Thermo- and pH-Responsiveness of Emulsions Stabilized with Acidic Thermosentive Polymers

Abstract

A temperature- and pH-responsive polymeric surfactant was prepared by copolymerizing N-isopropylacrylamide, methacrylic acid, and octadecylacrylate. Poly(N-isopropylacrylamide-co-methacrylic acid-co-octadecylacrylate) (P(NIPAM-MAA-ODA) was used as an emulsifier for the preparation of water-in-oil emulsions. The mean droplet size at room temperature was almost constant for 50 hours at pH 5.0, 7.0, and 9.0. However, the size markedly increased for 50 hours at pH 3.0, possibly because of the low hydrophilicity of the copolymer and the small interfacial area one molecule of the copolymer can stabilize at a low pH value. The droplet size markedly decreased from 4.7 to 1.8 µm, when the pH of medium increased from 5.0 to 9.0 with the temperature kept constant. This may be ascribed to that the hydrophilicity of the copolymer and the interfacial area one molecule of copolymer can stabilize will be higher at a higher pH value. When the temperature increased over 35°C with the pH kept constant, the droplet size significantly increased probably because the NIPAM segment of the copolymer becomes hydrophobic with increasing the temperature so the copolymer would poorly act as an emulsifier.

Keywords:

• Emulsion
• methacrylic acid
• N-isopropylacrylamide
• polymeric surfactant
• stability

Acknowledgments

This work was performed with the support of the Cooperative Research Program for Agriculture Science & Technology Development (PJ007479201005), Rural Development Administration, Republic of Korea and an external Collaborative Research Grant NSR-8978 (G.P.C.D.)

Notes

S. R. Seo and H. Y. Lee contributed equally to this work.