Structure of the n-alkane binary solid n-C19H40/n-C21H44 by infrared spectroscopy and calorimetry

Mark Maroncelli, H. L. Strauss, R. G. Snyder

Research output: Contribution to journalArticle

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Abstract

The n-alkane binary solid n-C19/n-C21 has been studied by differential scanning calorimetry (DSC) and infrared spectroscopy. Measurements on the low-temperature ordered solid (phase I) and the high-temperature disordered solid (phase II) have been made as a function of temperature and composition. From the DSC measurements, the phase diagram has been determined as well as the transition enthalpies for the phase I to phase II transition and the phase II to liquid transition. A plot of the excess enthalpy of mixing vs. composition is symmetric for both solid phases. For the 1:1 mixture, the excess enthalpies are 2.4 ± 0.2 and 1.5 ± 0.1 kcal/mol for phase I (275 K) and II (306 K), respectively. The infrared spectra of C19/C21 mixtures incorporating one n-alkane that is selectively deuterated, n-C19H38D2 (2,2) or n-C21H42D2 (2,2), have been measured, and, from these spectra, the concentrations of gauche bonds at the chain ends of both components have been determined. Phase I of the C19/C21 mixtures consists primarily of all-trans chains with some end-gauche C21. In general, the concentration of gauche bonds, which are mostly at the chain ends, is higher for the mixture than for the neat components. The concentration of end-gauche C21 is highly dependent on concentration, going to 100% at infinite C21 dilution. The concentration dependence of end-gauche C21 can be accounted for in terms of a model based on nearest-neighbor chain interaction. The conformational disorder in phase II mixtures appears to be separable into two types: (i) One type of conformational disorder is associated with the lamellar surface; this end-chain disorder arises from the chain-length mismatch between the two n-alkane components, and therefore its concentration is highly dependent on the composition of the mixture. (ii) The second type of conformational disorder is that inherent to phase II; therefore, the concentration of this type of disorder is nearly independent of composition.

Original languageEnglish (US)
Pages (from-to)5260-5267
Number of pages8
JournalJournal of Physical Chemistry
Volume89
Issue number24
DOIs
StatePublished - Jan 1 1985

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Alkanes
Calorimetry
Paraffins
alkanes
Infrared spectroscopy
heat measurement
infrared spectroscopy
disorders
Enthalpy
solid phases
Chemical analysis
enthalpy
Differential scanning calorimetry
scanning
Chain length
Temperature
Dilution
Phase diagrams
dilution
infrared spectra

All Science Journal Classification (ASJC) codes

  • Engineering(all)
  • Physical and Theoretical Chemistry

Cite this

@article{1aef2e400c5643aa87ca08ee8104a2c6,
title = "Structure of the n-alkane binary solid n-C19H40/n-C21H44 by infrared spectroscopy and calorimetry",
abstract = "The n-alkane binary solid n-C19/n-C21 has been studied by differential scanning calorimetry (DSC) and infrared spectroscopy. Measurements on the low-temperature ordered solid (phase I) and the high-temperature disordered solid (phase II) have been made as a function of temperature and composition. From the DSC measurements, the phase diagram has been determined as well as the transition enthalpies for the phase I to phase II transition and the phase II to liquid transition. A plot of the excess enthalpy of mixing vs. composition is symmetric for both solid phases. For the 1:1 mixture, the excess enthalpies are 2.4 ± 0.2 and 1.5 ± 0.1 kcal/mol for phase I (275 K) and II (306 K), respectively. The infrared spectra of C19/C21 mixtures incorporating one n-alkane that is selectively deuterated, n-C19H38D2 (2,2) or n-C21H42D2 (2,2), have been measured, and, from these spectra, the concentrations of gauche bonds at the chain ends of both components have been determined. Phase I of the C19/C21 mixtures consists primarily of all-trans chains with some end-gauche C21. In general, the concentration of gauche bonds, which are mostly at the chain ends, is higher for the mixture than for the neat components. The concentration of end-gauche C21 is highly dependent on concentration, going to 100{\%} at infinite C21 dilution. The concentration dependence of end-gauche C21 can be accounted for in terms of a model based on nearest-neighbor chain interaction. The conformational disorder in phase II mixtures appears to be separable into two types: (i) One type of conformational disorder is associated with the lamellar surface; this end-chain disorder arises from the chain-length mismatch between the two n-alkane components, and therefore its concentration is highly dependent on the composition of the mixture. (ii) The second type of conformational disorder is that inherent to phase II; therefore, the concentration of this type of disorder is nearly independent of composition.",
author = "Mark Maroncelli and Strauss, {H. L.} and Snyder, {R. G.}",
year = "1985",
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Structure of the n-alkane binary solid n-C19H40/n-C21H44 by infrared spectroscopy and calorimetry. / Maroncelli, Mark; Strauss, H. L.; Snyder, R. G.

In: Journal of Physical Chemistry, Vol. 89, No. 24, 01.01.1985, p. 5260-5267.

Research output: Contribution to journalArticle

TY - JOUR

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N2 - The n-alkane binary solid n-C19/n-C21 has been studied by differential scanning calorimetry (DSC) and infrared spectroscopy. Measurements on the low-temperature ordered solid (phase I) and the high-temperature disordered solid (phase II) have been made as a function of temperature and composition. From the DSC measurements, the phase diagram has been determined as well as the transition enthalpies for the phase I to phase II transition and the phase II to liquid transition. A plot of the excess enthalpy of mixing vs. composition is symmetric for both solid phases. For the 1:1 mixture, the excess enthalpies are 2.4 ± 0.2 and 1.5 ± 0.1 kcal/mol for phase I (275 K) and II (306 K), respectively. The infrared spectra of C19/C21 mixtures incorporating one n-alkane that is selectively deuterated, n-C19H38D2 (2,2) or n-C21H42D2 (2,2), have been measured, and, from these spectra, the concentrations of gauche bonds at the chain ends of both components have been determined. Phase I of the C19/C21 mixtures consists primarily of all-trans chains with some end-gauche C21. In general, the concentration of gauche bonds, which are mostly at the chain ends, is higher for the mixture than for the neat components. The concentration of end-gauche C21 is highly dependent on concentration, going to 100% at infinite C21 dilution. The concentration dependence of end-gauche C21 can be accounted for in terms of a model based on nearest-neighbor chain interaction. The conformational disorder in phase II mixtures appears to be separable into two types: (i) One type of conformational disorder is associated with the lamellar surface; this end-chain disorder arises from the chain-length mismatch between the two n-alkane components, and therefore its concentration is highly dependent on the composition of the mixture. (ii) The second type of conformational disorder is that inherent to phase II; therefore, the concentration of this type of disorder is nearly independent of composition.

AB - The n-alkane binary solid n-C19/n-C21 has been studied by differential scanning calorimetry (DSC) and infrared spectroscopy. Measurements on the low-temperature ordered solid (phase I) and the high-temperature disordered solid (phase II) have been made as a function of temperature and composition. From the DSC measurements, the phase diagram has been determined as well as the transition enthalpies for the phase I to phase II transition and the phase II to liquid transition. A plot of the excess enthalpy of mixing vs. composition is symmetric for both solid phases. For the 1:1 mixture, the excess enthalpies are 2.4 ± 0.2 and 1.5 ± 0.1 kcal/mol for phase I (275 K) and II (306 K), respectively. The infrared spectra of C19/C21 mixtures incorporating one n-alkane that is selectively deuterated, n-C19H38D2 (2,2) or n-C21H42D2 (2,2), have been measured, and, from these spectra, the concentrations of gauche bonds at the chain ends of both components have been determined. Phase I of the C19/C21 mixtures consists primarily of all-trans chains with some end-gauche C21. In general, the concentration of gauche bonds, which are mostly at the chain ends, is higher for the mixture than for the neat components. The concentration of end-gauche C21 is highly dependent on concentration, going to 100% at infinite C21 dilution. The concentration dependence of end-gauche C21 can be accounted for in terms of a model based on nearest-neighbor chain interaction. The conformational disorder in phase II mixtures appears to be separable into two types: (i) One type of conformational disorder is associated with the lamellar surface; this end-chain disorder arises from the chain-length mismatch between the two n-alkane components, and therefore its concentration is highly dependent on the composition of the mixture. (ii) The second type of conformational disorder is that inherent to phase II; therefore, the concentration of this type of disorder is nearly independent of composition.

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