm however,has a well-defined plateau
portion (Figure 1). So, the aim of the present investigation is to perform systematic foam film studies so as to
verify whether the peculiarities in the surface measurements might be related to the run of some of the foam film
drainagecharacteristicsagainstthe heptanolconcentration.
2.
Introduction
Previous investigations show that some surfactants ex"static" Surfacetension measurements
hibit peculiaritiesin
tl-31. In the surface tension isotherms kink and plateau
regions are observed.Experiments with thin liquid films
obtainedfrom solutions within the same concentrationinterval also show unusualrun of someof the film properties,
namely: unstableblack patterns (dots and spots) are observed;they have very short lifetimes and the films, which
contain them, rupture quickly [4-10]. Besides,severalof
the kinetic characteristicsof the films display a sharp
change within a naffow surfactant concentration range.
Theseexperimentshavebeeninterpretedon the basisof the
assumptionthat a seriesof self-assembledaggregatesexist
at the interfacesand inside the thin film. Thus the systematic studies of aqueoussolutions of sodium dodecyl sulfate (SDS) have shown that surfactantnanostructuresare
Materials and Instrumentation
The n-heptanol used is Merk, 997o purity. Triply distilled
water is used. Insofar as the n-heptanol is not very soluble
in water, the initial solution is set on a shaking machine for
about two hours for the complete solublization of the alcohol. The concentrationrange is the same as in the surface
C, : 2.2x 10-6+2.8x 10-b mol/l;
tensionmeasurements:
is
0.1M KCl, Merk and is heated
the added electrolyte
temperature is maintained at
The
at 600oC beforehand.
:
tension measurementsare
surface
The
20 * 0.1'C.
t
from
reproduced
[3].
The film characteristicsare investigatedvia microinterferometric method, which operateswith the measuringcell
of Scheludko-Exerowa(Figure 2). The experimental setup
is additionally improved by including video-recording and
consecutive image analysis according to the established
€ o.l
A
!
E
b
o
0.2
0.1
0.0
0 5 1 0 1 5 2 0 2 s 3 0
Amphiphileconcentration
[mol/l]
Figure 1. Surface tension isotherm of aqueous solution of nheptanol;C.t -- 0.1M KCl, t : 20oC.
Figure 2. Microinterferometric experimental setup with the measuring cell of Scheludko-Exerowa: I - Foam film in measuring
cell;2 - microscope;3 - CCD video camera;4 -PC with capture
video card: 5 - video-recorder.
230
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232
4.
D. Arabadzhieva,P. Tchoukov,E. Mileva, D. Exerowa
Concluding Remarks
Aqueous solutions of n-heptanol exhibit concentration
synchrony of the onset of black dots and the peculiarities of surface tension isotherm. The concentration coincidence of 'static' surfacetension measurementsand 'dynamic' foam film propertieshowever, is not so expressive
as in other casesof ionic surfactants.The causeis the structural propertiesof heptanol:nonionic amphiphile with relatively short hydrophobic chain. The resulting amphiphilic
structuresare very small and have less potential to affect
sensitivelymost of the drainagecharacteristicsof the foam
films. The obtained results outline the range of structural
propertiesof the amphiphilic molecules that could initiate
the onset of amphiphilic nanostructuresin surfactantsolutions.
Acknowledgements
The financial support by Project DAAD-02/20051No.42 is
gratefully acknowledged.
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