Structure, Rheology, and Microrheology of Wormlike Micelles made of PB-PEO Diblock Copolymers
Antonio Tavera-Vazquez, Brisa Arenas-Gomez, Cristina Garza, Yun Liu, Rolando Castillo
A diblock copolymer made of poly(but-2-ene-1,4-diyl)-block-poly(oxyethylene), with a degree of polymerization of the polybutadiene and polyethylene blocks of 37 and 57, respectively, self-assembles in water as worm-like micelles determined with small angle neutron average diameter of 12.7 nm, a core radius of 2.7 nm, a shell radius of 3nm, and an estimated persistence length of >225 nm. Worm-like micelles of almost the same diblock copolymer, but with a smaller polyethylene 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 self-assembly explains this uncommon behavior for the system. Any micellar rearrangement is impeded due to the extremely high hydrophobiicity 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 beahior showing where 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 obtain the worm-like micelle persistence lenghths that depends on the copolymer concentration.
, Arenas-Gomez, B.
, Garza, C.
, Liu, Y.
and Castillo, R.
Structure, Rheology, and Microrheology of Wormlike Micelles made of PB-PEO Diblock Copolymers, Soft Matter, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=925883
(Accessed December 4, 2023)