Unusual Morphologies of Poly(vinyl alcohol) Thin Films Adsorbed on Poly(dimethylsiloxane) Substrates
Unusual Morphologies of Poly(vinyl alcohol) Thin Films Adsorbed on Poly(dimethylsiloxane) Substrates
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吸附在聚（二甲基硅氧烷）基材上的聚（乙烯醇）薄膜的异常形貌
DOI：
10.1021/acs.langmuir.6b00470
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发表时间：
2016
期刊：
影响因子：
3.9
通讯作者：
Chen, Wei
中科院分区：
文献类型：
--
作者：
Karki, Akchheta;Nguyen, Lien;Sharma, Bhanushee;Yan, Yan;Chen, Wei
研究了99%和88%水解聚醋酸乙烯酯（PVOH）在聚二甲基硅氧烷（PDMS）表面的吸附行为。通过将2、9、17、49和116 kDa的线性PDMS聚合物共价连接到硅晶片上来制备基底。随着PDMS分子量/厚度的增加，吸附的PVOH薄膜逐渐从连续形态过渡到不连续形态，包括蜂窝和分形/液滴。这些结构是暴露于空气时发生的薄膜去湿的结果。PVOH膜厚度在这些PDMS基底上没有显著变化，暗示PDMS厚度是形态差异的原因。吸附的PVOH薄膜不太稳定，并且在较厚、更像液体的PDMS层上具有更强的去湿倾向。当比较PVOH 99%和PVOH 88%薄膜时，在高分子量PDMS基底上分别观察到分形和液滴形貌。PVOH 99%薄膜以及其他结晶和半结晶薄膜中独特分形特征的形成最有可能是由脱水过程中的结晶以扩散限制聚集方式驱动的。通过PVOH吸附的亲水性的唯一显著增强是在PDMS 2k上获得的，PDMS 2k完全被PVOH薄膜覆盖。为了模拟PDMS 2k基底的较低后退接触角和较不似液体的特征，对较高分子量的PDMS基底进行光等离子体处理。在处理过的PDMS基底上，吸附的PVOH薄膜呈更连续的蜂窝状形态，从而显著增强了润湿性。此外，在1周的时间内没有观察到疏水化的PDMS基底的疏水恢复。因此，光等离子体氧化和随后的PVOH吸附可用作有效地使常规PDMS基底固化的手段。这项研究表明，吸附的聚合物薄膜的稳定性和形态取决于聚合物的结晶度以及基板的物理性能。
Adsorption of poly(vinyl alcohol) (PVOH), 99% and 88% hydrolyzed poly(vinyl acetate), to poly(dimethylsiloxane) (PDMS) substrates was studied. The substrates were prepared by covalently attaching linear PDMS polymers of 2, 9, 17, 49, and 116 kDa onto silicon wafers. As the PDMS molecular weight/thickness increases, the adsorbed PVOH thin films progressively transition from continuous to discontinuous morphologies, including honeycomb and fractal/droplet. The structures are the result of thin film dewetting that occurs upon exposure to air. The PVOH film thickness does not vary significantly on these PDMS substrates, implicating the PDMS thickness as the cause for the morphology differences. The adsorbed PVOH thin films are less stable and have a stronger tendency to dewet on thicker, more liquid-like PDMS layers. When PVOH99%and PVOH88%thin films are compared, fractal and droplet morphologies are observed on high molecular weight PDMS substrates, respectively. The formation of the unique fractal features in the PVOH99%thin films as well as other crystalline and semicrystalline thin films is most likely driven by crystallization during the dehydration process in a diffusion-limited aggregation fashion. The only significant enhancement in hydrophilicity via PVOH adsorption was obtained on PDMS2k, which is completely covered with a PVOH thin film. To mimic the lower receding contact angle and less liquid-like character of the PDMS2ksubstrate, light plasma treatment of the higher molecular weight PDMS substrates was carried out. On the treated PDMS substrates, the adsorbed PVOH thin films are in the more continuous honeycomb morphology, giving rise to significantly enhanced wettability. Furthermore, hydrophobic recovery of the hydrophilized PDMS substrates was not observed during a 1 week period. Thus, light plasma oxidation and subsequent PVOH adsorption can be utilized as a means to effectively hydrophilize conventional PDMS substrates. This study illustrates that the stability and morphology of adsorbed polymer thin films depend on polymer crystallinity as well as substrate physical properties.