Effect of molecular branching and surface wettability on solid-liquid surface tension and line-tension of liquid alkane surface nanodroplets.

Hypothesis: Surface nanodroplets have important technological applications. Previous experiments and simulations have shown that their contact angle deviates from Young's equation. A modified version of Young's equation considering the three-phase line tension (τ) has been widely used in literature, and a wide range of values for τ are reported.

Tribological and Rheological Properties of Poly(vinyl alcohol)-Gellan Gum Composite Hydrogels.

Polymeric poly(vinyl alcohol) (PVA)-based composite hydrogels are promising materials with various biomedical applications. However, their mechanical and tribological properties should be tailored for such applications. In this study, we report the fabrication of PVA-gellan gum (GG) composite hydrogels and determine the effect of GG content on their rheological and tribological properties.

Anisotropic Wettability on One-Dimensional Nanopatterned Surfaces: The Effects of Intrinsic Surface Wettability and Morphology.

Large-scale molecular dynamic simulations were conducted to study anisotropic wettability on one-dimensional (1D) nanopatterned surfaces. Hexadecane (CH) and decane (CH) nanodroplets were used as wetting liquids. Initially, surfaces with various intrinsic wettability (oleophobic and oleophilic) were produced using surface lattice size as a control parameter.

The Origins of Enhanced and Retarded Crystallization in Nanocomposite Polymers.

Controlling the crystallinity of hybrid polymeric systems has an important impact on their properties and is essential for developing novel functional materials. The crystallization of nanocomposite polymers with gold nanoparticles is shown to be determined by free space between nanoparticles. Results of large-scale molecular dynamics simulations reveal while crystallinity is affected by the nanoparticle size and its volume fraction, their combined effects can only be measured by interparticle free space and characteristic size of the crystals.

Unravelling the effects of size, volume fraction and shape of nanoparticle additives on crystallization of nanocomposite polymers.

We conducted large scale molecular dynamics simulations to understand the effects of size, shape and volume fraction of additive nanoparticles on the crystallization of nanocomposite polymers. We used spherical and cubic gold nanoparticles of various sizes ranging from 2 to 8 nm to create hexacontane (CH)-gold nanocomposites at various volume fractions of 0.84-19.

Modelling mucosal surface roughness in the human velopharynx: a computational fluid dynamics study of healthy and obstructive sleep apnea airways.

We previously published a unique methodology for quantifying human velopharyngeal mucosal surface topography and found increased mucosal surface roughness in patients with obstructive sleep apnea (OSA). In fluid mechanics, surface roughness is associated with increased frictional pressure losses and resistance. This study used computational fluid dynamics (CFD) to analyze the mechanistic effect of different levels of mucosal surface roughness on velopharyngeal airflow.

Surface induced crystallization of polymeric nano-particles: effect of surface roughness.

Molecular dynamics simulations are conducted to study the crystallization of a polymeric system as a drop in an isolated state and on a surface. It is shown that crystallization kinetics for the polymeric system as a particle on a smooth surface is much faster than in the isolated form. We show however that as the surface becomes rough the crystallization rate of the polymeric particle decreases.

Thermostatic and rheological responses of DPD fluid to extreme shear under modified Lees-Edwards boundary condition.

Thermodynamic, hydrodynamic and rheological interactions between velocity-dependent thermostats of Lowe-Andersen (LA) and Nosé-Hoover-Lowe-Andersen (NHLA), and modified Lees-Edwards (M-LEC) boundary condition were studied in the context of Dissipative Particle Dynamics method. Comparisons were made with original Lees-Edwards method to characterise the improvements that M-LEC offers in conserving the induced shear momentum. Different imposed shear velocities, heat bath collision/exchange frequencies and thermostating probabilities were considered.

Effect of water on structural and frictional properties of self assembled monolayers.

Self-assembled monolayers (SAMs) of n-alkanethiols [(CH3(CH2)(n-1), n = 14, 15] on Au(111) in the presence of water have been simulated by molecular dynamics simulation. The behavior and effects of compression on structural characteristics and water penetration into monolayers under different ranges of normal pressures have been investigated. Frictional properties of hydrated SAM systems under various sliding velocities, and loading conditions are examined to explore correlation between the amount of water penetration and friction.

Frictional properties of two alkanethiol self assembled monolayers in sliding contact: odd-even effects.

Using molecular dynamics simulation, we have investigated the structural effects on the frictional properties of self assembled monolayers (SAM) of n-alkanethiols [CH(3)(CH(2))(n-1)SH, n = 12-15] in SAM-SAM contacts attached on Au (111) substrates. We have observed an odd-even effect where friction coefficient for SAM-SAM contacts with n = odd showed consistently higher values than those with n = even. This odd-even effect is independent of the sliding velocity and the relative tilt directions of the SAMs, and persists over a much higher pressure range than that reported before for SAM-Au contacts [L.

Effect of load on structural and frictional properties of alkanethiol self-assembled monolayers on gold: some odd-even effects.

We have conducted molecular dynamics simulations to study the frictional properties of alkanethiols CH(3)(CH(2))(n-1)SH (Cn, 12 ≤ n ≤ 15) self-assembled monolayers (SAMs) on Au(111) surfaces, under various loading and shearing conditions. For the examined alkanethiols, we found some evidence of the friction coefficient being dependent on the number of carbon atoms in the molecule being odd or even. Alkanethiols with n = odd show consistently higher friction coefficients than those with n = even.

Odd-even effects on the structure, stability, and phase transition of alkanethiol self-assembled monolayers.

Molecular dynamics simulations were conducted to predict the structural properties and phase transition temperatures of n-alkanethiols CH(3)(CH(2))(n-1)SH (Cn, 4 ≤ n ≤ 22) self-assembled monolayers (SAMs) on Au (111) surfaces. We studied the effects of chain length on the structural properties, including tilt and orientation angles, and on phase transition temperature. We found clear dependence of the structural properties, on both the number of carbon atoms, n; and on n being odd or even.