Linear and branched polyoxide‐based copolymers: Methods to determine the CMC

Abstract

Evaluation of the physical-chemical properties of aqueous solutions of nonionic surfactants based on polyoxides can be performed by different methods. Depending on the technique used, there can be a significant variation in the critical micelle concentration (CMC) found. This is related to the sensitivity of the technique regarding the unimers and micelles present in the solution as well as the structure of the surfactant evaluated. In this work, the CMC values of aqueous solutions of linear and branched poly(ethylene oxide-polypropylene oxide) (PEO-PPO) block copolymers were determined by tensiometry, fluorescence, and particle size analysis, using copolymers having adjacent structures (that is, hydrophilic and hydrophobic segments located adjacently in the copolymer) and alternating structures. Tensiometry was used to measure the surface tension as a function of the copolymer concentration in aqueous solution. Fluorescence was used to determine the fluorescence intensity of pyrene to plot the graphs of the I 1 /I 3 and I E /I M relations according to the surfactant concentration. Finally, particle size analysis was used to determine the diffusion coefficient of the particles. The results showed that the fluorescence and particle size techniques provide lower (and mutually concordant) CMC values and can be considered more precise because these methods directly analyze the bulk of the solution.

The influence of asphaltenes subfractions on the stability of crude oil model emulsions

“…The linear (L) and branched (B) PEO-PPO block copolymers used here were employed in a previous work 28 as demulsifiers, and it was observed that the branched copolymer was more efficient in breaking the synthetic water-in-oil emulsions tested. This efficiency was associated with: (i) their branched structure, where the EO and PO groups are more distributed in the chains, thus facilitating their dispersion between the phases of the W/O emulsion, and (ii) their average molar mass, since too long chains cannot diffuse through the oil phase because they form agglomerates and too short polymer chains diffuse too slowly, so requiring a molar mass near to an optimal value.…”

Synthesis, characterization and micellization of heterograft copolymers based on phosphoester functionalized macromonomers via “grafting through” method

“…42 To study the micellar behaviors of the heterograft copolymers herein with different compositions of PCL and PEG, the fluorescence technique has been employed and pyrene was used as a probe. As reported by Wilhelm et al, 47,48 pyrene molecules will transfer into hydrophobic microdomains with a concurrent change in the molecule's photophysical properties. In the excitation spectra, a sharp rise in the intensity ratio of the peaks at 338 and 333 nm of pyrene indicates the onset of micellization (CMC) for the amphiphilic copolymers.…”

“…Fluorescence excitation spectra were recorded on a HITACHI F-4500 fluorescence spectrometer at 390 nm emission wavelength and 2.5 nm slit width. Sample solutions for fluorescence investigation were obtained according to the literature, 47,48 and the concentration of the aqueous solutions ranged from 1.0 Â 10 À7 to 0.5 mg/mL. The pyrene concentration in the micellar solution was 6.0 Â 10 À7 mol/L.…”

Evaluation of the efficiency of polyether-based antifoams for crude oil

“…As mentioned already, the PEO-PPO block copolymers and silicon polyethers grafted with PEO and PPO chains have a peculiar behavior when dissolved in water, because these solutions cloud when submitted to temperature variations, according to their affinities and interactions with the water molecules (Mansur et al, 2007;Silva et al, 2009).…”