Optical examination of structured colloidal dispersions

We present the results from a Small Angle X-ray Scattering (SAXS) study of lateral drying in thin films. The films, initially 10 µm thick, are cast by dip-coating a mica sheet in an aqueous silica dispersion (particle radius 8 nm, volume fraction φs = 0.14). During evaporation, a drying front sweeps across the film. An X-ray beam is focused on a selected spot of the film, and SAXS patterns are recorded at regular time intervals. As the film evaporates, SAXS spectra measure the ordering of particles, their volume fraction, the film thickness and the water content, and a video camera images the solid regions of the film, recognized through their scattering of light. We find that the colloidal dispersion is first concentrated to φs = 0.3, where the silica particles form a gel with repulsive interactions. Then the particles aggregate until they form a cohesive wet solid at φs = 0.68 ± 0.02. Further evaporation from the wet solid leads to evacuation of water from pores of the film, but leaves a residual water fraction φw = 0.16. The whole drying process is completed within three minutes. An important finding is that, in any spot (away from boundaries), the number of particles is conserved throughout this drying process, leading to the formation of a homogeneous deposit. This implies that no flow of particles occurs in our films during drying, a behavior distinct to that encountered in the iconic coffee-stain drying. It is argued that this type of evolution is associated with the formation of a transition region that propagates ahead of the drying front. In this region the gradient of osmotic pressure balances the drag force exerted on the particles by capillary flow toward the liquid-solid front. INTRODUCTIONCoatings are often made through deposition of liquid colloidal dispersions. Common examples are paints, anticorrosion coatings and ceramic coatings. In most cases, the dispersion is applied as a liquid film, and it changes into a solid film as a result of solvent evaporation. A variety of deposition patterns can be obtained, depending on the evaporation profile over the liquid film and on the flows taking place inside the deposit during drying [1][2][3][4][5][6][7]. The two extreme situations are as follows:(a) Homogeneous film formation: in the simplest case, there is no lateral flow through the liquid film, and all volatile components are evaporated locally. The number of particles at each point of the film is conserved throughout the drying process. Therefore the deposition of a uniform liquid colloidal film leads to a final solid film that has homogeneous composition, thickness and microstructure. Relatively homogeneous films can also be obtained through mechanisms where there is a moving liquid-solid boundary, and there is a flow of liquid phase near this boundary [8,9].(b) Coffee-ring: this process has also been extensively studied [1, 2]. In this situation a macroscopic flow throughout the liquid carries nearly all the particles to the fixed edges of the film, where they pack into a dense rim. At the end o...

show abstract

“…Using calibration standards of known φ s we found good agreement with the law expected for a face-centred cubic structure [18][19][20] …”

Section: Changes In Peak Position Width and Heightsupporting

confidence: 72%

Drying Dip-Coated Colloidal Films

Cabane

Sztucki

et al. 2011

Langmuir

View full text Add to dashboard Cite

show abstract

“…[219] A qualitative agreement between theory and experimental data is obvious. Both first (m = 1) and second (m = 2) interference maxima are reproduced and the shift towards shorter wavelengths for increasingly less densely packed architectures as found experimentally is confirmed theoretically.…”

Section: Color Of the Monolayers As A Means To Control The Etching Prmentioning

confidence: 62%

“…The refractive index of the monolayer n mono depends on the refractive index of the polymer material n PS (here: polystyrene), the volume fraction of the colloids ϕ coll and the refractive index of the surrounding medium, n med (here: air), and can be expressed as: [219] ݊ ൌ ݊ ௌ ߮ ݊ ௗ ሺ1 െ ߮ ሻ Using the expression for n mono and taking n med = 1 for air as surrounding medium, an expression for the reflection maxima is obtained:…”

Section: Color Of the Monolayers As A Means To Control The Etching Prmentioning

confidence: 99%

Surface Patterning with Colloidal Monolayers

Vogel

2012

Springer Theses

View full text Add to dashboard Cite

This thesis focuses on the controlled assembly of monodisperse polymer colloids into ordered two-dimensional arrangements. These assemblies, commonly referred to as colloidal monolayers, are subsequently used as masks for the generation of arrays of complex metal nanostructures on solid substrates.The motivation of the research presented here is twofold. First, monolayer crystallization methods were developed to simplify the assembly of colloids and to produce more complex arrangements of colloids in a precise way. Second, various approaches to colloidal lithography are designed with the aim to include novel features or functions to arrays of metal nanostructures.The air/water interface was exploited for the crystallization of colloidal monolayer architectures as it combines a two-dimensional confinement with a high lateral mobility of the colloids that is beneficial for the creation of high long range order. A direct assembly of colloids is presented that provides a cheap, fast and conceptually simple methodology for the preparation of ordered colloidal monolayers. The produced two-dimensional crystals can be transformed into nonclose-packed architectures by a plasma-induced size reduction step, thus providing valuable masks for more sophisticated lithographic processes. Finally, the controlled co-assembly of binary colloidal crystals with defined stoichiometries on a Langmuir trough is introduced and characterized with respect to accessible configurations and size ratios.Several approaches to lithography are presented that aim at introducing different features to colloidal lithography. First, using metal-complex containing latex particles, the synthesis of which is described as well, symmetric arrays of metal nanoparticles can be created by controlled combustion of the organic material of the colloids. The process does not feature an inherent limit in nanoparticle size and is able to produce complex materials as will be demonstrated for FePt alloy particles. Precise control over both size and spacing of the particle array is presented.Second, two lithographic processes are introduced to create sophisticated nanoparticle dimer units consisting of two crescent shaped nanostructures in close proximity; essentially by using a single colloid as mask to generate two structures simultaneously. Strong coupling processes of the parental plasmon resonances of the two objects are observed that are accompanied by high near-field enhancements. A plasmon hybridization model is elaborated to explain all polarization dependent shifts of the resonance positions. Last, a technique to produce laterally patterned, ultra-flat substrates without surface topographies by embedding gold nanoparticles in a silicon dioxide matrix is applied to construct robust and re-usable sensing architectures and to introduce an approach for the nanoscale patterning of solid supported lipid bilayer membranes.

show abstract

“…Comparison with Eq. (9) shows that this enhancement occurs close to the first diffraction zero. Thus the bright ring of light mentioned in Section 1 is more due to the short-range semiordering of the condensation droplets on the window pane than it is to diffraction by individual droplets.…”

Section: Results Of the Model Calculationsmentioning

confidence: 77%

“…x Jo(2kr sin 0)} = NIa(0)S(0), (9) where the quantity in braces is called the scattering structure factor, and where Jo is the zero-order Bessel function. With the exception of the leading factor of unity and the number density a, the structure factor …”

Section: Introduction and Overview Of Correlated Scatteringmentioning

confidence: 99%

Correlated light scattering by a dense distribution of condensation droplets on a window pane

Lock

Chiu

1994

Appl. Opt.

View full text Add to dashboard Cite

An analytical model of the scattering structure factor for an assembly of noninteracting hard disks has recently appeared in the literature [Phys. Rev. A 42, 5978-5989 (1990)]. We employ this model to calculate correlated light scattering by monodispersions and binary mixtures of condensation droplets on a window pane. We find that an area fraction of f 2 0.6 is required for producing the near-forward direction scattering suppression and that a moderately wide polydispersion of droplet sizes is capable of producing the experimentally observed bright ring of colored light.

show abstract

Optical examination of structured colloidal dispersions

Cited by 93 publications

References 4 publications

Drying Dip-Coated Colloidal Films

Drying Dip-Coated Colloidal Films

Surface Patterning with Colloidal Monolayers

Correlated light scattering by a dense distribution of condensation droplets on a window pane

Contact Info

Product

Resources

About