Shape Dependent Colloidal Deposition and Detachment (original) (raw)

Self-assembly of colloidal particles on different surfaces

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2009

The self-assembly process of colloidal particles on different surfaces: mica, glass, Ag and Au thin films is presented. The quality of the self-assembled monolayers is dependent on the solid concentration of colloidal particles, roughness of the surface, contact angle of the water droplet and chemically produced surface charges on the substrate. The surfaces parameters where analyzed by contact angle measurements and atomic force microscopy (AFM). The final deposition was characterized by optical and scanning electron microscopy (SEM).

Simulation of surface deposition of colloidal spheres under flow

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004

The deposition kinetics of stable colloidal spheres from dilute dispersions flowing through a model pore in the high surface coverage range has been investigated. After deposition of each particle, the new flow field is calculated by using a flow simulator that solves the Navier-Stokes equations. The results provide both the surface coverage Γ and the hydrodynamic thickness δ h of deposited layer as a function of a "hydrodynamic shadowing" Péclet number Pe hs , which has been defined to be relevant for this process. A first result is that for Pe hs ≤ 1, both the surface coverage Γ and the equivalent hydrodynamic thickness of deposited layer show a definite plateau. In this regime, the plateau value of Γ at high surface coverage as well as deposition kinetics are identical to those given by the random sequential adsorption theory (RSA). A second result is that for Pe hs ≥ 1 both Γ and δ h are decreasing function of flow strength. In addition, although limited simulations have been carried out in that regime, the surface coverage seem to decrease as Pe −1/3 hs , in agreement with both a theoretical approach based on diffusion layer approximation and previous experimental results. This good agreement suggests that the numerical simulation approach described in this paper is valid so that, it could be used to investigate multi-layer deposition and the corresponding porous media permeability damage by introducing an attractive particle-particle potential.

The capture of colloidal particles on surfaces and in porous material: basic principles

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998

The deposition of colloidal particles onto surfaces can be considered a special case of hetero-coagulation. Deposition and detachment kinetics are determined by a combination of colloidal and hydrodynamic factors. For well-defined geometries and for systems in which particle-wall interactions are attractive, the deposition rate can be predicted accurately from first principles. When repulsive interactions are operative, theoretical difficulties arise from a number of sources, such as a coupling between hydrodynamics and electrokinetics, surface charge regulation, and shearinduced modification of configurations of adsorbed polymers. These complications prevent accurate prediction of slow deposition rates. Also, no good a priori models exist to predict detachment rates, although trends can be predicted. Experimental examples will be provided of colloidal particle deposition on flat surfaces in an impinging jet, in which the flow is well defined, and in porous beds consisting of pulp fibers, in which the flow is rather ill defined. Effects of electrolyte and polymers on deposition are discussed.

Capillary assembly of microscale ellipsoidal, cuboidal, and spherical particles at interfaces

Micron-sized anisotropic particles with homogeneous surface properties at a fluid interface can deform the interface due to their shape. The particles thereby create excess interfacial area and interact in order to minimize this area, which lowers the total interfacial energy. We present a systematic investigation of the interface deformations around single ellipsoidal particles and cuboidal particles with rounded edges in the near field for various contact angles and particle aspect ratios. The correlation of these deformations with capillary bond energies---the interaction energies of two particles at contact---quantifies the relation between the interactions and the near-field deformations. We characterize the interactions using effective power laws and investigate how anisotropic particles self-assemble by capillary forces. Interface deformations and particle interactions for cuboidal particles are weaker compared with those of ellipsoidal particles with the same aspect ratios. For both particle shapes, the bound state in side-by-side orientation is most stable, while the interaction in tip-to-side orientation is repulsive. Furthermore, we find capillary attraction between spherical and ellipsoidal particles. Our calculations therefore suggest cluster formation of spherical and ellipsoidal particles, which elucidates the role of spherical particles as stoppers for the growth of worm-like chains of ellipsoidal particles. The interaction between spherical and ellipsoidal particles might also explain the suppression of the ``coffee-ring effect" that has been observed for evaporating droplets with mixtures of spherical and ellipsoidal particles. In general, our calculations of the near-field interactions complement previous calculations in the far field and help to predict colloidal assembly and rheological properties of particle-laden interfaces.

Contact-line speed and morphology in vertical deposition of diluted colloids

Physical Review E, 2009

We report experimental results on the speed of a receding contact line, in a vertical deposition configuration, during the deposition of polystyrene colloidal particles. We study the effects of the initial concentration of the suspension and compare the measured speeds with the corresponding dried deposit. It is observed that multilayer structures are associated with high speeds. This result is explained through a region in the bulk of the suspension where the concentration of particles increases until multilayer is formed depending on the porosity of the previously deposited structures.

Capillary Assembly of Colloids: Interactions on Planar and Curved Interfaces

Annual Review of Condensed Matter Physics

In directed assembly, small building blocks are assembled into an organized structures under the influence of guiding fields. Capillary interactions provide a versatile route for structure formation. Colloids adsorbed on fluid interfaces distort the interface, which creates an associated energy field. When neighboring distortions overlap, colloids interact to minimize interfacial area. Contact line pinning, particle shape and surface chemistry play important roles in structure formation. Interface curvature acts like an external field; particles migrate and assemble in patterns dictated by curvature gradients. We review basic analysis and recent findings in this rapidly evolving literature. Understanding the roles of assembly is essential for tuning the mechanical, physical, and optical properties of the structure.

Spontaneous Pattern Formation by Dip Coating of Colloidal Suspensions on Homogeneous Surfaces

Langmuir, 2007

We study the slow withdrawal of a partially wet vertical plate at velocity U from a suspension of well-wet particles. Periodic horizontal striped assemblies form spontaneously at the three-phase contact line on energetically uniform surfaces. Stripe width and spacing depend on the withdrawal velocity U relative to a transition velocity U t. Thick stripes separated by large spaces form for U < U t. For U > U t , thin stripes separated by small spaces form. The stripe spacing is reduced by an order of magnitude and varies weakly with U until a maximum velocity is reached at which the stripes fail to form. A partially wet surface can entrain a meniscus. For U < U t , the meniscus forms a finite contact angle wedge with a pinned contact line. As the plate moves upward, it stretches the meniscus until it becomes too heavy to be retained by the wet, porous network provided by the particles at the contact line. The contact line then jumps backward to find a new equilibrium location, and the process begins anew. For U > U t , we infer that a film of thickness h is entrained above the meniscus. When h is smaller than the particle diameter D, particles aggregate where the entrained film thickens to match up to the wetting meniscus. When an entrained particle becomes exposed to air by evaporation, it becomes the new pinning site from which the next film is entrained. The film thickness h increases with U; at some velocity, h becomes comparable to D. Particles flow into the film and deposit there in a disordered manner. A diagram summarizing particle deposition is developed as a function of D, U, and h.

Effects of Particle Shape on Growth Dynamics at Edges of Evaporating Drops of Colloidal Suspensions

Physical Review Letters, 2013

We study the influence of particle shape on growth processes at the edges of evaporating drops. Aqueous suspensions of colloidal particles evaporate on glass slides, and convective flows during evaporation carry particles from drop center to drop edge, where they accumulate. The resulting particle deposits grow inhomogeneously from the edge in two-dimensions, and the deposition front, or growth line, varies spatio-temporally. Measurements of the fluctuations of the deposition front during evaporation enable us to identify distinct growth processes that depend strongly on particle shape. Sphere deposition exhibits a classic Poisson like growth process; deposition of slightly anisotropic particles, however, belongs to the Kardar-Parisi-Zhang (KPZ) universality class, and deposition of highly anisotropic ellipsoids appears to belong to a third universality class, characterized by KPZ fluctuations in the presence of quenched disorder.

Impact of the colloidal state on the oriented attachment growth mechanism

Nanoscale, 2010

In the last five years, several excellent reviews about oriented attachment (OA) have evidenced the advances achieved in this research area, detailing the growth mechanism and the kinetic models. The main focus of this review is to examine the dependence of the OA mechanism on the colloidal state and to demonstrate how the colloidal state modifies the OA mechanism. Basically, we can define two main possible approaches to achieve self-organization or mutual orientation of adjacent nanocrystals. One is the effective collision of particles with mutual orientation controlled by the number of collisions. This type of growth occurs in a well dispersed colloidal suspension and results in a statistical growth process. The second way is through coalescence induced by particle rotation. This mechanism must be dominant in a weakly flocculated colloidal state in which there is significant interaction among particles. This type of process leads to the formation of complex structures.

Role of Surface Roughness in Chemical Detachment of Colloids Deposited at Primary Energy Minima

Vadose Zone Journal, 2012

This study theore cally and experimentally examined eff ects of surface roughness on detachment of colloids deposited under favorable chemical condi ons on reduc on of solu on ionic strength. A superposi on approach based on elemental geometric models was developed to es mate varia on of Derjaguin-Landau-Verwey-Overbeek (DLVO) interac on energies between a colloid and a rough surface under diff erent solu on chemistries. Theore cal analysis showed that most colloids a ached at rough surfaces via primaryminimum associa on are irreversible on reduc on of solu on ionic strength because primary minima are deeper and the detachment energy barriers are greater at lower ionic strength. A frac on of colloids ini ally a ached at ps of nanoscale protruding asperi es, however, will detach from a rough surface at low ionic strength because the net force acting on the colloids can become repulsive (i.e., calculated DLVO interac on energy curves show monotonic decreases of interac on energies with separa on distance at low ionic strength). Column experiments were conducted with 1156-nm polystyrene latex par cles and rough sand (300-355-μm diameter) to examine the detachment of colloids ini ally deposited at primary minima. Experimental results confi rmed that a frac on of colloids are released at low ionic strengths. Our theore cal and experimental results are consistent with literature observa ons, adding convincing evidence to challenge the usual belief that colloids a ached at primary minima are irreversible on reduc on of solu on ionic strength. Although the importance of surface heterogeneity on colloid deposi on has been widely recognized, our study implies that surface heterogeneity also plays a cri cal role in colloid detachment under both favorable and unfavorable condi ons.