Surface modification of porous silicon-based films using dichlorosilanes dissolved in supercritical carbon dioxide

Eduardo Vyhmeister, Héctor Valdés-González, Anthony J. Muscat, David Suleiman, L. Antonio Estévez

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

Dimethyldichlorosilane (DMDCS), diethyldichlorosilane (DEDCS), and dibutyldichlorosilane (DBDCS) were dissolved in supercritical CO2 at two concentration levels to modify hydrolyzed porous surfaces via silylation reactions. Plasma-damaged methylsilsesquioxane samples were loaded in a batch reactor with the chlorosilanes; when introduced, the low-viscosity supercritical CO2 dissolved and transported the chlorosilanes to the porous surface. Samples were characterized using Fourier transform infrared spectroscopy (FTIR), ellipsometry, goniometry, and electrical measurements, and compared against untreated samples. Reactions between the chlorosilanes and substrate hydroxyls were strongly dependent on the length of the alkyl group on the chlorosilane, but independent of concentration. FTIR analyses showed a decreased intensity for infrared (IR)-isolated/geminal OH vibrations (100%, 93.9% ± 5.4%, and 95.4% ± 4.3% for DMDCS, DEDCS, and DBDCS, respectively), but DEDCS and DBDCS resulted in 3.9% ± 5.0% and 20.9% ± 8.7% increases in hydrogen bonding, respectively. DMDCS was more successful, showing a 14.4% ± 9.8% reduction in hydrogen bonding. Goniometry measured hydrophobic contact angles that were consistently greater than 81, irrespective of the chemistry used. Ellipsometry showed a strong dependence between the thickness of the deposited layers and the chlorosilane alkyl group (19.0 nm ± 1.6 nm, 31.3 nm ± 4.8 nm, and 74.2 nm ± 4.7 nm for DMDCS, DEDCS, and DBDCS, respectively). Electrical measurements indicated improved hydroxyl group elimination with shorter alkyl groups (dielectric constant decreased from 3.5 for plasma-ashed methylsilsesquioxane samples to 2.59, 2.97, and 3.4 for DMDCS, DEDCS, and DBDCS, respectively). DMDCS was found to participate in intramolecular and intermolecular reactions while the surface-modifying agents with longer hydrocarbon chains underwent predominantly intermolecular reactions, resulting in the thicker deposited layers.

Original languageEnglish (US)
Pages (from-to)4762-4771
Number of pages10
JournalIndustrial and Engineering Chemistry Research
Volume52
Issue number13
DOIs
StatePublished - Apr 3 2013

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Industrial and Manufacturing Engineering

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