arXiv subjects

Carlos E. Colosqui

Publications and source records attributed to Carlos E. Colosqui.

At least 19 recordsLinked to original sources

arXiv2026

Polymer-Iron Oxide Hybrid Films for Controlling Electrokinetic Properties

Electrokinetic phenomena at polymer-water interfaces are central to technologies for water purification, ion separations, and energy conversion, yet the ability to systematically control polymer surface charge and associated electrokinetic processes remains limited. Here, we demonstrate a simple liquid-phase infiltration (LPI) method to synthesize polymer-metal oxide hybrid films with controllable interfacial properties. Hydroxy-terminated poly(2-vinylpyridine) (P2VP-OH) brushes grafted to silicon substrates were infiltrated with iron nitrate from ethanolic solution, followed by low-temperature thermal treatment to convert the infiltrated precursor into iron oxide. Spectroscopic ellipsometry, X-ray photoelectron spectroscopy, and thermogravimetric analysis confirmed oxide incorporation and hybrid film formation without polymer degradation. Electrokinetic flow characterization reveals that the hybrid films acquire the electrokinetic properties of the infiltrated oxide, with concentration-dependent streaming potentials and surface conductivities closely matching those of pure iron oxide films. These results establish metal oxide infiltration as a scalable and low-cost strategy for controlling interfacial charge in polymer surfaces. The approach introduces new materials and design parameters for tailoring ion selectivity, transport, and energy conversion, with broad implications for the development of advanced membranes, electrokinetic harvesting devices, and polymer-supported oxide electrodes.

cond-mat.mtrl-sci↗

arXiv2025

A capillary diode for potential application in water-oil separation

A capillary device is designed and fabricated in glass to work as a fluidic diode with vanishingly small hydrodynamic conductance for imbibition of water within a finite range of immersion depths. This is attained through patterning a section of predefined length on the device surfaces using a single-step laser-based ablation process and without resorting to chemical treatment of the hydrophilic glass substrate. While the studied device works as a fluidic diode for water, it can behave as a conventional capillary slit for the imbibition of oils (e.g., alkanes, silicone oils) with low surface tension. A prototype device with simple geometric design is demonstrated for selective adsorption and separation of water and oil in vertical imbibition experiments at controlled immersion depths. Efficient devices for passive separation of water and oil can be designed based on the demonstrated physical mechanism and the analytical model proposed in this work.

physics.flu-dyn↗

arXiv2025

Thermodynamics, Dynamics, and Kinetics of Nanostructured Fluid-Solid Interfaces

This article covers thermodynamic, dynamic, and kinetic models that are suitable for the analysis of wetting, adsorption, and related interfacial phenomena in colloidal and multiphase systems. Particular emphasis is made on describing crucial physical assumptions and the validity range of the described theoretical approaches and predictive models. The classical sharp interface treatment of thermodynamic systems where a perfectly smooth surface is assumed to separate homogeneous phases can present significant limitations when analyzing systems that are subject to thermal motion and present multiple metastable states caused by interfacial heterogeneities of nanoscale dimensions. Mesoscopic approaches such as stochastic Langevin dynamics can extend the application of sharp interface models to a wide variety of systems exhibiting metastability as they undergo thermal motion. For such metastable systems, dynamic and kinetic equations can describe the evolution of observable (macroscopic) variables as the system approaches thermodynamic equilibrium. Sufficiently close to equilibrium, Kramers theory of thermally activated escape from metastable states can be effectively employed to describe diverse wetting and interfacial processes via kinetic equations. Future directions for further advancement and application of thermodynamic, dynamic, and kinetic models are briefly discussed in the context of current technological developments involving nanoparticles, nanofluidics, and nanostructured surfaces.

cond-mat.soft↗

arXiv2025

Diffusion in a rough potential: Dual-scale structure and regime crossovers

Diffusion in a `rough' potential parameterized by a reaction coordinate $q$ is relevant to a wide spectrum of problems ranging from protein folding and charge transport in complex media to colloidal stabilization and self-assembly. This work studies the case of a potential having coarse-scale structure with characteristic energy barrier $ΔU$ and period $\ell$, and fine-scale `roughness' of magnitude $ΔU'\lesssim ΔU$ and small period $\ell'\ll \ell$. Numerical solution of the Smoluchowski equation and analytical predictions from Kramers theory document distinct regimes at different distances $|Δq|=|q-q_E|$ from stable equilibrium at $q=q_E$. The physical diffusivity $D$ prescribed by dissipative effects can be observed farther than a distance $|Δq'| \propto (ΔU'/\ell' + ΔU/\ell)$. Rescaling the physical diffusivity to account for the fine-scale `roughness' is strictly valid when $|Δq| < Δq_I \propto (ΔU'/\ell' - ΔU/\ell)$. Farther than a critical distance $Δq_{II}\propto ΔU/\ell$ the diffusion process is free of coarse-scale metastable states, which facilitates determining the effective diffusivity $D'$ from the reaction coordinate trajectory. Closer to equilibrium the coarse-scale structure induces two diffusive regimes: nearly logarithmic evolution for $Δq_{II} > |Δq| > Δq_{III}$ and exponential decay over time for $|Δq| < Δq_{III}\propto 1/\ell$. The effective diffusivity derived in this work is sensitive to the coarse- and fine-scale energy barriers and periods, and for $\ell'/\ell \to 0$ and $ΔU'/k_B T \gg 1$ agrees closely with mean first-passage time estimates currently employed, which depend solely on the fine-scale energy barrier.

cond-mat.soft↗

arXiv2025

Dynamic-Kinetic Duality of Particulate and Multiphase Systems

The evolution of particulate and multiphase systems can transition from dynamic regimes, governed by classical transport equations with well-defined damping coefficients, to anomalously slow relaxation described by rate equations when the system is critically close to equilibrium. This regime crossover has been both theoretically predicted and experimentally observed in diverse multiphase systems relevant to numerous technological applications, including nanoparticle adhesion at interfaces and liquid imbibition under microscale confinement, and it is attributed to the presence of small nanoscale features of physical or chemical nature at liquid-solid interfaces. This article presents a theoretical framework to more accurately predict and control, advancing or delaying, the dynamic-to-kinetic regime crossover, and highlights strategies for harnessing this phenomenon to enhance or suppress different transport processes in confined multiphase systems.

cond-mat.soft↗

arXiv2025

Toward Efficient Electrokinetic Energy Conversion with Topographic Modulation of Electrical Conduction

This work presents experimental and theoretical analyses of electrokinetic flow in microchannels with glass and silica surfaces across a broad range of electrolyte concentrations (0.01 to 100 mM). We demonstrate simple but effective strategies for controlling electrical conduction by engineering nanoscale and microscale topographic features that directly modify the structure and extent of the electric double layer (EDL) and the interfacial ion conduction pathway. These tailored surface topographies modulate the overall electrical conductivity in slit microchannels through similar phenomena documented for nanochannels and nanopores due to the presence of liquid-filled nanoscale topographic features with high concentration of highly mobile protons. The findings of this work reveal that the interaction between tailored surface features and the EDL can substantially enhance energy conversion efficiency in microscale systems. These insights along with simple analytical models provide guidance for the rational design and optimization of scalable electrokinetic devices and are broadly relevant to numerous energy harvesting and charge-separation technologies.

cond-mat.soft↗

arXiv2023

Anomalous near-equilibrium capillary rise

We report and rationalize the observation of a crossover from the classical Lucas-Washburn dynamics to a long-lived anomalously slow regime for capillary rise in simple glass tubes. We propose an analytical model considering the role of thermal motion and the nanoscale surface topography to account for the experimental observations. The proposed model indicates that the contact line perimeter and the surface topography dimensions determine the crossover condition and anomalous imbibition rate. Our findings have important implications for the scientific understanding and technical application of capillary imbibition and suggest strategies to control the adsorption of specific liquids in porous materials.

cond-mat.soft↗

arXiv2020

Molecular dynamics and continuum analyses of the electrokinetic zeta potential in nanostructured slit channels

This work presents a theoretical and numerical study of electrokinetic flow and the zeta potential for the case of slit channels with nanoscale roughness of dimensions comparable to the Debye length, by employing molecular dynamics simulations and continuum-level analyses. A simple analytical model for considering the effects of the surface roughness is proposed by employing matched asymptotic solutions for the charge density and fluid flow field, and matching conditions that satisfy electroneutrality and the Onsager reciprocal relation between the electroosmotic flow rate and streaming current. The proposed analytical model quantitatively accounts for results from molecular dynamics simulations that consider the presence of ion solvation shells and surface hydration layers. Our analysis indicates that a simultaneous knowledge of the electroosmotic and pressure-driven flow rate or streaming current can be instrumental to determine unambiguously the zeta potential and the characteristic surface roughness height.

physics.flu-dyn↗

arXiv2018

Physical ageing of spreading droplets in a viscous ambient phase

Nanoscale topographic features of solid surfaces can induce complex metastable behavior in colloidal and multiphase systems. Recent studies on single microparticle adsorption at liquid interfaces have reported a crossover from fast capillary driven dynamics to extremely slow kinetic regimes that can require up to several hours or days to attain thermodynamic equilibrium. The observed kinetic regime resembling physical ageing in glassy materials has been attributed to unobserved surface features with dimensions on the order of a few nanometers. In this work, we study the spontaneous spreading of water droplets immersed in oil and report an unexpectedly slow kinetic regime not described by previous spreading models. We can quantitatively describe the observed regime crossover and spreading rate in the late kinetic regime with an analytical model considering the presence of periodic metastable states induced by nanoscale topographic features (characteristic area ~4 nm^2, height ~1 nm) observed via atomic force microscopy. The analytical model proposed in this work reveals that certain combinations of droplet volume and nanoscale topographic parameters can significantly hinder or promote wetting processes such as spreading, wicking, and imbibition.

cond-mat.soft↗

arXiv2017

Colloidal particle adsorption at water/water interfaces with ultra-low interfacial tension

Using fluorescence microscopy we study the adsorption of single latex microparticles at a water/water interface between demixing aqueous solutions of polymers, generally known as a water-in-water emulsion. Similar microparticles at the interface between molecular liquids have exhibited an extremely slow relaxation preventing the observation of expected equilibrium states. This phenomenon has been attributed to "long-lived" metastable states caused by significant energy barriers $Δ{\cal F}\sim γA_d\gg k_B T$ induced by high interfacial tension ($γ\sim 10^{-2}$ N/m) and nanoscale surface defects with characteristic areas $A_d \simeq$ 10--30 nm$^2$. For the studied water/water interface with ultra-low surface tension ($γ\sim 10^{-4}$ N/m) we are able to characterize the entire adsorption process and observe equilibrium states prescribed by a single equilibrium contact angle independent of the particle size. Notably, we observe crossovers from fast initial dynamics to slower kinetic regimes analytically predicted for large surface defects ($A_d \simeq$ 500 nm$^2$). Moreover, particle trajectories reveal a position-independent damping coefficient that is unexpected given the large viscosity contrast between phases. These observations are attributed to the remarkably diffuse nature of the water/water interface and the adsorption and entanglement of polymer chains in the semidilute solutions. This work offers some first insights on the adsorption dynamics/kinetics of microparticles at water/water interfaces in bio-colloidal systems.

cond-mat.soft↗

arXiv2016

Crossover from Shear-Driven to Thermally Activated Drainage of Liquid-Infused Microscale Capillaries

The shear-driven drainage of capillary grooves filled with viscous liquid is a dynamic wetting phenomenon relevant to numerous industrial processes and novel lubricant-infused surfaces. Prior work has reported that a finite length $L_\infty$ of the capillary groove can remain indefinitely filled with liquid even when large shear stresses are applied. The mechanism preventing full drainage is attributed to a balance between the shear-driven flow and a counterflow driven by capillary pressures caused by deformation of the free surface. The final equilibrium length $L_\infty$ is uniquely determined by physical properties of the filling liquid as well as the geometry and wettability of the capillary. In this work, we examine closely the approach to the final equilibrium length $L_\infty$ and report a crossover to a slow drainage regime that cannot be described by conventional dynamic models considering solely hydrodynamic and capillary forces. The slow drainage regime observed in experiments can be instead modeled by a kinetic equation describing a sequence of random thermally activated transitions between multiple metastable states caused by surface defects with nanoscale dimensions. Our findings provide new insights on the critical role that natural or engineered surface roughness with nanoscale dimensions can play in the imbibition and drainage of capillaries and other dynamic wetting processes in microscale systems.

cond-mat.soft↗

arXiv2016

Colloidal particle adsorption at liquid interfaces: Capillary driven dynamics and thermally activated kinetics

The adsorption of single colloidal microparticles (0.5--1 $μ$m radius) at a water-oil interface has been recently studied experimentally using digital holographic microscopy [Kaz \textit{et al., Nat. Mater.}, 2012, \textbf{11}, 138--142]. An initially fast adsorption dynamics driven by capillary forces is followed by an unexpectedly slow relaxation to equilibrium that is logarithmic in time and can span hours or days. The slow relaxation kinetics has been attributed to the presence of surface "defects" with nanoscale dimensions (1--5\,nm) that induce multiple metastable configurations of the contact line perimeter. A kinetic model considering thermally activated transitions between such metastable configurations has been proposed [Colosqui \textit{et al., Phys. Rev. Lett.}, 2013, \textbf{111}, 028302] to predict both the relaxation rate and the crossover point to the slow logarithmic regime. However, the adsorption dynamics observed experimentally before the crossover point has remained unstudied. In this work, we propose a Langevin model that is able to describe the entire adsorption process of single colloidal particles by considering metastable states produced by surface defects and thermal motion of the particle and liquid interface. Invoking the fluctuation dissipation theorem, we introduce a drag term that considers significant dissipative forces induced by thermal fluctuations of the liquid interface. Langevin dynamics simulations based on the proposed adsorption model yield close agreement with experimental observations for different microparticles, capturing the crossover from (fast) capillary driven dynamics to (slow) thermally activated kinetics.

cond-mat.soft↗

arXiv2015

Thermally Driven Imbibition and Drainage Induced by Terraced Nanostructures

Theoretical analysis and fully atomistic molecular dynamics simulations reveal a Brownian ratchet mechanism by which thermal fluctuations drive the net displacement of immiscible liquids confined in channels or pores with micro- or nanoscale dimensions. The thermally-driven displacement is induced by surface nanostructures with directional asymmetry and can occur against the direction of action of wetting or capillary forces. Mean displacement rates in molecular dynamics simulations are predicted via analytical solution of a Smoluchowski diffusion equation for the position probability density. The proposed physical mechanisms and derived analytical expressions can be applied to engineer surface nanostructures for controlling the dynamics of diverse wetting processes such as capillary filling, wicking, and imbibition in micro- or nanoscale systems.

cond-mat.soft↗

arXiv2015

Poiseuille flow past a nanoscale cylinder in a slit channel: Lubrication theory versus molecular dynamics analysis

Plane Poiseuille flow past a nanoscale cylinder that is arbitrarily confined (i.e., symmetrically or asymmetrically confined) in a slit channel is studied via hydrodynamic lubrication theory and molecular dynamics simulations, considering cases where the cylinder remains static or undergoes thermal motion. Lubrication theory predictions for the drag force and volumetric flow rate are in close agreement with molecular dynamics simulations of flows having molecularly thin lubrication gaps, despite the presence of significant structural forces induced by the crystalline structure of the modeled solid. While the maximum drag force is observed in symmetric confinement, i.e., when the cylinder is equidistant from both channel walls, the drag decays significantly as the cylinder moves away from the channel centerline and approaches a wall. Hence, significant reductions in the mean drag force on the cylinder and hydraulic resistance of the channel can be observed when thermal motion induces random off-center displacements. Analytical expressions and numerical results in this work provide useful insights into the hydrodynamics of colloidal solids and macromolecules in confinement.

physics.flu-dyn↗

arXiv2013

Rotational Dynamics and Angular Locking of Nanoparticles at liquid Interfaces

Nanoparticles with different surface morphologies that straddle the interface between two immiscible liquids are studied via molecular dynamics simulations. The methodology employed allows us to compute the interfacial free energy at different angular orientations of the nanoparticle. Due to their atomistic nature, the studied nanoparticles present both microscale and macroscale geometrical features and cannot be accurately modeled as a perfectly smooth body (e.g., spheres, cylinders). Under certain physical conditions, microscale features can produce free energy barriers that are much larger than the thermal energy of the surrounding media. The presence of these energy barriers can effectively "lock" the particle at specific angular orientations with respect to the liquid-liquid interface. This work provides new insights on the rotational dynamics of Brownian particles at liquid interfaces and suggests possible strategies to exploit the effects of microscale features with given geometric characteristics.

cond-mat.soft↗

arXiv2013

Engineering the geometry of stripe-patterned surfaces towards efficient wettability switching

The ability to control wettability is important for a wide range of technological applications in which precise microfluidic handling is required. It is known that predesigned roughness at a micro- or nano- scale enhances the wetting properties of solid materials giving rise to super-hydrophobic or super-hydrophilic behavior. In this work, we study the dependence of the apparent wettability of a stripe-patterned solid surface on the stripe geometry, utilizing systems level analysis and mesoscopic Lattice-Boltzmann (LB) simulations. Through the computation of both stable and unstable states we are able to determine the energy barriers separating distinct metastable wetting states that correspond to the well-known Cassie and Wenzel states. This way the energy cost for inducing certain wetting transitions is computed and its dependence on geometric features of the surface pattern is explored.

cond-mat.soft↗

arXiv2012

Crossover from fast relaxation to physical aging in colloidal adsorption at fluid interfaces

The adsorption dynamics of a colloidal particle at a fluid interface is studied theoretically and numerically, documenting distinctly different relaxation regimes. The adsorption of a perfectly smooth particle is characterized by a fast exponential relaxation to thermodynamic equilibrium where the interfacial free energy has a minimum. The short relaxation time is given by the ratio of viscous damping to capillary forces. Physical and/or chemical heterogeneities in a colloidal system, however, can result in multiple minima of the free energy giving rise to metastability. In the presence of metastable states we observe a crossover to a slow logarithmic relaxation reminiscent of physical aging in glassy systems. The long relaxation time is determined by the thermally-activated escape rate from metastable states. Analytical expressions derived in this work yield quantitative agreement with molecular dynamics simulations and recent experimental observations. This work provides new insights on the adsorption dynamics of colloidal particles at fluid interfaces.

cond-mat.soft↗

arXiv2012

Hydrodynamically-driven colloidal assembly in the thin-film entrainment regime

We study numerically the hydrodynamics of dip coating from a suspension and report a mechanism for colloidal assembly and pattern formation on smooth and uniform substrates. Below a critical withdrawal speed of the substrate, capillary forces required to deform the meniscus prevent colloidal particles from entering the coating film. Capillary forces are overcome by hydrodynamic drag only after a minimum number of particles organize in a close-packed formation within the meniscus. Once within the film, the formed assembly moves at nearly the withdrawal speed and rapidly separates from the next assembly. The interplay between hydrodynamic and capillary forces can thus produce periodic and regular structures within the curved meniscus that extends below the withdrawn film. The hydrodynamically-driven assembly documented here is consistent with stripe pattern formations observed experimentally in the so-called thin-film entrainment regime.

physics.flu-dyn↗