SAXS investigation of the effect of temperature on the multiscale structure of a macroporous poly(N-isopropylacrylamide) gel
Résumé
The temperature induced structural modifications of poly(N-isopropylacrylamide) hydrogel (pNIPA) were investigated by Small-Angle X-ray Scattering (SAXS) over a broad range of q-values (3.510 2 -12 nm -1) at temperatures ranging between 18 and 37°C. The sample studied was elaborated by cryopolymerization yielding a macroporous gel (cryogel). The pNIPA gel forms the walls (the thickness at 23°C is about 12 µm). The SAXS curves display an isoscattering (or isosbestic) point located at q iso 3.633 nm -1 and disappearing above 30°C. This feature has never been reported up to now. The SAXS curves obtained at each temperature are well fitted by a sum of four equations describing respectively the scattering resulting from the gel surface (power law), from the solid-like (Guinier equation) and liquid-like (Ornstein-Zernike equation) heterogeneities and from the chain-chain correlation yielding a broad peak (pseudo-Voigt equation) in the high-q domain. The temperature dependence of the parameters obtained from the fit is analyzed and discussed.
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