Glass Transition Temperature In Range Research Articles

Effect of magnetic and thermal properties of iron oxide nanoparticles (IONs) in nitrile butadiene rubber (NBR) latex

Nitrile butadiene rubber (NBR) gloves are one of the most important personal protective equipments but they are possible to tear off and contaminate food or pharmaceutical and healthcare products during manufacturing and packaging process. High tendency of torn glove remaining in food or products due to white or light flesh-coloured glove is not easy to be detected by naked eyes. In this paper, iron oxide nanoparticles (IONs) selected as additive for NBR to improve its detectability by mean of magnetic properties. IONs synthesized via precipitation method and compounded with NBR latex before casting on petri dish. The properties of IONs were investigated by X-ray Diffractometry (XRD), Transmission Electron Microscope (TEM), Raman Spectroscopy and Vibrating Sample Magnetometer (VSM). Meanwhile NBR/IONs composites were studied by Thermogravimetry Analysis (TGA), Differential Scanning Calorimetry (DSC) and Vibrating Sample Magnetometer (VSM). It observed that, synthesized IONs shows of 25.28nm crystallite with 25.86nm semipherical (changed as) shape. Meanwhile, Magnetite and maghemite phase are found in range of 670cm−1 and 700cm−1 respectively, which it contributes magnetization saturation of 73.96emu/g at 10,000G by VSM. Thermal stability and magnetic properties were increased with incorporating IONs into NBR latex up to 20phr. NBR/IONs 5phr has the optimum thermal stability, lowest glass transition temperature (−14.83°C) and acceptable range of magnetization saturation (3.83emu/g at 10,000G) to form NBR gloves with magnetic detectability.

Phosphazene High Polymers and Models with Cyclic Aliphatic Side Groups: New Structure–Property Relationships

Poly(dichlorophosphazene) is a versatile precursor material for accessing new polymeric materials via the introduction of various side groups by chlorine replacement reactions. Herein, methods are described for the synthesis of a new series of phosphazene single- and mixed-substituent high polymers containing cyclic aliphatic rings, −CnH2n–1 (where n = 4–8). These reactions were preceded by model reactions using small molecule cyclic trimeric phosphazenes. The new high polymers are amorphous, transparent, and film- and membrane-forming materials with a wide range of glass transition temperatures (−60 to +40 °C) depending on the side groups and cosubstituents. All are hydrophobic and resistant to hydrolytic breakdown.

Gradient Methylidene-Ethylidene Copolymer via C1 Polymerization: an Ersatz Gradient Ethylene-Propylene Copolymer.

We report the first synthesis of a gradient methylidene-ethylidene copolymer via a living C1 polymerization. The copolymer has a similar chemical structure as the corresponding ethylene-propylene copolymer. To achieve this goal a new and convenient source of the ethylide monomer, diethylsulfoxonium ethylide, was developed for the introduction of the methyl branch in the polymer backbone. The gradient copolymer contains a gradual change of instantaneous methyl branch content from 0% on one end of the polymer chain to 63% on the other end. Thermal analysis revealed that the gradient copolymers have a narrow glass transition temperature range with values intermediate between those of linear polyethylene and atactic polypropylene.

Quasi-isothermal and heat–cool protocols from MT-DSC

Understanding the evolution of the cooperative molecular mobility as a function of time and temperature remains an unsolved question in condensed matter physics. Many recent works concern the question of the molecular dynamic slowdown in a temperature domain ranging from the crossover temperature T c (beginning of cooperative relaxation) down to the calorimetric glass transition temperature T g. Recent studies have shown that the estimation of cooperativity length based on calorimetric investigations using Donth’s approach can be extended to a wider temperature range from T g to T c. To describe the relaxation time evolution and the characteristic length evolution of cooperative motions, besides the Donth’s fluctuation approach other models exist in the literature such as “4 points correlation function” model. Whatever the model used, calorimetric investigations are needed to estimate the heat capacity as a function of the temperature. In this work, we have focused our attention on the modulated temperature differential scanning calorimetry (MT-DSC) experiments and we have tested different MT-DSC protocols allowing the heat capacity determination. For this goal we decided to work on different amorphous glass formers in order to cover a large range of glass transition temperature. The influence of the protocol used on the cooperativity length calculation is discussed in detail. Lissajous figures were constructed to verify whether the steady state is reached.

Is ergodicity in an oxide glass ionic conductor a matter of time?

From the results of molecular dynamic simulations of lithium metasilicate glass–at temperatures above and below their transition temperature (Tg)–we propose a simple graphical representation to search for the broken ergodicity in an ionic oxide glass. Knowing when ergodicity is lost is critical for the proper use of statistical mechanics as a tool for measuring dynamical and structural properties through molecular dynamic simulation. This work shows how an abrupt qualitative transformation occurs in the way the system explores its possible states when it goes down below the glass transition temperature range. We revise the broken ergodicity phenomena through its relationship with the observation time and the dynamic diversity of their atoms.

Effect of free surface roughness on the apparent glass transition temperature in thin polymer films measured by ellipsometry.

Ellipsometry is one of the standard methods for observation of glass transition in thin polymer films. This work proposes that sensitivity of the method to surface morphology can complicate manifestation of the transition in a few nm thick samples. Two possible mechanisms of free surface roughening in the vicinity of glass transition are discussed: roughening due to lateral heterogeneity and roughening associated with thermal capillary waves. Both mechanisms imply an onset of surface roughness in the glass transition temperature range, which affects the experimental data in a way that shifts apparent glass transition temperature. Effective medium approximation models are used to introduce surface roughness into optical calculations. The results of the optical modeling for a 5 nm thick polystyrene film on silicon are presented.

From fatty acid and lactone biobased monomers toward fully renewable polymer latexes

Novel waterborne polymeric materials based on renewable resource monomers have been prepared by the environmentally friendly miniemulsion polymerization of an oleic acid-derivative monomer (MOA) and the α-methylene-γ-butyrolactone (α-MBL). The effect of the incorporation of different amounts of α-MBL on kinetics and polymer microstructure is investigated. The estimation of the monomer reactivity ratios (rα-MBL = 0.49 and rMOA = 1.26) shows the slight lower reactivity of the α-MBL, resulting in a random copolymer moderately enriched with MOA at the beginning of the reaction. The thermal and mechanical properties of the polymers demonstrate that by incorporating the lactone it is possible to produce copolymers in a broad range of glass transition temperatures, with high thermal stability and improved mechanical properties. This study provides a new green route toward the bio-sourced preparation of polymer latexes with tuneable properties, which can range from coatings to adhesives. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 3543–3549

New side chain ferroelectric liquid crystalline polymers based on (2S, 3S)-2-chloro-3-methylpentanoic acid: synthesis and phase behaviour

The synthesis of four new chiral mesogenic monomers (M1–M4) and side chain ferroelectric liquid crystalline polymers containing (2S, 3S)-2-chloro-3-methylpentanoate is described. The chemical structures and phase behaviour of the monomers and polymers obtained in this study were characterised by Fourier transform infrared, proton nuclear magnetic resonance, polarising optical microscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction. The selective reflection of light was investigated with ultraviolet/visible (UV/Vis). Their structure–mesomorphism relationships were discussed. M1 and P1 all showed a chiral smectic C (SmC*) phase. M2 and M3 revealed a SmC* phase and cholesteric phase, while their corresponding polymers P2 and P3 revealed a SmC* phase and smectic A (SmA) phase. M4 only exhibited a cholesteric phase, whereas the corresponding polymers P4 showed a SmA phase. Moreover, the selective reflection of light shifted to the long-wavelength region at the SmC* phase range and to the short-wavelength region at the cholesteric range with increasing temperature, respectively. The results seemed to demonstrate that the tendency towards melting temperature (Tm), glass transition temperature (Tg), isotropic temperature (Ti) and mesophase range for the monomers and polymers increased by increasing the mesogenic core rigidity or the number of phenyl ring. The polymerisation effect could lead to higher liquid crystalline to isotropic phase transition temperature, wider mesophase range and more ordered smectic phase formed. In addition, all the obtained polymers had a very good thermal stability and the corresponding Td increased by increasing the number of phenyl ring.

Relation between temperature memory effect and multiple-shape memory behaviors based on polymer networks

The temperature memory effect (TME) refers to the capability of shape memory materials to memorize the deformation temperature (Td). In this article, the TME of multiple-shape memory polymer based on a PMMA/PEG semi-interpenetrating polymer network (PMMA/PEG semi-IPN) and a PMMA-PCL covalently crosslinked polymer co-network (PMMA-PCL CPN) are studied, and the relation between the TME and the multiple-shape memory effect (SME) is investigated. The results indicate that both the PMMA/PEG semi-IPN and PMMA-PCL CPN can show the TME in a specific range of response temperatures but not in its entire range of glass transition temperatures (Tg). This paper further confirms that broad transition temperature is the key to realizing the TME and the multiple-SME. Furthermore, we discover that the characteristic temperature of the TME corresponds to the multi-step transition temperature of the multiple-SME for the first time. Consequently, the characteristic temperature of the TME can be directly used as a multi-gradient Td to achieve the multiple-SME. Thus it facilitates the selection of a multi-gradient Td in the multiple-SME. The paper also reveals the internal relation of broad Tg, TME and multiple-SME of PMMA/PEG semi-IPN and PMMA-PCL CPN.

Mechanical Behaviors and Thermoforming Features of PMMA Used In-Mold Decoration

Mechanical behaviors and thermoforming features of plastic material PMMA-IRK-304 used in-mold decoration are studied in this paper. Dynamic mechanical analysis experiments, uniaxial tension tests at several high temperatures and different stretching velocity were carried out to analysis and explain the phenomenon of yielding, strain softening and strain hardening. Results showed that the glass transition temperature range of PMMA-IRK-304 films was suitable for thermoforming of in-mold decoration.

Synchronized Tandem Catalysis of Living Radical Polymerization and Transesterification: Methacrylate Gradient Copolymers with Extremely Broad Glass Transition Temperature.

Gradient copolymers with differential sequences linearly changing from methyl methacrylate (MMA) to dodecyl methacrylate (DMA) were efficiently synthesized by a concurrent tandem catalysis in the ruthenium-catalyzed living radical (co)polymerization coupled with the in situ transesterification of MMA with 1-dodecanol assisted by titanium isopropoxide [Ti(Oi-Pr)4]. The key is to perfectly synchronize the two reactions throughout the tandem catalysis by using molecular sieves (MSs), which facilitates the MMA transesterification into DMA by removing the resulting methanol. The MMA/DMA gradient copolymers had an extremely broad glass transition temperature range (i.e., hardly detectable by differential scanning calorimetry (DSC)), in sharp contrast to the random and the block counterparts of similar compositions.

Large-scale preparation of SiBN ceramic fibres from a single source precursor

Large-scale production of SiBN ceramic fibres was achieved by the pyrolysis of N-methylpolyborosilazane. This precursor was prepared by a three-step synthesis starting from hexamethyldisilazane (HMDS), silicon tetrachloride (STC), boron trichloride (BTC), and methylamine. To prove the feasibility of the synthesis on both the large and laboratory scales, the structure and composition of the as-synthesised polymer was characterised by Fourier transform infrared (FT-IR) and Nuclear Magnetic Resonance (NMR) spectroscopy and elemental analysis (EA). Differential scanning calorimetry (DSC) showed that the obtained large-scale polymer had a wide glass transition temperature range (32°C to 50°C) and a low transition temperature (40.41°C), making it suitable for melt spinning. Both the large- and lab-scale synthesised polymers were successfully processed into polymer green fibres by a melt spinning process under an inert atmosphere, as the synthesised polymer is air and moisture sensitive. Endless and crack-free green fibres above 1000m in length were successfully collected on a rotating spool, followed by cross-linking and thermolysis up to 1000°C in an ammonia atmosphere. The SiBN ceramic fibres are amorphous up to 1600°C in a nitrogen atmosphere. The presented results emphasise a feasible approach to highly thermally stable SiBN ceramic fibres on a large scale starting from a greatly flexible single-source precursor.

A Renewable Lignin–Lactide Copolymer and Application in Biobased Composites

The need for renewable alternatives to traditional petroleum-derived plastics has driven recent interest in biobased composite materials that are sourced from carbon-neutral feedstocks. Lignin, an abundant plant-derived feedstock, has been a candidate for renewable materials; however, it is often difficult to blend with other biopolymers. In order to improve the miscibility of lignin with other bioplastics, we developed a catalytic and solvent free method for synthesis of a lignin–PLA copolymer. Graft polymerization of lactide onto lignin catalyzed by triazabicyclodecene (TBD) resulted in a lignin-g-poly(lactic acid) copolymer; chain length of the PLA is controlled by varying of the lignin/lactide ratio and preacetylation treatment. End-group analysis reveals high grafting efficiency and preferential grafting on lignin aliphatic hydroxyls over phenolic hydroxyls. The lignin-g-PLA copolymers display a glass transition temperature range from 45 to 85 °C and multiphase melting behavior. The lignin-g-PLA copolymers are used as dispersion modifiers in PLA-based materials to enhance UV absorption and reduce brittleness without a sacrifice in the modulus of elasticity.

Physical Modelling and Identification of Polymer Viscoelastic Behaviour above Glass Transition Temperature and Application to the Numerical Simulation of the Hot Embossing Process

The experimental processing parameters, such as applied pressure and forming temperature have been analysed during polymer hot embossing of micro-cavities. The viscoelastic characteristics of polymer above the glass transition temperature have been investigated with the classical viscoelastic models. Generalized Maxwell Model has been used to describe polymer behaviours in the glass transition temperature range. The parameters include relaxation time, storage modulus and loss modulus of the Generalized Maxwell Model that have been introduced. The identification of polymer characteristics has been carried out through Dynamic Mechanical Analysis (DMA). The storage modulus, the loss modulus and the damping factor of the selected polymer have been obtained with different imposed frequencies. The master curve of complex modulus has been obtained by applying the time temperature superposition principle. The experimental data has been identified with optimized fitting parameters of Generalized Maxwell Model. A proper agreement between the experimental measurement and the identification of viscoelastic model is observed. The resulting constitutive equations have been implemented in finite element software in order to achieve the numerical simulation of the hot embossing process.

State transformations and ice nucleation in amorphous (semi-)solid organic aerosol

Abstract. Amorphous (semi-)solid organic aerosol particles have the potential to serve as surfaces for heterogeneous ice nucleation in cirrus clouds. Raman spectroscopy and optical microscopy have been used in conjunction with a cold stage to examine water uptake and ice nucleation on individual amorphous (semi-)solid particles at atmospherically relevant temperatures (200–273 K). Three organic compounds considered proxies for atmospheric secondary organic aerosol (SOA) were used in this investigation: sucrose, citric acid and glucose. Internally mixed particles consisting of each organic and ammonium sulfate were also investigated. Results from water uptake experiments followed the shape of a humidity-induced glass transition (Tg(RH)) curve and were used to construct state diagrams for each organic and corresponding mixture. Experimentally derived Tg(RH) curves are in good agreement with theoretical predictions of Tg(RH) following the approach of Koop et al. (2011). A unique humidity-induced glass transition point on each state diagram, Tg'(RH), was used to quantify and compare results from this study to previous works. Values of Tg'(RH) determined for sucrose, glucose and citric acid glasses were 236, 230 and 220 K, respectively. Values of Tg'(RH) for internally mixed organic/sulfate particles were always significantly lower; 210, 207 and 215 K for sucrose/sulfate, glucose/sulfate and citric acid/sulfate, respectively. All investigated SOA proxies were observed to act as heterogeneous ice nuclei at tropospheric temperatures. Heterogeneous ice nucleation on pure organic particles occurred at Sice = 1.1–1.4 for temperatures below 235 K. Particles consisting of 1:1 organic-sulfate mixtures took up water over a greater range of conditions but were in some cases also observed to heterogeneously nucleate ice at temperatures below 202 K (Sice= 1.25–1.38). Polynomial curves were fitted to experimental water uptake data and then incorporated into the Community Aerosol Radiation Model for Atmospheres (CARMA) along with the predicted range of humidity-induced glass transition temperatures for atmospheric SOA from Koop et al. (2011). Model results suggest that organic and organic/sulfate aerosol could be glassy more than 60% of the time in the midlatitude upper troposphere and more than 40% of the time in the tropical tropopause region (TTL). At conditions favorable for ice formation (Sice > 1), particles in the TTL are expected to be glassy more than 50% of the time for temperatures below 200 K. Results from this study suggests that amorphous (semi-)solid organic particles are often present in the upper troposphere and that heterogeneous ice formation on this type of particle may play an important role in cirrus cloud formation.

A Temperature Modulated DSC Study of Glass Transition in Poly(ethylene terephthalate)

A dynamic heat capacity of poly(ethylene terephthalate) in the temperature range of glass transition has been examined by a new technique of temperature modulated differential scanning calorimetry. The shift of glass transition temperature caused by the desorption of water could be monitored by the change in the dynamic heat capacity. Under quasi-isothermal condition, the increase in the glass transition temperature causes the decrease in the magnitude of the dynamic heat capacity and a negative or positive change in the phase, depending on temperature.

The effects of para-, meta- and ortho-monosubstituted azobenzene moiety in the side chain on phase behavior of mesogen-jacketed liquid crystalline polymers

Three different mesogen-jacketed liquid crystalline polymers with monosubstituted azobenzene moiety in the side-chain have been studied. These are poly(2,5-bis{[para-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl] oxycarbonyl} styrene) (denoted as PPABCS), poly(2,5-bis{[meta-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl] oxycarbonyl} styrene) (denoted as PMABCS) and poly(2, 5-bis{[ortho-(4′-methoxy-4-oxyhexyloxy azobenzene) benzyl] oxycarbonyl} styrene) (denoted as POABCS). The chemical structures of the monomers were confirmed by 1H NMR, 13C NMR spectroscopy and elemental analysis. The structure characterization of the polymers was performed by 1H NMR spectroscopy and gel permeation chromatography (GPC), and the phase structures and transitions of the polymers were studied using differential scanning calorimetry (DSC), polarized light microscopy (PLM), and one- and two-dimensional (1D, 2D) wide-angle X-ray diffraction. The effects of monosubstituted azobenzene moiety in different positions on the liquid crystalline behaviors of the polymers were also investigated. The results show that the phase transitional behaviors of mesogen-jacketed liquid crystalline polymers containing monosubstituted azobenzene moiety depend strongly on the position of the substituent on the azobenzene moiety. We identify that PPABCS can form a hierarchically ordered structure with double orderings on both the nanometer and subnanometer length scales. Most likely, the thick main-chains of PPABCS obtained by “jacketing” the central rigid portion of side-chain to the polyethylene backbone construct a 2D centered rectangular scaffold. The azobenzene-containing side-chains pack inside the main-chain scaffold form smecitc A (SmA)-like structure and are perpendicular to the main-chains. We compared PPABCS with PMABCS and POABCS, and found that the hierarchically ordered structure of PMABCS was similar to that of PPABCS. It is surprising that the main-chains of POABCS also construct a 2D centered rectangular scaffold, however, the packing of azobenzene-containing side-chains inside the main-chain scaffold develops smecitc C (SmC)-like structure. Furthermore, the glass transition temperature (Tg), isotropic temperature (Ti) and liquid crystalline range (ΔT, from Tg to Ti) of the polymers decrease in the order, para > meta > ortho. It is very interesting phenomenon that the associated enthalpy changes of these polymers are also the same order, para > meta > ortho, which is different from those of MCLCPs and SCLCPs.

Crystallization Behaviors of PbSe Quantum Dots in Silicate Glasses

This study, composed of three parts, aims at studying the crystallization behaviors of PbSe quantum dots (QDs) in silicate host glasses. Firstly, due to the importance of the choice of base glass for the QDs' crystallization, the selection of base glass compositions, the glass fragility, and glass formation ability (GFA) are discussed in details, and the results show that the selected glass compositions have an intermediate fragility and accordingly an intermediate glass transition temperature range among a wide variety of inorganic glass systems together with a good GFA/glass stability (GS). Thus, this base glass is suitable as the host glass in which PbSe QDs crystallize. Secondly, the experimental results on PbSe QDs' crystallizations are presented, and the results show that PbSe QDs can precipitate from silicate glasses favorably with no other chemical compounds precipitation, and the optimized temperature for PbSe QDs crystallization is 600°C. Lastly, the classical nucleation theory is used to analyze the PbSe QD crystallization behaviors in host glasses. The steady‐state nucleation rates and the growth rates of PbSe QDs as well as the time–temperature transformation (TTT) curves are calculated. The results indicate that the free surface energy between the PbSe nuclei and the host glass has great influence on the nucleation rates of PbSe QDs, while it has less effect on the growth rates of PbSe QDs; the crystallization behaviors of PbSe QDs with different volume fractions can be described well by the TTT curves while keeping the dimensionless empirical constant, α, unchanged for one certain curve.

High-Temperature Dielectric Polyimide Films for Energy Storage Applications

ABSTRACTTwo new diamines containing three nitriles are synthesized via a 3-step route. They are polymerized with four commercial dianhydrides (i.e. 6FDA, OPDA, BTDA and PMDA) in N,N-dimethylacetamide (DMAc) to afford poly(amic acid)s, which are thermally cured at temperatures up to 300 °C to form tough, creasable films. Most of these polyimides are soluble in common solvents. Their glass transition temperatures range from 216 to 341 °C. The polyimides are stable up to 400 °C. The dielectric constants of these OPDA-based polyimides increase from 2.9 (CP2) to 4.7 as measured by the D-E loops.

Shallow magma‐mingling‐driven Strombolian eruptions at Mt. Yasur volcano, Vanuatu

Mt. Yasur volcano (Vanuatu) has been increasingly recognized for its high‐frequency Strombolian eruptions. Strombolian activity is often regarded as a product of the rapid ascent of gas slugs originating from a deep magma, which mingle with a batch of shallow magma upon eruption. Heterogeneous crystal distribution as well as bimodal bubble‐size distributions, in the eruptive products, generally supports this view. Here, the Strombolian activity at Mt. Yasur is analyzed. A rheological investigation indicates that the basaltic‐andesitic eruptive products contain an apparently homogeneous glass phase and yet, exhibit evidence of a distinct range of glass transition temperatures with multiple peaks occurring in individual samples. Such anomalous behavior is proposed to result from the mingling of magmas with contrasting oxidation states. The unstable nature of the measured glass transition behavior leads us to the inference that mingling is located in the shallow parts of the eruptive conduits, partly driven by rejuvenation of material slumped from the crater walls into an open conduit system. The dynamics of this process may expose the periodicity of the eruptions themselves.