Transport of matter upon annealing in crystalline polymethylene systems: a calorimetric and spectroscopic study

Zerbi, G.; Piazza, Roberto; Holland-Moritz, K.

doi:10.1016/0032-3861(82)90219-1

Cited by 40 publications

(18 citation statements)

References 25 publications

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“…Moreover, considerable molecular dynamics and, at the same time, a low amount of intrachain disorder (i.e., gauche conformations) have been attributed to bulk alkanes [17], as well as to Langmuir-Blodgett films of fatty acid salts [18], below their melting point. Finally, a substantial mass transport in mixed alkane crystals [19,20], as well as in polyethylene [21], has been attributed to a considerable longitudinal mobility along the extended polymethylene chains.…”

Section: Lmmentioning

confidence: 99%

Anisotropic molecular dynamics in the vicinity of order-disorder transitions in organic monolayers

1992

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Variable-temperature scanning tunneling microscopy has been used to observe molecular dynamics in the vicinity of order-disorder transitions in alkane monolayers at the interface between graphite and organic fluids. In crystalline lamellae adsorbed from solution a reversible increase in longitudinal molecular motion with increasing temperature is observed, until the amplitude becomes comparable to the lamella width and the order disappears. A two-dimensional smectic and a columnar phase are observed at the interface with a neat melt and a solution of a particularly long-chain alkane, respectively. PACS numbers: 68.55Jk, 61.16.Di, 81.15.Lm Order-disorder transitions at interfaces, like melting, roughening, and shape fluctuations, occur in various different condensed-matter systems, including metals, semiconductors, polymers, colloids, or biological membranes. Statistical mechanical models and scaling theories have been employed to investigate the underlying theoretical physics (see, e.g., [1,2]). Scattering techniques like ion scattering [3] and low-energy electron diffraction [4] allowed observation of surface premelting, holographic interferograms have been used to follow roughening transitions at the 4 He solid-superfluid interface [5], and optical microscopy was employed to study shape fluctuations in lipid vesicles as a function of temperature [6]. Scanning tunneling microscopy (STM) has been used before to investigate crystalline monomolecular layers adsorbed from liquid-crystalline ambients [7] or the frozen-in roughness of steps on a vicinal silicon surface [8]. However, for a molecular system a microscopical observation of orderdisorder transitions directly on the molecular level has not yet been reported.Monomolecular layers of long-chain w-alkanes, adsorbed at the interface between organic solutions or melts and the basal plane of graphite, are a simple model system for physisorbed organic monolayers. Their adsorption isotherms have been measured [9], and the molecular structure [10-12] and dynamics [13] of crystalline monolayers adsorbed from solution have been investigated recently by STM, indicating that long-chain alkanes may adsorb as epitaxial monolayers at room temperature. In the following we describe order-disorder transitions with increasing temperature and molecular weight and attribute them to anisotropic molecular dynamics within the monolayer.The STM was homebuilt [14]. It allows scan rates up to 1 ms per line, corresponding to an image recording rate of up to 10 frames (100x100 points each) per second. Real-time video recordings can be used to directly observe sufficiently slow molecular dynamics, like molecular reorientations associated with annealing processes [11,15]. They also offer a convenient way to identify thermal drifts. For variable-temperature STM studies between room temperature and 120°C the sample was mounted on a Peltier element, which was heated by a constant current. The sample temperature was measured with a thermoresistor attached with silver paint to the side of th...

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Section: Lmmentioning

confidence: 99%

Anisotropic molecular dynamics in the vicinity of order-disorder transitions in organic monolayers

1992

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“…In time, some sort of molecular diffusion occurs between the mechanically overlapping crystals to form the mixed chain lamellar solid. 21,22 It was postulated that this diffusion might be a longitudinal "flip-flop" process.21 Fractionation has been observed when the chain length difference becomes too large and the presumed diffusion was thought to be a reversal of the solubilization mechanism observed before.23…”

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confidence: 99%

Chain length and the cosolubility of n-paraffins in the solid state

Dorset¹

1990

Macromolecules

122

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found in earlier analyses, solid solutions are formed. As indicated by theoretical calculations of the melting point line, they are nearly ideal in their behavior. Outside of this chain length difference eutectics are formed, with liquidus curves also corresponding closely to the freezing point depression of an ideal liquid solution. Depending on chain length difference, the eutectic solid will be composed of an incommensurate layer structure (crystallized from a metastable solid solution) coexisting with the longer chain component. If no cosolubility is possible, a mixture of the two pure components separates. A boundary domain also exists before strict eutectic separation when a critical temperature is reached. Here, at the miscibility gap, metastable solid solutions fractionate, with a structure very similar to that of a secondary eutectic solid for binary combinations where limited solid solubility still exists. However, the incommensurate solid changes continuously with concentration unlike the mixed lamellar stacking in the eutectic, which has a constant composition. It is therefore possible to describe a progression of crystalline arrays between the stable solid solution and fully separated eutectic.

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“…The rototranslational motion in the direction of long axis is invoked also in several experimental observations [1,[15][16][17][18]. It appears to be the prime source of long-range migration of alkane chains observed between crystallites [15,16]. Interlamellar surface in the rotator phase was found to be considerably perturbed and it is estimated that up to 15 % of chains slipped out from crystallamella [16].…”

Section: Discussionmentioning

confidence: 90%

“…It appears to be the prime source of long-range migration of alkane chains observed between crystallites [15,16]. Interlamellar surface in the rotator phase was found to be considerably perturbed and it is estimated that up to 15 % of chains slipped out from crystallamella [16]. A diffusive process with independent rotational and longitudinal components as a mechanism for chain motion in the rotator phase was inferred from quasidastic neutron scattering [1].…”

Section: Discussionmentioning

confidence: 97%

Energetics of rotation and translation in hexagonal aggregates of extended chains

Bleha

Gajdoš

1987

Colloid & Polymer Sci

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Potential energy calculations have been made for hexane aggregates m the hexagonal arrangement as models of paraffin-like solids. As a part of the general energy hypersurface the feasibility of translation and rotation of extended chains in aggregate has been examined for various degrees of packing. The pure translation is favoured over the pure rotation at all interchain separations. The energy map of coupled rotation-translation motion has been developed for the intermediate degree of packing. The energy minima on the map correspond to the parallel orientation of chain backbones and are presumed to represent the prevailing short-range structure of the rotator phase in n-alkane crystals. The calculated barriers are used for the rationalization of chain dynamics in the rotator phase, and in the disorded phases with the similar alkyl chain packing as found in crystals, monolayers and bilayers of amphiphiles. Probability of formations of the translational, rotational and conformational defects in the above systems is discussed.

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Transport of matter upon annealing in crystalline polymethylene systems: a calorimetric and spectroscopic study

Cited by 40 publications

References 25 publications

Anisotropic molecular dynamics in the vicinity of order-disorder transitions in organic monolayers

Anisotropic molecular dynamics in the vicinity of order-disorder transitions in organic monolayers

Chain length and the cosolubility of n-paraffins in the solid state

Energetics of rotation and translation in hexagonal aggregates of extended chains

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