Equilibrium Dissolution Temperature Research Articles

Preparation of solution-grown lozenge-shaped poly(p-phenylene terephthalamide) single crystals and their structural stabilization by heat treatment

In this study, the preparation of poly (p-phenylene terephthalamide) (PPTA) single crystals was examined using crystallization from dilute solutions in concentrated sulfuric acid. Lozenge-shaped PPTA single crystals were successfully prepared using a self-seeding method with a low degree of supercooling, and they consisted of modification I crystals. The a-axis direction of the crystal corresponded to the long diagonal direction of the rhombus, the b-axis direction with the short diagonal direction, and the PPTA molecular chain direction (the c-axis direction) with the crystal's thickness direction. In addition, the PPTA single crystals had a (110) growth plane, where the thickness of each single crystal was approximately equal to the molecular chain length of the PPTA. Upon heat treatment of the PPTA single crystals, the symmetry changed from P1a1 to the more stable P11n. In addition, the heat treatment caused a difference in the density of each symmetric crystal, resulting in crack formation along the b-axis direction, which is the hydrogen-bonding direction. However, the heat treatment did not change the thickness of the PPTA single crystals. Conversely, the isothermal crystallization of the PPTA caused progression in the crystallization only under a high degree of supercooling, thus yielding plate-like PPTA crystals that consisted of modification II crystals. In these plate-like PPTA crystals, the length corresponded to the crystal a-axis direction, and the electron diffraction pattern was broad. Furthermore, the equilibrium dissolution temperature of the PPTA single crystals was discussed.

Precipitation and dissolution behavior of κ-carbide during continuous heating in Fe-9.3Mn-5.6Al-0.16C lightweight steel

The precipitation and dissolution behavior of κ-carbide were investigated during continuous heating of Fe-9.3Mn-5.6Al-0.16C (wt.%) lightweight steel with the triple phases of δ-ferrite, γ-austenite and α′-martensite mainly using a differential scanning calorimeter (DSC) and a dilatometer. The first exothermic peak appeared on the DSC curve at temperatures between 200 °C and 270 °C due to the precipitation of κ-carbide within α′-martensite. The κ-carbide platelets were dissolved again into γ-austenite, which was reverted from α′-martensite at approximately 300 °C. The reverse transformation and the dissolution of κ-carbide caused the second endothermic reaction. The new globular particles of κ-carbide formed at the grain boundaries of δ-ferrite at approximately 480 °C, although the pre-existing κ-carbide within α′-martensite vanished. The precipitation of κ-carbide in δ-ferrite also induced the exothermic reaction. When the specimen was heated up to 700 °C, which is higher than the equilibrium dissolution temperature of κ-carbide (638 °C), all κ-carbide precipitates were completely dissolved into γ-austenite.

Dynamic interactions between poly(3-hexylthiophene) and single-walled carbon nanotubes in marginal solvent.

Interfacial interactions between conjugated polymers and carbon nanotubes are pivotal in determining the device performance of nanotube-based polymer electronic devices. Here, we report on interfacial structures and crystallization kinetics of poly(3-hexylthiophene) (P3HT) in the presence of single-walled carbon nanotubes (SWNTs) in anisole by means of transmission electron microscope (TEM) and ultraviolet-visible (UV-vis) absorption spectroscopy. Confined on SWNT surfaces, the P3HT forms nanofibril crystals perpendicular to the long axis of SWNTs. The equilibrium dissolution temperature of the P3HT crystals in anisole is determined to be 381 ± 10 K according to the Hoffman-Weeks extrapolation approach. Upon cooling, the polymer solution spontaneously undergoes a time-dependent chromism. Various kinetics factors such as crystallization temperature, concentration, and SWNT loading have been investigated. It is found that the growth rate (G) of the crystals scales with concentration (C) as G ∝ C(1.70±0.16). The Avrami model is utilized to analyze the nucleation mechanism and the Avrami exponents vary between 1.0 and 1.3. The Lauritzen-Hoffman theory is applied to study the chain-folding process. The fold surface free energy is calculated to be (5.28-11.9) × 10(-2) J m(-2). It is evident that the addition of 0.30 wt % SWNTs reduces the fold surface free energy by 55.6%.

Dissolution Behaviour of NbC during Slab Reheating

It is common practice to reheat continuously cast slabs prior to hot-rolling. Here we examine the dissolution of niobium carbide precipitates present in the cast slabs, as a function of the temperature during heating at a typical rate. The initial condition of precipitates in slab is quantified with transmission electron microscopy. Kinetic simulations and interrupted quenching experiments indicate that the precipitates persist well beyond the equilibrium dissolution temperature. The coarsening of the precipitates during heating, as opposed to a general lowering in the mean size due to dissolution, occurs only at heating rates some two orders of magnitude slower than typical.

Effects of recrystallization annealing temperature on carbide precipitation, microstructure, and mechanical properties in Fe–18Mn–0.6C–1.5Al TWIP steel

The microstructure, dimple structure, and mechanical properties of a cold-rolled Fe–18Mn–0.6C–1.5Al TWIP steel were investigated as a function of annealing temperature. The recrystallization started at 600 °C and finished at 700 °C for the holding time of 10 min. The coarsening rate of recrystallized grains was increased over about 840 °C and Rockwell hardness was greatly decreased between 800 and 900 °C, which shows a good agreement with the equilibrium dissolution temperature of M 3C carbides. The reversion of the tensile strength occurred between 700 and 800 °C because of the carbide precipitation hardening. The precipitation-time-temperature diagram was generated by dilatometric tests, showing a nose temperature of 800 °C. The dimple size was decreased to 700 °C and then increased again with higher annealing temperature, having a strong proportional relationship with austenite grain size.

Onsets of Tethered Chain Overcrowding and Highly Stretched Brush Regime via Crystalline−Amorphous Diblock Copolymers

Lamellar single crystals grown in dilute solutions can be used as templates for tethered chain analysis. Two series of diblock copolymers, poly(ethylene oxide)-block-polystyrene (PEO-b-PS) and poly(l-lactic acid)-block-polystyrene (PLLA-b-PS), were used as model templates to generate tethered PS blocks on the single-crystal basal surfaces. Controlled and tunable reduced tethering density, σ, defined by σπRg2 (where σ is the tethered chain density and is equal to the reciprocal of the covered area of the chain and Rg is the radius of gyration of this tethered chain in its end-free state at the same conditions), could be achieved in a broad range (up to 24) by changing the molecular weights (MW's) of the crystalline and amorphous blocks and by varying the crystallization temperature (Tx) of different PEO-b-PS and PLLA-b-PS solutions. For PEO and PLLA homopolymers crystallized in dilute solutions, the lamellar crystal thicknesses (dCRYST) were observed to be proportional to the reciprocal undercooling ΔT (where ΔT = Td − Tx and Td is the equilibrium dissolution temperature of the crystals). The σ of the tethered PS chains on the crystal surface increased with decreasing ΔT because at a fixed MW of the PEO or PLLA block, an increase in the dCRYST was evidence of a decrease in the number of folds. When we plotted the relationships between 1/dCRYST and Tx for these two series of diblock copolymers, sudden and discontinuous changes of the slopes in some of these were observed at σ = 3.7 (σ*). This was as a result of the drastic interaction change of the neighboring PS tethered chains. An average reduced surface free energy of the tethered PS chains (ΓPS) was defined and used as a parameter to characterize the PS tethered chain interactions. The relationship between ΓPS and σ showed a discontinuous transition at σ*, which had a close similarity to the hard-sphere-like interaction model. This could be identified as the onset of the tethered PS chain overcrowding in solution. This transition indicates that the extra entropic surface free energy created by the repulsion of tethered PS chains started to affect the nucleation barrier of the PEO or PLLA block crystallization. On the basis of the scaling laws, the onset of highly stretched brush regime could be identified at σ = 14.3 (σ**). In the ΓPS vs σ plot, the transition appears to be continuous. Thus, a crossover regime in the tethered PS chains exists between σ* = 3.7 and σ** = 14.3. It is defined as the regime where the interaction of the tethered PS chains undergoes changes from being noninteracting toward penetration to, finally, chain stretching normal to the surface.

Shear-Induced Structures in Semidilute Solution of Ultrahigh Molecular Weight Polyethylene at Temperature Close to Equilibrium Dissolution Temperature

The shear-induced structure of a semidimute solution of ultrahigh molecular weight polyethylene (UHMWPE) with a paraffin wax as a solvent was investigated with shear small-angle light scattering (shear SALS) and shear microscopy. At a temperature of 124 °C, which is much higher than the nominal melting temperature (∼118 °C) and is approximately equivalent to or slightly lower than the equilibrium dissolution (crystal melting) temperature of the UHMWPE solution at quiescent state, the characteristic “butterfly” pattern was observed in shear SALS when the solution was subjected to shear flow at a shear rate larger than critical shear rate γc,butt. Lack of optical anisotropy in the sheared solution and disappearance of the butterfly pattern after cessation of the shear suggest that the pattern is attributed to shear-enhanced concentration fluctuations or phase separation. When γ further increased above a critical value γc,streak, a strong, sharp streaklike scattering pattern appeared perpendicular to the ...

Lamellar and Crystalline Layer Thickness of Single Crystals of Narrow Molecular Weight Fractions of Linear Polyethylene

The thermal dependence of the lamellar thickness (Lp) and the thickness of crystalline layers (Lcryst) of linear polyethylene single crystals has been revisited. LPE fractions with different average molecular weights were crystallized at the same temperatures to avoid the delicate problem of an arbitrary choice of their equilibrium dissolution temperature to calculate their degree of supercooling. This procedure allows direct check of the thicknesses of the crystalline layers dependence on the degree of supercooling. Indeed, the equilibrium melting and dissolution temperatures depend on the average molecular weight. Mats of linear polyethylene single crystals of various narrow molecular weight fractions were obtained from dilute p-xylene solutions. Their lamellar thickness was determined from the SAXS intensity curve. The crystalline layers thickness was calculated from the linear correlation function of the SAXS intensity curves and from the LAM mode frequency of the Raman spectrum. It depends as expected on the crystallization temperature. However, at a given crystallization temperature, both the thicknesses of the lamellae and of the crystalline layers are nearly independent of molecular weight and therefore also of the degree of supercooling estimated from a well-known semiempirical relationship.

Dissolution and crystallization behavior of poly(ethylene terephthalate)–diluent mixtures

AbstractThe solution crystallization kinetics and crystal dissolution behavior of three grades of poly (ethylene terephthalate) in N‐methyl–2‐pyrrolidinone were studied were using turbidimetric and calorimetric methods. The influence of concentration on the equilibrium dissolution temperature was described using Flory's melting point‐composition relationship. The effect of the solvent alkyl group was also investigated. N‐ethyl‐2‐pyrrolidinone was found to be a better solvent than N‐ethyl–2‐pyrrolidinone or N‐cyclohexyl–2‐pyrrolidinone for poly (ethylene terephthalate). From the calorimetric experiments, it was determined that two crystallization processes (primary and secondary crystallization) were responsible for the total crystallinity. The primary process dominated the early stages of the crystallization process and accounted for the majority of the final crystallinity for lower polymer concentrations. Based on coherent secondary nucleation theory, the effect of the crystallization temperature on the primary crystallization rate constant was quantified in terms of a temperature coefficient. This temperature coefficient was found to be relatively insensitive to PET concentration, PET structural impurities, and solvent alkyl group. © 1993 John Wiley & Sons, Inc.

Growth rate and morphology of isotactic polystyrene crystals in solution at high supercoolings

The morphology and temperature dependence of the lateral growth rate G are reported for isotactic polystyrene crystallized from 0.1% dimethyl phthalate solution at high supercoolings. The outline of a lamella is a rounded hexagon for the highest temperature and a ragged circle for lower temperatures. The edges of the lamellae become ragged and overgrowth is pronounced with decreasing temperature. A linear relationship is found between log( G η ) and 1 TΔT over a wide range of supercooling ( ΔT = T o d − T) from 70 to 170 K, where η is a retardation factor of Arrhenius form with an activation energy of 8400 K, and T o d is the equilibrium dissolution temperature. The value of T o d is determined to be 200°C by differential scanning calorimetry. In these high supercoolings, the nucleation theory of polymer crystallization loses its validity; in fact, the slope of the plot of log( G η ) versus 1 TΔT is four times as large as the value predicted by nucleation theory. Possible growth mechanisms at high supercoolings are discussed on the basis of the morphology.

Kinetics of poly(ethylene oxide) crystallization from solution: temperature and molecular weight dependence

From the dynamic light scattering study, it is found that the temperature influence on crystal growth kinetics in terms of logG vs 1/TΔT depends on the choice of the equilibrium dissolution temperature T d °. Regardless of the exact values of T d ° used for the range of molecular samples, it is found that for high PEO molecular weights (>3×10 5 ) a transition could be recognized in the dependance of the growth rate on the extent of supercooling. No such transition is found for intermediate (<3×10 5 ) molecular weight PEO

Equilibrium dissolution temperature of low molecular weight polyethylene fractions in dilute solution [Erratum to document cited in CA110(12):96260y

ADVERTISEMENT RETURN TO ISSUEPREVArticleEquilibrium dissolution temperature of low molecular weight polyethylene fractions in dilute solution [Erratum to document cited in CA110(12):96260y]Abaneshwar Prasad and Leo MandelkernCite this: Macromolecules 1989, 22, 12, 4666Publication Date (Print):December 1, 1989Publication History Published online1 May 2002Published inissue 1 December 1989https://doi.org/10.1021/ma00202a055RIGHTS & PERMISSIONSArticle Views30Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (116 KB) Get e-Alerts Get e-Alerts

Equilibrium dissolution temperature of low molecular weight polyethylene fractions in dilute solution

Equilibrium dissolution temperature of low molecular weight polyethylene fractions in dilute solution

Polymer crystallization at high supercoolings: 2. Molecular-weight dependence of lamellar thickness in isotactic polystyrene

We have examined the dependence of the lamellar thickness ( l) on the crystallization temperature ( T c) and on the molecular weight for isotactic polystyrene (i-PS) crystallized at high supercoolings. The temperature dependence is expressed by the formula l = δl + A exp(− B T c ) with A = 27 000 ( A ̊ ) and B = 3200 (K) for i-PS. The molecular-weight dependence, which is not a function of the equilibrium dissolution temperature, is reported for crystallization from dilute solution for the first time. The molecular-weight dependence of l is attributed to that of the limiting thickness δl. This result is explained by the molecular-weight dependence of the average length of loops created by folding.

Solution crystallization of polyethylene at high temperatures

Single crystals of polyethylene have been grown from solution in various solvents at temperatures between 70 and 120° C. This represents an overlap in crystallization conditions with those used for melt growth, where substantial isothermal thickening is known to occur during growth. The crystal thicknesses have been measured by Raman spectroscopy. Values of the equilibrium dissolution temperature and fold surface free energy are calculated for each solvent and the results analysed using the kinetic theory. Variations in crystal properties with time of crystallization are also investigated. A specific dependence of fold length on supercooling has been found to apply over the whole temperature range, consistent with predictions by the kinetic theories of crystallization in spite of changes in morphology which are incompatible with assumptions underlying the theoretical model. No evidence for isothermal thickening has been observed, except possibly for a small marginal effect at the highest temperature of 120° C investigated, over the same temperature range where melt crystallized material shows the effect prominently. Crystals grown at all temperatures displayed a rise in dissolution temperature with time which could be associated with an increase in surface perfection. All these findings have wider implications for our picture of polymer crystallization and crystal structure which are discussed here. A further, explicit, correlation with melt crystallization is deferred to a subsequent publication.

Isothermal growth of low molecular weight polyethylene single crystals from solution. 1. Variation of equilibrium dissolution temperature with molecular weight and lamellar thickness with crystallization temperature

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIsothermal growth of low molecular weight polyethylene single crystals from solution. 1. Variation of equilibrium dissolution temperature with molecular weight and lamellar thickness with crystallization temperatureW. M. Leung, R. St. John Manley, and A. R. PanarasCite this: Macromolecules 1985, 18, 4, 746–752Publication Date (Print):April 1, 1985Publication History Published online1 May 2002Published inissue 1 April 1985https://doi.org/10.1021/ma00146a029RIGHTS & PERMISSIONSArticle Views162Altmetric-Citations25LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (865 KB) Get e-Alerts Get e-Alerts

General crystallization behaviour of poly( l-lactic acid)

A study has been made of the general crystallization behaviour of poly( L-lactic acid), PLLA, and is intended to be the basis for further work on fibre formation processes. PLLA is shown to be a semicrystalline polymer that may crystallize from the melt and from solution, and that may form fibres. Spherulites grown from the melt were negatively birefringent and grew at a rate similar to that for polypropylene. The equilibrium melting point and the glass transition temperature were found to be about 215°C and 55°C, respectively. Solution crystallization resulted in lamellar crystals about 10 nm thick and electron diffraction revealed a hexagonal unit structure with dimensions smaller than reported earlier. The equilibrium dissolution temperature in p-xylene and the end surface free energy at the fold surface amounted to 126.5°C and about 0.075 J m −2 respectively. Fibres of PLLA were formed by precipitation in a non-solvent; some of the fibres were highly porous with a pore size in the range 0.1–0.6 μm.

Properties of solution‐grown crystals of fractions of isotactic polypropylene with different degrees of stereoregularity

AbstractSolution‐grown crystals of fractions of isotactic polypropylene (IPP) with different degrees of stereoregularity have been obtained by isothermal crystallization from α‐chloronaphthalene, using a self‐seeding technique. Electron micrographs of samples, crystallized under the same undercooling, show that, with decreasing fraction of isotactic pentads, the perfect rectangular shape of the single crystal is lost and the presence of more complex morphologies is increasingly observed. The equilibrium dissolution temperature Td of IPP fractions, from polymers prepared with a titanium based catalyst, decreases linearly with decreasing percentage of isotactic pentads. An extrapolated value of 171°C is obtained for the equilibrium dissolution temperature of a crystal of IPP with 100% isotactic pentads, i.e., an IPP crystal free of configurational defects. The melting temperature T′m and the apparent enthalpy of fusion ΔH of crystallized and annealed crystal aggregates have been determined by differential calorimetry. The equilibrium melting temperature Tm also depends greatly upon the isotactic pentad concentration. For 100% concentration the extrapolated value of Tm is 181°C. Tm decreases about 1°C per 1% decrease in the isotactic pentad population. The observed equilibrium melting and dissolution temperature depression does not follow the predictions of the Flory equation for copolymer crystallization. In fact, the effect of decreasing probability of isotactic sequence propagation is to depress Td and Tm much more rapidly. The apparent enthalpy of fusion of both solution‐grown crystals and melt‐recrystallized samples decreases with an increase in the number of configurational impurities along the chain. For the most stereoregular fraction the average length of isotactic stereoblocks has been compared with the lamellar thickness of solution‐grown lath‐shaped single crystals.

Properties of solution grown crystals of aliphatic polyesters with variable amount of double bonds along the chain

AbstractIn order to elucidate the relations between morphological habits, thermal behaviour and chemical structure of polymers, aliphatic polyesters with variable amount of trans‐double bonds along the backbone chain were crystallized from dilute solutions in 1‐propanol and 1‐butanol. The crystals were studied with electron microscopy, differential scanning calorimetry, and wide angle X‐ray diffraction. The morphology of solution grown single crystals and some thermodynamic quantities such as the equilibrium dissolution and melting temperature and the enthalpy and entropy of fusion are influenced by the percentage of unsaturated comonomer. The thermal behaviour and the X‐ray diffraction of these crystals suggest that saturated and unsaturated repeating units are able to cocrystallize.

Influence of crystallization conditions on single crystal formation

Abstract