Issue 35, 2018

Structure, rheology, and microrheology of wormlike micelles made of PB–PEO diblock copolymers

Abstract

A diblock copolymer made of poly(1,4-butadiene)-block-polyethylene oxide, with a degree of polymerization of the polybutadiene and polyethylene oxide blocks of 37 and 57, respectively, self-assembles in water as worm-like micelles determined by small angle neutron scattering with an average diameter of ∼12.7 nm, a core radius of ∼2.7 nm, a shell radius of ∼3 nm, and an estimated persistence length of >225 nm. Worm-like micelles of almost the same diblock copolymer, but with a smaller polyethylene oxide block (degree of polymerization 45) were also measured. The worm-like micelles were also observed with negative staining using low energy electron microscopy. The boundary between dilute and semidilute regimes was estimated to be ∼0.8 wt%. The viscoelastic spectra at low and intermediate frequencies do not follow the Maxwell model. These micelles do not present the same rheological behavior of worm-like micelle solutions of conventional surfactants. The slow dynamics of the self-assembly explains this uncommon behavior for the system. Any micellar rearrangement is impeded due to the extremely high hydrophobicity of the polybutadiene block; stress mainly relaxes by the reptation mechanism. Using diffusive wave spectroscopy, we measured the mean square displacement of particles in the micellar solution. From the mean square displacement, we obtained G′(ω) and G′′(ω) at high frequencies. |G*| exhibits a power law behavior showing the stress relaxation changes as frequency increases, first dominated by the Rouse–Zimm modes and then by the bending modes of the Kuhn segments. This allowed us to estimate the worm-like micelle persistence lengths that depend on the copolymer concentration.

Graphical abstract: Structure, rheology, and microrheology of wormlike micelles made of PB–PEO diblock copolymers

Supplementary files

Article information

Article type
Paper
Submitted
26 Jul 2018
Accepted
09 Aug 2018
First published
13 Aug 2018

Soft Matter, 2018,14, 7264-7276

Structure, rheology, and microrheology of wormlike micelles made of PB–PEO diblock copolymers

A. Tavera-Vázquez, B. Arenas-Gómez, C. Garza, Y. Liu and R. Castillo, Soft Matter, 2018, 14, 7264 DOI: 10.1039/C8SM01530A

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