Equilibrium Melting Temperature Research Articles

Mechanical Characterization of Vial Strain During Freezing and Thawing Operations Using Amorphous Excipients

The purpose of this study was to investigate the mechanical stresses and strains acting on pharmaceutical glass tubing vials during freezing and thawing of model pharmaceutical formulations. Strain measurements were conducted inside of a laboratory-scale freeze-dryer using a custom wireless sensor. In both sucrose and trehalose formulations at concentrations between 5-20%, the strain measurements initially increased before peaking in magnitude at temperatures close to the respective glass transition temperatures of the maximally freeze concentrated solutes, Tg’. We attribute this behavior to a shift in the mechanical properties of the frozen system from a purely elastic glass below Tg’ to a viscoelastic rubber-like material above Tg’. That is, when the interstitial region becomes mechanically compliant at temperature above Tg’. The outputs were less predictable below 5% w/v and tended to exhibit two separate peaks in strain output, one near the equilibrium melting temperature of pure ice and the other near Tg’. The peaks merged at concentrations between 4-5% w/v where the largest strain magnitude was observed. The strain on primary packaging has traditionally been applied to evaluate the risk of damage or breakage due to, for example, crystallization of excipients. However, data collected during this study suggest there may be utility in formulation design or as a process analytical technology to minimize potentially destabilizing stresses and strains in the frozen formulation.

Direct measurement of hydrate equilibrium temperature in CO2 and CO2 rich fluids with low water content

A high-pressure experimental setup was used to obtain experimental data on the hydrate equilibrium (melting) temperature (HET) of hydrates formed from low water content CO2 and CO2 rich mixtures. A novel method was used to measure hydrate formation temperature in addition to melting temperature directly at realistic temperature/pressure conditions encountered in transport by pipelines or ship. The method can be used to evaluate the likelihood of hydrate formation in pipelines/ships transporting pure CO2 and CO2 coming from capture processes as well as from high CO2 content produced gas. The data generated from the measurement can also be used to investigate the kinetics of hydrate formation and dissociation in low water content fluids at pipeline/ship conditions. This paper details the experimental equipment, methods, test fluids and results. Experimental results are compared against predictions of the simplified cubic plus association equation of state (sCPA-EoS) coupled with the van der Waals and Platteeuw solid solution theory.

Molecular dynamics simulation of homogeneous nucleation of melting in superheated sodium crystal

The melting process and nucleation behaviour of sodium (Na) crystals are crucial for the frozen start-up of high-temperature sodium heat pipes and the working performance of molten sodium batteries. Equilibrium melting and the homogeneous nucleation of melting in superheated Na crystal are studied by molecular dynamics simulation. The thermodynamic properties and nucleation of Na crystal during the heating process are investigated by the characterization of the density, radial distribution function (RDF), self-diffusion coefficient (D), nucleation rate (Ihom), etc. Firstly, the equilibrium melting of Na crystal is simulated and verified by the single-phase method. Results show that Na's equilibrium melting temperature, densities, and RDF simulated match well with experimental values, demonstrating that the EAM/FS potential is suitable for studying the melting processes of Na crystal. Secondly, the calculated D of liquid Na increases approximately linearly with rising temperature within 440 K∼540 K and fits with experimental data well. The activation energy for the diffusion of Na obtained by linear fitting is 1.6406·10-20 J, which agrees well with the observed values. Finally, the homogeneous nucleation of melting in superheated Na crystal is analyzed. It is found that the Ihom of melting in superheated Na crystal rises exponentially with increasing temperature, which is consistent with the prediction in literature. The kinetic stability limit of superheated Na crystal is 468.3 K, and the relation between the Ihom of melting in superheated Na crystal and temperature is given. The physical properties and nucleation theory of Na crystal simulated during the melting can provide theoretical support for sodium's heat and mass transfer-related applications, such as sodium heat pipes and sodium batteries.

Entropic barrier theory of polymer melting

AbstractWe present a theory of melting kinetics of semicrystalline polymers at temperatures above the equilibrium melting temperature, by accounting for conformational entropy of chains during melting. We have derived free energy landscapes for escape of individual chains from a lamella into the amorphous phase as a function of the characteristics of the initial lamella, such as the lamellar thickness, number of chain folds, fold‐ and lateral‐surface free energies, and mean energy of a monomer inside the lamella. We show that melting of lamellae is always accompanied by a free energy barrier which is entirely entropic in origin. In terms of the parameters characterizing the lamellae and the extent of superheating, closed‐form formulas are presented for the equilibrium melting temperature, driving force for crystallization, free energy barrier height, average expulsion time of a single chain from a lamella, and the melting velocity of lamellae. The present entropic barrier theory predicts that the dependence of melting velocity on superheating is nonlinear and non‐Arrhenius, in qualitative agreement with experimental observations reported in the literature. The derived formulas open an opportunity to further explore the role of various molecular features of semicrystalline polymers on their melting kinetics.

Analysis of differential scanning calorimetry (DSC): determining the transition temperatures, and enthalpy and heat capacity changes in multicomponent systems by analytical model fitting

We have developed an analytical method to quantitatively analyze differential scanning calorimetry (DSC) experimental data. This method provides accurate determination of thermal properties such as equilibrium melting temperature, latent heat, change of heat capacity which can be performed automatically without intervention of a DSC operator. DSC is one of the best techniques to determine the thermal properties of materials. However, the accuracy of the transition temperature and enthalpy change can be affected by artifacts caused by the instrumentation, sampling, and the DSC analysis methods which are based on graphical constructions. In the present study, an analytical function (DSCN(T)) has been developed based on an assumed Arrhenius crystal size distribution together with instrumental and sample-related peak broadening. The DSCN(T) function was successfully applied to fit the experimental data of a substantial number of calibration and new unknown samples, including samples with an obvious asymmetry of the melting peak, yielding the thermal characteristics such as melting and glass transition temperature, and enthalpy and heat capacity change. It also allows very accurate analysis of binary systems with two distinct but severely overlapping peaks and samples that include a cold crystallization before melting.

Kinetics and mechanism of nonisothermal crystallization of biobased poly(hexamethylene 2,5-furan dicarboxylate)

Biobased poly(hexamethylene 2,5-furan dicarboxylate) (PHF) was synthesized by the two-stage melt polycondensation method (transesterification and polycondensation) in a glass batch reactor. The nonisothermal crystallization from the melt and from the glass was studied by means of Differential Scanning Calorimetry, Fast Scanning Calorimetry and advanced kinetic analysis. It is shown that changes in the crystallization regime occurs at certain temperatures and that the end of the crystallization presents some deviation from what is predicted by the Hoffman-Lauritzen's theory of growth rate. A method is presented that allows the determination of the equilibrium melting temperature, the infinite glass transition temperature, the temperature at maximum of the growth rate, and accurate simulation of crystallization rate curves. An equation is proposed for modelling the crystallization process using a methodology that avoid the problem of local minima occurring when too many parameters must be determined simultaneously.

How 4-(7-Octen-1-yl)-N,N-diphenylaniline co-units induce strong melt memory effects in isotactic polypropylene random copolymers

The random incorporation of comonomer units in isotactic polypropylene usually disrupts the chemical regularity of the macromolecular chain, thereby remarkably affecting the crystallization and melting processes. We study the influence of a novel comonomer 4-(7-Octen-1-yl)-N,N-diphenylaniline (ODPA), in the concentration range of 1.1–6.8 mol%, on the crystallization and self-nucleation behavior of isotactic polypropylene copolymers. Non-isothermal and isothermal differential scanning calorimetry experiments demonstrated that crystallization kinetics are significantly retarded upon comonomer incorporation as the ODPA co-units are excluded to the amorphous regions. Furthermore, ODPA comonomer incorporation leads to a sharp increase in nucleation density; thus, spherulitic superstructures become significantly smaller. Remarkably, the ODPA co-units induce a strong melt memory effect that can persist even above the equilibrium melting temperature for copolymers with 4.4–6.8 mol% ODPA. The width of Domain IIa (exclusive melt-memory domain), an indicator of the self-nucleation strength, starts to increase sharply once the content of ODPA exceeds 1.8 mol%. In contrast, the width of Domain IIb (self-seeding domain) remains constant. We attribute the self-nucleation effect in these ODPA copolymers to the aggregation of co-units in the interlamellar amorphous regions that hinder, upon melting, the motion of the chain sequences that were initially packed within the crystal lattice. In this way, to reach the isotropic melt state, the sample must be heated to much higher temperatures than its apparent or even equilibrium melting point, depending on the comonomer content. Consequently, nucleation upon cooling from the self-nucleated melt becomes easier and faster.

Equilibrium Melting Temperature of the Hexagonal Crystals of Polybutene-1 and Its Copolymer

TheLamellar structures of form I in polymorphic isotactic polybutene-1 (iPB-1) and forms I and I′ in butene-1/ethylene random copolymer (iPB-1/C2) were investigated by studying their melting behavior using the combination of small-angle X-ray scattering (SAXS) and fast scanning chip calorimetry (FSC) techniques. Hexagonal form I was transformed from tetragonal form II obtained by crystallization of a homogeneous melt of iPB-1 and iPB-1/C2. Hexagonal form I′ was crystallized directly from a heterogeneous melt of iPB-1/C2. Despite the same hexagonal crystallographic structure, forms I and I′ have obviously distinct melting behaviors due to different ways of crystal formation. Well-defined linear dependences of the melting temperature against the reciprocal lamellar thickness were observed for forms I and I′ with frozen chain mobility in crystals. The slopes of the thus obtained melting lines for forms I and I′ are different. Their extrapolations to imaginary infinitely large lamellar thickness provide the equilibrium melting temperature Tm∞ for forms I and I′, which is associated with the stability of the lamellar crystals. In spite of crystal defects in form I′, a higher Tm∞ is observed for this form in iPB-1/C2 than Tm∞ for form I in both iPB-1 and iPB-1/C2. The difference in Tm∞ indicates a less perfect structure of form I crystal lamellae that is caused by the fragmentation of form II crystal lamellae during the polymorphic phase transition from form II to I. The lamellae broke into crystal blocks along the lamellar direction. The smaller lateral sizes of the fragmented lamellae clearly induce a decrease in the stability of crystals, as expressed in a lower Tm∞ for form I.

Melt Memory Effect in Polyethylene Random Terpolymer with Small Amount of 1-Octene and 1-Hexene Co-Units: Non-Isothermal and Isothermal Investigations.

Homo-polymers of reasonable molecular weight relax very fast in the molten state. Starting from a semi-crystalline structure, when the homo-polymer is heated up to a temperature higher than its nominal melting temperature, it relaxes quickly into a homogenous molten state. The following crystallization temperature during cooling remains constant irrespective of the melt temperature. However, the situation is evidently different in copolymers. A phenomenon named the crystallization melt memory effect denotes an increased crystallization rate during cooling after a polymer was melted at different temperatures, which is often observed. The melt temperature can be even higher than the equilibrium melting temperature of the corresponding polymer crystals. In this work, we investigated such memory effect in a polyethylene random terpolymer with a small fraction of 1-octene and 1-hexene co-units using differential scanning calorimetry techniques. Both non-isothermal and isothermal protocols were employed. In non-isothermal tests, a purposely prepared sample with well defined thermal history (the sample has been first conditioned at 200 °C for 5 min to eliminate the thermal history and then cooled down to -50 °C) was melted at different temperatures, followed by a continuous cooling at a constant rate of 20 °C/min. Peak crystallization temperature during cooling was taken to represent the crystallization rate. Whereas, in isothermal tests, the same prepared sample with well defined thermal history was cooled to a certain crystallization temperature after being melted at different temperatures. Here, time to complete the isothermal crystallization was recorded. It was found that the results of isothermal tests allowed us to divide the melt temperature into four zones where the features of the crystallization half time change.

Aqueous Solid Formation Kinetics in High-Pressure Methane at Trace Water Concentrations.

Natural gas containing trace amounts of water is frequently liquefied at conditions where aqueous solids are thermodynamically stable. However, no data are available to describe the kinetics of aqueous solid formation at these conditions. Here, we present experimental measurements of both solid formation kinetics and solid-fluid equilibrium for trace concentrations of (12 ± 0.7) ppm water in methane using a stirred, high-pressure apparatus and visual microscopy. Along isochoric pathways with cooling rates around 1 K·min-1, micron-scale aqueous solids were observed to form at subcoolings of (0.3-8.6) K, relative to an average equilibrium melting temperature of (253 ± 1.9) K at (8.9 ± 0.08) MPa; these data are consistent with predicted methane hydrate dissociation conditions within the uncertainty of both the experiment and model. The 36 measured formation events were used to construct a cumulative formation probability distribution, which was then fitted with a model from Classical Nucleation Theory, enabling the extraction of kinetic and thermodynamic nucleation parameters. While the resulting nucleation parameter values were comparable to those published for methane hydrate formation in bulk-water systems, the observed growth kinetics were distinctly different with only a small percentage of the water in the system converting into micron-scale solids over the experimental time scale. These results may help explain how cryogenic heat exchangers in liquefied natural gas facilities can operate for long periods without blockages forming despite being at very high subcoolings for aqueous solids.

Crystallization kinetics and equilibrium melting temperature of poly(ether ketone ketone) with high terephthalate content utilizing fast scanning calorimetry

Fast scanning calorimetry (FSC) was used to analyze the crystallization kinetics and determine the equilibrium melting temperature (Tmo) of KEPSTAN PEKK 8001 (PEKK 80/20) with a terephthalate to isophthalate (T/I) ratio of 80/20. Quantitative 1H, qualitative 13C and 2D HSQC NMR spectroscopy for KEPSTAN 8001 and KEPSTAN 7002 were collected to confirm linear topology and comonomer composition. Utilizing FSC, the isothermal crystallization kinetics for PEKK 80/20 are reported for the first time over a large temperature range from 200 °C to 310 °C utilizing an interrupted isothermal crystallization method. The crystallization kinetics of PEKK 80/20 exhibits parabolic behavior with the most rapid crystallization occurring at 260 °C. Compared to earlier studies of PEKK copolymers with lower T/I ratios (i.e., PEKK 70/30 and 60/40) using conventional DSC, PEKK 80/20 is observed to crystallize up to 1 to 2 orders of magnitude faster (i.e., at rates inaccessible with conventional DSC). The Tmo of PEKK 80/20 was determined utilizing the zero-entropy-production temperature (TZEP) allowing for the first time an accurate determination of the equilibrium melting temperature of 382 °C. This value was compared to a traditional Hoffman-Weeks linear extrapolation over a range of heating rates (500 K/s – 20,000 K/s) to arrest melt-reorganization upon heating. Due to unavoidable crystalline reorganization during slow heating scans with conventional DSC, this new value for Tmo using FSC is significantly higher than the commonly referenced literature value of 368 °C. The double melting peak behavior observed after isothermal crystallization of PEKK 80/20 is discussed and understood to be due to reorganization during heating at relatively slow heating rates, as commonly observed with conventional DSC.

Memory Effects in the Quiescent Crystallization of Polyamide 12: Self-Seeding, Post-Condensation, Disentangling, and Self-Nucleation beyond the Equilibrium Melting Temperature

This paper addresses the role of memory effects from earlier thermal protocols on the non-isothermal crystallization behavior of polyamide 12 (PA12). It turns out that memory effects can induce differences in crystallization temperatures as large as 30 °C when cooled from the melt at 10 °C/min. DSC experiments reveal that memory effects in PA12 result from (1) self-nucleation by the action of crystalline residues (self-seeding), (2) chemical post-condensation, and (3) polymer chain disentangling and re-entangling. Self-nucleation and disentangling facilitate crystallization, while melt post-condensation and re-entangling hamper it. It was demonstrated that repeated crystallization stimulates disentangling and that re-entangling in the liquid state proceeds more rapidly the higher the temperature. Effects due to solid-state post-condensation are very intriguing and particularly relevant to laser sintering based additive manufacturing. It was observed that solid-state post-condensation at 175 °C for 1 h negatively affects crystallization in a subsequent heating/cooling cycle but that solid-state annealing at 175 °C for 20 h leads to an enhanced crystal perfection and chain rearrangements whose non-crystalline self-nucleating remnants in the melt at 240 °C need more than 1 h to relax and no longer stimulate crystallization during cooling. Importantly, 240 °C is higher than the equilibrium melting temperature of PA12.

Evaluation of the Equilibrium Melting Temperature and Melting Behavior of Poly(Phenylene Sulfide) Crystals.

Focusing on the melting process of poly(phenylene sulfide) (PPS) crystals, one of the high-performance resins with a very wide range of applications, we attempted to clarify the melting process and derive the equilibrium melting temperature with structural analysis using X-ray scattering and thermal measurements. Two melting points were observed in the crystallized PPS films by DSC measurements. We focused on the low-temperature melting point, in situ small-angle and wide-angle X-ray scattering measurements using synchrotron radiation and DSC thermograms indicate the melting of microcrystals because of thickening of the amorphous part from small-angle X-ray scattering results. In addition, the Hoffman-Weeks plot based on the results of fast scanning calorimetry showed that the melting temperature is almost parallel to the straight line where melting temperature and crystallization temperature are equal, indicating that the melting is of a metastable structure. The melting point on the high temperature side was attributed to the melting of lamellar crystals. The equilibrium melting point was derived from the Hoffman-Week and Gibbs-Thomson plots as 318 °C.

Synthesis, Thermal and Mechanical Properties of Fully Biobased Poly (hexamethylene succinate-co-2,5-furandicarboxylate) Copolyesters

Poly (hexamethylene succinate) (PHS) is a biobased and biodegradable polyester. In this research, two fully biobased high-molecular-weight poly (hexamethylene succinate-co-2,5-furandicarboxylate) (PHSF) copolyesters with low hexamethylene furandicarboxylate (HF) unit contents (about 5 and 10 mol%) were successfully synthesized through a two-step transesterification/esterification and polycondensation method. The basic thermal behavior, crystal structure, isothermal crystallization kinetics, melting behavior, thermal stability, and tensile mechanical property of PHSF copolyesters were studied in detail and compared with those of PHS. PHSF showed a decrease in the melt crystallization temperature, melting temperature, and equilibrium melting temperature while showing a slight increase in the glass transition temperature and thermal decomposition temperature. PHSF copolyesters displayed the same crystal structure as PHS. Compared with PHS, PHSF copolyesters showed the improved mechanical property. The presence of about 10 mol% of HF unit increased the tensile strength from 12.9 ± 0.9 MPa for PHS to 39.2 ± 0.8 MPa; meanwhile, the elongation at break also increased from 498.5 ± 4.78% to 1757.6 ± 6.1%.

CO2 hydrate formation in NaCl systems and undersaturated aqueous solutions

A high-pressure experimental setup was used to obtain experimental data on the Hydrate Equilibrium (melting) Temperature (HET) of aqueous phases undersaturated with CO2, at different CO2 saturation levels and with different aqueous phase compositions (sodium chloride and sodium chloride/calcium chloride). This paper details the experimental equipment, methods, test fluids, and results. To study the phase equilibria of CO2-brine systems and further validate the results, hydrate dissociation conditions of CO2 in different concentrations of NaCl aqueous solutions were measured in the low-temperature region and over a wide range of pressure. Experimental results were compared against predictions of the simplified Cubic Plus Association Equation of State (sCPA-EoS) coupled with the van der Waals and Platteeuw solid solution theory.

Synthesis, Thermal Behavior, and Mechanical Properties of Fully Biobased Poly(Hexamethylene 2,5-Furandicarboxylate-Co-Sebacate) Copolyesters.

In this research, three fully biobased poly(hexamethylene 2,5-furandicarboxylate-co-sebacate) (PHFSe) copolyesters with low contents of hexamethylene sebacate (HSe) unit (10 mol%, 20 mol%, and 30 mol%) were successfully synthesized through a two-step transesterification/esterification and polycondensation method. The chemical structure and actual composition of PHFSe copolyesters were confirmed by hydrogen nuclear magnetic resonance. The thermal behavior and mechanical property of PHFSe copolyesters were investigated and compared with those of the poly(hexamethylene 2,5-furandicarboxylate) (PHF) homopolymer. Both PHFSe copolyesters and PHF showed the high thermal stability. The basic thermal parameters, including glass transition temperature, melting temperature, and equilibrium melting temperature, gradually decreased with increasing the HSe unit content. PHFSe copolyesters crystallized more slowly than PHF under both the nonisothermal and isothermal melt crystallization conditions; however, they crystallized through the same crystallization mechanism and crystal structure. In addition, the mechanical property, especially the elongation at break of PHFSe copolyesters, was obviously improved when the HSe unit content was greater than 10 mol%. In brief, the thermal and mechanical properties of PHF may be easily tuned by changing the HSe unit content to meet various practical end-use requirements.

Deviations from Arrhenius dynamics in high temperature liquids, a possible collapse, and a viscosity bound

Liquids realize a highly complex state of matter in which strong competing kinetic and interaction effects come to life. As such, liquids are more challenging to understand than either gases or solids generally. In weakly interacting gases, the kinetic effects dominate. By contrast, low temperature solids typically feature far smaller fluctuations about their ground state. Notwithstanding their complexity, with the exception of quantum fluids and supercooled liquids, various aspects of common liquid dynamics such as their dynamic viscosity are often assumed to be given by rather simple, Arrhenius-type, activated forms with nearly constant (i.e., temperature independent) energy barriers. In this work, we analyze experimentally measured viscosities of numerous liquids far above their equilibrium melting temperature to see how well this assumption fares. We find, for the investigated liquids, marked deviations from simple activated dynamics. Even far above their equilibrium melting temperatures, as the temperature drops, the viscosity of these liquids increases more strongly than predicted by activated dynamics dominated by a single uniform energy barrier. For metallic fluids, the scale of the prefactors of the best Arrhenius fits for the viscosity is typically consistent with that given by the product $nh$ with $n$ the number density and $h$ Planck's constant. In various fluids that we examined, $nh$ constitutes a lower bound scale on the viscosity. We find that a scaling of the temperature axis (complementing that of the viscosity) leads to a partial collapse of the temperature dependent viscosities of different fluids; such a scaling allows for a functional dependence of the viscosity on temperature that includes yet is far more general than activated Arrhenius form alone. We speculate on relations between non-Arrhenius dynamics and thermodynamic observables.

Enhanced crystallization of poly(lactic acid) bioplastics by a green and facile approach using liquid poly(ethylene glycol)

AbstractPolylactic acid (PLA) bioplastics have attracted increasing attention from both academic and industrial researchers due to their biomass‐derived nature and low toxicity for the human body and environment. A major drawback of PLA is slow crystallization during processing, which considerably limits its commercial applications. In this study, a simple and low‐cost approach involving the addition of eco‐friendly low molecular weight poly(ethylene glycol) (PEG; 400 g/mole) as a green solvent was developed to enhance the PLA crystallization process. Differential scanning calorimetry and polarized optical microscopy data revealed that the introduction of PEG into PLA considerably increased the PLA crystallization rate. In particular, the isothermal crystallization rate of a system with a PLA/PEG mass ratio of 70/30 was more than seven times greater than that of neat PLA. In addition, the miscibility, thermal properties, and microstructures of various PLA/PEG blends were determined. A substantial reduction in the equilibrium melting temperature of PLA after PEG addition confirmed that these polymer blends were thermodynamically miscible in the melt, which strongly influenced the PLA crystallization rate. Furthermore, the addition of PEG increased the regularity of PLA crystals and induced the formation of ring‐banded PLA spherulites with periodic twisted lamellae.

Crystallization and Phase Transition of 1‐Butene Copolymers with Distinct Cyclic Co‐Units

Comprehensive SummaryThe dimethylpyridylamidohafnium catalyst was used to synthesize 1‐butene/cyclohexene and 1‐butene/vinylcyclohexane random copolymers, which have extra six‐membered cyclic co‐units in main chain and side chain, respectively. For the obtained copolymers of different incorporations, the crystallization from amorphous melt and the solid phase transition from tetragonal to trigonal phases were investigated with differential scanning calorimetry. Both of the incorporated cyclic co‐units decrease the crystallization kinetics, but the presence of cyclohexene keeps the melting temperature of copolymers constant. Interestingly, the strong memory effect of crystallization can appear at the elevated temperature even above the equilibrium melting temperature, as the content of co‐units was increased. The 1‐butene/vinylcyclohexane copolymer with 1.52 mol% co‐units exhibits a rather strong memory effect with the broad Domain IIa width of 43°C and the crystallization temperature raising of 24°C. Furthermore, the transition of tetragonal phase into trigonal phase was also explored for different co‐units and incorporations. It was found that both of the cyclohexene co‐units and vinylcyclohexane co‐units effectively slow down the kinetics of phase transition. However, the vinylcyclohexane co‐units have a much higher efficiency in suppressing phase transition than the cyclohexene co‐units, where 0.53 mol% vinylcyclohexane can completely stop phase transition within 1320 h. Considering the fact that copolymers with vinylcyclohexane co‐units actually have lower glass transition temperatures, it was indicated that the suppression of phase transition is also largely influenced by the steric co‐units in the side chain for the helical and positional adjustments, not only by the segmental mobility.

Surface Roughness Enhances Self-Nucleation of High-Density Polyethylene Droplets Dispersed within Immiscible Blends.

Highly linear or high-density polyethylenes (HDPEs) have an intrinsically high nucleation density compared to other polyolefins. Enhancing their nucleation density by self-nucleation is therefore difficult, leading to a narrow self-nucleation Domain (i.e., the so-called DomainII or the temperature Domain where self-nuclei can be injected into the material without the occurrence of annealing). In this work, we report that when HDPE is blended (up to 50%) with immiscible matrices, such as atactic polystyrene (PS) or Nylon 6, its self-nucleation capacity can be greatly increased. In addition, temperatures higher than the equilibrium melting temperature of the HDPE phase are needed to erase the significantly enhanced crystalline memory in the blends. Morphological evidence gathered by Scanning and Transmission Electron Microscopies (SEM and TEM) indicates that these unexpected results can be explained by the modification of the interface between blend components. The filling of the solid HDPE surface asperities by the low viscosity polystyrene during heating to the self-nucleation temperature, or the crystallization of the matrix in the case of Nylon 6, enhances the interface roughness between the two polymers in the blends. Such rougher interfaces can remarkably increase the self-nucleation capacity of the HDPE phase via surface nucleation.