Gholap Shubhangi G, Badiger Manohar V, Gopinath Chinnakonda S
Polymer Science and Engineering Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India.
J Phys Chem B. 2005 Jul 28;109(29):13941-7. doi: 10.1021/jp050806r.
Irreversible adsorption of poly(vinyl alcohol) (PVA) on hydrophobic, porous poly(vinylidene fluoride) (PVDF) membranes was carried out using aqueous PVA solution. Water permeation was observed in PVDF microporous membranes after PVA adsorption, and maximum permeability was obtained after treatment with 4% PVA solution. Water permeability increased linearly with increasing PVA concentration up to 4%, and then a marginal decrease with a further increase in PVA concentration occurred. PVA adsorbed PVDF membranes were subjected to intense physicochemical analysis, especially with XPS. XPS results display the presence of an interface between PVA and PVDF, and the binding energy (BE) of the interface is low for the PVDF membranes treated with 4% PVA. Carbon from CF2-groups and F 1s core level clearly showed a decrease in its content on the surface after PVA adsorption and showed a minimum fluorine content at 4% PVA. F 1s BE shifts by 0.5 eV upon PVA adsorption and is independent of PVA concentration. EDAX analysis indicates that the bulk oxygen content remains within 4.5 +/- 0.6% and is independent of the PVA concentration. Nonetheless, a large amount of surface atom percentage of oxygen (20 +/- 4%) from O 1s core level shows an increase in PVA content on the surface of PVDF, and it is restricted mostly to the surface. The 4% PVA treated PVDF membrane clearly shows a broadening of O 1s core level to lower BE and indicates the interaction between PVDF and PVA which is significantly different compared to any other compositions. A new valence band feature at low BE, which is nonexistent on PVDF, develops after PVA adsorption. This indicates that the shift in the nature of the highest occupied molecular orbital (HOMO) derived mostly from oxygen; simultaneously, a suppression in the PVDF derived band indicates the change in nature of the PVA adsorbed surfaces from hydrophobic to hydrophilic. The above observations also suggest an irreversible electronic interaction between PVA and PVDF, possibly through charge transfer.
使用聚乙烯醇（PVA）水溶液，在疏水性多孔聚偏二氟乙烯（PVDF）膜上进行了PVA的不可逆吸附。PVA吸附后，在PVDF微孔膜中观察到了水渗透现象，用4%的PVA溶液处理后可获得最大渗透率。水渗透率随PVA浓度增加至4%呈线性增加，之后随着PVA浓度进一步增加出现了轻微下降。对吸附了PVA的PVDF膜进行了深入的物理化学分析，尤其是采用X射线光电子能谱（XPS）分析。XPS结果显示PVA和PVDF之间存在界面，对于用4% PVA处理的PVDF膜，该界面的结合能（BE）较低。CF2基团中的碳和F 1s核心能级在PVA吸附后表面含量明显降低，在4% PVA时氟含量最低。PVA吸附后F 1s BE位移0.5 eV，且与PVA浓度无关。能量散射X射线分析（EDAX）表明，整体氧含量保持在4.5±0.6%，且与PVA浓度无关。尽管如此，来自O 1s核心能级的大量表面氧原子百分比（20±4%）表明PVDF表面的PVA含量增加，且主要局限于表面。经4% PVA处理的PVDF膜O 1s核心能级明显向较低BE展宽，表明PVDF与PVA之间的相互作用与其他任何组成相比有显著差异。PVA吸附后出现了一个在PVDF上不存在的低BE新价带特征。这表明最高占据分子轨道（HOMO）性质的变化主要源于氧；同时，PVDF衍生能带的抑制表明吸附了PVA的表面性质从疏水性变为亲水性。上述观察结果还表明PVA和PVDF之间可能通过电荷转移存在不可逆的电子相互作用。
