Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 75

micelle over half the chain segments would be exposed to an aqueous phase at
any given time, as demonstrated by nuclear magnetic resonance (NMR) (Bunton
and Savelli 1986). A monomeric surfactant rapidly diffuses into micelles and
leaves them at much faster rates than thermal chemical reactions; hence, the
micelle is considered to be in a pseudo-phase. The cmc values of nonionic and
zwitterionic surfactants are generally much less than ionic ones if the size of the
hydrophobic part is similar (Table 2). Generally, the longer a hydrophobic alkyl
chain, the lower the cmc value. The various physicochemical parameters of sur-
factant solution and apparent substrate properties change across cmc (Fendler and
Fendler 1975; Ying 2006), which can be used to experimentally determine the
cmc value. As shown in Fig. 4, the apparent water solubility of a substrate
abruptly increases at surfactant concentrations above cmc, while the decreasing
surface tension of surfactant solution with an increase of surfactant concentration
reaches almost a plateau above cmc.

Table 2 Chemical structure and critical micelle concentration of a typical surfactant
Surfactant

Chemical structure cmc a AN b T (°C) Reference

Cationic
DTMA Br C 10 H 21 N + (CH 3 ) 3 Br − 1.82 × 10 4 48 25 Fendler and

Fendler
(1975)

DDTMA Br C 12 H 25 N + (CH 3 ) 3 Br − 4.62 × 10 3 50 25

TDTMA Br C 14 H 29 N + (CH 3 ) 3 Br − 1.18 × 10 3 75 25

HDTMA Br C 16 H 33 N + (CH 3 ) 3 Br − 0.33 × 10 3 61 25

DPC C 12 H 25 C 5 H 5 N + Cl − 4.48 × 10 3 Bunton and

Savelli
(1986)

Anionic
SDS

C 12 H 25 OSO 3 − Na + 2.3 × 10 3 62 25 Fendler and

Fendler
(1975)

SHDS C 16 H 23 OSO 3 − Na + 179 40

SDSO C 12 H 25 SO 3 − Na + 2.7 × 10 3 54 25

SDBS C 12 H 25 C 6 H 4 SO 3 − Na + 1 × 10 3 Cho et al.

(2002)

Nonionic
Tween 20

R = monolaurate c 60 25 Wan and Lee

(1974)

Tween 80 R = monooleate c 14 25

Triton X-45 (4-C 8 H 17 )C 6 H 4 O(CH 2 CH 2 O) 5 H 50 296 Heredia and

Bukovac
(1992)

Triton X-114 (4-C 8 H 17 )C 6 H 4 O(CH 2 CH 2 O) 7.5 H 110 189 Kile and Chiou

(1989)

Triton X-100 (4-C 8 H 17 )C 6 H 4 O(CH 2 CH 2 O) 9.5 H 130 146

(continued)