Structure and properties of polybutylene crystallized from the glassy state. I. X-ray scattering,DSC, and torsion pendulum

Isotactic polybutene (PB) can be quenched into a completely glassy state by quenching molten films into a solid-liquid mixture of isopentane, Freon, or ethanol. The crystallization of PB from the glass form was studied by x-ray scattering, differential scanning calorimetry (DSC), and dynamic mechanical spectroscopy (torsion pendulum). As for crystallization from the melt, PB crystallizes from the glass into a tetragonal crystal structure (Form II) at ca. 0°C, depending on sample thickness, and then transforms to the twinned hexagonal structure (Form I) upon aging at room temperature. In the presence of isopentane, PB crystallizes partially from the glass into the untwinned hexagonal (Form 1′) structure at ca. -70°C; the rest of the sample starts to transform to tetragonal structure at ca. -30°C and nearly completes crystallization at ca. 0°C. The exact temperatures of both transformations depend on the amount of isopentane present and sample thickness. Upon aging at room temperature the tetragonal structure converts to the twinned hexagonal structure even faster than in the absence of isopentane. Dynamic mechanical experiments show the presence of two relaxation-like peaks for the ultraquenched samples: T_r (L) = -27°C and T_r (U) = -15°C. X-ray diffraction, DSC, and torsion pendulum experiments show that PB crystallizes from the glass at T_r (U).     

Amorphous linear polyethylene: Annealing effects

The effect of annealing amorphous linear polyethylene films prepared by an improved ultraquenching technique at temperatures just below and above a dynamic mechanical relaxation peak (torsion braid) observed at ∽190K has been characterized by electron microscopy and torsion braid analysis. Based on the results described, this peak is believed related to the lower glass transition temperature T_g(L), the T_g of wholly amorphous linear polyethylene, whereas the β peak at 260K is T_g (upper). Annealing just below T_g (L) results in a growth in size of the nodules observed in the as-quenched samples, whereas annealing above T_g (L) can result in the growth of single crystal-like structures, spherulites, and shish-kebobs. Storage of the crystallized samples at room temperatures results in a decrease in size of the relaxation peak during subsequent torsion braid spectroscopy measurements. The results indicate significant amounts of molecular motion can occur during crystallization even at T_g.     

Crystallization process of Bi(Pb)-Sr-Ca-Cu-O glass

A crystallization study has been carried out for rapidly solidified Bi₂Pb_0.5Sr₂Ca₄Cu₅O_x glass. Glass transition temperature T _g, crystallized superconducting phases and microstructural changes were measured and analysed by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The crystallization mechanism of the three superconducting phases — (2201) 20 K phase, (2212) 80 K phase, and (2223) 110 K phase — has been discussed, and a time-temperature-transformation diagram for the glass has been constructed.     

Structural changes in glassy poly(ethylene terephthalate)

Structural changes in glassy poly(ethylene terephtbalate) and their effects on its crystallization, melting, and various properties were studied. Quenched, annealed below T_g, crystallized, and drawn samples were studied using calorimetry, wide-and small-angle X-ray diffraction, mechanical spectroscopy, and stress-strain analysis. All results indicate some level of order in the glassy polymer which can be increased by annealing below T_g. This order still exists at tempertures above T_g and affects the properties of the polymer.     

An apparent double glass transition in semicrystalline polymers

Thermal expansion and/or specific heat and/or dynamic mechanical loss data reveal the presence of two glass-like transitions in bulk crystallized polyethylene, polypropylene, polybutene-1, polypentene-1, cis-and trans-polyisoprene (natural), poly-4-methylpentene-1, isotactic polystyrene, poly(vinyl alcohol), nylon 6, the oxide polymers ?(CH₂)_nO?, with n = 1 to 4, polyethylene terephthalate, polyvinylidene fluoride, polyacrylonitrile, and polyvinylidene chloride. We designate the lower of these as T_g(L), which appears identical with the conventional T_g at zero crystallinity. The higher one, designated as T_g(U), is strongly increased with increasing levels of cystallinity. The differnece ΔT_g = T_g(U) ? T_g(L) tends to approach zero as the fractional crystallinity, X, approaches zero. For a X of 0.5 [Ptilde] 0.1, ΔT_g is about 50°C and T_g(U)/T_g(L) is about 1.2 with temperatures in °K. The increases in coefficient of thermal expansion, (Δα)_L and (Δα)_U, at these two transitions seem to depend on crystallinity and morphology in the expected manner for polyethylene and polypropylene: for × = 0.5–0.7, (Δα)_U is stronger than (Δα)_L; for X χ 0, (Δα)_L is stronger than (Δα)_U. Such data are not available for the other listed polymers. Some atactic polymers, poly-4-methylpentene-1, and polystyrene also seem to have a double T_g, the upper of which we tentatively ascribe to the presence of Geil-Yeh types of local order. Since polyethylene, polyvinylidene fluoride, and polyvinylidene chloride exhibit the apparent double T_g, tacticity, per se, is not necessary to produce it. Special care must be exercised to distinguish T_g(U) from the crystalline phase α_c relaxation occurring at temperature T_c. It is shown that T_c for well-annealed crystalline material tends to occur at about 0.83 to 0.85 T_M where T_M is the crystalline melting point in °K. Hence T_c is very close to the temperature at which rate of bulk crystallization is a maximum. While the phenomenon of a double T_g seems clear, its origin is in doubt. We suggest that T_g(L) and T_g(U) arise from tkie presence of different types of amorphous material. For example, polymer molecules not incorporated in the crystallites and/or cilia might give rise to T_g(L). Morphological entities under greater restraint, such as tie molecules or loose loops, might give rise to T_g(U). Conversely, pseudocrystalline structures (smectic or nematic) might be responsible for T_g(U), at least in polypropylene, poly-4-methylpentene-1, and possibly in some nylons.

Data available in the literature do not permit making a definite choice between different possible origins of the apparent double glass transition. Indeed, the origin may vary from polymer to polymer.     

Evidence for ordered regions in poly(n-butyl)methacrylate from light-scattering studies

From light-scattering studies on polybutylmethacrylate, a polymeric glass, the variation of the velocity and attenuation of thermally excited hypersonic phonons with temperature has been measured. Measurement of the temperature dependence of the ratio of the intensity of the Rayleigh line to the Brillouin lines is interpreted as due to a configurational rearrangement within the glass above the glass transition temperature, T_g . Only light scattered from longitudinal phonons was observed. The distinct change in the temperature dependence of the velocity, attenuation and intensity ratio identified the glass transition.

For samples annealed well above T_g, T_g was found to be about 0°C from the light-scattering studies, 12°C from differential scanning calorimetry (DSC), and 20°C from refractive index measurements. For an unannealed sample the behaviour of the above parameters with temperature was found to be different. T_g for the unannealed sample was 14°C from light-scattering, 18°C from DSC and 20°C from index of refraction measurements.     

铝诱导非晶硅薄膜的场致低温快速晶化及其结构表征

铝诱导非晶硅薄膜晶化可以降低退火温度、缩短退火时间，是制备多晶硅薄膜的一种重要方法.在此基础上，通过在退火过程中加入电场加速了界面处硅、铝原子间的互扩散，实现了非晶硅薄膜的快速低温晶化.实验结果表明，外加电场，退火温度为400℃，退火时间为60min时，薄膜的晶化率大于60％；退火温度为450℃退火时间为30min时，薄膜已经呈现明显的晶化现象；退火温度为500℃退火时间为15min时，薄膜的x射线多晶峰强度与非晶峰强度之比为未加电场的3—4倍. 关键词： 非晶硅薄膜 多晶硅薄膜 外加电场     

The effect of microtacticity on the glass temperature of poly[α-methyl styrene]

The effect of micrestructure on the glass temperature Tg of poly (α-methyl styrene) has been investigated. It has been observed that T_g increases as the syndiotacticity of the molecule increases-thus T_g = 446 ± 2°K for polymer with 67% syndiotactic placements, while a value of T_g = 453 ± 2°K is found for a sample with 95% syndiotactic placements. Coefficients of expansion for the liquid and glassy states have been calculated and from these a chain stiffness parameter δε/k has been estimated using the Gibbs-DiMarzio theory. The result indicates that the flex energy of the α-methyl styrene chain is 20% larger than for the polystyrene chain.     

Control of Crystallization Kinetics and Study of the Thermal, Structural and Morphological Properties of an Li2O–B2O3–Al2O3 Vitreous System

A glass matrix with nominal composition 50Li₂O·45B₂O₃·5Al₂O₃ (mol%) was synthesized, and its physical properties were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), and atomic force microscopy (AFM). The glass transition temperature T _g, the crystallization-onset temperature T _x,, the crystallization peak temperatures T _c1 and T _c2, and the fusion peak temperatures T _m1 and T _m2 were determined from at least two glass matrix phases to be approximately 382, 457, 486, 574, 761, and 787?°C, respectively, at 5?°C/min heating rate. Heat treatments at 450?°C for an increasing sequence of time intervals allowed control over the amount of crystallization. Additional information on the crystallization kinetics for the LBA glass matrix was gathered from AFM images, DTA thermograms, and XRD diffractograms. The latter technique showed that LiBO₂ (ICDD-16568) and Li₃AlB₂O₆ (ICDD-51754) phases are formed in the glass?Cceramic system. Debye?CScherrer analysis of the XRD peaks revealed a competition between the evolutions of crystal phases during heat treatment. Activation energies for crystallization, obtained from theoretical models applied to the DTA data showed that the crystallization is heterogeneous. The AFM images demonstrated that this heterogeneous crystallization starts at the surface of the LBA glass matrix and identified crystal sizes in agreement with the results of the Debye?CScherrer analysis. Our study shows that thermal and structural characterization techniques can be combined with theoretical results drawn from well-tested models to offer a unified view of crystallization in a glass?Cceramics system.     

Growth,optical, and electrical properties of silicon films produced by the metal-induced crystallization process

Amorphous Si (a-Si) and Ni films were deposited by electron beam evaporation on to borosilicate glass (BSG) substrate maintained at ambient temperature. The BSG/a-Si/Ni stack was subjected to post deposition annealing in air at various temperatures from 200 to 500 °C for 1 h. Electron diffraction was employed to characterize the crystallographic phases appearing on the stacks that were depending on initial conditions. Clear evidence of the formation of hexagonal Si and fcc NiSi₂ was shown by TEM. In parallel, an increase of refraction index was observed. Electrical resistivity measurements showed that resistance is of the order of kilo ohms in the as-deposited films, increasing sharply to giga ohms in films annealed at T higher than 300 °C. A large band gap of 2.23 eV which is the combined contribution from a-Si, wurtzite-Si, and Ni silicide phases, is observed.     

Change in the phase composition and defect structure of a multicomponent ordered Ni-based alloy upon high-temperature annealing

Phase transformations upon the high-temperature annealing of a multicomponent Ni-based alloy produced via direct crystallization are studied by diffraction electron microscopy. The alloy is annealed at T = 1000°C for a prolonged period. The phase composition is determined. The dislocation structure and behavior of the γ-phase during prolonged annealing are studied.     

Annealing induced transformations in structural and optical properties of Ge30Se70−xBix thin films

ABSTRACT

Thin films of Ge₃₀Se_70?xBi_x (x?=?5, 15, 20) were prepared by thermal evaporation method on glass substrates with thickness 800?nm. The films were annealed at 250°C and 320°C for 2?h to study the annealing-induced structural and optical change. The X-ray diffraction characterization revealed the amorphous to crystalline phase transformation with annealing. The indirect optical band gap decreased with annealing which is explained on the basis of phase transformation and density of localized states. The formation of surface dangling bonds around the crystallites during crystallization process reduced the band gap. The Tauc parameter and Urbach energy change show the degree of chemical disorderness in the films. The transmitivity decreased while the absorption coefficient increased with the annealing process. The microstructural study done by Field emission scanning electron microscopy shows the formation of crystallites upon annealing. Atomic force microscopy investigation on these films shows the influence of annealing on surface topography.     

Effects of gas temperature on optical and transport properties of a-Si:H films deposited by PECVD

Effects of silane temperature (T _g) before glow-discharge on the optical and transport properties of hydrogenated amorphous silicon (a-Si:H) thin films were investigated. The optical measurements show that the refractive index increases with increasing T _g. The transport characterizations show that when T _g increases, the dark conductivity increases. However, the temperature coefficient of resistance decreases. In addition, after holding at 130°C for 20 h, the resistance variation, ΔR/R, of the films deposited at T _g = room temperature (10.8%) is much larger than those deposited at silane temperatures of 80°C (3%) and 160°C (2%). This can be attributed to different rates of defect creation in a-Si:H films caused by various T _g.     

Compatibilization of Poly(Trimethylene Terephthalate)/Polycarbonate Blends by Epoxy. Part 2. Melting Behavior and Spherulite Morphology

The melting behaviors of poly(trimethylene terephthalate)/polycarbonate (PTT/PC) blends, compatibilized by epoxy, and PTT spherulite morphology in the blends were investigated. When epoxy was present during blending, the melting behaviors of PTT/PC blends changed substantially; glass transition temperatures (T_g's) and cold crystallization temperature (T_cc's) of the PTT‐rich phase shifted to higher temperatures, while T_m's shifted slightly to lower temperatures, indicating that epoxy suppressed considerably all processes of dynamic movements pertinent to molecular (or segmental) movements. The cold crystallization process responded sensitively to thermal history. Changes of T_cc's with composition suggested that the epoxy's compatibilization effect was pronounced when PTT and PC were in near equal content.

Recrystallization or reorganization exotherms appeared before melting for isothermally crystallized PTT/PC and PTT/PC epoxy (E) blends. A wide angle X‐ray diffraction (WAXD) analysis showed that, although the perfection of PTT crystallites was influenced either by PC content and the presence of compatibilizer or by the crystallization temperature and crystallization time, PTT's crystal structure was independent of these variables.

The polarized light microscopy (PLM) observations showed that PTT spherulite morphology was very sensitive to blend composition. Epoxy addition interfered severely with the growth of PTT spherulites, causing them to be much less developed. When the spherulites grew under a condition of varied composition, they would exhibit diversified spherulite morphology, though in one spherulite.     

The glass transition in some pigmented polymer systems used for tablet coating

The glass transitions in talc- and titanium-dioxide-filled free films of hydroxypropyl methylcellulose (HPMC) as well as HPMC in combination with either polyethylene glycol (PEG) 400 or polyvinyl alcohol (PVA) have been examined by differential scanning calorimetry. The glass transition temperatures (T_g's) of HPMC and HPMC/PEG 400 films were increased in the presence of either talc or titanium dioxide, with the former the more effective T_g enhancer. In contrast, the T_g 's of HPMC/PVA films were virtually unchanged in the presence of the fillers, and this behavior was attributed to the influence of the vinyl backbone of PVA. The T_g's of filled and unfilled HPMC and HPMC/PVA films were lower after storage for 1 year, but the T_g of HPMC/PEG 400 remained unchanged. Phase separation of the mixed polymer systems also occurred following prolonged storage. These phenomena were related to changes in the moisture content and crystal-linity of the films.     

Interphase Transfer of Tackifier between Immiscible Rubbers

Interphase transfer of a coumarone-indene tackifier between natural rubber (NR) and poly(isobutylene) (PIB) was studied. The laminated sheets, composed of a sheet of NR with the tackifier and a sheet of PIB with the tackifier, were annealed at various temperatures to promote the interphase transfer of the tackifier. After separating the two sheets, the infrared spectra were measured to evaluate the tackifier content in each rubber sheet. It was found that a large amount of the tackifier resided in PIB after annealing at ?20°C, whereas the tackifier moved to NR at 40°C. Consequently, the NR sheet exhibited a lower glass transition temperature T_g after annealing at ?20°C and a higher T_g when annealed at 40°C. The differential scanning calorimetry measurements revealed that the crystallization of NR was responsible for the tackifier transfer. This phenomenon should be of interest because the tackifier transfer, which results in the T_g shift of each rubber, would also occur in a blend system. When NR is the matrix of the blend, it would be an ideal blend because the matrix would show a low T_g in winter and a high T_g in summer.     

Morphology-property studies of amorphous polycarbonate

The relationship between morphology and several physical properties (tensile, thermal, dielectric, and dynamic mechanical properties) of amorphous poly-bisphenol-A-carbonate was examined as a function of annealingtime at temperatures below the glass transition temperature (T_g). The change in structure of the amorphous films was studied by means of X-ray diffraction and with electron diffraction using a rotating sector in an electron microscope as well as by electron micrographs of replicas of surfaces prepared by etching with dilute aqueous NaOH solutions. The changes in morphology and physical properties caused by annealing below T_g are, in general, closely related. The relationship cannot be explained only by changes in free volume; it is proposed that changes in the degree and type of order (nodular structure) also play a role. The design and application of the rotating sector is described in an Appendix.     

Crystallization kinetics of the TeO2–BaO glass system

Tellurite glasses of the system (100–x)TeO₂–xBaO, with x = 05, 10, 15 and 20 wt%, have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under non-isothermal conditions, applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC, using continuous-heating techniques. In addition, from the dependence of the glass-transition temperature (T _g) on heating rate, the activation energy for the glass transition was derived. Similarly, the activation energy of the crystallization process was determined and the crystallization mechanism characterized. The thermal stability of these glasses are considered in terms of the characteristic temperatures, T _g and T _in (the onset temperature of crystallization), via ΔT = T _in?T _g and a kinetic parameter K(T _g). The results confirm that thermal stability decreases with increasing BaO content. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of α-TeO₂, γ-TeO₂ and BaTeO₃ in the remaining amorphous matrix.     

Elaboration and structural characterization of glasses inside the ternary SrO-TiO2-P2O5 system

The glasses in the SrO-TiO₂-P₂O₅ system were prepared by the conventional quenching route. The amorphous state of samples was verified by X-ray diffraction (XRD). Density, molar volume, micro-hardness, glass transition temperature (T_g), and crystallization temperature (T_c) parameters are determined for each glass. The results show that they depend strongly on the chemical compositions. The structure approach of the glasses is determined by using Infrared spectroscopy (IR). This investigation highlights that the glassy-matrix contains various phosphate structural units. The crystallization of the glasses by heat-treatments is performed and the crystallized phases Sr₃P₄O₁₃, TiP₂O₇, Sr(PO₃)₂ are identified by XRD. The overall results are correlated to the glass structure and the nature of chemical bonds constituting the glass network.     

Confinement effects on glass transition temperature,transition breadth,and expansivity: Comparison of ellipsometry and fluorescence measurements on polystyrene films

Using ellipsometry, we characterized the nanoconfinement effect on the glass transition temperature (T _gof supported polystyrene (PS) films employing two methods: the intersection of fits to the temperature (Tdependences of rubbery- and glassy-state thicknesses, and the transition mid-point between rubbery- and glassy-state expansivities. The results demonstrate a strong effect of thickness: T_g(bulk)-T_g(23 nm) = 10 ^°\ensuremath T_{{\rm g}}({\rm bulk})-T_{{\rm g}}(23{\,\mbox{nm}})= 10 ^{\circ} C. The T -range needed for accurate measurement increases significantly with decreasing thickness, an effect that arises from the broadening of the transition with confinement and a region below T _g where expansivity slowly decreases with decreasing T . As determined from expansivities, the T _g breadth triples in going from bulk films to a 21-nm-thick film; this broadening of the transition may be a more dramatic effect of confinement than the T _g reduction itself. In contrast, there is little effect of confinement on the rubbery- and glassy-state expansivities. Compared with ellipsometry, T _g ’s from fluorescence agree well in bulk films but yield lower values in nanoconfined films: T _g(bulk) - T _g(23 nm) = 15^° C via fluorescence. This small difference in the T _g confinement effect reflects differences in how fluorescence and ellipsometry report “average T _g ” with confinement. With decreasing nanoscale thickness, fluorescence may slightly overweight the contribution of the free-surface layer while ellipsometry may evenly weight or underweight its contribution.