3 research outputs found
Micellar solubilization of poorly water-soluble drugs: effect of surfactant and solubilizate molecular structure
<p><b>Objective:</b> This study aims to clarify the role of surfactant and drug molecular structures on drug solubility in micellar surfactant solutions.</p> <p><b>Significance:</b> (1) Rationale for surfactant selection is provided; (2) the large data set can be used for validation of the drug solubility parameters used in oral absorption models.</p> <p><b>Methods:</b> Equilibrium solubility of two hydrophobic drugs and one model hydrophobic steroid in micellar solutions of 19 surfactants was measured by HPLC. The drug solubilization locus in the micelles was assessed by UV spectrometry.</p> <p><b>Results:</b> Danazol is solubilized much more efficiently than fenofibrate by ionic surfactants due to ion–dipole interactions between the charged surfactant head groups and the polar steroid backbone. Drug solubilization increases linearly with the increase of hydrophobic chain length for all studied surfactant types. Addition of 1–3 ethylene oxide (EO) units in the head group of dodecyl sulfate surfactants reduces significantly the solubilization of both studied drugs and decreases linearly the solubilization locus polarity of fenofibrate. The locus of fenofibrate solubilization is in the hydrophobic core of nonionic surfactant micelles and in the palisade layer of ionic surfactant micelles.</p> <p><b>Conclusions:</b> Highest drug solubility can be obtained by using surfactants molecules with long chain length coupled with hydrophilic head group that provides additional drug–surfactant interactions (i.e. ion–dipole) in the micelles.</p
Efficient Control of the Rheological and Surface Properties of Surfactant Solutions Containing C8–C18 Fatty Acids as Cosurfactants
Systematic experimental
study is performed about the effects of
chain length (varied between C8 and C18) and concentration of fatty
acids (FAc), used as cosurfactants to the mixture of the anionic surfactant
SLES and the zwitterionic surfactant CAPB. The following properties
are studied: bulk viscosity of the concentrated solutions (10 wt %
surfactants), dynamic and equilibrium surface tensions, surface modulus,
and foam rheological properties for the diluted foaming solutions
(0.5 wt % surfactants). The obtained results show that C8–C10
FAc induce formation of wormlike micelles in the concentrated surfactant
solutions, which leads to transformation of these solutions into viscoelastic
fluids with very high apparent viscosity. The same FAc shorten the
characteristic adsorption time of the diluted solutions by more than
10 times. In contrast, C14–C18 FAc have small effect on the
viscosity of the concentrated solutions but increase the surface modulus
above 350 mN/m, which leads to higher friction inside sheared foams
and to much smaller bubbles in the formed foams. The intermediate
chain C12 FAc combines some of the properties seen with C10 FAc and
other properties seen with C14 FAc. These results clearly demonstrate
how appropriate cosurfactants can be used for efficient control of
the rheological properties of concentrated surfactant solutions and
of some important foam attributes, such as bubble size and foam rheology
Effect of Cationic Polymers on Foam Rheological Properties
We study the effect of two cationic polymers, with trade
names
Jaguar C13s and Merquat 100, on the rheological properties of foams
stabilized with a mixture of anionic and zwitterionic surfactants
(sodium
lauryloxyethylene sulfate and cocoamidopropyl betaine). A series of
five cosurfactants are used to compare the effect of these polymers
on foaming systems with high and low surface dilatational moduli.
The experiments revealed that the addition of Jaguar to the foaming
solutions leads to (1) a significant increase of the foam yield stress
for all systems studied, (2) the presence of consecutive maximum and
minimum in the stress vs shear rate rheological curve for foams stabilized
by cosurfactants with a high surface modulus (these systems cannot
be described by the Herschel–Bulkley model anymore), and (3)
the presence of significant foam–wall yield stress for all
foaming solutions. These effects are explained with the formation
of polymer bridges between the neighboring bubbles in slowly sheared
foams (for inside foam friction) and between the bubbles and the confining
solid wall (for foam-wall friction). Upon addition of 150 mM NaCl,
the effect of Jaguar disappears. The addition of Merquat does not
noticeably affect any of the foam rheological properties studied.
Optical observations of foam films, formed from all these systems,
show a very good correlation between the polymer bridging of the foam
film surfaces and the strong polymer effect on the foam rheological
properties. The obtained results demonstrate that the bubble–bubble
attraction can be used for efficient control of the foam yield stress
and foam–wall yield stress, without significantly affecting
the viscous friction in sheared foams