Showing papers on "Glass transition published in 2003"
TL;DR: The distribution of Tgs across polystyrene films has been obtained by a fluorescence/multilayer method, revealing that the enhancement of dynamics at a surface affects Tg several tens of nanometres into the film.
Abstract: Despite the decade-long study of the effect of nanoconfinement on the glass-transition temperature (Tg) of amorphous materials, the quest to probe the distribution of Tgs in nanoconfined glass formers has remained unfulfilled. Here the distribution of Tgs across polystyrene films has been obtained by a fluorescence/multilayer method, revealing that the enhancement of dynamics at a surface affects Tg several tens of nanometres into the film. The extent to which dynamics smoothly transition from enhanced to bulk states depends strongly on nanoconfinement. When polymer films are sufficiently thin that a reduction in thickness leads to a reduction in overall Tg, the surface-layer Tg actually increases with a reduction in overall thickness, whereas the substrate-layer Tg decreases. These results indicate that the gradient in Tg dynamics is not abrupt, and that the size of a cooperatively rearranging region is much smaller than the distance over which interfacial effects propagate.
1,066 citations
TL;DR: The authors summarizes the known experimental facts and reviews critically theoretical and computational work aimed at interpreting the observations and providing a unified viewpoint on cold, non-crystalline, metastable states of water.
Abstract: The anomalous properties of cold and supercooled water, such as the fact that at sufficiently low temperatures it becomes more compressible and less dense when cooled, and more fluid when compressed, have attracted the attention of physical scientists for a long time. The discovery in the 1970s that several thermodynamic and transport properties of supercooled water exhibit a pronounced temperature dependence and appear to diverge slightly below the homogeneous nucleation temperature inspired a large number of experimental and theoretical studies. Likewise, an important body of work on glassy water has been stimulated by experiments, starting in the mid-1980s and continuing to this date, which suggest that vitreous water can exist in at least two apparently distinct forms. A coherent theory of the thermodynamic and transport properties of supercooled and glassy water does not yet exist. Nevertheless, significant progress towards this goal has been made during the past 20 years. This article summarizes the known experimental facts and reviews critically theoretical and computational work aimed at interpreting the observations and providing a unified viewpoint on cold, non-crystalline, metastable states of water.
1,041 citations
TL;DR: In this article, the stress-strain relations for the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (Vitreloy 1) over a broad range of temperatures and strain rates (10−5 to 103 s−1) were established in uniaxial compression using both quasi-static and dynamic Kolsky (split Hopkinson) pressure bar loading systems.
668 citations
TL;DR: In this paper, two new remendable highly cross-linked polymers, 2ME4F and 2MEP4F, were prepared without solvent, and they were used to study the thermal reversibility of Diels−Alder (DA) cross-linking, and it was found that DA connections and disconnections are thermally reversible.
Abstract: Two new remendable highly cross-linked polymers, 2ME4F and 2MEP4F, were prepared without solvent. Solid-state NMR (nuclear magnetic resonance) was used to study the thermal reversibility of Diels−Alder (DA) cross-linking, and it was found that DA connections and disconnections of both polymers are thermally reversible. Differential scanning calorimeter and dynamical mechanical analysis were applied to study thermal and mechanical properties of these materials, and it is found that the glass transition temperature (Tg) of 2ME4F is about 30−40 °C and that of 2MEP4F is about 80 °C. A qualitative study of the healing efficiency of 2MEP4F showed that cracks can be healed effectively with a simple thermal healing procedure. This process can be repeated to heal cracks multiple times.
653 citations
TL;DR: In this paper, the vibrational heat capacity of crystal and glass data was used for analysis of macromolecules in the semicrystalline state and the transitions of the rigid-amorphous phase and the major reversible processes involving latent heats.
572 citations
TL;DR: In this paper, the influence of silver nanoparticles on the properties of polyvinyl alcohol (PVA) was investigated by mixing a colloidal solution consisting of Silver nanoparticles with a water solution of PVA in appropriate ratios.
Abstract: The influence of silver (Ag) nanoparticles on the properties of poly(vinyl alcohol) (PVA) was investigated. The nanocomposite was prepared by mixing a colloidal solution consisting of silver nanoparticles with a water solution of PVA in appropriate ratios. Composite films with different contents of inorganic phase were obtained after solvent evaporation. The contents of the inorganic phase in the nanocomposites were determined by using atomic absorption spectroscopy (AA) for silver, and were found to be 0.19, 0.33, and 0.73 wt %. Transmission electron microscopy (TEM) of the nanocomposite films revealed the presence of Ag particles with average diameter of 20 nm. Comparison of the thermal properties of the pure polymer and the nanocomposite films showed that the thermal stability is improved by about 40 °C, and the glass transition temperature is shifted to a higher temperature up to 20 °C for the highest content of the nanofiller. An increase in Young's modulus and strength of the nanocomposite was also ...
567 citations
TL;DR: In this paper, the authors review experimental results and computer simulations on diffusion in metallic glasses and supercooled melts and show that diffusion in these glasses is significantly different from diffusion in crystalline metals and involves thermally activated, highly collective atomic processes.
Abstract: Amorphous metallic alloys, also called metallic glasses, are of considerable technological importance. The metastability of these systems, which gives rise to various rearrangement processes at elevated temperatures, calls for an understanding of their diffusional behavior. From the fundamental point of view, these metallic glasses are the paradigm of dense random packing. Since the recent discovery of bulk metallic glasses it has become possible to measure atomic diffusion in the supercooled liquid state and to study the dynamics of the liquid-to-glass transition in metallic systems. In the present article the authors review experimental results and computer simulations on diffusion in metallic glasses and supercooled melts. They consider in detail the experimental techniques, the temperature dependence of diffusion, effects of structural relaxation, the atom-size dependence, the pressure dependence, the isotope effect, diffusion under irradiation, and molecular-dynamics simulations. It is shown that diffusion in metallic glasses is significantly different from diffusion in crystalline metals and involves thermally activated, highly collective atomic processes. These processes appear to be closely related to low-frequency excitations. Similar thermally activated collective processes were also found to mediate diffusion in the supercooled liquid state well above the caloric glass transition temperature. This strongly supports the mode-coupling scenario of the glass transition, which predicts an arrest of liquidlike flow already at a critical temperature well above the caloric glass transition temperature.
509 citations
TL;DR: In the last decade metallic glasses have regained considerable interest due to the fact that new glass-forming compositions have been found that have a critical cooling rate of less than 100 K/s and can be made glassy with dimensions of 1 cm or more as discussed by the authors.
497 citations
TL;DR: A conceptual approach to evaluate glass-forming ability for variousGlass-forming systems has been proposed from a physical metallurgy point of view and this approach was confirmed and validated by experimental data in various glass-formation systems including oxide glasses, cryoprotectants, and metallic glasses.
Abstract: A conceptual approach to evaluate glass-forming ability for various glass-forming systems has been proposed from a physical metallurgy point of view. It was found that the glass-forming ability for noncrystalline materials was related mainly to two factors, i.e., 1/(T(g)+T(l)) and Tx (wherein Tx is the onset crystallization temperature, T ( g) the glass transition temperature, and T(l) the liquidus temperature), and could be predicated by a unified parameter gamma defined as T(x)/(T(g)+T(l)). This approach was confirmed and validated by experimental data in various glass-forming systems including oxide glasses, cryoprotectants, and metallic glasses.
458 citations
TL;DR: In this article, chemically functionalized multiwalled carbon nanotubes were incorporated into a polymer matrix by in situ polymerization, to improve the transfer of mechanical load through a chemical bond, which was demonstrated by Raman and infrared spectroscopies.
Abstract: Chemically functionalized multiwalled carbon nanotubes were incorporated into a polymer matrix by in situ polymerization, to improve the transfer of mechanical load through a chemical bond, which was demonstrated by Raman and infrared spectroscopies. The resulting composite shows higher storage modulus (E‘) and tensile strength than existing similar composites, with only 1 wt % of functionalized nanotubes. E‘ at 90 °C is increased by an outstanding 1135% and the glass transition temperature is exceptionally raised by ≅40 °C.
401 citations
TL;DR: In this paper, the effects of nanoclay particles such as montmorillonite on improving mechanical and thermal properties of fiber reinforced polymer matrix composite materials were investigated as a function of layered silicate content.
Abstract: This paper is primarily focused in studying the effects of nanoclay particles such as montmorillonite on improving mechanical and thermal properties of fiber reinforced polymer matrix composite materials. Basic correlations between polymer morphology, strength, modulus, toughness, and thermal stability of thermoset nanocomposites were investigated as a function of layered silicate content. S2-glass/epoxy-clay nanocomposites were manufactured through an affordable vacuum assisted resin infusion method (VARIM). The nanocomposites are formed during polymerization when the adsorbing monomer separates the clay particles into nanometer scales. Transmission electron microscopy (TEM) and wide angle X-ray diffraction(WAXD) were used to characterize the morphology of the dispersed clay particles. The thermal properties such as onset of decomposition and glass transition temperatures were determined by Thermo Gravimetric Analysis (TGA) and Dynamic Modulus Analyzer (DMA). Mechanical properties such as interlaminar sh...
TL;DR: In this article, a series of functional polyhedral oligomer silsesquioxnae (POSS)/polyimide (PI) nanocomposites were prepared using a two-step approach, first, the octa(aminophenyl)silsquioxane (OAPS)/NMP solution was mixed with polyamic acid (PAA) solution prepared by reacting 4,4′-diaminodiphenylmethane and 3,3′,4,4''-benzophenonetetracarboxylic dianhydride
TL;DR: In this article, high-density polyethylene (HDPE) was chemically crosslinked with various amounts of di-tert butyl cumyl peroxide (BCUP), and the results showed a new finding about decrease in Tg as a consequence of the chemical crosslinking of HDPE.
TL;DR: It is shown that three crystalline polymer electrolytes, poly(ethylene oxide)(6):LiXF(6), X = P, As, Sb, not only conduct but do so better than the analogous amorphous phases!
Abstract: Ionically conducting polymers (salts dissolved in a polymer matrix) are of great interest because they uniquely exhibit ionic conductivity in a soft but solid membrane. As such, they are critical to the development of devices such as all-solid-state lithium batteries. The established view of ionic conductivity in polymer electrolytes is that this occurs in amorphous materials above their glass transition temperature and that crystalline polymer electrolytes are insulators. In contrast, we show that three crystalline polymer electrolytes, poly(ethylene oxide)(6):LiXF(6), X = P, As, Sb, not only conduct but do so better than the analogous amorphous phases! It is also shown that the conductivities of all three 6:1 complexes are similar, consistent with the dimension of the bottlenecks to conduction derived from their crystal structures. An increase in ionic conductivity with reduction of molecular weight of the crystalline polymer electrolyte (from 2000 to 1000) is reported and shown to relate to the increase in crystallite size on reducing molecular weight.
TL;DR: The fragility concept is extended to the glassy state and it is found that the vibrational properties of the glass well below Tg are correlated with the fragility value.
Abstract: When a liquid is cooled below its melting temperature, it usually crystallizes. However, if the quenching rate is fast enough, the system may remain in a disordered state, progressively losing its fluidity upon further cooling. When the time needed for the rearrangement of the local atomic structure reaches approximately 100 seconds, the system becomes “solid” for any practical purpose, and this defines the glass transition temperature T g . Approaching this transition from the liquid side, different systems show qualitatively different temperature dependencies of the viscosity, and accordingly they have been classified by introducing the concept of “fragility.” We report experimental observations that relate the microscopic properties of the glassy phase to the fragility. We find that the vibrational properties of the glass well below T g are correlated with the fragility value. Consequently, we extend the fragility concept to the glassy state and indicate how to determine the fragility uniquely from glass properties well below T g .
TL;DR: In this paper, a small addition of yttrium oxides was found to be very effective in improving glass-forming ability of Fe-based alloys, and as-cast bulk amorphous alloys containing 2 at. % Y showed large thermal stability, with glass transition temperatures above 900 K and supercooled liquid regions above 55 K.
Abstract: In this study, we discovered that a small addition of Y is very effective in improving glass-forming ability of Fe-based alloys. As-cast bulk amorphous alloys containing 2 at. % Y showed large thermal stability, with glass transition temperatures above 900 K and supercooled liquid regions above 55 K, and high strength, with Vickers hardnesses larger than HV 1200. The beneficial effect of Y on glass formation is twofold: (1) Y adjusted the compositions closer to the eutectic and thus lowered their liquidus temperatures, and (2) Y improved the manufacturability of these alloys by scavenging the oxygen impurity from it via the formation of innocuous yttrium oxides.
TL;DR: Electrospun poly(glycolide-co-lactide) biodegradable nanofiber membranes possessed very high surface area to volume ratios and were completely noncrystalline with a relatively lowered glass transition temperature, which led to very different structure, morphology, and property changes during in vitro degradation, which were examined systematically.
TL;DR: In this paper, the epoxy-silica nanocomposites were obtained from directly blending diglycidylether of bisphenol-A and nanoscale colloidal silica and then curing with 4,4-diaminodiphenylmethane.
TL;DR: In this paper, the authors measured the capacity of 1-butyl-3-methylimidazolium hexafluorophosphate (C4mim][PF6) in a range of temperatures from (5 to 550) K, based on measurements by calorimetry.
Abstract: Thermodynamic functions for 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]) are reported in a range of temperatures from (5 to 550) K, based on new measurements by calorimetry. Heat capacities of the crystal, glass, and liquid phases for [C4mim][PF6] were measured with a pair of calorimeters. A vacuum-jacketed adiabatic calorimeter was used at temperatures between (5 and 310) K, and a heat bridge-scanning calorimeter was used from (300 to 550) K. With the adiabatic calorimeter, the fusion Tfus = 283.51 K, = 19.60 kJ·mol-1, and the glass transition Tg = 190.6 K were observed. The [C4mim][PF6] test sample was determined to have a mole fraction purity of 0.9956 by a fractional melting analysis. Densities of the liquid were measured in a range of temperatures from (298 to 353) K with a pycnometer equipped with a capillary neck. An unexpected endothermal transition, with a very small enthalpy change of 0.25 J·g-1 (0.071 kJ·mol-1), was observed in a range of temperatures from (394 to 412) K. He...
TL;DR: In this paper, a mixture of tributyl citrate (TbC) and two oligomers of TbC were synthesized by transesterification of TBC and diethylene glycol.
TL;DR: In this article, the authors examined the mechanical behavior of a styrene-butadiene rubber, containing 23.5% styrene and filled with up to 55% by weight with silica nanoparticles, and showed that the tan δ spectra of these composites show a second relaxation of relatively low intensity located about 40 °C above the main α relaxation.
TL;DR: In this paper, the synthesis and characterization of self-complementary multiple hydrogen-bonded polymers containing pendant 2-ureido-4[1H]-pyrimidone (UPy) units are described.
Abstract: The synthesis and characterization of novel self-complementary multiple hydrogen-bonded (SCMHB) polymers containing pendant 2-ureido-4[1H]-pyrimidone (UPy) units are described. SCMHB pendant polymers, poly(butyl acrylate-co-SCMHB methacrylate), were prepared via free radical copolymerization of butyl acrylate (BA) and a novel SCMHB methacrylate (SCMHB MA) monomer, which was synthesized via a quantitative coupling reaction between 2-isocyanatoethyl methacrylate (ICEMA) and methyl isocytosine (MIS) in DMSO. The glass transition temperatures of poly(BA-co-SCMHB MA) increased in a linear fashion as the SCMHB MA content increased. Thermogravimetric analysis of the copolymers exhibited an onset of weight loss at 217 °C. Solution viscosity analysis indicated that SCMHB pendant polymers strongly aggregated in nonpolar solvents, such as toluene and CHCl3, and dissociated in polar solvents, such as THF. Based on melt rheological characterization, the melt viscosity of soluble SCMHB pendant polymers was an order of ...
TL;DR: In this article, room temperature ionic liquids (ILs) based on imidazolium salts, were found to be excellent plasticizers for poly(methyl methacrylate), with improved thermal stability, and the ability to reduce glass transition temperatures to near 0 °C.
TL;DR: In this article, the authors reviewed the main theoretical concepts of the glass transition in polymers, including mode coupling theory (MCT), entropy theory, free-volume theory, the idea of a growing length describing the size of cooperative regions, etc.
TL;DR: In this article, a microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory.
Abstract: A microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory. Thermal fluctuations are included via a random force which destroys the idealized glass transition and restores ergodicity through activated barrier hopping. The approach is predictive, containing no adjustable parameters or postulated underlying dynamic or thermodynamic divergences. Detailed application to hard-sphere colloidal suspensions reveals good agreement with experiment for the location of the kinetic glass transition volume fraction, the dynamic incoherent scattering relaxation time, apparent localization length, and length scale of maximum nongaussian behavior. Multiple connections are predicted between thermodynamics, short-time dynamics in the nearly localized state, and long-time relaxation by entropic barrier crossing. A critical comparison of the fluid volume fraction dependence of the hopping time with fit formulas which contain ideal divergences has been performed. Application of the derivative Stickel analysis suggests that the fit functions do not provide an accurate description over a wide range of volume fractions. Generalization to treat the kinetic vitrification of more complex colloidal and nanoparticle suspensions, and thermal glass-forming liquids, is possible.
TL;DR: It is shown that nanophase separation of incompatible main and side- chain parts is a general phenomenon in amorphous side-chain polymers with long alkyl groups, and a comparison with data for other polymer series having alkyL groups reveals that important structural and dynamic aspects are main-chain independent.
Abstract: Nanophase separation on length scales of 1–5 nanometres has been reported previously for small-molecule liquids1, metallic glasses and also for several semicrystalline, liquid-crystalline2,3 and amorphous4 polymers. Here we show that nanophase separation of incompatible main and side-chain parts is a general phenomenon in amorphous side-chain polymers with long alkyl groups. We conclude from X-ray scattering and relaxation spectroscopy data for higher poly(n-alkyl acrylates) (PnAA) and poly(n-alkyl methacrylates) (PnAMA) that alkyl groups of different monomeric units aggregate in the melt and form self-assembled alkyl nanodomains with a typical size of 0.5–2 nm. A comparison with data for other polymer series having alkyl groups reveals that important structural and dynamic aspects are main-chain independent. A polyethylene-like glass transition within the alkyl nanodomains is observed and discussed in the context of a hindered glass transition in self-assembled confinements. This is an interesting link between central questions in glass-transition research and structural aspects in nanophase-separated materials.
TL;DR: In this article, homopolymer films of Gellan and polyvinyl alcohol (PVA) and blended films were prepared by a solution casting method from a polymer solution in water of Gellian and PVA using glycerol as plasticizer, and they were studied for thermal characteristics by differential scanning calorimetry, for intermolecular interactions by Fourier transform infrared spectroscopy and for the mechanical properties of tear strength, tensile strength (TS) and percentage elongation (%E).
TL;DR: A direct measurement of self-diffusion of a single-component glass-forming liquid at the glass transition temperature indicates a decoupling of translational diffusion coefficients from viscosity or rotation.
Abstract: We present a direct measurement of self-diffusion of a single-component glass-forming liquid at the glass transition temperature. Forward recoil spectrometry is used to measure the concentration profiles of deuterio and protio 1,3-bis-(1-naphthyl)-5-(2-naphthyl)benzene (TNB) following annealing-induced diffusion in a vapor-deposited bilayer. These experiments extend the range of measured diffusion coefficients in TNB by 6 orders of magnitude. The results indicate a decoupling of translational diffusion coefficients from viscosity or rotation. At ${T}_{g}$, ${D}_{T}$ is 400 times larger than expected from the Stokes-Einstein equation.
TL;DR: Protein function is significantly altered below this transition temperature; a fact that can be exploited to trap normally unstable intermediates in enzyme-catalyzed reactions and stabilize them for periods long enough to permit their characterization by high-resolution protein crystallography.
TL;DR: In this paper, the authors studied the relaxation behavior of organically modified layered silicate−epoxy nanocomposites using a combination of standard and temperature-modulated differential scanning calorimetry.
Abstract: The relaxation behavior of organically modified layered silicate−epoxy nanocomposites was studied using a combination of standard and temperature-modulated differential scanning calorimetry. For such nanocomposites, the silicate layers were intercalated in the matrix resin and epoxy networks were grafted onto the silicate layer surfaces. Enthalpy recovery that occurred during physical aging was used as a probe to detect restricted relaxation behavior in the nanocomposites. Addition of the intercalated nanoparticles resulted in a slower overall relaxation rate and a wider distribution of relaxation times. The nanocomposites also showed a higher glass transition temperature compared to that of the unreinforced resin. To explain the observed results, a domain relaxation model was proposed that included three possible relaxation modes. On the basis of this model, the restricted relaxation arising from intercalated and exfoliated layered silicates can be understood.