Surface-induced phase transition in normal alkane fluids

Earnshaw, J. C.; Hughes, Claire

doi:10.1103/physreva.46.r4494

Cited by 160 publications

(124 citation statements)

References 5 publications

Supporting

Mentioning

120

Contrasting

Order By: Relevance

“…[39][40][41] In these studies, just as in our temperature scans, the thermodynamic signature for the surface transition is a discontinuous change in d␥/dT while scanning temperature. This transition is clearly distinguished from the bulk transition by the fact that the surface transition temperature is greater than for the bulk transition.…”

Section: Systemmentioning

confidence: 99%

A determination of the phase diagram of relaxed Langmuir monolayers of Behenic acid

Bommarito

Foster

Pershan

et al. 1996

The Journal of Chemical Physics

View full text Add to dashboard Cite

Grazing incidence x-ray scattering ͑GIXS͒ and Brewster angle microscopy ͑BAM͒ are used to determine the -T phase diagram of Behenic acid monolayers supported on the surface of water ͑pHϭ2.0͒ over the temperature range of 3°C to 20.6°C. The phase diagram is constructed from measurements taken during isothermal compressions in which the surface pressure relaxed to a stable value at each surface density, and during temperature scans at fixed average surface density. The phase diagram is different than those previously reported for Behenic acid primarily because of the surface pressure relaxation. For temperatures less than 12°C the phase diagram exhibits similar phases and topology as the published diagrams, although the location of the phases in the -T plane is different. Temperature scans combined with the isotherms, and the Clausius-Clapeyron relation are used to determine three coexistence lines that meet in a triple point. Changes in entropy across the phase boundaries are determined. Near room temperature ͑20.6°C͒ only one phase is measured over the range of surface pressure from 0 dynes/cm to the collapse pressure in contrast to reported measurements on monolayers out of equilibrium ͑i.e., when the surface pressure is not allowed to relax͒ that exhibit several phases near room temperature at pressures higher than the collapse pressure. Discrepancies are observed between the average area per molecule (A T ) and the area per molecule determined from measurements of the unit cell (A X ) in the close packed regions of the phase diagram. It is conjectured that the -A X plane is a better representation of the ordered equilibrium monolayer phases than the -A T plane. Isotherms plotted in the -A X plane are used to determine the compressibility of the ordered phases and the nature of the phase transitions.

show abstract

Section: Systemmentioning

confidence: 99%

A determination of the phase diagram of relaxed Langmuir monolayers of Behenic acid

Bommarito

Foster

Pershan

et al. 1996

The Journal of Chemical Physics

View full text Add to dashboard Cite

show abstract

“…Elucidation of this relationship requires systematic study, and as a starting point, we have performed such a study for the n-alkane glasses. Interest here in the n-alkanes is motivated by the fact that these simple linear hydrocarbons exhibit a rich range of thermodynamic behavior as a function of the simplest molecular parameter, namely chain length n. For example, surface-freezing phenomena [49][50][51][52][53] and the even-odd effect 54 in their freezing temperatures have recently received special attention. Their critical pressure and mass density exhibit maxima at n ) 2 and 6, 55-57 respectively, and display power-law dependence for large n. 58 Furthermore, the n-alkanes serve as a convenient starting point for studying amorphous polymeric systems.…”

Section: Introductionmentioning

confidence: 99%

Energy Landscape and Isotropic Tensile Strength of n-Alkane Glasses

2002

View full text Add to dashboard Cite

We report results from a systematic simulational study of the ultimate mechanical strength of n-alkane glasses for carbon numbers n ) 1, 2, 3, 4, 6, 8, 16, 24, and 48. The ultimate isotropic tensile strength was determined by constructing the equation of state of energy landscape for this homologous series. The tensile strength depends nonmonotonically on carbon number, exhibiting a maximum at n ) 3. The mass density at which fracture occurs initially increases with chain length and then reaches a plateau value for n > 8. The predictions of the landscape equation of state are entirely consistent with results generated by a direct inherent structure deformation procedure. Although the ultimate isotropic tensile strength maximum at n ) 3 would seem to contradict physical intuition regarding chain entanglement, we present a simple mean-field theory that reveals the underlying physics responsible for the tensile strength maximum, namely the simple competition between intermolecular interactions and intramolecular packing effects.

show abstract

“…3. The onset of SF at T s = 54 • C is clearly manifested in this curve by the abrupt change in the slope from a negative to a positive value, due to the drop in the surface entropy upon SF [5]. Comparing this curve with the dynamic surface tension γ d (T ), extracted from our measurements using the dispersion relation above (Fig.…”

Section: ∼4mentioning

confidence: 99%

“…With T s = 54 • C and a bulk freezing temperature T b = 50 • C, it exhibits the largest temperature range of SF of all pure n-alkanes [5]. Our circular, 18-cm diameter, sample cell was filled with 300 g of C 24 H 50 (Aldrich, 99.9% pure) to a height of h = 1.5 cm above the cell bottom.…”

Section: ∼4mentioning

confidence: 99%

“…A transition from a liquid-like to a granular-solid-like shear response was observed at nano-scale confinements [4]. The surface freezing (SF) effect [5], where a solid monolayer forms at the surface of a pure normal-alkane (C n H 2n+2 ) melt, provides a unique system for studying semi-confined flow at a solid-liquid interface. The abrupt onset of SF at T s allows one to switch on (and off) the solid phase by a small temperature variation.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Faraday Instability in a Surface-Frozen Liquid

et al. 2005

View full text Add to dashboard Cite

Faraday surface instability measurements of the critical acceleration, ac, and wavenumber, kc, for standing surface waves on a tetracosanol (C24H50) melt exhibit abrupt changes at Ts = 54 • C, ∼4 • C above the bulk freezing temperature. The measured variations of ac and kc vs. temperature and driving frequency are accounted for quantitatively by a hydrodynamic model, revealing a change from a free-slip surface flow, generic for a free liquid surface (T > Ts), to a surface-pinned, no-slip flow, characteristic of a flow near a wetted solid wall (T < Ts). The change at Ts is traced to the onset of surface freezing, where the steep velocity gradient in the surface-pinned flow significantly increases the viscous dissipation near the surface.PACS numbers: 47.20.Ma, 61.25.Em, 64.70.Dv Spatial confinement of a liquid often changes its properties markedly. For example, superheating above the equilibrium melting temperature [1] and order quenching upon freezing [2] were observed under confinement only. In particular, flow under confinement is important for processes ranging from tribology to protein folding to transport through ion channels in cell membranes [3]. A transition from a liquid-like to a granular-solid-like shear response was observed at nano-scale confinements [4]. The surface freezing (SF) effect [5], where a solid monolayer forms at the surface of a pure normal-alkane (C n H 2n+2 ) melt, provides a unique system for studying semi-confined flow at a solid-liquid interface. The abrupt onset of SF at T s allows one to switch on (and off) the solid phase by a small temperature variation. Understanding such interfaces would also elucidate the role of flow in nucleation and growth processes of crystals from melts, which are dominated by such interfaces [6].SF occurs in melts of several chain molecules (alkenes, alcohols, semi-fluorinated alkanes, diols, C i E j ) [7], and at both liquid/liquid [8] and liquid/solid [9] interfaces. Related surface ordering effects were observed in melts of polymers comprising alkyl chains in the backbone or as side chains [10], in liquid alloys [11], and in several liquid crystals [12]. While the structural and thermodynamic aspects of SF have been studied in great detail [13], the influence of surface ordering on macroscopic near-surface flows has received little attention to date in this sizable, technologically-important class of materials.To study this issue, we employ the Faraday instability, which forms standing wave patterns (SWP) at the free surface of a vertically-vibrated liquid [14]. By virtue of its simplicity, this instability is outstanding among pattern-forming systems and a detailed theoretical description has been achieved. The SWP formed depend sensitively on, and allow a detailed study of, the changes in the surface hydrodynamics upon SF. As this study of SF demonstrates, the instability can therefore be employed to explore physical processes which are difficult to access by other, classical means. It also exemplifies the more general class of parametric inst...

show abstract

Surface-induced phase transition in normal alkane fluids

Cited by 160 publications

References 5 publications

A determination of the phase diagram of relaxed Langmuir monolayers of Behenic acid

A determination of the phase diagram of relaxed Langmuir monolayers of Behenic acid

Energy Landscape and Isotropic Tensile Strength of n-Alkane Glasses

Faraday Instability in a Surface-Frozen Liquid

Contact Info

Product

Resources

About