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In this article, polymer nanocomposites of polyisoprene with specific blend ratio 25/75 wt% of cis‐polyisoprene (CPI) and trans‐polyisoprene (TPI) with varying concentration (0.1, 1, and 5 wt%) of so synthesized silver nanoparticles (AgNPs) have been prepared and characterized through x‐ray diffraction, transmission electron microscope and scanning electron microscope. Experimental results on dynamic mechanical analysis show that addition of AgNPs to CPI/TPI blend reduces storage modulus, activation energy and fragility while enhances damping, however, glass transition temperature remains unaffected. Other mechanical properties such as toughness and tensile strength first increases on addition of AgNPs in the CPI/TPI blend, but a decrease is noticed on further increase of AgNPs concentration. Young's modulus shows a drastic decrease on addition of AgNPs into CPI/TPI blend, however, an increase is observed at higher concentration of AgNPs. Thermal analysis results show that thermal conductivity enhances with the enhancement in concentration of AgNPs into CPI/TPI blend. Highlights: Addition of AgNPs into CPI/TPI blend reduces storage modulus, activation energy and fragilityIncorporation of AgNPs into CPI/TPI blend enhances damping but does not change glass transition temperature.Increase in concentration of AgNPs in CPI/TPI blend increases the thermal conductivity. [ABSTRACT FROM AUTHOR]

Nuclear γ-resonance time-domain interferometry (TDI) was used to investigate the dynamics of the model glass-former o-terphenyl (OTP) at the μ s timescale and close to the peak of the static structure factor ( q max = 1.4 Å − 1 ) employing a recently introduced 3-lines scheme. The measured relaxation times (τ) agree with those available in the literature and confirm that in OTP the dynamics are dominated by the structural relaxation at the inter-molecular length-scale and by the Johari–Goldstein ( β J G ) relaxation at the intra-molecular one. The experimental scheme here employed presents the distinct advantage of providing access to the non-ergodicity factor ( f q ) on an absolute scale. The extracted f q values are qualitatively consistent with those derived in the previous neutron scattering experiments, with a very similar wavevector, q, and temperature dependence. Our data thus further establish the capability of multi-line TDI to measure the absolute strength of relaxation processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sur-saturated Curcumin/PVP amorphous solid dispersions (ASD) obtained by milling. • PVP low dispersity drastically increases glass transition temperature of ASD with Curcumin. • Shortest PVP chains reduce the anti-plasticisation effect of Curcumin-PVP interactions. • Solubility of Curcumin is increased in ASD formulated with well-defined PVP. Amorphous solid dispersions (ASD) are known to enhance the absorption of poorly water-soluble drugs. In this work we synthesise well-defined Polyvinylpyrrolidone (PVP) to establish the impact of dispersity and chain-end functionality on the physical properties of Curcumin (CUR)/PVP ASD. Thermodynamic characterisation of synthesised PVP emphasises a strong effect of the dispersity on the glass transition temperature (T g), 50 °C higher for synthesised PVP than for commercial PVP K12 of same molar mass. This increase of T g affects the thermodynamic properties of CUR/PVP ASD successfully formulated up to 70 wt% of CUR by milling or solvent evaporation. The evolution of both the T g and CUR solubility values versus CUR content points out the development of fairly strong CUR-PVP interactions that strengthen the antiplasticising effect of PVP on the T g of ASD. However, for ASD formulated with commercial PVP this effect is counterbalanced at low CUR content by a plasticising effect due to the shortest PVP chains. Moreover, the overlay of the phase and state diagrams highlights the strong impact of the polymer dispersity on the stability of CUR/PVP ASD. ASD formulated with low dispersity PVP are stable on larger temperature and concentration ranges than those formulated with PVP K12. [ABSTRACT FROM AUTHOR]

Abstract Mesoporous silica carriers have recently gained interest in the pharmaceutical domain because of their potential to significantly increase the solubility of poorly water-soluble drugs, by adsorbing the active molecule in an amorphous and relatively stable state. However, the use of organic solvents for drug loading and the limited loading capacity are real drawbacks in the context of therapeutic use. The present work shows that co-milling of porous SBA-15 matrix with the drug makes it possible the drug loading without significant damage for the structure of the matrix, enhancing thereby the capacity of loading to almost 40 wt%. Combining calorimetric, thermogravimetric, and low-frequency Raman investigations has allowed us to determine optimum conditions of loading, and to analyze the physical state, the molecular mobility and the phase transformations of the confined drug upon heating. It was shown that the physical state of ibuprofen (IBP) confined to silica carriers was amorphous between temperatures T g and T m of the bulk form of IBP. Graphical abstract Image 1 Highlights • Ibuprofen was loaded within SBA-15 by co-milling at room temperature. • Crystal - amorphous solid-state conversion is driven by confinement in 6.5 nm pores. • The loading capacity of API is about wt 40%. [ABSTRACT FROM AUTHOR]

Metallic glasses, with their short-range order structure, exhibit unique characteristics that do not exist in the corresponding crystalline alloys with the same compositions. These unusual properties are attributed to the absence of translational periodicity, grain boundaries, and compositional homogeneity. Cobalt (Co)-based metallic glassy alloys have been receiving great attention due to their superior mechanical and magnetic properties. Unluckily, Co-Ti alloys and its based alloys are difficult to be prepared in glassy form, due to their rather poor glass-forming ability. In the present work, the mechanical alloying approach was employed to investigate the possibility of preparing homogeneous (Co75Ti25)100−xBx starting from elemental powders. The feedstock materials with the desired compositions were high-energy ball-milled under argon atmosphere for 50 h. The end products of the powders obtained after milling revealed a short-range order structure with a broad amorphization range (2 at% ≤ B ≤ 25 at%). The behaviors of these glassy systems, characterized by the supercooled liquid region, and reduced glass transition temperature, were improved upon increasing B molar fraction. The results had shown that when B content increased, the saturation magnetization was increased, where coercivity was decreased.

Abstract The molecules of the supercooled liquids in the cooperative molecular dynamics are partitioning to specific dynamic units, known as "beads". The beads have been defined as the smallest units, forming the heat capacity of the supercooled liquids. The beads appear as a sub-molecular scale in the dynamics of the glass-forming liquids. In the Adam-Gibbs theory the number of molecules, rearranging simultaneously, has been defined as the size of the cooperative rearranging region and these regions form the second larger molecular scale in molecular dynamics. Due to a noticeable discrepancy in estimating the number of beads in the molecules by the empirical rules as well as by theoretical models the relations between these two scales are not well known. Recently, a new thermodynamic method for estimating the number of the beads in the molecules and a rule for the examination of their temperature dependence have been suggested. By these methods 48 low-molecular supercooled liquids are investigated and the relations between these two molecular scales and the structure of the molecules have been found. The estimated number of configuration beads is compared with the number of the structural units (the chemical groups, the ions and the atoms), with the assigned number by the empirical rules and with the ones calculated, based on a Lennar-Jones model of the random first order transition theory. A constant and two kinds of temperature dependence of the number of the beads in the molecules of different liquids have been revealed. A molecular basis, forming the fragility of the supercooled liquids, has been found. From the results obtained, the investigated liquids are classified in several groups following the logical line in the formation of the beads. Highlights • The molecules in the dynamics of glass-forming liquids are partitioning to the beads. • The number of the beads in the molecules and in the cooperative regions are estimated. • By these estimations a new insight into the dynamics of the liquids has been provided. [ABSTRACT FROM AUTHOR]

ABSTRACT: Composite manufacturing is currently one of the most challenging processes for industrial lightweight applications. To date, the process conditions for polymer‐based composite manufacturing are evaluated by laboratory measurements: usually, the flow behavior and the curing of the polymer matrix material are characterized by rheology and quality assurance is performed by thermo‐physical analysis in postprocess measurements. In contrast a dielectric in‐mold sensor offers the possibility to measure the real‐time behavior of the polymer during processing. This study focuses on the correlation of simultaneous rheological and dielectric measurements on Hexcel RTM6 using a coupled setup of both techniques. For dielectric measurements a reusable in‐mold sensor was used and a calibration, taking into account the cable response, was performed. The results show good agreement with respect to glass‐transition temperature and the gel‐point. This can be understood by the fluctuation–dissipation theorem that explicitly relates molecular dynamics to the macromolecular mechanical properties under dynamic time‐dependent load. Furthermore, it was found that the dynamic viscosity can directly be related to the electrical conductivity. This proves the high potential of dielectric analysis as online‐capable technique for material characterization during composite manufacturing. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 907–913 [ABSTRACT FROM AUTHOR]

The Johari-Goldstein (β J G) relaxation anticipates in time, and is closely connected to, the structural relaxation in deeply supercooled liquids. Probing its microscopic properties is a crucial step for a complete understanding of the glass-transition. We here report the investigation of the van der Waals glass-former cumene using time-domain interferometry, a technique able to probe microscopic density fluctuations at the spatial and temporal scales relevant for the β J G -relaxation. We find that the molecules participating in it undergo a restricted motion, though sufficient to induce local, cage-breaking events at the characteristic time-scale for molecular re-orientations. A detailed characterization of the relaxation strength, i.e. the fraction of molecules involved in the relaxation process, shows that such molecules are connected in a percolating cluster which, above the glass-transition temperature, T g , is weakly dependent on temperature. Our results confirm thus previous observations of a mosaic structure associated to the β J G -relaxation in the supercooled state, and provide additional information on its temperature evolution above the glass-transition temperature. We conclude that the observed microscopic properties of the β J G -relaxation, and thus of the associated mosaic structure, are generic and independent of the molecular interaction potential. In addition, we show that, while the dynamics within the percolating cluster becomes progressively slower on approaching T g , the fraction of the molecules involved in cage-breaking events within the β J G -relaxation is not affected by temperature. • The Johari-Goldstein relaxation of cumene is studied by nuclear γ -resonance time-domain interferometry. • The microscopic properties of the Johari-Goldstein relaxation are shown to be independent of the interaction potential. • The "mosaic structure" associated to the Johari-Goldstein relaxation is weakly dependent on temperature. [ABSTRACT FROM AUTHOR]

We use molecular dynamic simulations to investigate the relation between the presence of packing defects in a glass-former and the spontaneous cooperative motions called dynamic heterogeneity. For that purpose we use a simple diatomic glass-former and add a small number of larger or smaller diatomic probes. The diluted probes modify locally the packing, inducing structural defects in the liquid, while we find that the number of defects is small enough not to disturb the average structure. We find that a small packing modification around a few molecules can deeply influence the dynamics of the whole liquid, when supercooled. When we use small probe molecules, the dynamics accelerates and the dynamic heterogeneity decreases. In contrast, for large probes the dynamics slows down and the dynamic heterogeneity increases. The induced heterogeneities and transport coefficient modification increase when the temperature decreases and disappear around the onset temperature of the cage dynamics. [ABSTRACT FROM AUTHOR]

The plot scaling of viscosity by the reduced temperature as an important and vivid representation of the liquid fragility property has been utilized by materials scientists for more than four decades. In the present manuscript we discuss practical limitations on the high temperature part of the viscosity plot. It is valid up to the boiling point at pressure ranges from the triple point to the critical pressure and nearly up to the critical temperature at high pressure. Although, the high temperature viscosity estimation at T → ∞ is rather a result of overestimation of an Arrhenius or VFTH equitation fitting and does not have a physical meaning more attention is required to shed light on the behavior of glass-forming liquids in this temperature range by taking into account the supercritical liquid phenomenon. [ABSTRACT FROM AUTHOR]

The series of low-melting siloxane- and phosphate-bridged phthalonitriles are studied. The monomers of this type possess glass transition temperatures more than 100 °C lower than for common phthalonitriles. Based on the collected experimental data molecular dynamics simulations aimed to predict glass-transition temperatures of the considered types of low-melting phthalonitriles are reported. The validity of computational model is confirmed by successful synthesis of the new monomers, e.g. phosphate- and phosphonate-bridged phthalonitriles are introduced for a first time. Cured Bis(3-(3,4-dicyanophenoxy)phenyl) phenyl phosphate demonstrates thermal performance featured to phthalonitriles (HDT ∼ 450 °C, T 5% = 524 °C, Y c , (Ar) = 80%) along with increased thermo-oxidative stability. In aggregate with convenient processing the considered phthalonitriles can be used as high-temperature matrices for fiber-reinforced plastics production by vacuum infusion or RTM techniques. [ABSTRACT FROM AUTHOR]

Symmetrically and asymmetrically derived benzotriindole (diindolocarbazole) cores and their triply functionalized carbazolyl derivatives were synthesized and characterized. The synthesized compounds showed relatively high glass-transition temperatures. Carbazolyl substitutions at the periphery of benzotriindole cores improved their glass-forming ability as well as the thermal stability. Asymmetric benzotriindoles showed red-shifted absorption and emission spectra. Relatively decreased optical band gaps of the asymmetric derivatives suggested pronounced electronic communication between the indole segments and more effective π-conjugation in these derivatives. Oxidative redox profiles were distinct for differently linked benzotriindoles as characterized by cyclic voltammetry. Asymmetric benzotriindoles oxidized at comparatively lower potential and facilitated electropolymerization. Ionization potentials of thin films of the benzotriindole derivatives measured by photoelectron spectroscopy ranged from 4.95 to 5.43 eV. The method of charge extraction by linearly increasing voltage unlocked the hole-transport in both the symmetric and asymmetric benzotriindoles. Symmetric nature of benzotriindoles promoted the hole-transport in thin films. [ABSTRACT FROM AUTHOR]

Borosilicate glass (BSG) bonded composites of Sr-chloroapatite (SrApCl) and its simulated pyrochemical waste loaded compositions were synthesized by solid state reaction route. These compositions were characterized by XRD and SEM. Percentage (%) thermal expansion of the composites was measured by high temperature XRD (HT-XRD) and dilatometry. 10–16 wt.% waste loaded composites show minor variations in % linear expansion at 298–900 K. The composite with 10 wt.% waste loading and without BSG encapsulation exhibited slightly higher % of expansion compared to other compositions above 700 K. The coefficient of thermal expansion ( α m ) measured by HTXRD and dilatometry are found to be of the same order of magnitude. The % expansion measured by dilatometry shows higher values for waste loaded compositions compared to SrApCl; whereas values measured by HTXRD show a decreasing trend with respect to pristine SrApCl. The instantaneous coefficient of thermal expansion ( α i ) is used to determine the glass transition temperature (T g ) of the glass-bonded composites from the dilatometry data. The α i measured by HTXRD for the composites ranges from 2.40(1) × 10 −7 to 9.51(2) × 10 −6 K −1 along a -axis, 9.28(1) × 10 −8 to 7.68(1) × 10 −6 K −1 along c -axis and. α m measured by dilatometry ranges from 3.80(1) × 10 −7 to 13.14(1) × 10 −6 K −1 . [ABSTRACT FROM AUTHOR]

The data on the relaxation process of the polarized V component of the integral intensity of light scattering in glassy boric oxide at 320°C are presented. It was shown that the variations of the intensities were adequately described by the exponential function on time. The relaxation time of intensity was found to be equal about 50 min which far exceeds the expected times of structural relaxation at this temperature. The increase of both polarized and depolarized components of light scattering intensity in the process of low-temperature annealing of glass at 200°C was presumably related to the development of elastic stress in the sample volume. [ABSTRACT FROM AUTHOR]

Materials based on triphenylamino core linked with different alkoxyphenyl-substituents through olefinic spacers were synthesised, and their thermal, photophysical and photoelectrical properties were investigated. The synthesized compounds showed relatively good thermal stability. Derivatives containing shorter alkyl chains displayed glass-forming ability, while the compounds containing flexible alkyl termini demonstrated liquid-crystalline behaviour. Flexible alkyl substituents at the periphery of triphenylamine derivatives prevented the close packing of chromophores and hence, they showed relatively similar absorption and fluorescence in thin-films and solutions. Reduction in fluorescence quantum yield in thin-films upon decreasing the size of peripheral alkyl substituents confirmed enhanced intermolecular interactions and in turn, suggested migration-induced exciton quenching at nonradiative decay sites. Ionization potentials of thin solid layers estimated by photoelectron emission spectroscopy ranged from 5.21 to 5.47 eV. Hole-drift mobility of ethyl substituted triphenylamine measured using xerographic time-of-flight (XTOF) method was 1.3 × 10 −3 cm 2 V −1 s −1 at an electric field of 10 6 Vcm −1 . [ABSTRACT FROM AUTHOR]

We study a simple and versatile diatomic potential function coined to prevent crystallization in supercooled liquids. We show that the corresponding liquid does not crystallize even with very long simulation runs at the lowest temperature that we can access with ergodic simulations. The medium displays the usual features of supercooled materials and a non-Arrhenius dependence of the diffusion coefficient and α relaxation time with temperature. We also observe the breakdown of the Stokes–Einstein relation at low temperatures. [ABSTRACT FROM AUTHOR]

• The dynamical slowing down induced by confinement is washed out by the activation. • A permanent localization of the excitations inside the pore suggesting structural localization of dynamic heterogeneity. • The motor's opening angle controls the degree of activation of the liquid. • The Non Gaussian parameter increases suggesting an increase of the cooperative dynamics. Confinement of supercooled liquids into nano-pores induces a strong modification of the dynamics. In this work we raise the issue as how this confinement effect is modified when the liquid is out of equilibrium. To answer that question, we use molecular dynamics simulations to investigate the effect of confinement on a supercooled liquid activated by the periodic folding of a molecular motor. The excitation (i.e. elementary diffusion processes) density calculation shows that the motor's opening angle controls the activation of the medium. We then use that result to study the effect of different activations on the confined supercooled liquid. When our liquid is not activated, the confinement generates a strong slowing down of the dynamics, and the excitation density decreases sharply around the pore wall. In contrast when the liquid is activated the motor generates excitations inside the medium localized mostly in the pore center. The combination of these two effects leads to a localization of the excitation density when the motor is on. Results show that the activation is able to wash out the confinement-induced slowing down while the main characteristics of supercooled liquids are maintained or increased. We observe actually an increase of the tail of the Van Hove correlation function upon activation inside the pores leading to the increase of the Non Gaussian parameter, two signatures of dynamic heterogeneity in supercooled liquids. [ABSTRACT FROM AUTHOR]

Abstract: The glass-transition temperature (T g) of polymer thin films can be strongly influenced by the combined effects of the supporting solid substrate and the free surface. The relative importance of these two effects, which often compete with each other, depends on the strength of the substrate–film interactions. Utilizing an atomistically informed coarse-grained model for poly(methyl methacrylate) (PMMA), here we uncover the relationship between the substrate–film interfacial energy and the spatial distribution of T g across thin films. We find that above a critical interfacial energy, the linear dependence of film T g on the interfacial energy breaks down and film T g attains an asymptotic value. Analyses on the spatial variation of T g across the thin film reveal that the short-range interface near the cohesive surface generates a long-range interphase that leads a spatially uniform appreciation of T g throughout the film, unlike weakly cohesive surfaces that show sharp gradients along the depth of film. These findings explain recent experiments and reveal a versatile approach for tuning film T g via engineered substrate-film interactions. [Copyright &y& Elsevier]

Abstract: The Raman spectra of the 0.1Cs2O–0.9TeO2 melt were measured and analyzed over a broad temperature range including the glassy, supercooled and molten state in an effort to follow the varying structural and dynamical aspects caused by temperature and alkali modifier. The network structure of the glass/melt is formed by mixing TeO4 trigonal bipyramid and TeO3 trigonal pyramid units. Changing alkali content and/or temperature results to conversion of the TeO4 units to TeO3 units with a varying number of non-bridging oxygen atoms. The low-frequency Raman spectra reveal a well-resolved Boson peak whose frequency also depends on temperature. The variation of the maximum of the Boson peak has been determined and discussed in the framework of current phenomenological models. The short-time dynamics of the system experiences drastic changes when approaching the glass-to-liquid transition. The temperature dependent plot of the correlation times extrapolates to a crossover value, which we assign as spectral evidence of the system''s known thermodynamic glass transition temperature. Similar behavior exhibit several spectral features, such as the maximum of the Boson peak, the exponent of the susceptibility and the intensity ratio related to the structural transformation from TeO4 tbp to TeO3 tp species occurring in the medium range order structure. [Copyright &y& Elsevier]

In recent years there has been an increased interest in the use of fiber reinforced polymer (FRP) materials in concrete members. However, the behavior of such members in fire is still relatively unknown. Since this is the main reason limiting the widespread use of FRP in buildings, the use of FRP in fire vulnerable structures needs additional study. In this article, a model is developed that incorporates the temperature dependent progressive changes of Elastic-modulus of FRP in predicting the deflection behavior of FRP reinforced concrete structures within the range of practical elevated temperatures. Predictions from the model correlate well with experimental results from the literature. The new approach provides an additional tool to evaluate the deflection of FRP reinforced concrete structures in fire. [ABSTRACT FROM PUBLISHER]

Measurements of mechanical and thermal transport properties have been made on the blends of cis-polyisoprene (CPI) and trans-polyisoprene (TPI) prepared by a solution casting method. Characterization of these blends has been done using wide angle X-ray scattering. Thermo-mechanical, mechanical, and thermal transport properties have been determined employing dynamic mechanical analyzer (DMA) and transient plane source. Storage modulus and tan δ as determined from DMA have been found to increase and decrease with the increase in TPI content, respectively. Mechanical properties such as Young's modulus and tensile strength, as determined from strain-stress behavior of CPI/TPI blends, have been found to increase with increasing TPI content. This increase in properties has been explained on the basis of the crosslink density, calculated using theory of rubber elasticity. Thermal transport properties such as thermal conductivity, thermal diffusivity, and volumetric heat capacity are higher for all the three blends as compared to their pure components. [ABSTRACT FROM AUTHOR]

Abstract: We present here new specific heat measurements at low temperatures (2–20K) of the different phases of ethanol, characterized by the same calorimetric set-up at higher temperatures. We have extended and improved earlier measurements by implementing higher-accuracy calorimetric methods at low temperatures (using two complementary versions of the thermal relaxation method), as well as at higher temperatures (using a quasi-adiabatic, continuous method). The quantitatively very similar low temperature properties and glass-transition features of both structural glass and orientationally-disordered crystal of ethanol provide clear evidence that the lack of long-range crystalline order typical of amorphous solids is an unimportant factor regarding the universal properties of glasses. We have also employed these new measuring methods to study the possible effect of water impurities on the specific heat of the different solid phases of ethanol, and to study possible variations in the specific heat between different found phases of the monoclinic crystal of ethanol. [Copyright &y& Elsevier]

Abstract: The properties of water, ethanol and 1-butanol at cryogenic temperatures (10–220K) are discussed by investigating the interaction with the C6F14 molecule. The C6F14 molecules adsorbed on the surface are incorporated in the bulk of the glassy water and alcohol films. The wettability may arise from the formation of improper hydrogen bonding between the OH group and F atom. On the alcohol films, the incorporated C6F14 molecules segregate to the surface at 100K, since the hydrogen-bonded rings and chains of alcohols are formed due to the glass–liquid transition. The C6F14 molecules incorporated in the bulk of amorphous solid water can survive a viscous liquid phase that appears above 136K and desorb abruptly at 167K as a consequence of the liquid–liquid transition. [Copyright &y& Elsevier]

Copolyesters of isosorbide and 1,4-butane diol were prepared by Ti(OBu)4-catalyzed transesterifications with dimethyl terephthalate in bulk at temperatures up to 250°C. The content of isosorbide was considerably lower than expected from the feed ratio and the molar masses were low, so that no DSC measurements were conducted. Copolycondensations of isosorbide and 1,4-butane diol with terephthaloyl chloride were either performed in dichloromethane at 40°C or in toluene at 100°C. The second method gave the higher molar masses. However, both series of polycondensations had the content of isosorbide roughly paralleled the feed ratios in common. The DSC measurements revealed that even 6 mol% of isosorbide is sufficient to raise the glass-transition temperature (Tg) by 10-12°C (up to 55°C). With 50 mol% of isosorbide, the Tg reaches 100°C. Yet, incorporation of isosorbide also reduces the melting temperature Tm and the degree of crystallinity, and a mol percentage above 30% prevents crystallization completely. In summary, incorporation of isosorbide allows for fine-tuning of Tg and Tm of poly(butylene terephthalate) over a wide range. [ABSTRACT FROM AUTHOR]

Abstract: The formation of a supercooled liquid region and devitrification behaviour of metallic glasses on heating are discussed in relation with the glass-transition phenomenon observed using differential scanning and isothermal calorimetries as well as X-ray diffraction and transmission electron microscopy (TEM). One of the most clear sequences of the glassy↔supercooled liquid phase transition is the change of the devitrification behaviour and the kinetics of the devitrification reaction in Al-based and some other alloys after the transition from the glassy to the supercooled liquid state. The significant variation in the devitrification behaviour and thermodynamic parameters indicate the difference between the glassy and the supercooled liquid phases. [Copyright &y& Elsevier]

Abstract: By means of broadband dielectric spectroscopy the molecular dynamics of glass-forming ethylene glycol (EG) adsorbed in zeolites is investigated by varying the loading degree, the type of zeolites, and the Si/Al ratio. We only concentrate to the frequency and temperature range where relaxation processes may be observed which allow conclusions about the glass-transition. Although EG molecules in the bulk liquid show a Vogel–Fulcher–Tammann (VFT) type of activation at lower temperatures, measurements for EG molecules adsorbed in NaX zeolites always follow Arrhenius-type of behaviour independent of the loading degree. This effect is explored in more detail by measuring the dielectric relaxation rate for EG adsorbed in zeolite beta, EG/beta, with different Si/Al ratios. For the case of zeolite beta with a very large Si/Al ratio, a glass-transition is observed, i.e., a VFT-type of activation is detectable. For the system EG/beta with Si/Al ratio of 56, however, a clear Arrhenius-type of activation is observed. Obviously, due to a higher number of adsorption sites, surface–molecule interactions are of greater influence and suppress the glass-transition. For EG/beta with a Si/Al ratio between 56 and infinity, there is subtle interplay between “cooperative” and “local” motions, i.e., between VFT- and Arrhenius-type of activation behaviour. [Copyright &y& Elsevier]

Prediction and optimization of polymer properties is a complex and highly nonlinear problem with no easy method to predict polymer properties directly and accurately. The problem is especially complicated with high molecular weight polymers such as engineering plastics which have the greatest use in industry. The effect of modifying a monomer (polymer repeat unit) on polymerization and the resulting polymer properties is not easy to investigate experimentally given the large number of possible changes. This severely curtails the design of new polymers with specific end-use properties. In this paper, we show how properties of modified monomers can be predicted using neural networks. We utilize a database of polymer properties and employ a variety of networks ranging from backpropagation networks to unsupervised self-associating maps. We select particular networks that accurately predict specific polymer properties. These networks are classified into groups that range from those that provide quick training to those that provide excellent generalization. We also show how the available polymer database can be used to accurately predict and optimize polymer properties. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics simulations of amorphous silica are carried out on a large temperature range using a modified version of the BKS inter-atomic potential. We investigate the dependence on the screening procedure of the structural and dynamical properties of amorphous silica. We show that an increased screening of the electrostatic interaction leads to a decrease of the diffusion constants and then to better agreement with experimental data, while structural properties are unchanged. We show that the Arrhenius dependence of the diffusion constants may be reproduced in this case up to a temperature of 4000K with activation energies very similar to the experimental data. [Copyright &y& Elsevier]

The interactions between Carbopol and β-cyclodextrin (BCD) or hydroxypropyl-β-cyclodextrin (HPBCD) were studied by differential scanning calorimetry (DSC) and FTIR spectroscopy. Aqueous solutions of both components were desiccated by freeze-drying or heating in an oven (films) at various temperatures. The use of different drying procedures allowed their influence on the interactions to be studied. The evolution of the Carbopol glass-transition was also evaluated by DSC using first heating runs up to different temperatures. Disappearance of the Carbopol glass-transition was observed in the freeze-dried systems prepared with either of the cyclodextrins and in the films that contained HPBCD. The changes in the FTIR band of Carbopol at 1700 cm-1 confirmed the existence of interactions with both cyclodextrins, especially with HPBCD. This information may be useful for optimising the solubilizing capacity and controlled release performance of aqueous Carbopol-cyclodextrin systems. [ABSTRACT FROM AUTHOR]

At large length scales, polymers show typical soft matter properties, whereas glass-forming system features prevail at local scales. An intriguing dynamical complexity is thus inherent to these materials. With space–time resolution in a wide momentum transfer range, neutron scattering (NS) is a specially well-suited technique for unraveling dynamical processes in glass-forming polymers, since three correlation functions are accessible: the self motion of hydrogens, the collective motion involving deuterons and carbons and the single chain dynamic structure factor. In this work, we show how NS techniques have allowed to gain insight in the processes taking place at different length scales, like the entropy-driven dynamics and the structural relaxation, through the investigation of these correlators. In particular, the dynamical behavior in the unexplored intermediate length scales region, i.e., spatial scales of several times the typical interchain distances, is addressed. There, the microscopic details of the polymer begin to play a decisive role and induce deviations from the purely entropy-determined evolution of the single-chain dynamic behavior at large length scales. [Copyright &y& Elsevier]

A pulsed slow-positron beam using 22Na as the positron source has been constructed for characterizing thin polymer films, coating polymer materials and their interfaces. The construction is very simple and the time resolution achieved is about 500 ps, which is sufficient for measuring long-lived positron lifetime components in thin polymer films. The positron lifetime in a 45 nm thick epoxy resin thin film held on a single-crystal silicon substrate has been measured using this pulsed slow-positron beam. Formation of o-positronium (ortho-Ps) is not observed when the incident positron energy is more than about 1 keV. The surface effect of the glass-transition temperature of a 0.3 mm thick polystyrene (PS) film has been also studied. It has been found that the glass-transition temperature of the sub-surface region of PS is lower than that of the PS bulk. [Copyright &y& Elsevier]

Mid-infrared spectra of freeze-dried sucrose and lactose systems were acquired over a range of temperatures (30–200 °C) and water contents (0–6.3%). Starting from the glassy state, the experimental conditions were selected to cover the main thermal transitions: the glass–rubber transition, the crystallisation and, for some samples, the subsequent melting. The FTIR spectra were very sensitive to the physical state. While subtle but systematic spectral differences between the glassy and rubbery states were detectable throughout the spectrum, a very pronounced increase in spectral resolution was observed as crystallisation occurred and was followed by the expected spectral broadening during melting. The temperatures at which these changes occurred were in satisfactory agreement with the transition temperatures measured by differential scanning calorimetry (DSC). The increase in molecular mobility as a result of increasing temperature or plasticisation by water led to a significant shift of the O&z.sbnd;H stretching band to higher wavenumbers indicating a weakening of hydrogen bonding. This shift reached a maximum as the DSC measured crystallisation temperature range was approached. As expected, the crystallisation led to a highly effective hydrogen bonding network. This was more significant for lactose than for sucrose. No significant step change in hydrogen bonding was observed at Tg. As anticipated, the temperature at which these transitions occurred decreased with increasing water content but overlapped when observed in the context of the shifted temperature (T−Tg). [Copyright &y& Elsevier]