Relationships Between Nanofiller Morphology and Viscoelastic Properties in CNF/Epoxy Resins Maria Rossella Nobile, 1 Marialuigia Raimondo, 1 Khalid Lafdi, 2 Annalisa Fierro, 1 Salvatore Rosolia, 1 Liberata Guadagno 1 1 Department of Industrial Engineering – DIIn – University of Salerno, Via Giovanni Paolo II, 132 - 84084 Fisciano (SA), Italy (UE) 2 Department of Chemical and Materials Engineering, University of Dayton, 300 College Park, Dayton, Ohio 45440 This article investigated the rheological behavior of epoxy-amine resins/carbon nanofibers (CNFs) dispersions and its correlation with the nanofiller morphology. The use of the reactive diluent 1,4-butandiol diglycidyl ether into the tetraglycidylmethylene dianiline liquid epoxy precursor has proven to be a key in reducing the viscosity of the epoxy matrix. The effect of nanoadditives on the oscilla- tory shear behavior of the un-cured epoxy precursor matrix in the liquid state was studied. These nanofillers consist of CNFs as made and after high heat treatment temperature. The inclusion of as made CNFs at 0.5 wt% content had no influence on the Newtonian rheological behavior of the epoxy precursor. The morphological inves- tigation indicated that the as made nanofibers showed a tendency to bend and had functionalized surfaces which determined a large epoxy layer thickness around the nanofibers. Due to these events, the as made CNFs were further apart in the epoxy liquid precursor and, conse- quently, the rheological percolation network at 0.5 wt% was not formed. Conversely, when the heat-treated CNFs were used, the rheological results of the epoxy/0.5 wt% CNF dispersion indicated a transition from liquid-like to solid-like behavior at low frequencies showing that in this case the 0.5 wt% content of heat-treated CNFs is higher than the rheological percolation threshold. Indeed, the heat-treated CNFs exhibited an increase in their “equivalent length” and a smaller thickness of the epoxy layer around the nanofibers so that these heat-treated CNFs could easily form a percolation network. POLYM. COMPOS., 00:000–000, 2015. V C 2015 Society of Plastics Engineers INTRODUCTION Epoxy resins used to impregnate carbon fibers (CFs) of composite materials are becoming more important for many industrial applications. Their employment spans the aerospace, wind turbine, automotive, naval, and civil industries. In the field of aeronautic and aerospace struc- tures, aircraft parts made from composite materials, such as fairings, spoilers, and flight controls, were developed during the 1960s for their weight savings over aluminum parts. New generation large aircrafts are designed with all composite fuselage and wing structures. The primary advantages of composite materials are their high strength, relatively low weight, and corrosion resistance. On the other hand, unlike metallic counterparts, composite struc- tures do not readily conduct away the extreme electrical currents and electromagnetic forces generated by light- ning strike. Composite materials are either not conductive at all (e.g., glass fiber reinforced composites) or are sig- nificantly less conductive than metals (e.g., carbon fiber reinforced composites [CFRCs]). A lightning strike can cause severe damage to the aircraft and wind turbine blades [1–3]. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) have attracted significant attention due to their remarkable mechanical, thermal, and electrical properties. Resins filled with conductive nanofillers were mainly considered to overcome drawbacks related to insulating properties of the epoxy resins used to manufacture CFRCs [4–8]. Nanofilled resins made of conductive nano- structured forms of carbon show significant increases in their electrical conductivity even at low nanofiller con- centrations. Among mono-dimensional shaped forms of carbon, CNFs offer very promising results. The values of electrical conductivity of CNF filled epoxy resins are sim- ilar to those found for epoxy matrices filled with CNTs. However, CNFs/epoxy based nanocomposites resins are made using a low cost process. The process consists in dispersing CNFs into the epoxy liquid mixture. Prior to the epoxy cure, the quality of dispersion is a critical step. Conversely, CNFs can be manufactured with some mor- phological and structural properties suitable to reduce the Correspondence to: Maria Rossella Nobile; e-mail: mrnobile@unisa.it Contract grant sponsor: European Union’s Seventh Framework Pro- gramme for research, technological development and demonstration; contract grant number: Grant Agreement No. 313978. DOI 10.1002/pc.23362 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2015 Society of Plastics Engineers POLYMER COMPOSITES—2015