I. Abstract of the Paper’s Core Research

This study uses toluene‑based silver nanoparticle ink as the base material and systematically investigates the effects of cationic and various nonionic surfactants—both in terms of type and concentration—on the ink’s atomization performance, printed morphology, and electrical conductivity. Microscale conductive traces were fabricated on Kapton flexible films, followed by electrical characterization. The key findings are as follows:

Cationic surfactants significantly enhance the overall performance of inks.

AKM-0531 exhibits optimal performance when the cationic surfactant is added at 2 wt.%; the average droplet diameter is significantly reduced, and the porosity of the printed film is markedly decreased. Compared with the pristine ink without a surfactant, the sheet resistance drops by 95%, and the electrical conductivity reaches 2.22 × 10⁷ S/m, matching the level of commercially available high-end silver inks.

Quantitative Regulation Principles of Concentration Gradients

0.5/1/1.5/2 wt.%—four gradient tests: as the surfactant concentration increases, droplet size continuously decreases and line width becomes finer; exceeding 2 wt.% tends to cause excessive overflow, with the optimal formulation determined to be 2 wt.% AKM-0531.

The performance of different surfactants varies significantly.

Nonionic Triton and Span exhibit molding resistivity several times higher than that of cationic inks, while the Capstone system becomes completely nonconductive after molding. Cationic surfactants can simultaneously reduce ink surface tension and suppress nanoparticle agglomeration, delivering optimal atomization continuity.

High-precision micrometer-level circuit patterning capability

The optimal formulation delivers stable printing with an average line width of 7.2 μm; its multilayer stacked structure exhibits a dense cross-section, achieving an effective conductive cross-sectional area of 57% and exhibiting no large‑area void defects. The minimum carrier gas flow rate is only 16 sccm, resulting in reduced consumable usage.

Low-temperature photonic sintering is compatible with flexible substrates.

500W halogen lamp enables rapid curing without the need for a high‑temperature oven; Kapton film remains deformation‑free, making it suitable for mass production of the entire range of flexible printed electronics.

II. Complete Process Flow for Surfactant-Modified Silver Ink Aerosol

Ink Formulation: Silver nanopowder was dispersed in a toluene-based mixed solvent, with AKM-0531 added at gradient concentrations ranging from 0 to 2 wt.%; additionally, four types of 2 wt.% reference inks—Capstone, Triton, and Span—were prepared, and each was thoroughly dispersed through repeated ultrasonic treatment followed by mechanical stirring.

Equipment Commissioning: Optomec M3D aerosol system, 300 μm nozzle, carrier gas flow rate of 26 sccm, sheath gas flow rate of 40 sccm, printing speed of 1.5 mm/min;

Graphical Printing: Standard four-wire resistance test pattern, with uniform four-layer deposition;

Photon sintering: A 500-W halogen lamp positioned 2 cm from the sample achieves low-temperature densification in 1 minute.

Complete characterization: Optical and SEM observations of line width and cross-sectional porosity; four-point probe measurements of electrical resistivity; calibration of droplet size on filter paper discs; and testing of airflow rate limits.

III. Five Key Process Advantages of Aerosol Systems Using Activator-Modified Silver Ink

Electrical conductivity has increased dramatically, and line power consumption has been significantly reduced.

At the same printing thickness, resistivity decreases by 95%, and signal loss in RF antennas and sensor circuits is significantly reduced.

Micron-level ultra-high printing precision, with a minimum line width of just 7.2 μm.

The surfactant reduces the size of atomized droplets, enhancing beam‑focusing performance and making it compatible with Mini LED and micro‑MEMS electrodes.

The ink maintains stable atomization over long periods, and it is resistant to clogging during mass production.

It suppresses the sedimentation and agglomeration of silver particles, ensures nozzle‑free printing for several consecutive hours, and boosts production line utilization.

Low-temperature photonic rapid curing; thermosensitive flexible film compatibility.

No prolonged baking at temperatures above 200°C is required; PET, PI, and flexible textile substrates can all be processed.

Precious-metal ink savings, with reduced carrier-gas consumption.

The carrier gas flow rate required for atomization is significantly reduced, and the combined effects of spot‑on deposition and minimal material spillage further minimize waste of silver nanomaterials.

IV. Five Core Technological Innovations of This Study

Innovation 1: A completely new, optimized system for cationic surfactant‑modified aerosol silver ink.

Quantitative comparison of the effects of multiple surfactants on AJP silver paste reveals the unique dual‑enhancement mechanism of cationic additives.

Innovation 2: Active Agent Concentration – Atomization – Conductive Quantification Correspondence Database

A complete performance gradient curve spanning 0–2 wt.% is established, yielding an optimal 2 wt.% process window that can be directly implemented.

Innovation 3: Elucidation of the Drag-Reduction Mechanism via Fog-Droplet Size Control

Surfactants reduce surface tension and shrink droplet size, leading to a substantial decrease in the porosity of the thin film, thereby elucidating the mechanism behind the enhanced conductivity at the microscopic level.

Innovation 4: A Complete Set of Ink Solutions for Low-Temperature Photonic Sintering

It is compatible with photopolymerization processes, avoids high-temperature damage to flexible substrates, and simplifies the thermal‑treatment equipment on the production line.

Innovative Low-Flow, High-Precision Aerosol Forming Process

Modified inks can achieve stable atomization even under extremely low carrier gas flow rates, balancing line resolution with raw material efficiency.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Conventional silver ink produces large droplets, resulting in porous printed traces with high resistance.

✅ Adding 2 wt.% cationic AKM surfactant reduces droplet size, densifies the film, and lowers resistivity by 95%.

Challenge 2: Ink particles tend to agglomerate, leading to nozzle clogging during prolonged printing and frequent production line shutdowns.

✅ The surfactant enhances the dispersion of nano-silver, suppresses sedimentation, and significantly improves the stability of continuous printing.

Challenge 3: Conventional inks have wide line widths and insufficient precision, making them incompatible with microchip electrodes.

✅ After optimization, the droplet size is reduced, enabling the stable fabrication of 7.2 μm ultra-fine conductive traces to meet the requirements of microdevices.

Challenge 4: High-temperature sintering limits the use of flexible substrates, leading to yellowing and deformation of thin films.

✅ Compatible with photon‑induced instant sintering and low‑temperature forming, ensuring that all types of flexible substrates remain free from thermal damage.

Challenge 5: Conventional inks require a high carrier gas flow rate, leading to significant waste from precious-metal overflow.

✅ Modified inks have a lower atomization threshold, enabling stable deposition even at low air volumes and reducing production costs.

VI. Future Diversified Industrial Application Scenarios

1 Flexible Circuit for Wearable Physiological Sensing

Low-resistance ultra-fine silver wiring, flexible patches for ECG and sweat monitoring—ultrathin and highly sensitive.

2 Mini/Micro LED pixel interconnect micro-wires

Micron‑scale precision electrodes and low‑loss drive circuits for display panels are being manufactured in volume.

3 Miniature RF Antennas and Millimeter-Wave Passive Components

Low-resistance conductive microstrip, lightweight additive manufacturing for compact communication modules.

4 MEMS pressure/electrochemical sensing interdigitated electrodes

A highly dense conductive layer enhances the sensor’s signal-to-noise ratio.

5 High-Throughput R&D Platform for Flexible Electronics in the Laboratory

The modified silver ink process is stable and enables rapid iteration of various flexible circuit prototypes.

Image and Text Guide

• (1) Ink atomization : The ink is atomized to form a fine aerosol mist.
• (2) Mist Flow Transport : The atomized gas flow transports the droplets to the deposition print head.
• (3) Sheath Gas Focusing and Deposition : The annular sheath gas focuses and narrows the jet, depositing it onto the substrate.
• Features Non-contact, additive direct writing maintains nearly constant resolution within 10 mm of the substrate, enabling the fabrication of interconnect traces as narrow as approximately 8 μm.

• (1) Ultrasonic transducer (2) Surface excitation of liquid ink; (4) Capillary standing waves; (3) The combined action of sub‑surface acoustic cavitation bubbles shatters the liquid into droplets.
• (5) Large droplets : Falls back into the container due to gravity; (6) Fine aerosol droplets are carried away by the airflow.
• Parameter Requirements : Ink viscosity should be 0–20 cP (ultrasonic atomization); increased surface tension and shear viscosity will raise the atomization threshold.

• The Silvercon nAg silver nanopowder used has a particle diameter of less than 0.2 μm.
• The material was dispersed in toluene by mixing with a surfactant, followed by ultrasonic treatment (500 W, 30 s × 4 cycles) and mechanical stirring (5 min × 2 cycles). An alcohol-based solvent was then added to prepare an ink with a silver content of 24 wt.%.
• Nanometer-scale particle size ensures that the aerosol droplets can stably carry functional particles during atomization and delivery.

• (a) Line width : The measured average linewidth by SEM is approximately   7.2 μm (Values measured by optical microscopy tend to be overestimated due to overspray.)
• (b) Line height : The average line is approximately   9.8 μm (Standard deviation 0.87 μm).
• Printing parameters: Kapton HN film, deposition at room temperature, four-layer routing; shroud gas flow 40±5 sccm, carrier gas flow 26±4 sccm, scanning speed 1.5 mm/min; photon sintering with a 500 W halogen lamp at a distance of 2 cm for 1 minute.

• The tiny spatter points that escape from the ink flow are by Saffman force Spread of effects.
• Surfactants reduce particle size, widening the overspray footprint, while simultaneously increasing ultrasonic droplet density and decreasing droplet diameter, thereby enhancing pattern uniformity.
• This is the reason for the discrepancy between linewidth SEM and optical measurements, which must be accounted for in cross-sectional analysis.

• Estimated from the lateral cross-section for resistivity calculation Effective conductive area 。
• Through image processing and analysis, the path’s The effective conductive area is only 57% of the width × height footprint. — Due to the porosity of the printing layer (air dispersed within the silver).
• Resistivity is calculated as ρ = R·S/L, where S is the effective cross-sectional area after accounting for any reductions.

• (a) Concentration Test (AKM-0531) : Add   2 wt.%   Reduce the resistivity  95% (S0→S2); 0.5–1.5 wt.% also showed improvements; at 1.5–2 wt.%, the linewidth increased, so higher concentrations were no longer measured.
• (b) Type testing (both at 2 wt.%) : AKM-0531 (D2) has a resistivity four times lower than that of Triton X-100; Span 85 falls somewhere in between; Capstone ink is non-conductive.
• Optimal result :D2 Resistivity of 4.5×10⁻⁸ Ω·m, corresponding to a conductivity of 2.22×10⁷ S/m, is comparable to the best commercially available ink levels.

• Droplets are deposited on filter paper at the minimum carrier gas flow rate, and the diameter of the resulting spots is measured using an optical microscope.
• S0 (no surfactant) The imprint has a diameter of approximately 17.8 μm, S2 (2 wt.%) Reduced to approximately 10.0 μm—higher surfactant concentrations result in smaller droplets.
• Smaller droplets → less air in the printed layer → more uniform structure → lower resistivity (in S2 porous silver, the air volume fraction is approximately 55%).