PEO Penetration into Water-Plasticized Poly(vinylphenol) Thin Films

Neutron reflectivity was used to characterize the adsorption of poly(ethylene oxide) (PEO), 150 kDa, on both polystyrene (PS) and poly(vinylphenol) (PVPh), thin films in water. The PVPh films had thicknesses of 434 and 438 Å and contained 9% v/v water in contrast to the 492 Å PS film which contained no water. PEO did not adsorb on the PS film, while the specific adsorption of PEO on the PVPh film was 1.2 mg/m2 at pH = 6.6. Reflectivity profiles from both deuterated and hydrogenated PEO in D2O provided a comprehensive picture of PEO on/in the PVPh film. The PEO distribution was modeled by two uniform layers. The external layer was a 30 Å thick corona of PEO (12.5%v/v) in water. Between the corona and bulk PVPh film was a 25 Å interpenetration layer consisting of 22% PEO, 76% PVPh, and 2% water. Since the interpenetration layer accounted for 45% of the bound PEO, it is proposed that about half of each adsorbed PEO molecule enters the PVPh film. Thus, the PEO interaction with a PVPh hydrogel can be considered as an example of a polymer/polymer complex formation leading to nanoscale PEO/PVPh blend coated with a water-swollen PEO corona.