Basic surface-active properties in the homologous series of β-alkyl (C(12)H(25)/C(18)H(37)) polyethyleneoxy (n = 0-20) propionamides

BACKGROUND: Heterogeneous β-Alkyl (C(12)H(25)/C(18)H(37)) polyethyleneoxy (n = 0-20) propionamides [R(EO)(n)PD] represent new “hybrid” nonionic-ionic colloidal structures in the field of surface-active products (technical products). These “niche” compounds have three structural and compositional characteristics that also define their basic colloidal properties: mixture of R and PEO chain homologues; specific conformations due to the PEO chains; and the presence of side products from the addition of higher alcohols, polyethyleneglycols and traces of water to acrylamide. The proposed major objective of this paper is the basic informative colloidal characterization (functional classification, HLB balance, surface tension, critical micelle concentration) in direct correlation with the structural changes in the homologous series of LM(EO)(n)PD and CS(EO)(n)PD. The structures were obtained either indirectly by cyanoethylation followed by partial acid hydrolysis of the corresponding β-propionitriles, or directly by the nucleophilic addition under alkaline catalysis of linear higher alcohols C(12)H(25)/C(14)H(29) (7/3) (LM) and C(16)H(33)/C(18)H(37) (CS) as such and heterogeneous polyethoxylated (n = 3-20) to acrylamide monomer, through an adapted classic reaction scheme. RESULTS: In the series of basic colloidal characteristics investigated the structure-surface activity dependence is confirmed. Their indicative character for R(EO)(n)PD is based on the assumption that the structures studied are not unitary (heterogeneous) because: a) the hydrophobic chains C(12)H(25)/C(18)H(37) have been grouped in two variants, C(12)H(25)/C(14)H(29) (LM); C(16)H(33)/C(18)H(37) (CS), each with an internal mass ratio of 7/3; b) the hydrophilic polyoxyethylene chains (n = 3-20) have polydisperse character; the meaning and value the oligomerization degree, n, is that of weighted average. In these conditions the surface tension increases proportionally with the oligomerization degree of the polyoxyethylene chain, while the critical micelle concentration decreases in the same homologous series as well as with the increase of the hydrophobic chain in the C(12)H(25) to C(18)H(37) series. A mechanism of micellization is proposed, consistent with the experimental data recorded and the hypotheses known from the consulted literature. CONCLUSIONS: The idea of the obtaining and basic colloidal characterization of heterogeneous R(EO)(n)PD is justified. The knowledge and constructive approach of the heterogeneous character confirm the basic surface-active potential of R(EO)(n)PD, the structure-colloidal characteristics dependence and justifies further, more extensive research.