Origin of micro-scale heterogeneity in polymerisation of photo-activated resin composites

Abstract

Photo-activated resin composites are widely used in industry and medicine. Despite extensive chemical characterisation, the micro-scale pattern of resin matrix reactive group conversion between filler particles is not fully understood. Using an advanced synchrotron-based wide-field IR imaging system and state-of-the-art Mie scattering corrections, we observe how the presence of monodispersed silica filler particles in a methacrylate based resin reduces local conversion and chemical bond strain in the polymer phase. Here we show that heterogeneity originates from a lower converted and reduced bond strain boundary layer encapsulating each particle, whilst at larger inter-particulate distances light attenuation and monomer mobility predominantly influence conversion. Increased conversion corresponds to greater bond strain, however, strain generation appears sensitive to differences in conversion rate and implies subtle distinctions in the final polymer structure. We expect these findings to inform current predictive models of mechanical behaviour in polymer-composite materials, particularly at the resin-filler interface.

Aging-Dependent Changes in Mechanical Properties of the New Generation of Bulk-Fill Composites

“…Their ratio in the composition is not disclosed [ 10 ]. Sirovica et al recently found the microscopic heterogeneity in the degree of conversion in the polymer network surrounding individually dispersed silica fillers [ 52 ]. Unsilanized silica fillers were encapsulated with polymer of a locally lower degree of conversion, causing internal strain and stresses [ 52 ].…”

“…Sirovica et al recently found the microscopic heterogeneity in the degree of conversion in the polymer network surrounding individually dispersed silica fillers [ 52 ]. Unsilanized silica fillers were encapsulated with polymer of a locally lower degree of conversion, causing internal strain and stresses [ 52 ]. These events could facilitate water penetration in areas of a locally low degree of conversion.…”

Polymerization shrinkage behaviour of resin composites functionalized with unsilanized bioactive glass fillers

“…Nevertheless, the significantly different influence of the two types of BG fillers on the DC of experimental composites enabled insight into shrinkage behaviour that was either governed by the changing DC (C-series) or that was DC-independent (E-series). As DC has been shown to be diminished at the boundary layer of resin that is immediately adjacent to filler particles, incorporating larger particles reduces total filler surface area and thus can be expected to improve DC 37 . This improvement in DC was not identified in our study when smaller reinforcing filler particles (d50 = 1 µm) were replaced by larger BG fillers (d50 = 3 µm).…”

Reinforcing Poly(methyl methacrylate) with Bacterial Cellulose Nanofibers Chemically Modified with Methacryolyl Groups

“…On the other hand, inferior mechanical properties and transparencies were observed when 1.0 wt% or more MPC 1 was combined with PMMA, which we conclude to be due to significant differences in the physical properties of MPC and PMMA, such as density, molecular orientation, crystal structure, and crystallinity, which become more pronounced in composites with high MPC 1 concentrations. As a result, the addition of excess MPC resulted in a decrease in the strength of the PMMA composite, as structural heterogeneity with PMMA counteracts the increase in strength associated with the network structure of MPC [ 32 , 33 , 34 ].…”