Kinetics of a structural phase transition in Langmuir monolayers studied using x-ray diffraction

B. Lin; J. B. Peng; J. B. Ketterson; P. Dutta; B. N. Thomas; J. Buontempo; Stuart A. Rice

doi:10.1063/1.456653

Kinetics of a structural phase transition in Langmuir monolayers studied using x-ray diffraction

B. Lin^*, J. B. Peng, J. B. Ketterson, P. Dutta, B. N. Thomas, J. Buontempo, Stuart A. Rice

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

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Abstract

Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C₂₁,H₄₃OH): namely, a transition from a uniaxially distorted ("pseudohexagonal") structure, formed upon compression, to an undistorted hexagonal structure. For T > 20°C we observe only an apparently hexagonal phase, while at T = 5°C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20°C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure.

Original language	English (US)
Pages (from-to)	2393-2397
Number of pages	5
Journal	The Journal of Chemical Physics
Volume	90
Issue number	4
DOIs	https://doi.org/10.1063/1.456653
State	Published - 1989

ASJC Scopus subject areas

Physics and Astronomy(all)
Physical and Theoretical Chemistry

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abstract = "Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C21,H43OH): namely, a transition from a uniaxially distorted ({"}pseudohexagonal{"}) structure, formed upon compression, to an undistorted hexagonal structure. For T > 20°C we observe only an apparently hexagonal phase, while at T = 5°C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20°C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure.",

author = "B. Lin and Peng, {J. B.} and Ketterson, {J. B.} and P. Dutta and Thomas, {B. N.} and J. Buontempo and Rice, {Stuart A.}",

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AU - Lin, B.

AU - Peng, J. B.

AU - Ketterson, J. B.

AU - Dutta, P.

AU - Thomas, B. N.

AU - Buontempo, J.

AU - Rice, Stuart A.

PY - 1989

Y1 - 1989

N2 - Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C21,H43OH): namely, a transition from a uniaxially distorted ("pseudohexagonal") structure, formed upon compression, to an undistorted hexagonal structure. For T > 20°C we observe only an apparently hexagonal phase, while at T = 5°C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20°C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure.

AB - Frequently, time-dependent effects are seen in monolayers of amphiphilic molecules (Langmuir films) when they are compressed, so that the pressure after some time is different from that recorded immediately after compression. We have identified for the first time a microscopic relaxation mechanism in monolayers of heneicosanol (C21,H43OH): namely, a transition from a uniaxially distorted ("pseudohexagonal") structure, formed upon compression, to an undistorted hexagonal structure. For T > 20°C we observe only an apparently hexagonal phase, while at T = 5°C we observe only an apparently stable pseudohexagonal phase. When 10≤T≤20°C, the monolayer structure changes with time from pseudohexagonal to hexagonal. The rate at which this transformation occurs is strongly temperature dependent. We propose that the observed temperature dependence is determined by the rate of nucleation of a hexagonal phase from a metastable shear-induced structure.

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Kinetics of a structural phase transition in Langmuir monolayers studied using x-ray diffraction

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