Glass Transition Temperature Measurements Research Articles

Poly(ethylene oxide)–LiX rubbery electrolytes with −X–X − disulfonamide anions having two or three ether groups in their structures

This work deals with poly(ethylene oxide), PEO–MX (M=Li, K and Cs) amorphous electrolytes with −X–X −, [CF 3SO 2NCH 2(CH 2OCH 2) 2CH 2NSO 2CF 3] 2− (EDSA) and [CF 3SO 2NCH 2CH 2(CH 2OCH 2) 3CH 2CH 2NSO 2CF 3] 2− (TTSA) disulfonamide anions. These dianions have X − end-groups identical to anions [CF 3SO 2N(CH 2) 2OCH 3] − (MESA) and [CF 3SO 2N(CH 2) 3OCH 3] − (MPSA), one of which (MPSA) was reported to yield chelate-like associated species (presumably LiX 2 − triplets) at concentrations above EO/Li=20 in PEO. This feature of LiMPSA, evidenced through glass transition temperature ( T g) measurements, does not apply to Li 2EDSA and Li 2TTSA. Though none of these lithium salts form crystalline intermediate compounds with PEO, the limit of solubility of LiMESA (EO/Li=16) does not allow a clarification of this point for this salt. At lower concentrations, however, a conductivity comparison with the potassium and caesium salts shows that the apparent degree of dissociation ( α= C Li+/ C Li) of LiMESA is comparable to that of LiMPSA. As opposed to both these salts and to some extent to Li 2EDSA, a much greater dissociation takes place for Li 2TTSA, the anion of which contains an inner, third ether group in its structure.

Neutron scattering and thermal measurements on the superionic-conducting Ag 2S–AgPO 3 glass system

Superionic-conducting glasses (Ag 2S) x (AgPO 3) 1− x with x=0.1, 0.2, 0.3, 0.5, 0.7, 0.8 and 0.9 have been prepared by rapid quenching methods, although for x=0.8 and 0.9 they also contain crystalline Ag 2S. We report DTA measurements of the thermodynamic glass transition temperature, T g, and neutron diffraction data taken as a function of temperature through T g. The neutron measurements show no prepeak at any composition or temperature, indicating that there is no clustering, in contrast with the AgI–AgPO 3 system where clustering is found with a length scale of order 10 Å [1]. Both systems form superionic-conducting glasses, showing that clustering is not essential for such conductivity.

Verification of the chemical composition and specifications of haemodialysis membranes by NMR and GPC-FTIR-coupled spectroscopy

The chemical composition of a dialysis membrane is decisive towards determining its physical and biochemical properties—two fundamental determinants of the success of therapy offered to patients suffering from chronic renal failure. From the vast variety of synthetic polymers available, only a few are suitable for the manufacture of dialysis membranes that have to conform to the diverse demands of modern haemodialysis and related therapies. Recently, a membrane labelled as polyamide (Polyamide S™) has caused some confusion to end-users in that the product specification for the membrane is given as ‘polyarylethersulfone’ or simply as Polyamide S membrane. As the chemical and physical properties of these two polymer types are distinctly different, it is unclear whether the functional characteristics of Polyamide S™ are to be attributed to polyamide, polyarylethersulfone, or, to both polymers. We therefore undertook investigations to ascertain the exact chemical nature of the Polyamide S™ membrane using a series of chemical analytical tools and an appropriate polyamide reference. The analytical techniques were conventional gel permeation chromatography (GPC), GPC-FTIR coupled spectroscopy using dimethyl acetamide and hexafluoroisopropanol as solvents and nuclear magnetic resonance spectroscopy. Glass transition temperature measurements and quantitative elemental analysis were also carried out. None of the analytical techniques used showed any traces of polyamide in Polyamide S™; no aliphatic or aromatic polyamide chemical entities were detected in any of the samples tested. The Polyamide S™ dialysis membrane thus comprises, solely, of polyarylethersulfone, which is also known as polyethersulfone.

Molecular Dynamics Simulation of Bulk Atactic Polystyrene in the Vicinity of Tg

Molecular dynamics (MD) simulations of bulk atactic polystyrene have been performed for chains up to 320 monomer units in a temperature range from 100 to 600 K and in a broad pressure range from 0.1 to 1000 MPa. The MD-determined specific volume vs temperature curves are in a good agreement with experimental PVT data at different values of applied pressure, but the measured glass-transition temperature, Tg, is displaced to somewhat higher temperature than the longer time experimental value. Local translational mobility has been investigated by measuring the mean-square translational displacements of monomers as a function of time. The long-time asymptotic slope of these dependencies is close to 0.6 at T > Tg, showing diffusive behavior. The cage effect, when local translational motions are essentially frozen in the glassy state, has been studied. The characteristic time of cage release does not depend on molecular weight, but the duration of the crossover to the diffusive regime increases almost linearly with increasing chain molecular weight, for both the backbone monomers and phenyl side groups.

Enthalpy relaxation studies of celecoxib amorphous mixtures.

The purpose of this study was to compare the structural relaxation and molecular mobility of amorphous celecoxib (CEL) with that of CEL amorphous mixtures consisting of various excipients and to study the effect of different excipients on the relaxation of high-energy amorphous systems. The measurement of glass transition temperatures (Tg) and enthalpy relaxation were performed using differential scanning calorimetry. The interactions between drug and excipients and the absence of crystalline forms were further confirmed by conducting Fourier transform infrared spectroscopic and X-ray powder diffraction studies on same samples. All samples exhibited a single Tg value. Polymers had a prominent effect on the lowering of the relaxation rate in amorphous CEL. The lowering of the rate of relaxation was directly dependent on the concentration and type of polymer used. The total enthalpy required for relaxation was same, although additives affected the rate of relaxation. In absence of any specific interactions during Fourier transform infrared studies, it was concluded that the antiplasticizing activity of polymers is responsible for the stabilization of CEL amorphous systems. Glassy amorphous dispersions of CEL exhibited a complex type of relaxation pattern, which failed to fit in Kohlrausch-Williams-Watts equation with respect to calculation of relaxation time constants.

Microthermal analysis of polymeric materials

The technique of scanning thermal microscopy (SThM) with microthermal analysis (μTA) was used for examining the surface thermal properties of a wide selection of materials ranging from poorly thermal conducting polymers to highly conductive metals. We discuss μTA results in comparison with the data collected from conventional methods of thermal analyses, namely, differential scanning calorimetry (DSC) and thermomechanical analysis (TMA). The μTA measurements of melting and glass transition temperatures were conducted using a wide range of heating rates. We demonstrated that the trends observed were consistent with concurrent measurements by DSC. From the comparison of the μTA and TMA results, we concluded that the thermomechanical contribution, which is due to a variable physical contact area for a “sinking” tip, was dominant in the microthermal response of polymers.

Low‐energy electron beam‐induced cationic polymerization with onium salts

Demand for higher polymer performance with very short cure times has resulted in the development of low energy electron beam processes. This article presents the results of such a process for curing two epoxy systems, namely 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate and di-glycidyl ether of bisphenol A (DGEBA), using the cationic photoinitiator salts, triarylsulfonium hexafluoroantimonate, and diaryliodonium hexafluoroantimonate, respectively. Glass transition temperature measurements were done using a modulated DSC method while the degree of conversion was measured using FTIR spectroscopy. Results indicate that for both epoxy systems a relatively low dosage of not more than 5 Mrad was sufficient to achieve up to 60% conversion, with up to 80% conversion achievable using 30 Mrad. The diaryliodonium salt appeared to be more effective than the sulphonium salt in the above study. The effect of varying photoinitiator concentration and the resulting glass transition temperature has been studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3099–3108, 2001

A study of amorphous molecular dispersions of indomethacin and its sodium salt

Amorphous solid dispersions of indomethacin (IMC) and sodium indomethacin (NaIMC) over a range of compositions were prepared by physically mixing amorphous IMC and amorphous NaIMC, as well as by coprecipitation from methanol solution. Measurement of glass transition temperatures, Tg, for the physical mixtures revealed two values indicating, as expected, phase separation. In contrast, all samples of coprecipitated materials exhibited one value of Tg, which was greater than that predicted for ideal miscibility in the formation of a molecular dispersion. Such nonideality suggests a stronger acid‐salt interaction in the amorphous state than that between acid‐acid and salt‐salt. FTIR spectroscopic analysis provides evidence for interactions between NaIMC and IMC through a combination of hydrogen bonding and ion‐dipole interactions between the carboxylic group of the acid and the carboxylate anion of the salt. The inhibition of isothermal crystallization of IMC by NaIMC only when in molecular dispersion is believed to result from the interaction between the acid and the salt, which prevents the formation of hydrogen‐bonded carboxylic acid dimers for IMC, required for the formation of crystal nuclei and crystallization. © 2001 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:1991–2004, 2001

Low‐energy electron beam‐induced cationic polymerization with onium salts

AbstractDemand for higher polymer performance with very short cure times has resulted in the development of low energy electron beam processes. This article presents the results of such a process for curing two epoxy systems, namely 3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate and di‐glycidyl ether of bisphenol A (DGEBA), using the cationic photoinitiator salts, triarylsulfonium hexafluoroantimonate, and diaryliodonium hexafluoroantimonate, respectively. Glass transition temperature measurements were done using a modulated DSC method while the degree of conversion was measured using FTIR spectroscopy. Results indicate that for both epoxy systems a relatively low dosage of not more than 5 Mrad was sufficient to achieve up to 60% conversion, with up to 80% conversion achievable using 30 Mrad. The diaryliodonium salt appeared to be more effective than the sulphonium salt in the above study. The effect of varying photoinitiator concentration and the resulting glass transition temperature has been studied. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3099–3108, 2001

Interlaboratory Tests on Polymers by Differential Scanning Calorimetry (DSC): Determination of Glass Transition Temperature (Tg)

The present report presents results obtained from an interlaboratory test. 28 participants, mainly from industry and research institutes, measured glass transition temperatures (Tg) by differential scanning calorimetry (DSC) on four different polymers. The materials used were poly(methyl methacrylate) (PMMA), polycarbonate (PC), polysulfone (PSU) and amorphous polyamide (PA 6I/6T). The measured data were collected by EMPA and were evaluated using a robust statistical method. Repeatability and reproducibility data were of special interest. The repeatability limit (r) of glass transition temperatures measured according to DIN 53765 was found in the region of 1–2°C, and the reproducibility limit (R) was around 3–4°C. In addition to the DIN standard, the set of interlaboratory test data was evaluated and considered according to some different approaches and was correlated with data from other EMPA interlaboratory tests performed previously. It was shown that the investigated statistical parameter was always in a similar dimension. The data of the PA sample were found to be an exception. Due to the hygroscopic character of polyamide, the r and R values increase sharply, to an almost three times higher reproducibility limit. Overall, the evaluated data can be used to estimate the results of own and external Tg measurements and their compatibility. The report should therefore support daily work in analytical laboratories where glass transition temperatures are measured by DSC.

In situ high-pressure and high-temperature bubble growth in silicic melts

We present the first investigation of in situ high-pressure and high-temperature bubble growth in silicic melts. In a hydrothermal diamond-anvil cell, a haplogranite melt (79 wt% SiO2) is hydrated then subjected to cooling and decompression. With decreasing pressure, water exsolves from the melt and bubbles grow. The whole experiment is observed through an optical microscope and video-recorded, so that bubble nucleation, bubble growth, and the glass transition are directly monitored. Bubbles nucleate and expand in melt globules having radii from 15 to 70 μm. Bubbles reached 3.6–9.1 μm in radius within 6.1–11.7 s (until the glass transition is attained) while temperature decreases from 709–879°C to 482–524°C, corresponding to decompressions from 7.0–21.9 to 3.4–15.2 kbar. Bubbles nucleated either in a single event occurring within the first second or in successive pulses over a period of up to 7 s when the melt globules are in contact with a diamond culet of the cell. In these experiments, bubble growth can be fitted to the cube root or a logarithm of time, mainly ascribable to the combination of large water oversaturations due to rapid cooling and decompression. At pressures of 3.4–15.2 kbar, we measure glass transition temperatures that are 20–80°C higher than those calculated at atmospheric pressure.

Composite natural rubber-polychloroprene latex particles produced by the heterocoagulation technique

Composite natural rubber (NR) based latex particles were prepared using the heterocoagulation technique. A nonionic surfactant (Tween 80) whose molecules bear poly(ethylene oxide) (PEO) was adsorbed on polychloroprene (CR) latex particles and allowed to form complexes between PEO and indigenous surfactant (protein–lipid) on the NR particle surface. The heterocoagulated NR/CR–Tween particles produced were characterised by particle size, zeta-potential and glass-transition temperature measurements and the data indicated the presence of CR–Tween on the outer layer of the composite polymer particles. The results agreed well with the better oil resistance of films cast from heterocoagulated latex when compared with that of the NR film.

Change of glass transition temperature of polymers containing gas

The industries use polymer materials for many purposes for they have many merits. The costs of these materials take up too great a proportion of the overall cost of products that use these materials as their major material. It is advantageous for polymer industries to reduce these costs. The microcellular foaming process was developed in the early 1980s to solve this problem and has proved to be quite successful. Microcellular foaming process uses inert gases such as CO 2, N 2. As these gases solve into polymer matrices, many properties are changed. Glass transition temperature is one of these properties. DSC, DMA are devices that measure glass transition temperature, but these are not sufficient to measure the temperature of a polymer containing gas. In this paper, we devised a new tester that uses magnetism. We used this new device to acquire data on the changed glass transition temperature and make a new model that can predict the change of glass transition temperature as a function of quantity of gas. Using this new model, the change of glass transition temperature can be estimated as a function of weight gain of gas. The new model proved that Chow's model is inappropriate to predict the change of glass transition temperature of polymer matrices containing gas.

The development of novel functionalised aryl cyanate esters. Part 2. Mechanical properties of the polymers and composites

Carbon fibre preimpregnated tape (prepreg) was prepared from a range of prepolymers comprising several different blends of alkenyl-functionalised cyanate ester (CE) monomers with commercial CE and bismaleimide (BMI) monomers and blends. Carbon fibre composites were prepared by autoclave moulding. Dynamic mechanical thermal analysis (DMTA) was used to assess cure cycles by the measurement of glass transition temperatures (Tg). Mechanical properties are reported for neat resins and compared with the corresponding composite properties such as interlaminar shear strength, flexural strength, compressive strength and mode I fracture toughness (GIC). By incorporation of alkenyl-functionalised CE monomers into CE/BMI blends it is possible to raise the value of Tg while maintaining levels of GIC (when compared with an unmodified BMI/CE blend) and without leading to a degradation in other mechanical properties. This enhancement in neat resin fracture toughness was translated into the corresponding composite. For example, a novel modifier 5rPOCN, at an incorporation level of 15% by weight, produces a composite with Tg=170°C, interlaminar shear strength 113MPa and GIC=513J/m2, comparable with reported thermoplastic-toughened CE composites.

The measurement of the glass transition temperature of sucrose and maltose solutions with added NaCl

The measurement of the glass transition temperature of sucrose and maltose solutions with added NaCl

Structural Properties of GexSe1-x Thin Films Prepared by Semi-closed Space Technique

Bulk and thin film GexSe1-x alloys have been prepared with 0.1≤X≤0.5. The bulk materials were obtained by quenching from the melt. They have been used as source materials to produce thin film samples using the thermal evaporation method (semi-closed space technique). The composition of the obtained films was checked against the bulk ones by X-ray fluorescence (XRF) technique. X-ray diffraction patterns of the obtained compositions revealed the presence of some crystalline inclusions in the amorphous matrix for some compositions. Glass transition temperature measurements showed a maximum in the range X=0.25 to 0.32 where the glass forming ability is optimum. Measurements of the temperature dependence of the steady state dark current as a function of the Ge content has been recorded during heating and cooling cycles. A compensation effect has been found and characterized with two compensation temperatures, during the cooling cycle. Optical transmission, (UV) and infrared (IR), measurements have been performed. Energy band gap, width of the band tail and the refractive index have been calculated. Results have been interpreted in terms of the structural behavior of the samples under investigation in view of the models presented in literatures.

Glass transition temperatures of hydrocarbon blends: Adhesives measured by differential scanning calorimetry and dynamic mechanical analysis

A comparison of calculated and measured glass transition temperatures of a series of three-component hydrocarbon blends was performed. The blends were prepared as mixtures of an elastomer with different proportions of tackifying resin and oil. Glass transition temperature, Tg, was measured by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) at four measurement frequencies. Most of these blends had pressure-sensitive adhesive (PSA) properties, and were used to prepare a series of PSA tapes. The adhesion of the PSA tapes was shown to be strongly dependent on Tg. Tack of PSA tapes was measured at two different temperatures, and shown to be directly correlated to the blend Tg. Several predictive methods for blend Tg that are based on individual component Tgs were evaluated. The prediction of blend Tg is far more accurate if the individual component Tg values are determined by DMA instead of DSC. In addition, the Gordon-Taylor equation gave a significant improvement on predicted blend Tg when compared to the Fox equation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 826–832, 2000

Selective plasticization in electroluminescent block copolymers

Differential scanning calorimetry (DSC) measurements of glass transition temperature ( T g) and of changes in heat capacity at T g have been made on a series of electro-optically active alternating block copolymers of systematically varying hard and soft block structures and of their blends with the plasticizer, 1,12-dibromododecane (DBDD) in order to assess the nature of phase separation in these copolymers.

Effect of CO 2 treated polycarbonate membranes on gas transport and sorption properties

The effect of polycarbonate (PC) membranes treated with super critical carbon dioxide on gas sorption and transport properties was studied. It was found that the gas permeability of PC membranes hardly changed after the CO 2 treatment. However, the gas sorption and diffusion properties showed a significant change. The transport properties were determined by measuring the sorption and permeation properties. The oxygen and nitrogen sorption measurements were carried out at 35°C over the pressure range of 1–25 atm. It was found that exposed CO 2 treatment hardly changed the gas permeability but slightly increased the selectivity of oxygen to nitrogen. This study also showed that the increase in gas solubility was contributed by increasing Langmuir-type sorption of CO 2 treated membranes rather than Henry-type sorption. The change in polymer packing of membrane was evidenced by glass transition temperature measurements. This study showed that the free volume of membranes increased with the increase of exposed CO 2 density.

Water transport in crosslinked 2-hydroxyethyl methacrylate

Water transport in crosslinked 2-hydroxyethyl methacrylate (HEMA) was investigated. Crosslinked HEMA was irradiated by gamma ray in vacuum for this study. The sorption data of de-ionized water transport in crosslinked HEMA subjected to various gamma ray dosages are in excellent agreement with Harmon's model which accounts for Case I, Case II, as well as the anomalous transport processes. The diffusion coefficient for Case I transport and velocity for Case II transport satisfy the Arrhenius equation for all dosages. The transport process was exothermic and the equilibrium-swelling ratio satisfied the van't Hoff plot. The pH value of de-ionized water after the sorption/de-sorption treatment of the irradiated crosslinked HEMA specimen was analyzed. The transmittance of irradiated crosslinked HEMA treated by de-ionized water was also studied. The effect of irradiation on the polymer chains was revealed by the measurement of glass transition temperature and the quantitative determination of water structures in crosslinked HEMA hydrogel. The UV cut-off wavelength of crosslinked HEMA shifted to longer wavelength side with increasing irradiation dosage, but the trend of transmittance after water treatment was opposite. The effect of specimen thickness on water transport was also studied.