Tuning the mesopore size of titania thin films using a polymeric swelling Agent

Qing Liu Wu, Stephen E. Rankin

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


A method is reported to generate mesoporous titania thin films with large pores and large surface areas by adding poly(propylene glycol), PPG, to the coating sol of films prepared by templating with Pluronic surfactant P123. Because P123 has an average structure (PEO)20(PPO) 70(PEO)20 where PEO is a poly(ethylene oxide) unit and PPO is a poly(propylene oxide) unit, the hypothesis underlying this work is that PPG segregates to the PPO domains to induce swelling of the template micelles. With the introduction of PPG, the final calcined films are observed to have well-defined mesoporous structures, although the degree of long-range order diminishes with added PPG. The mesopore size of the films increases with increasing amounts of PPG, but PPG also introduces smaller mesopores into the films under our synthesis conditions to generate a bimodal pore size distribution. The size of these smaller pores remains nearly constant at ∼2.4 nm over a large range of PPG:P123 mass ratios, even as the larger mesopore size continues to increase. To understand the effect of PPG on mesostructured titania, the behavior in aqueous solution of the PPG polymer used for swelling is investigated and modeled with Flory-Huggins theory to estimate the full two-phase envelope. The phase diagram reveals that PPG (Mn ≈ 3500) and water have a lower consolute temperature of about -9 °C, so at the temperature used for aging of the films immediately after coating (4 °C), the composition is well within the two-phase region. Therefore, repulsion between PPG molecules and polar species is expected to drive PPG into the hydrophobic cores of P123 micelles, thus leading to final products with large pore size. However, because of partitioning of some PPG into the polar phase, a bimodal pore size distribution and decreasing long-range pore order are observed as the amount of PPG increases.

Original languageEnglish
Pages (from-to)11925-11933
Number of pages9
JournalJournal of Physical Chemistry C
Issue number24
StatePublished - Jun 23 2011

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • General Energy
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films


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