Smart Polymer Nanoparticles Designed for Environmentally Compliant Coatings
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- 作者：Mohsen Soleimani ; Jeffrey C. Haley ; Daniel Majonis ; Gerald Guerin ; Willie Lau ; Mitchell A. Winnik
- 刊名：Journal of the American Chemical Society
- 出版年：2011
- 出版时间：July 27, 2011
- 年：2011
- 卷：133
- 期：29
- 页码：11299-11307
- 全文大小：1044K
- 年卷期：v.133,no.29(July 27, 2011)
- ISSN：1520-5126
文摘
We describe the synthesis, characterization, and film-forming properties of two-component nanoparticles that undergo a reversible morphology transformation in water as a function of pH. The particles consist of a high molecular weight acrylate copolymer and an acid-rich oligomer designed to be miscible with the polymer when its 鈭扖OOH groups are protonated. Attaching a fluorescence resonance energy transfer (FRET) pair to components inside the nanoparticles enabled us to assess morphology at the molecular level. By inspecting changes in the donor fluorescence decay profile at different pH values, we established miscibility of the components in acidic solution but with charge-induced phase separation when the oligomers were neutralized to their carboxylate form. Complementary titration experiments revealed that the nanoparticles adopt a core鈥搒hell structure when the acid groups are deprotonated. We studied the effect of the acid-rich oligomer on the diffusion rate of the high molecular weight polymers following film formation. Our results show that the carboxylated oligomer enhanced the rate of diffusive mixing between high molecular weight molecules by more than 2 orders of magnitude. FRET measurements carried out on partially dried films using a low-resolution microscope showed that the carboxylate oligomer shell can delay coalescence for ca. 30 min after passage of the drying front. This delay is expected to help with increasing the 鈥榦pen time鈥?of latex paints, a desirable property of solvent-based paints that remains difficult to achieve with (environmentally compliant) waterborne paints. Use of ammonia as a volatile base resulted in synergistic effects: initial retardation of coalescence followed by acceleration of diffusive mixing as the ammonium salts dissociated and ammonia evaporated from the film.