I. Abstract of the Paper’s Core Research

This study matched a specialized aerosol ink for chemically compatible graphene and carbon nanonewspapers, and developed a dual‑atomization, in‑situ static‑mixing printing system. The system was used to validate two processing approaches—pre‑mixed static proportioning and on‑demand in‑situ dynamic mixing—and to characterize the correlations among compositional features, microstructural morphology, and electrical conductivity. This enabled the fabrication of laterally continuous, functionally graded carbon‑nanomaterial micro‑patterns. The key findings are as follows:

Dual-carbon-based compatible aerosol ink system

A blended solvent system comprising diethylene glycol monomethyl ether, isobutyl acetate, and the green solvent Cyrene was selected. The graphene and carbon nanonetwork ink exhibit colloid‑chemical compatibility, with no delamination or agglomeration. The electrical conductivity of graphene is approximately 20,300 S/m, whereas that of CNO is only about 110 S/m, resulting in a nearly 200‑fold difference in conductive performance between the two materials and providing a broad tunable range.

In-situ real-time mixing mechanism of the mist phase within the nozzle

Two independent ultrasonic atomizers generate two streams of aerosol, which are thoroughly mixed in an integrated helical mixing chamber within the print head. A mass flow controller (MFC) synchronously regulates the carrier gas flow rates of both streams, enabling dynamic adjustment of the graphene/CNO ratio during printing—eliminating the need to change inks or halt production.

Wide-range, precise electrical modulation

With the total mist flow rate held constant and only the ratio of the two ink streams varied, the film’s electrical conductivity can be continuously tuned from 110 to 20,300 S/m, while its sheet resistance spans 54 to 4,580 Ω/□, achieving a control range of two orders of magnitude.

One-dimensional continuous gradient thin-film fabrication

The carrier‑gas ratio is finely tuned every 100 μm along the printing path to fabricate a transversely graded carbon film with a total length of 40 mm; the material exhibits a smooth transition from a low‑conductivity CNO‑only region to a high‑graphene, high‑conductivity region, with the Raman I_D/I_G ratio varying continuously along the length and no abrupt compositional stratification.

The process has strong versatility.

Compatible with a variety of substrates, including glass and PI, and requiring only low‑temperature curing at 325°C during post‑processing; it enables the free design of conductive circuits with uniform composites, linear gradients, or segmented multi‑resistance profiles, making it well suited for the development of RF devices, strain sensors, and electrochemical components.

II. Complete Process Flow for In-Situ Mixing of Multiple Materials to Form Aerosols

Ink preparation: Graphene/ethyl cellulose dispersion ink and bio-based carbon nanonetwork onion ink both use the same compounded solvent to ensure colloidal compatibility.

Equipment Commissioning: Dual ultrasonic atomizers + two independent mass flow controllers; the print head incorporates a helical static mixing structure; nozzle diameter: 200 μm.

Glass slides with substrate pretreatment , the print bed is maintained at a constant 60°C to stabilize solvent evaporation;

Static sample: Fix the ratio of the two carrier gases and print uniform, composite conductive lines.

Dynamic gradient sample: During printing, the graphene feed rate and the CNO carrier gas flow are adjusted while the total flow remains constant.

Hold at 325°C in a tube furnace for 60 minutes. Remove the organic dispersant to achieve film densification.

Electrical and microstructural characterization was performed using a four-point probe resistivity meter, laser confocal microscopy, Raman spectroscopy, and SEM.

III. Multi-Material AJP Five Core Technological Advantages

Adjust ink formulations in real time during printing, eliminating the need to pre‑mix multiple composite inks.

Traditional methods require pre‑mixing dozens of inks at various ratios, whereas this process uses only two sets of stock solutions that are dynamically blended on‑line, significantly reducing consumable usage and sample‑preparation time.

A single continuous lateral gradient along the strike, with no interfacial fault.

In multilayer vapor deposition, the gradient films formed by spin coating are prone to delamination; however, uniform mixing in the gas phase ensures a smooth compositional transition with no distinct interface.

Digital precision and controllability, traffic - Quantitative correspondence of electrical conductivity

Carrier gas flow rate, carbon content, and resistance are used to construct standard calibration curves; the CAD software interfaces with the MFC for automated control, and gradient patterns can be generated with a single click.

Maskless micrometer-scale patterning compatible, conformal printing on curved surfaces

Retaining the aerosol’s non-contact, high-precision advantages, gradient conductive microelectrodes and RF‑tapered circuits are directly fabricated.

A universal low-temperature process for carbon materials, compatible with flexible thermosensitive substrates.

With a curing temperature of only 325°C, PI and PET flexible films remain free from high-temperature deformation, making them well-suited for wearable electronics manufacturing.

IV. Five Core Technological Innovations of This Study

Innovation 1: Built-in helical mixing chamber with a dual-channel in-situ aerosol co‑blending nozzle

The mist-phase real-time mixing structure ensures that the two streams of carbon nanodroplets are fully blended within the nozzle, resulting in uniform composition—unlike post‑printing layer‑by‑layer stacking approaches.

Innovation 2: Graphene/CNO Dual-Carbon-Based Matching Ink Formulation

The solvent and the dispersion system are fully compatible, enabling atomization without agglomeration and resolving the challenges of colloidal incompatibility and printing segregation between two types of carbon materials.

Innovation: A three-order-of-magnitude-wide, electrically tunable control system

By adjusting only two gas flow rates, the film’s electrical conductivity can be continuously tuned over a 130‑fold range, and a comprehensive process‑parameter database has been established.

Innovative Paradigm for the One-Dimensional Long-Range Continuous Functional Gradient Microstructure Fabrication

Achieves a single 40-mm carbon‑film linear gradient composition, with Raman spectra and electrical resistance varying smoothly along the length, free of abrupt defects.

Innovative Digital Rapid Prototyping Solution for 5-Grade Conductive Components

A single system enables the uniform fabrication of devices with homogeneous resistance, graded resistance profiles, and multi‑segment partitioned circuits, significantly shortening the iteration cycles for RF and sensor components.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Traditional composite inks require pre-mixing multiple formulations, leading to cumbersome consumables and inconsistent batch-to-batch performance.

✅ Only two base inks—graphene and CNO—are used, with online dynamic mixing during printing and real-time adjustment of the formulation on demand, eliminating the need for pre-mixed slurry in multiple bottles.

Challenge 2: In multilayer stacked gradient films, interfacial stresses are high, making them prone to cracking and delamination.

✅ The fog-phase material achieves molecular-level uniform co-deposition, with continuous compositional transitions and no distinct interlayer interfaces, resulting in superior mechanical stability.

Challenge 3: Vacuum co-deposition is costly and cannot produce custom localized gradient patterns.

✅ Digital aerosol direct writing enables the creation of gradient conductive regions only in specific areas of the device, while maintaining a fixed resistance elsewhere.

Challenge 4: Single-carbon-material thin films exhibit a narrow tunable resistance range, limiting device design.

✅ Synergistic integration of high- and low-conductivity carbon nanomaterials yields electrical properties spanning 130-fold, covering the full range of resistance values required for sensing and RF applications.

Challenge 5: The gradient‑structure fabrication process is lengthy, with frequent material changes that interrupt printing.

✅ Dual atomization with parallel material feeding, enabling continuous printing throughout the entire process without stopping to change inks, significantly boosting processing efficiency.

VI. Future Diversified Industrial Application Scenarios

1 RF Micro Antenna with Gradient Impedance

Linear-gradient conductive carbon thin film, which modulates electromagnetic wave matching loss, reduces the footprint of RF devices, and is compatible with 5G micro‑terminals.

2 High-Sensitivity Graded Strain Sensing Array

A gradient-resistance conductive circuit, capable of resolving minute deformation ranges, is employed in flexible electronic skin for monitoring human body movements.

3 Microelectrochemical Catalytic Electrode

Gradient carbon components regulate the electron transport rate, optimize the catalytic reaction window, and serve as the core electrode of a micro‑detection chip.

4 On-chip Adjustable Micro-Resistor Networks

The chip integrates gradient carbon conductive traces, replacing discrete resistive components and simplifying MEMS circuit integration.

5 High-Throughput R&D Platform for Carbon-Based Functional Materials

Print a single batch of samples across the entire compositional range to rapidly screen for the optimal conductive/catalytic carbon composite formulation.

Image and Text Guide
 

Figure 1. Single-ink printing benchmark: (a) On the left is a pre‑mixed ink printhead; on the right, a dual‑ink system (Ink 1/Ink 2) where the inks are mixed in situ within an internal helical static mixer and deposited as mixed or gradient samples; (b) The deposition rate increases approximately linearly with carrier gas flow rate (CGFR), with graphene and CNO exhibiting similar slope values and good carrier‑gas matching; (c) Graphene has a conductivity of about 2 × 10⁴ S/m, while CNO exhibits roughly 10² S/m, corresponding to a difference of approximately two orders of magnitude; (d) SEM images reveal dense, continuous stacking of graphene layers; (e) CNO films exhibit numerous interparticle voids and poor particle–particle contact.

Figure 2. Pre‑mixed ink components—performance characterization: (a) Electrical conductivity increases continuously with the graphene mass fraction in the total carbon mixture, ranging from 0 (pure CNO) to 1.00 (pure graphene), and approaches the conductivity of pure graphene when the graphene fraction exceeds ≳0.30; (b) The normalized Raman spectrum shows that, as the graphene content rises, the D‑peak intensity gradually diminishes relative to the G‑peak, with I_D/I_G decreasing from 0.45 to 0.07; (c) Plane‑view SEM of the sample with a mixing ratio of 0.12 reveals spherical CNO particles randomly dispersed between graphene sheets; (d) Cross‑sectional SEM indicates no significant compositional segregation across the thickness direction.

Table 1. Summary of discrete premixed samples: At mixing ratios of 0.00/0.03/0.06/0.09/0.12/0.17/0.25/1.00, the I_D/I_G ratio decreases from 0.45 to 0.07, while the average electrical conductivity increases continuously from 110 S/m to 20,300 S/m, spanning a range of approximately 130-fold.

Figure 3. Multi-material AJP in-situ mixing: (a) Two ultrasonic atomizers nebulize graphene and CNO ink, respectively; the two aerosol streams are mixed in an integrated helical static mixer within the print head and then focused by a sheath gas for deposition; (b) A 5×5 conductivity heatmap (graphene CGFR 3–15 sccm × CNO CGFR 3–15 sccm): along the matrix diagonal—where the component ratio remains constant—the conductivity varies smoothly, whereas along the anti-diagonal—where the composition changes abruptly—the conductivity increases from ~145 S/m to ~1.9×10⁴ S/m, with sheet resistance spanning roughly two orders of magnitude (54–4580 Ω/□); (c) Normalized Raman spectra obtained at a fixed CNO CGFR of 12 sccm while scanning graphene CGFR; the I_D/I_G ratio decreases monotonically as the graphene flow rate rises.

Table 2. Raman I_D/I_G and electrical conductivity of in-situ mixed samples as a function of graphene CGFR: at 3/6/9/12/15 sccm, I_D/I_G decreases from 0.44 to 0.08, while electrical conductivity increases from 167 ± 2 S/m to 7137 ± 79 S/m—trends that are consistent with those observed for pre‑mixed inks (Fig. 2a, Table 1).

Figure 4. Transversely graded functional sample: (a) A 6 mm × 40 mm strip fabricated on a glass substrate, with the left end (x = 0) at 15 sccm CNO / 3 sccm graphene and the right end (x = 40 mm) reversed; (b) Thickness gradually decreases along the length from ~450 nm to ~280 nm; (c) Electrical resistance drops from >2000 Ω to ~50 Ω; (d) Estimated electrical conductivity rises sharply from ~150 S/m over the first 10 mm to ~3000 S/m, then levels off, reaching ~17,000 S/m at x = 39 mm; (e) Raman I_D/I_G ratio decreases along the length from ~0.45 to ~0.1, correlating with the evolution of electrical conductivity. Process parameters: 200 μm tip diameter, stage temperature of 60 °C, sheath gas flow rate of 30 sccm, total carrier gas flow of 18 sccm, feed rate of 5 mm/s, with incremental adjustments of 0.03 sccm every 100 μm, followed by sintering from 70 °C to 325 °C.