Fluoride glasses: crystallization temperature

The homopolymers poly(methyl methacrylate) and poly-(ethyl methacrylate) are compatible with poly(vinylidene fluoride) when blended in the melt. True molecular com-patibility is indicated by their transparency and a single, intermediate glass transition temperature for the blends. The Tg results indicate plasticization of the glassy methacrylate polymers by amorphous poly(vinylidene fluoride). The Tg of PVdF is consistent with the variation of Tg with composition in both the PMMA-PVdF and PEMA-PVdF blends when Tg is plotted vs. volume fraction of each component. PEMA/PVdF blends are stable, amorphous systems up to at least 1 PVdF/I PEMA on a weight basis. PMMA/ blends are subject to crystallization of the PVdF component with more than 0.5 PVdF/1 PMMA by weight. This is an unexpected result. 

At least two different glass transition temperatures have been reported for PVdF homopolymer. Owing to the large proportion of crystalline structure in this polymer and the rapid crystallization which occurs while heating quenched amorphous samples, it is difficult experimentally to obtain an unambiguous, well-defined second-order transition. Mandel-kem, Martin, and Quinn (16) reported a value below — 40°C based upon an extrapolation of the Tg data for vinylidene fluoride-chlorotri-fluoroethylene copolymers in accordance with the Fox equation (6),... 

Mixtures of poly(vinylidene fluoride) with poly (methyl methacrylate) and with poly (ethyl methacrylate) form compatible blends. As evidence of compatibility, single glass transition temperatures are observed for the mixtures, and transparency is observed over a broad range of composition. These criteria, in combination, are acceptable evidence for true molecular intermixing (1, 19). These systems are particularly interesting in view of Bohns (1) review, in which he concludes that a compatible mixture of one crystalline polymer with any other polymer is unlikely except in the remotely possible case of mixed crystal formation. In the present case, the crystalline PVdF is effectively dissolved into the amorphous methacrylate polymer melt, and the dissolved, now amorphous, PVdF behaves as a plasticizer for the glassy methacrylate polymers. 

Another technique suitable for fluoride glass preform fabrication is extrusion. This technique consists in the preparation of preforms with the help of pressure (5 MPa) under moderate temperature (410°C). This is a high-viscosity process with less favorable conditions for crystal growth. Losses of 6 dB km-1 are obtained with multimode fluorozircoaluminate fibers drawn from extruded preforms [159,160]. 

Figure 1 Thermal analysis of a fluoride glass showing characteristic temperatures Tg is the glass transition temperature Tx corresponds to the begiiming of the crystallization T is where the crystalline phase starts to melt T is the liquidus temperature corresponding to the end of the melting process...

SMP based on miscible blends of semicrystalline polymer/amorphous polymer was reported by the Mather research group, which included semicrystalline polymer/amorphous polymer such as polylactide (PLA)/poly vinylacetate (PVAc) blend [21,22], poly(vinylidene fluoride) (PVDF)/PVAc blend [23], and PVDF/polymethyl methacrylate (PMMA) blend [23]. These polymer blends are completely miscible at all compositions with a single, sharp glass transition temperature, while crystallization of PLA or PVDF is partially maintained and the degree of crystallinity, which controls the rubbery stiffness and the elasticity, can be tuned by the blend ratios. Tg of the blends are the critical temperatures for triggering shape recovery, while the crystalline phase of the semicrystalline PLA and PVDF serves well as a physical cross-linking site for elastic deformation above Tg, while still below T ,. 

F%. 35a-d. Anomalous temperature broadening with the bend in the pe a octaethylporphin in polystyrene [99[t h doped silicate glass [1003- Time scale of the hole-burning > 100 s (dots) and < S s(circ(es cNddop BlGaZYTZ heavy metal fluoride glass (crosses) and Nddc >ed ED-2 silicate glass (circles) [101] d perylene doped n-octane crystal [102, 103]... 

First, studying different polar polymers [258,263-265] such as poly(ethylene oxide) (PEO), polyvinyUdene fluoride (PVdF), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and polyvinyl chloride (PVC) in order to enhance the ionic conductivity of the SPEs. PEO has been foimd to be the most successful host material for SPEs due to its low glass transition temperature (-60 °C) [266]. Second, increasing the niunber of charge carriers by use of highly dissociable salts, and increasing the salt concentration. Third, suppressing the crystallization of the polymer chains reduces the conductivity at room temperature ([Pg.1101]

Fluoride glasses have been known since 1926, when it was discovered that beryllium fluoride could be cooled below the liquidus temperature without crystallization. Little further development took place until 1974, when Poulain et al. made the first synthesis of ZrF4-NaF-BaF2-NdF3 [1]. During the past three decades, much attention has been paid to the family of fluoride glasses [2], especially fluorozirconates such as ZBLAN... 

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