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Showing papers on "Glass transition published in 1995"


Journal ArticleDOI
31 Mar 1995-Science
TL;DR: The onset of a sharp change in ddT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature.
Abstract: Glasses can be formed by many routes. In some cases, distinct polyamorphic forms are found. The normal mode of glass formation is cooling of a viscous liquid. Liquid behavior during cooling is classified between "strong" and "fragile," and the three canonical characteristics of relaxing liquids are correlated through the fragility. Strong liquids become fragile liquids on compression. In some cases, such conversions occur during cooling by a weak first-order transition. This behavior can be related to the polymorphism in a glass state through a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The sudden loss of some liquid degrees of freedom through such first-order transitions is suggestive of the polyamorphic transition between native and denatured hydrated proteins, which can be interpreted as single-chain glass-forming polymers plasticized by water and cross-linked by hydrogen bonds. The onset of a sharp change in d dT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature. The latter may originate in strong anharmonicity in modes ("bosons"), which permits the system to access multiple minima of its configuration space. These modes, the Kauzmann temperature T(K), and the fragility of the liquid, may thus be connected.

4,016 citations


Journal ArticleDOI
TL;DR: In the temperature range studied the model amorphous solids were in a transition zone between regions of very high molecular mobility above Tg and very low molecular mobility much further below Tg, which should be expected to experience significant molecular mobility at temperatures up to fifty degrees below their glass transition temperature.
Abstract: Purpose. To measure the molecular mobility of amorphous pharmaceutical solids below their glass transition temperatures (Tg), using indomethacin, poly (vinyl pyrrolidone) (PVP) and sucrose as model compounds. Methods. Differential scanning calorimetry (DSC) was used to measure enthalpic relaxation of the amorphous samples after storage at temperatures 16-47 K below Tg for various time periods. The measured enthalpy changes were used to calculate molecular relaxation time parameters. Analogous changes in specimen dimensions were measured for PVP films using thermomechanical analysis. Results. For all the model materials it was necessary to cool to at least 50 K below the experimental Tg before the molecular motions detected by DSC could be considered to be negligible over the lifetime of a typical pharmaceutical product. In each case the temperature dependence of the molecular motions below Tg was less than that typically reported above Tg and was rapidly changing. Conclusions. In the temperature range studied the model amorphous solids were in a transition zone between regions of very high molecular mobility above Tg and very low molecular mobility much further below Tg. In general glassy pharmaceutical solids should be expected to experience significant molecular mobility at temperatures up to fifty degrees below their glass transition temperature.

926 citations


Journal ArticleDOI
TL;DR: In this paper, the glass forming ability of quaternary alloys was investigated and it was shown that the glass formation ability of these alloys exceeds the ternary or binary alloys by at least two orders of magnitude.
Abstract: Formation of bulk metallic glass in quaternary Ti–Zr–Cu–Ni alloys by relatively slow cooling from the melt is reported. Thick strips of metallic glass were obtained by the method of metal mold casting. The glass forming ability of the quaternary alloys exceeds that of binary or ternary alloys containing the same elements due to the complexity of the system. The best glass forming alloys such as Ti34Zr11Cu47Ni8 can be cast to at least 4-mm-thick amorphous strips. The critical cooling rate for glass formation is of the order of 250 K/s or less, at least two orders of magnitude lower than that of the best ternary alloys. The glass transition, crystallization, and melting behavior of the alloys were studied by differential scanning calorimetry. The amorphous alloys exhibit a significant undercooled liquid region between the glass transition and first crystallization event. The glass forming ability of these alloys, as determined by the critical cooling rate, exceeds what is expected based on the reduced glass transition temperature. It is also found that the glass forming ability for alloys of similar reduced glass transition temperature can differ by two orders of magnitude as defined by critical cooling rates. The origins of the difference in glass forming ability of the alloys are discussed. It is found that when large composition redistribution accompanies crystallization, glass formation is enhanced. The excellent glass forming ability of alloys such as Ti34Zr11Cu47Ni8 is a result of simultaneously minimizing the nucleation rate of the competing crystalline phases. The ternary/quaternary Laves phase (MgZn2 type) shows the greatest ease of nucleation and plays a key role in determining the optimum compositions for glass formation.

703 citations


Journal ArticleDOI
TL;DR: In this article, dynamic mechanical measurements on several polymers filled with very fine silica particles revealed that these composites exhibit two tan δ peaks, one related to the usual polymer glass transition, while the other, occurring at a higher temperature, was assigned to the glass transition of regions containing reduced mobility.
Abstract: The dynamic mechanical measurements on several polymers filled with very fine silica particles revealed that these composites exhibit two tan δ peaks. One was related to the usual polymer glass transition, while the other, occurring at a higher temperature, was assigned to the glass transition of regions containing chains of reduced mobility. Since many aspects of this behavior were found to be analogous to those of random ionomers, the results support the validity of the EHM model of ionomer morphology. The particle content, the number of monomer units interacting strongly with the surface of the particles, the thermal history of the sample, and the average MW of the polymer were all found to have a significant effect on the area and the maximum of the new tan δ peak. These effects are discussed in terms of a model which is based on the EHM ionomer model but takes into account the formation of tightly bound and loosely bond polymer chains around the filler particles.

594 citations


Journal ArticleDOI
TL;DR: In this paper, the dielectric relaxation times of the α process of phenyl salicylate (salol) covering 11 decades in frequency were measured and a detailed and unambiguous analysis of the temperature dependence was conducted.
Abstract: We have measured the dielectric relaxation times of the α process of phenyl salicylate (salol) covering 11 decades in frequency. Being representative for the class of low molecular weight organic glass forming materials, the highly resolved temperature dependence of the dynamics in salol does not follow a particular function like the Vogel–Fulcher–Tammann (VFT) law over the entire accessible range of temperatures. In order to conduct a detailed and unambiguous analysis of the temperature dependence, we take advantage of the derivatives of the experimental log(fmax) values with respect to temperature, which allow us to either linearize the frequently used temperature laws or to resolve subtle changes in fmax(T) by decreasing the number of free parameters. In this manner we observe that none of the common routes for rationalizing the dynamics like Arrhenius, VFT, Souletie scaling, and idealized mode‐coupling theory account for the experimental findings properly. However, we do observe a VFT behavior within the limits 265 K≤T≤320 K, i.e., for temperatures ranging from significantly above the glass transition at Tg=220 K to far above the melting point.

475 citations


Journal ArticleDOI
TL;DR: In this article, a copper mold casting method was used to construct a bulk glassy alloys with diameters of 0.5 and 1.0 mm, and the results showed that the maximum thickness for glass formation is about 10 times larger than the largest thickness for Fe-based alloys reported up to date.
Abstract: Bulk glassy Fe 73 Al 5 Ga 2 P 11 C 5 B 4 alloys in cylindrical form with diameters of 0.5 and 1.0 mm were found to form by a copper mold casting method. The further increase in diameter causes the formation of coexistent glassy, Fe 3 (B, C), Fe 2 B and Fe 3 P phases for the 1.5 mm ? sample and coexistent Fe 3 (B, C), Fe 2 B and Fe 3 P phases for the 2.0 mm ? sample. It is to be noticed that the maximum thickness for glass formation is about 10 times larger than the largest thickness for Fe-based glassy alloys reported up to date. The glass transition temperature (T g ), crystallization temperature (T x ) and heat of crystallization of the 1.0 mm ? glassy alloy are 732 K, 785 K and 3.76 kJ/mol, respectively. No appreciable difference in the thermal stability and magnetic properties is seen between the bulk glassy alloys and the melt-spun ribbon. The 1.0 mm ? glassy alloy has ferromagnetism with a Curie temperature of 606 K and exhibits 1.26 T for saturation magnetization (B s ), 82 A/m for coercivity (H c ) and 0.38 for the ratio of residual magnetization to B s at room temperature. The large ΔT x ( = T x - T g ) and large glass-forming ability can be obtained for the Fe-based alloy containing simultaneously the five solute elements. The effectiveness of the multiplication is presumably due to the combination of the following three effects ; (1) the suppression of crystalline nuclei due to the increase in dense random packing density for the glassy structure containing P, C and B with significantly different atomic sizes, (2) the difficulty of atomic rearrangements for the precipitation of the Fe-metalloid compounds caused by the generation of Al-metalloid pairs with strongly attractive bonding nature, and (3) the decrease in the preferential precipitation tendency of Fe-B and Fe-C compounds by the dissolution of Ga which is immiscible to B and C and soluble to Fe.

380 citations



Journal ArticleDOI
TL;DR: Differential scanning calorimetry (DSC) was used to determine the thermodynamic functions of the undercooled liquid and the amorphous phase with respect to the crystalline state of the Zr412Ti138Cu125Ni100Be225bulk metallic glass forming alloy as mentioned in this paper.
Abstract: Differential scanning calorimetry (DSC) was used to determine the thermodynamic functions of the undercooled liquid and the amorphous phase with respect to the crystalline state of the Zr412Ti138Cu125Ni100Be225bulk metallic glass forming alloy The specific heat capacities of this alloy in the undercooled liquid, the amorphous state and the crystal were determined The differences in enthalpy, ∆H, entropy, ∆S, and Gibbs free energy, ∆G, between crystal and the undercooled liquid were calculated using the measured specific heat capacity data as well as the heat of fusion The results indicate that the Gibbs free energy difference between metastable undercooled liquid and crystalline solid, ∆G, stays small compared to conventional metallic glass forming alloys even for large undercoolings Furthermore, the Kauzmann temperature, TK, where the entropy of the undercooled liquid equals to that of the crystal, was determined to be 560 K The Kauzmann temperature is compared with the experimentally observed rate-dependent glass transition temperature, Tg Both onset and end temperatures of the glass transition depend linearly on the logarithm of the heating rate based on the DSC experiments Those characteristic temperatures for the kinetically observed glass transition become equal close to the Kauzmann temperature in this alloy, which suggests an underlying thermodynamic glass transition as a lower bound for the kinetically observed freezing process

318 citations


Journal ArticleDOI
31 Mar 1995-Science
TL;DR: The connection between this boson peak and the fast dynamic process appearing near Tg is discussed, and the time-temperature superposition principle, which is valid for polymers on a macroscopic scale, is not applicable for temperatures approaching Tg.
Abstract: Recent neutron scattering experiments on the microscopic dynamics of polymers below and above the glass transition temperature T g are reviewed. The results presented cover different dynamic processes appearing in glasses: local motions, vibrations, and different relaxation processes such as α- and β-relaxation. For the α-relaxation, which occurs above T g , it is possible to extend the time-temperature superposition principle, which is valid for polymers on a macroscopic scale, to the microscopic time scale. However, this principle is not applicable for temperatures approaching T g . Below T g , an inelastic excitation at a frequency of some hundred gigahertz (on the order of several wave numbers), the "boson peak," survives from a quasi-elastic overdamped scattering law at high temperatures. The connection between this boson peak and the fast dynamic process appearing near T g is discussed.

298 citations


Journal ArticleDOI
01 Jan 1995-Polymer
TL;DR: In this article, a physically based, three-dimensional constitutive model was developed for simulating this wide range of features in models of polymer products and processes, and is therefore an example of a glass-rubber constitutive approach.

297 citations


Journal ArticleDOI
31 Mar 1995-Science
TL;DR: A class of electron transport polymers [poly(aryl acrylate) and poly(aryl ether)s] is reported in which moieties with high electron affinities are covalently attached to stable polymer backbones, leading to an enhancement in power efficiency and stability.
Abstract: Operating lifetime is the main problem that complicates the use of polymeric light-emitting diodes (LEDs). A class of electron transport (ET) polymers [poly(aryl acrylate) and poly(aryl ether)s] is reported in which moieties with high electron affinities are covalently attached to stable polymer backbones. Devices based on poly(p-phenylenevinylene) (PPV) prepared with these materials exhibited a 30-fold improvement in stability and, in one case, dramatically lower (10 volts versus about 30 volts) operating voltage relative to those having conventional ET layers. The current-carrying capacity of indium tin oxide-PPV-polymeric ET layer-aluminum LEDs was also increased by a factor of 30. These improvements lead to an enhancement in power efficiency of nearly an order of magnitude. Choosing polymers with high glass transition temperatures increases device lifetime.

Journal ArticleDOI
TL;DR: In this paper, a multicomponent Fe 72 Al 5 Ga 2 P 11 C 6 B 4 alloy was found to form a glassy phase with a wide supercooled liquid region before crystallization and of ferromagnetism at room temperature.
Abstract: A multicomponent Fe 72 Al 5 Ga 2 P 11 C 6 B 4 alloy was found to form a glassy phase with a wide supercooled liquid region before crystallization and of ferromagnetism at room temperature. The glass transition temperature (T g ), crystallization temperature (T x ) and temperature intervals of supercooled liquid, ΔT x (=T x -T g ) for the glassy alloy are 732, 793 and 61 K, respectively. It is to be noticed that the supercooled liquid region exceeds 60 K which is about 3 times larger than the largest ΔT x value for the Fe-based glassy alloys reported up to date. The amorphous alloy also exhibits good bending ductility and rather good soft ferromagnetic properties at room temperature. The soft magnetic properties are improved by annealing at temperatures above the Curie temperature (T c ). The magnetic properties at room temperature for the glassy alloy annealed for 600 s at 723 K are 605 K for T c , 1.07 T for saturation magnetization, 5.1 A/m for coercivity, 9000 for permeability at 1 kHz and 2.0 x 10 -6 for magnetostriction. The finding of the ductile Fe-based glassy alloy exhibiting simultaneously the wide supercooled liquid region and good soft ferromagnetic properties is expected to create a new ferromagnetic bulk material with good deformability.

Journal ArticleDOI
TL;DR: In this paper, the physical properties of the ionic conductor, obtained by dissolution of lithium trifluoromethanesulphonylimide in polyethylene oxide, (PEO)nLi+((CF3SO2)2N)- have been investigated for several values of n. The phase diagram has been established from both DSC and NMR techniques.
Abstract: The physical properties of the ionic conductor, obtained by dissolution of lithium trifluoromethanesulphonylimide in polyethylene oxide, (PEO)nLi+((CF3SO2)2N)- have been investigated for several values of n. The phase diagram has been established from both DSC and NMR techniques. The diffusion coefficients of 7Li and 19F containing Species, determined by the pulsed magnetic field gradient (PMFG) technique, are interpreted as the measures of the cationic and anionic transport numbers, which are concentration dependent, and t+ reaches a value close to 0.3. This study is complemented by a systematic analysis of the behaviour of the 7Li relaxation time T1 versus temperature and concentration which is correlated to the glass temperature Tg.

Journal ArticleDOI
TL;DR: In this article, a good correlation between the glass transition temperature and the overall mean bond energy of a covalent network of a glass was found for 186 binary and ternary chalcogenide glasses.
Abstract: Good correlation between the glass-transition temperature, T g , and the overall mean bond energy, 〈 E 〉, of a covalent network of a glass was found for 186 binary and ternary chalcogenide glasses. This correlation satisfies the Arrhenius relation for viscosity where the apparent activation energy of viscosity, E μ , is empirically related to the overall mean bond energy. The chemical bond arrangement is probably the main factor influencing T g in chalcogenide glasses.

Journal ArticleDOI
TL;DR: In this paper, the segmental orientation in unoriented polyester films induced by argon ion laser irradiation has been followed and an irradiation-dependent order parameter for the cyanoazobenzene mesogens calculated.
Abstract: New side-chain liquid crystalline polyesters have been prepared by melt transesterification of diphenyl tetradecanedioate and a series of mesogenic 2-[ω-[4-[(4-cyanophenyl)azo]phenoxy]alkyl]-1,3-propanediols, where the alkyl spacer is hexa-, octa-, and decamethylene in turn. The polyesters have molecular masses in the range 5000-89 000. Solution 13 C NMR spectroscopy has been employed to identify carbons of polyester repeat units and of both types of end groups. Polyester phases and phase transitions have been investigated in detail by polarizing optical microscopy and differential scanning calorimetry for the hexamethylene spacer architecture with different molecular masses. Using FTIR polarization spectroscopy, the segmental orientation in unoriented polyester films induced by argon ion laser irradiation has been followed and an irradiation-dependent order parameter for the cyanoazobenzene mesogens calculated. FTIR is also utilized to follow the temperature-dependent erasure of the induced orientation. Optical storage properties of thin unoriented polyester films are examined through measurements of polarization anisotropy and holography. A resolution of over 5000 lines/mm and diffraction efficiencies of about 40% have been achieved. Lifetimes greater than 30 months for information stored have been obtained, even though the glass transition temperatures are about 20 °C. Complete erasure of the information can be obtained by heating the films to about 80 °C, and the films can be reused many times without fatigue.

Journal ArticleDOI
TL;DR: In this paper, an exponential increase of molecular mobility and decrease of viscosity were shown to govern time-dependent structural transformations such as stickiness and collapse in food processing and storage.


Journal ArticleDOI
TL;DR: In this paper, the changes of dynamic mechanical properties during thermal degradation indicated a shift of the glass transition temperature (Tg) to higher temperatures and a decrease in the peak value of the dynamic loss factor with an increasing of aging time.
Abstract: Using dynamic mechanical analysis (DMA) we have studied thermal degradation for a system containing a diglycidyl ether of bisphenol A (DGEBA) and 1,3-bisaminomethylcylohexane (1,3-BAC). The changes of dynamic mechanical properties during thermal degradation indicated a shift of the glass transition temperature (Tg) to higher temperatures and a decrease in the peak value of the dynamic loss factor (tan δ) with an increasing of aging time. The value of dynamic storage modulus (E′) at the rubbery state showed an increase with aging time, whiteE′ at the glassy state only underwent a moderate change with increased thermal degradation. From these results it can be argued that thermal degradation during the stage prior to the onset of the severe degradation involves structural changes in the epoxy system, as further crosslinking and loss of dangling chains in the crosslinked network.

Journal ArticleDOI
TL;DR: In this article, the authors reported the production of full strength compacts of metallic glass by warm extrusion of powders at the supercooled liquid state just above the glass transition temperature.
Abstract: We report the production of full strength compacts of metallic glass by warm extrusion of powders at the supercooled liquid state just above the glass transition temperature. The alloy used was Zr65Al10Ni10Cu15 (at. %) which has the lowest viscosity among Zr‐based metallic glasses with large supercooled liquid region. The tensile strength and Young’s modulus of the glassy powder compacts were 1520 MPa and 80 GPa, respectively, which are similar to that obtained in the as‐cast bulk alloy and melt‐spun ribbon. This opens up possibilities of producing high strength amorphous alloys with complex shapes.

Journal ArticleDOI
01 Jan 1995-Polymer
TL;DR: In this paper, structural changes in nylon-6 fibres were analysed using X-ray diffraction (X.r.d) and optical birefringence measurements.

Journal ArticleDOI
TL;DR: In this article, a new evaluation method for modulated temperature-DSC measurements based on linear response theory is presented, which yields a complex heat capacity with a real part (storage heat capacity) and an imaginary part (loss heat capacity).

Journal ArticleDOI
TL;DR: In this article, a twin-screw cooker extruder was used to extrude granular particles of gluten, wheat starch, and waxy maize starch, conditioned to a range of moisture contents.

Journal ArticleDOI
TL;DR: The connection between the anharmonicity in these modes, vibrational localization, the Kauzmann temperature, and the fragility of the liquid is proposed as the key problem in glass science.
Abstract: In this paper I review the ways in which the glassy state is obtained both in nature and in materials science and highlight a "new twist"--the recent recognition of polymorphism within the glassy state. The formation of glass by continuous cooling (viscous slowdown) is then examined, the strong/fragile liquids classification is reviewed, and a new twist-the possibility that the slowdown is a result of an avoided critical point-is noted. The three canonical characteristics of relaxing liquids are correlated through the fragility. As a further new twist, the conversion of strong liquids to fragile liquids by pressure-induced coordination number increases is demonstrated. It is then shown that, for comparable systems, it is possible to have the same conversion accomplished via a first-order transition within the liquid state during quenching. This occurs in the systems in which "polyamorphism" (polymorphism in the glassy state) is observed, and the whole phenomenology is accounted for by Poole's bond-modified van der Waals model. The sudden loss of some liquid degrees of freedom through such weak first-order transitions is then related to the polyamorphic transition between native and denatured hydrated proteins, since the latter are also glass-forming systems--water-plasticized, hydrogen bond-cross-linked chain polymers (and single molecule glass formers). The circle is closed with a final new twist by noting that a short time scale phenomenon much studied by protein physicists-namely, the onset of a sharp change in d /dT ( is the Debye-Waller factor)--is general for glass-forming liquids, including computer-simulated strong and fragile ionic liquids, and is closely correlated with the experimental glass transition temperature. The latter thus originates in strong anharmonicity in certain components of the vibrational density of states, which permits the system to access the multiple minima of its configuration space. The connection between the anharmonicity in these modes, vibrational localization, the Kauzmann temperature, and the fragility of the liquid is proposed as the key problem in glass science.

Journal ArticleDOI
TL;DR: In this paper, the effects of glass transition on the rates of collapse of non-crystallizing carbohydrates were investigated, where the authors measured the decrease in bulk specific volume (V) as a function of temperature and moisture content.

Journal ArticleDOI
TL;DR: In this article, a tetrapyridyl species and a diacid is shown to counteract the reversibility of the hydrogen bonding between carboxylic acids and pyridines, which can be used as a means of chain extension.
Abstract: Hydrogen bonding between carboxylic acids and pyridines can be used as a means of chain extension. However, the reversibility of hydrogen bond formation does not allow the chain-extended structure to be fixed, and a temperature-dependent chain length results. Complexation between a tetrapyridyl species and a diacid is shown to counteract the reversibility of the hydrogen bonding. These complexes form thermoreversible three-dimensional supramolecular networks which have properties typical of low molar mass materials at high temperatures but polymeric properties at low temperatures. The complexes exhibited a glass transition and could form fibers from the melt yet exhibited a low-viscosity isotropic liquid at elevated temperatures. Atypically, a complex incorporating a 2,2',6,6'-tetrasubstituted biphenyl moiety was found to be liquid crystalline.

Journal ArticleDOI
TL;DR: In this article, the structure and dynamics of fluid films confined to a thickness of a few molecular diameters are described, and a power law is found for a wide range of parameters, and extends to lower and lower velocities as a glass transition is approached.
Abstract: Simulations of the structure and dynamics of fluid films confined to a thickness of a few molecular diameters are described. Confining walls introduce layering and in-plane order in the adjacent fluid. The latter is essential to transfer of shear stress. As the film thickness is decreased, by increasing pressure or decreasing the number of molecular layers, the entire film may undergo a phase transition. Spherical molecules tend to crystallize, while short-chain molecules enter a glassy state with strong local orientational and translational order. These phase transitions lead to dramatic changes in the response of the film to imposed shear velocities v. Spherical molecules show an abrupt transition from Newtonian response to a yield stress as they crystallize. Chain molecules exhibit a continuously growing regime of non-Newtonian behavior where the shear viscosity drops as v−2/3 at constant normal load. The same power law is found for a wide range of parameters, and extends to lower and lower velocities as a glass transition is approached. Once in the glassy state, chain molecules exhibit a finite yield stress. Shear may occur either within the film or at the film/wall interface. Interfacial shear dominates when films become glassy and when the film viscosity is increased by increasing the chain length.

Journal ArticleDOI
TL;DR: A series of poly(anhydride-co-imides) based on trimellitylimidoglycine (TMA-gly), pyromellitylimidoalanine (PMA-ala), sebacic acid (SA), or 1,6-bis(carboxyphenoxy)hexane (CPH) were synthesized by condensation polymerization as discussed by the authors.
Abstract: A series of poly(anhydride-co-imides) based on trimellitylimidoglycine (TMA-gly), pyromellitylimidoalanine (PMA-ala), sebacic acid (SA), or 1,6-bis(carboxyphenoxy)hexane (CPH) were synthesized by condensation polymerization. Monomers and polymers were characterized by NMR and IR spectroscopy, elemental and thermogravimetric analyses, and thermal transition temperatures. Contact angle, intrinsic viscosity, and compressive strength measurements were also performed on the polymers. For all polymer systems, the molecular weights decreased as the amount of imide in the backbone increased. Polymers containing CPH are more hydrophobic, have higher compressive strengths, have higher glass transition and decomposition temperatures relative to polymers containing SA, and exhibit no melting transitions. The mechanical and thermal stability of the materials are increased by the incorporation of imide groups in the polymer backbone. The selection of imide monomers, TMA-gly vs PMA-ala, can significantly affect the resulting polymer characteristics. Both imide monomers affect the hydrophobicity of the resulting polymers in similar ways, with the materials becoming more hydrophilic as the imide content is increased. However, polymers containing PMA-ala have thermal transition temperatures that are higher than the corresponding polymers with TMA-gly.

Journal ArticleDOI
TL;DR: Modulated differential scanning calorimetry (MDSC) as mentioned in this paper can measure the glass transition temperature largely independent of the thermal history (and the heating or cooling rates), but dependent on the modulation frequency.

Journal ArticleDOI
TL;DR: In this article, the authors used modulated differential scanning calorimetry (MDSC) to study simultaneously the evolution of heat flow and heat capacity for the isothermal cure of thermosetting systems.

Patent
Todd R. Williams1, Daniel J. Kingston1
18 Dec 1995
TL;DR: In this article, a microstructure bearing article is produced that includes the steps of molding the micro-structure on the base, curing the resin that forms the micro structure, and heat treating the microstructures.
Abstract: A method of producing a microstructure bearing article (11) that includes the steps of molding the microstructure (22, 24, 26, 28) on the base (34), curing the resin that forms the microstructure, and heat treating the microstructure. The heat treating is performed at a temperataure that is at least equal to a normal glass transition temperature of the resin. The heat treating raises the glass transition temperature of the resulting polymer above approximately 333 ° K such that groove tip impression is reduced. Such articles are useful in backlit displays (10) which are useful in computers and the like.