Film pressures of some monosubstituted toluenes

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by  Thompson, Charles Earl

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FILM PRESSURES OF SOME
MONOSUBSTITUTED TOLUENES
by
Charles Earl Thompson
A THESIS
Presented to the Faculty of
The Graduate College In the Universi ty of Nebraska
In Partial Fulfillm ent of Requirements for the
Degree of Doctor of Philosophy
Department of Chemistry
Under the Supervision of Dr. E. R. Washburn
Lincoln, Nebraska
May 24, 1951
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UMI Number: DP13978
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The author wishes to express
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Dr. E, R. Washburn for the
advice and help given during
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TABLE OP CONTENTS
Page
I, IHTEGDUGTIOH« .................................. 1
II, MATERIALS . . . . . . . . . . . . . . . . . 6
III* APPARATUS ................................. IS
IV, PROCEDURE AND RESULTS . ........................ 19
A. Spreading Pressures .................... • • • • • 19
B. Surface Tensions. .................... 56
G* Interfacial Tensions. . . . . . . . . . 42
D. Spreading C oefficients. . . . . . . . . 48
V. DISCUSSION. . . . . . . . . . . . . . . . . 49
A. A Comparison of Spreading Pressures and
Spreading C oeffioients. 49
B. The Effeot of Substituents on the Spread­
ing Pressure o f Toluene . . . . . . . . 55
VI. ADDITIONAL OBSERVATIONS « 58
A. The Spreading of Wet Chloro toluenes . • 58
B. Stearic Acid Film Pressures in the
Presence of o-T olunitrile Vapors. . . . 60
C. The E lasticity of Palm itic Acid,
Steario Acid and Tristearin Films on
Water . . . . . . . . . . . . . . . . . 68
D. Differences in Observed Spreading
Pressures at D ifferent In itia l Film
P ressu res................................................................. 75
VII. SUMMARY . ................................................................... . 77
VIII. BIBLIOGRAPHY............................. 79
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I. INTRODUCTION
Many investigators have contributed to the development
of present day methods of studying film s which are spread on
water.
Rayleigh'*’ fir st measured the difference in surface ten­
sion between pure water and water on which a thin layer of
o il had spread. Poekels^ then found that these thin film s
on water could be moved about or confined to a given area of
surface by barriers and also that a water surface oould be
swept clean by means of barriers. Studies were then made of
the changes in surface tension with variation of the area to
which a film was confined. It was observed that, provided
the area exceeded a certain critica l amount for a given quan­
tity of o il, the surface tension was not noticeably changed
from that of pure water. When the area was reduced below
th is critica l amount the surface tension fe ll rapidly.
Bayleighr then suggested that, at th is critica l point, the
molecules were lying on the water surface in a layer just
one molecule thick, each molecule close enough to the sur­
rounding molecules to be aoted upon by them. The resistance
to compression of an insoluble surface film , which is con­
fined between two barriers, may be measured if one of the
barriers is a ligh t floating strip that has an instrument
attached for measuring the force exerted by the film against
the barriers. This force is often called the surface film
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2
pressure. The relationship between the surface film pressure
and the surfaoe tension of the film covered surface is simple*
Surface tension is the numerical equivalent of free energy per
unit of area of the surfsee, or the work whioh must be done to
increase the area of the surfaoe by one square oentimeter. If
the floating barrier is displaced a distance dx, so that the
area occupied by the surfaoe film is increased, the work done
a
on it by the surfaoe film pressure 7 is Fldx, where 1 is the
length of the flo a t. If is the surfaoe tension of the clean
/
.
water surfaoe and V that of the film oovered surface, an area
Idx of free energy has been replaced by one of free energy
Jr'w ,
and tie work don. «u.t b. O'. - Id*. Ib.M two .* -
pressions for the work done must be equal hence 7 ~ <^w - ^ .
The surface film pressure is therefore equal to the diminution
of the surfaoe tension of the water by the film .
Langmuir^ devised a surfaoe balance to measure surface
film pressures d irectly. He studied the change in film pres­
sure with change in area per molecule for many pure compounds
spread on water. By these studies Langmuir proved that the
molecules composing the film are oriented in a particular manner
on the water surfaoe. He was also able to measure the cross
sectional area of the molecules in the film* The most stable
surfaoe film s are formed by those substances that have a- water.
soluble group, suoh as a carboxyl or hydroxyl grodp,..a.tiiached
to one end of a long aliphatio hydrocarbon chain. Thewatsr
soluble group is pulled into the water and held firm ly, whereas
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