Crystalline morphology and polymorphic phase transitions in electrospun nylon-6 nanofibers
Crystalline morphology and polymorphic phase transitions in electrospun nylon-6 nanofibers
复制标题
DOI：
10.1021/ma070039p
复制
发表时间：
2007-08-21
期刊：
影响因子：
5.5
通讯作者：
Fong, Hao
中科院分区：
文献类型：
--
作者：
Liu, Yi;Cui, Li;Fong, Hao
采用静电纺丝法制备了直径约为200 nm的尼龙6纳米纤维。尼龙-6在无约束（即，作为静电纺丝）和高T-g（340摄氏度）聚酰亚胺约束纳米纤维进行了研究。与熔纺尼龙-6纤维类似，静电纺尼龙-6纳米纤维也表现出占主导地位的亚稳态γ晶型，并且γ晶（链）轴优先平行于纤维轴取向。在150摄氏度以上退火时，γ型晶体逐渐熔化并再结晶成结晶稳定的α型晶体，最终在220摄氏度熔化。释放的表面张力伴随着这个熔融重结晶过程中，所揭示的差示扫描量热法。对于受限的纳米纤维，熔融重结晶和表面张力释放过程都被大大抑制; γ-型晶体直到210 ℃才熔融和重结晶成α-型晶体，仅比220 ℃下的Tm低10 ℃。在240 ℃下完全熔化纳米限制晶体并在100 ℃下重结晶后，仅获得垂直于α轴取向的α型晶体。在聚酰亚胺约束的纳米纤维中，在180-190 ℃下观察到布里尔转变（从单斜α-形式到高温单斜形式），这比在类似于160 ℃下的无约束尼龙-6中的布里尔转变高至少20 ℃。这又是由于限制效应。
Uniform nylon-6 nanofibers with diameters around 200 nm were prepared by electrospinning. Polymorphic phase transitions and crystal orientation of nylon-6 in unconfined (i.e., as-electrospun) and a high T-g (340 degrees C) polyimide confined nanofibers were studied. Similar to melt-spun nylon-6 fibers, electrospun nylon-6 nanofibers also exhibited predominant, metastable gamma-crystalline form, and the gamma-crystal (chain) axes preferentially oriented parallel to the fiber axis. Upon annealing above 150 degrees C, gamma-form crystals gradually melted and recrystallized into thermodynamically stable alpha-form crystals, which ultimately melted at 220 degrees C. Release of surface tension accompanied this melt-recrystallization process, as revealed by differential scanning calorimetry. For confined nanofibers, both the melt-recrystallization and surface tension release processes were substantially depressed; gamma-form crystals did not melt and recrystallize into alpha-form crystals until 210 degrees C, only 10 degrees C below the T-m at 220 degrees C. After complete melting of nanoconfined crystals at 240 degrees C and recrystallization at 100 degrees C, only alpha-form crystals oriented perpendicular to the nanofiber axis were obtained. In the polyimide-confined nanofibers, the Brill transition (from the monoclinic alpha-form to a high-temperature monoclinic form) was observed at 180-190 degrees C, which was at least 20 degrees C higher than that in unconfined nylon-6 at similar to 160 degrees C. This, again, was attributed to the confinement effect.