This study aims to investigate the crystallization behavior and molecular dynamics of amorphous griseofulvin (GSF) in the presence of low-concentration poly(ethylene oxide) (PEO). We observe that the addition of 3% w/w PEO remarkably increases the crystal growth rate of GSF by two orders of magnitude in both the supercooled liquid and glassy states. The liquid dynamics of amorphous GSF in the presence and absence of PEO are characterized by dielectric spectroscopy. With an increase of the PEO content, the α-relaxation times of the systems decrease, indicating the increase of global molecular mobility. The couplings between molecular mobility and crystallization kinetics of GSF systems show strong time-dependences below Tg. The overlapping of α-relaxation times of GSF in presence and absence of PEO as a function of Tg/T suggest the “plasticization” effect of PEO additives. However, the crystallization kinetics of amorphous GSF containing low-concentration PEO do not overlap with those of pure GSF on a Tg/T scale. The remarkable accelerating effect of crystal growth of amorphous GSF by low-concentration PEO can be partially attributed to the increase of global mobility. The high segmental mobility of PEO is expected to strongly affect the crystal growth rates of GSF. These findings are relevant for understanding and predicting the physical stability of amorphous pharmaceutical solid dispersions.Keywords: crystal growth; dielectric spectroscopy; griseofulvin; molecular mobility; poly(ethylene oxide);

Differential fast scanning calorimetry (DFSC) was employed on the study of self-nucleation behavior of poly(butylene succinate) (PBS). The ultra-fast cooling ability of DFSC allows investigating the effect of self-nucleation on the isothermal crystallization kinetics over a wide temperature range. Crystallization half-time, instead of crystallization peak temperature, was used to describe the self-nucleation behavior, and the self-nucleation domain for the samples crystallized at different temperatures was determined. Due to the competition between homogenous nucleation and self-nuclei, the effect of self-nucleation was less pronounced at high supercooling than that for the sample isothermally crystallized at higher temperature. An efficiency scale to judge the efficiency of nucleating agents from the crystallization half-time was also introduced in this work.

•Fractionated crystallizations initiated by heterogeneous and homogeneous nucleation for sPP in large AAO nanopores are observed.•A systematic study of how cooling rate affects the crystallization of sPP confined in nanopores is presented.•Crystallization kinetics of sPP located inside nanopores is investigated by an isothermal step crystallization technique.•Both of the nuclei density and secondary nucleation rate are found to decrease for sPP in nanopores.Crystalline polymers can exhibit anomalous crystallization behaviors as restricted into nanodomains. Herein, syndiotactic polypropylene (sPP) was infiltrated into nanoporous alumina templates with different pore diameters, and their nonisothermal and isothermal crystallization kinetics were investigated. As located inside nanopores, the crystallization of sPP becomes sluggish. The crystallization temperatures reveal a pronounced cooling rate dependence for sPP in large nanopores. At fast cooling rates, the homogeneous nucleation is dominated. While, at slow cooling rates, the splits of crystallization peaks can be ascribed to fractionated crystallizations initiated by heterogeneous and homogeneous nucleation, respectively. For sPP in small nanopores, the homogeneous nucleation always predominates, which induces less cooling rate effect. In addition, based on the Avrami equation and Lauritzen-Hoffman growth theory, isothermal crystallization experiments indicate that the characteristic crystallization times of sPP under confinement are much longer, and both of the nuclei density and secondary nucleation rate are decreased for sPP confined in nanopores.Download high-res image (250KB)Download full-size image

•A mat composed of carbon nanofibers which contain numerous iron oxide/carbon nanoparticles is directly used as anode for lithium ion batteries.•A three dimensional electric conductive network is fabricated by the crosslinked nanofibers.•The mat anode exhibited good capacity retention and excellent rate capability.To meet the requirements for the quick charge for the hybrid electric vehicles (HEVs) or plug-in hybrid electric vehicles (PHEVs), better rate capability is urgently needed for the lithium ion batteries (LIBs). Here in our work, a new anode with excellent rate capability is developed. In this anode, nanoporous iron oxide nanoparticles coated with carbon (designated as Fe2O3@C NPs) are homogeneous distributed in carbon nanofibers (CNFs), which can be designated as Fe2O3@C CNFs. The CNF constrains the nanoporous Fe2O3@C NPs along the longitudinal direction and the fibers are cross-linked, establishing a three dimensional (3D) stable electric conductive network. The nanoporous Fe2O3@C NPs exposed on the surface of CNFs provide more active sites for electrode reactions. The thin carbon shell around the Fe2O3 NPs gives the additional protection and improves the conductive connection between the nanofibers, leading to an integral conductive network which links all the Fe2O3@C NPs. The Fe2O3@C CNFs structure exhibits good capacity retention and excellent rate capacity at high current density.

We report on the synthesis of heterotelechelic α,ω-dye-labeled polystyrene and poly(methyl methacrylate) via a combination of site-specific atom transfer radical polymerization (ATRP) and click chemistry. By using the advantages of the living polymerization characteristics and a robust coupling efficiency, the Förster/fluorescence resonance energy transfer (FRET) pairs (i.e., carbazolyl and anthryl) were dictated to be at the near-stoichiometric chain ends. The distribution of the end-to-end distance was well described by the energy transfer response of the fluorescent groups between chain ends, which is in reasonable agreement with Gaussian statistics. The synthetic approach described here provides an opportunity to prepare polymeric materials with customized responsive elements and in-depth insight into the statistical scaling dimension of polymers.

•Ultrasmall tin dioxide nanoparticles constrained in graphene gel: SnO2@GG.•SnO2@GG composite is prepared by a facile one-pot strategy.•The graphene framework provides large void space and good conductivity.•This composite exhibits an excellent electrochemical performance.Tin dioxide (SnO2) is an attractive material for anodes in energy storage devices, because it has four times the theoretical capacity of the prevalent anode material (graphite). The main obstacle hampers SnO2 from practical application is the pulverization problem caused by drastic volume change (∼300%) during lithium-ion insertion or extraction, which would lead to the loss of electrical conductivity, unstable solid-electrolyte interphase (SEI) formation and consequently severe capacity fading in the cycling. Here, we anchored the SnO2 nanocrystals into three dimensional graphene gel network to tackle this problem. As a result of the three dimensional (3-D) architecture, the huge volume change during cycling was tolerated by the large free space in this 3-D construction, resulting in a high capacity of 1090 mAh g−1 even after 200 cycles. What's more, at a higher current density 5 A g−1, a reversible capacity of about 491 mAh g−1 was achieved with this electrode.

Tin dioxide (SnO2) is one of the most promising anode materials for the next generation Li-ion batteries due to its high capacity. To solve the problems caused by the large volume change (over 300%) and the aggregation of the tin particles formed during cycling, nano SnO2/C composites are proved to be ideal anode materials for high performance Li-ion batteries. However, it is still a challenge to disperse ultrasmall (<6 nm) SnO2 nanoparticles with uniform size in carbon matrix. Here, we report a facile hydrothermal way to get such optimized nano SnO2/C composite, in which well dispersed ultrasmall SnO2 nanocrystals (3∼5 nm) are embedded in a conductive carbon matrix. With this anode, we demonstrate a high stable capacity of 928 mAh g−1 based on the total mass of the composite at a current density of 500 mA g−1. At high current density of 2 A g−1, this composite anode shows a capacity of 853 mAh g−1 in the first charge, in such high current density, we can even get a capacity retention of more than 91% (779 mAh g−1) after 1000 cycles.

A composite of nanoporous iron oxide (Fe2O3) nanoparticles coated with a thin layer of carbon (designated as nanoporous Fe2O3@C) is synthesized using a convenient one-pot solvothermal method. Although the thickness of the carbon framework is only 6 nm on average, which is very small compared to the size of Fe2O3 nanoparticles, the carbon framework significantly enhances the electrochemical performance of nanoporous Fe2O3@C composites when they are used as an anode material for lithium-ion batteries. Thanks partly to the relatively low carbon content of 6.7 wt%, the nanoporous Fe2O3@C anodes exhibit a high reversible capacity of 767 mA h g−1 after 100 cycles at a current density of 500 mA g−1 and 545 mA h g−1 even at a higher current density of 2 A g−1. In comparison to commercial Fe2O3 nanoparticles and bare nanoporous Fe2O3 nanoparticles, the nanoporous Fe2O3@C anodes show superior cycle life. The nanoporous structure offers void space for volume change of Fe2O3 nanoparticles, while the thin carbon framework improves the stability of structures and SEI (solid electrolyte interphase) films during the continuous intercalation/deintercalation processes of Li ions.

The glass transitions of poly(methyl methacrylate) (PMMA) oligomer confined in alumina nanopores with diameters much larger than the polymer chain dimension were investigated. Compared with the case of 80 nm nanopores, PMMA oligomer confined in 300 nm nanopores shows three glass transition temperatures (from from low to high, denoted as Tg,lo, Tg,inter, and Tg,hi). Such phenomenon can be interpreted by a three-layer model: there exists an interphase between the adsorbed layer and core volume called the interlayer, which has an intermediate Tg. The behavior of multi-Tg parameters is ascribed to the propagation of the interfacial interaction during vitrifaction process. Besides, because of the nonequilibrium effect in the adsorbed layer, the cooling rate plays an important role in the glass transitions: the fast cooling rate generates a single Tg; the intermediate cooling rate induces three Tg values, while the ultraslow cooling rate results in two Tg values. With decreasing the cooling rate, the thickness of interlayer would continually decrease, while those of the adsorbed layer and core volume gradually increase; meanwhile, the Tg,lo gradually increases, Tg,inter almost stays constant, and the Tg,hi value keeps decreasing. In such a process, the dynamic exchanges between the interlayer and adsorbed layer, core volume should be dominant.

The nucleation and crystallization kinetics of lamellar crystalline–amorphous diblock copolymer poly(ε-caprolactone)-b-poly(4-vinylpyridine) (PCL–P4VP) was investigated by ultrafast differential scanning calorimetry (UFDSC) with temperature scanning rates up to 10 000 K/s and compared with that of poly(ε-caprolactone) (PCL) homopolymer. We found that the critical cooling rate (ccr) to get the fully amorphous PCL is 1 order of magnitude slower than that for PCL homopolymer with the similar molecular weight. Isothermal nucleation and crystallization of PCL block in the PCL–P4VP copolymer and PCL homopolymer were studied covering times from 10–2 to 103 s and temperatures from 200 K (10 K below the glass transition temperature of PCL) to 300 K (about 40 K below the equilibrium melt temperature of PCL). It was found that the PCL block in PCL–P4VP copolymer experienced a slower homogeneous nucleation rate as well as crystallization rate than PCL homopolymer, indicating that even the local nucleation events of PCL chains is affected by the long-range glassy P4VP in copolymer. The confinement also hinders the long-range diffusion of PCL chains and becomes more effective once the chains get the mobility from the glassy state at crystallization temperatures above the Tg. Another effect of the confinement is the lower Avrami index in copolymer than that in homopolymer attributed to the restricted growth dimension under confinement. The results reported here might enhance the understanding of confinement effect on crystallization and give new details on the nucleation kinetics under nanoscale confinement.

The dynamics of poly(n-butyl methacrylate) confined in porous anodic aluminum oxide (AAO) templates are investigated using differential scanning calorimetry (DSC) and fluorescence nonradiative energy transfer (NRET). Two glass transition temperatures (Tg,low and Tg,high) are obtained at higher infiltration temperatures via capillary force followed by slow cooling. Tg,low resembles the Tg of the bulk phase and represents the transition of the core layer. Tg,high represents the transition of the adsorbed layer in the confined polymer glass. The temperature threshold to form one or two glass transitions is determined by adjusting the infiltration temperatures and the pore diameters. It is shown that the adsorbed layer has increased interchain proximity relative to the bulk. In addition, the glass transition behavior is hypothesized to be mediated by the counterbalance of the size and interfacial effects in the confined space. The easily synthesized core–shell nanofibers with one glassy and one rubbery component without the need for block polymers have promising potential for use in several processing strategies.

In this work, ultrafast differential scanning calorimetry (UFDSC) with heating and cooling rates up to 20000 K s−1 is used to study the transient polymorph transition of the liquid crystal 8OCB. The square plate form (SP), which was reported to grow only from the solution in binary solvent mixtures at low temperature, is found to be the only form growing from a deeply quenched smectic glass during very rapid heating. If the heating rate is slower than 8000 K s−1, reorganization to the parallelepiped form will start, and if the heating rate is slower than 1000 K s−1, the square plate form will reorganize to the parallelepiped form completely, and only melting of the parallelepiped form is observed. The capacity of the UFDSC to capture the unstable polymorphs of low molar mass organic molecules and to follow their rapid transition is demonstrated in this work.

When most prior studies on thin polymer films have shown that glass transition temperature (Tg) decreases under nanoconfinement, the differential alternating current chip (ac-chip) calorimetric method shows little dependence of Tg on thickness for supported film. To reveal this contradiction, we have manipulated a controlled interface by spin-coating polystyrene (PS) with immiscible surfactants such as tetraoctylammonium bromide or citric acid. Since the immiscible surfactants did not show plasticizing effect for PS, there was no observable reduction of Tg from the bulk value ether in powdered blends or in thick films. However, the ultrathin film with thickness h ∼ 25 nm, consisting of 95 wt % PS and 5 wt % surfactants, showed a reduction of Tg by 6–7 °C, as compared to thick film with the same composition. We propose that the surfactant molecules assembled on the interface between thin film and substrate due to phase separation. The molecular mobility of molecules at the interface was dramatically increased, which was detected by 1NMR with dipolar filter sequence. It appeared that the deviation range was not so large as that measured by other methods. But considering that we were measuring Tg at a high frequence (10 Hz), this amount of deviation was quite significant for ac-chip calorimetry. As a result, ac-chip calorimetry measured Tg data unambiguously demonstrate that thickness dependence of Tg is a real property of confined thin film.

In this paper, we characterized the interdiffusion of deuterated polystyrene (PS-D) and hydrogenated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) by 1H dipolar filter solid-state NMR under fast magic angle spinning (MAS). It is observed that the interdiffusion process of PS-D/PPO is composed of two stages, the wetting stage and the diffusion stage. The characteristic time of the transition from the wetting to diffusion stage is independent of the temperature and PS-D molecular weight. On the other hand, the increment of dipolar filtered 1H NMR signal intensity at the wetting stage depends strongly on the temperature. The PS-D chains can be easily mixed with the PPO chains intimately when the temperature is above the glass transition temperature (Tg) of PPO. However, when the temperature is below the Tg of PPO, the PPO chains are frozen and it is more difficult for the PS-D chains to approach the PPO at a molecular level.

Here we review on the thin-film chip calorimeter with controllable cooling as well as heating rates up to 106 K·s−1 developed in the last 5 years at the Institute of Physics, Rostock University. The calorimeter has been successfully used for fast thermal processing and simultaneous calorimetric measurements of many polymer samples, the physical properties of which are generally dependent strongly on their thermal history. Besides, owing to the very small addenda heat capacity, the calorimeter is very sensitive to study samples of only several tenths of nanograms. With differential alternating current (AC) design, the sensitivity of the calorimeter increased to a few tenths of pico-Joules per Kelvin. Therefore, it can be used to study glass transition of polymers confined in ultra-thin films down to several nanometers thickness. After the discussion of the strategy to realize fast cooling, we describe the static and dynamic thermal properties of the sensors used for the setup of the calorimeter. Finally, we present examples to show the performance of the calorimeter in different measurement modes.

The glass transition of poly(2,6-dimethyl-1,5-phenylene oxide) (PPO) films with thickness ranging from about 6 nm (approximately half of radius of gyration, Rg) to 330 nm (∼29 Rg) was studied by the recently developed differential alternating current chip calorimeter with sensitivity on the order of tenths of a pJ K−1. No thickness dependence of the glass temperature Tg was found for this polymer. Tgs of all the films measured in the available frequency range (∼0.5 to ∼1000 Hz) can be fit by a single Vogel−Fulcher−Tammann function in the activation plot within an uncertainty of ±3 K, thus showing no deviation from the common VFT behavior even for the thinnest film. There is also no detectable change in the shape or width of the step in heat capacity at Tg. Finally, we found that calorimetric relaxation strength at the glass transition was proportional to the thickness of the film within an uncertainty of about 25%. Consequently, we estimate the thickness of the layer deviated from the bulky behavior to be within 1.5 nm.

The association and aggregation of polymers in the semidilute solution regime during cooling from above to below the Θ temperature were investigated by the nonradiative energy transfer (NET) and rheological method. The molecular size of the solvent was found to affect the association and aggregation behaviors of the chains. When the normal small-sized solvent, for example decalin or cyclohexane is used, the polystyrene chains first associate among each other, and form aggregates of chains with strong interchain interpenetration at the end of cooling process. However, when the solvent with larger molecular size (also called middle-sized solvent), for example dioctyl phthalate (DOP) is used, polystyrene chains contract separately and form aggregates of collapsed globules at the end of cooling process. The interpenetration between chains for the polystyrene solid sample freeze-dried from different concentrations was detected by a new strategy using dipolar filter 1H solid-state NMR under fast magic angle spinning. We found that when the small-sized solvent was used, the extent of interpenetration in the polystyrene glasses basically kept constant with the concentration of the original solution and it increased suddenly near the critical overlapping concentration ([η]c ∼ 4). However, in the case of middle-sized solvent, even up to [η]c = 10, the extent of the interpenetration kept in a very low level comparable to that from extremely dilute ([η]c ∼ 0.01) small-sized solvent solution. Such results help us to understand the behaviors of fast crystallization and relaxation dynamics of serials of polymer samples freeze-dried from middle-sized solvent solutions discovered in this laboratory.