Colloidal Films Research Articles

Rapid fabrication of colloidal crystal films by spin coating using polymeric particles synthesized by dispersion polymerization

Rapid fabrication of colloidal photonic crystals was successfully carried out by spin coating using polymeric beads. To this end, monodisperse polystyrene (PS) nanospheres were synthesized by dispersion polymerization using alcohol as a reaction medium to prepare coating solution. Transmission of visible light at a specific wavelength could be observed, which is measured by transmittance spectra of coating samples. The transmission intensity of light at specific wavelength could be controlled by adjusting rotation speed or the concentration of coating solution, while peak wavelength could be adjusted by the size of PS nanospheres. Inorganic inverse opal like macroporous silica or titania films were fabricated by diffusion of silica or titania nanoparticles through colloidal crystal film, followed by calcination for removal of PS nanospheres. As a demonstrative application of inverse opal films, photocatalytic decomposition of organic dye was performed under UV light illumination by immersing the macroporous titania film in aqueous solution. The rate constant of decomposition reaction could be estimated from transient data of the dye concentration.

Gold vs. Silver Colloidal Nanoparticle Films for Optimized SERS Detection of Propranolol and Electrochemical-SERS Analyses.

The increasing pollution of surface and groundwater bodies by pharmaceuticals is a general environmental problem requiring routine monitoring. Conventional analytical techniques used to quantify traces of pharmaceuticals are relatively expensive and generally demand long analysis times, associated with difficulties in performing field analyses. Propranolol, a widely used β-blocker, is representative of an emerging class of pharmaceutical pollutants with a noticeable presence in the aquatic environment. In this context, we focused on developing an innovative, highly accessible analytical platform based on self-assembled metal colloidal nanoparticle films for the fast and sensitive detection of propranolol based on Surface Enhanced Raman Spectroscopy (SERS). The ideal nature of the metal used as the active SERS substrate was investigated by comparing silver and gold self-assembled colloidal nanoparticle films, and the improved enhancement observed on the gold substrate was discussed and supported by Density Functional Theory calculations, optical spectra analyses, and Finite-Difference Time-Domain simulations. Next, direct detection of propranolol at low concentrations was demonstrated, reaching the ppb regime. Finally, we showed that the self-assembled gold nanoparticle films could be successfully used as working electrodes in electrochemical-SERS analyses, opening the possibility of implementing them in a wide array of analytical applications and fundamental studies. This study reports for the first time a direct comparison between gold and silver nanoparticle films and, thus, contributes to a more rational design of nanoparticle-based SERS substrates for sensing applications.

High performance NIR photodetector based on Cd(1-x)CuxS colloidal quantum dots thin films

Thin films of Cd(1-x)CuxS (x = 0.0 to 0.05 with interval of 0.01) colloidal quantum dots (CQDs) are employed to develop NIR photodetectors (PDs) with significantly high performance parameters and selectivity. Two very cost effective and easy chemical routes are used to synthesize Cd(1-x)CuxS CQDs and to fabricate the PD devices. The Cd(1-x)CuxS CQDs thin films are primarily characterized by various techniques in order to study the influence of Cu doping on different properties of the films. Further, the impact of doping on device performance under the exposure of laser light of different wavelengths is investigated. The tunability in sensing range from visible (635 nm) to NIR (782 nm) of the PDs with a huge improvement in selectivity and device performance due to the incorporation of the dopant is noticed. The maximum selectivity is observed for device S2 (2% Cu in CdS) with maximum responsivity and external quantum efficiency of ∼39 A/W and ∼6.2 × 103% respectively. Whereas the device S4 (4% Cu in CdS) is found to be the fastest with response times of 102 ms/109 ms, sensitivity of ∼3 × 105%, and detectivity of ∼1 × 1014 cmHz1/2W−1. In present study, device S4shows best optimal performance parameters.

Optical Properties of Slot‐Die Coated Hybrid Colloid/Cellulose‐Nanofibril Thin Films

AbstractCorrelating nanostructure and optical properties of thin hybrid films is the crucial ingredient for designing sustainable applications ranging from structural colors in anticounterfeiting to sensors. Here, the tailoring of the refractive index of hybrid cellulose nanofibril/water‐dispersed colloidal ink thin films is presented. The authors apply scalable, layer‐by‐layer slot‐die coating for preparing the cellulose nanofibril and hybrid thin films. Making use of the mobility of the polymer chains in the colloids upon annealing, the influence of the different colloid sizes and their glass transition temperature on the refractive index of the hybrid material is shown. The complex refractive indices of the thin films are characterized by spectroscopic ellipsometry and correlated to the different nanostructures of the thin films. The authors find that post‐deposition annealing changes the colloidal nanostructure from particulate to agglomerates. Depending on the size of the colloids, imbibition of the colloids into the cellulose nanofibril template is observed. This scalable approach offers new avenues in structural color functional biomaterial hybrid layers.

Effect of Pickering emulsion on the physical properties, microstructure and bioactivity of corn starch/cassia gum composite films

This study aimed to evaluate the effects of anise essential oil Pickering emulsion (AEO-PE) on the corn starch/cassia gum (CS/CG) composite films in terms of mechanical properties, microstructure and bioactivity, to obtain non-polluting food-active packaging composite films that can replace plastic products. The results of scanning electron microscope (SEM) image results demonstrated that AEO-PE with an oil/water phase ratio of 6:4 (AEO-PE-6:4) was evenly distributed within the matrix of the composite films. The results of thermogravimetric analysis (TGA) demonstrated an improvement in the thermal stability of the composite films. The results of water vapor permeability (WVP) showed a significant improvement in the capacity of the composite film to block water vapor. Further, the DPPH and ABTS radical scavenging rates of the composite films significantly increased after adding of AEO-PE emulsion, and an excellent barrier effect on UV light was observed. These results proved that the composite films had good antioxidant activity. It was also found that the combination of the CS/CG films and AEO-PE-6:4 effectively inhibited the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Overall, the incorporation of AEO-PE-6:4 resulted in enhanced antioxidant, antibacterial, mechanical, and barrier properties of the CS/CG composite films. The application of the CS/CG-PE-0.7% film to A. bisporus effectively retarded browning and spoilage and maintained the texture and color of the A. bisporus. This study might provide a theoretical basis for the incorporation of PE into starch hydrophilic colloidal matrix composite films, facilitating the disposal of plastic waste.

Concentration-dependent enhancement of nonlinear optical properties in Ge-Te-Bi nano colloidal solutions

ABSTRACT We have investigated the preparation and nonlinear optical characterization of Ge20Te75Bi5 (GTB) nano colloidal solutions using the z-scan technique for three different concentrations. The transmission spectra of GTB nano colloid films have been investigated. FTIR spectra have been measured to confirm the presence of amines in nano colloidal solutions. Z-scan traces at 78 × 1012 W/cm2 laser intensity were used to study the nonlinearity of the samples. The nonlinear absorption coefficient increases with an increase in the concentration of nano colloids. The reported high nonlinear response is useful for optical limiting applications. The optical limiting behavior is also studied against different concentrations.

Tailored Band Edge Positions by Fractional Ligand Replacement of Nonconductive Colloidal Quantum Dot Films

The tunable band edge position of colloidal quantum dot (CQD) films is a key part of efficient optoelectronic device design of various forms such as photovoltaics, light-emitting diodes, and photodetectors. An accurate estimation of shifts in the band edge position of CQD layers is still considered challenging, especially when the CQD films are nonconductive. Here, we investigate the effect of nonconductive CQD films on photoelectron spectroscopy (PES) and photoelectron yield spectroscopy (PYS). We demonstrate control of systematic band edge positions by fractional ligand replacement of nonconductive CQD film characterized with photoelectron yield spectroscopy and density functional theory calculations. As-synthesized CQDs with insulating oleate ligands were fractionally replaced with trans-3,5-difluorocinnamic acid molecules in a nonpolar solution. The fractionally replaced surface-bound ligands are quantitatively analyzed using 1H and 19F nuclear magnetic resonance (NMR) spectroscopy. We found that the energy levels of nonconducting CQD films shift linearly as a function of the number of bound trans-3,5-difluorocinnamates with specific dipole moments while retaining hydrophobic wettability.

Rupture dynamics of flat colloidal films

Foams, films, and bubbles are ubiquitous in our everyday lives and in processes such as textile dyeing and fermentation. The rupture dynamics of Newtonian soap films is well-studied, especially in the inviscid case. Here we explore the rupture of soap films formed from a non-Newtonian fluid, a colloidal suspension. When these films are thick compared to the length scale of the colloidal particles they are composed of, they rupture in a manner similar to a Newtonian fluid, even at quite high colloidal volume fractions. However, when allowed to thin before rupture to a thickness comparable to the colloidal size, they exhibit exotic instabilities such as wrinkling and folding like a fabric.

The Formation and Transformation of Manganese Oxide Minerals on the Surface of Kaolinite

AbstractThe formation of manganese (Mn) oxides is influenced by environmental conditions and, in some red soils, Mn oxides occur as coatings on the surface of kaolinite particles in the form of colloidal films or fine particles. The present study aimed to explore the types of formation mechanisms of Mn oxide minerals on the surface of kaolinite. Mn oxide minerals synthesized by reducing the Mn in KMnO4 with a divalent Mn salt (MnSO4) were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of various initial molar ratios of Mn2+/Mn7+ (R = 1:0.67, 1:1, 1:2, and 1:4), cationic species (Na+ or Mg2+), synthesis temperatures (30, 60, and 110°C), and amount of added kaolinite (0.25, 0.5, 1.0, 2.0, and 5.0 g) on the formation of Mn oxides were studied. The results showed that Mn oxide mineral types were affected by the initial R value and the background cation. With decreases in the initial R value, the synthesized minerals transformed from cryptomelane to birnessite. The relative mass ratios of kaolinite to Mn oxide were calculated as 1:0.92, 1:0.63, 1:1.15, and 1:1.63. The sodium cation (Na+) had a greater role than Mg2+ in promoting the dissolution–recrystallization of birnessite to cryptomelane. The synthesis temperature had no effect on mineral types, but Mn content increased as temperature increased. When the amount of added kaolinite was increased from 0.25 to 5.0 g, Mn oxide minerals formed gradually and transformed from birnessite to cryptomelane. This work revealed a possible formation process and reaction mechanism on the surface of kaolinite particles in some red soils.

Tuning of Optical Stopband Wavelength and Effective Bandwidth of Gel-Immobilized Colloidal Photonic Crystal Films.

We show that both the optical stopband wavelength and effective bandwidth of films of gel-immobilized loosely packed colloidal photonic crystals can be controlled over a wide range. When the gelation reagent of the charge-stabilized colloidal crystals was photopolymerized under ultraviolet light using different upper- and bottom-light intensities, it resulted in a gel-immobilized colloidal crystal film with a broadened Bragg reflection peak. Moreover, the width of the Bragg peak increased from 30 to 190 nm as the difference between the light intensities increased. Films with wider Bragg peaks exhibited a brighter reflection color because of the superposition of the shifted Bragg reflections. Furthermore, the Bragg wavelength could be varied over a wide range (500-650 nm) while maintaining the same broadened effective bandwidth by varying the swelling solvent concentration. These findings will expand the applicability of colloidal crystals for use in photonic devices and color pigments.

The Study of Mineral Elements Participation in Brewing Products Foam Structure Formation

The article is devoted to the study of the metal ion’s role in the formation of the foam colloidal structure. The nitrogenous compounds prominent role as structuring compounds of the colloidal film on the carbon dioxide bubbles surface is noted. Based on the calculation of the correlation strength between beer samples organic compounds obtained based on light and dark malts, as well as barley and corn as unmalted raw materials, the effect of Ca, Mg, Mn, Co and Na mineral ions on the foam structure was evaluated. It was shown that Ca, Mg, Mn, Na, Co ions take part in the foam structure formation in conjunction with the grain raw materials thiol nitrogen, and Ca, Mg, Mn ions in conjunction with catechins of both grain and hop raw materials. High correlation coefficients between foam resistance and all ions (r-0.991÷0.998), foam resistance, catechins and Co ions (r 0.991), as well as foam resistance and Ca and Mg ions (r -0.987) ensure the elasticity of the foam structure colloidal film.

Evaluation of covalent coupling strategies for immobilizing ligands on silica colloidal crystal films by optical interferometry.

Immobilizing ligands is a crucial part of preparing optical sensors and directly connected to the sensitivity, stability, and other characteristics of sensors. In this work, an ordered porous layer interferometry (OPLI) system that can monitor the covalent coupling process of ligands in real time was developed. Films of silica colloidal crystal (SCC), as optical interference substrates, were surface modified by three different reagents: chloroacetic acid, glutaric anhydride, and carboxymethyl dextran. Staphylococcus aureus protein A (SPA), the ligand, was immobilized on SCC films. The covalent coupling process of SPA and SCC films can be dynamically monitored by the OPLI system. In addition, the three different strategies were evaluated by comparing the efficiency of the sensors prepared by different methods for binding Immunoglobulin G (IgG). The glutaric anhydride-modified sensor offers apparent advantages in terms of bound IgG quantity and affinity. This system provides a simple and intuitive way to determine the efficiency of different covalent coupling strategies. Furthermore, the sensor covalently coupled with SPA also excels in the determination of IgG content in complex systems such as milk. At the same time, the covalent coupling gives the sensor the ability to be stored stably over time.

Enhancement of infrared absorption through a patterned thin film of magnetic field and spin-coating directed self-assembly of gold nanoparticle stabilised ferrofluid emulsion.

Molecular vibration signals were amplified by the gold strip gratings as a result of grating resonances and nearby electric field hotspots. Colloidal gold island films exhibit similar enhancement; however, the uneven geometrical characteristics of these films restrict the tunability of the vibrational enhancement. Infrared absorption is enhanced by regular metallic patterns such as arrays of strips fabricated using a top-down approach such as nanolithography, although this technology is expensive and difficult. The significant infrared absorption may serve as tuneable antenna sensitization to improve the sensor performance. In this article, we present a simple one-step process for fabricating optically sensitive ordered arrays of a gold nanoparticle ferrofluid emulsion in polyvinyl alcohol (PVA) using a magnetic field-directed and spin-coating self-assembly (MDSCSA) process. Techniques such as UV-visible absorption, scanning electron microscopy, and grazing-angle infrared spectroscopy were used to evaluate various parameters associated with the nanostructures. Unlike the gold strips, the chain-like features in the iron oxide nanoparticle arrays were discontinuous. The fabricated chain-like ordered arrays have been shown to increase the local field to enhance the infrared absorption corresponding to the symmetric vibration of the -CH2 (2918 cm-1) group present in PVA by ∼667% at a 45° grazing angle, as the chain thickness (CT) increased by 178%. This scalable and simple method can potentially generate low-cost patterns for antenna sensitisation.

Facile fabrication of chitosan colloidal films with pH-tunable surface hydrophobicity and mechanical properties

Chitosan is an attractive biopolymer with great potential to be applied in biomaterial and food packaging fields. However, this natural polymer is only soluble in acidic condition at which the chitosan is highly hydrophilic in nature, thus limiting its widespread application. Here, we report a facile fabrication of surface hydrophobic chitosan films through pH adjustment, homogenization, and casting of the film-forming suspensions. With an increase in pH above its pKa (6.5), chitosan molecules experienced gradual aggregation due to the decrease of electrostatic repulsion and consequently the rise in hydrogen bonds and hydrophobic effect among and inside chitosan chains. Accordingly, the film water contact angle progressively increased from 81.8° to 93.8° as the pH increased from 6.0 to 7.0, indicating the formation of hydrophobic films at pH values close to neutral. In contrast, the pristine chitosan films at pH 4.0 were completely hydrophilic. FTIR observations confirmed the formation of stronger inter and intramolecular hydrogen bonds in the neutralized chitosan films than in the film at pH 4.0. The analyses of mechanical properties and microstructure further indicated that the mechanical properties and surface microstructure of the films were modulated by the pH adjustment of the chitosan suspensions. Findings from this study are relevant for the development of functional chitosan films with pH-tunable surface wettability.

Colloidal Crystal Films with Narrow Reflection Bands by Hot-Pressing of Polymer-Grafted Silica Particles.

Previous reports have shown that colloidal crystal (CC) films with visible Bragg reflection characteristics can be fabricated by the surface modification of monodisperse silica particles (SiPs) with poly(methyl methacrylate) (PMMA) chains, followed by hot-pressing at 150 °C. However, the reflection bands of the CC films were very broad due to their relative disordering of SiPs. In this report, we attempted to fabricate the CC films using SiPs surface-modified with poly(n-octyl acrylate) (POA) chains by hot-pressing. When the cast films of POA-grafted SiPs were prepared by hot-pressing at 100 °C, the reflection bands were narrow rather than those of CC films of PMMA-grafted SiPs. This can be ascribed to easy disentanglement of POA chains during the hot-pressing process, thereby enabling the formation of well-ordered CC structures. Moreover, the reflection colors of CC films could be easily tuned by controlling the molecular weight of POA chains grafted on the SiP surface.

Optical and topographic characteristics of silver films deposited from a colloidal solution on polyelectrolytes for IgG-FITC fluorescence analysis

Abstract The optimization of the fluorescence enhancement factor of the IgG-FITC conjugate as an immunofluorescent marker, depending on the optical and topographic parameters of the colloidal silver film on the surface of a polystyrene plate for immunoassay, was carried out for the first time, and the factors effecting the enhancement were identified. By means of time-resolved spectroscopy as well as by detection the relative concentrations of IgG-FITC adsorbed on the solid phase with enzyme-linked immunoassay, it was shown that fluorescence enhancement in the presence of silver nanoparticles is a resonance process associated with plasmon effects. The most important parameters correlating with the fluorescence enhancement factor are the optical density value at the wavelength of excitation and emission of the fluorophore. The maximum enhancement factor of 10.2 times was obtained for Ag films with the highest optical density.

Monitoring of silica colloidal crystal-embedded chitosan hydrogel films swelling and its drug release application

The hydrogels, because of their swelling properties in response to the environmental stimulus, are being widely considered for the design of controlled drug release systems. To meet the need for developing effective drug delivery methods, we developed special silica colloidal crystal (SCC)-embedded chitosan hydrogel films. The SCC films served as an interference substrate and drug storage layer, while the chitosan hydrogel served as a cover to regulate the drug release. The optical interferometry was performed to dynamically monitor the volume phase transition of chitosan hydrogel response to pH stimulation. Furthermore, the effects of crosslinking ratio and hydrogel thickness on the swelling properties of chitosan hydrogel were also evaluated. More importantly, the pH-responsive swelling of chitosan hydrogel was used to slowly release indomethacin. This system may provide support for drug delivery studies, therefore further expected to apply in the enhancement of the treatment efficiency of new drug therapies.

Real-Time Monitoring of Curcumin Release with a Lipid-Curcumin-Loaded Silica Colloidal Crystal Film Using Optical Interferometry.

A novel efficacious strategy for real-time monitoring of the release of hydrophobic cargo curcumin (molecule model nutraceuticals) from a lipid-curcumin-loaded silica colloidal crystal (L(Cur)-SCC) film controlled by lipase was developed. Curcumin was dispersed in a proportion of a digestible lipid complex (glycerol trioleate and glycerol tristearate) to prepare a lipid-curcumin complex and then loaded into the SCC film by a capillary to prepare an L(Cur)-SCC film. Lipase-triggered degradation of the digestible lipid complex resulted in curcumin release being tracked in real-time by ordered porous layer interferometry (OPLI). The optical thickness changes (ΔOT) of the L(Cur)-SCC film depend on the mass changes of the lipid-curcumin complex due to the migration of interference fringes caused by the lipase degradation of the digestible lipid complex. Curcumin release from the L(Cur)-SCC film was characterized and analyzed in combination with an ultraviolet-visible spectrophotometer, a nanoparticle size analyzer, and an attenuated total reflection infrared spectrometer. The introduction of a soluble dietary fiber (pectin) into the L(Cur)-SCC film delayed the release rate of curcumin. Furthermore, the real-time sustained release of curcumin from the L(Cur)-SCC film in the simulated digestive fluids was tracked. This study provides an early exploration of the real-time controlled release of lipid-soluble nutraceuticals in the gastrointestinal tract.

Ligands for CsPbBr3 perovskite quantum dots: The stronger the better?

Surface ligands play important roles in synthesis, surface passivation, colloidal stability, and modulation of optoelectronic properties for quantum dots (QDs). It is well known that conventional ligands exhibit weak binding on the surface of perovskite QDs (PQDs), resulting in uncontrolled growth and unsatisfied stability during purification and operation. This impedes the device performance progress and practical applications severely. Stronger ligands anchoring on PQDs tightly and passivating surface defects efficiently have been reported to solve the problems. Herein, we choose a representative strong ligand, dodecylbenzene sulfonic acid (DBSA), to investigate its influence on PQD growth, stability under high-temperature with various solvents and additives, and the possibility of core–shell structure construction. Interestingly, the DBSA capped PQDs exhibit abnormally ripening under above conditions. Besides, a new mechanism for ion migration suppression is proposed based on internal lattice relaxation and inter-particle migration pathway elimination. Although DBSA-PQDs can be purified several times and maintain a high quantum yield, the corresponding light-emitting diodes show poor external quantum efficiency, which might be assigned to the unbalanced colloidal stability and film conductivity. This work indicates that strong ligands provide wider space for PQD modulation and the balance between stability and device performance should also be considered.

Computational Study on the Interaction of Iodide Electrolyte/Dye/TiO2 Interface in Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) represent an emerging and promising candidate as a future renewable energy resource because of their potential low-cost fabrication cost, environmentally friendly, stability, and efficient solar energy conversion1. However, the intrinsic dye/iodide interaction with the dye on the semiconductor surface in understanding the DSSCs mechanism remains unclear2.In this work, three metal-free organic dyes based on D–π–A architecture were designed and computationally investigated for understanding the DSSCs mechanism and improving its efficiency2 - 4. The different donor groups were employed for the comparative study noted as D1Y, D2Y, and D3Y. This computational study mainly aims at determining the effect of the interaction of the iodide/triiodide with the dye on the semiconductor surface using the first-principles calculations (see scheme.1). We investigated the structural and electronic properties of these dyes when standing alone and being adsorbed on the oxide surface with the iodide electrolyte. Our studies revealed that the incorporation of a strong donor unit in D1Y and D 2 Y dyes in combination with iodide electrolytes on the TiO2 surface provides better adsorption and electronic properties in comparison to those from the dye alone on the TiO2 surface. Analysis of density of states (DOS) revealed that the dye with a strong electron-donating group, mainly D1Y and D2Y with an iodide electrolyte on the surface remarkably upshifts the Fermi energy, thereby improving the efficiency of the DSSCs by increasing the open-circuit voltage (Voc). These current findings provide a valuable hint for attaining a deeper understanding of the intrinsic interaction taking place at the electrolyte/dye/TiO2 interface. References O’Regan, B.; Grätzel, M.A Low-Cost High-Efficiency Solar Cell Based on Dye-Sensitized Colloidal TiO2 Films. Nature 1991, 353, 737– 740.Hailu, M. and J.-C. Jiang Phys. Chem. Chem. Phys., 2020, 22, 26410-26418.Hailu, W.-R. Shie, S. Nachimuthu and J.-C. Jiang, ACS Sustain. Chem. Eng., 2017, 5, 8619-8629.Hailu, M. T. Nguyen and J.-C. Jiang, Phys. Chem. Chem. Phys., 2018, 20, 23564-23577. Figure 1