Influence of the Molecular Geometry of Nonionic Surfactants on Surface and Micellar Properties in Aqueous Solutions

Abstract

The influence of the molecular geometry of corresponding differently branched nonionic surfactants on surface and micellar properties in aqueous solution was investigated by surface tension measurements. The nonionic surfactants with a branched hydrophilic moiety are described as Y surfactants (C n G(E m /2M)2) and with a branched lipophilic moiety as V surfactants: symmetrical Vs (C n /2)2GE m M and asymmetrical Va (C k )(C n -k )GE m M; where C n and C k denote an alkyl chain, G a triglyceryl unit, and E m M an oligo(oxyethylene) monomethyl ether with k = 4, n = 10, 12, 14, 16, and m = 6, 8, 10. The critical micelle concentration (cmc), the standard free energy of micellization (ΔG m), the equilibrium surface tension (γcmc), and areas per molecule at cmc (A cmc) at the air−water interface were determined as a function of the total hydrocarbon number (n) m =const in the lipophilic part and oxyethylene group number (m) n =const, in the hydrophilic part of the surfactant. The results are discussed on the basis of structural factors for the corresponding Y, Vs, Va surfactants and compared with data of the conventional unbranched surfactants C n E8M (I surfactants). Within these homologous series the increase of (n) m leads to the lowering and an increase of (m) n to the increasing of the cmc's and ΔG m's. For the corresponding surfactant series the negative contribution to the cmc and ΔG m of each CH2 group promotes micellization and increases in the sequence I > Y > Vs. On the other hand the positive contribution of each EO group opposes the micellization and is larger for Y than for Vs surfactants. The γcmc and A cmc for Y surfactants are significantly larger than for V surfacants. In the gorup of the V surfactants the cohesive forces of the hydrocarbon chains significantly influence the γcmc's.

Effect of branching on the interfacial properties of nonionic hydrocarbon surfactants at the air–water and carbon dioxide–water interfaces

“…9). For a branched tail, A m did not increases with the EO length [85] since A HD of the branched tail was greater than that of the EO groups [85]. We found the same behavior for the series of surfactants 2EH-PO 5 -EO m , where m = 9, 11 and 15 in Table 1, where the A m was about the same for all three.…”

Preparation and Evaluation of Monodisperse Nonionic Surfactants Based on Fluorine-Containing Dicarbamates

“…However in most cases, this strategy led to monocatenar (one perfluorinated tail) monopodal surfactants (one oligooxyethylated moiety). Even if the evaluation of these compounds shows interesting properties (20) as compared to hydrocarbon homologues (21,22) for the formation of microemulsions (23)(24)(25) or lyotropic liquid crystals (26)(27)(28), or as a component for the preparation of emulsions or microemulsions for biomedical uses (29)(30)(31), in most cases, these compounds have been shown to be toxic against biological membranes after in vivo injection. It would seem, according to toxicological studies using luminescent bacteria, that the parameter responsible for this toxicity is due to the presence of long ethylene glycol tails which have disorganizing effects on the biological membranes.…”

Quantitative assessment of alkyl chain branching in alcohol‐based surfactants by nuclear magnetic resonance

“…All NMR experiments were performed at 303 K. One-dimensional (1-D) 1 H NMR measurements, as well as two-dimensional (2-D) total correlation spectroscopy (TOCSY) and heteronuclear single-quantum coherence (HSQC) experiments (17,18) generally were performed with a Varian Unity400 NMR spectrometer, operating at 400 MHz for 1 H. 13 C NMR measurements were taken with a Bruker DMX600 spectrometer, running at 150 MHz. Samples for the 13 C NMR measurements were placed in 10-mm tubes, and a 30-s relaxation delay was used (to prevent signal saturation). Liquid chromatography (LC)-NMR analyses were performed using a 120-µL LC-NMR probe head, interfaced to the LC by means of a Bruker Peak Sampling Unit, which was under the control of an NT Workstation (Hystar software; Bruker BioSpin, Rheinstetten, Germany).…”

“…So far, no general NMR approach has been described that can assess hydrophobe branching in a detailed (site-specific) and quantitative manner. However, it is well recognized that such detailed descriptions are required to make rational predictions and explanations of the properties (11)(12)(13) and environmental behavior (8,14,15) of surfactants with branched hydrophobes. In this study an NMR approach is described that provides more structural detail than the methods currently available.…”

“…13 C and 1 H connectivities in the HSQC spectrum of an alcohol ethoxylate. Horizontal and vertical dashed boxes correspond to integral regions for the 13 C and 1 H branching indices, respectively.…”