Search

Poly(vinylidene fluoride) (PVDF) has been widely studied because of its various crystal phase transformations as well as its special dielectric, piezoelectric, and other electrical properties. In this study, a temperature gradient (T-gradient) was constructed for studying the temperature dependence of the crystallization behavior of PVDF and the heterogeneous nucleation effect of multiwall carbon nanotubes (MWCNTs). The nanoscale structure of PVDF was investigated through three different dimensions using FTIR for the surface, WAXD/SAXS for the bulk and AFM for the cross-section. The results showed that low temperature and a heterogeneous nucleating agent were both conducive to the formation of the γ phase of PVDF. The distance of MWCNT nucleation effect is about 15 μm, and it is more significant in 0–5 μm. The content of the γ phase reached 77% when Tc was lower than 61 °C. The higher content and lower crystallite size of the γ phase lead to a higher dielectric constant, which can lay a foundation for its future application in the field of dielectrics. [ABSTRACT FROM AUTHOR]

For isotactic polybutene-1 (iPB-1), II-I transition is of great industrial importance; however, the traditional nucleation-controlled solid-solid II-I transition mechanism eventually encountered challenges and the roles of iPB-1 amorphous phase gained the interest of many researchers. With three nucleating agents, namely WBQ-88, TMB-5 and WBG-II, incorporated into iPB-1, the amorphous phase was tuned with a form II crystalline structure remaining fixed. Based on the observed Tm,II decrease and Tm,I increase during the II-I transition as well as the resulting final Tm,I synergistically tuned by nucleating agent incorporation and crystallization conditions, it is proposed that the entire II-I transition of iPB-1 involves a form II consumption process and a form I formation process. The same as-crystallized form II structures of iPB-1 containing various nucleating agents are involved in a fixed form II consumption process. The amount of iPB-1 chain segments in the amorphous phase, which have the ability to crystallize, as well as their actual ability to crystallize synergistically determine the initiation of form I crystallization. Consequently, the started form I crystallization triggers II-I transition by overcoming the energy barrier for form II crystal cells to be destroyed. Both the initiation and the subsequent form I crystallization process can be enhanced by nucleating agent incorporation or isothermal crystallization at different Tc values, comprehensively resulting in a fast II-I transition process with final form I crystalline structures determined. The results provide an understanding of the II-I transition mechanism and shed light on the development of techniques to accelerate the II-I transition for iPB-1 industrial applications. [ABSTRACT FROM AUTHOR]

As a new type of two-dimensional material, black phosphorus (BP) has great potential for development. However, the unclear synthesis mechanism means that its practical application is challenging. In this study, after BP synthesis (without a process intervention such as an interrupted reaction), the material transformation mechanism was studied by studying the product state under various process factors. Based on the Schäfer chemical vapor transport equations, the BP crystal growth model was deduced. In the five temperature stages of BP growth, the existing form and state, position and function, as well as the formation and transformation mechanism of each substance are described in detail. The key temperature stages of the formation and transformation of the nucleating agent and its precursors were determined to be stage III and stage IV. The influence and mechanism of temperature distribution and pressure in a muffle furnace on BP synthesis were ascertained, which provided a basis for controllable and efficient synthesis of BP. [ABSTRACT FROM AUTHOR]

As the main factor restricting the production of poly(1-butene), the slow phase transition of poly(1-butene) from form II to form I has not been avoided effectively because of the lack of effective methods. Blending with other polyolefins to directly transit into the stable form I′ crystals could be a possible solution; however, such a method hardly inhibits the formation of form II completely. What is worse, the obtained form I′ crystal even has a lower thermostability than that of form II, which makes it hard to be an ideal solution. In this study, employing FTIR spectroscopy, XRD, SEM, and POM, we found that adding a moderate amount of WBG-II, a nucleating agent of iPP, into isotactic polypropylene/poly(1-butene) (iPP/PB-1) blends could greatly promote the formation of form I′. More importantly, the melted form I′ can rapidly recrystallize into form II on heating, improving thermostability. The lower the quenching temperature, the more significant the role of WBG-II. We conjectured that the effect of WBG-II could be related to iPP chains in the PB-rich domains because the promotion effect of WBG-II becomes significant only when the PB-1 content is greater than 20% but smaller than 80%, where PB-rich domains may exist. The addition of WBG-II enhanced the nucleating ability of iPP chains in the PB-rich domains and therefore increased its ability to promote form I′ nucleation. After increasing the temperature above the melting point of form I′, the iPP nuclei formed under the assistance of WBG-II, in turn, act as nucleation sites of form II, promoting form I′ transiting into form II after melting. This study provides a new idea to avoid the influence of slow form II to form I phase transition on the production of PB-1 and improve the thermostability of PB-1. [ABSTRACT FROM AUTHOR]

Although investigated extensively in past decades, the factors affecting β-crystallization in β-nucleating agent/iPP composites have not been identified completely. In this study, β-crystallization in mesomorphic melt and free melt with 0.05 wt% WBG-II was investigated at various melting and crystallization temperatures, employing polarized optical microscopy, scanning electron microscopy, differential scanning calorimetry, and synchrotron small-angle and wide-angle X-ray diffraction. It was found that β-nucleation efficiency and thermodynamic stability of β-crystals depended strongly on the melting temperature. Higher β-nucleation efficiency and thermodynamic stability can be obtained only when the melting temperature was below 195 °C, where the β-nucleating agent (β-NA) was well dispersed in the melt. Further, ordered structures in the mesomorphic structured melt can further promote the formation of more perfect β-crystals. It is thought that β-NA distribution and ordered structures in the polymer melt are the two key factors affecting the formation of β-crystals. The former affects the number of β-nucleating sites accessible for iPP chains, while the latter affects the growth of β-crystals. Only when β-NA is well dispersed and the iPP melt exists massive chiral intrachain clusters similar to β-crystals, can perfect β-crystals be induced fully. [ABSTRACT FROM AUTHOR]

The nucleation efficiency of substrates towards a specific polymer is usually based on empirical methods, which depend on the employed experimental conditions. A more quantitative method to study the efficiency of nucleating agents promoting polypropylene β-phase is reported here. When a polymer is dispersed into sufficiently small droplets, the overall crystallization kinetics is controlled by nucleation, as growth can be orders of magnitude faster than nucleation. Confinement of polypropylene containing the nucleating agent particles into micro-domains (i.e., droplets) within a polystyrene matrix allows the isolation of the nucleation process and the determination of the surface free energy difference, Δσ. This parameter describes the intrinsic nucleation efficiency of a particular nucleating agent. Isothermal crystallization measurements were performed for dispersed polypropylene droplets containing three nucleating agents which catalyze the formation of both α- and β-phase (N,N′-dicyclohexylterephthalamide, quinacridone quinone, and tris-2,3-dimethyl-hexylamide of trimesic acid), and the data were analyzed via a first-order kinetics model. According to the calculated Δσ values, the nucleating efficiency scale is DCHT > TATA > QQ for α-phase, while DCHT > QQ for β-phase, in spite of the higher total amount of β-crystals generated by QQ particles. [ABSTRACT FROM AUTHOR]

In this study, we synthesized a type of microcrystalline H-ZnOc with columnar structure by controlling the solubility of the reaction solution. Poly(ethylene 2,6-naphthalate) (PEN) and hexagonal zinc oxide column (H-ZnOc) composite materials were prepared by a twin screw extruder and the properties of the composites were characterized. The results showed that H-ZnOc has a remarkable nucleation effect on PEN, especially when the loading amount of H-ZnOc is 1.5 wt%; the nucleation efficiency is as high as 52.28%, and the crystallization temperature increased by nearly 23 °C. The crystal morphology changed, with the disappearance of the cold crystallization peak after the addition of H-ZnOc, the size of spherulites decreased and the number of spherulites increased. During the isothermal crystallization process, H-ZnOc significantly reduced the crystallization time of PEN. The impact strength of PEN increased from 1.86 kJ m-2 to 2.73 kJ m-2. Our results showed that H-ZnOc can be used as an effective nucleating agent for PEN, effectively improving the crystallization ability and mechanical properties, and its performance is comparable to the proprietary polymer nucleating agents NX8000, HPN68L, and TMB-5, etc. [ABSTRACT FROM AUTHOR]

Bader's atoms-in-molecules theory holds that a bond path between an atom pair indicates a bonded interaction, including when the interaction is intermolecular. There is now considerable evidence from a variety of sources that this proposition is unreliable, not least when the bond path is observed in an experimental electron density distribution. In any case, to conclude that a weak interaction is bonding does not show that the interaction will be useful in crystal engineering. For this it must also be competitive, i.e. likely to win out over other interactions that might form when a crystal nucleates and grows. Database techniques have been developed for identifying interactions that are generally competitive in organic structures, or competitive in specific types of structures. They have also been applied to protein–ligand complexes. Representative results are discussed. As would be expected, the most competitive interactions are usually the strongest but this is not invariably the case. [ABSTRACT FROM AUTHOR]

A series of poly(1,3-trimethylene carbonate-b-(L -lactide-ran-glycolide)) (PTLG) with the three-armed PDLA and PLLA stereoblock copolymer (sc-PLA) acting as the nucleating agent was prepared via the solution-casting method. The effects of the incorporation of various amounts of sc-PLA crystallites on the crystallization behavior and mechanical properties of the PTLG matrix were characterized via DSC, WAXD, POM, and mechanical measurements. The results exhibited that the sc-PLA crystallites obviously enhanced the crystallization rate of the PLLA segments in the PTLG matrix. The results from the investigation of non-isothermal crystallization behavior showed that the crystallization process was significantly accelerated with the sc-PLA crystallites, and with an increase in the content of sc-PLA crystallites, the crystallization temperature shifted to 123.5 °C compared to that of the pure PTLG matrix. The results from the isothermal crystallization behavior study showed that the relative degree of crystallinity (Xt) gave a typical S-shape curve and the half-time of crystallization (t0.5) decreased with an increase in the amount of added sc-PLA crystallites. The crystallization accelerating effects mainly depended on the preeminent nucleation ability of the sc-PLA crystallites, which was proven by POM measurement. The mechanical measurement results showed that with the introduction of sc-PLA crystallites, the tensile strength of the blends was remarkably improved from 21.1 to 85.8 MPa. Furthermore, the biocompatibility of PTLG/sc-PLA was evaluated using the CCK-8 assay and live/dead staining. The results indicated that PTLG/sc-PLA presented very low cytotoxicity. Therefore, the low crystallization rate of the PLLA segments in the PTLG matrix can be largely improved by using sc-PLA crystallites as nucleating agents, and PTLG/sc-PLA blends possess good cytocompatibility and are expected to be used as bioresorbable vascular stents in the bio-medical field. [ABSTRACT FROM AUTHOR]

The role of silver as a nucleating agent in BaO/SrO/ZnO/SiO2 glasses is studied with a range of microstructure characterization techniques, such as scanning transmission electron microscopy, ultraviolet-visible spectroscopy, and X-ray diffraction. For this purpose, glasses with different silver and antimony concentrations were synthesized. It was found that silver-particle formation depends strongly on the silver concentration but also on the ratio Ag/Sb. A comparison of the measured plasmon resonances with those calculated from Mie theory enables a calculation of the particle size. This size depends on composition and varies depending on the chosen temperature between 11 and 60 nm. The addition of 1.5 mol% of Sb2O3 is necessary to achieve volume crystallization of Ba1−xSrxZn2Si2O7 (LEAZit) in the glass. This is due to the formation of core–shell structures with metallic silver particles in the center and an oxidic shell, which is highly enriched in Sb and Zn. The metallic silver particles surrounded by a shell show a plate-like shape and provoke the growth of LEAZit crystals with low thermal expansion. [ABSTRACT FROM AUTHOR]

Electroactive phase transition in polyvinylidene fluoride (PVDF) can be economically achieved readily by addition of nanofillers. In this work, we have demonstrated the influence of rational design and structural control of nanofillers on nucleation and stabilization of an electroactive polymorph in PVDF. Different architectures of zinc ferrite (ZF) i.e. nearly spherical, nearly cubic, and rod-like were synthesized and further introduced in PVDF as a nucleating agent with different filler to polymer ratios. A comparative study of the dielectric and ferroelectric properties and energy harvesting performance of the corresponding nanocomposite was performed to obtain the best architecture based composite. It has been observed that one dimensional nanofillers are more favorable for polar phase transformation and stabilization with incorporation of a lower fraction of fillers. Thus, they exhibited maximum electrical performance (an energy storage density of 7.68 mJ cm−3 with an energy discharge efficiency of ∼77%, and an output piezoresponse of ∼39.10 V with a power density of 2.96 μW mm−3). This may be due to the preferred ‘in-plane’ orientation of the nanorod structure in the polymer matrix which helps to accumulate the entire short chain all-trans (TTTT) conformation and form an extended all-trans conformation corresponding to an electroactive β-polymorph. This study may open a new strategy to design and fabricate ferrite-PVDF based electroactive nanocomposites with desired shapes for high performance energy storage and harvesting application. [ABSTRACT FROM AUTHOR]

Recently, it has been shown that the Ba1−xSrxZn2Si2O7 crystal phase has a negative coefficient of thermal expansion. However, technological applications of this material as low thermal expansion glass ceramics are limited by the undesired surface crystallization of the corresponding glass. Surface nucleation, however, can be turned into bulk nucleation by adding nucleating agents. Here, glasses in the base system BaO–SrO–ZnO–SiO2 with small additions of ZrO2 and WO3 were synthesized and their crystallization behavior was investigated using thermal analysis, X-ray diffraction, electron microscopy, and density functional theory simulations. The addition of WO3 leads to the formation of volume crystals with a scheelite crystal structure (Ba1−xSrxWO4) in high number density. The limited incorporation of Si4+ ions into these crystals is discussed. Possible crystal lattice sites for Si4+ were located by density functional theory simulations. In a much lower number density, crystals with a crystal structure similar to the high-temperature polymorph of BaZn2Si2O7 and the Ba1−xSrxZn2Si2O7 composition crystallize as well. These crystals can reach a larger size than the scheelite crystals that occur in parallel. The overall microstructure is thus formed by small dendritic crystals with a scheelite structure and huge Ba1−xSrxZn2Si2O7 crystals. Both of them seem to grow independently of each other. In spite of the high anisotropy of both phases, the microstructure is revealed to be free of cracks. [ABSTRACT FROM AUTHOR]

The morphology evolution of an organic nucleating agent (NA) in poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) blends was investigated under a series of multi-step isothermal and nonisothermal processes at identical NA solubility achieved via the same NA concentration and final molten temperature of heating (Tf). It was found that the morphology of NA frameworks depended on the supercooling determined by the recrystallization temperature of the NA in the polymer melt, except for NA solubility. When the NA partly dissolved in the matrix, the residuum of the original flat-plate NA acting as a nucleus induced recrystallization at a low degree of supercooling, and small sheet-like NA particles formed in the melt. When the NA dissolved in the matrix absolutely, NA aggregation increased in the melt due to the low nucleation density of the NA itself. The shape of the NA aggregation depended on the recrystallization temperature. With the increase in the supercooling, the large aggregated sheet-like NA transformed into a dendritic-like framework accompanied by a decrease in the stem size of the NA frameworks. Moreover, the stereocomplex efficiency of the blend was influenced by the effective nucleation surface induced by the shape of the NA aggregation. For PLLA/PDLA blends with 1.0 wt% NA, the crystallization half time (t1/2) of stereocomplex (sc) crystallites at the crystallization temperature of 180 °C is as long as 79.8 min for the sample with a large aggregated sheet-like NA, with 1 order of magnitude reduction for that with a dendritic-like NA framework, leading to a t1/2 of 7.9 min. The morphological control of NA frameworks is of great significance to guide the formation of various crystal morphologies of sc crystallites. The established relationship between the self-assembled morphology of NA and NA concentration, NA solubility and supercooling affords guidance in practical processing to control the crystal morphology and polymorphic crystalline morphology of PLLA/PDLA blends via tuning the crystal morphology of NA in the polymer matrix. [ABSTRACT FROM AUTHOR]

Poly(butylene succinate-co-butylene fumarate) (PBSF) can work as a highly efficient polymeric nucleating agent for poly(butylene succinate) (PBS) and this is based on epitaxial crystallization, namely matching of the crystal lattice. Benefiting from the unique behavior in which PBSF can enhance the spherulite growth rate (G) of PBS, a new method combining the addition of a fixed amount of PBSF and self-nucleation has been proposed to regulate G of isothermally crystallized PBS for the first time. [ABSTRACT FROM AUTHOR]

In the present work, a new approach to significantly accelerate the crystallization of poly(l-lactide) (PLLA) by utilizing poly(d-lactide) (PDLA) crystallites is presented. In particular, a PDLA with a high melting point (25 °C higher than that of PLLA) and high crystallinity (hPDLA) was introduced into the PLLA matrix via melt blending at a temperature between the melting points of PLLA and hPDLA. It was proved that the hPDLA crystallites were not melted and were instead reserved in the PLLA matrix. Results showed that a small amount of hPDLA crystallites can largely elevate the crystallization temperature, reduce the crystallization half-time and promote the crystallization rate of PLLA. In situ polarizing microscope observations showed that the great improvement of the crystallization rate was caused by the excellent nucleation effect of the hPDLA crystallites. Wide-angle X-ray diffraction results showed that the crystalline structures of the PLLA crystallites and hPDLA crystallites showed very good lattice match, which results in a largely reduced energy barrier for nucleation and increased crystallization kinetics. [ABSTRACT FROM AUTHOR]

Even though self-nucleation is considered to be the ideal case for polymer nucleation, it has rarely been used to enhance polymer crystallization in practical processing techniques. Inspired by self-nucleation theory and by utilizing the large difference in melting points of various poly(l-lactide) (PLLA) resins, we introduced high-melting-point PLLA (hPLLA) crystallites into a low-melting-point PLLA (lPLLA) matrix via melt blending at a processing temperature between the two melting points of the selected PLLA resins. The hPLLA crystallites turn out to be efficient nucleating agents (NAs) for lPLLA and high crystallinity (＞40%) PLLA samples with a greatly accelerated crystallization rate can be easily obtained. The results of non-isothermal crystallization show that the crystallization process is remarkably accelerated with a small amount (0.1 wt%) of hPLLA. With a further increase of hPLLA content, the crystallization temperature of the blends continues to shift to higher temperature. This crystallization promoting effect results from the excellent nucleation ability of the hPLLA crystallites, as revealed by in situ optical microscopy observation. Furthermore, an incredibly high nucleation efficiency of 103.0% (exceeding 100%) was obtained for the PLLA sample with 5.0 wt% hPLLA. The nucleation mechanism for hPLLA was studied systematically. It was found that the lPLLA matrix and hPLLA crystallites possess an absolutely identical crystal structure of α-form crystals and an excellent interfacial interaction between the nucleating agent, i.e., hPLLA crystallite, and the lPLLA matrix is achieved, resulting in the reduction of the energy barrier for heterogeneous nucleation and acceleration of crystallization kinetics. Therefore, by using high-melting-point polymer crystals as NAs, the crystallization rate of their low-melting-point polymer matrix can be improved largely, thus providing a simple way to obtain high crystallinity products for semicrystalline polymers with very low crystallization rates. [ABSTRACT FROM AUTHOR]

In this report, we demonstrate the ability of ethanol to act as a solvent and reducing agent to nucleate nanocrystalline Co and Ni particles. Under solvothermal conditions, Co and Ni particles can be produced at 200 °C. The Ni and Co particles crystallized into FCC and a mixture of FCC and HCP crystal phases, respectively. Ni particles possessed a spherical morphology with diameters in the range of 200 nm to 300 nm. Co particles took on an ellipsoidal morphology, with diameters greater than 500 nm. Magnetizations for the Ni and Co particles were commensurate with bulk values, showing their high crystallinity and the presence of little oxide impurity. By finding inexpensive solvents with a lowered environmental impact, steps towards a “greener” synthetic process for ferromagnetic nanoparticles can be established. [ABSTRACT FROM AUTHOR]

In this work, the thermodynamic interrelationship of the two known polymorphs of p-aminobenzoic acid has been explored, and primary nucleation in different organic solvents investigated. The solubility of both polymorphs in several solvents at different temperatures has been determined and the isobaric solid-state heat capacities have been measured by DSC. The transition temperature below which form α is metastable is estimated to be 16 °C by interpolation of solubility data and the melting temperature of form β is estimated to be 140 °C by extrapolation of solubility data. Using experimental calorimetry and solubility data the thermodynamic stability relationship between the two polymorphs has been estimated at room temperature to the melting point. At the transition temperature, the estimated enthalpy difference between the polymorphs is 2.84 kJ mol−1 and the entropy difference is 9.80 J mol−1 K−1. At the estimated melting point of form β the difference in Gibbs free energy and enthalpy is 1.6 kJ mol−1 and 5.0 kJ mol−1, respectively. It is found that the entropic contribution to the free energy difference is relatively high, which explains the unusually low transition temperature. A total of 330 nucleation experiments have been performed, with constant cooling rate in three different solvents and with different saturation temperatures, and multiple experiments have been carried out for each set of conditions in order to obtain statistically significant results. All performed experiments resulted in the crystallization of the high-temperature stable α-polymorph, which is kinetically favoured under all evaluated experimental conditions. The thermodynamic driving force required for nucleation is found to depend chiefly on the solvent, and to be inversely correlated to both solvent polarity and to solubility. [ABSTRACT FROM AUTHOR]

This study examined the polymorphic crystallization behavior of poly(1,4-butylene adipate) (PBA) with the addition of nucleation agents such as the α-cyclodextrin (α-CD) inclusion complex (IC) of PBA (PBAIC) and the IC of poly(ε-caprolactone) (PCLIC). The formation of PBAIC and PCLIC was characterized by 1H NMR, Fourier-transform infrared (FT-IR) spectroscopy and wide-angle X-ray diffraction (WAXD). The differential scanning calorimetry (DSC) and WAXD results suggest that some of the PBA segments remained outside the α-CD cavities even after the formation of ICs with α-CD. WAXD investigation also confirmed that the ICs had a channel structure. The DSC and polarized optical microscopy (POM) results showed the ICs to exhibit nucleation effects on the crystallization and polymorphic behavior of the PBA. The cooling rate played a significant role in the polymorphic crystallization behavior of the pure PBA. Thus, when the cooling rate was decreased, the crystal structures changed from β to α-form and vice versa. The blending of a nucleating agent with the PBA led to higher crystallization temperatures, thus favoring the nucleation of the α-form crystal of PBA rather than pure PBA. The nucleating activity of the PCLIC during the crystallization of the PBA was higher than that of PBAIC. [ABSTRACT FROM AUTHOR]