Continuous Electrophoretic Deposition and Electrophoretic Mobility of Ligand-Free, Metal Nanoparticles in Liquid Flow

Abstract

Direct current electrophoretic deposition (DC-EPD) of ligand-free metal nanoparticles in a flow-through reactor is studied by analyzing the educt colloid and the outflow of the flow through chamber while the concentration of the colloid and the strength of the electric field is varied. Metal nanoparticles synthesized by pulsed laser ablation in liquid (PLAL) are used to ensure that the colloidal nanoparticle surface is free of any ligands and that the colloid's stability and movement in an electric field is solely influenced by electrostatic forces. Electrophoretic mobility and deposition kinetics of these ligand-free nanoparticles on plain surfaces are examined for different electric field strengths. Additionally, a continuous liquid flow DC-EPD process is presented and optimized regarding deposition rate, colloid stability, and liquid flow rate. The reported parameter window for high deposition rates of nanoparticles without a negative impact on the colloid, allows to define an efficient stationary EPD process suitable for high throughput applications.Electrophoretic deposition (EPD) is a process in which charged colloidal nanoparticles are guided by an applied electric field in order to adsorb suitable particles on an adsorbant substrate. An often-used application is the deposition of nanoparticles to create nano-and microstructures. 1 Electrophoretic deposition generally requires a system containing two electrodes. 2 Charged particles move in liquid in the direction of the oppositely charged electrode. During EPD, electrophoresis of charged particles in solution is followed by adsorption or assembling of particles on the oppositely charged electrode. [2][3][4] This electrode is also the desired product of the EPD-based nanostructuring, e.g. for use as a medical device like a nanostructured neural electrode. 5 EPD is a relatively simple and cost efficient technique. Therefore, it is highly suitable for coatings of a broad range of materials e.g. metals or biomaterials. 5-9 As the applied electric field is directed perpendicularly to the curved surface of a shaped target and the particles follow this direction (with some limitations), EPD is predestined for controlled and fast coating of 3-dimensional materials. 10 Since first experiments in the field of electrophoresis were performed by Bose in 1740 11 the process of EPD was studied by several researchers (which is reviewed elsewhere). 1 The first study concerning the rate of nanoparticle deposition on a substrate was investigated by Hamaker in 1940. 12 Since then EPD has been established as a reliable and promising application technique. [13][14][15] Despite these different studies on the field of EPD there is still a need for a better understanding of the process itself. As a consequence, a suitable model system for EPD is desirable.EPD of nanoparticles is often carried out with a variety of different surfactants or ligands like citrate, polymers or other additives, which may, at least partially, block the particle's surface. 7,16 The approach in this work i...

Perspective of Surfactant‐Free Colloidal Nanoparticles in Heterogeneous Catalysis

“…dressed by many researchers working in the area of pulsed laser ablation in liquids. [50,71,152,153,[235][236][237] Accordingly, this technique is based on applying a homogenous electric field to charged NPs (see Figure 12a) that introduces a directed nanoparticle motion towards the counter electrode, finally resulting in a deposition. [50,71,235] The same principle is also applicable under constant colloid flow.…”

“…[50,71,235] The same principle is also applicable under constant colloid flow. [236] The electrostatic charge of the NPs results from surface oxidation as well as adsorbed ions or ionic surfactants (see chapter 3). [54,129,130,238] Typical applications of EPD are solar cells, [50] batteries [153] and supercapacitors [239] as well as catalyst development [152,235] and performance improvement of certain measurement techniques.…”

“…[131] During electrophoretic deposition of surfactant-free NPs, the initial nanoparticle diameter does not change as annealing steps are being avoided. [153,236] Yet this method requires either catalyst support materials with low impedance or placement of the support material between the electrodes, forcing mass flow through the support. [234] In order to load NPs onto oxides, a second method called electrostatic or dielectrophoretic deposition has been established exploiting the natural electrostatic charge being present in aqueous media on nearly all nanomaterials, represented by their measurable zeta potential (compare Figure 12b and Figure 13a).…”

Kinetically-controlled laser-synthesis of colloidal high-entropy alloy nanoparticles

“…Lasergenerated NP colloids exhibit a high potential for various applications. 24 The NPs can be immobilized easily on conductive [41][42][43][44][45][46][47][48] and non-conductive [49][50][51][52][53][54] substrates and be used, for instance, in additive manufacturing, 48,51 as sensors, 41,54 or in energy conversion and storage. 43,45 For colloids based on polar solvents, an optimization of the deposition process can be achieved by adjusting the static charge on the surfaces of the NPs and the substrate, 52 or by applying an electric eld between the substrate and a counter electrode.…”

Thin films of copper indium selenide fabricated with high atom economy by electrophoretic deposition of nanocrystals under flow

“…Recently there has been a report of combining the two concepts and using EPD to deposit metal nanoparticles in a flow reactor. (Koenen et al, 2015) However, semiconductor film fabrication presents formidable challenges for EPD, and on the commercial scale it has been applied only to insulators and conductors thus far. Semiconductor NCs have been deposited by EPD in batch reactors previously using applied bias typically in the range of hundreds of volts.…”