Structural Transition of Non-ionic Poly(acrylamide) Gel

Abstract

We discuss the structure of the opaque poly(acrylamide) gel that is synthesized at higher mole fractions of the cross-linking agent above 0.2. The structure of the opaque gel is analyzed by the small angle neutron scattering technique. The fractal analysis of the scattering function yields that the polymer network of the opaque poly(acrylamide) gel can be seen as a mass fractal of the fractal dimension of about D_M ∼ 2.7 when the mole fraction of the cross-linker is higher than 0.3. On the other hand, much larger exponents are obtained in the lower concentration region of the cross-linker less than 0.3. It suggests that the polymer network of the gel behaves as a surface fractal of the fractal dimension of D_S ∼ 2.5. The structure of the polymer network changes from the surface fractal to the mass fractal at the mole fraction of the cross-linker is 0.3 when the mole fraction of the cross-linker is increased from 0.2 to 0.5. The structure of the gel is also observed by using the confocal laser scanning microscope. The fractal analysis of the confocal images indicate that the fractal dimension of the two dimensional distribution of the colloidal particles in the cross section of the colloidal aggregate is found to be about 1.7.