Thermal diffusion of dextran in aqueous solutions in the absence and the presence of urea.

2006

The Ludwig-Soret effect was studied for aqueous solutions of dextran in the temperature range 15T55 degrees C taking into account the effect of the addition of urea. In the absence of urea, the Soret coefficient S(T) changes sign; it is positive for T45.0 degrees C but negative for T45.0 degrees C. The positive sign of S(T) means that the dextran molecules migrate toward the cold side of the fluid; this behavior is typical for polymer solutions, whereas a negative sign indicates the macromolecules move toward the hot side. The addition of urea to the aqueous solution of dextran rises S(T) and reduces the inversion temperature. For 2 M urea the change in the sign of S(T) is observed at T = 2…