Talley Samantha J, Vivod Stephanie L, Nguyen Baochau A, Meador Mary Ann B, Radulescu Aurel, Moore Robert B
Department of Chemistry, Macromolecules Innovation Institute (MII) , Virginia Tech , Blacksburg , Virginia 24061 , United States.
NASA Glenn Research Center , 21000 Brookpark Road , Cleveland , Ohio 44135 , United States.
ACS Appl Mater Interfaces. 2019 Aug 28;11(34):31508-31519. doi: 10.1021/acsami.9b09699. Epub 2019 Aug 16.
The phase diagram for the thermoreversible gelation of poly(ether ether ketone) (PEEK) in 4-chlorophenol (4CP) was constructed over broad temperature and concentration ranges, revealing that PEEK is capable of dissolving and forming gels in both 4CP and dichloroacetic acid (DCA) up to a concentration of 25 wt %. Highly porous aerogels of PEEK were prepared through simple solvent exchange followed by one of two drying methods of solvent removal from the wet gel: freeze-drying or supercritical CO fluid extraction (SC-drying). The field-emission scanning electron microscopy analysis showed that gelation of PEEK in 4CP, followed by SC-drying, produced aerogels with well-defined lamellar aggregates as compared to less ordered aggregates formed from DCA. Mechanical properties (in compression) were shown to improve with increasing density, resulting in equivalent compressive moduli at comparable density, regardless of the preparation method (gelation solvent selection, concentration variation, or drying method). Nitrogen adsorption-desorption isotherms indicate that PEEK aerogels are comprised of mesopores (2-50 nm diameter pores) formed from stacked crystalline lamella. PEEK aerogels prepared using SC-drying exhibit higher Brunauer-Emmett-Teller surface areas than freeze-dried aerogels of comparable density. The ultra-small-angle X-ray scattering/small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering analysis revealed a hierarchical morphology of the PEEK aerogels with structural features from PEEK crystallites to agglomerates of stacked lamella that spanned a wide range of length scales. SANS contrast-matching confirmed that the morphological origin of the principle scattering feature in PEEK aerogels is stacked crystalline lamella. Nitrogen sorption measurements of porosity and the specific surface area of the PEEK aerogels were correlated with the SAXS analysis to reveal a remarkably high surface area attributed to the platelet-like, lamellar morphology. Contact angle and contact angle hysteresis (CAH) revealed that low-density PEEK aerogels (ρ < 0.15 g/cm) have water contact angles above the superhydrophobicity cutoff angle (>150°) and a very low CAH near 1°.
在较宽的温度和浓度范围内构建了聚醚醚酮（PEEK）在4-氯苯酚（4CP）中的热可逆凝胶化相图，结果表明，PEEK在4CP和二氯乙酸（DCA）中均能溶解并形成凝胶，最高浓度可达25 wt%。通过简单的溶剂交换，然后采用从湿凝胶中去除溶剂的两种干燥方法之一（冷冻干燥或超临界CO₂流体萃取（SC干燥）），制备了高度多孔的PEEK气凝胶。场发射扫描电子显微镜分析表明，与由DCA形成的无序聚集体相比，PEEK在4CP中凝胶化后进行SC干燥，产生的气凝胶具有明确的层状聚集体。结果表明，机械性能（压缩性能）随着密度的增加而提高，在可比密度下，无论制备方法（凝胶化溶剂选择、浓度变化或干燥方法）如何，压缩模量相当。氮气吸附-解吸等温线表明，PEEK气凝胶由堆叠的结晶薄片形成的介孔（直径为2-50 nm的孔）组成。使用SC干燥制备的PEEK气凝胶比密度相当的冷冻干燥气凝胶具有更高的布鲁诺尔-埃米特-泰勒表面积。超小角X射线散射/小角X射线散射（SAXS）/广角X射线散射分析揭示了PEEK气凝胶的分级形态，其结构特征从PEEK微晶到堆叠薄片的聚集体，跨越了广泛的长度尺度。小角中子散射对比度匹配证实，PEEK气凝胶中主要散射特征的形态起源是堆叠的结晶薄片。对PEEK气凝胶的孔隙率和比表面积进行的氮气吸附测量与SAXS分析相关联，以揭示由于片状层状形态而具有的非常高的表面积。接触角和接触角滞后（CAH）表明，低密度PEEK气凝胶（ρ < 0.15 g/cm）的水接触角高于超疏水截止角（>150°），且CAH非常低，接近1°。
