PDMS colloids as a new contrast agent for NMR imaging: oscillatory-shear rheology properties

Abstract

The oscillatory-shear rheology properties of the linear polydimethylsiloxane (PDMS) emulsions and the crosslinked PDMS colloidal solutions were investigated. The linear PDMS emulsions have been proposed as a new contrast agent for the gastro-intestinal nuclear magnetic resonance (NMR) imaging [US patent 5,380,514, 1995]. This work suggested the crosslinked PDMS colloidal solutions as an alternative to avoid possible absorption by the intestine. Coordinating the lower viscosity for comfortable oral administration and the desired signal for NMR imaging, we prepared our emulsions and colloidal solutions with volume fractions near ϕ c. When ϕ ≧ ϕ c , both emulsions and colloidal solutions had a yield stress ( τ y), which was linear with ϕ 1/3/2 R. Under compression ( ϕ> ϕ c), their oscillatory-shear responses could be categorized into an elastic and a viscoelastic regions, which were distinguished by the yield stress. For the uncompressed colloids ( ϕ< ϕ c), the apparent variations of the storage and loss moduli exhibited three distinguishable regions.