What causes the anomalous aggregation in pluronic aqueous solutions?

Pluronic (PL) block copolymers have been widely used as delivery carriers, molecular templates for porous media, and process additives for affecting rheological behavior. Unlike most surfactant systems, where unimer transforms into micelle with increased surfactant concentration, anomalous large PL...

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Bibliographic Details
Published in:Soft matter 2018, Vol.14 (37), p.7653-7663
Main Authors: Shih, Kuo-Chih, Shen, Zhiqiang, Li, Ying, Kröger, Martin, Chang, Shing-Yun, Liu, Yun, Nieh, Mu-Ping, Lai, Hsi-Mei
Format: Article
Language:English
Subjects:
Acetic acid
Additives
Aggregates
Block copolymers
Citric acid
Hydrophobicity
Light scattering
Micelles
Molecular dynamics
Neutron scattering
Photon correlation spectroscopy
Porous media
Rheological properties
Salting
Sodium hydroxide
Surfactants
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Summary:Pluronic (PL) block copolymers have been widely used as delivery carriers, molecular templates for porous media, and process additives for affecting rheological behavior. Unlike most surfactant systems, where unimer transforms into micelle with increased surfactant concentration, anomalous large PL aggregates below the critical micelle concentration (CMC) were found throughout four types of PL (F108, F127, F88 and P84). We characterized their structures using dynamic light scattering and small-angle X-ray/neutron scattering. Molecular dynamics simulations suggest that the PPO segments, though weakly hydrophobic interaction (insufficient to form micelles), promote the formation of large aggregates. Addition of acid or base (e.g. citric acid, acetic acid, HCl and NaOH) in F108 solution significantly suppresses the aggregate formation for up to 20 days due to the repulsion force from the attached H3O+ molecules on the EO segment in both PEO and PL and the reduction of CMC through the salting out effect, respectively.
ISSN:1744-683X
1744-6848
DOI:10.1039/c8sm01096j