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Sato T, Akahane T, Amano K, et al. Scattering and Spectroscopic Study on the Hydration and Phase Behavior of Aqueous Alcohol Ethoxylate and Methyl Ester Ethoxylate: Effects of Terminal Groups in Hydrophilic Chains. J Phys Chem B. 2016;120(24):5444-54doi: 10.1021/acs.jpcb.6b04275.
Sato, T., Akahane, T., Amano, K., Hyodo, R., Yanase, K., & Ogura, T. (2016). Scattering and Spectroscopic Study on the Hydration and Phase Behavior of Aqueous Alcohol Ethoxylate and Methyl Ester Ethoxylate: Effects of Terminal Groups in Hydrophilic Chains. The journal of physical chemistry. B, 120(24), 5444-54. https://doi.org/10.1021/acs.jpcb.6b04275
Sato, Takaaki, et al. "Scattering and Spectroscopic Study on the Hydration and Phase Behavior of Aqueous Alcohol Ethoxylate and Methyl Ester Ethoxylate: Effects of Terminal Groups in Hydrophilic Chains." The journal of physical chemistry. B vol. 120,24 (2016): 5444-54. doi: https://doi.org/10.1021/acs.jpcb.6b04275
Sato T, Akahane T, Amano K, Hyodo R, Yanase K, Ogura T. Scattering and Spectroscopic Study on the Hydration and Phase Behavior of Aqueous Alcohol Ethoxylate and Methyl Ester Ethoxylate: Effects of Terminal Groups in Hydrophilic Chains. J Phys Chem B. 2016 Jun 23;120(24):5444-54. doi: 10.1021/acs.jpcb.6b04275. Epub 2016 Jun 14. PMID: 27237225.
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J Phys Chem B. 2016 Jun 23;120(24):5444-54. doi: 10.1021/acs.jpcb.6b04275. Epub 2016 Jun 14.

Scattering and Spectroscopic Study on the Hydration and Phase Behavior of Aqueous Alcohol Ethoxylate and Methyl Ester Ethoxylate: Effects of Terminal Groups in Hydrophilic Chains.

The journal of physical chemistry. B

Takaaki Sato, Takesi Akahane, Kenshi Amano, Ryo Hyodo, Keiichi Yanase, Taku Ogura

Affiliations

  1. Department of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University , Ueda, Nagano 386-8567, Japan.
  2. Functional Materials Science Research Laboratories, R&D, Lion Corporation , Tokyo 132-0035, Japan.

PMID: 27237225 DOI: 10.1021/acs.jpcb.6b04275

Abstract

Using dielectric relaxation spectroscopy (DRS), small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), and viscometry, we have investigated the hydration behavior, static structures, Brownian dynamics, and mechanical properties of aqueous solutions of alcohol ethoxylate (C12E15) and methyl ester ethoxylate (C12MEE), hereafter abbreviated as AE and MEE, respectively, in which we especially focus on the effects of the endcaps of these nonionic surfactants. We find that AE and MEE exhibit fairly different phase behaviors in water: AE produces liquid crystalline phases at w (surfactant weight fraction) > 0.35, whereas MEE retains a liquid phase in an extremely wide concentration range (w < 0.7) at ambient temperature. The structure factor deduced from SAXS intensities using a generalized indirect Fourier transformation technique and the effective hydration number evaluated from the negative excess bulk water relaxation amplitude revealed by DRS unambiguously demonstrate that hydration water molecules, exhibiting about 4-times-slower collective reorientational dynamics than that of bulk water, contribute to the excluded volume of the micelles. The blocked terminal hydrogen-bond donor/acceptor site of MEE leads to smaller hydration number of MEE than compared to that of AE, and consequently the lower excluded volume of the MEE micelles. The effective micellar volume fraction, ϕ(eff), should be defined by incorporating such different hydration effects. Importantly, voluminosity, defined as the micellar volume fraction per unit mass, is clearly a decreasing function of w, demonstrating progressive dehydration at a higher w. The collective diffusion constants determined by DLS for the AE and MEE micelles show a monotonous increase up to ϕ(eff) ≈ 0.5, as expected for the hard spheres. Low-shear-rate viscosities follow a Krieger-Dougherty model in the identical micellar packing fraction range. All static, dynamic, and mechanical properties of these micellar solutions can be explained in a consistent and quantitative manner only when the excluded volume of hydration water molecules is properly taken into account.

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