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Surfactant solubility and aggregate orientation in hydrofluoroalkanes
Kristin B Ridder1, Craig J Davies-Cutting, Ian W Kellaway
1Department of Pharmaceutics, The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1 AX, UK.
International Journal of Pharmaceutics
|April 26, 2005
Summary
Researchers identified surfactants soluble in hydrofluoroalkane (HFA) propellants and assessed 2H,3H-decafluoropentane (DFP) as a model. Surfactant aggregation and orientation in HFAs were also investigated.
Area of Science:
- Pharmaceutical Sciences
- Materials Science
Background:
- Hydrofluoroalkanes (HFAs) are used as propellants in metered-dose inhalers.
- Understanding surfactant behavior in HFAs is crucial for formulation development.
Purpose of the Study:
- Identify surfactants soluble in HFA-134a and HFA-227ea.
- Evaluate 2H,3H-decafluoropentane (DFP) as a liquid model propellant for HFAs.
- Investigate surfactant aggregation and orientation within HFAs.
Main Methods:
- Solubility was assessed by adding HFA to known surfactant amounts until dissolution.
- Surfactant aggregation in DFP was determined using an iodine solubilization method.
- Fluorescence spectroscopy with a lipophilic probe (1,3-dipyrenylpropane) examined surfactant aggregate orientation and microenvironment viscosity in HFAs.
Main Results:
- Polyoxyethylene-ethers and POE-PPO-block copolymers showed solubility in HFAs.
- DFP solubility correlated with HFA-134a but not HFA-227ea.
- Brij 30 micellized in DFP (type II), while L-44 showed continuous aggregation (type I).
- Fluorescence studies confirmed probe incorporation into HFA surfactant aggregates.
Conclusions:
- DFP is a suitable model for HFA-134a, but not HFA-227ea.
- Surfactants in HFAs exhibit an L1-aggregate orientation, differing from the L2 orientation in chlorofluorocarbon propellants.