Direct analysis of annealing of nodular crystals in isotactic polypropylene by atomic force microscopy, and its correlation with calorimetric data

The process of isothermal annealing of nodular monoclinic crystals of isotactic polypropylene (iPP) was analyzed by atomic force microscopy (AFM) and temperature-modulated differential scanning calorimetry (TMDSC). Initially nodular and mesomorphic domains were obtained by controlled melt-crystallization at high cooling rate. Subsequent heating triggers transition from mesomorphic to monoclinic structure, and melting of unstable nodules. Annealing allows re-crystallization, which is recognized by enlargement of domains from initially about 20 nm to about 35 and 55 nm after annealing at 393 and 433 K, respectively. Furthermore, the re-crystallization process is connected with a slight change of the aspect ratio of crystals. The isothermal re-crystallization of the liquid is superimposed by aggregation of crystals, to yield blocky, and string-like objects. The direct analysis of structure on isothermal annealing by AFM is for the first time compared with the isothermal decrease of the apparent specific heat capacity, or change of enthalpy, monitored by TMDSC. The apparent specific heat capacity decreases during annealing with an identical non-linear time dependence as the directly observed growth of the crystal size. Analysis of the annealing processes at different temperatures yields proportionality between the increase of the crystal size and the reduction of the apparent specific heat capacity.     

聚乙二醇／聚丙烯酰胺共混物的制备及性能研究

通过微波加热法制备聚丙烯酰胺,将其与聚乙二醇共混制备聚乙二醇／聚丙烯酰胺（PEG,PAM）共混物,采用傅立叶变换红外线光谱（FTIR）,差示扫描量热仪（DSC）,X射线粉末衍射仪（XRD）,熔点偏光显微镜等测定共混物的性能。结果显示共混物中PEG与PAM形成氢键,共混物的升降温过程中具有吸热和放热峰,相变温度和相变焓随共混物中PAM含量的增加,逐渐降低。PAM的存在对PEG的结晶过程造成了破坏,共混使PEG难以形成均匀球晶,结晶粒子变大。     

Two equilibrium melting temperatures and physical meaning of DSC melting peaks in poly(ethylene terephthalate)

For poly(ethylene terephthalate), two equilibrium melting temperatures, 262 °C and 276 °C, were found with DSC. They should be assigned to two forms of crystals with the infinite crystal length, respectively. This finding made it possible every crystal form to derive the end surface free energy per unit area of crystals and the transition enthalpy of the ordered parts in the amorphous regions and using these thermodynamic quantities to convert DSC melting curves into the crystal length distribution. Through the derivation of them, the participation of the crystallization temperature on cooling in the thermal analysis of DSC melting curves was revealed thermodynamically.     

Influences of processing on the phase transition and crystallization of polypropylene cast films

Phase transition and changes of properties of isotactic polypropylene (i‐PP) cast films with the processing conditions have been investigated by wide‐angle X‐ray diffraction, two‐dimensional small‐angle X‐ray scattering, and atomic force microscopy. It was found that chill roll temperature was a major factor, which influenced the formation of mesomorphic phase and its transition to spherulitic structure. Only mesomorphic phase was observed in the films produced under a chill roll temperature of below 40°C. When the roll temperature was increased to 60°C, mesomorphic phase coexisted with spherulitic crystal structure, and totally transformed to monoclinic structure at the roll temperature of 80°C. Differential scanning calorimetry, tensile, and optical tests were also performed on the films. The results showed that the observed structure changes were closely related to the thermal behavior, tensile, and optical properties of the PP films. The influence of die temperature on the films was also discussed, but the effect was much less than chill roll temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41100.     

Differential Scanning Calorimetric Study of the Effect of Cholesterol on the Thermotropic Phase Behavior of the Phospholipid 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine

Using the differential scanning calorimetric (DSC) technique, the thermal properties of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) phospholipid and its mixture with cholesterol (Chol), in the range between 10 and 50 mol.%, were investigated. A considerable modification of the structural conformation and the biophysical properties of the bilayer of the phospholipid system after the Chol incorporation were detected. Concentrations below 30 mol.%, and especially in the range 10–20 mol.%, were found to be optimal in the effective miscibility of SOPC and Chol components. The effective miscibility completeness, mainly in the gel and liquid crystal phases, was indicated. It was discovered that Chol mixed with SOPC slightly shifts its gel (L _β) to liquid crystal (L _α) phase transition temperature, decreases cooperativity, expressed by the van't Hoff enthalpy, and markedly and progressively reduces the transition enthalpy to almost zero at 50 mol.%. By deep incubation of the cholesteric phospholipid mixture, it was revealed that the endothermic peak associated with laminar crystal to gel phase transition does not exist in conventional pure SOPC bilayer systems.     

Energy Crossovers in Nanocrystalline Zirconia

The synthesis of nanocrystalline powders of zirconia often produces the tetragonal phase, which for coarse-grained powders is stable only at high temperatures and transforms into the monoclinic form on cooling. This stability reversal has been suggested to be due to differences in the surface energies of the monoclinic and tetragonal polymorphs. In the present study, we have used high-temperature oxide melt solution calorimetry to test this hypothesis directly. We measured the excess enthalpies of nanocrystalline tetragonal, monoclinic, and amorphous zirconia. Monoclinic ZrO₂ was found to have the largest surface enthalpy and amorphous zirconia the smallest. Stability crossovers with increasing surface area between monoclinic, tetragonal, and amorphous zirconia were confirmed. The surface enthalpy of amorphous zirconia was estimated to be 0.5 J/m². The linear fit of excess enthalpies for nanocrystalline zirconia, as a function of area from nitrogen adsorption (BET) gave apparent surface enthalpies of 6.4 and 2.1 J/m², for the monoclinic and tetragonal polymorphs, respectively. Due to aggregation, the surface areas calculated from crystallite size are larger than those measured by BET. The fit of enthalpy versus calculated total interface/surface area gave surface enthalpies of 4.2 J/m² for the monoclinic form and 0.9 J/m² for the tetragonal polymorph. From solution calorimetry, the enthalpy of the monoclinic to tetragonal phase transition for ZrO₂ was estimated to be 10±1 kJ/mol and amorphization enthalpy to be 34±2 kJ/mol.     

Effect of triglycerides containing 9,10-dihydroxystearic acid on polymorphism of sal (Shorea robusta) fat

The effect of the triglycerides containing 9,10-dihydroxystearic acid (DHS-TG) on the phase transition of polymorphic forms of normal triglycerides (TG) of sal fat was investigated by differential scanning calorimetry (DSC) under different cooling and heating modes. Four levels of DHS-TG, 2, 5, 8 and 10%, were used. DHS-TG accelerated the phase transition of lower melting crystal forms I → II → III of TG obtained under rapid (20°C/min) or slow (2°C/min) rates of cooling. They delayed the phase transition of crystal form III to IV of TG at 0°C. Also, DHS-TG reduced the heat of fusion (ΔH) of the stable form (V) of TG obtained after tempering at 0°C and at 26°C.     

DSC determination of thermally oxidized olive oil

The feasibility of using DSC as an analytical method to evaluate the autoxidation of olive oil at 50°C and thermal oxidation at 93 and 180°C in 10-mL airtight vials was studied. DSC peak enthalpy and peak crystallization temperatures were compared with headspace oxygen depletion and headspace volatiles in oxidized oil samples. A single crystallization peak was found in olive oil. The crystallization peak shifted to lower temperatures, and the enthalpy associated with this phase transition decreased as the exposure time increased at 93 and 180°C. DSC peak enthalpy in olive oil at 50, 93, and 180°C showed correlations of 0.84, 0.91, and 0.95, respectively, with headspace oxygen depletion in sample bottles. Correlation of DSC initial peak temperature with headspace oxygen depletion was 0.53, 0.87, and 0.95 at 50, 93, and 180°C, respectively. Correlations of DSC peak enthalpy and initial peak temperature with headspace volatiles at 180°C were 0.95 and 0.97, respectively. These results indicate that DSC is a good analytical method to determine the oxidative stability of olive oil at frying temperature.     

High-Temperature Phase Transition of Y4Al2O9

Reversible thermal phase transition was observed for Y₄Al₂O₉ at 1377°C with a hysteresis width of 78°C using differential scanning calorimetry. The enthalpy of the transition (Δ H ) was about 300 cal/mol. Powder X-ray diffraction peaks of the high-temperature phase, as well as the peaks of the low-temperature phase, were characterized with a monoclinic unit cell. Thermal hysteresis was also confirmed by the temperature dependence of the lattice parameter. The unit cell volume of the high-temperature phase was 0.5% smaller than that of the low-temperature phase at 1400°C.     

The role of interlamellar chain entanglement in deformation-induced structure changes during uniaxial stretching of isotactic polypropylene

In-situ small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD) were carried out to investigate the deformation-induced structure changes of isotactic polypropylene (iPP) films during uniaxial stretching at varying temperatures (room temperature, 60 °C and 160 °C). From the WAXD data, mass fractions of amorphous, mesomorphic and crystal phases were estimated. Results indicate that at room temperature, the dominant structure change is the transformation of folded-chain crystal lamellae (monoclinic α-form) to oriented mesomorphic phase; while at high temperatures (>60 °C); the dominant change is the transformation of amorphous phase to oriented folded-chain crystal lamellae. This behavior may be explained by the relative strength between the interlamellar entangled network of amorphous chains, which probably directly influence the tie chain distribution, and the surrounding crystal lamellae. It appears that during stretching at low temperatures, the interlamellar entanglement network is strong and can cause lamellar fragmentation, resulting in the formation of oriented mesomorphic phase. In contrast, during stretching at high temperatures, the chain disentanglement process dominates, resulting in the relaxation of restrained tie chains and the formation of more folded-chain lamellae.     

Morphology, reorganization and stability of mesomorphic nanocrystals in isotactic polypropylene

The morphology and thermodynamic stability of crystals of isotactic polypropylene (iPP) were analyzed as a function of the path of crystallization by atomic force microscopy (AFM) and differential scanning calorimetry (DSC). Samples were melt-crystallized at different rates of cooling using a “controlled rapid cooling technique”, and subsequently annealed at elevated temperature. Mesomorphic equi-axed domains with a size less than 20 nm were obtained by fast cooling from the melt at a rate larger about 100 K s⁻¹. These domains stabilize on heating by growing in chain direction and cross-chain direction, to reach a maximum size of about 40-50 nm at a temperature of 433 K, with the quasi-globular shape preserved. Annealing at 433 K additionally triggers formation of different types of lamellae. It is suggested that these lamellae either develop by coalescence of nodules, or by recrystallization from the melt. The transition from the disordered mesomorphic structure, evident at ambient temperature after fast crystallization, to monoclinic structure on heating at about 340 K occurs at local scale within existing crystals, and cannot be linked to complete melting of mesomorphic domains and recrystallization of the melt. The temperature of melting of initial mesomorphic domains, after reorganization at elevated temperature, is identical to the temperature of melting of rather perfect lamellae, obtained by initial slow melt-crystallization, followed by annealing. The close-to-identical temperatures of melting of these crystals of largely different shapes are confirmed by model calculations, using the Gibbs-Thomson equation. Modeling of the melting temperature reveals that nodular crystals, stabilized by annealing at high temperature, exhibit a similar fold-surface as lamellar crystals.     

1,3-二(二苯基氯硅烷基)-2,2,4,4-四苯基环二硅氮烷的合成及液晶性表征

用1,3-二(二甲基氯硅烷基)-2,2,4,4-四甲基环二硅氮烷与二苯基二氯硅烷反应,得1,3-二(二苯基氯硅烷基)-2,2,4,4-四苯基环二硅氮烷,用甲苯与正辛烷提纯化合物,熔点200～206℃,收率75%～78%。产品经IR和1H NMR确证了结构,用示差扫描量热法(DSC)与偏光显微镜分析,发现该化合物具有液晶性,属于热致型液晶,显示六方相。经教育部科技查新工作站(L03)2007年11月22日出具的第2007236号《科技查新报告》证实,在国内文献中未见关于1,3-二(二苯基氯硅烷基)-2,2,4,4-四苯基环二硅氮烷液晶性表征的相关报道。     

改性SiO2杂化层相变微胶囊的制备与表征

以相变温度为32℃的石蜡为芯材，三聚氰胺-甲醛树脂/改性SiO₂杂化层为壁材，采用原位聚合法制备相变微胶囊。使用接触角测定仪考察了KH-570对纳米SiO₂的有机改性效果；运用扫描电子显微镜（SEM）和X射线能谱仪（EDS）分析了微胶囊表面形貌及壳层表面的元素分布；采用差示扫描量热仪（DSC）测定了相变微胶囊的热性能参数。结果表明：使用KH-570有机改性的纳米SiO₂颗粒制备杂化层能显著提升微胶囊的热稳定性与使用耐久性。当改性SiO₂质量分数为3%时，制得的微胶囊呈光滑球形，SiO₂颗粒在胶囊壳层表面分散均匀，其相变焓为135.1J/g，相变过程滞后，并且微胶囊芯材在有机溶剂中的渗透率由66.1%降至45.8%，经历1000次热循环后的质量与相变焓损失率仅为7%与24.4%。     

Characterization of the dual crystal population in an isothermally crystallized homogeneous ethylene-1-octene copolymer

The melting of a homogeneous ethylene-1-octene copolymer after isothermal crystallization is discussed based on DSC and time-resolved SALS, SAXS and WAXD data. Two melting peaks appear in DSC suggesting the presence of two crystal fractions. All crystals grow in a lamellar habit and there is no evidence for fringed micellar or isolated block-like crystals. The high melting fraction crystallizes while segregating comonomer-rich parts into separate regions where in a later stage the low melting fraction crystallizes. The data support the view of lamellae that grow via the secondary nucleation of crystalline blocks from a preexisting layer-like mesomorphic phase with preservation of the mesomorphic layer thickness. The stability of these blocks increases due to sintering, forming lamellae that melt slightly above the crystallization temperature. The high melting fraction is generated from those lamellae that are able to reduce the crystalline-amorphous interfacial tension.     

侧向二氟代酯类液晶的合成

以4-溴-2,3-二氟苯酚为原料,通过与烷基双环己基甲酸或烷基环己基苯甲酸的酯化,生成三环溴代物;然后在氮气保护下,以四三苯基磷钯为催化剂与丁基苯硼酸偶联,制备了两个系列6种四环侧向二氟取代酯类液晶化合物,其总收率大于50%,气相色谱测定了其质量分数均大于99%。目标化合物经IR,1HNMR和MS确认了分子结构。DSC分析表明,该类液晶化合物有很高的清亮点(>280℃)和较宽的介晶相温度范围。     

Solid‐state structure of thermally crystallized syndiotactic polystyrene

The solid‐state structure of syndiotactic polystyrene (s‐PS) after crystallization from the melt and the glassy state was examined by differential scanning calorimetry (DSC), density, and X‐ray diffraction analysis. It was possible to prepare semicrystalline s‐PS containing either the pure α‐ or the pure β‐crystalline form by melt crystallizing s‐PS from 280 or 330°C. The measurements confirmed the low density of both crystalline forms, which in the case of α‐crystalline form was smaller and in the case of β‐crystalline form was only slightly larger than the density of the glassy amorphous s‐PS. An endeavor to introduce the crystalline phase in s‐PS through cold crystallization at constant temperature above the glass transition resulted in a complex ordered phase. This ordered phase, depending on the crystallization temperature, contained the planar chain mesomorphic phase and the α‐crystalline phase with a low degree of perfection (cold crystallization in the range 120–175°C) or a mixture of the α‐ and β‐crystalline forms with a high degree of perfection (cold crystallization in the range 210–260°C). The combination of DSC and X‐ray measurements enabled us to resolve the complex ordered structure in semicrystalline s‐PS after cold crystallization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2705–2715, 2002     

Phase behavior of homologous series of monoesters of polyols

Phase behavior of anhydrous monopalmitates and stearates and of most laurates, myristates and behenates of ethylene glycol, erythritol, xylitol, sorbitol, and mannitol has been studied. The compounds, substantially free of diesters, are mostly not isomerically pure but are predominantly primary esters. Also studied were the (nonisomeric) palmitate and stearate of pentaerythritol (Pe) and the oleate of erythritol. Mesomorphism, absent in anhydrous monoglycerides unless of short chain length and symmetrical, is a prominent feature of the members of the present group of compounds containing at least three unesterified hydroxyls. In general, crystal melting points rise with length of polyol, and mesomorphic melting points rise faster. Crystal melting points rise with acyl chain length while mesomorphic melting points run through a maximum. Heats of fusion are of the order 40 cal/g for crystal melting and 0.5 cal/g for melting of mesomorphic states. In the range explored, mesomorphic values fall with both polyol length and acyl length. At higher acyl chain length, notably with behenates, there are new features of mesomorphic behavior. Crystalline phase, from solvent, melts to a neat or lamellar phase, which in turn melts to liquid with subsequent appearance of higher melting middle or cylindrical phase. Polymorphism is general among the crystal states and tends to be complex. In a brief study of solvent crystallized 50–50 binary mixes of xylitol stearate with other xylitol esters and other stearates, considerable evidence of solid solution in Form I crystals (of xylitol stearate type) was observed with very modest eutectic lowering of crystal melting point. Mesomorphic points were almost linearly intermediate between those of components. Of particular interest were mixtures of xylitol stearate and 1-monostearin (50–50 and 25–75), for which mesomorphic melting points were realized, and for which an extrapolation to 100% monostearin leads to a hypothetical mesomorphic melting point far below any monoglyceride crystalline melting point. A brief examination of an aqueous xylitol palmitate system explored to a maximum temperature of 165 C shows extensive occurrence of aqueous mesomorphic state somewhat after the manner of monoglyceride systems. Mesomorphic melting level rises rapidly from the value for anhydrous ester.     

Process analysis of phase transformation of α to β-form crystal of syndiotactic polystyrene investigated in supercritical CO2

Mechanism of solid phase transformation of α to β form crystal of syndiotactic polystyrene (sPS) was investigated in supercritical CO₂. The phase transformation occurred in the original pure α and mixed (α+β) form sPS in supercritical CO₂ was traced as a function of temperature and pressure by means of wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC). At appropriate temperature and pressure, sPS underwent solid phase transitions from α to β form. Higher temperature or higher pressure favored this transformation. Compared to the original pure α form sample, the original β form crystal in the mixed (α+β) form sample acted as the nucleus of β form crystal, so that reduced the transition temperature and pressure.     

溶剂对FOX-7晶体相变和热性能的影响

采用重结晶法在二甲基甲酰胺(DMF)/H2O、二甲基亚砜(DMS)O/H2O和N-甲基吡咯烷酮(NMP)/H2O等不同溶剂体系中得到FOX-7晶体,用扫描电子显微镜(SEM)测试晶体的形貌、变温X-射线粉末衍射(XRD)分析晶型和相变、差示扫描量热仪(DSC)测试其热性能。结果表明,不同溶剂重结晶得到的FOX-7晶体形貌有较大差别,在DMSO/H2O溶剂中得到的晶体质量要优于其他两种;3种溶剂中得到FOX-7晶体的晶型和相变过程相同,即常温下FOX-7的晶型为α晶型,在120℃时,FOX-7完成α→β相变,至185℃时,完成β→γ相变;重结晶的FOX-7晶体5s爆发点温度提高了4~9℃,说明热稳定性增强。     

Structural Investigation of Monoclinic‐Rhombohedral Phase Transition in Na3Zr2Si2PO12 and Doped NASICON

Aliovalent doping of the zirconium site in Na₃Zr₂Si₂PO₁₂ (NASICON) was performed with a range of +3 (Al, Y, Fe) and +2 (Co, Ni, Zn) valent cations. The monoclinic‐rhombohedral phase transition was analyzed with high‐temperature in situ X‐ray diffraction, and differential scanning calorimetry (DSC). From the lattice parameters extracted at room temperature up to 300°C it was determined that the high‐temperature rhombohedral phase distorts to the low‐temperature monoclinic phase through a shear deformation of the unit cell. DSC confirmed the phase transition and demonstrated that the phase transition temperature was lowered by doping the NASICON structure. Furthermore, the distortion of the lattice was less severe for all doped samples. Ultimately aliovalent substitution for zirconium stabilized the higher symmetry rhombohedral phase of NASICON, with yttrium doping providing the lowest phase transition temperature and the smallest distortion of the lattice through the phase change.