Let light-cured composite microscopic changes sweeping with synchrotron

The photocurable (meth) acrylate composite material in a resin matrix, an inorganic filler material dispersed in the polymer composite, in-situ radical polymerization agent may be cured by light field, having easy operation advantages, so widely used, can be used as adhesives, coatings, 3D printing materials, aerospace materials in the biomedical field, such as the large number of applications in dental materials is to promote the study of this material. At present, large-scale application of dental composites, in clinical application The reaction conversion rate group 55 to 75%. The higher the conversion rate of the reactive group, the strength of the composite material, surface hardness, and flexural modulus of elasticity, the better the performance, and a low residual monomer amount, unreacted monomer may be reduced immersion risk from composite materials to the surrounding tissue. Addition of nano and micro inorganic filler can be improved composite strength, toughness and wear resistance, reduced volume shrinkage stress during solidification, but at the expense of the conversion rate of the reactive groups of the cost. Infrared spectroscopy (FTIR) method This study is a reactive group conversion system most commonly used method, differences in band by comparing aliphatic monomers and polymers absorption, can be quantitatively described group change of conversion (DC) of. However, the fatal drawback of this method is characterized by the lateral resolution is too low, difficult to study microscopic scale, such as the conversion rate of the reaction space is between the filler particles and the matrix particles changes. This is important, however, because of the microstructure, in particular the conversion of the group at the interface with the resin and the filler determines the physical and mechanical properties of the material.

The results presented in

Based on the above analysis, Oral Rehabilitation Department of King\’s College London Professor Owen Addison Task Force [123 ] the infrared light imaging environment (IRENI), with a multi-beam source and the synchrotron focal plane array (FPA) detector IR microscope, photocurable (meth) acrylate composite micro-scale the reaction of the substrate conversion and residual strain in a quantitative study , found that conversion is the lowest group near the filler particles in a resin matrix, and only 40%, with an increase from the particle from the center of the group conversion continuously improve,It may be up to nearly 80%, and the efficiency of initiation is higher than the TPO photoinitiator camphorquinone (CQ). at the center of the filler particles, the residual strain of the material is low, as the distance increases, the residual strain is gradually increased. This study illustrates the composition of the matrix resin, filler and how conversion MICROSTRUCTURE composite material was established, a filler – the link between the interface and the material properties of the resin. Note: According to 2020QS World University Rankings, KCL\’s dentistry ranked first in the world.

IRENI Schematic experimental setup and

Figure 1. The photocurable (meth) acrylate, a wide field of view imaging infrared ester Composites experimental schematic. (A) IRENI a schematic view, wherein a mirror M1-M4; (b) 12 separate light beams are combined into a 3 × 4 matrix, the illuminated focal plane array (FPA) of the long exposure photograph; (c) containing a single 8μm dispersing spherical silica filler, matrix resin of 60/40 wt% Bis-GMA / TEGDMA, TPO initiator composite bright field microscope image visible.used in the study, is located in the center of the synchrotron radiation University of Wisconsin-Madison, ray synchrotron storage ring 25 is formed milliradians (vertical) and 320 milliradians (horizontal) by bending magnet radiation band, then the strip into separate synchrotron light beam 12, side by side into a 3 × 4 matrix composition, the matrix is ​​then irradiated with light (mercury telluride infrared microscope equipped Hyperion 3000 and MCT infrared spectrometer Bruker 70 Cd) 60 × 40 μm2 region on the focal plane array detector, using 74 times magnification objective lens transmission measurements. This optical configuration and spatial oversampling in combination, can be imaged in the entire diffraction spectrum in the infrared range (2.5 to 10 m), and provides an effective pixel size of 0.54 μm × 0.54 μm in the sample plane, a spectral resolution of 2 cm -1.

The conversion of a group change between the filler particles

Figure 2. The conversion rate of the composite material and residual strain between particles. (A)Visible bright field microscopic image composite TPO initiator, the resin of the composite material is Bis-GMA / TEGDMA (60/40 wt%), silica filler particles is 8 m, the content of 50 wt%, scale 8μm; (b) reactive group converted image, the blue and red regions on the same region shown in (a) respectively correspond to the relatively low conversion rate and a high region; (c) on the same aromatic region (1608 cm- 1) the absorption wave number band position, wherein the lower wave number corresponding to a large residual strain is stored in a polymer (red region), corresponding to the white area does not pass the test or poor spectral fitting; (d) of the after correction Mie scattering composite material of the same TPO initiator (solid black line), obtained from a single pixel in the infrared spectrum.Researchers at 60/40 wt% bisphenol A- diglycidyl methacrylate / triethylene glycol – dimethacrylate (Bis-GMA / TEGDMA) as the matrix resin, 8μm silica particles as filler in TPO as initiator, the conversion rate was studied between the particles and residual strain in the composite material changes. They distinguish the color difference conversion of the composite material, the region is relatively low blue, high red absorption bands obtained aromatic peak position 1608 cm-1, semi-quantitative calculation by deconvolution the determined high and low residual strain in the vicinity of the state-space distribution of the filler particles, lower and higher wave number of red and blue, respectively, numerals, corresponding to the residual strain.

FIG. 3 between the filler particles reactive group conversion from the particle with the distance from the center curve.researchers in FIG. 1 visualization FIG converted into a graph interparticle conversion with distance distance the particle center distance varies found lowest group conversion at center of the particles, it is 40%, with the left center of the particles increases the distance, and continuously improve the conversion rate, the maximum close to 80%. TPO photoinitiator CQ initiator than initiation efficiency: 70/30 and 60/40 wt% blend of the system, when the initiator is in TPO, CQ system conversion ratio 20% and 10%, respectively.

Figure 4 between particles characterized by AFM-IR reactive group conversion. (A) AFM-IR images 60/40 wt% (Bis-GMA / TEGDMA) CQ initiated composite; (b) on the same target area as shown in (a) the reactive groups in space conversion profile, red and blue regions corresponding to higher and lower conversion of reactive groups, while the white areas represent non-tested by mass spectra, the scale 8 m; wire cross-section shown in (c) (b) is expressed by two conversion of the reactive groups of the silica sphere center.Researchers atomic force microscopy infrared spectroscopy (AFM-IR) studied the changes of the reactive conversion matrix between the filler particles, the silica found in the area occupied by the group conversion rate is low, as 52%, as the distance farther away from the filler, the conversion rate is gradually increased to 62%.

micro residual strain in the composite material change

Figure 5. Analysis of Strain aromatic residue.Researchers deconvolution calculation using the absorption peak of the infrared spectrum, obtained in the aromatic system offset lower wavenumber of the absorption band, quantitative analysis of the residual strain of the composite material, wherein the aromatic absorption peak wave number of 1581 and 1608 cm-1, cis-aliphatic absorption peak wave number 1632.5 cm-1, trans at 1638.5 cm-1.

FIG 6. strain remains between the particles. Peak position (a) corresponds to the absorption band of the monomers BisGMA aromatic group, which is a function of the distance from the center of the filler particles; (b) Changes aromatic wave number.The researchers found that the particles in the center position of the different blends of aromatic bands near 1608.4 cm-1, and the change is small, indicating a low strain at the center; as farther from the center of the particle , falls to the low absorption at the wave number, the strain increases. For the CQ initiator system, the wave number change is negligible, while the TPO initiator system, when the resin ratio of 70/30 and 60/40 wt%, with increasing distance to the lower wave number displaced 0.8 respectively and 1.7 cm-1.

Summary In order to clarify the photocurable group on the conversion of (meth) acrylate composite micro-scale difference and the strainIsobutyl, King\’s College London Professor Owen Addison TF using IRENI technique to study the Bis-GMA TPO and CQ initiated / TEGDMA / SiO2 composite free-radical polymerization photoinitiator difference between groups during the conversion of the filler particles and strain. Group conversion was found at the center of the lowest 40% of the particles, with the distance from the center of the particles increases, increasing rate of conversion, up to 80%. TPO photoinitiator efficient than CQ initiator: 70/30 and 60/40 wt% blend of the system, when the initiator is in TPO, CQ system conversion ratio increased by 20% and 10%. Residual strain in the composite filler particles in the lower center, with the center farther from the particle, the strain increases. For the CQ initiator system, a negligible change in strain, and strain TPO initiator system is large. Original link: https: //www.nature.com/articles/s41467-020-15669-z