The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform
Georgina K. Such - One of the best experts on this subject based on the ideXlab platform.
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rapid photochromic switching in a Rigid Polymer matrix using living radical Polymerization
Macromolecules, 2006Co-Authors: Georgina K. Such, Richard A. Evans, Thomas P DavisAbstract:Fast switching of a photochromic dye in a Rigid host matrix has been achieved without any modification of electronic nature of the photochromic entity. The method utilizes living radical Polymerization (atom transfer radical Polymerization (ATRP)) to grow a low glass transition temperature (Tg) poly(n-butyl acrylate) Polymer from a spirooxazine core, creating a low-Tg environment to cushion the photochromic dye while keeping the bulk matrix Rigid. In these systems, decoloration speed of the photochromic (t1/2) was reduced by 40−75% depending on the molecular weight of the poly(n-butyl acrylate) attached. We have demonstrated with this methodology a controlled tuning of photochromic switching. Coarse and fine tuning can be achieved by adjusting first the choice of Polymer and second the molecular weight of the Polymer.
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the generic enhancement of photochromic dye switching speeds in a Rigid Polymer matrix
Nature Materials, 2005Co-Authors: Georgina K. Such, Richard A. Evans, Tracey Hanley, Melissa A Skidmore, Thomas P DavisAbstract:The switching or isomerization speed of photochromic dyes in a Rigid Polymeric matrix (such as an ophthalmic lens) is generally significantly slower than that observed in the mobile environment of a solution. Here we describe that the attachment of flexible oligomers having a low glass-transition temperature—such as poly(dimethylsiloxane)—to photochromic dyes greatly increases their switching speeds in a Rigid Polymer matrix. The greatest impact was observed in the thermal fade parameters T1/2 and T3/4—the times it takes for the optical density to reduce by half and three quarters of the initial optical density of the coloured state—which were reduced by 40–95% and 60–99% respectively for spirooxazines, chromenes and an azo dye in a host Polymer with a glass-transition temperature of 120 °C. The method does not alter the electronic nature of the dyes but simply protects them from the host matrix and provides greater molecular mobility for the switching process. In addition to ophthalmic lenses, the generic nature of the method may find further utility in data recording or optical switching.
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Research trends in photochromism: Control of photochromism in Rigid Polymer matrices and other advances
Australian Journal of Chemistry, 2005Co-Authors: Richard A. Evans, Georgina K. SuchAbstract:Photochromism is receiving increasing attention because of its current application in high value-added ophthalmic lenses and potential applications in data storage and molecular switching. The performance of photochromic dyes, such as spirooxazines, chromenes, and diarylethenes, in Polymers is important because the above applications require the dyes to be in a host Polymer. The dyes can be broadly divided into P (photo) and T (thermal) types depending on the availability of a thermal decolouration route. Current research themes for the two types are presented with an emphasis on a new method of manipulating switching speeds in Polymer matrices.
Thomas P Davis - One of the best experts on this subject based on the ideXlab platform.
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rapid photochromic switching in a Rigid Polymer matrix using living radical Polymerization
Macromolecules, 2006Co-Authors: Georgina K. Such, Richard A. Evans, Thomas P DavisAbstract:Fast switching of a photochromic dye in a Rigid host matrix has been achieved without any modification of electronic nature of the photochromic entity. The method utilizes living radical Polymerization (atom transfer radical Polymerization (ATRP)) to grow a low glass transition temperature (Tg) poly(n-butyl acrylate) Polymer from a spirooxazine core, creating a low-Tg environment to cushion the photochromic dye while keeping the bulk matrix Rigid. In these systems, decoloration speed of the photochromic (t1/2) was reduced by 40−75% depending on the molecular weight of the poly(n-butyl acrylate) attached. We have demonstrated with this methodology a controlled tuning of photochromic switching. Coarse and fine tuning can be achieved by adjusting first the choice of Polymer and second the molecular weight of the Polymer.
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the generic enhancement of photochromic dye switching speeds in a Rigid Polymer matrix
Nature Materials, 2005Co-Authors: Georgina K. Such, Richard A. Evans, Tracey Hanley, Melissa A Skidmore, Thomas P DavisAbstract:The switching or isomerization speed of photochromic dyes in a Rigid Polymeric matrix (such as an ophthalmic lens) is generally significantly slower than that observed in the mobile environment of a solution. Here we describe that the attachment of flexible oligomers having a low glass-transition temperature—such as poly(dimethylsiloxane)—to photochromic dyes greatly increases their switching speeds in a Rigid Polymer matrix. The greatest impact was observed in the thermal fade parameters T1/2 and T3/4—the times it takes for the optical density to reduce by half and three quarters of the initial optical density of the coloured state—which were reduced by 40–95% and 60–99% respectively for spirooxazines, chromenes and an azo dye in a host Polymer with a glass-transition temperature of 120 °C. The method does not alter the electronic nature of the dyes but simply protects them from the host matrix and provides greater molecular mobility for the switching process. In addition to ophthalmic lenses, the generic nature of the method may find further utility in data recording or optical switching.
Richard A. Evans - One of the best experts on this subject based on the ideXlab platform.
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rapid photochromic switching in a Rigid Polymer matrix using living radical Polymerization
Macromolecules, 2006Co-Authors: Georgina K. Such, Richard A. Evans, Thomas P DavisAbstract:Fast switching of a photochromic dye in a Rigid host matrix has been achieved without any modification of electronic nature of the photochromic entity. The method utilizes living radical Polymerization (atom transfer radical Polymerization (ATRP)) to grow a low glass transition temperature (Tg) poly(n-butyl acrylate) Polymer from a spirooxazine core, creating a low-Tg environment to cushion the photochromic dye while keeping the bulk matrix Rigid. In these systems, decoloration speed of the photochromic (t1/2) was reduced by 40−75% depending on the molecular weight of the poly(n-butyl acrylate) attached. We have demonstrated with this methodology a controlled tuning of photochromic switching. Coarse and fine tuning can be achieved by adjusting first the choice of Polymer and second the molecular weight of the Polymer.
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the generic enhancement of photochromic dye switching speeds in a Rigid Polymer matrix
Nature Materials, 2005Co-Authors: Georgina K. Such, Richard A. Evans, Tracey Hanley, Melissa A Skidmore, Thomas P DavisAbstract:The switching or isomerization speed of photochromic dyes in a Rigid Polymeric matrix (such as an ophthalmic lens) is generally significantly slower than that observed in the mobile environment of a solution. Here we describe that the attachment of flexible oligomers having a low glass-transition temperature—such as poly(dimethylsiloxane)—to photochromic dyes greatly increases their switching speeds in a Rigid Polymer matrix. The greatest impact was observed in the thermal fade parameters T1/2 and T3/4—the times it takes for the optical density to reduce by half and three quarters of the initial optical density of the coloured state—which were reduced by 40–95% and 60–99% respectively for spirooxazines, chromenes and an azo dye in a host Polymer with a glass-transition temperature of 120 °C. The method does not alter the electronic nature of the dyes but simply protects them from the host matrix and provides greater molecular mobility for the switching process. In addition to ophthalmic lenses, the generic nature of the method may find further utility in data recording or optical switching.
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Research trends in photochromism: Control of photochromism in Rigid Polymer matrices and other advances
Australian Journal of Chemistry, 2005Co-Authors: Richard A. Evans, Georgina K. SuchAbstract:Photochromism is receiving increasing attention because of its current application in high value-added ophthalmic lenses and potential applications in data storage and molecular switching. The performance of photochromic dyes, such as spirooxazines, chromenes, and diarylethenes, in Polymers is important because the above applications require the dyes to be in a host Polymer. The dyes can be broadly divided into P (photo) and T (thermal) types depending on the availability of a thermal decolouration route. Current research themes for the two types are presented with an emphasis on a new method of manipulating switching speeds in Polymer matrices.
Joseph P. Dinnocenzo - One of the best experts on this subject based on the ideXlab platform.
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low power green to blue and blue to uv upconversion in Rigid Polymer films
Journal of Luminescence, 2009Co-Authors: Paul B. Merkel, Joseph P. DinnocenzoAbstract:Abstract Green light excitation of platinum octaethylporphyrin (PtOEP) in poly(methyl methacrylate) (PMMA) films containing 9,10-diphenylanthracene (DPA) yielded emission of blue light under ambient conditions. This energy upconversion process was easily observed using low-power monochromatic excitation. The blue light emission arose from fluorescence of the lowest excited singlet state of DPA formed by spin-allowed annihilation of two DPA triplets excited by the transfer of the triplet energy from PtOEP to DPA. The upconversion emission intensity was proportional to the square of the excitation intensity, and an upconversion quantum efficiency of ∼0.0002 was measured at an excitation intensity of only 0.9 mW cm−2. High concentrations of molecularly doped emitter facilitated triplet energy migration in Rigid PMMA. Upconverted fluorescence was also observed from other emitters and with other sensitizers, including blue-to-UV upconversion in a PMMA film containing the non-heavy metal sensitizer 2-methoxythioxanthone and the emitter 2,5-diphenyloxazole.
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Experimental and theoretical study of triplet energy transfer in Rigid Polymer films.
The journal of physical chemistry. A, 2008Co-Authors: Paul B. Merkel, Joseph P. DinnocenzoAbstract:With the judicious selection of triplet energy donor (D) and acceptor (A) pairs, a laser flash photolysis procedure has provided a sensitive method for the study of triplet energy transfer in Rigid Polymer films. By monitoring changes in triplet-triplet (T-T) absorptions the kinetics of triplet energy transfer were evaluated at short time scales, and overall energy-transfer quantum yields were also obtained. Combinations of xanthone- or thioxanthone-type donors and polyphenyl acceptors were particularly suited to these measurements because the former have high intersystem-crossing quantum yields and the latter have very high extinction coefficients for T-T absorption. For exothermic transfer most of the energy transfer that occurred within the lifetime of triplet D ( (3)D) took place in less than a few microseconds after (3)D formation in poly(methyl methacrylate), and triplet A yields were limited largely by the number of A molecules in near contact with (3)D. The kinetics of triplet energy transfer were modeled using a modified Perrin-type statistical arrangement of D/A separations with allowance for excluded volume in combination with a Dexter-type formula for the distance-dependent exchange energy-transfer rate constant. Experimental observations were best explained by constraining D/A separations to reflect the dimensions of intervening molecules of the medium. Rate constants, k 0, for exothermic energy transfer from (3)D to A molecules in physical contact are approximately 10 (11) s (-1) and very similar to triplet energy-transfer rate constants determined from solution encounters. Energy-transfer rate constants, k( r), fall off as approximately exp(-2 r/ 0.85), where r is the separation distance between D and A centers in angstroms. Exchange energy transfer is not restricted to (3)D and A in physical contact, but at
Enyong Ding - One of the best experts on this subject based on the ideXlab platform.
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Study on transition characteristics of PEG/CDA solid–solid phase change materials
Polymer, 2002Co-Authors: Yong Jiang, Enyong Ding, Li GuokangAbstract:Abstract New kinds of solid–solid phase change materials (PCMs) with netted structure have been prepared. In these new materials, the Rigid Polymer cellulose diacetate (CDA) serves as skeleton, and the flexible Polymer polyethylene glycol (PEG) serves as functional branch chain. The transition mechanism of these functional Polymers is the transfer between the amorphous and crystal states of the PEG. During the transition, PEG gives or takes in latent heat, and at the same time, the whole composite always remains in the solid state. The series experiments show that the PCMs' latent heats, phase transition temperatures and mechanical strengths depend on the molecular weights and weight percentages of PEG.
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study on transition characteristics of peg cda solid solid phase change materials
Polymer, 2002Co-Authors: Yong Jiang, Enyong DingAbstract:Abstract New kinds of solid–solid phase change materials (PCMs) with netted structure have been prepared. In these new materials, the Rigid Polymer cellulose diacetate (CDA) serves as skeleton, and the flexible Polymer polyethylene glycol (PEG) serves as functional branch chain. The transition mechanism of these functional Polymers is the transfer between the amorphous and crystal states of the PEG. During the transition, PEG gives or takes in latent heat, and at the same time, the whole composite always remains in the solid state. The series experiments show that the PCMs' latent heats, phase transition temperatures and mechanical strengths depend on the molecular weights and weight percentages of PEG.
