Thin polymer fiber mats, in particular those made of nonwoven polypropylene (PP) fibers, are extensively used for medical and industrial filtration. The recent pandemic has increased the demand for the fabrication of protective masks. The nonwoven PP filter has limitations in filtration efficiency and lacks advanced functionalities. Here, we propose a simple, effective, and low-cost method to functionalize PP filters and endow antimicrobial and photothermal properties. Our approach is based on the deposition of an ultrathin hybrid coating composed of graphene oxide (GO) and polydopamine on the surface of PP filters by spraycoating. The complementary properties and synergic effects of GO and polydopamine in the ultrathin coating improved the filtration efficiency of the PP filter by 20% with little change in pressure drop. Single component coatings did not result in similar improvements in performance. The ultrathin coating also makes the surface of the filter more hydrophilic with negative charges. The photothermal property of GO enables a rapid temperature increase of the surface-coated filter upon light irradiation for easy sterilization. Furthermore, cationic polymer brushes can be grafted to the ultrathin hybrid coating, which adds the highly desired antimicrobial property to the PP filters for their more effective protection against microorganisms.

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Electrical charges on fabrics, films, and membrane materials are of scientific interest for material development and performance. In many applications, available instruments do not have sufficient sensitivity to detect variations in charge needed for scientific investigations. This paper discusses the design and construction of a custom-made Faraday bucket for measuring the charge of electrospun polyvinylidene fluoride fiber mats of sizes 3 × 3 cm2 and 4 × 4 cm2. An electrometer directly measured the change in the voltage potentials of the inner conductor of the Faraday bucket due to the insertion of fiber mat samples. The measured potentials were converted to electrical charge by modeling the Faraday bucket as a source-free resistance–capacitance circuit. The results show that the Faraday bucket was sufficiently sensitive and measured differences in the potential and charge of the fiber mats due to variations in sample size (or mass), and it detected differences in charge depending on whether the sample was taken from the center or the edges of the electrospun fiber mats.

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Electrospun polymeric nanofibers with flexible three-dimensional porous structures and high surface-to-volume ratio are potential resources for several novel applications in the fields of micro-and nanoscale filtration, water desalination, drug delivery, life sciences, catalysis, and energy harvesters. Functionalized polymeric fibers with enhanced molecular orientation, surface textural morphologies, and piezo-, pyro-, and ferroelectric properties are of technical and commercial interest around the world. Several emerging technologies including electrical polarization, vacuum plasma treatment, corona discharge, surface fluorination, and chemical treatments to functionalize the polyvinylidene fluoride nanofibers are discussed as potential applications of electroactive materials.

Electrospun fibers are of interest in a number of applications due to their small size, simplicity of fabrication, and ease of modification of properties. Piezoelectric polymers such as Polyvinylidene Fluoride (PVDF) can be charged when formed in the electrospinning process. This chapter discusses fabrication of PVDF fiber mats and fiber yarns and the measurement of their charge using a custom-made Faraday bucket. The results show the measured charge per mass of fiber mats was greater than the values measured for the yarns of the same mass. The measured charges may be related to both mass and external surface areas of the mats and yarn samples. It was observed the area/mass ratios of the fiber yarns were more than 30% less than the fiber mats.