Chemical interaction mechanism of 10-MDP with zirconia

Abstract

Currently, the functional monomer 10-methacryloyloxy-decyl-dihydrogen-phosphate (10-MDP) was documented to chemically bond to zirconia ceramics. However, little research has been conducted to unravel the underlying mechanisms. This study aimed to assess the chemical interaction and to demonstrate the mechanisms of coordination between 10-MDP and zirconium oxide using ¹H and ³¹P magic angle spinning (MAS) nuclear magnetic resonance (NMR) and two dimensional (2D) ¹H → ³¹P heteronuclear correlation (HETCOR) NMR. In addition, shear bond-strength (SBS) tests were conducted to determine the effect of 10-MDP concentration on the bonding effectiveness to zirconia. These SBS tests revealed a 10-MDP concentration-dependent SBS with a minimum of 1-ppb 10-MDP needed. ³¹P-NMR revealed that one P-OH non-deprotonated of the PO₃H₂ group from 10-MDP chemically bonded strongly to zirconia. ¹H-³¹P HETCOR NMR indicated that the 10-MDP monomer can be adsorbed onto the zirconia particles by hydrogen bonding between the P=O and Zr-OH groups or via ionic interactions between partially positive Zr and deprotonated 10-MDP (P-O^-). The combination of ¹H NMR and 2D ¹H-³¹P HETCOR NMR enabled to describe the different chemical states of the 10-MDP bonds with zirconia; they not only revealed ionic but also hydrogen bonding between 10-MDP and zirconia.

Figure 1

(A) Shear bond strength to zirconia for different concentrations of 10-MDP (mean in MPa with standard deviation). (B) Feg-SEM photomicrograph of the zirconia surface polished with 15-μm diamond particles at low (a) and high magnification (b).

Figure 2

(A) ¹H MAS NMR spectra of zirconium powder reacted with 10-MDP together with two characteristic slice spectra taken at −7.1 and −2.8 ppm in the ¹H dimension of the 2D ¹H → ³¹P HETCOR NMR spectrum obtained with a CP contact time of 3 ms. (B) 2D ¹H → ³¹P HETCOR NMR spectrum obtained with a CP contact time of 3 ms. (C) ³¹P MAS-DD NMR spectrum of the interaction between 10-MDP and zirconia together with three characteristic slice spectra taken at 4.0, 6.8, and 11.0 ppm in the ³¹P dimension of the 2D ¹H → ³¹P HETCOR NMR spectrum obtained with a CP contact time of 3 ms.

Figure 3. Schematic explaining the interactions of 10-MDP with zirconium and with the hydrated layer at the zirconia surface.