Researches Of Surfactants Properties
Researches of surfactants properties
by a method of collateral adsorption
N.V. Nikolenko, Z.V. Masuta, A.P. Korpach
Ukrainian State Chemical Technology University,
Gagarin Av., 8, Dniepropetrovsk 49005,Ukraine
It is known, that a function interrelations exist between quantities of two substances in a solution after their adsorption on the same adsorbent. For example, for collateral monolayer adsorption of two substances the equality is carried out:
q1 = 1 - (1 + 1/B2C2) q2 ,
where: q - surface coverage (q = Гi/Гmax), B2 - adsorptive constant of the Langmure isotherm, C2 - equilibrium concentration. Under condition of B2C2 >> 1 between q1 and q2 should be observed reverse dependence (q1 » 1 - q2) that was confirmed by us experimentally on an example of collateral adsorption on silica of methylene blue dye and cationic surfactants. The extrapolation of linear sites of dependences Г1 = f (Г2) to Г2 = 0 has allowed to define the maximal adsorption of surfactant monomers and micelles. These values are usually estimated theoretically because of complexity of the adsorption isotherms.
The individual adsorption isotherms of cationic surfactants etony and katamin on silica gel were established. It is shown that monolayer of their monomer particles is not formed. The processes of micelles formation in bulk and on an adsorbent surface "hide" adsorption of surfactants monomer ions [1]. On the isotherms the new rise of adsorption begins and the break of the curve Г1 = f (Г2) is observed. For the description of cations adsorption on the negatively charged surface of silica gel we utilized the Shtern-Langmure isotherm and model of collateral two-layer adsorption [2].
It is established that the methylene blue adsorbed on silica gel even at formation of superficial surfactants micelles, that testifies to presence of a free adsorbent surface accessible to adsorption of dye ions. This conclusion well corresponds to the data [1] about a fragmentariness of an adsorptive phase of micellar surfactants.
At the description of the experimental data for katamin in coordinates of the Hill – De Bur isotherm it is established that for constant values of aggregation the energy of micelles adsorption is systematically increased with growth of the surface coverage. And on the contrary, the value of adsorption energy remains constant if to consider that with growth of solution concentration the aggregation of micelles is increased. Adsorption with increasing of the sizes of superficial aggregates at their invariable amount on an oxides surface is experimentally proved by the authors [3]. The prevalence of katamin micelles adsorption energy (-12 kT) and energy of their association (-11,8 kT) above energy of adsorption of its ions (-9,7 kT) allows to conclude that from micellar solutions katamin is adsorbed on a hydrophilic surface of silica mainly as micelles.
As result of the investigations of non-ionic surfactants adsorption (neonol: AФ 9-10, АФ 9-12) from micellar solutions on the silica it is established the presence of isotherm maximum. Their occurrence is caused by change of the micelles sizes owing to increase their aggregation. The dependences Г1 = f (Г2) for initial parts of the adsorption isotherms of neonol are linear that testifies to a constancy of composition of micelles and their thermodynamic stability both in a solution and on a surface of silica. The adsorption of micelles is considered as result of formation of multipoint hydrogen bridges between their OH-groups and adsorbent. On the basis of model of adsorption with the charging control [4] it is shown that the atoms of oxygen in chains -CH2CH2O- are not capable to form individual hydrogen bridges with groups ºSiOH owing to a competition with molecules of water.
References
1. Клименко Н.А. В сб.: Успехи коллоидной химии.- Л.: Химия, 1991.С.156.
2. Муллер В.М., Сергеева И.П., Чураев Н.В.//Коллоидн. журн. 1995. Т.57. №3. С.368.
3. Адсорбция органических веществ из воды. /А.М.Когановский, Н.А.Клименко, Т.М.Левченко, И.Г.Рода.- Л.: Химия, 1990. С. 256.
4. Николенко Н.В., Таран И.Б., Плаксиенко И.Л. и др.//Коллоидн. журн. 1999. Т.61. №4. С.525.
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