Document Type

Article

Publication Date

2008

Journal or Book Title

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics

Volume

78

Issue

2

First Page

021802-1

Last Page

021802-9

DOI

10.1103/PhysRevE.78.021802

Abstract

We investigated the structural features of micelles formed by the self-association of the pentablock copolymer poly [N,N -(diethyl amino)ethyl methacrylate]-block-poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethyleneoxide)-block-poly [N,N -(diethylamino)ethyl methacrylate] (PDEAEM-PEO-PPO-PEO-PDEAEM) in aqueous solutions by using small-angle neutron scattering SANS. The pentablock copolymer solutions exhibit micellar and gel phases in response to changes in both the temperature and pH by virtue of (1) the lower critical solution temperature of the PPO blocks and (2) the polyelectrolyte character of the pendant PDEAEM blocks. Two modeling schemes were employed to describe the SANS data of semidilute copolymer solutions at higher temperature as they contain interacting charged micelles at pH<7.5 and interacting neutral micelles at higher pH. We have elucidated the structures of the micelles in terms of size, shape, polydispersity, association number, number density, and surface charge. At low pH the charged spherical micelles are less packed with the copolymers presumably due to the electrostatic repulsion between the charged pendant groups. On the other hand, at higher pH the hydrophobic character of the neutral pendant groups enable them to sequester within the micelle core along with the PPO, thus increasing the number density and the core size of the spherical micelles. At higher copolymer concentration reversible thermoresponsive sol-gel transitions were observed at all pH conditions and the rheological behavior of the gels nicely correlates with different organization of micelles with different shapes.

Comments

This article is from Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 78 (2008): 021802, doi: 10.1103/PhysRevE.78.021802.

Copyright Owner

The American Physical Society

Language

en

File Format

application/pdf

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