Aqueous dye diffusion in thin films of water-soluble poly(vinyl pyrrolidone) copolymers: A dynamic secondary ion mass spectrometry study

作者：Pinto JR^*; Novak SW; Nicholas M

来源：Journal of Physical Chemistry B Materials, 1999, 103(37): 8026-8032.

DOI：10.1021/jp9911292

We examine the effect of solute binding on aqueous dye diffusion in model poly(vinylpyrrolidone) (PVP) copolymer films. The dye-binding property associated with PVP derives from the unique combination of hydrophilicity, polarity, and hydrophobicity contributed by the lactam ring, thereby enabling the complexation of polarizable, anionic organic dyes. On the basis of dynamic secondary ion mass spectrometry (SIMS), we rationalize the depth profile of the aqueous dye solute in both charged and uncharged copolymer systems. Utilizing the essentially invariant carbon signal of the polymer to normalize the sulfur signal that uniquely identifies the dye molecule, we compare the depth profiles for each of the individual copolymer films in terms of relative dye concentrations. The opposing and intricately related processes of solute dye-binding and aqueous solvent imbibition preclude the retention of anionic dye molecules at the surface of any system characterized by a measurable amount of firm free volume, by the dilution of VP moieties, or by the presence of positively charged pendant groups. Therefore, the number of dye molecules diffusing into the bulk for each particular PVP copolymer is not constant. The intrinsic thermodynamic capacity of the more hydrophilic copolymers to imbibe water molecules is manifested by the beneficial effect of water plasticization on diffusion, reflecting the relationship between dye mobility and free volume. Because of the significant difference in mobility distinguishing dye molecules from water molecules, the transport process is also influenced by subtle variations in polymer microstructure and morphology.

• 出版日期1999-9-16