Chemistry Reference
In-Depth Information
Figure 3 displays a sequence of responses of dynamic surface tension,
excited by harmonic disturbances of the bubble surface area, for a sea wa-
ter sample collected in the late summer. By keeping the bubble surface at a
constant value during increasing time intervals, the J(
t
) response pro-
gressively shifts toward a lower value, but with a larger oscillation ampli-
tude. Such behaviour manifests a slowly adsorbing organic material.
Sea water ( Leghorn ) - Septem ber 03, 1998
74
a , b
72
c
70
d
68
66
64
e
62
60
150
200
250
300
350
400
450
tim e ( s )
Fig. 3.
Time evolution of the dynamic surface tension response, J(
t
), excited by
harmonic changes of relative surface area, 'ln
A
(
t
), for a sea water sample col-
lected in the Tyrrhenian Sea. Observed values at different time of bubble surface
creation:
a)
fresh bubble surface;
b)
10-minute age;
c)
40-minute age;
d)
1-hour
age;
e)
3-hour age. Temperature T = 20.0 °C
Figure 4 represents a (zoomed) part of the J(
t
) data of Figure 3, to-
gether with the (synchronous) surface area data. In this case, the phase an-
gle between response and perturbation is almost zero. In other words, the
film appears as purely elastic. In contrast, a viscoelastic film shows an an-
ticipating response, as Figure 5 illustrates for example.
The relationship between dynamic surface tension, J(
t
), and surface
viscoelasticity (which is one of the parameters relevant to wave damping)
is well defined in the literature (Loglio et al. 1994, 1995, Dukhin et al.
1995, Noskov and Loglio 1998, Zholkovskij et al. 2000, Kovalchuk et al.
2000, 2004, 2005, Joos 1999, and references therein). Figures 2-5 also
demonstrate a satisfactory sensitivity for marine applications of the meas-
urement technique.
