A modified underwater captive bubble technique was used to determine the air-water contact angle of water on a series of polymer biomaterials, including polydimethylsiloxane blends. These consisted of unfunctionalized polydimethylsiloxane (PDMS) blended with small percentages of either ethylene oxide (EO)-or phosphorylcholine (PC) ester-terminated polydimethylsiloxanes to increase surface hydrophilicity. The latter was formed by the hydrosilation of a dimethylsilane-terminated polydimethylsiloxane with omega-vinylphosphorylcholine ester. The ester was synthesized from 9-hydroxy-1-decene and 2-chlorotrimethylamine incorporating the phosphoryl functionality. The blends were cast from a dilute solution of chloroform onto low-density polyethylene (LDPE). A comparison of methods to implement the underwater captive bubble (UWCB) technique, the curved UWCB technique or the modified UWCB technique, a convenient method for determining theta(AW) on curved surfaces, demonstrated that both methods were accurate and precise. As the percentage of functionalized polydimethylsiloxane in a family of blends increased, theta(AW) decreased. The theta(AW) value on the EO-siloxane blends was nonetheless typically 30 degrees less than that on the PC-siloxane blends. The values of theta(AW) on blends determined with the modified UWCB technique demonstrated that too little functionalized polydimethylsiloxane was present to produce a hydrophilic surface promising hemocompatibility.