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An insight into the Structure of Copolymer Surfactants

The structure of inhomogeneous (core-shell) nanoparticles was studied with the SAXSpoint system. The internal structure of Pluronic P123 micelles in water was determined by calculating the radial electron density profile.

Surfactants and SAXS

Pluronic P123 is amphiphilic triblock copolymer. Its nominal formula is PEO20-PPO70-PEO20 (PEO: polyethylene glycol; PPO: polypropylene glycol). In aqueous solution it forms micellar systems of various geometires depending on concentration. P123 is a commonly used structure directing agent in the sysnthesis of mesoporous materials (e. g., SBA-15).

Small-angle X-ray scattering (SAXS) allows to obtain the shape and size of such nano-sized micelles and - due to its sensitivity to electron-density differences - to determine the internal (core-shell) structure.
 This is of great importance for understanding and controlling the role of surfactants in different materials, e.g. the stability of emulsions or the release rate of the active ingredient in drug carrier systems.

Experimental and Results

A solution of Pluronic P123 in water was measured with the SAXSpoint system. The scattering pattern is shown in Fig. 1. The Pair-Distance Distribution Function (PDDF) was calculated using program GIFT1 (see Fig. 2) indicating inhomogeneous spherical particles with a maximum diameter of 19 nm.


Fig.1    2D scattering curve of P123 in water.

Fig.2    Pair-distance distribution function.


Furthermore, the internal structure of the P123 particles was evaluated with program DECON1. The PDDF is converted (“deconvoluted”) into the radial electron density profile showing the core-shell structure of the inhomogeneous micelles and the respective dimensions.

 


1 O. Glatter, J. Phys.: Condens. Matter 18 (2006) 2403

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