Eur. Phys. J. E (2014) 37: 128
https://doi.org/10.1140/epje/i2014-14128-8

Regular Article

Interactions between microemulsion droplets decorated with hydrophobically modified polymers: A small-angle neutron scattering study

¹ Laboratoire de Physique théorique et appliquée (LPTA), Université Sidi Mohamed Ben Abdellah, Faculté des Sciences Dhar El Mahraz, BP 1796 Fes, Atlas, Maroc
² Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Université Montpellier 2, F-34095, Montpellier, France
³ Laboratoire Léon Brillouin, UMR 12 CEA/CNRS, F-91191, Gif-sur-Yvette, France

^* e-mail: Julian.Oberdisse@univ-montp2.fr

Received: 18 July 2014
Revised: 26 November 2014
Accepted: 1 December 2014
Published online: 29 December 2014

Abstract

The shape and interactions between microemulsion droplets (R = 8.2 nm, polydispersity 20%) either decorated with PEO modified with a single hydrophobic end function (PEO-m: C₁₂H₂₅ - (EO)_n , M _PEO = 5.2 kg/mol), or with telechelic polymers of twice the mass (PEO-2m: C₁₂H₂₅ - (EO)_2n - C₁₂H₂₅, M _PEO = 10.4 kg/mol) have been studied by small-angle neutron scattering (SANS). The results as a function of droplet and polymer concentration have been compared to the reference case of the bare microemulsion which was shown to be unchanged using Porod representations. The interactions between bare and decorated droplets have been analyzed using the structure factor S(q), at first in a model-free way based on its low-q limit S(q → 0). This analysis provides clear evidence on the concentration-dependent repulsive or attractive nature of the contributions to the pair droplet-droplet pair potential of the polymers. Model pair potentials describing the steric repulsions and attractions by copolymer bridging are used to describe the low-q behavior of the structure factor based on an integral equation approach, giving an estimate of the range and amplitude of the potentials. Moreover, they provide an explanation for the observed transient clustering in terms of a shallow minimum of the total potential, as they establish the respective repulsive and attractive contributions of the polymer molecules.