Absorption-induced deformations of nanofiber yarns and webs
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1129-V05-05
Absorption-induced deformations of nanofiber yarns and webs Daria Monaenkova, Taras Andrukh, and Konstantin G.Kornev School of Materials Science and Engineering, 161 Sirrine Hall, Clemson University, Clemson, South Carolina 29634, [email protected]
ABSTRACT Current advances in manufacturing of nanotubular and nanofibrous materials with high surface- to - volume ratios call for the development of adequate characterization methods and predictive estimates of the materials absorption capacity. Extremely high flexibility of these materials poses a challenge: their pore structure easily changes upon contact with the fluid in question. This paper sets a physical basis for analyses of absorption processes in nanotubular and nanofibrous materials. As an example, we study absorption of droplets by yarns and webs made of nanofibers and microfibers. We show that absorption can induce different types of deformations: visible deformations of the sample profile and deformations of the yarn diameter/length caused by the capillary forces. Using experimental data and theory, we estimate elastic and transport characteristics of the nanofibrous materials. The reported experiments and proposed theory open a new area of research on absorption-induced deformations of nanotubular and nanofibrous materials and show their potential applications as sensors to probe minute amount of absorbable liquids.
INTRODUCTION Due to recent progress in electrospinning, the number of applications of electrospun nanofibers and webs grow exponentially (1-3). Varying the density of nanofibers in the web, one can significantly decrease the weight of electrospun mats. In addition to that, the nanofibers can be made porous (4). These materials are very important for some micro and nanofluidic applications which require a hierarchical pore structure with the range of pore sizes varying from nanometers to micrometers (5, 6). In Figure1, we show some typical electrospun nanofibrous structures from polyvinylidene difluoride/polyethylene oxide (PVDF/PEO) blends which we use to control fluid release/absorption. These 0.5 µm - 2 µm diameter fibers have about 83% porosity (7)! The characterization of nanoweb properties is a challenging task, especially when the web thickness is very small; in our case it is comparable with the nanofiber diameter. In this paper we report on development of a new method for characterization of fiberbased materials. The proposed method allows us to measure the permeability of the fiber-based materials and the internal stresses induced by the capillary forces and the weight of absorbed liquids.
50 µm
4 µm
(a)
100 µm
20 mm (b)
Figure 1. a) Yarn made of nanoporous PVDF nanofibers produced by electrospinning, b) electrospun PVDF webs.
EXPERIMENTAL In the proposed method, a sample of fiber-based material (yarn or film) hangs freely under its own weight between two posts. One end of the specimen is immersed into a vessel with a wetting liquid. If the sample is highly-porous, the liquid invades the pores spontaneously tha
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