Anisotropic and heterogeneous thermal expansion of polyethylene foam blocks: Effect of thermal treatments

Crosslinked closed cell polyethylene foams produced in blocks by compression moulding present an anisotropic and heterogeneous thermal expansion behaviour when the temperature is increased. This paper analyses the main reason for this particular behaviour and presents a way to reduce it by using thermal treatments.In order to perform this analysis, an experimental study on the cellular structure, lamellar distribution and thermal expansion is presented as a function of two kinds of thermal treatments. The experimental results have showed that the main factor controlling the foams thermal expansion is an anisotropic and heterogeneous cellular structure of the original foams. It has been also proved that an adequate thermal treatment allows homogenising the foams thermal expansion.     

Characterization of polymeric dielectric insulation by thermomechanical analysis

Use of a thermomechanical analyzer, TMA, affords a rapid, precise method for determining linear expansion coefficients and linear expansivities of cross-linked polymeric insulation material. Completed cable samples were dissassembled and insulation specimens were cut longitudinally and examined with repeated temperature cycling: ethylene—propylene copolymer rubbers and filled and unfilled crosslinked polyethylenes. The TMA results indicated that all specimes were oriented, likely incurred from extrusion processing. The facility of TMA for investigating potential anisotropic behavior from prior orientation is illustrated by examples of TMA measurements on radial specimens, similarly free of mechanical constraints.     

The thermal expansion of cellulose II and IIIII crystals

Highly crystalline samples of cellulose II and III_II have been prepared from repeated mercerization of ramie fibers and supercritical ammonia treatment of the mercerized ramie fibers, respectively. The thermal expansion behavior of cellulose II and III_II was investigated using X-ray diffraction at temperatures ranging from room temperature to 250 °C. With increasing temperature, the unit cell of cellulose II expanded in the lateral directions and contracted in the longitudinal direction, with the a and b axes increasing by 0.54 and 3.4%, respectively, and the c axis decreasing by 0.09%. The anisotropic thermal expansion in these three directions was closely related to the crystal structure and the hydrogen bonding in cellulose II. A similar anisotropic thermal expansion was also observed in cellulose III_II. Cellulose III_II expanded in the lateral direction but contracted in the longitudinal direction.     

Mechanism of glass ampoule breakage prevention during the freeze-drying process of sodium thiopental lyophilization products on addition of sodium chloride

Glass ampoule breakage during the freeze-drying process was prevented by the addition of sodium chloride to the formulation of lyophilization products of sodium thiopental. In order to clarify the ampoule breakage prevention mechanism, the physicochemical behavior of the freeze-drying process was monitored by simultaneous XRD-DSC measurements and thermal mechanical analysis (TMA). During the freezing process of formulated solution, the smaller heat of fusion of crystallized ice with the addition of sodium chloride was observed in comparison to that without sodium chloride. Although a greater amorphous portion remained, a higher crystal habit of hexagonal ice was reproducibly observed in the XRD patterns with the addition of sodium chloride during the freezing process. In the measurement of TMA, the scattering of the thermal expansion rate of formulated solution was significantly reduced by the addition of sodium chloride. These observations indicated that the addition of sodium chloride minimized the scattering of the thermal expansion rate and might be a cause for the inhibition of glass ampoule breakage during the freeze-drying process.     

光伏组件封装材料进展

封装材料是影响目前太阳能等光伏组件使用性能的重要因素。结合最新研究进展,本文从化学观点出发,综述和评论了实用的乙烯-乙烯醋酸酯共聚物(EVA)、聚乙烯醇缩丁醛(PVB)和聚二甲基硅氧烷(PDMS)材料在使用过程出现的问题以及改性研究方法,强调了PDMS材料在太阳能光伏组件封装中的重要性。     

电极界面缓冲层对P3HT:PC61BM太阳能电池热稳定性的影响

基于溶液法加工制备的聚合物太阳能电池的高温热稳定性是决定器件能否兼容后续高温热封装工艺, 如热压封装、高温原子层沉积(ALD)等的一个关键. 本文分别利用聚(3, 4-乙烯二氧噻吩)-聚苯乙烯磺酸(PEDOT:PSS)和MoO₃作为阳极缓冲层, 以及ZnO和LiF 作为阴极缓冲层, 制备了结构为氧化铟锡(ITO)/阳极缓冲层/3-己基取代聚噻吩:(6, 6)-苯基C₆₁-丁酸甲酯(P3HT:PC₆₁BM)/阴极缓冲层/Al 的太阳能电池, 系统地比较研究了不同界面缓冲材料对器件光电转换性能及稳定性的影响, 特别是在高温煺火条件下器件的性能稳定性差异. 结果表明, 聚合物太阳能电池的热稳定性同器件的结构以及所用的缓冲层材料有密切的相关性. 其中, 利用MoO₃及ZnO分别作为阳极与阴极界面修饰层的P3HT:PC₆₁BM器件在120-150 ℃的温度范围内能够较好地保持器件的光电转换性能. 这一结果为后续需要高温封装工艺的器件提供了有意义的结构优化指导. 此外, 研究结果还表明利用ZnO作为阴极缓冲层能够改善器件的长时间稳定性.     

Colossal Anisotropic Thermal Expansion through Coupling Spin Crossover and Rhombus Deformation in a Hexanuclear {FeIII4FeII2} Compound

Colossal and anisotropic thermal expansion is a key function for microscale or nanoscale actuators in material science. Herein, we present a hexanuclear compound of [(Tp*)Fe^III(CN)₃]₄[Fe^II(Ppmp)]₂⋅2 CH₃OH ( 1 , Tp*=hydrotris(3,5-dimethyl-pyrazol-1-yl)borate and Ppmp=2-[3-(2′-pyridyl)pyrazol-1-ylmethyl]pyridine), which has a rhombic core structure abbreviated as {Fe^III₂Fe^II₂}. Magnetic susceptibility measurements and single-crystal X-ray diffraction analyses revealed that 1 underwent thermally-induced spin transition with the thermal hysteresis. The Fe^II site in 1 behaved as a spin crossover (SCO) unit, and significant deformation of its octahedron was observed during the spin transition process. Moreover, the distortion of the Fe^II centers actuated anisotropic deformation of the rhombic {Fe^III₂Fe^II₂} core, which was spread over the whole crystal through the subsequent molecular rearrangements, leading to the colossal anisotropic thermal expansion. Our results provide a rational strategy for realizing the colossal anisotropic thermal expansion and shape memory effects by tuning the magnetic bistability.     

氯化乙丙共聚物的热行为与稳定性研究

用TMA、DSC和丁G/DTG研究了氯化乙丙共聚物CEP的热行为和稳定性。结果表明:在相同氯含量时,丙烯组份含量高的CEP的软化温度和分解活化能均较高;乙、丙组份比相同的CEP的软化温度随氯含量增加而升高。在氯含量大于50％时,CEP脱HCl活化能显著增加。在CEP中加入热稳定剂,可有效地改善它的稳定性。在所试验的6种稳定剂中,以二盐基亚磷酸铅的效果最好。     

Thermo-mechanical characterisation of in-plane properties for CSM E-glass epoxy polymer composite materials – Part 1: Thermal and chemical strain

The in-plane thermo-mechanical properties and residual stresses of a CSM E-glass/Epoxy material are characterised through the use of DSC and TMA. The measured data is used to generate material models which describe the mechanical behaviour as a function of conversion and temperature. The in-plane thermal expansion coefficient (α) of the composite material decreases above the glass transition temperature (T_g), which is compensated by a higher out of plane deformation above T_g. Comparison of α and chemical shrinkage measurements suggests that chemical bonds between the polymer matrix and the glass fibres are formed prior to shrinkage of the epoxy matrix, i.e., at an early processing stage. This suggests that production of composites with low residual stresses requires focus on reactivity between the matrix and the sizing rather than the matrix cure properties. As a consequence, residual stresses in the composite material are mainly a result of restricted cure shrinkage rather than mismatch between thermal expansion coefficients.     

脂肪族聚酰胺热膨胀行为的研究

通过热膨胀测试,示差扫描量热分析(DSC)、广角X射线衍射(WAXD)与傅里叶变换红外光谱(FTIR)等方法研究了4种脂肪族聚酰胺玻璃化转变温度(Tg)、结晶行为以及氢键强度对热膨胀行为的影响,探索了影响脂肪族聚酰胺热膨胀的本质.DSC和X射线衍射结果表明,聚酰胺中结晶部分的热膨胀系数要低于无定形部分,但聚酰胺的熔融温度和结晶度对热膨胀的影响不够明确.相比较其它脂肪族聚酰胺,聚酰胺56(PA56)具有较高的玻璃化转变温度和较低的亚甲基/酰胺基(CH2/CONH)比例,表现出较低的热膨胀系数.研究发现,在相同条件下制备的脂肪族聚酰胺体系中,CH2/CONH比例或Tg与热膨胀系数具有明显的线性关系,随着CH2/CONH比例的降低或Tg的升高,热膨胀系数显著减小.FTIR的结果表明,聚酰胺分子链间的氢键密度和氢键强度随温度升高衰减的程度是影响其热膨胀行为的关键因素.     

Colossal Anisotropic Thermal Expansion in a Diazo-Functionalized Compound with Switchable Solid-State Behavior

Achieving substantial anisotropic thermal expansion (TE) in solid-state materials is challenging as most materials undergo volumetric expansion upon heating. Here, we describe colossal, anisotropic TE in crystals of an organic compound functionalized with two azo groups. Interestingly, the material exhibits distinct and switchable TE behaviors within different temperature regions. At high temperature, two-dimensional, area zero TE and colossal, positive linear TE (α=211 MK⁻¹) are attained due to dynamic motion, while at low temperature, moderate positive TE occurs in all directions. Investigation of the solid-state motion showed the change in enthalpy and entropy are quite different in the two temperature regions and solid-state NMR experiments support motion in the solid. Cycling experiments demonstrate that the solid-state motions and TE behaviors are completely reversible. These results reveal strategies for designing significant anisotropic and switchable behaviors in solid-state materials.     

Fabrication of mesoporous silica/polymer composites through solvent evaporation process and investigation of their excellent low thermal expansion property

We fabricate mesoporous silica/epoxy polymer composites through a solvent evaporation process. The easy penetration of the epoxy polymers into mesopores is achieved by using a diluted polymer solution including a volatile organic solvent. After the complete solvent evaporation, around 90% of the mesopores are estimated to be filled with the epoxy polymer chains. Here we carefully investigate the thermal expansion behavior of the obtained mesoporous silica/polymer composites. Thermal mechanical analysis (TMA) charts revealed that coefficient of linear thermal expansion (CTE) gradually decreases, as the amount of the doped mesoporous silica increases. Compared with spherical silica particle without mesopores, mesoporous silica particles show a greater effect on lowering the CTE values. Interestingly, it is found that the CTE values are proportionally decreased with the decrease of the total amount of the polymers outside the mesopores. These data demonstrate that polymers embedded inside the mesopores become thermally stable, and do not greatly contribute to the thermal expansion behavior of the composites.     

Catalytic degradation of polyethylene using thermal gravimetric analysis and a cycled-spheres-reactor

Commercial samples of pure polyethylene were decomposed over H-ZSM-5 and Y-type zeolites using thermal gravimetric analysis (TGA) and a laboratory-scale-plant, so-called the cycled-spheres-reactor. By the TGA measurements, the activity and the deactivation behavior of the zeolite catalysts were determined. The plastic to catalyst ratio was varied to find out the optimal value for catalyst screening and for the operation of the cycled-spheres-reactor. In addition, the deactivation behavior of the zeolite catalysts was investigated. Y-type zeolites revealed lower activity and faster deactivation behavior than H-ZSM-5. Higher module of H-ZSM-5 and Y-type zeolite showed slower deactivation, but lower activity than lower module of those. Experiments in the cycled-spheres-reactor proved the results of the TGA measurements in terms of activity. The main products in the non-catalytic degradation were waxes, and when catalysts were applied, a high yield of oils was obtained at the expense of waxes. The product spectra of product oils obtained with catalysts lay mainly in the range C₄–C₁₀.     

Uniaxial negative thermal expansion in crystals of tienoxolol

The thermal expansion of tienoxolol has been investigated by X-ray powder diffraction up to its melting temperature. The data indicate that the expansion is anisotropic and even negative in one direction of the unit cell. The supramolecular structure formed by hydrogen-bonds reflects that of a trellis, which explains the observed behavior of tienoxolol crystals.     

含酰胺结构超低膨胀聚酰亚胺薄膜的热膨胀行为

采用联苯二酐与3种含酰胺结构二胺制备了具有不同取代基团的聚酰胺-酰亚胺薄膜, 考察了酰胺结构对薄膜力学、 耐热及尺寸稳定性的影响, 研究了聚集态结构与薄膜热膨胀行为的关系和规律. 该系列薄膜具有超高强度和优异的耐热性能, 拉伸强度高达280.5 MPa, 玻璃化转变温度在389~409 ℃, 并在30~300 ℃温度范围内表现出超低负膨胀, 热膨胀系数(CTE, ppm/℃, 即10 ⁶ cm·cm ^-1·℃ ^-1)在-3.05~-1.74 ppm/℃之间. 聚集态分析结果表明, 酰胺结构使分子链间形成了强氢键相互作用, 分子链在薄膜面内方向高度有序取向, 并在膜厚方向堆积更为紧密, 使薄膜表现出热收缩现象. 通过不同体积大小的取代基团进一步调控分子链间相互作用及排列堆积, 可实现薄膜在高温下近乎零尺寸形变, 为设计制备超低膨胀聚合物基板材料提供了新思路.     

Thermal characterization of a series of poly(vinylidenefluoride–chlorotrifluoroethylene–trifluoroethylene) terpolymer films

A number of solution-casted poly(vinylidenefluoride–chlorotrifluoroethylene–trifluoroethylene) [P(VDF–CTFE–TrFE)] terpolymer films with different CTFE content have been characterized by a series of thermal analysis techniques, including thermogravimetric analysis (TG), differential scanning calorimetry, dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA). The work intends to provide more comprehensive information about thermal behavior of these ferroelectric polymers. TG results suggest that the introduction of the CTFE units slightly decreases the thermal stability of the polymer due to the instability of C–Cl bond during heating. DMA detected a relatively weak α_a relaxation and a broad α_c relaxation in the samples of low CTFE content. These two relaxation processes completely mixed together in the sample with high CTFE content, revealing the crystalline structures in the polymer, become a more imperfect and diffuse state as CTFE units increasing. The polymer with less CTFE units possesses an enhanced stiffness due to its higher degree of crystallinity. A contraction process after a slight amount of thermal expansion upon heating is detected by TMA, due to the release of internal tensile strain/stress generated during solidification of the films. The higher crystallinity of the polymer film generated the greater strain/stress, leading to the larger degree of shrinkage. Also, the higher melting point of the polymer with less CTFE units allows the film soften at a higher temperature.     

Effect of TiO2 on Altering Direction of Interfacial Charge Transfer in a TiO2‐Ag‐MPY‐FePc System by SERS

Interfacial charge transfer (CT) is of interest owing to its effect on the performance of molecular photovoltaic (PV) devices. The characteristics and structures of interfacial materials, such as TiO₂ nanoparticles (NPs) in some solar cells, are employed to adjust the CT process. In this study, three kinds of interfacial systems, including a solar cell‐like TiO₂‐Ag‐ p‐mercaptopyridine (MPY)‐ iron phthalocyanine (FePc) system, are compared to investigate the interfacial CT process using surface‐enhanced Raman scattering (SERS) spectroscopy. The SERS results show the significance of TiO₂ NPs in the system on altering the direction and path of the interfacial CT, which is closely associated with the CT enhancement contribution to SERS in such an interfacial system. SERS spectroscopy is expected to be a promising technique for the exploration and estimation of the interfacial CT behavior in PV devices, which may further extend the applications of SERS in the field of solar cells.     

Thermochemical and physical properties of printed circuit board laminates and other polymers used in the electronics industry

Theories behind four thermal analysis techniques are reviewed, and relevant case studies are used to illustrate the application of these techniques to measure; various parameters relevant to printed circuit board laminates and engineering polymers.Thermogravimetric analysis (TGA) is used to determine the filler content of polymers and composites and when combined with Fourier transform infrared (FTIR) spectroscopy can be used for the chemical analysis of evolved gases.Differential scanning calorimetry (DSC) is used to measure the melting point of polymers and the degree of cure of prepregs, laminates and adhesives.Thermomechanical analysis (TMA) is used to measure the coefficient of thermal expansion (CTE) and the glass transition temperature (Tg) of laminates, and dynamic mechanical analysis (DMA) is used to measure the storage modulus, loss; modulus and Tan δ of polymers.     

Anisotropic linear thermal expansivity of poly(ether-ether-ketone)

This paper deals with anisotropic behavior of thermal expansivity (α) of poly(ether-ether-ketone) (PEEK) sample prepared by compression molding above the melting point of polymer. The α was determined using thermo mechanical analyzer (TMA) for the temperature interval 50-250 °C in expansion mode. It is found that out-of-plane thermal expansivity (α_z) is 3.8-fold of the in-plane thermal expansivity (α_xy) below the glass transition temperature (T_g) of PEEK while α_z is decreased to 1.8-fold of the α_xy above the T_g. Moreover, the average α_z over the range studied is about 2.2-fold of the α_xy. This anisotropic behavior may be attributed to the alignment of polymer spherulites and chains along in-plane direction due to compressive forces under hot compression molding.