Znd. Eng. Chem. Res. 1994,33, 2102-2106
2102
Synergistic Behavior of the Nonylphenol(9) Ethoxylate and Alkylbenzyldimethylammonium Chloride Binary Mixture Saadet Yapar and Sumer Peker* Chemical Engineering Department, Ege University, 35100 Bornova, Izmir, Turkey
In this investigation, the interaction between the cationic alkylbenzyldimethylammonium chloride (ABDAC) and nonionic nonylphenol (9) ethoxylate (NPSEO), expected to interact very weakly according t o criteria proposed by Rosen, was investigated. T h e criteria for synergism were found to be in the order of magnitude of an anionic-cationic surfactant pair. T h e reasons for this strong interaction were explained with the help of the shifts in the peaks of charqcteristic IR absorption bands. Disappearance of the peaks corresponding to C-N stretches and appearance of the peaks of C-C stretching in the wavelength interval of the 1250-1000-~m-~ region were interpreted as the seclusion of the positively charged amine group of ABDAC by the electrophilic ethoxylate group of NPSEO.
Introduction
A mixture of surfactants is said to exhibit synergism, if the interfacial properties of the mixture deviate from that of the expected weighted average value of the individual components. In a series of papers Rosen (Hua and Rosen, 1982; Rosen and Zhu, 1984; Zhu and Rosen, 1984; Rosen, 1989) derived the criteria for the existence of synergism in binary mixtures of surfactants in terms of mixed monolayer formation,mixed micelle formation, and surface tension reduction effectiveness. The attractive forces between the molecules causing synergism could be due to electrostatic attraction of oppositely charged hydrophilic head groups or to van der Waals attraction of their hydrophobic groups, the former leading to stronger interactions. The degree of interaction with cationic surfactants follows the order anionic > zwitterionic > nonionic (Rosen, 1989). The extent of the interactions in the mixed micelle and that in the mixed monolayer at the air/solution interface are given by the PM and p" parameters, respectively.
x;c,/c,= Xii
(1)
The parameter should be the same for the mutually interacting components. Taking the ratio of eq 5 to eq 6 gives the basic equation for synergism in mixed micelles:
where (8) is obtained from eq 5. Synergismin mixed micelle formation causes the critical micelle concentration (cmc) of the solution to be lower than that of either component surfactant when used alone. Conditions for the presence of such a synergism are
> Iln(Cy/Cy)I
where f i is the activity coefficient signifying the deviation from ideality. Rosen (1989) has expressed this deviation from ideality with an interaction parameter p as
fi = xiexp[P(1- XJ'I
(2)
When eq 2 is substituted in eq 1
is obtained for the first component, for interaction in mixed micelles, and
for the second component. The logarithms of eqns 3 and
4 are
pM
