Electrospraying is a method of liquid atomisation by subjecting a liquid at a capillary nozzle to an electrical stress. The liquid meniscus maintained at high electric potential elongates into jet and disrupts into fine droplets. The droplets obtained by this method are highly charged and can be of submicron size, which can be readily controlled via liquid flow rate and voltage applied to the nozzle. Since last decade, there is increasing interest in applying electrospray processes in nanotechnology. The deposition efficiency of a charged spray on an object is manifolds higher than for un-charged one. The droplets can be directly deposited onto a substrate enabling surface coating or direct writing in submicron scale.

The paper presents experimental results of deposition of nanopowder on microfibers using electrospraying. The process is aimed at formation of fibrous filters of enhanced collection efficiency in submicron range by making tighter unwoven fabric covered with a catalytic material.

In the presented experiments a layer of MgO particles was formed on an polyamide fiber 30 mm in diameter by deposition the particles from a methanol suspension via electrospraying. Low particle concentration and ease evaporation of the solvent used enabled deposition of uniform tight layer on the fibers. The spraying process was carried out using a fine stainless steel capillary of 200 mm i.d., and 400 mm o.d. The obtained layer was grainy and composed of particles smaller than 200 nm.

The electrospray process is very efficient, cheap, flexible, and can take place at atmospheric pressure and ambient temperature.

Fig. 1. The cone-jet mode of electrospraying. Exposure: 3 ms. Liquid: MgO suspension in methanol, voltage: 5.1 kV.

Fig. 2. SEM images of MgO particle layer deposited by electrospraying on a polyamide fiber 30 mm diameter. Inset: a fragment of the coated fiber showing grainy structure of the layer.

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