A comparative study of nanoscale glass filler reinforced epoxy composites: Electrospun nanofiber vs nanoparticle Guolong Wang a, b , Demei Yu a, ** , Ram V. Mohan b , Spero Gbewonyo b , Lifeng Zhang b, * a Department of Chemistry, School of Science, State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, Shaanxi, 710049, China b Joint School of Nanoscience and Nanoengineering, North Carolina Agricultural and Technical State University, Greensboro, NC, 27401, USA article info Article history: Received 20 November 2015 Received in revised form 3 March 2016 Accepted 5 April 2016 Available online 13 April 2016 Keywords: Nano composites Mechanical properties Fiber bridging Electro-spinning abstract Electrospun glass nanofibers (EGNFs) are emerging fillers to improve mechanical properties of polymer matrix composite materials. However, questions concerning their reinforcing effectiveness in comparison with other nanoscale fillers such as glass/silica nanoparticles (GNPs) are still to be answered because reinforcing mechanisms for conventional fiber reinforced polymer composites might not be applicable at distinctive nanometer scale. Herein a comparative study on reinforcing effect of EGNFs and their con- ventional counterpart GNPs was carried out for the first time. Four types of glass nanofillers, including pristine EGNFs and GNPs as well as amino surface-functionalized EGNFs and GNPs were investigated to make epoxy matrix nanocomposites at ultra-low loading level (0.5 wt%). Mechanical properties of these glass nanofiller reinforced epoxy composites were investigated and corresponding reinforcing and toughening mechanisms at nanometer scale were discussed. Due to shape factor (aspect ratio), EGNFs demonstrated much more pronounced reinforcing and toughening effectiveness and completely out- performed GNPs in all cases despite much lower specific surface area. This research provided meaningful data to fully understand the merit of EGNFs as reinforcing filler in polymer nanocomposites and paved the road for designing and modeling next-generation polymer matrix composite materials. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Nano-scaled fillers have attracted growing attention in the field of polymer matrix composite (PMC) on account of their remarkable potential for improvement of mechanical properties [1e3]. Recently electrospun nanofibers have been explored as a new promising reinforcing filler in PMCs [4]. Compared to traditional engineering fibers such as Kevlar, glass, and carbon fibers for fiber reinforced polymer (FRP) composites, benefits of electrospun nanofibers come from their significantly higher specific surface area and concurrent enormous interfacial area. This may lead to substantially stronger interfacial bonding between electrospun nanofiber filler and polymer matrix and consequently significant mechanical property improvement in resultant composite mate- rials. As a result, there is increasing research effort that is devoted to electrospun nanofiber reinforced composite materials in the past few years. Among all electrospun nanofibers that are currently involved in reinforcing polymer composites, polymer based nano- fibers so far have received the most of attention because they were firstly developed and relatively matured for applications. Non-polymer nanofibers such as glass (SiO 2 ), ceramic or carbon nanofibers have been successfully developed in recent years through electrospinning with primary goal to explore their elec- tronic, energy, and/or catalytic applications [5]. A noteworthy fact is that these inorganic nanofibers may also possess outstanding me- chanical properties like their bulk counterpart and thus can be employed as reinforcing fillers to make high performance FRP composites [6]. Up to date, however, very limited research en- deavors have been devoted to electrospun glass nanofibers (EGNFs) for reinforcement purpose in polymer composites. Fong et al. used EGNFs as reinforcing filler in Bis-GMA/TEGDMA dental composites for the first time [7]. Their results indicated that 7.5 wt% substitu- tion of conventional glass powder filler with short EGNFs brought about considerable improvement in flexural strength, modulus, and work of fracture of the dental composite by 44%, 29%, and 66%, respectively. Short EGNFs (ca. 400 nm diameter) were applied to SC-15A epoxy resin later and remarkably outperformed * Corresponding author. ** Corresponding author. E-mail addresses: dmyu@mail.xjtu.edu.cn (D. Yu), lzhang@ncat.edu (L. Zhang). Contents lists available at ScienceDirect Composites Science and Technology journal homepage: http://www.elsevier.com/locate/compscitech http://dx.doi.org/10.1016/j.compscitech.2016.04.006 0266-3538/© 2016 Elsevier Ltd. All rights reserved. Composites Science and Technology 129 (2016) 19e29