Anisotropic swelling of doubly oriented nylon-11 with a lamellar structure

Rolled smaples of nylon-11 annealed in formic acid (90%) at 80°C remain doubly oriented and have the same allotropic form as filter mats of single crystals. the basal planes of the crystals are parallel to (00l) planes. the long spacing is larger than in filter mats. Experimental swelling results obtained on such samples are discussed on the basis of two extreme models, the lamellar and the switchboard models. The long spacing d_y and the length of the sample (along 0Y) change reversibly by the same proportion during swelling. Insertion of solvent between lamellae is invoked to explain such changes of dimension. As linear swelling ratios computed from macroscopic dimensions and SAXS measurements can reach 100%, lamellar crystals are only bonded by a few chains. The large increase of the SAXS intensity observed when annealed doubly oriented samples of nylon-11 are wetted with allylic alcohol cannot be explained on the basis of the switchboard model but only with a three-phase lamellar model. These three phases are the crystalline phase, the fold region, and a dilute solution of polymer in the swelling agent.     

Ferroelectric polarization switching in nylon-11

Cold-drawn Nylon-11 films, which were prepared by stretching the melt-quenched films to a draw ratio of 2.8: 1 at room temperature, were found to exhibit an electric displacement versus electric field hysteresis loop. The results confirmed that the Nylon-11 film exhibited ferroelectric behavior at or below room temperature. The coercive fields were 65, 98, 125, 160, and 215 MV/m at 20, 0, ?20, ?40, and ?60°C and the remanent polarization at ?20°C (where there was considerably less dc conduction) was 56 mC/m². Switching of the polarization was almost completed within 20 ms.     

On the thickening of lamellar crystals during isothermal crystallization

Summary Two theories on the mechanism of the thickening of chain-folding lamellae occurring during isothermal crystallization are conflicting. One attributes the thickening to an annealing process by which isothermal crystallization should be accompanied. An alternative explanation proposed by the author in the preceding paper, was that the effect should be due to molecular fractionation during crystallization. In order to clarify which of the two conflicting theories is preferable, x-ray long spacings were measured for carefully fractionated polyethylene samples crystallized isothermally and quenched after varying time intervals. In contrast with the previous observation made by Hoffman and Weeks at the crystallization temperature, much less thickening was observed for these samples as compared with the unfractionated polymer (Marlex-50). The effect of crystallization temperature on the thickening behaviour was also examined. Again in favour of the fractionation theory the total amount of the thickening observed decreased remarkably with the decreasing temperature. Further, according to the above two theories the distribution of the fold lengths in the crystals formed was calculated as a function of time for the crystallization of the Marlex-50 polymer. Comparing the results of the calculations with experimental data obtained so far, it has been pointed out that the experimental results afford an evidence in favour of the fractionation theory. A possible effect of an amorphous surface layer on the individual lamella on the observed long spacing increase is also discussed briefly.

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Zusammenfassung Zwei Theorien über den Mechanismus der Dickenzunahme von Faltungslamellen w?hrend der isothermen Kristallisation stehen miteinander in Widerspruch. Die eine schreibt das Dicken-Wachstum dem Temperungsproze? zu, durch den die isotherme Kristallisation begleitet sein sollte. Die andere Erkl?rung, die von den Autoren dieser vorliegenden Arbeit vorgeschlagen wurde, war die, da? Effekte einer molekularen Fraktionierung durch die Kristallisation hinzukommen. Um den Widerspruch zwischen den beiden Theorien zu erkl?ren und zu sehen, welche davon vorzuziehen ist, wurden Weitwinkel-Interferenzen für sorgf?ltig fraktionierte Poly?thylenproben gemessen, die isotherm kristallisiert und nach verschiedenen Zeiten abgeschreckt wurden. Im Gegensatz zu den vorangehenden Beobachtungen durch Hoffman und Weeks bei der Kristallisationstemperatur wurde ein viel geringeres Dicken-Wachstum für diese Proben beobachtet, verglichen mit dem unfraktionierter Proben (Marlex-50). Der Effekt der Kristallisationstemperatur auf das Dicken-Wachstumsverhalten wurde ebenfalls geprüft. Wieder nahm zugunsten der Fraktionierungstheorie der Totalbetrag des beobachteten Dicken-Wachstums betr?chtlich mit abnehmender Temperatur ab. Weiterhin wurde entsprechend den zwei oben angeführten Theorien die Verteilung der Faltungsl?ngen in den gebildeten Kristallen als Funktion der Zeit für die Kristallisation von Marlex-50-Polymeren berechnet. Vergleiche der Ergebnisse der Berechnungen mit den bisher erhaltenen experimentellen Daten zeigen, da? die experimentellen Ergebnisse eine Deutung mit Hilfe der Fraktionierungstheorie begünstigen. Ein m?glicher Effekt einer amorphen Oberfl?chenschicht auf den individuellen Lamellen in dem beobachteten Langperioden-Zuwachs wird ebenfalls kurz diskutiert.

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The major part of this work was done during the author's stay in H. H. Wills Physics Laboratory, University of Bristol, England, and was read at the Annual Meeting of High Polymer Soc. Japan. May, 1965, Tokyo.

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Thanks are due to Dr. A. Keller, University of Bristol, for numerous helpful discussions.     

Morphology of polypropylene crystals. II. Twinning of lamellar crystals

Twinned crystals were obtained from fractionated isotactic polypropylene of M?_w = 600,000 by isothermal crystallization at 130°C. for 20 hr. from dilute α-chloronaphthalene solution (0.005 wt.-%). Electron microscopic observations confirm that the molecular chains of polypropylene lamellar crystals extend along the [100] direction while the folding itself occurs within the (010) planes in the monoclinic crystal form. On this basis it is shown that polypropylene forms twinned crystals in which the composition plane is the (1k0) planes. It can be deduced that the formation of twin nucleus occurs before twinning, and then growth occurs from the neighboring region of the crystal boundary by chain folding along the [100] direction.     

Morphology of polypropylene crystals. I. Dilute solution-grown lamellar crystals

The dependence of crystalline morphology of isotactic polypropylene crystallized from dilute solutions on its molecular weight and growing conditions and the mechanism of crystal growth were studied by electron microscopy and electron diffraction. Lathshaped lamellar crystals 150–300 A. in thickness are obtained from fractionated polypropylene powders of M _w (average molecular weight) = 600,000 and 240,000, but not from the samples of M _w = 82,000 and 44,000, by means of isothermal crystallization at 130°C. for 20 hr. in dilute α-chloronaphthalene solution (0.005 wt.-%). Precipitation of the fractionated polypropylene sample of M _w = 82,000 from a dilute solution of carbitol gives typical dendritic crystals under the same isothermal crystallizing conditions as mentioned above. The mode of chain folding in these crystals based on the orientation and the crystal structure of the lamellar crystals agrees with that proposed by Sauer, Morrow, and Richardson. From the morphological observations, the mechanism of growth pertinent to polypropylene lamellar crystals is presumed to be as follows: fibrils at first aggregate, then the molecular chains are folded to form small lamellae, and then these small lamellae accumulate compactly to grow to large, lath-shaped, lamellar crystals.     

Synthesis and characterization of single-layer silver-decanethiolate lamellar crystals

We report the synthesis of silver-decanethiolate (AgSC10) lamellar crystals. Nanometer-sized Ag clusters grown on inert substrates react with decanethiol vapor to form multilayer AgSC10 lamellar crystals with both layer-by-layer and in-plane ordering. The crystals have strong (010) texture with the layers parallel to the substrates. The synthesis method allows for a precise control of the number of layers. The thickness of the lamellae can be manipulated and systematically reduced to a single layer by decreasing the amount of Ag and lowering the annealing temperature. The single-layer AgSC10 lamellae are two-dimensional crystals and have uniform thickness and in-plane ordering. These samples were characterized with nanocalorimetry, atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray reflectivity (XRR), Fourier transform infrared spectroscopy (FTIR), and Rutherford backscattering spectroscopy (RBS).     

Proton nuclear magnetic resonance lineshapes in lamellar liquid crystals

The nuclear magnetic resonance lineshape of the protons in the amphiphile alkyl chains in lamellar liquid crystals is calculated. It is found that the inclusion of intra molecular dipolar interactions not averaged to zero explains the shape of the experimentally observed spectrum.     

Phenomenological theory of the nematic to lamellar phase transition in lyotropic liquid crystals

A phenomenological theory is presented to describe the nematic to lamellar phase transition in lyotropic liquid crystals. The problem of the first or second order transition is explored by means of the variation of the surfactant concentration. The possibility of the tricritical point at the nematic to lamellar phase transition is discussed in a phenomenological way. The influence of the electrolyte on this transition is also discussed by varying the coupling between the electrolyte concentration variables and the order parameters. The theoretical prediction is found to be in good qualitative agreement with experimental results.     

Orientation of anthracene molecules in naphthalene single crystals

The orientation of anthracene in naphthalene matrix has been determined by EPR of the triplet state of the guest molecule. It differs from the host molecule orientation mainly by a rotation of 25° about the z axis.     

Orientation of guest molecules in doped organic crystals

The orientation of guest molecules in the doped systems, naphthalene-in-anthracene, anthracene-in-naphthalene and tetracene-in-anthracene has been obtained by the use of atom-atom (6-1-exp) potentials. The results indicate that the guest molecules assume nearly the same orientation as the replaced host with only small perturbation on the host lattice. The results are in good agreement with recent ESR studies.     

Structure analysis of chain-folded lamellar polyamide crystals from X-ray diffraction

Folded-chain crystals of certain polyamides present some novel diffraction effects due to the small number of repeat units within the lamellar thickness. X-ray diffraction evidence is available in the complete range from low to wide angles. This information is interpreted in terms of the structure factor of an individual lamella together with the lattice factor appropriate for the stacking of lamellae. When due account is taken of the lattice factor, whose effect can be detected even at large angles, three features of the lamellar structure can be deduced. First, the evidence is in favor of the straight-chain stems traversing almost the total thickness of each lamella, implying sharp folds at the lamellar surfaces. Some consequences of this result on the interpretation of data obtained from annealed mats are mentioned. Second, the detailed determination of the stem structure demands that the majority of the folds in nylon 66 lie in the acid group. Third, there are regions of depleted electron density at the lamellar surfaces, though features of the crystal structure are still retained. This indicates the presence of some folds deeper in the crystal than the majority.     

Enzymatic degradation of poly(octamethylene suberate) lamellar crystals

Enzymatic degradation of poly(octamethylene suberate) single crystals was investigated by electron microscopy. Different lamellar morphologies were obtained using 2.5-hexanediol as a solvent and at a temperature between 42 and 51 °C. Crystals with a different degree of truncation and with monolayer or bilayer organization were analyzed. Lipases from Rhizopus oryzae were found to be highly effective in degrading crystalline domains and showed different attack mechanisms. Thus, enzymes preferentially attacked the lateral crystal growth faces or the lamellar fold surfaces depending on the crystallization conditions. Temperature and indeed its fluctuation during the crystallization process were crucial to determine how degradation started and progressed. The most interesting results were obtained for single crystals characterized by a low degree of truncation and formed in crystallization baths with a small temperature oscillation. In this case, it was shown that degradation started on the folding surface of specific sectors and progressed along a preferred crystal direction.     

Azeotropic-like (congruent melting) phenomena of lamellar liquid crystals

The binary system of water and didecyldimethylammonium bromide (DDeAB), having a double hydrocarbon chain, was found to exhibit exhibit an azeotropic-like phase transition from lamellar liquid crystal to micellar solution. That is, the maximum limiting value of temperatures where the present system is allowed to exist in a lamellar liquid crystal corresponds to the socalled azeotropic point (AZP) or congruent melting point. At this temperature, the compositions of the liquid crystal and micellar solution phases become identical. Upon addition of a small amount of NaBr, the AZP shifts to a high temperature, but the point disappears above 0.375 wt% NaBr in water. The AZP is also increased by adding cholesterol. On the other hand, the transition enthalpies at AZPs are extremely small and almost constant, even if NaBr and cholesterol are added. The sharp DSC peak is observed in the presence of salt, whereas it is broad in the presence of cholesterol. It is considered that salt induces a closely packed state of the liquid crystal phase. Although cholesterol also has an ordering effect on the surfactant aggregates its hydrophobic property increases the phase transition temperature. The phase transition occurs due to a packing change of the hydrocarbon chains of DDeAB molecule from the lamellar to micellar states. The correlation between the movement of AZP and the phase behavior in the presence of salt is also discussed.     

Thickening of crystals during rapid heating. I. Linear polyethylene and nylon-6

The change of long spacing in polyethylene and nylon-6 during heating at 18°C/min. was measured with an apparatus devised for rapid measurement of the small-angle x-ray diffraction. The apparatus made it possible to obtain a diffraction profile in 1.8 sec. Long spacings increased notably at high temperatures near the melting point, as has been observed during low-rate heating. However, the increase in long spacing during heating was very small in a methoxymethylated nylon-6 sample. This suggests that the increase in the long spacing at high temperature is due to the thickening of crystals. The long spacing in polyethylene samples in the vicinity of the melting point is apparently independent of thermal history.     

Study on the formation and rheological properties of sucrose stearate lamellar liquid crystals

The phase diagrams of S1570–Brij 97/oleic acid/water system at two different S1570/Brij 97 mass ratios of 1/1 (system S) and 7/3 (system P) were determined at 37°C, respectively. The microstructures and rheological properties of liquid crystals at constant surfactants/water mass ratio of 1/1 were studied with increase in oil content. Small-angle x-ray scattering measurements showed that system S exhibited a typical lamellar liquid crystals and the repeat distance (d) decreased as oil content increased. While for system P, two couples of scattering peaks were observed when oil content reached 28 wt%. This indicated that adding oil content may give rise to a multilamellar structures in the higher S1570/Brij 97 mass ratio system. The rheological tests indicated that a transition from elastic gel-like properties to viscoelastic liquid-like properties appeared in both system S and P when oil content reached 20 wt%, corresponding to the polarizing optical microscopy textures changing from oily streak to cruciate flower. This supplies a way to adjust structure, rheological properties, and even phase transition by altering the S1570/Brij 97 mass ratio and oleic acid content in system.     

Diffusion-controlled growth of lamellar crystals in an isotactic polystyrene–polyphenylene oxide blend

The growth rates of lamellar crystals grown onto preseeded fibrillar crystals (“shishes”) in isotactic polystyrene and blends of isotactic polystyrene (iPS) with polyphenylene oxide are followed by using transmission electron microscopy. The preseeded fibrillar crystals avoid the problem of timedependent primary nucleation. The time dependence of lamellar growth is investigated. At a concentration of 50% PPO in iPS, the lateral lamellar growth rate of the precipitating isotactic polystyrene crystals conforms to a time law characteristic of diffusion-controlled growth (R ∝ t^1/2). Diffusion coefficients are estimated from the growth kinetics. The method could prove a simple means of measuring diffusion coefficients in polymer blends in which one component is crystallizable.     

Polymorphism of nylon-6 in nylon-6/nanoclay/functionalized polyolefin blends

The crystallization behavior of Nylon-6 and the interaction in Nylon-6/nanoclay/functionalized polyolefin blends were investigated by X-ray diffraction and Fourier transform infrared spectroscopy. For samples without any thermal history, the interaction between Nylon-6 and nanoclay or the interaction between Nylon-6 and functionalized polyolefin favors the formation of γ form crystal. In contrast, the presence of both nanoclay and functionalized polyolefin together in Nylon-6 was found to have an antagonistic effect on each other's ability to promote the formation of γ form crystal. This was attributed to the complex interactions between the constituents. The crystallization behavior of Nylon-6 in Nylon-6/nanoclay/functionalized polyolefin blends is clearly affected by the cointeraction of these effects. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1494–1502, 2007     

Supercooled dynamics of grain boundary particles in two-dimensional colloidal crystals

We experimentally investigate the dynamics of particles constituting grain boundaries in a two-dimensional colloidal crystal, using video-microscopy. A clear plateau in the mean square displacement of the grain boundary particles is found, followed by an upswing indicative of cage breaking. The van Hove correlation functions and the non-Gaussian parameter show that grain boundary particle dynamics are highly heterogeneous. Furthermore, we identified clusters of cooperatively moving particles and analyzed the time-dependence of the weight-averaged mean cluster size. We find good correlation between the behavior of the mean square displacement, and the time dependence of the non-Gaussian parameter and the cluster size, as also reported for various supercooled systems. Our results therefore provide experimental support for the similarity between particle dynamics in grain boundaries and in supercooled liquids as suggested by recent computer simulations.