Influences Of Grooved Surface And Fiber Orientation On The Hydrophobic Properties Of Ultrafine Fiber Fabrics

Through millions of years of natural selection and species competition,many creatures have evolved to possess exquisite structural features that are critical to their survival.One of the most intriguing structures is the hierarchical surface formed by grooved units at the nanometre scale.For instance,large numbers of oriented nanogrooves from the setae of water striders enable the insects to stand effortlessly and move quickly on water.Also,the grooves on the surface of the cactus spine endow the drought-resistant plant with excellent capacity of fog collection and water transportation.These close structural–functional relationships have attracted considerable efforts towards the synthesis and application of materials having a grooved surface.Among them,fibrous materials fabricated by electrospinning are considered as ideal candidates.The high similarity between a fiber and a single groove,along with the easy fabrication process,paves a promising path to mimic the exquisite grooved structures in nature.Inspired by these findings,this study aims to fabricate biomimetic hierarchical grooved fibrous surfaces through electrospinning technique.The primary grooves of the surface are formed by aligned fiber,while the secondary grooves are achieved by oriented nanogrooves on the fiber surface.The forming mechanism of secondary groove is explained by the theory of thermodynamics.Meanwhile,the dynamic and static wettabilities of the surface are tested to verify whether it has the same good wettability as the organism.The specific research process and results are as follows:At first,according to the influence of polymer molecular weight,concentration of spinning solution,environment humidity and ratios of solvent on the fiber morphology,we successfully fabricate the secondary nanogrooves on the electrospun fibers.It should be noted that longitudinally aligned nanogrooves are firstly generated on the surface of biodegradable nanofiber such as PLLA.The second step is to explore the forming mechanism of nanogrooved structure using thermodynamic theory and electrospinning process.Investigation into the formation mechanism reveals that the nanogrooves can be readily tailored through adjusting the solvent ratio and relative humidity.With this understanding,a variety of polymers have been successfully electrospun into fiber having the same nanogrooved feature such as PS,CAB,PVDF and PVDF-HFP.Therefore,the mechanism is proved to be correct and universal.Third,the existence of nanogrooves are found to result in an apparent increase of hydrophobicity on the surface composed of randomly oriented fiber attributing to the increase of specific surface and higher roughness.The anisotropic hydrophobicity is demonstrated on membrane composed of aligned fibers.The results show that existence of nanogrooves significantly enhances the anisotropic hydrophobicity,which shares high resemblance to natural hierarchical structures.Finally,the experiment of fog collection on the double grooved fiber membrane proves a high collection efficiency of fog,confirming the excellent performance of double-grooved fiber surface in collecting and transporting water.