6
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.30
0.25
0.20
C) 0.15
0.10 J:
C) 0.05
0.00
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0.00
JOURNAL OF COSMETIC SCIENCE
(a)
---
(b)
(c)
0.0 0.2
D'Arcy-Watt
GAB
:2
.....1
:;;:.----_
.,· • ·
2
-·····
..·· .............:·''"" 1
· • • ".....·····
0.4 0.6 0.8 1.0
X
Figure 3. Isotherm model fits to the data in Figure 1. The solid lines represent the D' Arey-Watt model
and the dashed lines represent the GAB model. The dotted lines are components of the D'Arcy-Watt model
as discussed in the text. Uptake (a), desorption (b), and data from Baden (17) (c).

THE HUMAN NAIL: SORPTION ISOTHERMS 7
Table I
Regression Parameters from Least Squares Fits of the D'Arcy-Watt Model to the Data in Figure 1
Uptake Desorption Baden (17)
Parameters Units (Figure 3a) (Figure 36) (Figure 3c)
b 1.21 ± 0.53 0.98 ± 0.31 3.48
B g H20/g dry tissue 0.22 ± 0.07 0.37 ± 0.08 0.15
0.89 ± 0.01 0.89 ± 0.08 0.92
C g H
2 O/g dry tissue 0.022 ± 0.007 0.017 ± 0.019 0.024
n 12 14 9
r 2 0.9980 ± 0.0009 0.9963 ± 0.0018 0.9991
g H2O/g dry tissue 0.0085 ± 0.0024 0.0121 ± 0.0035 0.0057
Table II
Regression Parameters from Least Squares Fits of the GAB Model to the Data in Figure 1
Uptake Desorption Baden (17)
Parameters Units (Figure 3a) (Figure 36) (Figure 3c)
VT}}
g H20/g dry tissue 0.061 ± 0.009 0.112 ± 0.021 0.068
8.68 ± 1.22 6.41 ± 1.22 24.5
K 0.79 ± 0.08 0.62 ± 0.11 0.80
n 12 14 9
r 2 0.9965 ± 0.0012 0.9935 ± 0.0033 0.9974
g H20/g dry tissue 0.0108 ± 0.0002 0.0150 ± 0.0033 0.0092
The water sorption data for human nail was described by the D' Arey-Watt model with
an average r2 of 0.9980 for sorption and 0.9963 for desorption (Table I). Examination
of the model components (dotted curves in Figure 3) shows that most of the water sorbed
at up to 80% RH (x =0.80) may be described as strongly bound water according to this
analysis. This component, which corresponds to the first term on the right-hand side of
equation 1, is shown by the curves labeled "1." Water associated with multilayer
formation (the second term in equation 1) is labeled "2." This observation is consistent
with findings of Wessel et al. (32), who, using Raman spectroscopy, showed that mainly
bound water is present in human nail. In a similar vein, El-Shimi and Princen (26)
argued from a D'Arcy-Watt analysis that multilayer formation is a minor component of
the overall sorption isotherm for wool and hair, but a significant component for human
stratum corneum. The difference was attributed to the difference in the total equilibrium
water uptake of these tissues.
The parameters B and C may be thought of as the number of strong binding sites and
the number of water clusters, respectively (33). In comparison with Baden's data, our
value of B for uptake was directionally higher and that of C was directionally lower,
implying a higher ratio of bound water to multilayer water. This difference could be
related to temperature, as Baden's work was conducted at 25 ° C and ours at 32°C. In
other systems analyzed by this procedure, including wool (34) and plant seeds (3 3 ),the
values of both B and C have been found to decrease with increasing temperature. The
dependence for C is not surprising (higher temperature =less water clusters) however,
the dependence for B is not anticipated from the theory. By analogy with the BET
model, where the binding parameter varies as exp[-(Qz-QYRTJ (20), the constant b