Epoxide-based organic inorganic nano-hybrid materials using surface modifier-free hybridization method toward highly effective filling of ZrO2 nano-particles

  A versatile and promising organic-inorganic nano-hybridization method is developed to fabricate epoxide-based transparent hybrid bulk materials containing crystalline ZrO2 nanoparticles (NPs) with the number-averaged... [ view full abstract ]

  A versatile and promising organic-inorganic nano-hybridization method is developed to fabricate epoxide-based transparent hybrid bulk materials containing crystalline ZrO₂ nanoparticles (NPs) with the number-averaged diameter of 3.1 nm. Two proposed key technologies are how to surface-treat, -hydrophobize, and -functionalize the ZrO₂ NPs originally dispersed in water, and how to nano-disperse them into polymer matrixes without any coagulations and/or agglomerations.  Herein, a unique surface treatment method is demonstrated in which the hydrophobization and phase transfer of ZrO₂ NPs from water to organic solvent is simultaneously and gently conducted.  We propose a new concept “surface modifier-free hybridization method” (Figure 1).  In this method, bi-(or multi-) functional epoxy monomers are used as a surface modifier to give the monomer functionalized NPs directly dispersed in the monomers.

  To demonstrate the versatility of this method, three types of epoxy monomers were examined for the preparation of epoxide-based hybrids.  The direct phase transfer of ZrO₂ NPs was conducted by solvent exchange method to give transparent viscous monomer dispersions (Figure 2).  These dispersions were cured by copolymerization with acid anhydride curing agent MHHPA and accelerator PX.  Figure 3 shows the optical images of the prepared three types of epoxide-based hybrids with several filling ratio of ZrO₂ NPs and TEM images of these ultrathin section.  In all systems, highly transparent hybrids were successfully prepared regardless of high filling ratio (W_ZrO2 ≥ 60 wt%).  Figure 4 denotes the refractive indices (○) and its wavelength dependence or ν_D (●) of the hybrids.  The solid and dashed lines indicated the theoretical values calculated from the Lorentz-Lorenz theory.  All experimental values were quantitatively described by the theory, in which the optical values of ZrO₂ monocrystal (n_D = 2.15, ν_D = 35) were used.  Generally, the functional surface modifier is often used to prevent the polymerization induced coagulations but it also decreases the optical performances.  In remarkable contrast, the present surface modifier-free hybridization method allows one to fabricate the nano-hybrids composed of crystalline ZrO₂ NPs and epoxy resins.  In the poster, we will also report in-depth characterizations of these hybrid systems using DLS, NMR, UV-vis spectroscopy, SAXS, and TGA.