First‐Principle Calculation and Assignment for Vibrational Spectra of Ba(Mg1/2W1/2)O3 Microwave Dielectric Ceramic

Ba(Mg_1/2W_1/2)O₃ ceramic was synthesized using a conventional solid‐state reaction method at 1500°C for 4 h. The face‐centered cubic crystal structure of the material was confirmed by Rietveld refinement of X‐ray diffraction (XRD) data, and vibrational modes were obtained by Raman and Fourier transform far‐infrared (FTIR) reflection spectroscopies. First‐principle calculations based on density functional theory with local density approximation were used to calculate Gamma‐point modes and dielectric properties of Ba(Mg_1/2W_1/2)O₃. The Raman spectrum with nine active modes can be fitted with Lorentzian function, and the modes were assigned as F_2g⁽¹⁾ (126 cm^?1), F_2g⁽²⁾ (441 cm^?1), E_g(O) (538 cm^?1), and A_1g(O) (812 cm^?1). Far‐infrared spectrum with 12 infrared active modes was fitted using both the Lorenz three‐parameter classical and four‐parameter semiquantum models. Consequently, the modes were assigned as F_1u⁽¹⁾ (144 cm^?1), F_1u⁽²⁾ (284 cm^?1), F_1u⁽³⁾ (330–468 cm^?1), and F_1u⁽⁴⁾ (593–678 cm^?1). The active modes were represented by linear combinations of symmetry coordinates that were obtained by group theory analyses. The Raman mode A_1g, which has the highest wave number (812 cm^?1) is dominated by the breath vibration of the MgO₆ octahedron. The infrared modes F_1u⁽²⁾, that can be described as the inverted vibrations of Mg atoms in the MgO₆ octahedron along the x_i, y_i, and z_i axes have the most contributions to the microwave permittivity and dielectric loss.     

Formation and electrochemical properties of composites of the C60–Pd polymer and multi-wall carbon nanotubes

Preparation and electrochemical properties of a novel type of the composite made of multi-wall carbon nanotubes (MWCNTs) and two-component polymer of palladium and C₆₀ (C₆₀–Pd) were investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and piezoelectric microgravimetry. A composite film was prepared by electrochemical deposition of C₆₀–Pd on the layer of MWCNTs immobilized on the electrode surface. The polymer forms islands of shells on the carbon multi-wall core. This composite is electrochemically active in the negative potential range due to the electroreduction of the fullerene moiety. In this potential range, specific pseudo-capacitance of the film of the MWCNT/C₆₀–Pd composite is 425 F g⁻¹ in the acetonitrile solution of tetra(n-butyl)ammonium perchlorate. The presence of MWCNTs makes the composite conductive also at potentials less negative than potentials of the C₆₀ electroreduction. The double-layer specific capacitance of this film is close to 15 F g⁻¹.     

The correlation between surface conductivity and adsorbate coverage on diamond as studied by infrared spectroscopy

A high-resolution analysis of CH vibrational modes on a single crystal diamond(100) surface using Fourier-transform infrared (FTIR) spectroscopy in combination with conductivity measurements is reported. On a plasma-hydrogenated diamond(100) surface, the IR spectra measured in the multiple internal reflection mode reveal three absorption lines. Two of them at 2921 and 2854 cm⁻¹ vanish in air at an annealing temperature of 190°C and are assigned to the antisymmetric and symmetric CH₂ stretching modes of a physisorbed hydrocarbon species, respectively. The third band at 2897 cm⁻¹ has a width of 16 cm⁻¹, is stable up to 230°C and is associated with the stretching frequency of C₂H₂ monohydride units on the C(100) 2×1:2H surface. Upon annealing in air at temperatures lower than 200°C, the surface conductivity is reversibly reduced by up to five orders of magnitude. After cooling down to room temperature, it recovers the value of 1×10⁻⁵ Ω⁻¹ measured immediately after the plasma hydrogenation with a time constant of several days. Annealing at 230°C destroys the surface conductivity irreversibly and yields conductance values below the measurement limit of 5×10⁻¹² Ω⁻¹. We show that the chemisorbed hydrogen in the C₂H₂ configuration, together with at least one physisorbed species, is responsible for the surface conductivity of hydrogen-terminated diamond(100).     

Fourier transform infrared spectroscopic study of transitions above Tg in atactic polystyrene

Fourier transform infrared spectroscopy (FT-IR) has been applied to the study of the molecular mechanisms of transitions of atactic polystyrene above T_g. Intensity measurements of vibrational modes as a function of temperature revealed two transitions above T_g, which are designated as T_u and T′_u. T′_u is independent of molecular weight as opposed to the molecular weight dependent T_u whose behavior is similar to T_g. Infrared measurements are more sensitive to T′_u than T_u. Conformationally sensitive bands show that T′_u may be related to disruption of local order where there is a negligible barrier to conformational change.     

Diffusion of m-nitroaniline into polyacylonitrile

The diffusion of nonionic penetrant, m-nitroaniline, into polyacrylonitrile was studied in detail on a range of temperature from 50.6°C to 95.0°C. The penetrant distribution in polymer is Fickian, which is different from that of cationic dye, Malachite Green reported earlier. The diffusion coefficient D increases with the rise of temperature. The sharp inflection point (72°C) of the Arrhenius plot, log D versus 1/T, corresponds to T_g of polyacrylonitrile in the presence of water, which is lower than that measured in the dry state by a dynamic mechanical testing method. The activation energy is constant below T_g (ca. 10 kcal/mole), suddenly reaches a maximum at T_g and then gradually decreases with increasing temperature. General trends of Arrhenius plot for different polymer–penetrant systems are discussed. The temperature dependence of penetrant diffusion above T_g can be described by a general form of the WLF equation, log a_T = log (D_Tg/D_T) = ? C₁^g(T ? T_g)/(C₂^g + T ? T_g), where the values of C₁^g and C₂^g were calculated to be 4.03 and 24.54, respectively. A comparison was made between m-nitroaniline and Malachite Green. The difference in the respective T_g and the constants C₁^g and C₂^g of the WLF equation in polyacrylonitrile is attributed to the size of the penetrants and their ionic character. The surface concentration increases below T_g and decreases above T_g with rise in temperature.     

Straining phenomena of POY revealed by thermal retraction and other techniques

Partially oriented polyesters yarns (POY) were strained at different strain rates (0.03–12.00 min^?1) and temperatures above and below T_g (3–92°C). Thermal retraction, density, DSC, and WAXS techniques show that strain-induced crystallization takes place by straining at temperatures above as well as below T_g. Above T_g, depending upon the strain rate, two regimes are observed: Below the strain rate of 1.5 min^?1, the flow regime; the degree of crystallinity is reduced as the strain rate increases. Above the strain rate of 1.5 min^?1, the strain-induced crystallization regime; the degree of crystallinity increases as the strain rate increases. Thermal retraction, stress–relaxation, and sonic modulus techniques indicate that, upon cold straining, instead of the original T_g at 65–69°C, two glass transitions occur: an upper T_g (u) and a lower T_g (l). For POY strained at 3°C and at a strain rate of 10 min^?1, the values are 78°C and 37°C, respectively. The higher the strain rate and the lower the straining temperature, the large the difference between T_g (u) and T_g (l).     

Why C1 = 16–17 in the WLF equation is physical-and the fragility of polymers

From the well-recognized equivalence of the Williams-Landel-Ferry (WLF) equation and the Vogel-Tammann-Fulcher (VTF) equation, τ = τ_o exp (B/[T - T_o]), we shall show that the parameter C₁ in the former is just the number of orders of magnitude between the relaxation time at the chosen reference temperature and the pre-exponent of the VTF equation. Thus C₁^g = log(τ_g/τ_o) (a relation which is not found in the present polymer literature), measures the gap between the two characteristic time scales of the polymer liquid, microscopic and α-relaxation, at the glass transition temperature. For systems which obey these two equations over wide temperature ranges, τ_o is consistent with a quasilattice vibration period in accord with theoretical derivations of the VTF equation and also with the microscopic process of mode coupling theory. Thus for such systems, C₁^g is obliged to have the value 16–17 (depending on how T_g is defined), while C₂^g scaled by T_g will reflect the non-Arrhenius character, i.e. fragility, of the system. In fact when C₁^g has the physical value of 16–17, then (1 − C₂^g/T_g), which varies between 0 and unity, conveniently gives the ‘fragility’ of the polymer within the ‘strong/fragile’ classification scheme. This is useful because it permits prediction from the WLF parameters of other properties such as physical ageing behaviour through the now-established correlation of fragility with other canonical characteristics of glassforming behaviour. Where the best fit C₁^g is not 17 ± 2, the corresponding best fit τ_o must be unphysical, and then the range of relaxation times for which the VTF or WLF equations are valid with a single parameter set will be limited, and the predictions of other properties based on that parameter set will be unreliable. © 1997 Elsevier Science Ltd.     

A novel “plane-line-plane” nanostructure of the sandwich-like CNTs@SnO2/Ti3C2Tx 3D nanocomposite as a promising anode for lithium-ion batteries

As one of the novel two-dimensional metal carbides, Ti₃C₂T_x has received intense attention for lithium-ion batteries. However, Ti₃C₂T_x has low intrinsic capacity due to the fact that the surface functionalization of F and OH blocks Li ion transport. Herein a novel “plane-line-plane” three-dimensional (3D) nanostructure is designed and created by introducing the carbon nanotubes (CNTs) and SnO₂ nanoparticles to Ti₃C₂T_x via a simple hydrothermal method. Due to the capacitance contribution of SnO₂ as well as the buffer role of CNTs, the as-fabricated sandwich-like CNTs@SnO₂/Ti₃C₂T_x nanocomposite shows high lithium ion storage capabilities, excellent rate capability and superior cyclic stability. The galvanostatic electrochemical measurements indicate that the nanocomposite exhibits a superior capacity of 604.1 mAh g^?1 at 0.05?A?g^?1, which is higher than that of raw Ti₃C₂T_x (404.9 mAh g^?1). Even at 3?A?g^?1, it retains a stable capacity (91.7 mAh g^?1). This capacity is almost 5.6 times higher than that of Ti₃C₂T_x (16.6 mAh g^?1) and 58 times higher than that of SnO₂/Ti₃C₂T_x (1.6 mAh g^?1). Additionally, the capacity of CNTs@SnO₂/Ti₃C₂T_x for the 50th cycle is 180.1 mAh g^?1 at 0.5?A?g^?1, also higher than that of Ti₃C₂T_x (117.2 mAh g^?1) and SnO₂/Ti₃C₂T_x (65.8 mAh g^?1), respectively.     

Novel Ni and Pd(benzocyclohexan‐ketonaphthylimino)2 complexes for copolymerization of norbornene with octene

Two novel late transition metals complexes with bidentate O?N chelate ligand, Mt(benzocyclohexan‐ketonaphthylimino)₂ {Mt(bchkni)₂: bchkni ?C₁₀H₈(O)C[N(naphthyl)CH₃]; Mt ? Ni, Pd}, were synthesized. In the presence of B(C₆F₅)₃, both complexes exhibited high activity toward the homo‐polymerization of norbornene (NB) (as high as 2.7 × 10⁵ g_polymer/mol_Ni·h for Ni(bchkni)₂/B(C₆F₅)₃ and 2.3 × 10⁵ g_polymer/mol_Pd·h for Pd(bchkni)₂/B(C₆F₅)₃, respectively). Additionally, both catalytic systems showed high activity toward the copolymerization of NB with 1‐octene under various polymerization conditions and produced the addition‐type copolymer with relatively high molecular weights (0.1–1.4 × 10⁵g/mol) as well as narrow molecular weight distribution. The 1‐octene content in the copolymers can be controlled up to 8.9–14.0% for Ni(bchkni)₂/B(C₆F₅)₃ and 8.8–14.6% for Pd(bchkni)₂/B(C₆F₅)₃ catalytic system by varying comonomer feed ratios from 10 to 70 mol %. The reactivity ratios of two monomers were determined to be r_1‐octene = 0.052, r_NB = 8.45 for Ni(bchkni)/B(C₆F₅)₃ system, and r_1‐octene = 0.025, r_NB = 7.17 for Pd(bchkni)/B(C₆F₅)₃ system by the Kelen‐TÜdÕs method. The achieved NB/1‐octene copolymers were confirmed to be noncrystalline and exhibited good thermal stability (T_d > 400°C, T_g = 244.1–272.2°C) and showed good solubility in common organic solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Hydrogen adsorption on partially truncated and open cage C60 fullerene

C₆₀ buckyball molecules were partially truncated by a controlled oxidation at 400 °C and 2 bar oxygen pressure to create unique pore textures suitable for hydrogen adsorption. Pore textural analysis and density measurement confirmed the success of cage-opening and the creation of pore structures accessible to gas molecules. The specific surface area of the C₆₀ sample were increased from below detection to a measurable value (BET: 85 m²/g). Raman spectral study showed that the three main bands of C₆₀, H_g(1), A_g(1) and A_g(2) remained and significant defects were created after the C₆₀ fullerenes were partially oxidized. XRD and SEM measurements suggested that the C₆₀ fullerenes lost their crystallinity and the crystal surfaces were etched after the oxidation step. Hydrogen adsorption on the C₆₀ fullerenes were measured at three temperatures (77, 143 and 228 K) and hydrogen pressures up to 150 bar. Hydrogen adsorption capacity on C₆₀ fullerenes at 77 K at 120 bar was more than tripled (from 3.9 to 13 wt.%) after the C₆₀ fullerenes were partially oxidized. The average heat of adsorption of hydrogen on the partially oxidized C₆₀ fullerene molecules (2.38 kJ/mol) is within the range of the reported values of heat of adsorption on other porous adsorbents.     

Coexistence of Ferroelectric Phases and Phonon Dynamics in Relaxor Ferroelectric Na0.5Bi0.5TiO3 Based Single Crystals

A combination of polarized Raman technique, infrared reflectance spectra, and first‐principles density‐functional theoretical calculations were used to investigate structure transformation and lattice vibrations of Na_0.5Bi_0.5TiO₃, Na_0.5Bi_0.5TiO₃–5%BaTiO₃, and Na_0.5Bi_0.5TiO₃–8%K_0.5Bi_0.5TiO₃ single crystals. It was found that Na_0.5Bi_0.5TiO₃ is of a two‐phase mixture with rhombohedral and monoclinic structures at room temperature. Correspondingly, three Raman‐active phonon modes located at 395, 790, and 868 cm^?1, which were previously assumed as A₁ modes of rhombohedral phase have been reassigned as A^′′, A^′, and A^′ modes of monoclinic phase in the present work. In particular, a strong low‐frequency A^′′ mode at 49 cm^?1 was found and its temperature dependence was revealed. Two deviations from linearity for the abrupt frequency variation in the A^′′ mode and Ti–O bond have been detected at temperatures of ferroelectric to antiferroelectric phase transition T_F–AF and dielectric maximum temperature T_max. The appearance of Na–O vibrations at 150 cm^?1 was found below T_max, indicating the existence of nanosized Na⁺TiO₃ clusters. The observed Raman and infrared active modes belonging to distinct irreducible representations are in good agreement with group‐theory predictions, which suggests 9A₁+9E and 36A^′′+24A^′ modes for the rhombohedral and monoclinic phases of Na_0.5Bi_0.5TiO₃, respectively.     

Investigation of the Tu(>Tg) relaxation in homopolymers and block copolymers of styrene by torsional braid analysis

Investigation of the T_u (>T_g) relaxation in amorphous polymers of styrene by the technique of torsional braid analysis is reviewed. For the most part the relaxation behaves like the glass transition (T_g) in its dependence on molecular weight, on average molecular weight in binary polystyrene blends, and on composition in a polystyrene homogeneously plasticized throughout the range of composition. Diblock and triblock copolymers also display a T > T_g relaxation above the T_g, of the polystyrene phase. Two results in particular suggest that the T_u relaxation is molecularly based. (1) The T_u temperature is determined by the number average molecular weight for binary blends of polystyrene when both components have molecular weights below M_c. (the critical molecular weight for chain entanglements). (2) Homopolymers, and diblock and triblock copolymers of styrene, have a T > T_g relaxation at approximately the same temperature when the molecular weight of the styrene block is equal to that of the homopolymer.     

Antibacterial effect of nanometer-size grafted layer of quaternary ammonium polymer on poly(ether ether ketone) substrate

Owing to its excellent physicochemical properties, poly(ether ether ketone) (PEEK) has been used clinically for medical implants. However, its surface properties should be improved to further enhance its compatibility with a living organism and infection resistance. Here, we examined the surface construction via a combined process, that is, the self-initiated photoinduced graft polymerization of N,N-dimethylaminoethyl methacrylate (DMA) on PEEK substrate followed by polymer quaternization using various bromoalkanes (Q-PDMA-g-PEEK). Using a Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, the grafting and quaternarization of poly(DMA) (PDMA) on the PEEK substrate was confirmed. The degree of quaternizations was at least 60% even when the various bromoalkanes were reacted. The Q-PDMA-g-PEEK with 1-bromooctane (BrC₈) (C₈-Q-PDMA-g-PEEK) substrate exhibited the highest ζ-potential of other Q-PDMA-g-PEEK substrates. However, no significant differences were observed in the degree of quaternization, thickness of the polymer layer, and hydrophilicity of all modified PEEK substrates. In addition, from antibacterial test with Escherichia coli, the C₈Q-PDMA-g-PEEK substrate exhibited the highest antibacterial rate (80%) among Q-PDMA-g-PEEK substrates examined. Therefore, we concluded that the surface ζ-potential is the one an important parameter for manufacturing PEEK substrates with bactericidal properties.     

Electrochemical supercapacitors based on industrial carbon blacks in aqueous H2SO4

It is shown that industrial carbon blacks (CBs) are interesting materials for electrochemical supercapacitors (ECSCs). The specific areas A _s ranged from 28 to 1690 m² g^–1. The highest values were realized through activation in CO₂ at 1100 °C. Precompacted carbon black electrodes with 5–10 wt% PTFE as a binder in the pellet in 10–12 M H₂SO₄ were characterized by constant current cycling, CCC, j = 20–50 mA cm^–2. Voltage–time curves showed nearly pure capacitive behaviour. Specific capacitance of single electrodes, C _s,1, could be derived therefrom. A plot of C _s,1 against A _s shows a linear behavior according to C _s,1 = C _A,DL A _s, where C _A,DL is the Helmholtz double layer capacitance per atomic surface area. Best fit was obtained with C _A,DL = 16 F cm^–2. The highest experimental values, C _s,1 = 250 F g^–1, are due to 60% of the theoretical maximum, which corresponds to an A _s calculated from both faces of isolated graphene layers. Only marginal pseudocapacitances are observed. Model cells for ECSCs (with microporous Celgard^TM separators) could be extensively cycled (CCC). A monopolar cell endured Z > 2000 cycles. Bipolar cells (5 units) allowed 700 cycles. Practical problems such as the development of electrode holders and of carbon black filled polypropylene composites for current collectors are discussed. It is concluded that entirely metal-free ECSCs with low cost can be produced.     

Glass transitions of styrene/α-methylstyrene statistical copolymers and of their blends with PPO® resin

The glass transition temperatures (T_g) and specific heat increments (ΔC_p) at T_g of S/AMS statistical copolymers having weight fractions AMS of 0.00, 0.09, 0.17, 0.26, 0.36, and 0.44 are (by DSC) 380.0 (0.280), 384.2 (0.275), 388.8 (0.284), 391.5 (0.275), 398.3 (0.272), and 405.9 (0.27) °K (J·g^? ·deg^?), respectively. The T_g (ΔC_p) for the PPO resin are 492.2 (0.221). The glass transitions of P(S/AMS) (1) + PPO resin (2) blends having w2 = 0.25, 0.50, and 0.75 were also measured. Examination of the copolymer and blend T_g vs. composition data indicates that a relation recently proposed by Couchman gives a somewhat better approximation than the simple Fox relation. However, the nonadjustable k = ΔC_p2/ΔC_p1 constant in the Couchman relation must be replaced by a smaller empirical k to give a true match of calculated to observed T_g.     

Effective photopolymerization of C60 films under simultaneous deposition and UV light irradiation: Spectroscopy and morphology study

An effective method for uniform photopolymerization of C₆₀ films using simultaneous deposition and irradiation with ultraviolet (UV) light is described. The photopolymerization process was monitored as a function of irradiation time using Raman and infrared (IR) spectroscopy. New features appeared in the Raman (near the pentagonal pinch A_g(2) mode) and IR spectra (400-1500 cm⁻¹) after more than 20 h of UV irradiation testifying to the transformation of pristine C₆₀ to polymerized C₆₀ phases. Band shape analysis of the vibrational data revealed: (i) the degree of photopolymerization to be ∼90% after 20 h of irradiation, and (ii) the presence of orthorhombic, tetragonal, and rhombohedral phases in the photopolymerized films. Electron microscopy and diffraction studies revealed the amorphous nature of the photopolymerized films which comprised of crystals with a linear dimension of ∼40-60 nm. No evidence for cracks in the surface of the polymerized film was found. The proposed route for photopolymerization provides an opportunity to prepare extended polymeric C₆₀ films suitable for technological applications.     

Reaction kinetics modeling and thermal properties of epoxy–amines as measured by modulated‐temperature DSC. I. Linear step‐growth polymerization of DGEBA + aniline

A mechanistic approach including both reactive and nonreactive complexes can successfully simulate both nonreversing (NR) heat flow and heat capacity (C_p) signals from modulated‐temperature DSC in isothermal and nonisothermal reaction conditions for different mixtures of diglycidyl ether of bisphenol A + aniline. The reaction of the primary amine with an epoxy–amine complex initiates cure (E_1A1 = 80 kJ mol^?1), whereas the reactions of the primary amine (E_1OH = 48 kJ mol^?1) and secondary amine (E_2OH = 48 kJ mol^?1) with an epoxy–hydroxyl complex are rate determining from about 2% epoxy conversion on. The reliability of the proposed mechanistic model was verified by experimental concentration profiles from Raman spectroscopy. When cure temperatures are chosen inside or below the full cure glass‐transition region, vitrification takes place partially or completely, respectively, as can be concluded from the magnitude of the stepwise decrease in C_p. The effect of the epoxy conversion (x) and mixture composition on thermal properties such as the glass‐transition temperature (T_g), the change in heat capacity at T_g [ΔC_p(T_g)], and the width of the glass transition region (ΔT_g) are considered. The Couchman relationship, in which only T_g and ΔC_p(T_g) of both the unreacted and the fully reacted systems are needed, was evaluated to predict the T_g– x relation by using simulated concentration profiles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2798–2813, 2004     

Superconducting and normal state properties of the A3C60 compounds

This report is a critical review of the measurements and their interpretations of the normal and superconducting state of the A₃C₆₀ compounds, where A = alkali atom. These compounds are highly ionic [A⁺]₃ · [C₆₀]³⁻ and form fcc lattices (cryolite structure) which locate the C₆₀ icosahedra in sites of local cubic symmetry, thereby preserving the degeneracy of the t_lu orbitals, allowing for the formation of a narrow half-filled band of a width comparable to or smaller than the different molecular excitation energies. The T_c -s of the more than a dozen compounds synthesized so far span the range 2–33 K; the variation of T_c with pressure and from material to material is assessed as an empirical T_c lattice parameter relation, suggestive that the attraction responsible for the Cooper pair formation is a local property of the C₆₀ molecules and variations of the density of state ρ(_f) at the Fermi level (i.e., band width) determine T_c. The superconducting parameters, λ_L and ξ₀ determined from critical field and μSR measurements, favoring a local pairing image, are marginally supportive of the expected density of state variations. The so far available ¹³C nuclear relaxation, susceptibility and ESR measurements in the normal state manifest several features more related to the complex correlated nature of the C₆₀ molecules than free electron band effects of the simple lattice they are arranged in. The paper emphasizes these unusual characteristics.     

Characterization of optical properties of acrylate based adhesives exposed to different temperature conditions

Optical adhesives combine the traditional function of structural attachment with a more advanced function of providing an optical path between optical interconnects. This article aims to characterize refractive index and birefringence of such adhesives under environmental exposure to different temperature conditions. Optical time domain reflectometery (OTDR) and prism coupling methods were employed to measure optical properties of an optical adhesive. Thermo‐optic coefficient (dn/dT) of the adhesive was observed to decrease noticeably from ?2 × 10^?4°C^?1 to ?4 × 10^?4°C^?1 around the glass transition temperature (T_g ～ 78°C). It is observed that refractive indices for both T_E and T_M modes increase with increasing annealing temperature, but the birefringence (T_E ? T_M) is decreasing. This suggests that the material has become more isotropic due to the annealing. The environmental changes in optical properties of the adhesive are discussed in the light of Lorentz–Lorenz equations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 950–956, 2005     

Contributions of torsional braid analysis to Tu

The accomplishments of Borden Award Winner John K. Gillham and his colleagues using Torsional Braid Analysis (TBA) and Differential Scanning Calorimetry (DSC) to investigate the T_g and T > T_g or T_u regions of anionic and thermal poly styrenes (PS) are evaluated and related to work on PS and other polymers and to controversies surrounding TBA and the Tu transition. Arguments are presented to refute the contention that T_u by TBA is an artifact produced by the braid and the contention that T_u has a relaxational nature but no thermodynamic basis. Two distinct behavior patterns are found for T_u vs log M?_n plots: quasi-static methods such as DSC on fused films show T_u to level off above M_c and approach an asymptotic value of ～435K; dynamic methods involving melt flow show that T_u increases without limit above M_c because of entanglements. A compilation is presented of 25 investigations of T_u on polybutadiene, poly(methyl methacrylate) (PMMA), PS, plasticized PS, and atactic polypropylene, involving twenty experimental techniques. The behavior of zero shear melt viscosity for PS is summarized. Gillham's work has not only led to clarification of many isolated papers in the literature but has also inspired various parallel experimental and literature studies on T_u. We conclude that T_u is a molecular level transition which, like T_g, exhibits both kinetic (relaxational) and thermodynamic aspects. It is shown that heat capacity should be a more sensitive method than dilatometry for studying the T_u transition.