arXiv subjects

Ramanathan Varadharajan

Publications and source records attributed to Ramanathan Varadharajan.

4 recordsLinked to original sources

arXiv2019

Elastic Properties of Symmetric Liquid-Liquid Interfaces

The mean ($κ$) and Gaussian ($\barκ$) bending rigidities of liquid-liquid interfaces, of importance for shape fluctuations and topology of interfaces, respectively, are not yet established: even their signs are debated. Using the Scheutjens Fleer variant of the self-consistent field theory, we implemented a model for a symmetric L/L interface and obtained high precision (mean field) results in the grand canonical $(μ, V, T)$-ensemble. We report positive values for both moduli when the system is close to critical where the rigidities show the same scaling behavior as the interfacial tension $γ$. At strong segregation, when the interfacial width becomes of the order of the segment size, $\barκ$ turns negative. The length scale $λ\equiv \sqrt{κ/γ}$ is of order the segment size for all strengths of interaction; yet the $1/\sqrt{N}$ chain length correction reduces $λ$ significantly when the chain length $N$ is small.

cond-mat.stat-mech↗

arXiv2018

Microemulsion sponge phase as a manifestation of the superflexibility critical point of tensionless balanced liquid-liquid interfaces

We have analyzed the mechanical properties of surfactant loaded tensionless balanced liquid/liquid interfaces using self-consistent field theory implementing a coarse grained model. Such a tensionless state, as occurring in microemulsions, signals a first-order interfacial phase transition. Consequently, the interfacial area is set by the amount of surfactant in the system. Near the bulk critical point, such systems suffer an interfacial, so-called superflexibility (SF) critical point as soon as the tensionless state ceases to exist. This happens when the width of the L/L interface becomes comparable to the surfactant size. The bending rigidities vanish upon approaching the SF-point as a power-law. Exclusively near the SF-point, the saddle splay modulus is positive featuring the sponge phase to be its main characteristic.

cond-mat.soft↗

arXiv2017

Sign switch of Gaussian bending modulus for microemulsions; a self-consistent field analysis exploring scale invariant curvature energies

Bending rigidities of tensionless balanced liquid-liquid interfaces as occurring in microemulsions are predicted using self-consistent field theory for molecularly inhomogeneous systems. Considering geometries with scale invariant curvature energies gives unambiguous bending rigidities for systems with fixed chemical potentials: The minimal surface Im3m cubic phase is used to find the Gaussian bending rigidity, $\barκ$, and a torus with Willmore energy $W=2 π^2$ allows for direct evaluation of the mean bending modulus, $κ$. Consistent with this, the spherical droplet gives access to $2 κ+ \barκ$. We observe that $\barκ$ tends to be negative for strong segregation and positive for weak segregation; a finding which is instrumental for understanding phase transitions from a lamellar to a sponge-like microemulsion. Invariably, $κ$ remains positive and increases with increasing strength of segregation.

cond-mat.soft↗

arXiv2017

Reynolds number effects on transition, turbulence intensity and axial-velocity decay rate of turbulent round jets

Numerical simulations of turbulent round jets, using explicit-filtered LES technique, are performed, for three different Reynolds numbers(Re = 3600, 88000, 400000), to understand the Reynolds number effect on subsonic jets with Mach number 0.9. Eigth-order compact schemes are used for spatial derivative estimation. Second order Runge-Kutta method is used for Time evolution of flow. One-parameter fourth-order compact filter is used for low-pass explicit filtering of transported variables. Decreased centreline axial velocity decay rate and reduced turbulence intensities are observed as jet Reynolds number increases. Jet spread-rate is observed to be independent of the Reynolds number. An early potential-core collapse and transition to turbulent regime is observed in jets with high Reynolds number, for same inflow turbulence seeding. Role of increased smaller length scales with increase in Reynolds number is analyzed. It is observed that behavior of turbulent round jets is similar to that of plane jets, irrespective of gain in dimensional freedom. Detailed discussions of the observations made from numerical experiments are presented.

physics.flu-dyn↗