Photoinitiated polymerization of a dental formulation: 1. Influence of photoinitiating system, temperature and luminous intensity

The photoinitiated polymerization of a dental formulation is composed of Mixture of monomers 75%Bis-GMA/25%TEGDMA and CQ/DMAEMA as radical photoinitiator was studied by using isothermal photocalorimetry. The effect of temperature, light intensity and photoinitiating system concentration on reaction was investigated. A maximum conversion was obtained for a photoinitiator system concentration of 1% (w/w) and for the highest light intensity studied. It should be noted that a correlation between the glass transition temperature of the final polymer and the conversion has been studied.Keywords: dental composite; photopolymerization; dimethacrylate resin; photoinitiator syste

Interfacial Profile and Propagation of Frontal Photopolymerization Waves

We investigate the frontal photopolymerization of a thiol–ene system with a combination of experiments and modeling, focusing on the interfacial conversion profile and its planar wave propagation. We spatially resolve the solid-to-liquid front by FT-IR and AFM mechanical measurements, supplemented by differential scanning calorimetry. A simple coarse-grained model is found to describe remarkably well the frontal kinetics and the sigmoidal interface, capturing the effects of UV light exposure time (or dose) and temperature, as well as the front position and resulting patterned dimensions after development. Analytical solutions for the conversion profile enable the description of all conditions with a single master curve in the moving frame of the front position. Building on this understanding, we demonstrate the design and fabrication of gradient polymer materials, with tunable properties <i>along</i> the direction of illumination, which can be coupled with lateral patterning by modulated illumination or grayscale lithography

Lower bound for the spatial extent of localized modes in photonic-crystal waveguides with small random imperfections

Light localization due to random imperfections in periodic media is paramount in photonics research. The group index is known to be a key parameter for localization near photonic band edges, since small group velocities reinforce light interaction with imperfections. Here, we show that the size of the smallest localized mode that is formed at the band edge of a one-dimensional periodic medium is driven instead by the effective photon mass, i.e. the flatness of the dispersion curve. Our theoretical prediction is supported by numerical simulations, which reveal that photonic-crystal waveguides can exhibit surprisingly small localized modes, much smaller than those observed in Bragg stacks thanks to their larger effective photon mass. This possibility is demonstrated experimentally with a photonic-crystal waveguide fabricated without any intentional disorder, for which near-field measurements allow us to distinctly observe a wavelength-scale localized mode despite the smallness (∼1/1000 of a wavelength) of the fabrication imperfections

Right on time – Socio-ecological strategy and implications of turbulence in the Swiss watchmaking field

We explore how the socio-ecological approach to strategy extends and enriches current theory on fields (especially Fligstein and McAdam, 2012). We do so with a socio-ecological (Ramirez and Selsky, 2016) lens which helps us analyse how contention and change work in conditions of turbulence, conditions where macro-level issues play a central role in transforming a field. Our empirical exploration of the Swiss watchmaking field in its current turbulent causal texture enables us to examine the locus of strategic action (intra-field vs inter-field) by both incumbents and challengers, and how they enact the strategic stances of preparation, relocating and reinventing collaboration. With this lens we also analyse the roles a legacy technology can play in the framing-reframing contention, where incumbents favour an ‘intra-field’ framing (i.e. centred in the legacy technology) whereas challengers favour an ‘interfield’ reframing (i.e. open to emerging technologies). Our research further contributes to the literature by providing a clarification of the Ramirez and Selsky (2016) strategic stances in relation to its core unit of analysis: field-level vs organizational-level vs inter-organizational network level and does so with empirical data

Right on time – Socio-ecological strategy and implications of turbulence in the Swiss watchmaking field

We explore how the socio-ecological approach to strategy extends and enriches current theory on fields (especially Fligstein and McAdam, 2012). We do so with a socio-ecological (Ramirez and Selsky, 2016) lens which helps us analyse how contention and change work in conditions of turbulence, conditions where macro-level issues play a central role in transforming a field. Our empirical exploration of the Swiss watchmaking field in its current turbulent causal texture enables us to examine the locus of strategic action (intra-field vs inter-field) by both incumbents and challengers, and how they enact the strategic stances of preparation, relocating and reinventing collaboration. With this lens we also analyse the roles a legacy technology can play in the framing-reframing contention, where incumbents favour an ‘intra-field’ framing (i.e. centred in the legacy technology) whereas challengers favour an ‘interfield’ reframing (i.e. open to emerging technologies). Our research further contributes to the literature by providing a clarification of the Ramirez and Selsky (2016) strategic stances in relation to its core unit of analysis: field-level vs organizational-level vs inter-organizational network level and does so with empirical data

Refractive index evolution of various commercial acrylic resins during photopolymerization

A set of commercial (meth)acrylic resins was photopolymerized under identical irradiation conditions and evolution of their refractive index was monitored as a function of double bond conversion. Initial refractive index values ranged from 1.4445 to 1.5454 and then linearly increased with conversion as long as the material was not in the glassy state. This increase was related to an increase of the material density arising during polymerization. Final refractive index values ranged from 1.4804 to 1.5632. The knowledge of the refractive index and of its evolution during the photocuring is indispensable, in particularly to elaborate composite materials (polymer matrix + filler) with well controlled optical properties

Gradient structure materials from homogeneous system induced by UV photopolymerization

International audienc

Stereolithography process: Influence of the rheology of silica suspensions and of the medium on polymerization kinetics - Cured depth and width

International audienceUV laser stereolithography is a rather new shaping technique that makes it possible the fabrication of complex 3D ceramic structures with a high dimensional accuracy. The green part is built through layer by layer photopolymerization of a light sensitive suspension. Polymerization is thus a critical step to control in this shaping technique. Photopolymerization, with the initiation, propagation and termination reactions, involves the mobility of reactive species and is then sensible to the rheology of the media. This study investigated the influence of the rheology of suspensions of silica particles in an acrylate oligomer and of the intergranular curable organic phase on the UV polymerization. In this respect, the effects of the powder concentration, the state of dispersion and of the dilution of the reactive oligomer on polymerization, are measured. In addition, the influence of the powder loading on the cure depth and cure width, which are respectively pertinent indicators of the reactivity of the suspension and of the dimensional accuracy of the green part, is evaluated