Films Of Colloidal Particles Research Articles

Water-induced reversible deformation materials: Synthesis and UV polymerization of sulfonic based polyacrylates

Reversible deformable materials driven by water or humidity have crucial applications in many areas. A novel sulfonic based cross-linked polyacrylates were prepared by simple UV emulsion copolymerization of functional sulfonic based acrylates with conventional acrylates and epoxy acrylate resins. The structure of sulfonic based acrylates was characterized by FT-ATR,1H-NMR, high-resolution mass spectrometry. The thermal properties, surface morphology and structure of the cured polymers were analyzed. The reversible deformation induced by water and humidity were explored. Based on analysis of surface morphology, XPS and etching experiments, a reasonable deformation mechanism is proposed that the hydrophilic groups migrate to the surface of the oil-in-water colloidal particle film due to the difference in polarity and show a gradient distribution, and hydration of hydrophilic groups results in water absorption and film expansion. Reversible deformation materials driven by water or humidity are of great significance in the field of research on smart material systems.

An Undergraduate Project on the Assembly of Langmuir–Blodgett Films of Colloidal Particles

An Undergraduate Project on the Assembly of Langmuir–Blodgett Films of Colloidal Particles

Tension gradient-driven oil/water interface rapid particle self-assembly and its application in microdroplet motion control

HypothesisA binary mixture was used during injection with one water-miscible component and the other water-immiscible, which can help particles to migrate toward and then self-assemble at the interface. ExperimentsThe ethanol-tetrachloromethane binary mixture was used to verify the self-assembly method, with the diameter of droplets being about 1 mm. As the ethanol diffused into the colloidal solution, the colloidal particles efficiently moved towards and self-assembled on the oil/water interface, while a colloidal particle film with high-coverage was able to rapidly form on the droplet surface even in an ultra-low concentration colloidal solution. The effects of ethanol concentration and particle concentration on self-assembly were investigated. FindingsThe driving force for self-assembly originated from the tension gradient generated by ethanol's concentration gradient at the particle/liquid interfaces, where the concentrations of ethanol and the colloidal solution had significant effects on self-assembly. The simulation and calculations results aligned well with experiments, providing the theoretical basis for this self-assembly method. Further, as-prepared magnetic particle-coated droplets transformed into a non-wetting soft solid, which had long lifetimes and could be precisely moved, coalesced, and transferred in various two-dimensional and three-dimensional liquid environments. Thus, wider applications are facilitated, such as droplet transfer, microreactor and other potential fields.

Bioinspired Production of Noniridescent Structural Colors by Adhesive Melanin-like Particles.

Structural color printing of colloidal photonic films with tunable structures or optical properties is of great importance owing to their practical applications. In this article, we present a general method for the fabrication of colloidal particle films with tailored packing geometries by self-assembly of adhesive melanin-like polydopamine (PDA)-coated particles. The adhesion of particles is controlled by varying the thickness of the PDA coating, making it possible for dip coating of colloidal crystals, partly ordered or amorphous colloidal arrays (ACAs) with a tunable degree of order. We further studied the structural color printing of adhesive particles by infiltration-assisted or standard inkjet printing methods. Compared with bare particles, PDA-coated particles not only allow for control over color brightness/angle dependence of the photonic films but also significantly enhance the color quality of ACAs, both of which are useful for display, anticounterfeiting, or sensing applications. Owing to the inherent strong adhesiveness of PDA to virtually all types of surfaces, this PDA-based methodology can be potentially extended to a diverse range of colloidal particles toward the development of photonic devices.

Self-Assembly of Cu2O Monolayer Colloidal Particle Film Allows the Fabrication of CuO Sensor with Superselectivity for Hydrogen Sulfide.

CuO monolayer colloidal particle films with controllable thickness and homogeneous microstructure were prepared by self-assembly and subsequent calcination based on Cu2O colloidal particles. Large-scale CuO monolayer colloidal particle films have the particle size of 300-500 nm, and CuO colloidal particles are hollow. It was found that such a structure exhibits excellent room-temperature H2S-gas-sensing properties. It not only has high sensing response and excellent selectivity, but also has a low limit of detection of 100 ppb. The sensors exhibit different sensitive characteristics at low and high concentrations of H2S. At low concentration (100-500 ppb), the sensor can be recovered with the increase of gas response, although it takes a longer recovery time at room temperature. At medium concentration (1-100 ppm), although the gas response still increases, the sensor is irreversible at room temperature. When the concentration continues to increase (>100 ppm), the sensor is irreversible at room temperature, and the gas response first increases and then decreases. Two reaction mechanisms are proposed to explain the above-mentioned sensing behavior. More importantly, quasi in situ X-ray photoelectron spectra confirm the existence of CuS. The CuO sensor with room-temperature response and superselectivity will find potential applications in industry, environment, or intelligent electronics.

Structure analysis of layer-by-layer multilayer films of colloidal particles

We have mimicked the layer-by-layer self-assembling process of monodisperse colloidal particles at a solid–liquid interface using the extended random sequential adsorption model of hard spheres. We have studied five multilayer structures of similar thickness, each created at a different single-layer surface coverage. For each multilayer, we have determined its particle volume fraction as a function of distance from the interface. Additionally, we have characterized the film structure in terms of 2D and 3D pair-correlation functions. We have found that the coverage of about 0.3 is optimal for producing a uniform, constant-porosity multilayer in a minimum number of adsorption cycles. The single-layer coverage has also a significant effect on the primary maximum of 2D radial distribution function. In the case of multilayer with the coverage lower than 0.30 the 2D pair-correlation functions of even layers exhibit maxima decreasing with the increase in the layer number. We have verified our theoretical predictions experimentally. We have used fluorescence microscopy to determine the 2D pair-correlation functions for the second, third, and fourth layers of multilayer formed of micron-sized spherical latex particles. We have found a good agreement between our theoretical and experimental results, which confirms the validity of the extended RSA model.

Electrohydrodynamic controlled assembly and fracturing of thin colloidal particle films confined at drop interfaces

Particles can adsorb strongly at liquid interfaces due to capillary forces, which in practice can confine the particles to the interface. Here we investigate the electrohydrodynamic flow driven packing and deformation of colloidal particle layers confined at the surface of liquid drops. The electrohydrodynamic flow has a stagnation point at the drop equator, leading to assembly of particles in a ribbon shaped film. The flow is entirely controlled by the electric field, and we demonstrate that AC fields can be used to induce hydrodynamic “shaking” of the colloidal particle film. We find that the mechanical properties of the film is highly dependent on the particles: monodisperse polystyrene beads form packed granular monolayers which “liquefies” upon shaking, whereas clay mineral particles form cohesive films that fracture upon shaking. The results are expected to be relevant for understanding the mechanics and rheology of particle stabilized emulsions.

Self-Assembly of Large Scale and High-Quality Colloidal Particle Films by Spin-Coating

Colloidal crystal has attracted much attention both in fundamental crystal growth science and optical applications. This paper reports a simple and efficiency spin-coating method to fabricate high ordered colloidal crystals which have specific structures. We used the cleaned glass slide as substrates, the well dispersity 300nm (±1.2%) polystyrene (PS) spheres aqueous suspension (6.6 wt%) to assemble, and obtained highly organized colloidal crystal thin film by controlling spin-coating condition. Mostly, we got the large area plane hexagonal structure at the first layer and tetragonal construction at the second layer. The mechanism for this stacking way was studied. The obtained thin films were demonstrated by Field emission scanning electron microscope (FESEM) and Fast Fourier transform (FFT).

Effects of Substrate Constraint on Crack Pattern Formation in Thin Films of Colloidal Polystyrene Particles

Crack formation and the evolution of stress in drying films of colloidal particles were studied using optical microscopy and a modified cantilever deflection technique, respectively. Drying experiments were performed using polystyrene particles with diameters of 47 ± 10 nm, 100 ± 16 nm, and 274 ± 44 nm that were suspended in water. As the films dried, cracks with a well-defined spacing were observed to form. The crack spacing was found to be independent of the particle size used, but to increase with the film thickness. The characteristic crack spacing was found to vary between 20 and 300 μm for films with thickness values in the range 3-70 μm. Cantilever deflection measurements revealed that the stresses that develop in the film increase with decreasing film thickness (increasing surface-to-volume ratio). The latter observation was interpreted in terms of the effects of a substrate constraint which causes the build up of stresses in the films. This interpretation was confirmed by crack formation experiments that were performed on liquid mercury surfaces in which removal of the substrate constraint prevented crack formation. Experiments were also performed on compliant elastomer surfaces in which the level of constraint was varied by changing the substrate modulus. The cracking length scale was found to increase with decreasing substrate modulus. A simple theory was also developed to describe the substrate modulus dependence of the cracking length scale. These combined experiments and theory provide convincing evidence that substrate constraints are an important factor in driving crack formation in thin colloidal films.

Spin-coating of dilute magnetic colloids in a magnetic field

Spin-coating of colloids is a versatile method in fabricating films of colloidal particles at a short span of time. Controlling key parameters like the rate of rotation, the initial concentration and the nature of the continuum phase is easy to perform experimentally. However, the effects of these parameters are not fully understood yet. To enhance the understanding of the coating process, we study the spin-coating of dilute magnetic col- loids. The coating process is controlled externally by means of a magnetic field and we investigate its effects by studying the morphology of the dried coating obtained after the experiments. Morphological transitions are explained through the mean area and the number density of clusters, together with anisotropy properties. Further, we relate the occupation factor of clusters to the non-planarization conditions observed in this kind of experiments. Introduction. Dispersions of magnetic particles significantly change their behaviour when introduced in a homogeneous magnetic field. The magnetic par- ticles form clusters, which change the overall properties of the dispersion under stresses. In other words, an applied magnetic field can change the rheological prop- erties of magnetic colloids. In this framework, we pour a sample of the dispersion onto a rapidly rotating substrate. We investigate the effects due to the applied field and compare them to the case of zero-field condition. If the continuum phase of the dispersion is a volatile solvent, it evaporates as the rotation continues and leaves a solid coating of colloidal magnetic particles. This process is done with the help of a commercial spin-coater and a Helmholtz pair. The fabrication of magnetic thin film devices is gaining research and commer- cial interests (1, 2). By varying the size of the magnetic particles, their applications can be classified. Among other ways, self assembly of magnetic particles is of par- ticular interest due to lower complexity during the fabrication and comparatively high quality structures (3, 4). Spin-coating of colloidal dispersion has a great advantage in producing resultant morphologies at a short span of time (5-7). Although cluster formation in magnetic colloids has been investigated numer- ically (8-15), the kind of colloidal particles (nano-sized) and the high concentration (typical of ferrofluids) have undergone difficult experimental studies. Lately some groups paid attention to core-shell superparamagnetic particles (micron-sized) at low dilution, much easier to characterize in experiments under constant magnetic fields (16), or under rotating magnetic fields ((17), among others). The main differ- ence of these works from our system is the presence of inertial effects in the fluid, such as a centrifugal force, and the existence of free surface, where the solvent is evaporating.

Rapid fabrication of crystalline films with double layers and dual members by spin-coating method

Ordered colloidal particle films with double layers and dual members could be prepared by stepbystep spincoating method. Monolayer film of larger sized PS or SiO2 colloids was utilized as template to selfassemble second layer of SiO2 colloidal particles with smaller diameter. The size ratio γ of smaller and larger colloidal particles was 0.20—0.56 in the composite films. Larger （L） and smaller （S） dual member colloidal particles formed composite crystalline doublelayer films with multifarious arraymodes, whose structures could be expressed as LSx （here, L represents larger sized particles, S represents smaller colloidal particles, and x represents the stoichiometry of larger and smaller colloidal particles）, and x=1, 2, …, 13. The performance of composite colloidal films were influenced mainly by several factors, including spincoating velocity, spincoating time, viscosity of suspension medium, number density of colloidal suspension, and the wetting properties of substrates, etc.. On the prerequisite of complete wetting between colloidal suspension and substrate, appropriate number density of colloidal suspension, velocity and time of spincoating were the necessary conditions for ordered selfassembling to crystalline film of colloidal particles by spincoating method.

Fabrication, Characterization, and Surface‐Enhanced Raman Activity Study of Silver Coated Gold Nanoparticulate Films

AbstractThis paper reports a study on the preparation of Ag‐clad Au colloidal monolayer films by a combination of colloid self‐assembly and liquid phase microwave high‐pressure technique. Firstly, monodisperse Au nanoparticles prepared by microwave heating method were assembled onto a quartz slide. Then, these Au colloidal particles on the quartz surface acted as seeds for growing the Ag‐clad Au composite particulate films. The obtained particulate films were characterized by UV‐Vis spectra and atomic force microscopy. It was found that the thickness of the shell and thus the size of particles in the composite colloidal films could be controlled by deposition of Ag on the preformed Au colloidal particle film in the microwave reaction system, and such films significantly increased the surface‐enhanced Raman scattering enhancement (SERS) ability compared with Au colloidal particle films. Their strong enhancement ability may mainly stem from relatively large particle consisting of Ag cladding as well as effective coupling among particles in the Ag‐clad Au particle films.

Modeling of Drying in Films of Colloidal Particles

The process of film formation on a solid substrate from polymer colloid dispersion during solvent evaporation has been investigated by means of the Monte Carlo simulation method. Colloid particles are modeled as hard spheres. Time evolution of the colloid density distribution and coverage of the solid substrate are studied. Both density and structure of colloid film is shown to depend strongly on the evaporation rate. At a low evaporation rate, the coexistence of hexagonal and tetragonal domains of dried colloid monolayer has been observed. The results of monolayer structure are in good agreement with the confocal scanning laser microscopy observations of Dullens et al. (2004).

Facile Surface Modification of Colloidal Particles Using Bilayer Surfactant Assemblies: A New Strategy for Electrostatic Complexation in Langmuir−Blodgett Films

Preliminary investigations have recently indicated that interdigitated bilayer assemblies of fatty acid molecules form spontaneously on colloidal silver particle surfaces while such bilayer structures are not observed on planar silver films. In this paper, this problem is probed further through contact angle and quartz crystal microgravimetry measurements of monolayer formation of lauric acid molecules on well-defined hydrophobic monolayers (formed from octadecanethiol chemisorbed on gold films) as a function of solution pH. The repulsive interaction between the ionized carboxylic acid groups in the lauric acid molecules prevents the formation of bilayer assemblies on planar surfaces. However, nanoscale surface curvature of colloidal particles permits interdigitation of the hydrocarbon chains in the bilayers, thereby maximizing the hydrophobic interaction as well as considerably reducing the electrostatic repulsive interactions of the headgroups, leading to stable bilayer assemblies. The strategy based on bilayer formation on colloidal particles is flexible and is used to derivatize colloidal silver particles with carboxylic acid and amine functional groups and thereafter electrostatically immobilize them at the air−hydrosol interface using the conjugate Langmuir monolayer. Good quality multilayer colloidal particle films can be deposited by the Langmuir−Blodgett technique, indicating that the bilayer assemblies on the colloidal particles are quite robust. This novel approach considerably extends the scope for the generation of nanoscale architectures using self-assembly of surface-modified colloidal particles.