Characterization of Multilamellar Vesicles for Cleansing Applications

Nov 1, 2008 | Contact Author | By: Lawrence A. Hough, Denis Bendejacq and Tobias J. Fütterer, Rhodia Inc.
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Title: Characterization of Multilamellar Vesicles for Cleansing Applications
Multilamellar vesiclesx depositionx shear thinningx suspensionx rheologyx
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Keywords: Multilamellar vesicles | deposition | shear thinning | suspension | rheology

Abstract: In the present article, the authors characterize a multilamellar vesicle (MLV) system used in personal care and verify its structure via X-ray scattering, rheology and fluorescence microscopy. This enabled the study of MLV formation to investigate bulk rheology characteristics. The results are presented here as application-relevant properties.

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Surfactant molecules have the ability to self-assemble at concentrations greater than a critic micellar concentration (CMC) into several types of supra molecular aggregates. These aggregates include spheres (micellar phase), cylinders (hexagonal phase) or bilayers (lamellar phases) depending on the amount and types of surfactants that are used. Lamellar phases are not rigid, sheetlike bilayers but rather are elastic and can undulate. Upon shearing, lamellar phases can rearrange into soft colloidal objects of spherical shape consisting of a concentric stack of surfactant bilayers. These objects are called multilamellar vesicles (MLV).

The MLV phase typically exists under shear and thus its structure is considered to be metastable. As a result, orientational phase diagrams frequently are used to describe the structure and phase space. Indeed, MLVs are not in thermodynamic equilibrium. Since they are formed by shear, they inevitably relax into a simple lamellar phase in time. This relaxation can take from hours to several months or years depending on the surfactant system used. Moreover, the stability of MLVs is sensitive to the conditions of process and the purity of the components. Specific mixtures of anionic, amphoteric and nonionic surfactants have proven to be effective for the formation of MLV systems with longtime stability, and numerous rinse-off products based on this technology have been commercialized; for example, sodium-trideceth sulfate and sodium-lauroamphoacetate in combination with lauric acid or alkanolamides have been used.

Considered to be soft solids, MLV systems obey the dynamics of soft glasses. The elasticity and yield stress originates from the close packing of the MLVs. MLV systems are used in body washes and shampoos because they impart the rheology necessary to suspend water-insoluble additives without stringy or tacky extensional properties. Upon dilution, the MLV phase breaks apart, allowing for foaming and efficient deposition.

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Rheology Terminology

Rheology Terminology 

Figure 1. A schematic of the structuring process

Figure 1. A schematic of the structuring process 

Figure 2. X-ray scattering

Figure 2. X-ray scattering 

Figure 3. The X-ray scattering patterns

Figure 3. The X-ray scattering patterns  

Bragg-reflection

Bragg-reflection 

Figure 4. Viscosity curves

Figure 4. Viscosity curves 

Figure 5. The structuring time

Figure 5. The structuring time 

Figure 6. Stress and viscocity

 Figure 6. Stress and viscocity

Hough: Cleansing Applications Footnotes

 a Miracare SLB 365 (INCI: Water (aqua) (and) sodium trideceth sulfate (and) sodium lauroamphoacetate (and) cocamide MEA (and) methylparaben), is a product of Rhodia Inc., Cranbury NJ, USA.

b BODIPY FL C5-ceramide is a specific boron-dipyrromethene dye manufactured by Molecular Probes (InVitrogen).

c Model DMLB  is a fluorescent microscope from Leica Microscopes.

d Ares 4 is a product of TA Instruments New Castle, Delaware USA.

e AR-G2 is a rheometer produced by TA Instruments.

 

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