含氟聚合物与水的亲和性起源及其对膜性能的影响,ACS Applied Polymer Materials

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含氟聚合物与水的亲和性起源及其对膜性能的影响
ACS Applied Polymer Materials ( IF 4.4 ) Pub Date : 2020-10-26 , DOI: 10.1021/acsapm.0c00975
Aatif Ali Shah _{1,

2} , Hyeon Jun Heo ₂ , Sanggil Park ₃ , Eunsung Yi ₁ , YoungHoon Cho ₁ , Seung-Eun Nam ₁ , You-In Park _{1,

2} , Hyungjun Kim ₃ , Eun-Ho Sohn ₄ , Hosik Park _{1,

2} , Jeong F. Kim _{1,

5,

6}

Affiliation

含氟聚合物由于存在氟基团而显示出非常高的疏水性。然而，取决于它们的晶体多晶型物，它们有时表现出特殊的极性（称为“极性疏水性”）。尚未清楚地理解这种有趣的现象，并且为所需的应用定制这种稀有特性仍然是一个挑战。特别地，经由膜蒸馏（MD）的水脱盐是新兴的方法，其需要对水分子具有极低亲和力的疏水膜。在这项研究中，我们研究了含氟聚合物，即偏二氟乙烯（VDF）和六氟丙烯（HFP）基团的水亲和性，以及它们与膜性能的关系。通过密度泛函理论分析检查了含氟聚合物极性的分子起源，它揭示了β相VDF晶体的水位是α相的两倍，而HFP基团与水的相互作用能最低。为了最大化膜的疏水性，我们合成了P（VDF-VDF与HFP的比值不同的聚合物（共-HFP）和使用电纺丝技术制成的具有相似孔径的多孔膜。经过彻底的表征，在β相VDF晶体与所观察到的疏水性和性能之间观察到明显的反相关关系，从而证实了含氟聚合物极性的来源。与原始聚偏二氟乙烯膜相比，多晶型物控制的膜在8％HFP含量下表现出独特的最佳性能，其MD长期稳定性提高了35倍。在这项工作中强调指出，在膜接触器工艺中，聚合物的机械性能不能超过所需的疏水性能。

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Origin of Fluoropolymer Affinity toward Water and Its Impact on Membrane Performance

Fluoropolymers exhibit very high hydrophobicity because of the presence of fluorine groups. However, they sometimes exhibit peculiar polarity—referred to as “polar hydrophobicity”—depending on their crystal polymorphs. This intriguing phenomenon is not yet clearly understood, and it remains a challenge to tailor this rare property for desired applications. Particularly, water desalination via membrane distillation (MD) is an emerging process, which requires hydrophobic membranes with extremely low affinity toward water molecules. In this study, we investigated the water affinity of fluoropolymers, namely, vinylidene fluoride (VDF) and hexafluoropropylene (HFP) groups, and their correlation with membrane performance. The molecular origin of fluoropolymer polarity was examined via density functional theory analysis, which unveiled that β-phase VDF crystals have twice as many water-favorable sites as the α-phase, whereas HFP groups exhibit lowest interaction energy with water. To maximize membrane hydrophobicity, we synthesized P(VDF-co-HFP) polymers with varying VDF-to-HFP ratios and fabricated porous membranes with similar pore sizes using the electrospinning technique. Upon thorough characterization, a clear inverse correlation was observed between the β-phase VDF crystals and the observed hydrophobicity and performance, confirming the source of fluoropolymer polarity. The polymorph-controlled membranes exhibited a unique optimum at 8% HFP content with 35-fold enhancement in MD long-term stability compared to that of pristine polyvinylidene fluoride membranes. It is highlighted in this work that the polymer mechanical properties cannot be compromised over the desired hydrophobic properties in membrane contactor processes.

更新日期：2020-11-13

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