The glass transition and enthalpy recovery of polystyrene nanorods using Flash differential scanning calorimetry.

The glass transition (Tg) behavior and enthalpy recovery of polystyrene nanorods within an anodic aluminum oxide (AAO) template (supported nanorods) and after removal from AAO (unsupported nanorods) is studied using Flash differential scanning calorimetry. Tg is found to be depressed relative to the bulk by 20 ± 2 K for 20 nm-diameter unsupported polystyrene (PS) nanorods at the slowest cooling rate and by 9 ± 1 K for 55 nm-diameter rods. On the other hand, bulk-like behavior is observed in the case of unsupported 350 nm-diameter nanorods and for all supported rods in AAO.

Prediction of the Synergistic Glass Transition Temperature of Coamorphous Molecular Glasses Using Activity Coefficient Models.

The glass transition temperature () of a binary miscible mixture of molecular glasses, termed a coamorphous glass, is often synergistically increased over that expected for an athermal mixture due to the strong interactions between the two components. This synergistic interaction is particularly important for the formulation of coamorphous pharmaceuticals since the molecular interactions and resulting strongly impact stability against crystallization, dissolution kinetics, and bioavailability. Current models that describe the composition dependence of for binary systems, including the Gordon-Taylor, Fox, Kwei, and Braun-Kovacs equations, fail to describe the behavior of coamorphous pharmaceuticals using parameters consistent with experimental Δ and Δα.

A model-free analysis of configurational properties to reduce the temperature- and pressure-dependent segmental relaxation times of polymers.

The segmental relaxation time data for poly(vinyl acetate), poly(vinyl chloride), and linear and star polystyrene are analyzed using a model-free method to determine how the temperature- and pressure-dependent relaxation times, τ, scale with the relative configurational thermodynamic properties. The model-free method assumes no specific mathematical form, such as reciprocal linearity, and the configurational properties are referred to an isochronal state to eliminate the bias associated with the definition of the ideal glassy state. The scaling ability of a given configurational property is strongly material-dependent with the logarithm of τ scaling better with TS and H for poly(vinyl acetate), with TS, H, and U for poly(vinyl chloride), and with TS, H, and V for linear and star polystyrene.

The glass transition and enthalpy recovery of a single polystyrene ultrathin film using Flash DSC.

The kinetics of the glass transition are measured for a single polystyrene ultrathin film of 20 nm thickness using Flash differential scanning calorimetry (DSC). T is measured over a range of cooling rates from 0.1 to 1000 K/s and is depressed compared to the bulk.

Rheology of Imidazolium-Based Ionic Liquids with Aromatic Functionality.

A series of imidazolium-based ionic liquids with cyclic and aromatic groups and a bis[(trifluoromethane)sulfonyl]amide anion were characterized using dynamic and steady shear rheology in a wide temperature range. The cations investigated include 1-(cyclohexylmethyl)-3-methylimidazolium ([CyhmC1im](+)), 1-benzyl-3-methylimidazolium ([BnzC1im](+)), 1,3-dibenzylimidazolium ([(Bnz)2im](+)), and 1-(2-naphthylmethyl)-3-methylimidazolium ([NapmC1im](+)). Rheological properties are reported from terminal flow to the glassy state.

Using 20-million-year-old amber to test the super-Arrhenius behaviour of glass-forming systems.

Fossil amber offers the opportunity to investigate the dynamics of glass-forming materials far below the nominal glass transition temperature. This is important in the context of classical theory, as well as some new theories that challenge the idea of an 'ideal' glass transition. Here we report results from calorimetric and stress relaxation experiments using a 20-million-year-old Dominican amber.

Modeling ring/chain equilibrium in nanoconfined sulfur.

The effect of nanoconfinement on the thermodynamics of free radical polymerization of sulfur is examined. We extend Tobolsky and Eisenberg's model of bulk sulfur polymerization to nanopores accounting for the confinement entropy of the chains and ring using scaling reported in literature. The model quantitatively captures literature data from Yannopoulos and co-workers for the extent of polymerization versus temperature for bulk sulfur polymerization and for polymerization in 20, 7.

Crystallization and vitrification of a cyanurate trimer in nanopores.

The effects of nanopore confinement on the crystallization and vitrification of a low molecular weight organic material, tris(4-cumylphenol)-1,3,5-triazine, are investigated using differential scanning calorimetry. The material shows cold crystallization and subsequent melting in the bulk state. Under the nanoconfinement of controlled pore glasses (CPG), cold crystallization and melting shift to lower temperatures.

Thermodynamic scaling of polymer dynamics versus T-T(g) scaling.

A thermodynamic scaling law for the relaxation times of complex liquids as a function of temperature and volume has been proposed in the literature: τ(T,V) = f(TV(γ)), where γ is a material-dependent constant. We test this scaling for six materials, linear polystyrene, star polystyrene, two polycyanurate networks, poly(vinyl acetate), and poly(vinyl chloride), and compare the thermodynamic scaling to T-T(g) scaling, where τ = f(T-T(g)). The thermodynamic scaling law successfully reduces the data for all of the samples; however, polymers with similar structures but different glass transition (T(g)) and pressure-volume-temperature (PVT) behavior, i.

Effect of cation symmetry on the morphology and physicochemical properties of imidazolium ionic liquids.

In this paper, the morphology and bulk physical properties of 1,3-dialkylimidazolium bis{(trifluoromethane)sulfonyl}amide ([(C(N/2))(2)im][NTf(2)]) are compared to that of 1-alkyl-3-methylimidazolium bis{(trifluoromethane)sulfonyl}amide ([C(N-1)C(1)im][NTf(2)]) for N = 4, 6, 8, and 10. For a given pair of ionic liquids (ILs) with the same N, the ILs differ only in the symmetry of the alkyl substitution on the imidazolium ring of the cation. Small-wide-angle X-ray scattering measurements indicate that, for a given symmetric/asymmetric IL pair, the structural heterogeneities are larger in the asymmetric IL than in the symmetric IL.

Kinetic study of trimerization of monocyanate ester in nanopores.

A kinetic study of the trimerization of monocyanate ester both in the bulk and in the nanoconfinement of controlled pore glass is performed using differential scanning calorimetry. Both isothermal and dynamic experiments are analyzed. Although the activation energy for the reaction is the same within experimental error for the bulk and nanoconfined samples (approximately 21-23 kcal/mol), the reaction is accelerated under nanoconfinement by approximately 50 times in 13 nm pores compared with bulk.

Trimerization of monocyanate ester in nanopores.

The effects of nanoconfinement on the reaction kinetics and properties of a monocyanate ester and the resulting cyanurate trimer are studied using differential scanning calorimetry (DSC). On the basis of both dynamic heating scans and isothermal reaction studies, the reaction rate is found to increase with decreasing nanopore size without a change in reaction mechanism. Both the monocyanate ester reactant and cyanurate product show reduced glass transition temperatures (T(g)s) as compared to the bulk; the T(g) depression increases with conversion and is more pronounced for the fully reacted product, suggesting that molecular stiffness influences the magnitude of nanoconfinement effects.

A new pressurizable dilatometer for measuring the time-dependent bulk modulus and pressure-volume-temperature properties of polymeric materials.

A new piston-cylinder-type pressurizable dilatometer controlled by a stepper motor has been developed to measure the time-dependent bulk modulus and pressure-volume-temperature (PVT) behavior of polymeric materials. The dilatometer can be operated from 35 to 230 degrees C and at pressures of up to 250 MPa. The sample cell, which contains the sample and a fluorinated oil as the confining fluid, is totally submerged into a high precision oil bath to achieve a temperature stability of better than 0.

Confinement effects on the glass transition of hydrogen bonded liquids.

The glass transition behavior of glycerol and propylene glycol confined in nanoporous glass is investigated using differential scanning calorimetry. Both silanized and unsilanized porous glasses are used to confine the liquids with nominal pore sizes ranging from 2.5 to 7.

Chain length dependence of the thermodynamic properties of linear and cyclic alkanes and polymers.

The specific heat capacity was measured with step-scan differential scanning calorimetry for linear alkanes from pentane (C(5)H(12)) to nonadecane (C(19)H(40)), for several cyclic alkanes, for linear and cyclic polyethylenes, and for a linear and a cyclic polystyrene. For the linear alkanes, the specific heat capacity in the equilibrium liquid state decreases as chain length increases; above a carbon number N of 10 (decane) the specific heat asymptotes to a constant value. For the cyclic alkanes, the heat capacity in the equilibrium liquid state is lower than that of the corresponding linear chains and increases with increasing chain length.