Particle-surface Interactions Research Articles

Understanding adsorption behavior of silica nanoparticles over a cellulose surface in an aqueous medium

The suspension and adsorption of silica nanoparticles on a cellulose surface, in an aqueous medium is investigated using Brownian dynamic simulations. The inter particle and particle–surface interactions are modeled within the framework of the DLVO theory. Our analysis predicts the accumulation of negatively charged nanoparticles near a negatively charged surface depending on the Debye screening length of the medium. A crossover from the suspension to the adsorption of negatively charged silica nanoparticles onto a negatively charged cellulose surface has been reported as the screening length (k−1) of the medium increases. The crossover is observed at k−1=100nm, due to the interplay between the nanoparticle–nanoparticle and the nanoparticle–surface interactions. The adsorption behavior of nanoparticles is explained using the potential of mean force analysis. The amount of nanoparticles adsorbed depends on their bulk volume fraction (ϕ) and the screening length of the medium. Further, the effects of electrical potentials of nanoparticle (ΨP) and surface (ΨS) on the adsorption are reported. The data suggests that the adsorption of nanoparticles increases either with increasing ΨP magnitude, or/and, with decreasing ΨS magnitude. The adsorbed particles form a disordered monolayer, and undergo subdiffusive motion. We have also observed a transition from the gas-like structure to the liquid-like structure of nanoparticles in the adsorbed monolayer as their bulk volume fraction increases.

Interaction of a finite‐size particle with the moving lid of a cavity

AbstractThe motion of a solid particle in a lid‐driven cavity is investigated. If the tangential velocity of the lid is large the streamlines are dense near the moving lid and the finite size of a particle can have a profound effect on its trajectory. To assess this effect different particle‐motion models are examined: inertial point particles (Maxey–Riley equation) one‐way coupled to the flow and finite‐size particles the flow around which is fully resolved (two‐way coupling). We compare the corresponding trajectories with those obtained using the particle–surface interaction model originally introduced by Hofmann and Kuhlmann [Phys. Fluids 23, 0721106 (2011)]. The finite‐size effect on the particle's trajectory is quantified and discussed. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Hydrophobic nano-asperities in control of energy barrier during particle–surface interactions

To explain differences in colloidal interactions for spherical hydrophobic particles, a theoretical analysis of the interaction potential was carried out for a model rough particle interacting with a smooth and flat surface in an electrolyte solution. The attractive hydrophobic interaction potential was added to repulsive retarded van der Waals and repulsive electrical double layer interaction potentials. The rough microscopic particles were modeled as spheres decorated with nano-sized hemispherical asperities. Parameters that reflect common flotation separation systems were selected for testing this theoretical model and computation of the energy barrier applicable to particle–surface interactions. It was found that hydrophobic asperities with the radius of only a few nanometers reduced the energy required for particle attachment to a hydrophobic surface by several times. The value of this energy barrier was reduced by as much as two orders of magnitude when the radius of nano-sized asperities increased to a few tens of nanometers. Theoretical analysis also revealed that surface coverage of microscopic particles by nano-sized asperities was not as important as the size of the asperities.

Hydrophobic nano-asperities in control of energy barrier during particle–surface interactions

Hydrophobic nano-asperities in control of energy barrier during particle–surface interactions

Particle Deposition and Removal of Relevance to Wet Processing in Semiconductor Manufacturing

Removal of particulate contaminants from surfaces is a critical area in the processing of wafers to build integrated circuits and is typically done using wet chemical formulations. Strategies for particle removal require an understanding of particle deposition mechanisms. In the first part of this review paper, colloid chemical principles underlying particle deposition on surfaces is discussed. Specifically, the importance of van der Waals and electrical double layer interaction energy on particle–surface interaction is reviewed. This is followed by a description of commonly used particle removal methods in wafer processing, viz., megasonic cleaning, brush cleaning, and nanospray cleaning. The importance of particle deposition conditions used in research on particle removal efficiency is highlighted through a study on the effect of aging.

Hydrophobic nano-asperities in control of energy barrier during particle-surface interactions

Hydrophobic nano-asperities in control of energy barrier during particle-surface interactions

Fabricating bio-inspired micro/nano-particles by polydopamine coating and surface interactions with blood platelets

Although bio-inspired polydopamine (PDA) micro/nano-particles show great promise for biomedical applications, the knowledge on the interactions between micro/nano-particles and platelets is still lacking. Here, we fabricate PDA-coated micro/nano-particles and investigate the platelet–particle surface interactions. Our strategy takes the advantage of facile PDA coating on polystyrene (PS) microsphere to fabricate particles with varied sizes and surface properties, and the chemical reactivity of PDA layers to immobilize fibrinogen and bovine serum albumin to manipulate platelet activation and adhesion. We demonstrate that PS particles activate the platelets in the size-dependent manner, but PDA nanoparticles have slight effect on platelet activation; PS particles promote platelet adhesion while PDA particles reduce platelet adhesion on the patterned surface; Particles interact with platelets through activating the glycoprotein integrin receptor of platelets and providing physical sites for initial platelet adhesion. Our work sheds new light on the interaction between platelets and particles, which provides the basic principle to select biocompatible micro/nano-particles in biomedical field.

Casimir-Polder effect with thermally excited surfaces

We take a closer look at the fundamental Casimir-Polder interaction between quantum particles and dispersive dielectric surfaces with surface polariton or plasmon resonances. Linear response theory shows that in the near field, van der Waals, regime the free energy shift of a particle contains a thermal component that depends exclusively on the population/excitation of the evanescent surface polariton/plasmon modes. Our work makes evident the link between particle surface interaction and near field thermal emission and demonstrates how this can be used to engineer Casimir-Polder forces. We also examine how the exotic effects of surface waves are washed out as the distance from the surface increases. In the case of molecules or excited state atoms, far field approximations result in a classical dipole-dipole interaction which depends on the surface reflectivity and the mean number of photons at the frequency of the atomic/molecular transition. Finally we present numerical results for the CP interaction between Cs atoms and various dielectric surfaces with a single polariton resonance and discuss the implications of temperature and retardation effects for specific spectroscopic experiments.

The critical velocity of rebound determined for sub-micron silver particles with a variable nozzle area impactor

The critical velocity of rebound was determined for spherical silver aerosol particles in the size range of 20–1000nm. A novel instrument, a variable nozzle area impactor, was especially designed for measuring the particle–surface interaction as a function of the particle impact velocity. The experimental results were combined with a numerical model in order to obtain the impact velocities. The experiments were carried out using a plain aluminum collection substrate in the impactor. Our results show that the critical velocity of rebound decreases from 14 to 0.022m/s as the particle size increases from 20 to 1000nm. Furthermore, the critical velocity was found to be proportional to the power of −1.6 of the particle size, instead of the theoretical inverse proportionality. This result is in line with the previous studies for micron-sized particles. In the nanoparticle size range, the obtained values are approximately 3–10 times greater than the recent literature values. This discrepancy can most likely be explained by the different surface materials. All in all, our results give valuable information about the particle–surface interactions in the sub-micron size range.

Diffusivity in multiple scattering systems

We consider random flights of point particles inside n n -dimensional channels of the form R k × B n − k \mathbb {R}^{k}\times \mathbb {B}^{n-k} , where B n − k \mathbb {B}^{n-k} is a ball of radius r r in dimension n − k n-k . The sequence of particle velocities taken immediately after each collision with the boundary of the channel comprise a Markov chain whose transition probabilities operator P P is determined by a choice of (billiard-like) random mechanical model of the particle-surface interaction at the “microscopic” scale. Markov operators obtained in this way are natural, which means, in particular, that (1) the (at the surface) Maxwell-Boltzmann velocity distribution with a given surface temperature, when the surface model contains moving parts, or (2) the so-called Knudsen cosine law, when this model is purely geometric, is the stationary distribution of P P . Our central concern is the relationship between the surface scattering properties encoded in P P and the constant of diffusivity of a Brownian motion obtained by an appropriate limit of the random flight in the channel. We show by a suitable generalization of a central limit theorem of Kipnis and Varadhan how the diffusivity is expressed in terms of the spectrum of P P and compute, in the case of 2 2 -dimensional channels, the exact values of the diffusivity for a class of parametric microscopic surface models of the above geometric type (2).

Characterization of nanoparticle transport through quartz and dolomite gravels by magnetic resonance imaging

AbstractMagnetic resonance imaging (MRI) has tremendous potential for revealing transport processes in engineered and geologic systems. Here, we utilize MRI to image nanoparticle (NP) transport through a saturated coarse-grained system. Commercially available paramagnetically tagged NPs are used; the paramagnetic tag making the NP visible to MRI. NP transport was imaged as NPs migrated through packed columns of quartz and dolomite gravel. Changes in T2-weighted image intensity were calibrated to provide fully quantitative maps of NP concentration at regular time intervals (T2being the spin–spin relaxation time of1H nuclei). Transport of nanoparticles was significantly retarded in dolomite compared to quartz due to electrostatic attraction between nanoparticle and dolomite surfaces. NP concentration profiles were evaluated with the CXTFIT computer package to estimate nanoparticle transport parameters at multiple points along the length of the column. This provided temporally resolved parameters that standard breakthrough curve analysis cannot provide. Particle–surface interaction energy profiles were described through Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. While dispersion coefficients and fast deposition rate constant (kfast) were found to increase with distance, deposition rate constant (k) and collision efficiency (α) were found to decrease with distance. These length-dependant variations have significant scaling-up implications for transport models used to predict NP transport in natural and engineered coarse-grained systems, such as sustainable urban drainage systems and river beds.

Nanophotonic force microscopy: characterizing particle-surface interactions using near-field photonics.

Direct measurements of particle-surface interactions are important for characterizing the stability and behavior of colloidal and nanoparticle suspensions. Current techniques are limited in their ability to measure pico-Newton scale interaction forces on submicrometer particles due to signal detection limits and thermal noise. Here we present a new technique for making measurements in this regime, which we refer to as nanophotonic force microscopy. Using a photonic crystal resonator, we generate a strongly localized region of exponentially decaying, near-field light that allows us to confine small particles close to a surface. From the statistical distribution of the light intensity scattered by the particle we are able to map out the potential well of the trap and directly quantify the repulsive force between the nanoparticle and the surface. As shown in this Letter, our technique is not limited by thermal noise, and therefore, we are able to resolve interaction forces smaller than 1 pN on dielectric particles as small as 100 nm in diameter.

Tuning the particle-surface interactions in aqueous solutions by soft microgel particles.

Due to the softness and deformability, interaction between colloidal surfaces induced by soft particles varies in a more complex way than for solid particles and thus has attracted much attention in recent years. In the present study, we use total internal reflection microscopy (TIRM) to directly measure the interaction between polystyrene (PS) microparticles and a flat glass surface in a poly(N-isopropylacrylamide) (PNIPAM) microgel dispersion with concentration varying from dilute (0.1 wt %) to highly concentrated regime (7.5 wt %). Our result shows that the PS particle-surface interactions mediated by the soft microgels are greatly affected by the particle concentration, the configuration of those microgels adsorbed on the surfaces, and the structure and packing of microgels in bulk solution. With increasing the microgel concentration (Cmicrogel), the interaction between the PS particle and surface turned from bridging attraction to steric repulsion, and then depletion attraction, which were mainly governed by the adsorption amount and configuration of microgels on the two surfaces. By further increasing Cmicrogel to condensed situation, structural force with oscillated energy wells was detected. The variation of interactions induced by the soft microgels was further confirmed by optical imaging. Crystallization of the PS microparticles appeared at moderate Cmicrogel; however, crystallization was hindered at higher Cmicrogel where the microgels are highly packed in the bulk solution. Furthermore, using TIRM, microgel packing with local energy well (0.1-1.0 kBT) at the highly condensed state (7.5 wt %) was resolved from the interaction profiles. Therefore, the shear force and modulus generated by such microgel packing can be determined as ∼0.2 pN and tens of mPa, respectively, which are much weaker than data given by conventional active methods.

Aqueous aggregation and surface deposition processes of engineered superparamagnetic iron oxide nanoparticles for environmental applications.

Engineered, superparamagnetic, iron oxide nanoparticles (IONPs) have significant potential as platform materials for environmental sensing, imaging and remediation due to their unique size, physicochemical and magnetic properties. To this end, controlling the size and surface chemistry of the materials is crucial for such applications in the aqueous phase, and in particular, for porous matrixes with particle-surface interaction considerations. In this study, superparamagnetic, highly monodispersed 8 nm IONPs were synthesized and transferred into water as stable suspensions (remaining monodispersed) by way of an interfacial oleic acid bilayer surface. Once stabilized and characterized, particle-particle and model surface interactions (deposition and release) were quantitatively investigated and described systematically as a function of ionic strength (IS) and type with time-resolved dynamic light scattering (DLS), zeta potential, and real-time quartz crystal microbalance with dissipation monitoring (QCM-D) measurements. The critical coagulation concentration (CCC) for oleic acid bilayer coated iron oxide nanoparticles (OA-IONPs) were determined to be 710 mM for NaCl (matching DLVO predictions) and 10.6 mM for CaCl2, respectively. For all conditions tested, surface deposition kinetics showed stronger, more favorable interactions between OA-IONPs and polystyrene surfaces compared to silica, which is hypothesized to be due to increased particle-surface hydrophobic interactions (when compared to silica surfaces).

Substrate directed self-assembly of anisotropic nanoparticles

We present a molecular dynamics study on the self-assembly of anisotropic nanoparticles—triangles and tetrahedrons on a flat surface. We observe ordered and disordered aggregates of nanoparticles depending on the particle–particle and surface–particle interactions. Anisotropic particles induce directionality in the assembly process. In particular, a cross over from the isotropic (spherical) assembly to the anisotropic (non-spherical) assembly of nanoparticles is identified as their size increases for weak nanoparticle–surface interactions. However, at strong nanoparticle–surface interactions, clusters of nanoparticles grow uniformly on the surface. We present phase diagrams that depict all possible structures of triangles and tetrahedrons depending on their size (L) and the nanoparticle–surface interaction strength (εns). We show a disorder to order transition in the L−εns plane, as L and εns increase.

ChemInform Abstract: Direct Measurements of Particle—Surface Interactions in Aqueous Solutions with Total Internal Reflection Microscopy

AbstractReview: 89 refs.

Flow of nanofluids through porous media: Preserving timber with colloid science

Understanding the flow of particles through accessible paths in timber is important to optimising the timber preservation process. In this paper, we identify inconsistencies between the previously established flow paths in timber for simple liquids, and those for particulate systems. We show that the flow paths of nanofluids are through the rays of Pinus sylvestris (Scots pine) sapwood, then into adjoining tracheids through ruptured cross-field pits with effective pore size of 1.75–3.0μm. We then present data from a custom-designed apparatus, with which we have studied the effect of size, charge and concentration of silica nanoparticles on their flow through pine sapwood. Our results show that particles smaller than 60nm passed well through timber irrespective of their zeta potential. The flow of positively charged particles was significantly reduced when particle diameter exceeded 100nm; whereas negatively charged particles with diameter of 250nm still passed through timber reasonably well, provided the concentration of particles was below 0.5% (w/w). Furthermore, we rationalise such flow data with AFM and sessile drop contact angle measurements, which gauge the interactions between the nanofluids and a functionalised silica surface as a model timber surface. Whilst negatively charged nanofluids showed better wettability on the model surface that the positive nanofluids, the wettability did not show any particle-size dependence. We suggest that such contact angle measurements, performed under quiescent conditions, could not fully predict the flow and deposition of nanofluids through timber, which would be more complex due to the presence of an applied external pressure that could affect inter-particle and particle-surface interactions.

Designing Bioinspired Artificial Cilia to Regulate Particle-Surface Interactions.

Biological cilia play a critical role in a stunning array of vital functions, from enabling marine organisms to trap food and expel fouling agents to facilitating the effective transport of egg cells in mammals. Inspired by the performance of these microscopic, hair-like filaments, researchers are synthesizing artificial cilia for use in lab-on-a-chip devices. There have, however, been few attempts to harness the artificial cilia to regulate the movement of particulates in these devices. Here, we review recent computational studies on the interactions between actuated artificial cilia and microscopic particles, showing that these cilia are effective at transporting both rigid and deformable particles in microchannels. The findings also reveal that these beating filaments can be used to separate microparticles based on their size and stiffness. Importantly, these studies indicate that artificial cilia can be used to prevent fouling by a wide variety of agents because they can expel both passive particulates and active swimmers from the underlying surface. These results can help guide experimental efforts to fully exploit artificial cilia in controlling particle motion within fluid environments.

Collective dynamics of flowing colloids during pore clogging.

Based on direct numerical simulations of the coupled motion of particles and fluid, this study analyzes the collective hydrodynamic and colloidal effects of flowing microparticles during the formation of different 3D clogging patterns at a pore entrance. Simulations of flowing suspensions through a pore with various simulation conditions show that particle concentration and surface interactions play a major role in the occurrence of the bridging phenomenon (simultaneous adhesion of many particles). In the absence of DLVO repulsive forces, plugging is characterized by the temporal reduction of the bulk permeability when increasing the volume fraction of the flowing suspension up to 20%. Under these conditions, different structures of particle aggregates (from cluster to cake plug) are formed at the pore entrance yielding different evolution rates of hydrodynamic resistance to the flow. Taking into account DLVO repulsive forces in simulations for a particle concentration equal to 10%, we observe the transition from dendritic structures (for low repulsion) to dense aggregates (for high repulsion). At high DLVO repulsive forces, the scenario of pore clogging is controlled by the collective behavior of many interacting particles. It leads to the formation of a jamming phase (Wigner glass phase) with transient clusters of interacting particles at the pore entrance. The network of jammed particles collapses when the force chains among the particles are overcome by the flow stress. The build-up and the collapse of the jammed phase at the pore entrance induce temporal permeability fluctuations. According to the relative magnitude of particle-particle and particle-wall interactions, when the jammed phase is disorganized by the flow, the residual force in the network can accelerate particles and lead to particle adhesion at the wall inducing a pore blockage and a rapid reduction of the bulk permeability.

Direct measurements of particle–surface interactions in aqueous solutions with total internal reflection microscopy

Non-covalent intermolecular forces, such as van der Waals, electrostatic, steric, and hydrophobic interactions, have played essential roles in determining the association, aggregation, adhesion and sedimentation processes of colloidal particles, surfactant micelles, and macromolecules, in solutions and biological systems. These interaction forces, however, are normally weak (<pN) and are challenging and difficult to be directly measured by common force techniques. In this feature article, we discuss recent advances in the development of the non-intrusive optical technique of Total Internal Reflection Microscopy (TIRM) for studying the interactions between a single colloidal particle and a flat surface. We begin with a brief overview of quantitative measurements of particle-surface interactions in aqueous solutions, and then show recent developments associated with TIRM for measuring kT-scale interactions between a single particle and surface in the presence of polymer chains, micelles, and colloidal particles with different softness based on our recent work. We also highlight how TIRM can be used to measure particle-surface interactions after the particle and the flat surface are physically adsorbed or grafted with polyelectrolytes, as well as to investigate the non-specific and specific interactions between proteins and protein-carbohydrate in biological systems. Lastly, we conclude with some perspectives on future research efforts in this field.