Brill Transition Research Articles

Role of Superheated Water in the Dissolution and Perturbation of Hydrogen Bonding in the Crystalline Lattice of Polyamide 4,6

Here, we demonstrate that water, in the superheated state, is a solvent for polyamide 4,6 (PA4,6) and that the water molecules can strongly influence hydrogen bonding. In the presence of superheated water, the melting temperature of PA4,6 can be suppressed by nearly 100 degrees C. The depression in the melting temperature follows the Flory-Huggins principle. The instantaneous dissolution of the polymer hardly influences the molar mass of the polymer. However, if the polymer is retained in solution above the dissolution temperature for more than 10 min, hydrolysis occurs. These findings suggest that the dissolution of the aliphatic polymer in superheated water is mainly a physical process as opposed to a chemical process. Time resolved X-ray studies show that the dissolution occurs prior to the Brill transition temperature, as reported earlier. Crystals grown from the water solution show a lath-like morphology with interchain and intersheet distances that are similar to the distances obtained for crystals grown from other known solvents. Electron diffraction further confirmed that the crystals grown from superheated water are single crystals, where the chains are perpendicular to the ab-plane. SAXS performed on dried sedimented water grown single crystals showed a lamellar thickness of 6 nm. The lamellar thickness is in accordance with other reported studies on PA4,6, confirming that the single crystals incorporate four repeat units between re-entrant folds with an amide group incorporated in the tight fold. Solid state NMR studies performed on mats of these single crystals showed two different mobilities of the proton associated with the amide groups: a higher mobility linked to the amide protons in the fold and a reduced mobility of the hydrogen bonded amide protons within the crystal. Additionally, the solid state NMR studies on the dried water crystallized single crystals show the presence of water molecule(s) in the vicinity of the amide groups. This was confirmed by infrared studies that conclusively demonstrated the appearance of two new bands arising due to the binding of a water molecule in the vicinity of the amide group (i.e., NH3(+) and COO(-) bands that disappear upon heating at approximately 200 degrees C). Additionally, DSC traces of the water crystallized PA4,6 show an exothermic event in the same temperature region (i.e., in the vicinity of the Brill transition temperature, where the bound water exits from the lattice). Furthermore, this event was corroborated by TGA data.

Crystalline Morphology and Polymorphic Phase Transitions in Electrospun Nylon-6 Nanofibers

Uniform nylon 6 nanofibers with diameters around 200 nm were prepared by electrospinning. Polymorphic phase transitions and crystal orientation of nylon 6 in unconfined (i.e., as-electrospun) and a high T(g) (340 degrees C) polyimide confined nanofibers were studied. Similar to melt-spun nylon 6 fibers, electrospun nylon 6 nanofibers also exhibited predominant, meta-stable gamma crystalline form, and the gamma-crystal (chain) axes preferentially oriented parallel to the fiber axis. Upon annealing above 150 degrees C, gamma-form crystals gradually melted and recrystallized into the thermodynamically stable alpha-form crystals, which ultimately melted at 220 degrees C. Release of surface tension accompanied this melt-recrystallization process, as revealed by differential scanning calorimetry. For confined nanofibers, both the melt-recrystallization and surface tension release processes were substantially depressed; gamma-form crystals did not melt and recrystallize into alpha-form crystals until 210 degrees C, only 10 degrees C below the T(m) at 220 degrees C. After complete melting of nano-confined crystals at 240 degrees C and recrystallization at 100 degrees C, only alpha-form crystals oriented perpendicular to the nanofiber axis were obtained. In the polyimide-confined nanofibers, the Brill transition (from the monoclinic alpha-form to a high temperature monoclinic form) was observed at 180-190 degrees C, which was at least 20 degrees C higher than that in unconfined nylon 6 at approximately 160 degrees C. This, again, was attributed to the confinement effect.

Investigation on the Brill transition of polyamide 618

The Brill transition of even-even polyamide 618 was investigated using differential scanning calorimetry (DSC), temperature-dependent wide angle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR). The X-ray diffraction results indicate that the melt-crystallized sample of polyamide 618 transforms from the triclinic unit cell to the pseudo-hexagonal phase in the range of 120–180°C. In this range, the thermograph of polyamide 618 presents a broad endothermal peak. From the FTIR spectra, it was found that during the transition process of polyamide 618, the intensity of the intra-sheet hydrogen bonds becomes weak. At the same time, the CH2-amide bonds twist, and the all-trans conformation of methylene sequences is disordered by inserting the gauche conformation. The CH2 segments are in a mobile state because of the enhanced stretching and twisting vibrations of the C-CO and C-N bonds.

Structural Phase Transitions of Aliphatic Nylons Viewed from the Simultaneous Measurements of WAXD and SAXS

AbstractStructural changes occurring in the high temperature region of doubly‐oriented nylon 10/10 sample have been investigated through the temperature‐dependent simultaneous measurements of wide‐angle and small‐angle X‐ray scatterings, and the results were compared with the infrared spectral data as well as the molecular dynamics simulation results. In the Brill transition region of 150–180 °C the methylene segments are conformationally disordered with keeping the intermolecular hydrogen bonds. During this phase transition the stacked lamellar structure did not change very much: the lamellae are tilted by ca. 34° from the draw axis and the long period is almost 160 Å. In the temperature region immediately below the melting point the molecular chains were found to be contracted by ca. 10% the original repeating period and the intermolecular hydrogen bonds were almost broken, causing the violent rotational and translational motions of the chains around the chain axis. At the same time the long period increased remarkably from 160 Å to 410 Å and the originally tilted lamellae stood up in parallel to the draw axis.

In situ high-temperature Raman study of crystalline nylon 6,12 fibers gamma-irradiated in argon atmosphere

Samples of crystalline fibers of Nylon 6,12 gamma-irradiated under argon atmosphere were characterized by in situ high-temperature Raman spectroscopy. Identification of the most important Raman bands that characterize the nylon 6,12 is reported. In this study we show the effect of the preferred orientation of the crystals in the fiber on the Raman spectra, showing the Brill transition from triclinic to pseudo-hexagonal system. The stability of the crystalline fibers, which depends on the temperature as well as on the gamma-radiation applied, is another important result of this work.

The Brill Transition in Transcrystalline Nylon-66

The Brill transition in transcrystalline nylon-66 occurs at a temperature that is 15 K higher than in the parent spherulitic nylon-66. This difference is assigned to the high level of crystalline orientation and chain packing order in the former. The similarity of the influence of the orientated morphology on the Brill transition and on the glass transition is pointed out, suggesting that the Brill transition, which is inherently a first-order process, comprises a second-order element. Utilizing the brightness of the synchrotron microbeam WAXD to make in situ diffraction measurements during relatively rapid heating and by running two consecutive cycles at different heating rates, the activation energy for the Brill process is derived for the first time. The values of 77 and 28 kJ/mol are calculated for transcrystalline and spherulitic nylon-66, respectively.

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

AbstractSome salient results in nylon research are reviewed to identify the fundamental principles that are applicable to other strongly interacting or hydrogen‐bonded polymers, including proteins. The effects of hydrogen bonds on stress‐, heat‐, and solvent‐induced changes in macroscopic properties are discussed. These data provide a window into the chain mobility and linkages between the crystalline and amorphous domains, both of which are important for any predictive model. The changes in the characteristics of the amorphous phase with the crystallinity and orientation require that it be modeled with at least two components: a rigid/immobile/anisotropic component and a soft/mobile/isotropic component. The deformation and shrinkage behavior of these polymers are discussed in terms of the relative contributions of the amorphous and crystalline domains and of the interactions between them. The premelting crystalline transition is accompanied by the merging of intersheet and intrasheet diffraction peaks in some nylons, as observed by Brill, and not in others even though the underlying mechanism that gives rise to these transitions, the onset of volume‐increasing librational motion of the crystalline stems, is the same. Because the effects of the temperature, deformation, and solvent have a common origin associated with mobility, a fictive temperature can be associated with a given solvent activity or stress level. The magnitude of this fictive temperature is the amount by which the glass or Brill transition temperature is reduced in the presence of solvents (∼50 °C) or stress or by which the annealing temperature can be reduced in the presence of a solvent (or active stress) to achieve the same structural state as that of a dry (or static) polymer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1763–1782, 2006

Influence of Hydrogen Bonding on the Conformational Changes, the Brill Transition, and Lamellae Thickening in (Co)polyamides

Copolyamides, based on 1,12-dodecanedicarboxylic acid and different ratios of 1,2-ethylenediamine and piperazine, i.e., PA2,14-co-pip,14 as well as the homopolymers PA2,14 and PApip,14 are studied. Incorporation of the piperazine component in the homopolymer PA2,14 reduces the number of hydrogen bonds. This provides a unique opportunity to investigate the influence of hydrogen bonding on the origin of the Brill transition and chain mobility within polymer crystals. Time-resolved conformational, structural, and morphological changes during heating are followed by FTIR spectroscopy, WAXD, and SAXS. The findings are that from 0 to 62 mol % of piperazine the Brill transition occurs in the same temperature region. The transformation is triggered by the conformational changes in the methylene sequences of the main chain, followed by twisting in the methylene sequences next to the amide group. This results in enhanced chain mobility along the c-axis, causing lamellar thickening. For 80 mol % of piperazine and higher, no Brill transition is observed. However, conformational changes in the methylene sequences of the main chain occurs, triggering lamellar thickening.

繰り返し温度変化による高強力ナイロン６繊維の構造変化

Nylon 6 fibers are used as tire cord in carcass of automobile tire for rubber reinforcement to keep internal pressure. During run state, the internal part of tire is heated up to 100 °C and cooled by stopping, resulting in the same thermal history of Nylon 6 tire cord. It has been reported that crystal phase of Nylon is transformed to other phase under high temperature condition. In room temperature, two reflection peaks assigned to α-phase were observed by wide angle X-ray diffraction measurement for Nylon 6 fiber. On heating, these two peaks became one peak of pseudohexagonal phase at around 70 °C. This transition referred as the Brill transition took place repeatedly by heating and cooling. Also, tensile strength decreased with increasing temperature by heating and increased by cooling. For higher-order structure measured by small angle X-ray scattering, the long period of Nylon 6 lamella was constant on cyclic temperature changes. On the other hand, it was observed that the slope against fiber direction and the size of lamella were irreversibly changed at around 70 °C. It has been reported in former study that the Brill transition was observed at higher temperature region than 150 °C because samples were Nylon 6 pellets and films. Accordingly, the Brill transition temperature changed much lower in high oriented Nylon 6 fiber.

Crystal Transition of Nylon‐12,12 under Drawing and Annealing

AbstractSummary: Wide‐angle X‐ray diffraction (WAXD) was used to investigate the crystal transition of nylon‐12,12 under annealing and drawing. The triclinic α‐form could be obtained by crystallizing from a melted state or by annealing the γ‐form at high temperature (above 150 °C). The crystal structure of the α‐form annealed at 90 °C didn't change with time except for the perfection of crystals and an increase in the degree of crystallinity. The pseudo‐hexagonal γ‐form could be produced by crystallizing from the melted state at low temperature (90 °C) or by drawing at 90 and 160 °C. This is the first time a Brill transition has been observed under drawing conditions, instead of under the traditional conditions of continuous heating and cooling. Experimental results also confirm that drawing inducement is preferable to produce the γ‐form and plays an important role in determining the crystal structure; there is a competition between drawing inducement and thermal inducement.The WAXD patterns of the nylon‐12,12 α‐form drawn different drawing ratios at 90 °C.imageThe WAXD patterns of the nylon‐12,12 α‐form drawn different drawing ratios at 90 °C.

Preparation, characterization and crystalline transitions of odd–even polyamides 11,12 and 11,10

The novel odd–even polyamides 11,12 (P11, 12) and 11,10 (P11, 10) were synthesized via step-heating melting-polycondensation of 1,11-diaminoundecane with dodecanedioic acid and decanedioic acid, respectively. Their chemical structures were confirmed by various spectroscopic techniques (FTIR, Raman, NMR). The thermal properties of the polyamides under consideration were measured by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The crystalline transitions of the prepared polyamides were studied by wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR). The variable temperature WXRD results indicated that P11,10 undergoes the Brill transition during the heating process before melt while P11,12 does not. From the real time FTIR spectra of P11,10, it was found that the intensity of hydrogen bond becomes weak, and the twisting of the C–CO and C–N bonds becomes enhanced. The vibration of the methylene units strengthens and the trans-zigzag conformation decreases. The ordered stacking of the methylene segments becomes gradually disordered by insertion of the gauche conformation during the crystalline transition process.

Conformational disorder in the Brill transition of uniaxially-oriented nylon 10/10 sample investigated through the temperature-dependent measurement of X-ray fiber diagram

X-ray fiber diagram of uniaxially-oriented nylon 10/10 sample has been measured at the various temperatures. The 11th layer line originating from the methylene zigzag sequences became diffuse above the Brill transition region (140–170 °C), while the layer reflections corresponding mainly to the original repeating period of the parent nylon chains were kept almost unchanged. This observation makes us confirm that in the Brill transition region, the conformational disordering occurs in the methylene sequential parts with keeping the repeating period of the whole skeletal chain by still forming the intermolecular hydrogen bonds between the amide groups of the neighboring chains. This conclusion is consistent with the already-reported infrared spectral data. The characteristic X-ray diffraction patterns observed at the various temperatures were reproduced well by a computer simulation technique utilizing the previously-reported molecular dynamics calculation results.

Molecular dynamics simulation of the structural and mechanical property changes in the Brill transition of nylon 10/10 crystal

In order to confirm the structural features in the Brill transition of aliphatic nylons, molecular dynamics calculation has been performed at the various temperatures for nylon 10/10 crystal as a model. With an increase in temperature, the torsional motions around the methylene–amide and methylene–methylene bonds were activated. These motions became more remarkable above 420 K and the interconversion between trans and gauche forms occurred frequently, resulting in the disordered conformation of the methylene sequences and the pseudo-hexagonal packing of these parts. During such a drastic structural disordering, however, the hydrogen bonds were kept alive although the bond strength became weaker. These calculations were found to be consistent with the experimental results by the temperature-dependent X-ray diffraction and infrared spectral measurements. The Young's modulus along the chain axis was also calculated as a function of temperature: it decreased remarkably from 250 GPa at 0 K to 180 GPa at 300 K due to a small contraction of the skeletal chain by only about 0.2–0.5% through the torsional motion of the skeletal chains, and the modulus decreased furthermore to 80 GPa at 550 K because of the larger conformational disordering of the skeletal chains. The Young's modulus in the direction perpendicular to the chain axis was also found to decrease remarkably in parallel to the change of the chain packing mode.

Phase Transition in Even–Even Nylon Crystals

Temperature dependence of crystal structures is examined with X-ray diffraction at normal pressure or elevated pressures for solution-grown nylons with octamethylene moiety between amino or carboxy groups (nylons 82, 410, 610, 810). Although octamethylene moiety between amino groups has the potential to cause the phase transition, the low melting point veils the transition appearance. Considering this comprehensively with previous results, it is concluded for all even–even nylons, that the phase transition in the two-dimensional methylene layer system can be experimentally observed only in nylon 6Y (Y≤8) crystals at normal and/or high pressures, where the hexamethylene moiety between amino groups plays an intrinsic role. The so-called `Brill transition' widely reported for melt-crystallized nylons is not a phase transition but an abrupt thermal expansion.

A study of the crystalline transitions of polyamides X 18

The crystalline transition behavior of polyamides X 18, where X = 2, 4, 6, 8, 10 and 12, has been studied by variable-temperature wide-angle X-ray diffraction (WAXD) and real-time Fourier-transform infrared (FTIR) spectroscopy. It was found that polyamides 2 18 and 4 18 undergo the Brill transition on heating for both the melt-crystallized samples and the solution-crystallized samples. For polyamide 6 18, the melt-crystallized sample undergoes Brill transition before melting but the solution-crystallized sample melts prior to the complete crystalline transition. Polyamides 8 18, 10 18 and 12 18 do not undergo the Brill transition perfectly in advance of melting for either melt-crystallized or solution-crystallized samples. Real-time FTIR analysis of polyamides X 18 provided helpful information for understanding the mechanism of the crystalline transition. Copyright © 2004 Society of Chemical Industry

Investigation on Brill transition of nylons 6/16, 4/16 and 2/16 by variable‐temperature WAXD and FTIR

AbstractBrill transition behaviour of nylons 6/16, 4/16 and 2/16 has been studied systematically by variable‐temperature wide‐angle X‐ray diffraction (WAXD) and real‐time FTIR. It is shown that all nylons investigated undergo Brill transitions before melting on heating. Brill temperatures detected by real‐time FTIR are consistent with the results of variable‐temperature WAXD measurements. In addition, Brill bands were identified based on real‐time IR spectra and further consideration of —NH— groups provided additional information for discussing the mechanism of the crystalline transition. Copyright © 2003 Society of Chemical Industry

Multiple melting and crystallization of nylon‐66/montmorillonite nanocomposites

AbstractNylon‐66 nanocomposites were prepared by melt‐compounding nylon‐66 with organically modified montmorillonite (MMT). The organic MMT layers were exfoliated in a nylon‐66 matrix as confirmed by wide‐angle X‐ray diffraction (WAXD) and transmission electron microscopy. The presence of MMT layers increased the crystallization temperature of nylon‐66 because of the heterogeneous nucleation of MMT. Multiple melting behavior was observed in the nylon‐66/MMT nanocomposites, and the MMT layers induced the formation of form II spherulites of nylon‐66. The crystallite sizes L100 and L010 of nylon‐66, determined by WAXD, decreased with an increasing MMT content. High‐temperature WAXD was performed to determine the Brill transition in the nylon‐66/MMT nanocomposites. Polarized optical microscopy demonstrated that the dimension of nylon‐66 spherulites decreased because of the effect of the MMT layers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2861–2869, 2003

Structural Changes in Phase Transitions of Nylon Model Compounds. 1. Transition Behavior of Model Compounds of R-NHCO-R‘ Type

To clarify the essential features of Brill transition of aliphatic nylons, structural changes have been investigated by X-ray diffraction and infrared spectroscopic methods for the compounds CH3(CH2)10NHCO(CH2)9CH3 (designated as N11) and CH3(CH2)9NHCO(CH2)8CH3 (N10) which were assumed to be the simplest models of nylons 11/11 and 10/10, respectively. Depending on the preparation conditions, N11 crystallized to the α and γ forms and N10 to the α form at room temperature. Infrared and X-ray diffraction data clarified that the α form took essentially the same chain packing structure as that of the α form of parent nylons, in which the all-trans methylene segments were packed in a triclinic subcell and the amide groups were connected by intermolecular hydrogen bonds to form a sheet structure and these sheets were stacked by a weak van der Waals force. In the DSC thermograms, the α form of N10 and N11 showed two main endothermic peaks in the Brill transition (ca. 50 °C) and melting regions. The temperature re...

Polymer concepts in microscopically‐viewed phase transition behavior of crystalline polymers

AbstractStructural evolution process in crystalline phase transition, isothermal crystallization from melt and solvent‐induced crystallization has been investigated for crystalline polymers on the basis of the time and/or temperature dependence of small‐angle X‐ray scattering (SAXS), wide‐angle X‐ray scattering (WAXS) and infrared/Raman spectra. As examples of isothermal crystallization study, polyethylene and polyoxymethylene were investigated. As for polyoxymethylene, the time‐resolved infrared spectral measurement clarified the appearance of infrared bands characteristic of folded chain crystal (FCC) in the early stage of crystallization process, followed by the detection of infrared bands characteristic of extended chain crystal (ECC) in a later stage. From the time‐resolved SAXS measurement, the stacked lamellar structure of ca. 14 nm long period was detected at first and it was followed by an appearance of the new lamellae in the amorphous region sandwiched between the original lamellae, resulting in the tightly stacked lamellar structure of 7 nm long period. The timing of detecting the SAXS 14 nm peak was almost the same with the observation of infrared FCC bands and the SAXS 7 nm peak with the infrared ECC band. This correspondency allowed us to speculate that some chains bridging several lamellae became fully extended when the new lamellae were formed in the amorphous region sandwiched between the original lamellae. As a result the ECC‐like structural parts were formed, giving the ECC infrared bands. As other examples, the Brill transition of aliphatic nylons and the solvent‐induced crystallization of syndiotactic polystyrene have been reviewed.

Structural change in the Brill transition of Nylon m/n (1) Nylon 10/10 and its model compounds

Structural changes in the Brill transitions of Nylon 10/10 and its model compounds have been investigated by carrying out the temperature-dependent measurements of X-ray diffraction and infrared spectra along with the DSC measurement. The crystal structure at room temperature was found to be the so-called α form with the all-trans zigzag methylene segments. When the samples were heated, the infrared progression bands of the methylene segments, which are sensitive to the length of all-trans segmental parts, were found to change their spectral patterns in the transition temperature region: the progression bands decreased in intensity and disappeared above the transition region. At the same time several new bands were observed to appear, which were found to correspond to the progression bands of (CH2)7–(CH2)5trans-zigzag segments. These spectral changes indicate that the methylene segments were conformationally disordered by an invasion of some gauche bonds and as a result the effective length of trans-zigzag segments became shorter. This conformational disordering was found to occur more remarkably in the methylene segment of NH–(CH2)10–NH part than the CO–(CH2)8–CO part. At the same time the infrared bands of amide groups, in particular the bands sensitive to the twisting angles about the CH2–amide bonds were found to show the remarkable change, indicating the local conformational change from planar-zigzag to twisted form in the CH2–amide moiety. The frequency shift of amide A band (NH stretching mode) indicated a weakening of intermolecular hydrogen bonds, which however, did not disappear up to the melting region. From these data combined with the X-ray diffraction data, the structural disordering in the Brill transition phenomena was deduced concretely.