Solvation in hydrofluoroalkanes: how can ethanol help?

Authors

  • Denise S. Conti,

    1. Department of Chemical Engineering and Materials Science, College of Engineering, Wayne State University, Detroit, MI, USA
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  • Jordan Grashik,

    1. Department of Chemical Engineering and Materials Science, College of Engineering, Wayne State University, Detroit, MI, USA
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  • Lin Yang,

    1. Department of Chemical Engineering and Materials Science, College of Engineering, Wayne State University, Detroit, MI, USA
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  • Libo Wu,

    1. Department of Chemical Engineering and Materials Science, College of Engineering, Wayne State University, Detroit, MI, USA
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    • Present address: MAP Pharmaceuticals, Mountain View, CA 94043, USA.

  • Sandro R. P. da Rocha

    Corresponding author
    1. Department of Chemical Engineering and Materials Science, College of Engineering, Wayne State University, Detroit, MI, USA
      Sandro R. P. da Rocha, Wayne State University, College of Engineering, Department of Chemical Engineering and Materials Science. 5050 Anthony Wayne Drive, Office 1133ENG, Detroit, MI, 48202, USA. E-mail: sdr@eng.wayne.edu
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Sandro R. P. da Rocha, Wayne State University, College of Engineering, Department of Chemical Engineering and Materials Science. 5050 Anthony Wayne Drive, Office 1133ENG, Detroit, MI, 48202, USA. E-mail: sdr@eng.wayne.edu

Abstract

Objectives  The goal of this work was to evaluate the ability of ethanol mixed with hydrofluoroalkanes (HFAs) to improve solvation of moieties of relevance to pressurized metered-dose inhalers (pMDIs).

Methods  Chemical force microscopy was used to measure the adhesion force (Fad) between alkyl-based, ether-based and ester-based moieties (C8/C8, COC/COC and COOC/COOC interactions) in 2H,3H-perfluoropentane (HPFP)/ethanol mixtures. HPFP is a liquid that mimics propellant HFAs. The Fad results are thus a measure of solvation in HFAs. Johnson–Kendall–Roberts (JKR) theory was used to model the results.

Key findings  The Fad normalized by the tip radius of curvature (Fad/R) decreased upon the addition of ethanol, suggesting its ability to enhance the solvent environment. At 15% (v/v) ethanol, the Fad/R was reduced 34% for the alkyl, 63% for the ether, and down 67% for the ester tails. Thus, the solvation could be ranked as: ester > ether > alkyl. JKR theory was a reasonable model for the Fad/R.

Conclusions  Ethanol, within the concentration range of interest in commercial pMDIs, provided limited enhancement in solvation of alkyl moieties. On the other hand, the cosolvent significantly enhanced solvation of ether-based and ester-based moieties, thus suggesting its potential for formulations containing amphiphiles with such groups.

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