Tailoring 3-component photoinitiating systems for use as efficient photopolymerizable holographic material

8 pagesInternational audienceTo enhance the efficiency of photopolymerizable systems as holographic recording materials, the use of 3-component photoinitiating systems was explored. In order to get more insight into the hologram formation, gratings' recording curves were compared to those of monomer conversion obtained by RTFTIR spectroscopy. This work outlines the differences between the photoinitiating systems. A holographic 3-component recording material giving rise to thick phase holograms with both high diffraction yield and high rate of formation is highlighted

Photocyclic initiating system for free radical photopolymerization studied through holographic recording

International audienceThis paper discusses the efficiency of photocyclic initiating system (PCIS) based on a pyrromethene dye (EMP), an amine as electron donor (NPG) and an iodonium salt as electron acceptor (I250) under homogenous irradiation and holographic recording. It is shown that the PCIS is more efficient than the corresponding two component systems. This high efficiency is due to a photocyclic reaction that takes places during the irradiation, inducing the recovery of the dye in the ground state and the formation of two initiating radicals. The beneficial effect on the rate of grating formation and on the diffraction efficiency is clearly noticed. At high irradiation time, the fast polymerization observed with EMP-NPG-I250 even induces the polymerization in the dark fringes leading to a decrease of the holographic diffraction efficiency. This confirms the high performance of the photoinitiating system which can be used in holographic recording provided that the irradiation dose could be controlled

Photopolymérisation et modulation d'indice de réfraction en holographie

5 pagesNational audienceLes systèmes ici mis en œuvre en tant que support d'enregistrement holographique reposent sur la mise en commun des compétences, d'une part, du LPIM dans le domaine des photoamorceurs et des supports d'enregistrement holographique, et celles, d'autre part, du laboratoire Foton. Les systèmes photoamorceurs considérés sont composés de trois éléments : un colorant et deux co-amorceurs (un donneur d'électron et un accepteur d'électron). Le système SFH+-NPG-ClHABI est, après optimisation des formulations, celui qui conduit aux meilleures performances holographiques, tant du point de vue rendement final de diffraction que de la vitesse de formation du réseau, tout en se stabilisant rapidement à son maximum

Optimisation de nouveaux systèmes photoamorceurs de polymérisation pour le stockage d'informations par holographie

2 pagesNational audienceDifférents systèmes photoamorceurs mettant en jeu trois composants et destinés à la polymérisation d'un mélange d'acrylates sont ici optimisés en tant que support pour le stockage d'informations par holographie. Ces matériaux donnent naissance à des réseaux de phase épais, fonctionnant en transmission. L'étude basée sur l'enregistrement de réseaux sinusoïdaux sous forme d'une modulation d'indice de réfraction a permis de comparer les systèmes 3-composants aux 2-composants correspondants, les premiers étant plus performants d'un point de vue photochimique (vitesse et taux de polymérisation élevés). L'optimisation des matériaux a conduit à des rendements de diffraction corrigés dans l'ordre 1 supérieurs à 90%

Photoinduced hydrosilylation through hydrogen abstraction: an NMR and computational study of the structural effect of silane

The hydrosilylation reaction, describing the addition of Si–H bonds to unsaturated bonds, is performed in the presence of catalysts, usually highly active platinum catalysts. This work focuses on the study of a photoinduced hydrosilylation by the use of benzophenone which promotes the addition reaction of olefin on different hydrosilanes. The reactivity of silanes towards addition onto the double bond during hydrosilylation appears to depend on their structure. It was observed that the consumption of Si–H and C[double bond, length as m-dash]C functional groups increases with the irradiation time, and reaches a maximum of approx. 51% in the case of diphenylsilane. The hydrosilylation products are determined with (1)H NMR, HSQC, DEPT, COSY and (13)C NMR. The main product corresponds to the single adduct of the silyl radical onto the double bond. Substitution of the Si–H bond by two or three phenyls groups (triphenylsilane, diphenysilane) enhances the yield of the reaction, although diphenylsilane was found to be more efficient than triphenylsilane because of its lower steric hindrance. The ketyl radical formed after hydrogen abstraction by the triplet state of benzophenone likely forms benzopinacol, a reaction which reduces the overall yield of the hydrosilylation reaction. All these experiments are in line with DFT calculations of the Gibbs free energy of the reactions involved. This sheds new light on the photoinduced hydrosilylation process and opens the way to more active combinations of photoinitiator/silane/vinylsilane systems

Optimization of a photopolymerizable material based on a photocyclic initiating system using holographic recording

9 pagesInternational audienceA set of photoinitiating systems (PIS) for free radical photopolymerization was studied using time-resolved spectroscopic experiments, real-time FTIR and holographic recording. It is shown that the efficiency of the photoinitiating system can be drastically increased when a redox additive is added to the conventional dye/coinitiator system by virtue of photocyclic behaviour. The homogeneous photopolymerization process was found to reach a fast vitrification, limiting the conversion at about 55%. By contrast, holographic recording underlines the differences in photoinitiating system reactivity, allowing diffraction efficiencies close to unity for the most reactive PIS

Holography, reconstructing by light thanks to a photostructurable medium

During holographic recording, interference patterns produced by a reference beam and the light waves scattered by the object are stored by building-up of refractive index variations or relief profiles in the photosensitive medium. Early holograms used silver halide photographic emulsions as the recording medium. Being able to memorize an incident complex fringe pattern with small features at the submicrometer scale, different polymeric media are also successfully usable. All this optimizing work generated different applications

UV-cured self-replenishing hydrophobic polymer films

Self-healing functional polymer surfaces, designed with an intrinsic and spontaneous mechanism which replenishes the damaged surfaces with the original chemical functionalities, are of great interest to maintain a high performance of the functionality and extend the life-time of materials. We report self-replenishing UV-cured hydrophobic polymer films prepared through the incorporation of methacrylate-terminated perfluorinated-dangling chains into poly(ethylene glycol diacrylate) (PEGDA)-based networks. The films are able to spontaneously and fully self-replenish the surface hydrophobicity, multiple times, upon consecutive intentional damages. The rate of recovery was found to be dependent on the glass transition temperature (Tg) of the networks, which directly correlates to the PEG block length in the PEGDA oligomer used. This study demonstrates that an intrinsic self-replenishing mechanism can be implemented in new network architectures, created rapidly and efficiently by free radical UV-polymerization, which allows preparing self-healing functional polymer films in a faster and eco-friendlier way

Experimental and theoretical investigations of free radical photopolymerization: Inhibition and termination reactions

In this work, the inhibition and termination reactions occurring throughout a free radical photopolymerization initiated by a type-I photoinitiator are studied by kinetic modeling. The role of the macroradicals as the main oxygen trapping agents during the inhibition time is identified, and the absence of primary radical consumption by oxygen can be related to a high initiation efficiency at early times. The ratio of the termination reactions reveals that bimolecular termination remains the principal pathway for the cessation of macromolecule growth, even at high polymer conversion. Moreover, the evolution of the termination ratio during the polymerization can be correlated to both the diffusional control of the polymerization reactions as the polymer network grows and the photoinitiator consumption. Finally, the effect of the incident light intensity and the initial photoinitiator concentration on the termination reactions is assessed, and the validity of the steady-state assumption applied to the macroradical concentration discussed

Development of photoinitiating systems for free radical Photopolymerization usable for laser Imaging

Le sujet de thèse sur lequel je travaille depuis trois ans est l étude et le développement des systèmes photoamorceurs pour des applications holographiques. Ce travail a lieu en collaboration avec l équipe BMS (Bayer Material Science) de Bayer-Leverkusen (Allemagne). Mes études se sont limitées aux systèmes utilisables avec une source d irradiation appartenant à la partie visible du spectre électromagnétique de la lumière (400 nm 700 nm).Parmi les différents types des réactions de polymérisation, nous avons choisi la polymérisation radicalaire. L étape cruciale dans cette réaction réside dans la génération des radicaux qui amorcent la réaction. Ces derniers sont formés par transformation, via absorption de lumière, d un composé photosensible. La formation de ces espèces est en général en compétition avec plusieurs processus de désactivation. Les polymérisations radicalaires sont en particulier fortement inhibées par l oxygène de l air. Pour réduire l effet de l oxygène et pour avoir des conditions comparables à ceux appliqués dans l industrie, nos échantillons ont été préparés en utilisant la technique laminée (l échantillon est mis entre deux films de polypropylène). [...]The subject of the thesis I have been working on for three years is the study and development of photoinitiating systems for holographic applications. This work takes place in collaboration with the BMS (Bayer Material Science) team from Bayer Leverkusen (Germany). My studies have been limited to systems used with a radiation source belonging to the visible part of the electromagnetic spectrum of light (400 nm - 700 nm). Among the different types of polymerization reactions, we chose the radical polymerization. The critical step in this reaction is the generation of radicals which initiate the reaction. These are formed by transformation via absorption of light of a photosensitive compound. The formation of these species is generally in competition with several deactivation process. [...]MULHOUSE-SCD Sciences (682242102) / SudocSudocFranceF