Dendrimer adsorption on charged particulate surfaces

The adsorption of a negatively charged poly-L-lysine dendrimer SPL-7013 on alumina particle surfaces was investigated as a function of solution ionic strength and pH. The Langmuir model satisfactorily describes experimental adsorption isotherms; the free energies of adsorption Delta G(ads), surface affinity constants, maximum adsorbed amounts, and areas per adsorbed dendrimer molecule were calculated. Delta G(ads) for various solution conditions were in the range of -46 to -59 kJ mol(-1); these are significantly greater in magnitude than for small molecules and reflect the multivalent nature and strong adsorption affinity of dendrimer to oppositely charged surfaces, thus confirming electrostatic attraction as a major driving force. The adsorption affinity and interfacial packing of the dendrimer increase with increased solution salt concentration due to the screening of the electrostatic forces and increased surface charge density of the adsorbent. Similarly, increased adsorption at low pH is ascribed to a greater adsorption site density on alumina. (C) 2008 Curtin University of Technology and John Wiley & Sons, Ltd.