| The adsorption behavior of hydrophobically modified polyelectrolytes has been investigated by ellipsometry measurements. Model polyelectrolytes were quenched polyelectrolytes, poly (tert butyl styrene)-sodium-poly (styrene sulfonate) (PtBS-NaPSS), and annealed polyelectrolytes, poly styrene-poly (acrylic acid) (PS-PAA). All polymeric materials were synthesized by anionic polymerization with narrow polydispersities. To ensure the water solubility, all polymers have short hydrophobic blocks ({dollar}<{dollar}10%) and long hydrophilic blocks. The effects of the ionic strength, counterion valence, polyelectrolyte concentration, polyelectrolyte structure, substrate wettability, and the pH value (charge density) on the adsorption behavior of polyelectrolytes with hydrophobic modification have been probed. Silica and octadecyltriethoxysilane (OTE) modified silicon wafers were chosen to represent hydrophilic and hydrophobic substrates respectively.; On hydrophilic substrates, a critical salt concentration was found for the adsorption of PtBS-NaPSS diblock copolymer below which no adsorption happened and above which the adsorption was readily detectable. The threshold ionic strength was the same for both NaCl and CaCl{dollar}sb2.{dollar} When calcium ions were added to the polyelectrolyte system, higher adsorbed amount was observed which indicated the formation of ion-bridges by the calcium ions. When aluminum ions were added to the polyelectrolyte solution, however, phase separation happened at a certain range of the salt concentration (0.0003M-0.12M).; The scaling relationships predicted by a model proposed by Dan and Tirrell have been shown to fit the adsorption results of quenched polyelectrolytes on hydrophobic substrates the best among available models. The predictions are: the adsorbed density scales with the 4/23{dollar}sp{lcub}rm rd{rcub}{dollar} power of NaCl concentration, the {dollar}-{dollar}6/23{dollar}sp{lcub}rm rd{rcub}{dollar} power of the length of the hydrophilic block and the {dollar}-{dollar}12/23{dollar}sp{lcub}rm rd{rcub}{dollar} power of that of the hydrophobic block. For annealed polyelectrolytes, the adsorbed density on hydrophobic substrates has been found to roughly follow the 2/9{dollar}sp{lcub}rm th{rcub}{dollar} power of the charge density along the chain, predicted by a model proposed by Israels et al.; The self-assembly of the PtBS-NaPSS diblock copolymer has been used to modify the surface of blood contacting biomaterials: polycarbonate and polypropylene used in the manufacture of oxygenators. The modified surface has reduced platelet adhesion, prolonged thrombin time and prolonged whole blood clotting time. Therefore, the adsorption of polyelectrolytes improved the blood compatibility. |
