Theoretical Consideration on Preparing Silver Particle Films by Adsorbing Nanoparticles from Bulk Colloids to an Air−Water Interface

Abstract

In our previous paper, a method for preparing enormous surface-enhanced Raman scattering (SERS) active substrates through the aggregation of silver particles trapped at an air-water interface was reported. Here, further efforts were devoted to investigate the origin of assembling silver particle films by adsorbing nanoparticles from bulk colloids to the air-water interface. It was revealed that it is thermodynamically favorable for a colloidal particle in bulk colloids to adsorb to the air-water interface; however, a finite sorption barrier between it and the nearby particles usually restrains the adsorption process. When an electrolyte such as KCl, which is commonly used as an activating agent for additional SERS enhancement, was added into silver colloids, it largely reduced the sorption barrier. Thus, silver nanoparticles can break through the sorption barrier, pop up, and be trapped at the air-water interface. The trapped silver particles are more inclined to aggregate at the interface than those in bulk colloids due to the increase of van der Waals forces and the reduction of electrostatic forces. The morphology of the as-prepared silver particle films was characterized by scanning electron microscope, and their SERS activity was tested using NaSCN as a probe molecule. The surface enhancement of the silver particle films is about 1-2 orders of magnitude higher compared with that of silver colloids, because most of the silver particles in the films are in the aggregation form that provides enormous SERS enhancement. Furthermore, the stability of such type of films is much better that of colloid solutions.

Surface-enhanced Raman scattering of silver-gold bimetallic nanostructures with hollow interiors

“…Additionally, the laser was focused ͑approximately 100 m spot size͒ with a fixed focusing distance for all the samples, which was estimated to be 180 m. Figure 1 shows field emission scanning electron microscopy ͑FE-SEM͒ image of the hollow nanostructures on ITO, in which the hollow interiors of the nanostructures can be clearly observed because the center position was darker than the edge, and the surface coverage of the hollow nanostructures can be obtained to be 3.8 particles/ m 2 from the high Meanwhile some aggregates ͑occupying ϳ15%͒ can also be observed, which may be formed at the air-water interface. 30,31 SERS spectra of p-ATP on the silver-gold bimetallic hollow nanostructure with a mean diameter of 100 nm…”

A Universal Approach for the Self‐Assembly of Hydrophilic Nanoparticles into Ordered Monolayer Films at a Toluene/Water Interface

“…[12,13] However, the area of the resultant film was rather small and the particles sparsely distributed on the substrates did not form a continuous thin film. Moreover, it took about two days for the Ag colloidal particles to be trapped to form a film at the interface.…”

“…Moreover, it took about two days for the Ag colloidal particles to be trapped to form a film at the interface. [13] In the present method, ethanol serves as a mediator instead of an inorganic salt and the hydrophilic nanoparticles are rapidly extracted from the solution to fluctuate at the interface. Such an effect has been discussed by considering that ethanol decreases the surface charge of the nanoparticles.…”

Composite interfacial layers containing micro-size and nano-size particles

“…The inter-particle interaction energy can be calculated on the basis of the classical DLVO theory [62], with additional consideration of hydrophobic interaction energy [85] or other non-DLVO forces acting between the particles [6,11,86]. It is supposed that enhanced lateral repulsion between the particles is possible due to electrostatic interaction through the oil phase in a case when the interaction in the aqueous phase is screened by electrolyte [7].…”