Conformational properties ofn-alkanes

Würflinger, A.

doi:10.1007/bf01417542

Cited by 16 publications

(10 citation statements)

References 26 publications

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“…The entropy of fusion of n -undecane is reported to be (Δ S m ) P = 89.6 J mol -1 K -1 . Adoption of γ = 1.2 MPa K -1 in eq 1 yields Δ S V = 18.0 J mol -1 K -1 , leading to (Δ S m ) V = 71.6 J mol -1 K -1 , in an approximate agreement with the configurational entropy (Δ S conf = 61.9 J mol -1 K -1 ) estimated by the RIS model .…”

Section: Discussionsupporting

confidence: 64%

“…16 Adoption of γ ) 1.2 MPa K -1 in eq 1 yields ∆S V ) 18.0 J mol -1 K -1 , leading to (∆S m ) V ) 71.6 J mol -1 K -1 , in an approximate agreement with the configurational entropy (∆S conf ) 61.9 J mol -1 K -1 ) estimated by the RIS model. 26 n-Alkanes comprising an odd number of carbons (n ) 11-43) are however known to exhibit the rotator solid phase in the vicinity of the melting point. 16 In n-undecane, the low-temperature orthogonal form turns into the hexagonal (rotator) packing at -36.6 °C.…”

Section: Discussionmentioning

confidence: 99%

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A Critical Study of the Entropy−Volume Relation of Chain Molecules in the Fluid State: Computer Simulation of n-Undecane and Comparison with Experimental PVT Data

et al. 2001

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A conventional method of estimating conformational entropy change at the melting point of polymers has been set forth in Mandelkern's book. The entropy separation according to this method involves a hypothetical assumption that the volume of the isotropic fluid may be compressed to that of the solid state without affecting the configurational part of the entropy of molecules. In this work, we have extensively examined the volume dependence of thermal pressure coefficient γ ) (δP/δT) V ) (δS/δV)T of n-undecane. Molecular dynamic simulations were performed using the software package Insight II/Discover. In the standard calculation, a cubic box containing 30 n-undecane molecules was used under the conventional periodic boundary conditions. The experimental observations were well reproduced by the MD simulation performed as above, and accordingly the γ vs specific volume (vsp) relations derived from the simulation are favorably compared with those obtained from the experimental PVT data. The γ values remain quite insensitive to vsp over a wide range at given temperatures. Values of the trans fraction were found to decrease with an increase in temperature, while they tend to remain quite insensitive to pressure (0-200 MPa). It was concluded on this basis that the aforementioned treatment of the volume change at the phase transition seems to be supported by the present analysis.

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Section: Discussionsupporting

confidence: 64%

Section: Discussionmentioning

confidence: 99%

A Critical Study of the Entropy−Volume Relation of Chain Molecules in the Fluid State: Computer Simulation of n-Undecane and Comparison with Experimental PVT Data

et al. 2001

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“…While this contribution is small for short alkyl chains, the same cannot be expected when the chain length increases, since molecules in a monolayer structure are much more limited to adopt different conformations. For gas-phase alkanes and related compounds such as thiols, one can use a simple rotational isomeric state model , to estimate the conformational free energy. In this model the number of conformations achievable by applying one or more gauche(±) defects along an all-trans alkyl chain are counted.…”

Section: Methodsmentioning

confidence: 99%

Understanding the Phase Diagram of Self-Assembled Monolayers of Alkanethiolates on Gold

et al. 2016

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Alkanethiolate monolayers on gold are important both for applications in nanoscience as well as fundamental studies of adsorption and self-assembly at metal surfaces. While considerable experimental effort has been put into understanding the phase diagram of these systems, theoretical work based on density functional theory (DFT) has long been hampered by the inability of conventional exchange-correlation functionals to describe dispersive interactions. In this work, we combine dispersion-corrected DFT calculations using the new vdW-DF-CX functional with the ab initio thermodynamics method to study the stability of dense standing-up and low-coverage lying-down phases on Au(111). We demonstrate that the lying-down phase has a thermodynamic region of stability starting from thiolates with alkyl chains consisting of n ≈ 3 methylene units. This phase emerges as a consequence of a competition between dispersive chain–chain and chain–substrate interactions, where the strength of the latter varies more strongly with n. A phase diagram is derived under ultrahigh-vacuum conditions, detailing the phase transition temperatures of the system as a function of the chain length. The present work illustrates that accurate ab initio modeling of dispersive interactions is both feasible and essential for describing self-assembled monolayers.

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“…From eq it then becomes obvious that τ 0 contains all entropic changes of the process. As demonstrated in Figure b, log τ 0 ∝ Δ S ‡ ∝ n , suggesting that the contribution may be due to conformational entropy which naturally scales with n . , …”

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confidence: 91%

Effect of Core Crystallization and Conformational Entropy on the Molecular Exchange Kinetics of Polymeric Micelles

et al. 2015

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Here we systematically study the equilibrium molecular exchange kinetics of a series of amphiphilic n-alkyl-poly(ethylene oxide) (C n -PEO) micelles containing partly crystallized cores. Using differential scanning calorimetry (DSC), we determined the melting transition and extracted the enthalpy of fusion, ΔH fus, of the n-alkyl chains inside the micellar core. Molecular exchange kinetics was measured below the melting point using a time-resolved small-angle neutron scattering technique (TR-SANS) based on mixing deuterated and proteated but otherwise identical micelles. Comparing both kinetic and thermodynamic data, we find that crystallinity within the micellar cores leads to significant enthalpic and the entropic contributions to the activation barrier for molecular exchange. While the former leads to an enhanced stability, the positive entropic gain favors the process. Interestingly, the entropic term contains an excess term beyond what is expected from the measured entropy of fusion. Based on calculations using the Rotational Isomeric State (RIS) model, we suggest that the excess entropy is due to the gain in conformational entropy upon releasing the chain from the confined state in the core. The study thus provides deep insight into the fundamental processes of micellar kinetics and which might be relevant also to other semicrystalline soft matter and biological systems including lipid membranes.

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Conformational properties ofn-alkanes

Cited by 16 publications

References 26 publications

A Critical Study of the Entropy−Volume Relation of Chain Molecules in the Fluid State: Computer Simulation of n-Undecane and Comparison with Experimental PVT Data

A Critical Study of the Entropy−Volume Relation of Chain Molecules in the Fluid State: Computer Simulation of n-Undecane and Comparison with Experimental PVT Data

Understanding the Phase Diagram of Self-Assembled Monolayers of Alkanethiolates on Gold

Effect of Core Crystallization and Conformational Entropy on the Molecular Exchange Kinetics of Polymeric Micelles

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