Nanomechanical study of polycarbonate/boehmite nanoparticles/epoxy ternary composite and their interphases

Abstract

Thermoplastic modified thermosets are of great interest especially due to their improved fracture toughness. Comparable enhancements have been achieved by adding different nanofillers including inorganic particles such as nanosized boehmite. Here, we present a nanomechanical study of two composite systems, the first comprising a polycarbonate (PC) layer in contact with epoxy resin (EP) and the second consisting of a PC layer containing boehmite nanoparticles (BNP) which is also in contact with an EP layer. The interaction between PC and EP monomer is tested by in situ Fourier transformed infrared (FT‐IR) analysis, from which a reaction induced phase separation of the PC phase is inferred. Both systems are explored by atomic force microscopy (AFM) force spectroscopy. AFM force‐distance curves (FDC) show no alteration of the mechanical properties of EP at the interface to PC. However, when a PC phase loaded with BNP is put in contact with an epoxy system during curing, a considerable mechanical improvement exceeding the rule of mixture was detected. The trend of BNP to agglomerate preferentially around EP dominated regions and the stiffening effect of BNP on EP shown by spatial resolved measurements of Young's modulus, suggest the effective presence of BNP within the EP phase.

Carrier Fibers for the Safe Dosage of Nanoparticles in Nanocomposites: Nanomechanical and Thermomechanical Study on Polycarbonate/Boehmite Electrospun Fibers Embedded in Epoxy Resin

“…The contribution to the Young's modulus of the PC fiber phase is still differentiable with a mean value of 1.188 ± 0.523 GPa in fiber/BNP. A second contribution with a mean Young's Modulus value of 2.473 ± 0.799 GPa is attributed to a stiffening of the PC domain, this value being in agreement with our previous result for a reinforced PC film in a model sample [25]. The mean Young's modulus value for the EP phase (3.555 GPa) and a region showing higher values of the Young's Modulus around 5.108 GPa are contributing to the total mechanical response that seems to be more uniform when compared to the EP/PC fiber neat system.…”

“…Interestingly, the boehmite aggregates are located at the boundary between the two polymers as suspected, as if the BNP migrated from the PC phase towards the EP -rich phase. A similar result was already found in our previous work on a model sample, in which the BNP have a trend to agglomerate around the EP region [25]. This tendency could arise from a mobilizing effect of the DGEBA in PC, which along the high curing temperatures, set the conditions for a semi-organized packing of PC chains in which BNP would not take place and are left aside.…”

“…The features clearly correspond to one or more PC fibers. The phase separation from the epoxy resin is evident as was already reported for a model system consisting of a layer of PC in contact with an interacting epoxy layer [25], in which a trend of the PC phase to form spherulite-like domains was found. The constitution of spherulites arises from an inherent nodular structure of PC, high chain mobility and the exposure of PC to temperatures between 80°C and below its Tg ≈ 149°C.…”

Bulk chemical composition contrast from attractive forces in AFM force spectroscopy

“…On the left side, the bimodal distribution of the stiffness is shown (grey bars), which reflects the bimodal composition of the material. Any distinguishable mechanical response from a possible third phase (an interphase) cannot be distinguished, which was already reported by Cano Murillo and coworkers [ 19 ].…”

“…Here, we consider a sample that was previously described in detail but analyzed in a different context by Cano Murillo and coworkers [ 19 ]. The sample is a binary composite consisting of PC and epoxy.…”