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J Surfact Deterg (2010) 13:75–81
the structure with the spreading properties of trisiloxane
surfactants. For example, a bulkier and more polar carbo-
hydrate unit and the incorporation of hydrophilic spacer
elements can reduce the trisiloxane surfactants spreading
ability (SA) [9]; it seems that only the T-shaped trisiloxane
surfactants are able to spread rapidly on solid surfaces,
while flexible linear chain surfactants cannot do so [10];
their spreading performance is apparently affected by the
HLB values and the molecular volume of the surfactants
tail trisiloxane surfactants, but that their spreading perfor-
mance is not satisfactory.
As a further contribution, this paper reports on the
synthesis and interfacial properties of four types of novel
double-tail trisiloxane surfactants, and analyzes the influ-
ence of substructure on the SA and HRA.
Experimental Procedures
[
8] and the structure of the trisiloxanyl units (hammer-like,
Materials
linear) is not a critical parameter for the spreading of the
trisiloxane surfactants as long as surfactant bilayers can be
formed [11].
Type A single-tail trisiloxane surfactants (1A, 2A, 3A, and
4A), whose structures are shown in Scheme 1, were syn-
Additionally, the trisiloxane surfactants currently avail-
able exhibit a poor resistance to hydrolysis [12, 13]. Some
of them hydrolyze rapidly when placed in an aqueous
environment where the pH value is below 5 or above 9, and
are stable only for 40 days even in a neutral aqueous
environment (pH 7.0). This shortcoming limits their
application as agricultural adjuvants, because they are
likely to lose their efficacy as pesticides emulsifiers during
transportation or storage. Therefore, the development of
hydrolysis resistant superspreading surfactants is a quite
important issue in formulating pesticide products.
thesized as described in our previous report [19]. Paraffin
wax was purchased from Shanghai Specimen and Model
Factory, China. All of other chemicals were of analytical
grade. Water was doubly distilled.
Synthesis
The synthesis route to the double-tail trisiloxane surfactants
is shown in Scheme 1. Procedures (a) and (b) were carried
out in accordance with references [20] and [21], respec-
tively. One difference is that the used solvent is toluene,
rather than methanol in procedure (b). Procedures (c) and
Nevertheless, the study of hydrolysis resistant silicone
surfactants has rarely been reported. A kind of hydrolysis
resistant trimethylsiloxane surfactant was mentioned by
Wagner et al. [14]. However, its aqueous solutions can only
spread effectively on solid surfaces whose solid/vapor
(d) were carried out in the light of the reference [19].
Four types (E, F, G and H) and sixteen double-tail tri-
siloxane surfactants (1E, 2E, 3E, 4E, 1F, 2F, 3F, 4F, 1G,
G, 3G, 4G, 1H, 2H, 3H and 4H) were prepared. Their
molecular structures are shown in Scheme 1.
2
interfacial energies (c ) are no less than 40 mN/m, which
sv
indicates that it does not match the agricultural adjuvant
requirements. Recently, hydrolysis resistant disiloxane
surfactants [12] and trisiloxane surfactants [13] have been
synthesized by Leatherman MD et al. Unfortunately, these
two types of siloxane surfactant can only reduce the surface
tension of water to about 23 mN/m. Moreover, the silox-
anes used to synthesize the above hydrolysis resistant
surfactants have a very special structure, and they are not
easily available on the market. As a consequence, the
industrial production of these hydrolysis resistant siloxane
surfactants is not easy.
1
13
The H- and C-NMR spectra of double-tail trisiloxane
surfactants prepared were analyzed according to the rule
that different chemical environments of H and C result in
different chemical shifts, and by comparing the chemical
shifts of related compounds [19, 22, 23], The assignments
1
13
of the chemical shifts in H- and C-NMR spectra of 1E,
IF, 1G and 1H are listed in Tables 1 and 2.
Structural Characterization
1
13
H-and C-NMR spectroscopy analyses were carried out
It is known that certain double-tail hydrocarbon chain
surfactants, e. g., sodium bis (2-ethylhexyl) sulfosuccinate,
exhibit an ability to reduce the surface tension of water, to
wet and spread on low-energy surfaces which are superior
to those of the corresponding single-tail surfactants [15–
with a Varian Mercury-plus 300 spectrometer in CDCl3.
Surface Activity and Hydrolysis Resistant Ability
(HRA) Determination
1
8]. It is also known that the incorporation of a methyl
Surface activity experiments were all carried out under
constant atmospheric conditions (32 ± 2 °C room tem-
perature, 60 ± 3% relative humidity). Aqueous solution
surface tension (c) values were obtained by the Wilhelmy
plate method using a BZY-1 completely automatic surface
tensiometer (Shanghai Equity Instruments Factory, China).
The critical micelle concentration (CMC) values, the
group in the spacer of a trisiloxane surfactant is able to
improve its hydrolysis resistance [13]. Consequently, to
accumulate the previously mentioned features, we synthe-
sized a series of new double-tail trisiloxane surfactants
[
19]. It was found that their hydrolysis resistant ability
HRA) is greatly improved with respect to original single-
(
1
23