Effects of nanoparticles on the dynamic morphology of electrified jets

Abstract

We investigate the effects of nanoparticles on the onset of varicose and whipping instabilities in the dynamics of electrified jets. In particular, we show that the non-linear interplay between the mass of the nanoparticles and electrostatic instabilities, gives rise to qualitative changes of the dynamic morphology of the jet, which in turn, drastically affect the final deposition pattern in electrospinning experiments. It is also shown that even a tiny amount of excess mass, of the order of a few percent, may more than double the radius of the electrospun fiber, with substantial implications for the design of experiments involving electrified jets as well as spun organic fibers.Dynamic instabilities of charged polymeric liquid jets play a crucial role in many natural phenomena and industrial processes, such as electrospinning, ink-jet printing, electrospray, and many others [1,2,3,4,5].In this Letter, we investigate the effects of nanoparticles (NPs) inserted in a polymeric liquid bulk on the resulting charged jet dynamics (see Fig. 1). Interest in this process has been spurred by the possibility of tailoring the material composition and the physical properties of nanocomposite nanofibers [6]. Examples include reinforced yarns with carbon nanotubes [7], fluorescent quantum dots embedded in fibers to show suppressed energy transfer [8] or single-photon coupling to optical modes transmitted in sub-wavelength waveguides [9], nanodiamonds loaded at high concentrations to obtain coatings for UV protection and scratch resistance [10], application of metal NPs to surface-enhanced Raman scattering [11] and to nonvolatile flash memories [12].In all aforementioned applications, the polymer component serves as a three-dimensional topological network of filaments in which NPs compose distributed functional domains. However, encoding the spatially-resolved information embedded in the nanofibers requires a detailed understanding of the way that electrospinning instabilities are modulated by the presence of NPs or clusters thereof, which can profoundly affect the ultimate jet morphology. Despite the major interest in above phenomena, to the best of our knowledge, numerical investigations of the dynamic behavior of electrified jets loaded with NPs are still lacking. In this Letter we take a first step along this line.In the present study, we extend the discrete element model originally introduced by Reneker and co-workers [13], as discussed in Refs. [14,15], and recently implemented in the open source code JETSPIN [16,17].Briefly, the jet is discretized into n particle-like elements, representing a cylindrical jet segment, each labeled by the discrete index i = 1, .., n, with mass m i , charge q i and volume V i . Each jet element is inserted at the nozzle at a mutual distance l i = l step (initial length step of discretization), * Electronic address: m.lauricella@iac.cnr.it; Corresponding author 1 arXiv:1710.01246v2 [physics.comp-ph] 12 Oct 2017 Figure 1: On the top, a simulation snapshot illustrating the electrospin...