Apparent Nucleation Research Articles

Improved crystallization capability and mechanical properties of poly(l‐lactide) achieved by tailoring the grafted chain structure on graphene oxide

AbstractInterfacial interaction is crucial in modulating the microscopic morphology and macroscopic properties of composites. Generally, grafting polymer molecular chains on nanoparticles is an approach for enhancing the interfacial interaction, but the dependence of enhancement degree on molecular chain structure is not clear. In this work, nanosheets were obtained by grafting poly(d‐lactide) (PDLA) and poly(l‐lactide) (PLLA) molecular chains onto graphene oxide (GO), respectively, then PLLA‐based composites containing shallow loading (0.3 wt%) were obtained by melt‐blending. The findings indicated that grafting PDLA on the GO was more efficacious in enhancing the crystallization capability of PLLA, and the mechanism was primarily owing to stronger interfacial binding energy between the PLLA matrix and GO‐g‐PDLA, which was approximately 1.5 times that of the PLLA/GO‐g‐PLLA composite. Compared to the GO‐g‐PLLA nanosheets, GO‐g‐PDLA nanosheets exhibited apparent strengthening and toughening effect, and the composite sample exhibited significantly improved tensile strength and tensile ductility, with a respective increase of 21.5% and 52.2% compared with pure PLLA sample, respectively. Furthermore, all composite films (90 μm) maintain high transmittance close to 80%. This work further confirms that enhancing the interfacial binding energy by grafting PDLA molecular chains on nanoparticles is advantageous for enhancing both the crystallization and mechanical characteristics of the PLLA‐based composites.Highlights GO‐g‐PDLA and GO‐g‐PLLA were successfully synthesized. GO‐g‐PDLA showed more apparent nucleation effect in PLLA crystallization. GO‐g‐PDLA showed higher interfacial binding energy compared with GO‐g‐PLLA. Synchronously strengthening and toughening were achieved for PLLA/GO‐g‐PDLA.

(Invited, Digital Presentation) Electrochemistry at the Atomic Scale

Electrochemistry is at the heart of many important industrial processes or systems, ranging from electrolysis and hydrogen evolution over corrosion, metal deposition up to batteries, fuel cells and photoelectrochemical devices. Here, the interface between the electrolyte and the electrolyte, which can be considered the site where electrocatalytic processes occur, is of particular interest. Due to its complexity and multi-component environment even after many decades of research, our understanding of the properties of this interface is still scarce. In this talk we will discuss how modern theoretical multi-scale methods in conjunction with in-situ experiments on well-defined model systems is capable to unravel the structure and composition of these interfaces as well as the ongoing electrochemical processes.We will concentrate on metal-ion based energy storage systems, including Li-ion and Mg-ion batteries. In our experimental work we concentrated on realizing and investigating the deposition of these metal ions on model electrodes in order to understand apparent nucleation and growth processes (e.g. dendrite formation/growth). By combining different in-situ structure sensitive techniques we could resolve the initial stages of dendrite formation, which we believe is prerequisite to avoid or control their appearance [1]. The experimental work was accompanied with corresponding theoretical studies [2] on the self-diffusion on transition metal electrodes, battery-relevant materials and finally the dynamics of alloy-based electrocatalysts under operation conditions, showing the importance and urgent need for in-operando experimental studies. Further, we will discuss our recent work on understanding plasma-electrochemical systems and how plasmas are capable to alter the structure and properties of materials [3].[1] Berger, C.; Ceblin M.; Jacob T., ChemElectroChem 2017, 4, 261.[2] Gaißmaier, D.; Fantauzzi, D.; Jacob T., J. Chem. Phys. 2019, 150, 041723.[3] Menezes, P.V.; Elnagar, M.M.; Eckl, M.; Al-Shakran, M.; Menezes, P.W.; Jacob, T., Adv. Funct. Mater., DOI: 10.1002/adfm.202107058.

Atom-Selective Analyses Reveal the Structure-Directing Effect of Cs Cation on the Synthesis of Zeolites.

To understand the crystallization mechanism of zeolites, it is important to clarify the detailed role of the structure-directing agent, which is essential for the crystallization of zeolite, interacting with an amorphous aluminosilicate matrix. In this study, to reveal the structure-directing effect, the evolution of the aluminosilicate precursor which causes the nucleation of zeolite is analyzed by the comprehensive approach including atom-selective methods. The results of total and atom-selective pair distribution function analyses and X-ray absorption spectroscopy indicate that a crystalline-like coordination environment gradually forms around Cs cations. This corresponds to the fact that Cs is located at the center of the d8r units in the RHO structure whose unit is unique in this zeolite, and a similar tendency is also confirmed in the ANA system. The results collectively support the conventional hypothesis that the formation of the crystalline-like structure before the apparent nucleation of the zeolite.

Effect of trace sodium polystyrene sulfonate on the solubility, nucleation and crystallization of thiourea from metastable zone width data

The nucleation parameters from two deterministic approaches; the self-consistent Nývlt-like approach (SCA) and the linearized integral nucleation-only (NO) approach, were used to examine the effect of sodium polystyrene sulfonate (NaPSS) on the metastable zone width (MSZW) of Thiourea (TU) in aqueous solution. The addition of NaPSS enhanced the interfacial tensions, γ, of TU (2.52–3.27 mJ.m−2 for SCA model and 1.91–2.95 mJ.m−2 for NO model) leading to increased apparent nucleation progression, m, (1.54–3.44). The MSZW and growth of TU crystals in the presence of NaPSS occurs by instantaneous and heterogeneous nucleation. NaPSS delayed the nucleation of TU, a factor which correlates with increased TU crystal size distribution (38.1 μm in water to ∼ 88.36 μm). High values of m also correspond to observed lower solubility of TU in the presence of NaPSS. Finally, molecular modelling shows NaPSS strongly binds to the TU crystal surfaces during crystallization, inhibiting the nucleation.

Determination of Primary Nucleation Kinetics of Acetylsalicylic Acid in Ethanol

AbstractThe metastable zone width (MSZW) for the acetylsalicylic acid‐ethanol system was determined by the polythermal method. Nucleation parameters were calculated applying the self‐consistent Nyvlt‐like approach and the classical three‐dimensional theory approach. The results showed the usual increments in MSZW with increases in the cooling rate, mixed effects when raising the agitation rates, and an unusual behavior that reduced MSZW when the saturation temperature decreased. The apparent nucleation order proved to be independent of all three analyzed variables. The interfacial energy increased with higher saturation temperature and activation energies incremented when agitation rates raised. In general, the two approaches explained closely the experimental results.

Biased-angle effect on diffusion dynamics and phase separation in anisotropic active particle system.

A deep understanding for collective behavior in an active matter system with complex interactions has far-reaching impact in biology. In the present work, we adopt Langevin dynamics simulations to investigate diffusion dynamics and phase separation in an anisotropic active particle system with a tunable biased angle α defined as the deviation between the active force direction and anisotropic orientation. Our results demonstrate that the biased angle can induce super-rotational diffusion dynamics characterized by a power-law relationship between the mean square angle displacement (MSAD) and the time interval Δt in the form of MSAD ∼ Δtβ with β > 1 and also result in non-trivial phase separation kinetics. As activity is dominant, nucleation time shows a non-monotonic dependence on the biased angle. Moreover, there arises a distinct transition of phase separation, from spinodal decomposition without apparent nucleation time to binodal decomposition with prominent nucleation delay. A significant inhibition effect occurs at right and obtuse angles, where the remarkable super-rotational diffusion prevents particle aggregation, leading to a slow nucleation process. As active force is competitive to anisotropic interactions, the system is almost homogeneous, while, intriguingly, we observe a re-entrant phase separation as a small acute angle is introduced. The prominent super-rotational diffusion under small angles provides an optimum condition for particle adsorption and cluster growth and, thus, accounts for the re-entrance of phase separation. A consistent scenario for the physical mechanism of our observations is achieved by properly considering the modulation of the biased angle on the interplay between activity and anisotropic interactions.

Enhanced Water Nucleation and Growth Based on Microdroplet Mobility on Lubricant-Infused Surfaces.

Lubricant-infused surfaces (LISs) can promote stable dropwise condensation and improve heat transfer rates due to a low nucleation free-energy barrier and high droplet mobility. Recent studies showed that oil menisci surrounding condensate microdroplets form distinct oil-rich and oil-poor regions. These topographical differences in the oil surface cause water microdroplets to rigorously self-propel long distances, continuously redistributing the oil film and potentially refreshing the surface for re-nucleation. However, the dynamic interplay between oil film redistribution, microdroplet self-propulsion, and droplet nucleation and growth is not yet understood. Using high-speed microscopy, we reveal that during water condensation on LISs, the smallest visible droplets (diameter: ∼1 μm, qualitatively representing nucleation) predominantly emerge in oil-poor regions due to a lower nucleation free-energy barrier. Considering the significant heat transfer performance of microdroplets (<10 μm) and transient characteristic of microdroplet movement, we compare the apparent nucleation rate density and water collection rate for LISs with oils of different viscosities and a solid hydrophobic surface at a wide range of subcooling temperatures. Generally, the lowest lubricant viscosity leads to the highest nucleation rate density. We characterize the length and frequency of microdroplet movement and attribute the nucleation enhancement primarily to higher droplet mobility and surface refreshing frequency. Interestingly and unexpectedly, hydrophobic surfaces outperform high-viscosity LISs at high subcooling temperatures but are generally inferior to any of the tested LISs at low temperature differences. To explain the observed nonlinearity between LISs and the solid hydrophobic surface, we introduce two dominant regimes that influence the condensation efficiency: mobility-limited and coalescence-limited. We compare these regimes based on droplet growth rates and water collection rates on the different surfaces. Our findings advance the understanding of dynamic water-lubricant interactions and provide new design rationales for choosing surfaces for enhanced dropwise condensation and water collection efficiencies.

Analysis of the relative supercooling enhancement of two emerging supercooling techniques

We present herein an experimental study on the ice-nucleation kinetics of two recently introduced aqueous supercooling modalities—oil-sealed isobaric supercooling and isochoric supercooling. A series of constant-cooling rate experiments compare the apparent nucleation temperatures of pure water supercooled under these modalities with conventional open-air isobaric supercooling, demonstrating that both methods significantly enhance the supercoolability of the system as compared to open-air supercooling. However, while the mean nucleation temperatures of the two methods are statistically comparable, isochoric supercooling displays approximately half the variability of isobaric oil-sealed supercooling, which may have important implications on the design of supercooling-based biopreservation protocols in which stability and reproducibility are paramount.

Highly Toughened and Heat-Resistant Poly(lactic acid) with Balanced Strength Using an Unsaturated Liquid Crystalline Polyester via Dynamic Vulcanization

Poly(lactic acid) (PLA) is a well-known sustainable plastic but with an inherent brittleness, slow crystallization rate, and poor heat resistance, which significantly limits its application. In this work, toughened PLA with a balanced tensile strength, fast crystallization rate, and great heat resistance was obtained by dynamic vulcanization with an unsaturated liquid crystalline polyester (PBDPSM) in the presence of a free radical initiator of dicumyl peroxide (DCP). PBDPSM is efficient in enhancing the tensile toughness of PLA in that the elongation at break of PLA significantly increased from 15 to 179% while adding only 1 wt % PBDPSM. When adding 8 wt % PBDPSM, the PLA/PBDPSM8 blend has an elongation at break of 265%, tensile toughness of 107.2 MJ/m3, and notched Izod impact strength of 22.5 kJ/m2. Moreover, it keeps a high tensile strength of 62.6 MPa. In addition, the crystallization rate of PLA has dramatically accelerated due to the apparent nucleation effect induced by DCP and PBDPSM. PLA/PBDPSM3 shows the highest crystallinity with 44.4%. Furthermore, it shows a high Vicat softening temperature of 152.2 °C, which is 92.2 °C higher than that of neat PLA. Finally, highly toughened PLA materials with balanced tensile strength and good heat-resistant properties were realized.

Solvent-free synthesis of MFI-type zeolites and their degradation properties of gas-phase styrene

In this study, a series of MFI-type zeolites with various compositions were synthesized by a solvent-free synthesis method at a comparatively mild condition. The results of investigations showed that the as-synthesized samples displayed a good crystallinity grade and regular morphology of layered structure. The crystallization process of TS-1 was systematic investigated. It was revealed that the transition stage of crystallization process was the formation of nucleation intermediates (Na2SiF6), which was the key factor for dropping Ti atoms into MFI framework. Meanwhile, it showed a high apparent nucleation activation energy (64.8 kJ mol−1), and low growth activation energy (25.3 kJ mol−1) in a spontaneous nucleation system, and the nucleation activation energy could be reduced to 17.2 kJ mol−1 in non-spontaneous nucleation system. The as-synthesized zeolites were evaluated for their catalytic activity for the degradation of gas-phase styrene. The titanium silicalite-1 sample doped with iron exhibited excellent catalytic activity with 100% degradation of styrene. The method employed in this work not only decreases the production cost and energy-consumption of MFI-type zeolites, but also significantly enhances their production yield. Moreover, it is an efficient pathway to solve the pollution of volatile organic compounds using solid waste.

N-Methyl-2-pyrrolidone-promoted crystallization of MEL zeolite and its acceleration mechanism

NMP can break the hydration layer around TBA+ and aluminosilicate and reduce the apparent nucleation activation energy, thus accelerating nucleation.

Influence of Carbon Coating on Intercalation Kinetics and Transport Properties of LiFePO4

AbstractWe report on a comparative study of Li+ intercalation kinetics for LiFePO4 materials with polydopamine‐derived and glucose‐derived carbon coatings. We demonstrate that the uniform polydopamine‐derived carbon coating affects the charge transfer rates and transport properties (electronic conductivity) of composite electrodes only slightly (compared to the inhomogeneous glucose‐derived coatings), whereas much more pronounced effects are observed for the apparent diffusion coefficients and nucleation barriers. Thick and uniform carbon surface layers cause a sharp decrease in the ionic diffusion coefficients, which results in the loss of capacity at higher charge/discharge rates for LiFePO4 composite electrodes. The new phase nucleation rates are also demonstrated to decrease significantly for the samples with thicker coatings inducing higher potential differences between charge and discharge curves. The analysis of the rate determining factors for the LiFePO4 electrodes points to the rate limitations induced by the slow nucleation and slow ionic diffusion, whereas the formation of a polydopamine‐derived uniform carbon layer tends to hinder the (de)intercalation reaction and does not provide additional benefits compared to glucose‐derived carbon coatings comprising conductive yet inhomogeneous layers.

Determination of the Metastable Zone and Induction Period of Urea Phosphate Solution

Abstract Determination of the metastable zone width and induction period of urea phosphate. The effects of saturation temperature, cooling rate, stirring rate, and impurity ions on the width of metastable region of urea phosphate crystals and the effect of supersaturation on its induction period were studied. The results show that the width of the crystallization metastable zone narrows with the increase of the saturation temperature, the stirring rate, and the decrease of the cooling rate. The apparent nucleation series m is calculated to be 1.021. The crystallization induction period becomes shorter as the increasing supersaturation S. Impurity ions increase the width of the metastable zone of phosphoric acid. F- has the most significant effect on the width of the metastable zone, and the effect of SO42- is relatively weakest.

Effect of Impurity Ions on Solubility and Metastable Zone Width of Lithium Metaborate Salts

The metastable zone width (MZW) of lithium metaborate salts at various concentrations was determined using the laser technique. The solubility data for lithium metaborate salts was nearly the same in the presence of NaCl at various concentrations. The MZW of lithium metaborate salts decreased when the stirring rate increased, but increased remarkably with increasing cooling rates and an increasing concentration of sodium chloride. The apparent secondary nucleation order for lithium metaborate salts was obtained using the Nývlt’s approach. The apparent secondary nucleation order m of lithium metaborate salts is 4.00 in a pure LiBO2−H2O system with an improved linear regression method. The m for lithium metaborate salts was enlarged in the system LiBO2−NaCl−H2O.

Synthesis of zeolite Y promoted by Fenton's reagent and its application in photo-Fenton-like oxidation of phenol

Zeolite Y was synthesized by hydrothermal method with adding Fenton's reagent. The materials were characterized by X-ray powder diffraction (XRD) and the crystallization kinetics was investigated. The results showed that hydroxyl free radical (∙OH) produced by Fenton's reagent accelerated both the nucleation process and the crystal growth process of zeolite Y. The apparent nucleation activation energy (En) and apparent growth activation energy (Eg) with Fenton's reagent were 67.98 and 42.66 kJ/mol, respectively. Compared with traditional synthesis of zeolite Y, the synthesis adding moderate Fenton's reagent presented shorter induction period, faster nucleation and growth rate, and lower apparent activation energy. In addition, iron was incorporated into the zeolite at the same time and the material showed high catalytic performance for photo-Fenton-like oxidation of phenol.

Very Low Nucleation Rates of Glucose Isomerase Crystals under Microgravity in the International Space Station

In situ observation of the nucleation and growth of glucose isomerase (GI) crystals under microgravity was conducted using an optical microscope during the first flight of the Advanced Nano Step project undertaken in the International Space Station (ISS). Very low apparent nucleation rates (J’) of GI crystals in the solution and on the substrate of the growth container were confirmed compared with those on the ground. In particular, J’ of GI crystals in the solution were a few times lower than that on the substrate. The growth rates (R) of the {101} faces of GI crystals on the substrate and the apparent growth rates (R’) in the solution were measured. The very low nucleation rates allowed us to successfully measure R at a very high supersaturation region (up to ln(C/Ce) = 6), at which R cannot be measured on the ground.

Enhanced Sn incorporation in GeSn epitaxial semiconductors via strain relaxation

We investigate the effect of strain on the morphology and composition of GeSn layers grown on Ge/Si virtual substrates. By using buffer layers with controlled thickness and Sn content, we demonstrate that the lattice parameter can be tuned to reduce the strain in the growing top layer (TL) leading to the incorporation of Sn up to 18 at. %. For a 7 at. % bottom layer (BL) and a 11-13 at. % middle layer (ML), the optimal total thickness tGeSn = 250-400 nm provides a large degree of strain relaxation without apparent nucleation of dislocations in the TL, while incorporating Sn at concentrations of 15 at. % and higher. Besides facilitating the growth of Sn-rich GeSn, the engineering of the lattice parameter also suppresses the gradient in Sn content in the TL, yielding a uniform composition. We correlate the formation of the surface cross-hatch pattern with the critical thickness hG for the nucleation and gliding of misfit dislocations at the GeSn-Ge interface that originate from gliding of pre-existing threading dislocations in the substrate. When the GeSn layer thickness raises above a second critical thickness hN, multiple interactions between dislocations take place, leading to a more extended defective ML/BL, thus promoting additional strain relaxation and reduces the compositional gradient in the ML. From these studies, we infer that the growth rate and the Ge-hydride precursors seem to have a limited influence on the growth kinetics, while lowering temperature and enhancing strain relaxation are central in controlling the composition of GeSn. These results contribute to the fundamental understanding of the growth of metastable, Sn-containing group-IV semiconductors, which is crucial to improve the fabrication and design of silicon-compatible mid-infrared photonic devices.

Heterogeneous versus homogeneous crystal nucleation of hard spheres.

Hard-sphere model systems are well-suited in both experiment and simulations to investigate fundamental aspects of the crystallization of fluids. In experiments on colloidal models of hard-sphere fluids, the fluid is unavoidably in contact with the walls of the sample cell, where heterogeneous crystallization may take place. In this work we use simulations to investigate the competition between homogeneous and heterogeneous crystallization. We report simulations of wall-induced nucleation for different confining walls. Combining the results of these simulations with earlier studies of homogeneous crystallization allows us to assess the competition between homogeneous and heterogeneous nucleation as a function of the wall type, fluid density and the system size. On flat walls, heterogeneous nucleation will typically overwhelm homogeneous nucleation. Even for surfaces randomly coated with spheres with a diameter that was some three times larger than that of the fluid spheres - as has been used in some experiments - heterogeneous nucleation is likely to be dominant for volume fractions smaller than ∼0.535. Only for a disordered coating that has the same structure as the liquid did we find that nucleation was likely to occur in the bulk. Hence, such coatings might be used to suppress heterogeneous nucleation in experiments. Finally, we report the apparent homogeneous nucleation rate taking into account the formation of crystallites both in the bulk and at the walls. We find that the apparent overall nucleation rates coincide with those reported in "homogeneous nucleation" experiments. This suggests that heterogeneous nucleation at the walls could partly explain the large discrepancies found between experimental measurements and simulation estimates of the homogeneous nucleation rate.

Stochastic Nucleation of Polymorphs: Experimental Evidence and Mathematical Modeling

In this work, we investigate the primary nucleation of isonicotinamide, i.e., a compound exhibiting several different polymorphs, from ethanol at several supersaturations and at isothermal conditions. Experiments have been performed over a broad range of supersaturation and in two different volumes, collecting hundreds of data points. These data show that not only the detection times, but also the polymorphs observed in the system in different repetitions of the same experiments are statistically distributed. By using the wealth of experimental data produced and building upon previous theoretical work, we develop a simple stochastic model of primary nucleation from solution for a compound forming an arbitrary number of polymorphs. The model shows that, if the polymorphism of the compound cannot be monitored, the primary nucleation rate estimated from the experiments represents only an apparent nucleation rate. Furthermore, the first polymorph nucleating in the system is not expected to be a function of th...

Largely enhanced dielectric properties of poly(vinylidene fluoride) composites achieved by adding polypyrrole-decorated graphene oxide

In this work, polypyrrole (PPy) particles were first decorated on the surface of graphene oxide (GO), then the hybrid PPy@GO particles were incorporated into poly(vinylidene fluoride) (PVDF) to prepare the PVDF/PPy@GO composites. The microstructure characterizations showed that PPy particles were successfully decorated on the GO platelets and simultaneously, GO was partially reduced. With the aid of GO, PPy particles with much smaller diameters exhibited good dispersion in the PVDF/PPy@GO composites. Interestingly, different from the apparent nucleation effect of PPy particles on PVDF crystallization, the nucleation effect of PPy particles in the PVDF/PPy@GO composites was greatly reduced. The PVDF/PPy@GO composites exhibited higher electrical conductivity compared with the PVDF/PPy composites. More interestingly, compared with the PVDF/PPy composites, largely enhanced permittivity and slightly reduced dielectric loss were simultaneously achieved for the PVDF/PPy@GO composites. The mechanisms were related to the construction of multiple-interfacial polarization and the enhanced conductivity of the composites.