Fictive Temperature Research Articles

Low Loss Multimode Optical Fibers via Fictive Temperature Reduction by Means of Outer-Cladding Na Doping

The reduction of the intrinsic Rayleigh scattering of the optical fibers by slightly altering the outer-cladding composition via the introduction of alkali is the goal of this paper. In this view, multimode fibers with Al- and Na-doped outer-cladding were fabricated via the PCVD process. In optimal conditions (typ. 10-80 ppm Na), we obtained a reduction of 0.06 dB/km at 850 nm for 50/125 multimode fibers corresponding to an attenuation decrease from 2.21 dB/km down to 2.15 dB/km. This is attributed to Rayleigh scattering reduction due to a fictive temperature lowering. In addition, the minor amounts of Na incorporated in the outer-cladding results in much lower NBOHC defects related absorption at 650 nm.

Physical changes and sorption/desorption behaviour of amorphous and semi-crystalline PLLA exposed to water, methanol and ethanol

The purpose of this study was to study the effects of water, methanol and ethanol on the structure of fully amorphous and semi-crystalline poly(l-lactic acid) (PLLA), which is important for applications in which the material is in contact with body fluids (water), and also in order to tailor properties by adjusting the crystallinity and glass transition temperature using penetrants. Amorphous and semi-crystalline PLLA tubes were exposed to the afore-mentioned liquids at 37°C and the mass crystallinity, fictive temperature and the rigid amorphous fraction were assessed by DSC and WAXS. The diffusivity and solubility of the penetrant were assessed by gravimetric sorption and desorption experiments. Water has a plasticizing effect on the glassy structure, which enhances the equilibration of the glass as revealed by a lowering of the fictive temperature of the subsequently dried samples, but the plasticization was not sufficient to induce cold-crystallisation. The moderate effect of water at 37°C was further demonstrated by the almost constant water diffusivity. Both methanol and ethanol induced cold-crystallisation at 37°C, primarily forming crystals of the α′-form, which in the case of methanol led to a marked increase in the fictive temperature and the formation of a rigid amorphous fraction in the subsequent dried samples. The crystal growth was restricted according to an Avrami analysis of the crystallisation kinetics data. The complexity of the sorption and desorption kinetics of methanol and ethanol was caused by the progressing cold-crystallisation on sorption, which resulted in several phenomena. Very notable was the extremely high concentration-dependence of the penetrant diffusivity as revealed on desorption, which could not be explained by plasticization alone. Instead it is believed that the formed crystals caged a significant fraction of the penetrant molecules.

Response of complex networks to compression: Ca, La, and Y aluminoborosilicate glasses formed from liquids at 1 to 3 GPa pressures.

Aluminoborosilicate glasses containing relatively high field strength modifiers (Ca, La, and Y) have been compressed at pressures up to 3 GPa and near the glass transition temperature (Tg) and quenched to room temperature at high pressure followed by decompression. Structural changes were quantified with high-resolution (27)Al and (11)B MAS nuclear magnetic resonance at 14.1-18.8 T. The changes with pressure in Al and B coordinations in the recovered samples are quite large with more than 50% decreases in tetrahedral aluminum ((IV)Al) and 200%-300% increases in tetrahedral boron ((IV)B). Glasses with higher field strength modifiers (La and Y) contain more high coordinated aluminum ((V,V I)Al) at all pressures studied. More high coordinated boron also correlates with higher field strength modifier if all three compositions are compared on an isothermal basis. Although lowering fictive temperature and increasing pressure both increase Al and B coordinations, our study shows that the actual mechanisms for structural changes are most probably different for temperature and pressure effects. Using a rough thermodynamic model to extrapolate to higher pressures, it appears that a simple non-bridging oxygen (NBO) consumption mechanism is not sufficient to convert all the aluminum to octahedral and boron to tetrahedral coordination, suggesting other mechanisms for structural changes could occur at high pressure as NBO becomes depleted.

Nanoscale femtosecond laser milling and control of nanoporosity in the normal and anomalous regimes of GeO_2-SiO_2 glasses

Glass modifications on the nanoscale occurring after femtosecond laser irradiation give rise to strong form birefringence. This birefringence is related to the so-called nanogratings. By observing induced tracks in various germanosilicate glasses using scanning electron microscopy (SEM), we demonstrate that porous nanoplanes can be formed not only in silicate glasses with anomalous density behaviour with fictive temperature, but also within glassy systems with normal density behaviour. The nanoporous oxide is likely due to fast decomposition and volume expansion along with glassy condensation of the oxide creating extreme conditions far from equilibrium. The porosity filling factor and the average pore size significantly decreases when increasing the GeO2 content. Precise laser translation and control of these nanoporous structures allows arbitrary milling, tuning and positioning within the glass, an important top-down approach to control micro and nanostructure and consequently optical properties for molecular sieves, catalysts, composites and optoelectronics applications. At a fundamental level, femtosecond laser milling of glass allows access to glassy regimes that may have no obvious natural counterpart.

Separating the effects of composition and fictive temperature on Al and B coordination in Ca, La, Y aluminosilicate, aluminoborosilicate and aluminoborate glasses

Glass transition temperatures often change significantly (100's of degrees) as the boron oxide to silica ratio, or the field strength of the modifier oxide, is varied in aluminoborosilicate glasses. At the same time, fictive temperature itself can strongly affect the glass structure, most notably in the coordination environments of the network cations boron and aluminum. The latter are especially significant when proportions of [5]Al (AlO5 groups) and [6]Al (AlO6 groups) are high, as in glasses with high field-strength (small, highly charged) modifier cations. To obtain a clearer picture of how composition and temperature independently control structure, we present new data from differential scanning calorimetric (DSC) and high-field 11B and 27Al NMR on a series of Ca, La, and Y aluminosilicate, aluminoborosilicate and aluminoborate glasses prepared with different cooling rates, and compare results in detail with other recently published data on the same compositional joins. We find that previous, apparently disparate results on effects of temperature on Al coordination are in fact related to B/Si ratios: average Al coordination number increased with increased T in aluminosilicates and low-B aluminoborosilicates, but decreased with increased T in glasses with high B/Si ratios, indicating some interaction of the two network cations. We find that effects of T on boron coordination (always lower at higher T) are consistent with a simple thermodynamic view, but may be difficult to detect in some compositions simply because of relative proportions of species. We confirm as well that in boron-rich aluminoborosilicates, B and Al coordination number decreases with increasing temperature are quantitatively linked when calculated per formula unit, again suggesting a strong coupling, and that Al coordination systematically increases with modifier field strength and B2O3/SiO2 ratio.

Polarization tomography of residual stresses in trigonal single crystals

A way to determine residual stresses in cylindrical trigonal single crystals the optical axis of which is directed along the crystal axis is proposed. It is assumed that the residual deformation tensor is of thermal character and is characterized by fictive temperature. The measurements are performed in the middle part of a single crystal the length of which is much larger than its diameter; therefore, the stresses in this part do not vary along the single crystal axis. The reconstruction of stresses is based on determining characteristic parameters of polarized light by use of the tomographic method in the plane orthogonal to the single crystal axis.

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The structural evolutions of potential energy landscape (PEL) are investigated in a metallic glass modeling system with different cooling histories spanning more than five orders of magnitude. The local minima in the PEL are observed to be spatially more separated in the samples with lower fictive temperature Tfic than in the samples with higher Tfic. An Arrhenius scaling between the local minima density and Tfic is observed, which directly links the distribution of inherent structures in the PEL to the population of shear transformation zones (STZ) in amorphous solids. Moreover, very interestingly, the Arrhenius scaling breaks at 1.3–1.4 Tg, above which an invariant PEL structure with a saturated density of local minima is achieved. The hereby obtained critical temperature coincides with the experimentally observed dynamics crossover temperature, which suggests a profound connection between the PEL structure and dynamics in glassy system.

The dependence of Raman defect bands in silica glasses on densification revisited

This paper focuses on the densification signature measured by Raman spectroscopy in silica-based glasses. We have studied a pure silica glass and a 25GeO2–75SiO2 binary glass fabricated by plasma chemical vapor deposition (PCVD), using the fictive temperature T f as a variable parameter ranging from 950 to 1400 °C. Macroscopic density measurements highlighted two opposite behaviors: the higher the fictive temperature, the lower the density of the GeO2–SiO2 glass, in contrast to what is observed in the pure silica glass. Yet, Raman spectra of both these glasses showed similar trends: the intensities of the two defect bands, D1 and D2, increase with increasing fictive temperature. Therefore, the D1 and D2 bands cannot be used as a reliable signature of densification in binary glasses.

Aluminosilicate melts and glasses at 1 to 3 GPa: Temperature and pressure effects on recovered structural and density changes

In the pressure range in the Earth’s mantle where many basaltic magmas are generated (1 to 3 GPa) (Stolper et al. 1981), increases in the coordination numbers of the network-forming cations in aluminosilicate melts have generally been considered to be minor, although effects on silicon and particularly on aluminum coordination in non-bridging oxygen-rich glasses from the higher, 5 to 12 GPa range, are now well known. Most high-precision measurements of network cation coordination in such samples have been made by spectroscopy (notably 27 Al and 29 Si NMR) on glasses quenched from high-temperature, high-pressure melts synthesized in solid-media apparatuses and decompressed to room temperature and 1 bar pressure. There are several effects that could lead to the underestimation of the extent of actual structural (and density) changes in high-pressure/temperature melts from such data. For non-bridging oxygen-rich sodium and calcium aluminosilicate compositions in the 1 to 3 GPa range, we show here that glasses annealed near to their glass transition temperatures systematically record higher recovered increases in aluminum coordination and in density than samples quenched from high-temperature melts. In the piston-cylinder apparatus used, rates of cooling through the glass transition are measured as very similar for both higher and lower initial temperatures, indicating that fictive temperature effects are not the likely explanation of these differences. Instead, transient decreases in melt pressure during thermal quenching, which may be especially large for high initial run temperatures, of as much as 0.5 to 1 GPa, may be responsible. As a result, the equilibrium proportion of high-coordinated Al in this pressure range may be 50 to 90% greater than previously estimated, reaching mean coordination numbers (e.g., 4.5) that are probably high enough to significantly affect melt properties. New data on jadeite (NaAlSi 2 O 6 ) glass confirm that aluminum coordination increase with pressure is inhibited in compositions low in non-bridging O atoms.

Inverse Ablation Analysis and the Calibration Integral Equation Method

The calibration integral equation method has been demonstrated for resolving inverse heat conduction problems based on an invariant sample geometry. This paper proposes to extend its applicability to the investigation of ablation through an abstraction based on forming a fictive surface temperature poised at the nonrecessive origin. Resolving this time-dependent temperature history provides a boundary condition that can be used in a restricted space defined between the nonrecessive origin and an in-depth thermocouple. This fictive temperature (or heat flux) provides an equivalence-based formulation defined in the original spatial domain because the calibration integral equation method is based on conservation principles. The extraction of the fictive boundary condition does not require knowledge of the thermophysical properties or probe position(s) because it is based on calibration. The complexity of ablation requires a compromise between a fully calibrative technique and forward solving approaches. The second step of the two-step process now requires the specification of the thermophysical and geometrical parameters. For this preliminary study, the classical single-ablation temperature inverse problem is revisited but without any additional constraints being imposed. The recession, recession rate, and recession heat flux for a single-temperature ablative material can be solved for by direct means. This paper presents the first test study illustrating the concept and provides highly favorable results using simulated test data based on a Teflon sample with known ablation temperature while under significant thermal loading conditions.

Impact of micro-alloying on the plasticity of Pd-based bulk metallic glasses

Micro-alloying was performed using additions of Co and Fe to monolithic Pd40Ni40P20 bulk metallic glass. Compression tests showed a plastic strain of 13% for the Co addition (1at.%), whereas the Fe addition (0.6at.%) led to immediate failure after reaching the elastic limit. Plasticity is not reflected by the high Poisson’s ratio of 0.4 since it remained unaffected by minor alloying. Applying the fictive temperature concept to analyze the impact of minor alloying suggests that the total amount of free volume frozen-in during vitrification is less important for the mechanical properties of bulk metallic glasses than its local distribution.

FLOCCULATION IN ELASTOMERIC POLYMERS CONTAINING NANOPARTICLES: JAMMING AND THE NEW CONCEPT OF FICTIVE DYNAMIC STRAIN

ABSTRACT Understanding the physics of the particle network in filled rubber is key to developing reduced energy loss compounds for automobile tires and other applications. Progress toward that goal is evident in the recent literature, which reveals some fascinating parallels between the effect of temperature on traditional glassy materials and the role of deformation on the behavior of granular materials, foams, and particle-filled polymers and pastes. The phenomenological treatment of structural relaxation (physical aging) in the nonequilibrium state of glasses, which includes the characteristic features of nonexponentiality and nonlinearity, is extended in the present work to model the progressive structural arrest (jamming) that occurs during the filler flocculation process in uncrosslinked elastomers. A new concept of fictive dynamic strain is developed for nanoparticle-reinforced rubbery polymers by drawing an analogy to the use of fictive temperature in nonequilibrium glasses. The fictive strain converges toward the actual strain as the system approaches steady state. The utility of the approach is demonstrated using literature data for the filler flocculation process of a nanoparticle-filled elastomer.

The effect of chemical structure on the stability of physical vapor deposited glasses of 1,3,5-triarylbenzene.

We detail the formation and properties associated with stable glasses (SG) formed by a series of structural analogues of 1,3-bis(1-naphthyl)-5-(2-naphthyl)benzene (α,α,β-TNB), a well-studied SG former. Five compounds with similar structural properties were synthesized and physical vapor-deposited with a constant deposition rate at various substrate temperatures (Tdep) in the range between 0.73 Tg and 0.96 Tg. These molecules include α,α,β-TNB, 3,5-di(naphthalen-1-yl)-1-phenylbenzene (α,α-P), 9-(3,5-di(naphthalen-1-yl)phenyl)anthracene (α,α-A), 9,9'-(5-(naphthalen-2-yl)-1,3-phenylene)dianthracene (β-AA), and 3,3',5,5'-tetra(naphthalen-1-yl)-1,1'-biphenyl (α,α,α,α-TNBP). Ellipsometry was used to study the transformations from the as-deposited glasses into ordinary glasses (OG). The stability of each film was evaluated by measuring the fictive temperature (Tf) and density difference between the as-deposited glass and OG. It is demonstrated that all five molecules can form SGs upon vapor deposition in this temperature range. In-depth studies on the dependence of the stability of as-deposited glasses upon Tdep were performed with three molecules, α,α,β-TNB, α,α-P, and α,α-A. The general trends of stability were comparable at the same Tdep/Tg for these three compounds. Similar to previous studies on α,α,β-TNB, vapor-deposited glasses of α,α-P and α,α-A formed the most stable structures around Tdep = 0.8-0.85 Tg. The most stable glass of each molecule showed the lowest thermal expansion coefficient compared to OG and a positive optical birefringence. However, the SGs of α,α-A were less stable compared to α,α-P and α,α,β-TNB at the relative Tdep/Tg. Based on Arrhenius extrapolation of the aging time, as a measure of stability, the most stable α,α-A glass was only aged for a few years as opposed to hundreds or thousands of years for other glasses. We hypothesize that the reduced stability is due to slower mobility at the free surface of α,α-A glass compared to the other two molecules.

Sintering and piezoelectric properties of K0.5Na0.5NbO3 glass microspheres

Laser-fused K0.5Na0.5NbO3 (KNN) powder of 75% transparent fraction has been sintered by pressureless sintering, spark plasma sintering (SPS), and hot isostatic pressing (HIP). The laser-fused KNN has a fictive temperature of 503°C and an onset crystallization temperature of around 529°C. The results have shown that sintering of the laser-fused KNN powder utilizing the viscous flow of the transparent microspheres (amorphous content)–at the kinetic window (26°C)–is possible. The highest yield relative density is around 83% at a sintering temperature of 525°C and at a sintering pressure of 280MPa. Limited density has been reached because of formation of crystalline surface layers around the amorphous areas. The samples hipped at 525°C have low piezoelectric coefficient d33 of 5 pC/N because of the residual porosity that led to early dielectric breakdown during the polarization. The sintering behavior, the resulting microstructure as well as the measured properties will be discussed.

Control of zero-crossing temperature of coefficient of thermal expansion and reduction of mechanical residual stress for TiO2–SiO2 glass optical cavity

We developed a procedure for fabricating a Fabry–Perot optical cavity with less long-term length variation. We fabricated a homogenized TiO2–SiO2 ultralow-expansion (ULE) glass ingot from a commercial TiO2–SiO2 ULE glass ingot with striae. We also controlled the zero-crossing temperature of the coefficient of thermal expansion of the homogenized ingot to approximately 30 °C by heat treatment at 970 °C for 72 h to change the fictive temperature of the ingot. A 100-mm-long cavity spacer was carefully fabricated while reducing the mechanical residual stress introduced by machining. A cavity composed of the spacer and two mirrors of 39-layered Ta2O5/SiO2 films exhibited a high finesse of 420,000 at 729 nm and a high length stability of 13 fm/day after 500 days from the beginning of the measurement at a constant temperature of 29.78 °C.

Roles of intermediate-range orders on the glass transition process: Fictive temperature, residual entropy, relaxation time and boson peak

Intermediate-range orders (IROs) have important roles on the glass transition process which is explained by their self-organization. We propose that a periodic Turing pattern, which is based on the reaction diffusion equation proposed by Turing, is constituted in a supercooled liquid and glass by IROs in a wide temperature range. The nonequilibrium structural state determines the fictive temperature and the residual entropy of a glass at the hypothetical equilibrium transition. There are two structural relaxation times in a glass with their own fictive temperatures, namely, Tf1 and Tf2, which are indicated by the configurational states of molecules inside and outside IROs, respectively (Tf1<Tf2). Tf1 introduces a long relaxation time and Tf2 introduces a short relaxation time, where the equilibrium temperature T has vibrational contributions to both relaxation times. The boson peak is excited by the thermal phonons at the Ioffe–Regel limit due to the periodic Turing pattern. The glass transition is a purely kinetic phenomenon, so that the activity of slow configurational dynamics governs the structural relaxation to inhibit crystal nucleation and vitrify a supercooled liquid. The glass transition is a nano-emergence of IROs and a melted glass is a nanomaterial which is composed of a periodic nano-structure with IROs.

Pressure‐volume‐temperature and glass transition behavior of silica/polystyrene nanocomposite

ABSTRACTThe pressure‐volume‐temperature (PVT) behavior and glass transition behavior of a 10 wt % silica nanoparticle‐filled polystyrene (PS) nanocomposite sample are measured using a custom‐built pressurizable dilatometer. The PVT data are fitted to the Tait equation in both liquid and glassy states; the coefficient of thermal expansion α, bulk modulus K, and thermal pressure coefficient γ are examined as a function of pressure and compared to the values of neat PS. The glass transition temperature (Tg) is reported as a function of pressure, and the limiting fictive temperature (Tf′) from calorimetric measurements is reported as a function of cooling rate. Comparison with data for neat PS indicates that the nanocomposite has a slightly higher Tg at elevated pressures, higher bulk moduli at all pressures studied, and its relaxation dynamics are more sensitive to volume. The results for the glassy γ values suggest that thermal residual stresses would not be reduced for the nanocomposite sample studied. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1131–1138

Crystallinity effect on the structural relaxation of polyethylene naphtalate (PEN) by TSDC and DSC experiments

The effect of physical ageing process on the electrical and thermal properties of amorphous and semi-crystalline PEN was investigated by means of the thermally stimulated depolarization currents (TSDC) and the differential scannig calorimetry (DSC). The TSDC measurements revealed a significant decrease in the mobility of the molecular chains in the amorphous PEN (PENa), aged at a temperature Tg-10K (Tg is the glass transition temperature). This mobility is directly related to the polarisation corresponding to the main relaxation of the material. This phenomenon was also observed in the case of biaxially stretched PEN (PENbiax). However, it is much less important in this case. The calorimetric technique (DSC) showed, in the case of PENa, that the effect of ageing is particularly important when the ageing time increases with a maximum effect for ageing temperature equal to Tg-10 K. In the other side, no effect was observed on the semi crystalline PENbiax by the DSC technique unlike the TSDC technique. These results confirm again the high resolving power of this latter. Also, the effect of crystallinity on the structural relaxation of PEN was highlighted and is summeryzed as following : firstly, we have observed a decrease in the TSDC peak's intensity of the α-relaxation and in the recovery enthalpy of the structural relaxation when the crystallinity rate increases. Secondly, an increase in the activation energy Δh* with the increase in the crystallinity rate and a decrease in the limit fictive temperature T'f were observed.

Structural recovery in plastic crystals by time-resolved non-linear dielectric spectroscopy.

The dielectric relaxation of several different plastic crystals has been examined at high amplitudes of the ac electric fields, with the aim of exploring possible differences with respect to supercooled liquids. In all cases, the steady state high field loss spectrum appears to be widened, compared with its low field limit counterpart, whereas peak position and peak amplitude remain almost unchanged. This field induced change in the loss profile is explained on the basis of two distinct effects: an increased relaxation time due to reduced configurational entropy at high fields which affects the low frequency part of the spectrum, and accelerated dynamics at frequencies above the loss peak position resulting from the added energy that the sample absorbs from the external electric field. From the time-resolved assessment of the field induced changes in fictive temperatures at relatively high frequencies, we find that this structural recovery is slaved to the average rather than mode specific structural relaxation time. In other words, the very fast relaxation modes in the plastic crystal cannot adjust their fictive temperatures faster than the slower modes, the equivalent of time aging-time superposition. As a result, an explanation for this single fictive temperature must be consistent with positional order, i.e., translational motion or local density fluctuations do not govern the persistence time of local time constants.

Combining Flash DSC, DSC and broadband dielectric spectroscopy to determine fragility

New experimental results focused on Flash DSC, DSC and broadband dielectric spectroscopy investigations are reported in this work. The fictive temperatures and fragility indexes are estimated from Flash DSC experiments and compared to values obtained from classical DSC. The consistency of the Tool–Narayanaswamy–Moynihan model and fragility concept is then investigated over a large range of cooling rates. Indeed, the Flash DSC allows exploring thermal properties of materials over a continuous and broad range of heating and cooling rates, complementary to rates usually available with DSC. The reliability of investigations is also demonstrated by comparing results obtained from two model amorphous polymeric systems: polystyrene and poly(ethylene terephthalate)-glycol. The temperature dependence of the cooling rate obtained by Flash DSC and DSC is also compared to the temperature dependence of the relaxation times obtained from broadband dielectric spectroscopy, experiment considered as the reference concerning the fragility measurements. The comparison of these two dependencies implies a better understanding about the origin of the temperature dependence of the cooling rate.