Water and Solute Permeability of Plant Cuticles: Measurement and ...

7.1 Sorption of Plasticisers in Wax and Cutin 209
Table 7.1 Wax/water partition coefficients Kww of monodisperse alcohol ethoxylates in reconstituted
wax of Hordeum vulgare, Stephanotis floribunda and Chenopodium album. Cx gives the
number of carbon atoms of the fatty alcohol, and Ey refers to the number of ethylene oxide units
in the polar part of the alcohol ethoxylates
Compound cmc(mol kg −1 ) a Kww
H. vulgare S. floribunda b C. album c
C4E2 0.589 0.083 d – –
C6E 3 0.06 0.83 d – –
C8E 4 0.0062 4.9 d – –
C10E 5 0.00063 35.7 d – –
C10E 8 0.0012 5.6 e – –
C12E2 0.000028 2,000 e 21,125 –
C12E3 0.000035 1,300 e – 1,610
C12E4 0.000043 670 e 7,909 –
C12E5 0.000053 400 e 4,439 687
C12E6 0.000066 201 d 2,626 268
C12E7 0.000079 160 e – 203
C12E8 0.000098 104 b 962 109
C14E3 0.0000029 – – 19,700
C14E5 0.0000044 – – 8,040
C14E6 0.0000054 – – 3,700
C14E7 0.0000066 1,561 d – –
C14E8 0.0000081 1,200 e – 1,410
C16E 3 0.00000024 – – 231,000
C16E 8 0.00000068 12,350 d 13,700
a Calculated according to Riederer and Schreiber (1995)
b Data from Simanova et al. (2005)
c Data from Burghardt et al. (2006)
d Data from Schreiber et al. (1996b)
e Data from Burghardt et al. (1998)
With all three wax samples, log Kww decreased by the factor of −0.23 to −0.24
for each additional ethylene oxide (E) unit. For barley (7.1) and Chenopodium wax
(7.2), log Kww increased by the factor of 0.53–0.54 for each additional C atom.
Equations for barley and Chenopodium wax are identical within experimental error
(Burghardt et al. 1998, 2006). With Stephanotis the number of C atoms was constant
(C12), and only Ey was varied (Simanova et al. 2005). Hence, (7.3) is only available
in a reduced form describing the influence of Ey units on Kww. These results are
consistent with data published for linear alcohols and fatty acids by Dunn et al.
(1986), from which it can be calculated that for each -CH2 group added log Kow
increased by a factor 0.55–0.52. Thus, the influence of the number of E and C units
on log Kww is similar for all three wax samples; however, the absolute values can
vary by a factor of 10 depending on plant species. Using (7.1)–(7.3), Kww can be
estimated accurately for other monodisperse alcohol ethoxylates.
Cmc of surfactants and their lipophility (i.e., Kww) are related (Table 7.1). With
increasing lipophility of the surfactants, micelles form at lower concentrations. The
maximum concentration (g kg −1 ) of alcohol ethoxylates sorbed in reconstituted