Effect of pH on the Micellar Morphology of Semicrystalline PCL-b-PEO Block Copolymers in Aqueous Solution

• Published in: Macromolecular chemistry and physics 2012-05, Vol.213 (9), p.952-964
• Main Authors: He, Wei-Na, Xu, Jun-Ting, Du, Bin-Yang, Fan, Zhi-Qiang, Sun, Fang-Li
• Format: Article
• Language: English
• Subjects: Applied sciences; block copolymers; crystallization; Exact sciences and technology; micelles; morphology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Solution and gel properties
• ISSN: 1022-1352; 1521-3935
• DOI: 10.1002/macp.201100615

The effect of pH on the micellar morphology of a semicrystalline poly(ϵ‐caprolactone)‐block‐poly(ethylene oxide) block copolymer (PCL66‐b‐PEO44) in aqueous solution is investigated. Spherical micelles are formed in neutral and acidic solutions. However, addition of alkali to the neutral micellar solution triggers a sphere‐to‐cylinder transformation of the micellar morphology. The micelles are stable in both neutral and acidic solutions, but the size of the micelles becomes gradually larger in the alkali solution. This phenomenon is interpreted in terms of the effect of pH value on the reduced tethering density of the corona in the semicrystalline micelles. When alkali is introduced into an aqueous solution of PCL‐b‐PEO, a sphere‐to‐cylinder transformation of the micellar morphology is observed, while the micellar morphology remains unchanged in the acidic solution. This is attributed to the decrease of the reduced tethering density by the destruction of hydrogen bonds in the alkali solution.