Polyethylene Single Crystals Research Articles

Fast growth rates of polyethylene single crystals grown at high temperatures and their relevance to crystallization theories

AbstractThe rates of growth of polyethylene single crystals grown from dilute solution in hexadecane and tetradecanol have been measured over the temperature range Tc = 98–120°C by following the change in turbidity during crystallization of a suspension of crystals of known shape and final size. The rates decrease similarly with Tc in each solvent, but for a given supercooling crystals grow much faster in tetradecanol where the corresponding crystallization temperature is higher. Similarly, the rates are much higher in hexadecane than those previously reported from xylene at equivalent supercoolings but lower Tc. Changes in the corresponding crystal morphologies as Tc is raised are quantified in terms of the axial ratio and the degree of curvature of the nominally {100} faces, both of which increase with Tc. The results can be interpreted as showing a transition from regime I to regime II growth in both solvents, which agrees both qualitatively and quantitatively with the predictions of the nucleation‐based kinetic theories. Such a transition has never before been reported for solution crystallization. Using this analysis, reasonable values are obtained for the crystal side‐surface energy σ of 7.4–7.5 erg cm−2 and for the regime I substrate length L of 0.14 μm. No correlation is found between crystal morphology and growth rate and there are no discontinuous changes in morphology at the proposed transition points. The occurrence of curved crystal edges raises the fundamental issue of how to reconcile noncrystallographic growth surfaces with nucleation‐controlled growth. A new approach to polymer crystal growth based on equilibrium surface roughening, which does not require nucleation, is therefore very pertinent in this respect and this is discussed.

Lattice imaging in polyethylene single crystals

On montre que les images reticulaires de monocristaux de PE peuvent etre aussi enregistrees avec une microscopie electronique en transmission conventionnel si les conditions experimentales sont choisies avec soin

Chain conformation of polyethylene in the solid state as studied by 13C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy

High-resolution 13C nuclear magnetic resonance (n.m.r.) spectra of melt-quenched polyethylene and polyethylene single crystals are measured by the cross-polarization/magic angle spinning technique. Melt-quenched polyethylene and polyethylene single crystals have four small upfield peaks, a shoulder on the main peak and three small peaks, respectively. Based on the 13C n.m.r. resonance lines of cyclic paraffin C 64H 128 reported previously, it is concluded that the main peak and the three upfield peaks arise from the trans zigzag structure region and the folded structure region, respectively. From these peak intensities, it is estimated that the stem length of polyethylene single crystals is approximately 125 Å. Taking into account an error in the estimation of the small peak intensities, the calculated stem length of 125 Å is consistent with the crystal thickness (120–150 Å) observed directly by electron microscopy. It can be concluded, therefore, that polyethylene single crystals mainly contain sharply folded structure. Melt-quenched polyethylene may contain sharply folded structure to some extent in addition to loose loops.

Analysis of anisotrophy of small-angle neutron scattering of polyethylene single crystals. Erratum

Analysis of anisotrophy of small-angle neutron scattering of polyethylene single crystals. Erratum

Studies of low molecular weight polyethylene single crystals by differential scanning calorimetry

Fusion behaviour of solution-grown low molecular weight polyethylene single crystals was studied by differential scanning calorimetry at different heating rates. The results were correlated to the polymer chain conformation in the crystal. It was found that in the molecular weight range studied, crystals of shorter chain length and fewer foldings per chain are less stable and more susceptible to heat annealing. Melting endotherms of the crystals of the lowest molecular weight fraction grown at various temperatures indicate that during crystallization, a fractional stem at the end of a folding chain will be rejected outside the lamellae of the crystal.

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.

A Kinetic Theory on the Growth Rate of Polymer Single Crystals

The growth of polymer crystals in a dilute solution is theoretically investigated in terms of secondary nucleation and growth. Effects of the finiteness of molecular chain length and the nucleation of cilia are considered on the basis of the kinetic theory studied by Seto and Frank. The dependence of the growth rate of polyethylene single crystals on concentration and supercooling is explained as regime II growth where the growth of lower molecular weight materials ( M w <2.5×10 4 ) is controlled by the nucleation of solute molecules while that of higher ones ( M w <8×10 4 ) by the nucleation of cilia.

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

Isothermal growth of low molecular weight polyethylene single crystals from solution. 3. Kinetic studies

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIsothermal growth of low molecular weight polyethylene single crystals from solution. 3. Kinetic studiesW. M. Leung, R. St. John Manley, and A. R. PanarasCite this: Macromolecules 1985, 18, 4, 760–771Publication Date (Print):April 1, 1985Publication History Published online1 May 2002Published inissue 1 April 1985https://doi.org/10.1021/ma00146a031RIGHTS & PERMISSIONSArticle Views184Altmetric-Citations39LEARN 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 (2 MB) Get e-Alerts Get e-Alerts

Isothermal growth of low molecular weight polyethylene single crystals from solution. 2. Melting and dissolution behavior

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIsothermal growth of low molecular weight polyethylene single crystals from solution. 2. Melting and dissolution behaviorW. M. Leung, R. St. John Manley, and A. R. PanarasCite this: Macromolecules 1985, 18, 4, 753–759Publication Date (Print):April 1, 1985Publication History Published online1 May 2002Published inissue 1 April 1985https://doi.org/10.1021/ma00146a030RIGHTS & PERMISSIONSArticle Views100Altmetric-Citations18LEARN 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 (748 KB) Get e-Alerts Get e-Alerts

Thickening process of polyethylene single crystals at an early stage of annealing

Mecanisme combine de diffusion glissante de segments moleculaire et recristallisation locale a l'etat fondu

Chlorination of irradiated polyethylene single crystals: 1: Analysis of alkyl radical decay kinetics

The chlorination of electron beam-irradiated polyethylene (PE) single crystals was studied for a range of irradiation doses, temperatures and chlorine interaction times. The results of this work are presented in two parts: (1) Electron paramagnetic resonance (e.p.r.) analysis of irradiated PE without chlorination and (2) characterization of chlorine uptake in irradiated PE by use of X-ray energy of spectroscopy (XES) and electron spectroscopy for chemical analysis (e.s.c.a.). Spectra were obtained for 75 – 600 Mrad doses over 136 to 333 K temperature range. Alkyl radical concentrations and decay kinetics were derived from e.p.r. spectra and provided a basis for the chlorination analysis in Part II. A first-order alkyl radical decay constant of 4.3 × 10 −5s −1 at 298 K was determined in agreement with previous research. Alkyl radical migration was modelled as a one, two or three-dimensional unsteady-state Fickian diffusion process. E.p.r. alkyl radical concentration data was used to estimate alkyl radical diffusion coefficients yielding values of 10 to 4 × 10 −18cm 2−1 at 298 K for the three models evaluated, respectively. These values are consistent with a diffusivity estimated by Seguchi and Tamura based on a 3-D model. A three-dimensional diffusion model seems to be the most realistic since it permits a zig-zag radical trajectory due to the staggered arrangement of −CH 2- units in crystalline PE. Although a 3-D model would allow diffusion in all directions, it is still consistent with the observation that consecutive migration steps are most likely intermolecular.

A unified approach to line-shape analysis in polymer crystallography

General line shapes in the diffraction patterns of polymeric crystalline systems have been investigated on the basis of the interaction among the scattering units. A perturbation term has been incorporated into the Hamiltonian of the harmonic molecular lattice and the corresponding intensity distribution has been deduced from first principles with the assumption of elastic scattering. The various line broadenings, formerly interpreted as results of microlattice strains within a crystal or paracrystallinity, have been shown to be special cases of the general consequence of the higher-order interactions. Finally, the explicit temperature dependence of a line width was deduced and verified against experimental work on polyethylene single crystals.

Preparation and hydrogenation studies of rhodium(I) catalyst supported on polymer crystal surfaces

AbstractIn recent years polymers have been utilized as binding sites for transition metal catalysts (e.g. crosslinked polystyrene beads). However, general problems exist with the above system. The rate of reaction depends on the presence of solvents that adequately swell the polystyrene bead in order to allow access to the catalytic sites. Differences in polarity and reactant size can inhibit diffusion into the bead. Recently a new system has been developed whereby tris(triphenyl phosphine) chlororhodium (Wilkinson's catalyst) is bound to the surface of polyethylene single crystals. Polyethylene single crystals have a very high surface to volume ratios allowing for greater ease of reaction compared to the polystyrene system. Diffusion control of the reactant poses no problem as the catalyst is bound to the surface of the crystal rather than the interior (as in the case of polystyrene beads). In addition, many solvents can be used due to the difficulty of dissolving crystalline polyethylene (except at high temperatures). The polyethylene crystals were tested for their catalyst content using neutron activation analysis. Test results showed 3.11 wt% catalyst present on the surface of the PE single crystals. Hydrogenation studies have been conducted using the PE supported catalyst system to show the potential effectiveness of the new system.

EQUILIBRIUM SORPTION OF DISPERSE DYE BY ANNEALED POLYETHYLENE SINGLE CRYSTAL MATS

Polyethylene (PE) single crystals prepared from 0.01 wt% solution of PE in xylene were sedimented to form mats. These mats were annealed at various temperatures ranging from 70_??_120°C, and then were dyed at 80°C with C. I. Disperse Yellow 7 (Y-7) or p-aminoazobenzene. The equilibrium sorption (Mo), density, long period, and crystallinity (Cv) obtained for these single crystal mats increased with an increase in annealing temperature (Ta). These values increased rapidly over Ta=110°C (Cv=0.858). The change in Mo was analyzed in terms of the mosaic-block dyeing model by use of above fine structural data. It was suggested that Mo was governed by the sorption in the amorphous side region (Ms) located between crystalline cores parallel to the molecular chain axis, and the sorption in the end amorphous region (Me) located between lamellar surfaces was very small. From the view point of paracrystal model proposed by Hosemann, the amorphous side region corresponds to a grain boundary of microparacrystals. Hence, this region is rich in tie chains having trans type conformation. The difference between Ms and Me is attributable to the fraction of tie molecules on which a long rod-like molecule, Y-7, is easily absorbed; few tie molecules exist in the end region of a single crystal mat. The conformation of tie chains in side region probably becomes more extended by the thickening of lamellae during annealing. This leads to the increase in Mo with increasing Cv.

Chlorination of irradiated polyethylene single crystals: 2: XES and e.s.c.a. analysis of irradiated-chlorinated PE

Chlorination of irradiated polyethylene single crystals was characterized in this study by the X-ray energy spectroscopy and electron spectroscopy for chemical analysis techniques. Results presented show that PE chlorination was extensive, even in unirradiated PE single crystals at 298 K in the dark. The data obtained indicates that PE chlorination consists of a two-step mechanism: (1) a fast uptake with occurs in the first few minutes of chlorine exposure, constituting approximately 50% of total uptake, followed by (2) a slower, approximately first-order rate of uptake. A first-order rate constant of 5 × 10 −4s −1 was estimated for all of the irradiation doses and temperatures studied. The similarity in chlorine uptake trends for both unirradiated and irradiated samples at various temperatures suggests that the rate of Cl 2 diffusion is the rate determining step. Although the magnitude of chlorine uptake increased with increasing irradiation dose, the rate of uptake remained constant. Rapid uptake probably occured in the amorphous surface zones, followed by a slower step attributable to Cl 2 diffusion into the crystalline regions and subsequent chlorination there.

Longitudinal acoustic mode in polymers. VII. Surface structure from swelling studies of freeze‐dried polyethylene single crystals

AbstractRaman longitudinal acoustic mode (LAM) spectra have been obtained from freeze‐dried polyethylene single‐crystal samples swollen in decalin. The changes in ν(LAM) have been studied as a function of molecular weight, temperature of crystallization, and temperature of measurement. These data, together with knowledge of how terminal “defects” influence ν(LAM) of the trans stems, lead to the conclusion that surface folds and cilia are the components responding to the swelling agent. The analysis also shows what the relative effects of these structures are as a function of molecular weight and crystallization temperature. This study indicates that cilia are primarily responsible for the large increases in x‐ray long period observed for swollen single‐crystal mats.

Characterization of striations in polyethylene single crystals

New observations of polyethylene single crystals by electron microscopy are reported. Systematic studies of the contrast of striations and bend contours in bright and dark fields have been carried out. It is confirmed that bend contours are related to corrugations of the crystal. When rolled, these corrugations are changed into pleats. The quantity of extramaterial out of the substrate plane has been evaluated with the aid of the dynamical theory of contrast. Striations appear in the flat area and are proved to be due to local rotation and shearing of crystallographic planes. The change of contrast due to radiation damage is depicted and assigned to cross-linking in preferential planes which glide. The previous model of Bassett et al. of an initially non-flat-based pyramid-shaped crystal that coalesces to form corrugations is appropriate but the crystal lographic characteristics must be changed to fit our observations and we propose another structure.

Growth Rate of Polyethylene Single Crystals at High Pressure

The growth kinetics of extended-chain single crystals (ECSC) of polyethylene are studied. The results of an expertment on the growth rate and the structure of the high-pressure form suggest that the segments in the crystal slide along their own axes very easily and that the ends of the segments form uneven contour surfaces so as to minimize the boundary free energy. On such a secondary nucleus model, we assume that the elementary step of the growth is the “creeping in” of a repeating unit linked directly to a crystalline segment through the boundary surface of the nucleus. We have the normal growth rate V∝=Texp (-G*/3 kT), where ΔT is the degree of supercooling and G* is the least free energy of formation of a critical nucleus. By fitting this relation with the experimental one, we obtain G*=134/ΔT (kJ/mol) at 300 MPa, a value 1/14 of that at 0.1 MPa.

Thickening process of polyethylene single crystals at an early stage of annealing

By the use of a position sensitive proportional counter, changes in small and wide angle X-ray scattering during annealing of polyethylene single crystal mats were measured from the start in successive spans of very short measuring time. At high temperatures, the long period relating to stacking of lamellae rapidly increased at an early stage, passed through a plateau, and thereafter again increased gradually. With a decrease in annealing temperature, the amount of its first rapid increase was reduced and the plateau changed into an ascending slope. At much lower annealing temperatures, the long period increased following the logt law after an induction time. The integral breadth of a peak corresponding to the long period first increased rapidly, simultaneously with the rapid increase in the long period, and thereafter decreased. Wide angle X-ray measurement showed that the integrated intensity of 110 reflection first decreased and then increased during annealing at high temperatures. This fall and rise process was more marked, when the annealing temperature is higher and the initial thickness of lamellae is smaller. From these observations, it was inferred that in the thickening process, stacking order of lamellae at first decreased because of rapid reorganization due to partial melting or melt-recrystallization and subsequently increased through increasing evenness of lamellar thickness.