Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · cond-mat/0411411

Phase Transitions in Hexane Monolayers Physisorbed onto Graphite

M. W. Roth·C. L. Pint·Carlos Wexler
View original source ↗Read source document ↗Export metadata ↓

Abstract

We report the results of molecular dynamics (MD) simulations of a complete monolayer of hexane physisorbed onto the basal plane of graphite. At low temperatures the system forms a herringbone solid. With increasing temperature, a solid to nematic liquid crystal transition takes place at $T_1 = 138 \pm 2$K followed by another transition at $T_2 = 176 \pm 3$K into an isotropic fluid. We characterize the different phases by calculating various order parameters, coordinate distributions, energetics, spreading pressure and correlation functions, most of which are in reasonable agreement with available experimental evidence. In addition, we perform simulations where the Lennard-Jones interaction strength, corrugation potential strength and dihedral rigidity are varied in order to better characterize the nature of the two transitions through. We find that both phase transitions are facilitated by a ``footprint reduction'' of the molecules via tilting, and to a lesser degree via creation of gauche defects in the molecules.

Explore related subjects

cond-mat.softcond-mat.mtrl-sci

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

M. W. Roth, C. L. Pint, Carlos Wexler. 2004-11-16. Phase Transitions in Hexane Monolayers Physisorbed onto Graphite. https://doi.org/10.1103/physrevb.71.155427

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Broadband molecular dynamics simulation of confined Brownian motion

Molecular dynamics with an explicit solvent resolves the hydrodynamic response of a Brownian colloid in bulk and near a rigid wall over acoustic, inertial, and diffusive time scales. Bulk spectra establish a continuum reference and reveal departures associated with discrete-solvent dynamics. Under confinement, thermal spectra provide a measurement of the space-dependent added mass, while velocity autocorrelations determine space-dependent, anisotropic hydrodynamic memory and diffusion. All together, these measurements connect the enhanced added mass and reduced mobility near a wall, and probe the discrete-continuum crossover.

cond-mat.soft↗
arXiv2026

Tunable Signal Penetration and Response Plateaus in Bistable Mechanical Media

Dynamic processing of mechanical signals is crucial for soft robotics and mechanosensing, yet classical viscoelastic materials lack intrinsic tunability and quantitative design rules. We show that internal bistability provides a simple but powerful mechanism to tailor response and signal attenuation in mechanical (meta)materials. In our model, bistable elements switch discretely with an intrinsic timescale between states that differ in potential energy $ε$, equilibrium length $Δl$, and spring constant $Δk$. We combine Brownian dynamics simulations with discrete Poisson switching at rate $ν$ and a nonlinear continuum (field) theory for the macroscopic strain relaxation. The model yields closed-form solutions for the linear response and the spatial penetration depth, revealing two complementary phenomena: a universal screening mechanism (akin to the electrostatic `skin effect') that strongly reduces signal penetration when the driving frequency exceeds the internal relaxation rate, and a frequency-insensitive response plateau arising from timescale separation. The attenuation strength, expressed by a screening length, is controlled primarily by the conformational length change $Δl$, while the attenuation regime and plateau position are tuneable via $ν$. A parameter study exposes a fundamental design trade-off: larger $Δl$ strengthen dissipation but also raise the elastic energy barrier for state transitions, eventually causing state-locking where damping vanishes. Optimal attenuation thus emerges from a compromise between pronounced bistability and a surmountable barrier. Owing to its analytical tractability and generic formulation, our framework yields explicit design rules applicable to systems from biopolymers to synthetic catch bonds and metamaterials, enabling the design of soft materials with frequency-selective mechanical response.

cond-mat.soft↗
arXiv2026

A numerical study to analyze the interplay of Weissenberg number and viscosity ratio in a log-strain tensorial model for viscoelastic fluids

We present a computational study aimed at exploring the different and independent roles of the Weissenberg number and of the ratio between the polymeric and solvent viscosity contributions in a viscoelastic fluid model. The tensorial model under investigation, recently proposed, is based on a logarithmic relation between the elastic (or recoverable) strain and the elastic stress. In this model, the elastic strain plays the role of a conformation tensor and its evolution equation inherently preserves its determinant and positive definiteness. These properties are also enforced in the computational method employed in the study. A finite-difference discretization in time is combined with a stabilized mixed finite element formulation based on the Variational Multiscale method for the spatial discretization and with a generalized Lie derivative approach for the advection terms. The behavior of the model is analyzed in paradigmatic pressure-driven flows and we find that the value of the viscosity ratio is crucial in determining to which extent non-Newtonian flow profiles are observed upon increasing the Weissenberg number. By comparing the solutions of the log-strain tensorial model with those of a suitable Generalized Newtonian Fluid model, we show that flow-type dependence and memory play a significant role even in the simple planar flow past a cylinder.

cond-mat.soft↗