Adsorbed film of n-tetradecylphosphocholine at the tetradecane/water interface studied by interfacial tensiometry and X-ray reflection

S. Hiraki, T. Goto, H. Tanida, K. Nitta, T. Ina, T. Uruga, Hiroki Matsubara, Makoto Aratono, Takanori Takiue

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Abstract

The adsorbed film of n-tetradecylphosphocholine (C14PC) at the tetradecane (C14)/aqueous solution (W) interface was studied by interfacial tensiometry and X-ray reflection (XR). The interfacial tension γ was measured as a function of molality mC14PC and temperature T under atmospheric pressure. The interfacial density of C14PC ΓC14PCH increases with increasing mC14PC and converges into 3μmolm-2 (first saturation) at mC14PC≈0.08mmolkg-1 and into 4.2μmolm-2 (second saturation) at the critical micelle concentration (CMC). The electron density profile determined by XR indicated that C14PC molecules form monolayer with relatively loose packing at the first saturation. In the second saturation, on the other hand, the molecules form bilayer in which charge separated phosphocholine groups take upside-down arrangement to interact attractively between neighbors. The positive entropy changes associated with adsorption both from monomeric and from micellar states result from that the contribution of dehydration around C14PC molecules, especially around PC groups, by the adsorption from aqueous solution overcomes that of a comparatively ordered molecular orientation at the interface. By comparing the results at the C14/W interface with those at the Air (A)/W one, it was shown that in the monolayer and bilayer states, hydrophobic chains of C14PC molecules are more ordered at the C14/W than at the A/W interface because of attractive interaction between C14PC and C14 molecules. This leads to smaller value of the partial molar entropy and energy changes associated with the adsorption at the C14/W than at the A/W interface. Furthermore the entropy of micelle formation changes from positive to negative with increasing T, suggesting that the entropy gain due to the dehydration exceeds the entropy loss by the aggregation at low temperatures, while the gain is less than the loss at high temperature.

Original languageEnglish
Pages (from-to)454-463
Number of pages10
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume482
DOIs
Publication statusPublished - Oct 5 2015

Fingerprint

Entropy
entropy
X rays
Molecules
Water
saturation
water
molecules
x rays
Dehydration
Adsorption
dehydration
adsorption
Monolayers
micelles
aqueous solutions
Phosphorylcholine
electron density profiles
Molecular orientation
Critical micelle concentration

All Science Journal Classification (ASJC) codes

  • Surfaces and Interfaces
  • Physical and Theoretical Chemistry
  • Colloid and Surface Chemistry

Cite this

@article{190e29d2e9cf44078c9d6229b04d9044,
title = "Adsorbed film of n-tetradecylphosphocholine at the tetradecane/water interface studied by interfacial tensiometry and X-ray reflection",
abstract = "The adsorbed film of n-tetradecylphosphocholine (C14PC) at the tetradecane (C14)/aqueous solution (W) interface was studied by interfacial tensiometry and X-ray reflection (XR). The interfacial tension γ was measured as a function of molality mC14PC and temperature T under atmospheric pressure. The interfacial density of C14PC ΓC14PCH increases with increasing mC14PC and converges into 3μmolm-2 (first saturation) at mC14PC≈0.08mmolkg-1 and into 4.2μmolm-2 (second saturation) at the critical micelle concentration (CMC). The electron density profile determined by XR indicated that C14PC molecules form monolayer with relatively loose packing at the first saturation. In the second saturation, on the other hand, the molecules form bilayer in which charge separated phosphocholine groups take upside-down arrangement to interact attractively between neighbors. The positive entropy changes associated with adsorption both from monomeric and from micellar states result from that the contribution of dehydration around C14PC molecules, especially around PC groups, by the adsorption from aqueous solution overcomes that of a comparatively ordered molecular orientation at the interface. By comparing the results at the C14/W interface with those at the Air (A)/W one, it was shown that in the monolayer and bilayer states, hydrophobic chains of C14PC molecules are more ordered at the C14/W than at the A/W interface because of attractive interaction between C14PC and C14 molecules. This leads to smaller value of the partial molar entropy and energy changes associated with the adsorption at the C14/W than at the A/W interface. Furthermore the entropy of micelle formation changes from positive to negative with increasing T, suggesting that the entropy gain due to the dehydration exceeds the entropy loss by the aggregation at low temperatures, while the gain is less than the loss at high temperature.",
author = "S. Hiraki and T. Goto and H. Tanida and K. Nitta and T. Ina and T. Uruga and Hiroki Matsubara and Makoto Aratono and Takanori Takiue",
year = "2015",
month = "10",
day = "5",
doi = "10.1016/j.colsurfa.2015.06.033",
language = "English",
volume = "482",
pages = "454--463",
journal = "Colloids and Surfaces A: Physicochemical and Engineering Aspects",
issn = "0927-7757",
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TY - JOUR

T1 - Adsorbed film of n-tetradecylphosphocholine at the tetradecane/water interface studied by interfacial tensiometry and X-ray reflection

AU - Hiraki, S.

AU - Goto, T.

AU - Tanida, H.

AU - Nitta, K.

AU - Ina, T.

AU - Uruga, T.

AU - Matsubara, Hiroki

AU - Aratono, Makoto

AU - Takiue, Takanori

PY - 2015/10/5

Y1 - 2015/10/5

N2 - The adsorbed film of n-tetradecylphosphocholine (C14PC) at the tetradecane (C14)/aqueous solution (W) interface was studied by interfacial tensiometry and X-ray reflection (XR). The interfacial tension γ was measured as a function of molality mC14PC and temperature T under atmospheric pressure. The interfacial density of C14PC ΓC14PCH increases with increasing mC14PC and converges into 3μmolm-2 (first saturation) at mC14PC≈0.08mmolkg-1 and into 4.2μmolm-2 (second saturation) at the critical micelle concentration (CMC). The electron density profile determined by XR indicated that C14PC molecules form monolayer with relatively loose packing at the first saturation. In the second saturation, on the other hand, the molecules form bilayer in which charge separated phosphocholine groups take upside-down arrangement to interact attractively between neighbors. The positive entropy changes associated with adsorption both from monomeric and from micellar states result from that the contribution of dehydration around C14PC molecules, especially around PC groups, by the adsorption from aqueous solution overcomes that of a comparatively ordered molecular orientation at the interface. By comparing the results at the C14/W interface with those at the Air (A)/W one, it was shown that in the monolayer and bilayer states, hydrophobic chains of C14PC molecules are more ordered at the C14/W than at the A/W interface because of attractive interaction between C14PC and C14 molecules. This leads to smaller value of the partial molar entropy and energy changes associated with the adsorption at the C14/W than at the A/W interface. Furthermore the entropy of micelle formation changes from positive to negative with increasing T, suggesting that the entropy gain due to the dehydration exceeds the entropy loss by the aggregation at low temperatures, while the gain is less than the loss at high temperature.

AB - The adsorbed film of n-tetradecylphosphocholine (C14PC) at the tetradecane (C14)/aqueous solution (W) interface was studied by interfacial tensiometry and X-ray reflection (XR). The interfacial tension γ was measured as a function of molality mC14PC and temperature T under atmospheric pressure. The interfacial density of C14PC ΓC14PCH increases with increasing mC14PC and converges into 3μmolm-2 (first saturation) at mC14PC≈0.08mmolkg-1 and into 4.2μmolm-2 (second saturation) at the critical micelle concentration (CMC). The electron density profile determined by XR indicated that C14PC molecules form monolayer with relatively loose packing at the first saturation. In the second saturation, on the other hand, the molecules form bilayer in which charge separated phosphocholine groups take upside-down arrangement to interact attractively between neighbors. The positive entropy changes associated with adsorption both from monomeric and from micellar states result from that the contribution of dehydration around C14PC molecules, especially around PC groups, by the adsorption from aqueous solution overcomes that of a comparatively ordered molecular orientation at the interface. By comparing the results at the C14/W interface with those at the Air (A)/W one, it was shown that in the monolayer and bilayer states, hydrophobic chains of C14PC molecules are more ordered at the C14/W than at the A/W interface because of attractive interaction between C14PC and C14 molecules. This leads to smaller value of the partial molar entropy and energy changes associated with the adsorption at the C14/W than at the A/W interface. Furthermore the entropy of micelle formation changes from positive to negative with increasing T, suggesting that the entropy gain due to the dehydration exceeds the entropy loss by the aggregation at low temperatures, while the gain is less than the loss at high temperature.

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JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects

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