(216v) Effect of Molecular Weight of Polyelectrolyte On the Interaction Between Surfactant and Polyelectrolyte

The interactions between oppositely charged tetradecyltrimethylammonium bromide (C₁₄TAB) and anionic polymers poly(acrylic acid) (PAA) with the molecular weight ranging from 1800 to 450000 g/mol were investigated by using isothermal titration calorimetry (ITC) at 25 ^oC. The ITC was performed by titrating C₁₄TAB aqueous solution into 0.05wt% PAA aqueous solution Thermo-histogram exhibits an exothermic peak due to the formation of PAA/C₁₄TAB complex. The driving force is simply the electrostatic attraction between opposite charged PAA and C₁₄TAB. When the C₁₄TAB concentration reaches the saturated concentration (C_s), PAA is saturated with bound C₁₄TAB molecules. And when the C₁₄TAB concentration further increased up to the second critical micelle concentration (C_m), the C₁₄TAB free micelle started to form. The PAA molecular weights would also affect the result. Based on the titration of C₁₄TAB into PAA with six different molecular weights ranging from 1800 to 450000, it was found that when the PAA molecular weight larger than 25000 g/mol, they show the tendency as the above-mentioned, but there is a different mechanism in low molecular weights PAA/C₁₄TAB system (1800 and 5000 g/mol), C₁₄TAB started to form free micelles before the saturated concentration. The interaction of C₁₄TAB and PAA is independent of PAA molecular weight when the PAA molecular weight is larger than 250000 g/mol.