pH and Salt Effects on Surface Activity and Self-Assembly of Copolymers Containing a Weak Polybase

Neta Cohen, Department of Chemical Engineering , Ben-Gurion University of the Negev, Beer-Sheva, Israel
Lana Binyamin, Department Of Chemical Engineering , Ben-gurion University Of The Negev, Beer-sheva, Israel
Yael Levi-Kalisman, The Center For Nanoscience And Nanotechnology, The Institute For Life Sciences, The Hebrew University Of Jerusalem, Jerusalem, Israel
Anthony Convertine, Department Of Bioengineering, University Of Washington, Seattle, Usa
Patrick Stayton, Department Of Bioengineering, University Of Washington, Seattle, Usa
Rachel Yerushalmi – Rozen , Department Of Chemical Engineering, The Ilze Katz Institute For Nanoscience And Technology, Ben-gurion University Of The Negev, Beer-sheva, Israel

Assembly of amphiphilic copolymers that contain ionizable or charged residues at the water –air interface and in the bulk solution is driven by various interactions (hydrophobic, electrostatic, acid-base equilibrium, specific ion affects) with energies of the order of k_bT (the thermal energy). Understanding the relations between molecular composition and the salt-and-pH responsiveness as well as the size and shape of copolymers assemblies may assist in a variety of applications such as design of pH-sensitive materials that would assemble into desired structures and enable efficient drug delivery and controlled release of hydrophobic molecules. Here we investigated the  combined effect of pH and salt composition on the surface activity and self-assembly of copolymers contain poly(dimethylaminoethyl methacrylate) pDEAEMA residues in aqueous solutions at pH 7-7.4 and pH 5.5, via surface tension measurements and cryo-TEM. Our findings suggest that both pH and salt composition of the buffer solutions affect the surface activity, the shape and size of the self-assembled aggregates in solutions of copolymers that contain DEAEMA group. Our findings indicate that covalently linked hydrophobic groups moderate the pH responsiveness of the DEAEMA residue as compared to non-ionic and hydrophilic groups. Cryo-TEM imaging of the bulk solutions reveal a variety of aggregates and the co-existence of a variety of assemblies.