Electrostatically Active Polymer Hybrid Aerogels for Airborne Nanoparticle Filtration Sung Jun Kim, † Prasad Raut, † Sadhan C. Jana,* ,† and George Chase ‡ † Department of Polymer Engineering and ‡ Department of Chemical and Biomolecular Engineering, The University of Akron, Akron, Ohio 44325-0301, United States ABSTRACT: The role of electrostatic force on separation of airborne nanoparticles is evaluated in this work by considering a hybrid monolithic aerogel of syndiotactic polystyrene (sPS) and polyvinylidene fluoride (PVDF). The sPS part accounts for open pore structures in the monolith, while the PVDF chains contribute spontaneous polarity for particle capture by the electrostatic force. The hybrid aerogels are fabricated by thermoreversible gelation of sPS from a solution with PVDF in tetrahydrofuran followed by supercritical drying of the gel. sPS is present as the δ-form clathrate crystalline phase and PVDF as α- and γ-form crystalline phases in the hybrid. The presence of PVDF induces significant static charges on the surfaces of hybrid aerogels. The filtration efficiency is determined by passing airborne NaCl nanoparticles with diameter in the range 25−150 nm through the filter media. The experimental data reveal that air permeability of the hybrid system (∼10 −10 m 2 ) is close to that of sPS monoliths. The hybrid materials show filtration efficiency ≥99.999% in comparison to 98.889% observed for a sPS monolith with the same solid content. KEYWORDS: airborne nanoparticles, aerogels, air permeability, sPS, PVDF, electrostatic force ■ INTRODUCTION A number of health hazards such as nausea, birth defects, bronchitis, and weakened immune systems are tied to exposure to air pollution. 1,2 According to a recent report published by the World Health Organization (WHO), the death of approx- imately 7 million people in 2012 is attributed to exposure to air pollution. 3 The buoyant particulate matters in air generated from the natural activities or anthropogenic emissions are responsible for air pollution. 4 The small buoyant particles can easily reach the pulmonary alveoli in the human body. Accordingly, small airborne particles are classified as fine and ultrafine particles with diameter of, respectively, 0.1−1 μm and <0.1 μm. 5 The pathogens residing on the surfaces of the particles compound the situation by causing more serious and complex hazardous effects. 6 The above health hazards can be significantly mitigated if airborne particles are removed from air streams using filter media. The filter media are generally fabricated from fiber mats. The high efficiency particulate absorption (HEPA) filters are a class of widely used filter media for high efficiency air purification. The filtration efficiencies of HEPA filters are over 99.95% for removing around 0.3 μm size particles as per EN 1822−1:2009 classification. However, an efficient means of removal of airborne nanoparticles with size 25−150 nm is scarce, although as discussed above, the particles of this size range are more detrimental to human health. Aerogels present a class of materials with strong potential to serve as efficient filter media for removing airborne nanoparticles of size 10−300 nm. 7,8 The aerogels offer open, tortuous pores with high porosity (80−95%) and large surface area (300−1000 m 2 /g). 7−30 For example, silica aerogel provides surface area up to 1000 m 2 /g and 90% porosity with significant mesopore fraction of diameter 2−50 nm. 11−23 The δ-form syndiotactic polystyrene (sPS) aerogel provides porosity up to 97% with a significant fraction of pores as macropores (diameter >50 nm). 24−30 Despite strong promise, airborne nanoparticle filtration using aerogels has not been studied much. Only a few studies used aerogel granules or microspheres arranged in packed beds for the purpose of removal of particles. 31−34 Several studies focused on the use of bio- luminescent organisms contained in silica aerogels for viral particle detection 35 and monolithic silica aerogel composites for removal of pollutants. 1,19,36,37 In a recent work, macroporous monolithic sPS aerogels were used for high efficiency (>99.95%) removal of airborne nanoparticles of size 25−150 nm (mean size 75 nm) with air permeability of the order of 10 −11 − 10 −10 m 2 . 8 In another study, we evaluated the function of mesoporous silica particle networks grown inside the macro- pores of sPS in an organic−inorganic hybrid aerogel system on airborne nanoparticle filtration. 7 It was found that the meso- porous silica particle networks increased the particle capture efficiency significantly without affecting much the values of air permeability. The filtration of airborne individual particles is governed by one or more of the five recognized mechanisms. 38−43 Direct interception is the primary contributor of filtration of large particles by direct contact of the particles with the filter medium. Received: November 17, 2016 Accepted: January 23, 2017 Research Article www.acsami.org © XXXX American Chemical Society A DOI: 10.1021/acsami.6b14784 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX