Calorimetric and Volumetric Investigations of the Effect of the Hydrophobicity of the Surfactant on the Binding between (Ethylene oxide)₁₃-(propylene oxide)₃₀-(ethylene oxide)₁₃ and Sodium Alkanoates in Aqueous Solutions

Abstract

The enthalpy and the volume of transfer (∆Yt) of the unassociated (ethylene oxide)13-(propylene oxide)30-(ethylene oxide)13 (L64) from water to the aqueous sodium alkanoate solutions as functions of the surfactant concentrations (mS) were determined at 298 K. The surfactants studied are sodium hexanoate, sodium heptanoate, sodium octanoate, sodium undecanoate, and sodium dodecanoate. As a general feature, for the short alkyl chain surfactants, ∆Y t describes an S-shaped curve in the range of mS analyzed whereas for the more hydrophobic surfactants the ∆Yt vs mS trends exhibit maxima which appear at mS values very close to the critical micellar concentration in water. The experimental properties were quantitatively treated by means of a thermodynamic model, recently proposed by us, which assumes that the processes of micellization and the formation of both the surfactant-copolymer aggregation complex and the micelle-copolymer mixed aggregate take place simultaneously. The thermodynamics for the surfactant/copolymer aggregation complex formation states that both the compounds release water molecules from their nonpolar moieties which interact through the van der Waals forces generating a hydrophobic microenvironment in the aggregation complex similar to that in the micellar state. Conformational variations of the copolymer produced by the attachment of the surfactant molecules induce the formation of some hydrogen bonds between the ether oxygen of the ethylene oxide units and water. The thermodynamics of transfer of L64 from the aqueous phase to the sodium alkanoate micelles was also determined. The interactions in the mixed micelles and the surfactant-copolymer aggregation complex are similar. However, due to the large size of the micelle, the conformational effects caused by the L64 solubilization in the micelle are quite significant.

A thermodynamic study to evidence the -dichloroalkane/ block copolymer mixed aggregates formation: Effect of the copolymer architecture

“…However, their profiles are different from the present ones. The functions of transfer of long alkyl chain alcohols [27][28][29][30][31][32] and unimeric copolymers [33][34][35][36] in surfactant solutions showed trends similar to those illustrated in Figs. 1 and 2.…”

“…On this basis, the experimental data were treated by means of a model [36] which was applied to several systems and different thermodynamic functions [26,[34][35][36]40]. Briefly, the following equilibria were assumed: (b), and Cl 2 (CH 2 ) 3 (c) from water to the aqueous L35 (") and 10R5 (!)…”

Adsorption of triblock copolymers and their homopolymers at laponite clay/solution interface. Role played by the copolymer nature

“…The bulk experimental property is determined as a function of internal parameters and treated by means of proper theoretical approaches to obtain information at molecular level. Such a technique was successful in describing, from a quantitative viewpoint, cyclodextrin þ surfactant, 28,29 homopolymer þ surfactant 30,31 and copolymer þ surfactant [32][33][34][35] aqueous systems. The adsorption of conventional surfactants onto a solid substrate is generally studied through the ITC method.…”

Interaction between cationic, anionic, and non-ionic surfactants with ABA block copolymer Pluronic PE6200 and with BAB reverse block copolymer Pluronic 25R4

“…Several studies are present on the interaction between Pluronics and surfactants: the more studied systems are those involving ABA polymers and sodium dodecyl sulfate, SDS [7][8][9][10][11][12][13][14]; less abundant bibliography involving non-ionic [15] and cationic [16] surfactants can be found. In particular, De Lisi et al [17][18][19][20] thoroughly investigated this field. In contrast, not much has been written on the interaction between BAB polymers and surfactants [21].…”