Hydroxyapatite/poly（L-lactide） （HA/PLLA） nanocomposites were prepared by the solvent mixing method. The isothermal crystallization behavior was studied by differential scanning calorimetry （DSC） and polarized op...Hydroxyapatite/poly（L-lactide） （HA/PLLA） nanocomposites were prepared by the solvent mixing method. The isothermal crystallization behavior was studied by differential scanning calorimetry （DSC） and polarized optical microscopy （POM）. The results show that the crystallization behavior of HA/PLLA composites was strongly affected by the content of HA and crystallization temperature, and the addition of HA could promote nucleation and enhance the crystallization rate. When isothermal crystallization was carried out at 110℃, the HA/PLLA nanocomposite with 1% HA content crystallized most rapidly among all the composites and the half crystallization time was only 1.0 min. Banded spherulites were observed for the HA/PLLA composites, but no banded spherulites were seen in the crystals of PLLA under the same condition.展开更多
Isotactic polypropylene（i PP） samples obtained by pressure vibration injection molding（PVIM） and conventional injection molding（CIM） were studied by polarized-light microscopy（PLM）, respectively. It was found ...Isotactic polypropylene（i PP） samples obtained by pressure vibration injection molding（PVIM） and conventional injection molding（CIM） were studied by polarized-light microscopy（PLM）, respectively. It was found that the alternating bright and dark banded spherulites were generated in the transitional region of PVIM parts. It is the first time that the banded spherulites of isotactic polypropylene were observed in polymer processing. What＇s more, the banded spherulites were proved to be constituted of α-form crystal by hot stage polarized-light microscopy（HT-PLM） and wide angle X-ray diffraction（WAXD）. Morphology of the banded spherulites was also studied by scaning electronical microscopy（SEM）.展开更多
The surface morphology of free-surface PCL ringed spherulites was investigated by using atomic force microscopy. The spherulites were obtained by crystallization of PCL/PVC blends of different compositions. It was fou...The surface morphology of free-surface PCL ringed spherulites was investigated by using atomic force microscopy. The spherulites were obtained by crystallization of PCL/PVC blends of different compositions. It was found that the ringed spherulite exhibited regularly fluctuating rings on its surface. Compared with the bright-dark ring pattern of the spherulite under a polarizing microscope, it was proved that the optical characteristics of the ringed spherulite under polarizing microscope coincided with its surface characteristics. The bright rings in polarizing micrographs of the spherulite coincided with the convex rings on its surface, while the dark rings coincided with the concave rings.展开更多
Poly(L-lactic acid)(PLLA)has drawn much attention due to its excellent medical and pharmaceutical applications for decades.As a semi-crystalline polymer,morphology and crystal structure of PLLA greatly determine its p...Poly(L-lactic acid)(PLLA)has drawn much attention due to its excellent medical and pharmaceutical applications for decades.As a semi-crystalline polymer,morphology and crystal structure of PLLA greatly determine its properties.Here,w e demonstrate,for PLLA films,a nonconventional texture featuring two types of spherulites emerging in pairs to form a distinct nested structure where a small spherulite(〜10μm)is embedded in a large one(100μm to 300μm).In addition to the size,the molecular weight and polymorph are different in the large and small spherulites.Crystallographic a-form and relatively low molecular weight are identified in the large spherulites,while meta-stable a'-form and relatively high molecular weight in the small ones.These differences suggest that the polydisperse PLLA polymers fractionate during film formation and the high-molecular-weight fraction crystallizes into the small spherulites with meta-stable structure because of its complicated polymer entanglement and high viscosity.In contrast,the rest of polymers crystallize into the large spherulites with the thermodynamically stable polymorph.Furthermore,this texture exhibits accelerated PLLA degradation initiated from the small spherulites,which is distinct from the typical PLLA spherulites.Insights provided by this work may lead to new texture-properties relationship associated with polydispersity of molecular weight.展开更多
The ring-banded spherulite is a special morphology of polymer crystals and has attracted considerable attention over recent decades. In this study, a new phase field model with polymer characteristics is established t...The ring-banded spherulite is a special morphology of polymer crystals and has attracted considerable attention over recent decades. In this study, a new phase field model with polymer characteristics is established to investigate the emergence and formation mechanism of the ring-banded spherulites of crystalline polymers. The model consists of a nonconserved phase field representing the phase transition and a temperature field describing the diffusion of the released latent heat. The corresponding model parameters can be obtained from experimentally accessible material parameters.Two-dimensional calculations are carried out for the ring-banded spherulitic growth of polyethylene film under a series of crystallization temperatures. The results of these calculations demonstrate that the formation of ring-banded spherulites can be triggered by the self-generated thermal field. Moreover, some temperature-dependent characteristics of the ring-banded spherulites observed in experiments are reproduced by simulations, which may help to study the effects of crystallization temperature on the ring-banded structures.展开更多
Several NNW-trending Cretaceous rhyolite dikes in the northeastern Cheongsong area of southern Korea contain spherulitic fabrics and are locally quarried as an ornamental stone. The dikes, part of the Cheongsong dike ...Several NNW-trending Cretaceous rhyolite dikes in the northeastern Cheongsong area of southern Korea contain spherulitic fabrics and are locally quarried as an ornamental stone. The dikes, part of the Cheongsong dike swarm, contain a variety of spherulites which are characterized by radial array of acicular intergrowths from fibrous quartz and alkali feldspars. They are classified as some simple, multiple and compound spherulite types from flower-like patterns, and the types are different each other in spatial distribution within the dikes. The various radial fabrics suggest that they crystallized under the different cooling mechanisms and processes in rapidly cooling dikes. Spheroids lacking a flower-like pattern may be precipitated after compositional segregation in a supercooled magma. Simple acicular spherulites could be crystallized by devitrification of true glass which cooled rapidly below the transformation temperature, whereas layered multiple spherulites could result from a crystallization of supercooled magma at relatively rapid cooling rates above the transformation temperature. Acicular multiple spherulites could be produced from a combination of the above three mechanisms operating at slower cooling rates.展开更多
Polyethylene oxide(PEO)-based solid polymer electrolytes(SPEs)have long faced limitations due to low ionic conductivity at ambient temperature and poor interfacial stability with lithium metal anodes.Here,we present a...Polyethylene oxide(PEO)-based solid polymer electrolytes(SPEs)have long faced limitations due to low ionic conductivity at ambient temperature and poor interfacial stability with lithium metal anodes.Here,we present a structural engineering strategy to address these challenges through shear-induced crystallization of concentrated PEO-LiTFSI solutions,which self-assemble into flower-like spherulites with radially aligned lamellar crystals.This unique structure creates continuous Li^(+)transport highways through densely packed crystalline domains,achieving a record-high ionic conductivity of 1.70×10^(-4) S/cm at 25℃ for pristine PEO-based systems.Strategic incorporation of lithium montmorillonite(MMTli,10 wt%)further optimizes the composite electrolyte,balancing high ionic conductivity(1.47×10^(-4) S/cm)with enhanced electrochemical stability(4.99 V vs.Li^(+)/Li),elevated Li^(+)transference number(0.62),and mechanical robustness.The composite electrolyte enables stable Li plating/stripping over 800 h in symmetric Li||Li cells and powers LiFePO_(4)||Li solid-state batteries with 82%capacity retention after 200 cycles at 0.2 C under ambient conditions.This work pioneers a scalable processing paradigm for crystalline polymer electrolytes,offering new insights into ion transport mechanisms and validating clay minerals as multifunctional additives for next-generation energy storage systems.展开更多
Spherulites are generally fabricated from cooling polymer melts,while their fabrication under mild conditions or from small molecule materials has been barely reported.Besides,organic luminescent molecules typically s...Spherulites are generally fabricated from cooling polymer melts,while their fabrication under mild conditions or from small molecule materials has been barely reported.Besides,organic luminescent molecules typically suffer from low quantum yields in a solid state.Moreover,preparing material with interconnected and simultaneous changes in structural and fluorescent colors is challenging.Here,we present the first solution-derived spherulites with unique interconnected structural and fluorescent colors,self-assembled from stearoylated monosaccharides at room temperature.D-galactose stearoyl ester self-assembled into banded spherulites,containing twisted nanoplates and interconnected simultaneously changing structural and fluorescent colors.In comparison,D-mannose stearoyl ester can only form nonbanded spherulites,which contain oriented nanoplates and uniform structural and fluorescent colors.Such materials revealed a novel negative correlation between fluorescence and birefringence,termed alignment-promoted quenching propensity.Remarkably,the solid-state fluorescence quantum yields of galactose and mannosederived spherulites are as high as 49±2%and 51±2%respectively,approximately ten times higher than those of unmodified monosaccharides.These quantum yield values are among the highest of reported organic nonconventional fluorophores and even comparable to those of conventional aromatic chromophores.Moreover,these spherulites manifested an unexpected excitation-dependent multicolor photoluminescence with a broad-spectrum emission(410−620 nm).They show multiple peaks in the photoluminescent emission spectra and broad fluorescence lifetime distributions,which should be attributed to the clustering of a variety of oxygen-containing functional groups as emissive moieties.展开更多
Lamellar structures of banded spherulites of poly(e-caprolactone)/poly(vinylchloride) (PCL/PVC) blends are observed using tapping mode atomic force microscopy (AFM). Thesurface of the PCL/PVC banded spherulites presen...Lamellar structures of banded spherulites of poly(e-caprolactone)/poly(vinylchloride) (PCL/PVC) blends are observed using tapping mode atomic force microscopy (AFM). Thesurface of the PCL/PVC banded spherulites presents to be concentric periodic ups and downs. Theperiod of the bands corresponds to the extinction rings under the polarized optical microscopyobservation. The lamellae with edge-on orientation in the ridges and the flat-on lamellae in thevalleys of the banded spherulites are observed clearly. The twisting between the edge-on and flat-onlamellae is also observed.展开更多
Herein,phloroglucinol tristearate(PhgTS)was used to study the crystallization process due to its unique symmetric structure containing a benzene ring and three aliphatic chains.Spherulites of crystallized PhgTS from f...Herein,phloroglucinol tristearate(PhgTS)was used to study the crystallization process due to its unique symmetric structure containing a benzene ring and three aliphatic chains.Spherulites of crystallized PhgTS from four solvents under diverse conditions were analyzed in detail and their formation process was studied.Maltese cross is shown by PhgTS spherulites obtained from aprotic solvents via polarized optical microscopy.In comparison,no Maltese cross can be observed from branch-like crystals formed from protic solvents.Independent on the micro-scaled morphology,lamellae were found to be the basic blocks constructing both PhgTS spherulites and branch-like crystals,which were formed predominantly by stacked PhgTS molecules.Although differential characters of the solvents did not affect the formation of lamellas,the solvents played a crucial role in the formation of self-assembled microscaled morphologies.In particular,the morphologies of spherulites were strongly affected by the concentration of PhgTS solutions,surrounding tempera-ture and evaporation rate of solvents.Generally,a higher concentration of PhgTS led to more homogeneous spherulites,a lower evaporation rate resulted in more compact spherulites,and a higher surounding temperature generated preferentially more ring-banded spherulites of PhgTS.展开更多
Drug particles with spherical morphology possess amazing advantages in terms of particle flowability,mechanical properties,drug solubility,and bioavailability.The growth mechanism of drug spherulite is of great import...Drug particles with spherical morphology possess amazing advantages in terms of particle flowability,mechanical properties,drug solubility,and bioavailability.The growth mechanism of drug spherulite is of great importance for the preparation and regulation of spherulites.Herein,ceftriaxone sodium spherulites were fabricated by the antisolvent crystallization method using dropwise addition of ceftriaxone sodium solution to acetone.Online observation of the whole crystallization process combined with electron microscopy technique revealed the spherical growth process from amorphous form to spherulites.As the supersaturation of the crystallization system was adjusted,the ceftriaxone sodium crystals transformed from amorphous form to spherulites.In the process of antisolvent crystallization with acetone as antisolvent,when the theoretical supersaturation degree S was higher than 2.62,the crystallization system tended to appear amorphous form;when S was between 2.57 and 2.62,the amorphous form transformed into clustered spherulites;when S was less than 2.57,the surface of spherulites will be covered with flaky crystal,which transformed into urchin-like type.With the understanding of the spherical growth mechanism,the ceftriaxone sodium spherulites prepared in this research with modified supersaturation control had a low residue of antisolvent acetone,and the flowability was significantly improved.展开更多
Spherulitic morphology of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The morphology of spherulite of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The e...Spherulitic morphology of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The morphology of spherulite of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The effect of both annealing temperature and crystallization temperature on the formation of cracks was described by polarized optical microscope (POM). Non banded spherulite (fibrils) with cracks was detected in PLLA film after annealing at 160°C (180 min.) and isothermal crystallization temperatures at 140°C and 150°C. With increasing temperature after annealing treatment the size of spherulite is increased and more cracks are formed. The maximum growth rate of spherulites was found at 130°C. The physical ageing was carried out by annealing the PLLA sample at room temperature for several annealing time (ta) from 0 h to 720 h. The enthalpy relaxation has been studied by differential scanning calorimetry (DSC) through analysis of the endothermic peak of glass transition temperature, which increased and shifted towards higher temperature as the annealing time increased.展开更多
The physical vapour deposition （PVD） of gallium monotelluride （GaTe） in different crystalline habits was established in the growth ampoule, strongly depending on the temperature gradient. Proper control on the tem...The physical vapour deposition （PVD） of gallium monotelluride （GaTe） in different crystalline habits was established in the growth ampoule, strongly depending on the temperature gradient. Proper control on the temperatures of source and growth zones in an indigenously fabricated dual zone furnace could yield the crystals in the form of whiskers and spherulites. Optical and electron microscopic images were examined to predict the growth mechanism of morphologies. The structural parameters of the grown spherulites were determined by X-ray powder diffraction （XRD）. The stoichiometric composition of these crystals was confirmed using energy dispersive analysis by X-rays （EDAX）. The type and nature of electrical conductivity were identified by the conventional hot probe and two probe methods, respectively. The mechanical parameters, such as Vickers microhardness, work hardening index, and yield strength, were deduced from microindentation measurements. The results show that the vapour grown p-GaTe crystals exhibit novel physical properties, which make them suitable for device applications.展开更多
The effect of sintering dispersed and bulk,low molecular weight(M_n=50,000 Da),nano-emulsionpolytetrafluoroethylene(PTFE)particles near their melting point is described.With the nascent particles consisting of ca.75 n...The effect of sintering dispersed and bulk,low molecular weight(M_n=50,000 Da),nano-emulsionpolytetrafluoroethylene(PTFE)particles near their melting point is described.With the nascent particles consisting of ca.75 nm diameter,hexagonal,single crystals,sintering at,e.g.,350℃,results,initially,in merger of neighboring particles,followed by individual molecular motion on the substrate and the formation of folded chain,lamellar single crystals andspherulites,and on-edge ribbons.It is suggested these structures develop,with time,in the mesomorphic“melt”.Sintering ofthe bulk resin yields extended chain,band structures,as well as folded chain lamellae;end-surface to end-surface merger,possibly by end-to-end polymerization,occurs with increasing time.展开更多
The spherulite morphology of the rolled and subsequent heat-treated isotactic polypropylene （iPP） was observed by polarized microscopy, and the crystallinity evolution of materials was also measured by the wide angl...The spherulite morphology of the rolled and subsequent heat-treated isotactic polypropylene （iPP） was observed by polarized microscopy, and the crystallinity evolution of materials was also measured by the wide angle X-ray scattering （WAXS）. Rolling led to the oblate spherulites in the deformed iPP samples. The sheared crystalline lamellae broke apart into sets of crystalline blocks during rolling. As a result, the crystallinity of the iPP samples was greatly reduced during deformation, which induced the unclear spherulites and spherulite boundaries. Subsequent heat treatment resulted in the strong reerystallization of the rolled iPP samples. But the recrystaUizatinn in this work only meant the rearrangement of the macromolecule along the unbroken crystalline lamellae and the existing small crystalline blocks in the deformed spherulites. Heat treatment did not change the shape of the spherulites formed during deformation. The recrystallization also resulted in very clear spherulites and spherulite boundaries.展开更多
By using polybutene-1 as a typical example, we illustrate the initiation, development and stabilization of cavities in the sample during tensile deformation. Samples with the same crystallinity, long spacing and cryst...By using polybutene-1 as a typical example, we illustrate the initiation, development and stabilization of cavities in the sample during tensile deformation. Samples with the same crystallinity, long spacing and crystalline lamellar thickness but very different sizes of spherulites were prepared via changing the melt history. Dimension of cavities during stretching the samples was determined by in situ ultra small angle X-ray scattering techniques. It turned out that the size of the cavities was bigger in the sample with larger spherulites than the one with smaller spherulites. The results show clear evidence of initiating cavities within crystalline phase at the grain-boundary of crystalline blocks, growing of cavities passing through parallel stacked lamellar crystals and amorphous layers and finally stablized by tilted lamellae at both ends of the plate-like cavities within the spherulites.展开更多
In this research, the morphologies, isothermal-crystallization kinetics, and spherulite growth of aliphatic polyketone/polyamide-6 blends were studied. A single glass-transition temperature （Tg） was determined, and ...In this research, the morphologies, isothermal-crystallization kinetics, and spherulite growth of aliphatic polyketone/polyamide-6 blends were studied. A single glass-transition temperature （Tg） was determined, and the composition dependence of Tg for these blends was well described by the Kwei equation. The strong intermolecular interaction between the two polymer components was confirmed by melting-point depression. The isothermal-crystallization kinetics were analyzed on the basis of the Avrami approach. A linear increase in the radii of the spherulites with time was observed for all compositions. All the spherulites continued to grow at nearly identical growth rates. With increasing polyamide-6 content, the size of the spherulites in the polyketone/polyamide-6 blends gradually decreased, and the number of spherulites in the blends increased.展开更多
Spherulites are the most common crystalline morphology and thus the visual expression of crystal structures for polymers.The diversified patterns have provided intuitive morphology probes for various crystallization b...Spherulites are the most common crystalline morphology and thus the visual expression of crystal structures for polymers.The diversified patterns have provided intuitive morphology probes for various crystallization behaviors,while the correlations between them are still needed to be enriched.In this work,the complicated spherulitic morphology of poly(propylene fumarate)(PPF),which is sensitive to crystallization temperature,is investigated.PPF melt,respectively,crystallizes into rough spherulites,regularly banded spherulites,and spherulites containing both two kinds of morphology at low,high,and mediate temperatures.By systematically assaying,it is clear that the growth axis along the radial direction changes from a-axis to b-axis as the crystallization temperature increases,which leads to the formation of unique crystallization-temperature-dependent spherulites.Based on detailed characterization of Fourier transform infrared spectroscopy,the packing state of the specific hydrogen bonds of"C=C-H…O=C-C=C"in PPF crystal lattices is determined,and furthermore,the mechanism for temperature-dependent selection of growth axes for PPF spherulites in melt is reasonably speculated.展开更多
The morphologies of poly(L-lactic acid)(PLLA)spherulites,when crystallized within the pre-existed poly(oxymethylene)(POM)crystal frameworks,have been investigated.PLLA/POM blend is a melt-miscible crystalline/crystall...The morphologies of poly(L-lactic acid)(PLLA)spherulites,when crystallized within the pre-existed poly(oxymethylene)(POM)crystal frameworks,have been investigated.PLLA/POM blend is a melt-miscible crystalline/crystalline blend system.Owing to the lower melting point but much faster crystallization rate than PLEA,POM crystallized first upon cooling from the melt state and then melted first during the subsequent heating process in this blend system.Lamellar assembly of PLLA crystals within the pre-existed POM spherulitic frameworks was directly observed with the polarized light microscopy by selectively melting the POM frameworks.The investigation indicated that PLLA crystals fully replicated the spherulitic morphology and optical birefringence of the POM crystal frameworks,which was independent of T_(o).On the other hand,POM could also duplicate the pre-existed PLLA morphologies.The result obtained provides us a possibility to design the lamellar assembly and crystal structures of polymer crystals in miscible crystalline/crystalline polymer blends.展开更多
In this work the nucleation and growth of spherulites for the below polylactide （PLA） layer in poly（ε- caprolactone）/polylactide （PCL/PLA） double-layer films during isothermal crystallization at various tempera...In this work the nucleation and growth of spherulites for the below polylactide （PLA） layer in poly（ε- caprolactone）/polylactide （PCL/PLA） double-layer films during isothermal crystallization at various temperatures above the melting point of PCL have been investigated by using polarized optical microscopy （POM）. It is revealed that two types of spherulitic morphologies are observed in PCL/PLA double-layer films. One is the well defined highly birefringent spherulites, and the other one is the coarse spherulites. It is interesting to find that the spherulitic growth rate of the coarse spherulites is higher than that of the well defined spherulites. It is thought that the coarse spherulites nucleate and grow with the assistance of the interfaces between the PCL and PLA layers, and the well defined highly birefringent spherulites only nucleate and grow in the PLA layer.展开更多
基金supported by the National Natural Science Foundation of China(Key Project No.50733003 and Project No.20604030)the International Cooperation fund of Science and Technology(Key project 20071314) from the Ministry of Science and Technology of Chinathe fund from Chinese Academy of Sciences(KGCX-YW-208)
文摘Hydroxyapatite/poly（L-lactide） （HA/PLLA） nanocomposites were prepared by the solvent mixing method. The isothermal crystallization behavior was studied by differential scanning calorimetry （DSC） and polarized optical microscopy （POM）. The results show that the crystallization behavior of HA/PLLA composites was strongly affected by the content of HA and crystallization temperature, and the addition of HA could promote nucleation and enhance the crystallization rate. When isothermal crystallization was carried out at 110℃, the HA/PLLA nanocomposite with 1% HA content crystallized most rapidly among all the composites and the half crystallization time was only 1.0 min. Banded spherulites were observed for the HA/PLLA composites, but no banded spherulites were seen in the crystals of PLLA under the same condition.
文摘Isotactic polypropylene（i PP） samples obtained by pressure vibration injection molding（PVIM） and conventional injection molding（CIM） were studied by polarized-light microscopy（PLM）, respectively. It was found that the alternating bright and dark banded spherulites were generated in the transitional region of PVIM parts. It is the first time that the banded spherulites of isotactic polypropylene were observed in polymer processing. What＇s more, the banded spherulites were proved to be constituted of α-form crystal by hot stage polarized-light microscopy（HT-PLM） and wide angle X-ray diffraction（WAXD）. Morphology of the banded spherulites was also studied by scaning electronical microscopy（SEM）.
基金This work was supported by The National Natural Science Foundation of China and also The State Science and Technology Commission of China under The National Key Project for Fundamental Research "Macromolecular Condensed State".
文摘The surface morphology of free-surface PCL ringed spherulites was investigated by using atomic force microscopy. The spherulites were obtained by crystallization of PCL/PVC blends of different compositions. It was found that the ringed spherulite exhibited regularly fluctuating rings on its surface. Compared with the bright-dark ring pattern of the spherulite under a polarizing microscope, it was proved that the optical characteristics of the ringed spherulite under polarizing microscope coincided with its surface characteristics. The bright rings in polarizing micrographs of the spherulite coincided with the convex rings on its surface, while the dark rings coincided with the concave rings.
基金supported by the National Natural Science Foundation of China(Nos.51625304 and 51873182).
文摘Poly(L-lactic acid)(PLLA)has drawn much attention due to its excellent medical and pharmaceutical applications for decades.As a semi-crystalline polymer,morphology and crystal structure of PLLA greatly determine its properties.Here,w e demonstrate,for PLLA films,a nonconventional texture featuring two types of spherulites emerging in pairs to form a distinct nested structure where a small spherulite(〜10μm)is embedded in a large one(100μm to 300μm).In addition to the size,the molecular weight and polymorph are different in the large and small spherulites.Crystallographic a-form and relatively low molecular weight are identified in the large spherulites,while meta-stable a'-form and relatively high molecular weight in the small ones.These differences suggest that the polydisperse PLLA polymers fractionate during film formation and the high-molecular-weight fraction crystallizes into the small spherulites with meta-stable structure because of its complicated polymer entanglement and high viscosity.In contrast,the rest of polymers crystallize into the large spherulites with the thermodynamically stable polymorph.Furthermore,this texture exhibits accelerated PLLA degradation initiated from the small spherulites,which is distinct from the typical PLLA spherulites.Insights provided by this work may lead to new texture-properties relationship associated with polydispersity of molecular weight.
基金Project supported by the National Key Basic Research Program of China(Grant No.2012CB025903)the National Natural Science Foundation of China(Grant No.11402210)+1 种基金the Northwestern Polytechnical University Foundation for Fundamental Research(Grant No.JCY20130141)the Ministry of Education Fund for Doctoral Students Newcomer Awards of China
文摘The ring-banded spherulite is a special morphology of polymer crystals and has attracted considerable attention over recent decades. In this study, a new phase field model with polymer characteristics is established to investigate the emergence and formation mechanism of the ring-banded spherulites of crystalline polymers. The model consists of a nonconserved phase field representing the phase transition and a temperature field describing the diffusion of the released latent heat. The corresponding model parameters can be obtained from experimentally accessible material parameters.Two-dimensional calculations are carried out for the ring-banded spherulitic growth of polyethylene film under a series of crystallization temperatures. The results of these calculations demonstrate that the formation of ring-banded spherulites can be triggered by the self-generated thermal field. Moreover, some temperature-dependent characteristics of the ring-banded spherulites observed in experiments are reproduced by simulations, which may help to study the effects of crystallization temperature on the ring-banded structures.
文摘Several NNW-trending Cretaceous rhyolite dikes in the northeastern Cheongsong area of southern Korea contain spherulitic fabrics and are locally quarried as an ornamental stone. The dikes, part of the Cheongsong dike swarm, contain a variety of spherulites which are characterized by radial array of acicular intergrowths from fibrous quartz and alkali feldspars. They are classified as some simple, multiple and compound spherulite types from flower-like patterns, and the types are different each other in spatial distribution within the dikes. The various radial fabrics suggest that they crystallized under the different cooling mechanisms and processes in rapidly cooling dikes. Spheroids lacking a flower-like pattern may be precipitated after compositional segregation in a supercooled magma. Simple acicular spherulites could be crystallized by devitrification of true glass which cooled rapidly below the transformation temperature, whereas layered multiple spherulites could result from a crystallization of supercooled magma at relatively rapid cooling rates above the transformation temperature. Acicular multiple spherulites could be produced from a combination of the above three mechanisms operating at slower cooling rates.
基金supported by the National Natural Science Foundation of China(No.42272044)the High-performance Computing Platform of China University of Geosciences Beijing。
文摘Polyethylene oxide(PEO)-based solid polymer electrolytes(SPEs)have long faced limitations due to low ionic conductivity at ambient temperature and poor interfacial stability with lithium metal anodes.Here,we present a structural engineering strategy to address these challenges through shear-induced crystallization of concentrated PEO-LiTFSI solutions,which self-assemble into flower-like spherulites with radially aligned lamellar crystals.This unique structure creates continuous Li^(+)transport highways through densely packed crystalline domains,achieving a record-high ionic conductivity of 1.70×10^(-4) S/cm at 25℃ for pristine PEO-based systems.Strategic incorporation of lithium montmorillonite(MMTli,10 wt%)further optimizes the composite electrolyte,balancing high ionic conductivity(1.47×10^(-4) S/cm)with enhanced electrochemical stability(4.99 V vs.Li^(+)/Li),elevated Li^(+)transference number(0.62),and mechanical robustness.The composite electrolyte enables stable Li plating/stripping over 800 h in symmetric Li||Li cells and powers LiFePO_(4)||Li solid-state batteries with 82%capacity retention after 200 cycles at 0.2 C under ambient conditions.This work pioneers a scalable processing paradigm for crystalline polymer electrolytes,offering new insights into ion transport mechanisms and validating clay minerals as multifunctional additives for next-generation energy storage systems.
基金EU,Grant/Award Number:NEuM(ZW7-85191973)German Research Foundation(DFG),Grant/Award Numbers:ZH 546/8-1,INST186/1397-1/FUGG,INST208/761-1FUGG+3 种基金Lower Saxony Ministry of Science and Culture,Grant/Award Number:INST186/1397-1/FUGGChina Scholarship CouncilNatural Sciences and Engineering Research Council of CanadaAlexander von Humboldt Foundation。
文摘Spherulites are generally fabricated from cooling polymer melts,while their fabrication under mild conditions or from small molecule materials has been barely reported.Besides,organic luminescent molecules typically suffer from low quantum yields in a solid state.Moreover,preparing material with interconnected and simultaneous changes in structural and fluorescent colors is challenging.Here,we present the first solution-derived spherulites with unique interconnected structural and fluorescent colors,self-assembled from stearoylated monosaccharides at room temperature.D-galactose stearoyl ester self-assembled into banded spherulites,containing twisted nanoplates and interconnected simultaneously changing structural and fluorescent colors.In comparison,D-mannose stearoyl ester can only form nonbanded spherulites,which contain oriented nanoplates and uniform structural and fluorescent colors.Such materials revealed a novel negative correlation between fluorescence and birefringence,termed alignment-promoted quenching propensity.Remarkably,the solid-state fluorescence quantum yields of galactose and mannosederived spherulites are as high as 49±2%and 51±2%respectively,approximately ten times higher than those of unmodified monosaccharides.These quantum yield values are among the highest of reported organic nonconventional fluorophores and even comparable to those of conventional aromatic chromophores.Moreover,these spherulites manifested an unexpected excitation-dependent multicolor photoluminescence with a broad-spectrum emission(410−620 nm).They show multiple peaks in the photoluminescent emission spectra and broad fluorescence lifetime distributions,which should be attributed to the clustering of a variety of oxygen-containing functional groups as emissive moieties.
基金supported by the National Natural Science Foundation of China(Grant Nos.20174049 and 20131160730)
文摘Lamellar structures of banded spherulites of poly(e-caprolactone)/poly(vinylchloride) (PCL/PVC) blends are observed using tapping mode atomic force microscopy (AFM). Thesurface of the PCL/PVC banded spherulites presents to be concentric periodic ups and downs. Theperiod of the bands corresponds to the extinction rings under the polarized optical microscopyobservation. The lamellae with edge-on orientation in the ridges and the flat-on lamellae in thevalleys of the banded spherulites are observed clearly. The twisting between the edge-on and flat-onlamellae is also observed.
基金Y.Y.thanks the China Scholarship Council(CSC)for financial support.K.Z.thanks Georg-August-University of Goettingen for the Anschubfinanzierung(Funding for the Promotion of Young Academics of University of Goettingen)and Fonds der Chemischen Industrie(FCI)for the financial support.The authors declare no conflicts of interest.
文摘Herein,phloroglucinol tristearate(PhgTS)was used to study the crystallization process due to its unique symmetric structure containing a benzene ring and three aliphatic chains.Spherulites of crystallized PhgTS from four solvents under diverse conditions were analyzed in detail and their formation process was studied.Maltese cross is shown by PhgTS spherulites obtained from aprotic solvents via polarized optical microscopy.In comparison,no Maltese cross can be observed from branch-like crystals formed from protic solvents.Independent on the micro-scaled morphology,lamellae were found to be the basic blocks constructing both PhgTS spherulites and branch-like crystals,which were formed predominantly by stacked PhgTS molecules.Although differential characters of the solvents did not affect the formation of lamellas,the solvents played a crucial role in the formation of self-assembled microscaled morphologies.In particular,the morphologies of spherulites were strongly affected by the concentration of PhgTS solutions,surrounding tempera-ture and evaporation rate of solvents.Generally,a higher concentration of PhgTS led to more homogeneous spherulites,a lower evaporation rate resulted in more compact spherulites,and a higher surounding temperature generated preferentially more ring-banded spherulites of PhgTS.
基金the financial contribution from Central Guidance on Local Science and Technology Development Fund of Liaoning Province(grant No.2023JH6/100100004)National Key Research and Development Program of China(grant No.2021YFC2901300)+3 种基金National Natural Science Foundation of China(grant No.22021005,22378041)Fundamental Research Funds for the Central Universities(grant No.DUT22YG208,DUT22LAB603)Key Research and Development Projects in Shandong Province(grant No.2022CXGC010303)acknowledge the assistance of Dalian University of Technology Instrumental Analysis Center.
文摘Drug particles with spherical morphology possess amazing advantages in terms of particle flowability,mechanical properties,drug solubility,and bioavailability.The growth mechanism of drug spherulite is of great importance for the preparation and regulation of spherulites.Herein,ceftriaxone sodium spherulites were fabricated by the antisolvent crystallization method using dropwise addition of ceftriaxone sodium solution to acetone.Online observation of the whole crystallization process combined with electron microscopy technique revealed the spherical growth process from amorphous form to spherulites.As the supersaturation of the crystallization system was adjusted,the ceftriaxone sodium crystals transformed from amorphous form to spherulites.In the process of antisolvent crystallization with acetone as antisolvent,when the theoretical supersaturation degree S was higher than 2.62,the crystallization system tended to appear amorphous form;when S was between 2.57 and 2.62,the amorphous form transformed into clustered spherulites;when S was less than 2.57,the surface of spherulites will be covered with flaky crystal,which transformed into urchin-like type.With the understanding of the spherical growth mechanism,the ceftriaxone sodium spherulites prepared in this research with modified supersaturation control had a low residue of antisolvent acetone,and the flowability was significantly improved.
文摘Spherulitic morphology of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The morphology of spherulite of pure poly lactic acid (PLLA) PLLA have investigated after thermal annealing. The effect of both annealing temperature and crystallization temperature on the formation of cracks was described by polarized optical microscope (POM). Non banded spherulite (fibrils) with cracks was detected in PLLA film after annealing at 160°C (180 min.) and isothermal crystallization temperatures at 140°C and 150°C. With increasing temperature after annealing treatment the size of spherulite is increased and more cracks are formed. The maximum growth rate of spherulites was found at 130°C. The physical ageing was carried out by annealing the PLLA sample at room temperature for several annealing time (ta) from 0 h to 720 h. The enthalpy relaxation has been studied by differential scanning calorimetry (DSC) through analysis of the endothermic peak of glass transition temperature, which increased and shifted towards higher temperature as the annealing time increased.
基金financially supported by the Major Research Project of University Grants Commission,New Delhi(No.33-38/2008-10(SR))
文摘The physical vapour deposition （PVD） of gallium monotelluride （GaTe） in different crystalline habits was established in the growth ampoule, strongly depending on the temperature gradient. Proper control on the temperatures of source and growth zones in an indigenously fabricated dual zone furnace could yield the crystals in the form of whiskers and spherulites. Optical and electron microscopic images were examined to predict the growth mechanism of morphologies. The structural parameters of the grown spherulites were determined by X-ray powder diffraction （XRD）. The stoichiometric composition of these crystals was confirmed using energy dispersive analysis by X-rays （EDAX）. The type and nature of electrical conductivity were identified by the conventional hot probe and two probe methods, respectively. The mechanical parameters, such as Vickers microhardness, work hardening index, and yield strength, were deduced from microindentation measurements. The results show that the vapour grown p-GaTe crystals exhibit novel physical properties, which make them suitable for device applications.
文摘The effect of sintering dispersed and bulk,low molecular weight(M_n=50,000 Da),nano-emulsionpolytetrafluoroethylene(PTFE)particles near their melting point is described.With the nascent particles consisting of ca.75 nm diameter,hexagonal,single crystals,sintering at,e.g.,350℃,results,initially,in merger of neighboring particles,followed by individual molecular motion on the substrate and the formation of folded chain,lamellar single crystals andspherulites,and on-edge ribbons.It is suggested these structures develop,with time,in the mesomorphic“melt”.Sintering ofthe bulk resin yields extended chain,band structures,as well as folded chain lamellae;end-surface to end-surface merger,possibly by end-to-end polymerization,occurs with increasing time.
文摘The spherulite morphology of the rolled and subsequent heat-treated isotactic polypropylene （iPP） was observed by polarized microscopy, and the crystallinity evolution of materials was also measured by the wide angle X-ray scattering （WAXS）. Rolling led to the oblate spherulites in the deformed iPP samples. The sheared crystalline lamellae broke apart into sets of crystalline blocks during rolling. As a result, the crystallinity of the iPP samples was greatly reduced during deformation, which induced the unclear spherulites and spherulite boundaries. Subsequent heat treatment resulted in the strong reerystallization of the rolled iPP samples. But the recrystaUizatinn in this work only meant the rearrangement of the macromolecule along the unbroken crystalline lamellae and the existing small crystalline blocks in the deformed spherulites. Heat treatment did not change the shape of the spherulites formed during deformation. The recrystallization also resulted in very clear spherulites and spherulite boundaries.
基金financially supported by the National Natural Science Foundation of China(Nos.51525305 and 21134006)the Newton Advanced Fellowship of Royal Society(No.NA150222)
文摘By using polybutene-1 as a typical example, we illustrate the initiation, development and stabilization of cavities in the sample during tensile deformation. Samples with the same crystallinity, long spacing and crystalline lamellar thickness but very different sizes of spherulites were prepared via changing the melt history. Dimension of cavities during stretching the samples was determined by in situ ultra small angle X-ray scattering techniques. It turned out that the size of the cavities was bigger in the sample with larger spherulites than the one with smaller spherulites. The results show clear evidence of initiating cavities within crystalline phase at the grain-boundary of crystalline blocks, growing of cavities passing through parallel stacked lamellar crystals and amorphous layers and finally stablized by tilted lamellae at both ends of the plate-like cavities within the spherulites.
文摘In this research, the morphologies, isothermal-crystallization kinetics, and spherulite growth of aliphatic polyketone/polyamide-6 blends were studied. A single glass-transition temperature （Tg） was determined, and the composition dependence of Tg for these blends was well described by the Kwei equation. The strong intermolecular interaction between the two polymer components was confirmed by melting-point depression. The isothermal-crystallization kinetics were analyzed on the basis of the Avrami approach. A linear increase in the radii of the spherulites with time was observed for all compositions. All the spherulites continued to grow at nearly identical growth rates. With increasing polyamide-6 content, the size of the spherulites in the polyketone/polyamide-6 blends gradually decreased, and the number of spherulites in the blends increased.
基金supported by the National Natural Science Foundation of China(No.21674128)Science Foundation of China University of Petroleum,Beijing(No.ZX20200097).
文摘Spherulites are the most common crystalline morphology and thus the visual expression of crystal structures for polymers.The diversified patterns have provided intuitive morphology probes for various crystallization behaviors,while the correlations between them are still needed to be enriched.In this work,the complicated spherulitic morphology of poly(propylene fumarate)(PPF),which is sensitive to crystallization temperature,is investigated.PPF melt,respectively,crystallizes into rough spherulites,regularly banded spherulites,and spherulites containing both two kinds of morphology at low,high,and mediate temperatures.By systematically assaying,it is clear that the growth axis along the radial direction changes from a-axis to b-axis as the crystallization temperature increases,which leads to the formation of unique crystallization-temperature-dependent spherulites.Based on detailed characterization of Fourier transform infrared spectroscopy,the packing state of the specific hydrogen bonds of"C=C-H…O=C-C=C"in PPF crystal lattices is determined,and furthermore,the mechanism for temperature-dependent selection of growth axes for PPF spherulites in melt is reasonably speculated.
基金financially supported by the National Natural Science Foundation of China(Nos.21674033,21374027)National Key R&D Program of China(No.2017YFB0307704)
文摘The morphologies of poly(L-lactic acid)(PLLA)spherulites,when crystallized within the pre-existed poly(oxymethylene)(POM)crystal frameworks,have been investigated.PLLA/POM blend is a melt-miscible crystalline/crystalline blend system.Owing to the lower melting point but much faster crystallization rate than PLEA,POM crystallized first upon cooling from the melt state and then melted first during the subsequent heating process in this blend system.Lamellar assembly of PLLA crystals within the pre-existed POM spherulitic frameworks was directly observed with the polarized light microscopy by selectively melting the POM frameworks.The investigation indicated that PLLA crystals fully replicated the spherulitic morphology and optical birefringence of the POM crystal frameworks,which was independent of T_(o).On the other hand,POM could also duplicate the pre-existed PLLA morphologies.The result obtained provides us a possibility to design the lamellar assembly and crystal structures of polymer crystals in miscible crystalline/crystalline polymer blends.
基金supported by the National Basic Research Program of China (No. 2012CB025901)National Natural Science Foundation of China (No. 21174139)
文摘In this work the nucleation and growth of spherulites for the below polylactide （PLA） layer in poly（ε- caprolactone）/polylactide （PCL/PLA） double-layer films during isothermal crystallization at various temperatures above the melting point of PCL have been investigated by using polarized optical microscopy （POM）. It is revealed that two types of spherulitic morphologies are observed in PCL/PLA double-layer films. One is the well defined highly birefringent spherulites, and the other one is the coarse spherulites. It is interesting to find that the spherulitic growth rate of the coarse spherulites is higher than that of the well defined spherulites. It is thought that the coarse spherulites nucleate and grow with the assistance of the interfaces between the PCL and PLA layers, and the well defined highly birefringent spherulites only nucleate and grow in the PLA layer.
