I. Abstract of the Paper’s Core Research

This study designs a glycerol‑based, multi‑phase‑transition graphene aerosol ink that leverages solvent evaporation to induce polymer chain coiling and in‑situ gelation of the system, thereby addressing the challenge of spreading and collapse during high‑speed printing at its very source. Comprehensive validation is carried out across ink rheology, line accuracy, 2.5‑μm pillar fabrication, and multi‑material compatibility. The key findings are as follows:

Core Mechanism of Glycerol-Induced Phase Transition in Aerosol Droplets

The ink uses isobutyl acetate and diethylene glycol as the primary volatile solvents, with glycerol serving as a low‑volatility, poorly soluble co‑solvent. During aerosol‑jet delivery to the substrate, the highly volatile solvents continuously evaporate, causing the glycerol concentration to rise and triggering phase separation of the ethyl cellulose polymer, resulting in gelation of the droplets. Upon landing, the ink’s flowability is drastically reduced, effectively suppressing lateral spreading.

Completely resolving the trade-off between frame rate and resolution

When using glycerin-free conventional inks, linewidth variation exceeds 215 μm as the deposition rate increases; by contrast, phase-change inks exhibit only 38 μm of linewidth variation under the same conditions, delivering sharply defined edges during high-speed continuous printing without the need for segmented pauses to allow drying, thereby significantly boosting production efficiency.

Ultra-High Aspect Ratio 2.5D Graphene Microarray

Layer-by-layer continuous printing eliminates the need for intermittent pauses; up to 300 molded micro‑columns can be fabricated, with a base diameter of approximately 100 μm and an optimal aspect ratio of 10. After annealing, the structures remain intact without collapse, enabling the free design of staggered, hollow cylindrical three-dimensional electrodes.

Multi-material universal ink system

The formulation logic can be directly adapted to copper oxide nano‑ink, enabling stable fabrication of ceramic‑based 2.5D microstructures under the same processing conditions, with broad applicability and scalability.

Integrated Verification of Multifunctional Microdevices

A 64-channel high-density microelectrode array is fabricated by in situ printing of micropillar arrays on a planar graphene electrode, integrated with a PMMA dielectric isolation layer. Its surface wettability can be tuned, making it suitable for diverse applications including microfluidics, electrochemical sensing, and neural recording.

II. Complete Preparation Process for Phase-Transition Ink Aerosols

Ink formulation: Graphene powder was dispersed in a mixture of ethyl cellulose and nitrocellulose dispersants, with isobutyl acetate, diethylene glycol, Cyrene, and glycerol used as a composite solvent. The resulting stable dispersion was prepared via ultrasonic stirring for 16 hours; a control group without glycerol was simultaneously prepared using the same base ink formulation.

Aerosol Equipment Commissioning: A 200-μm conical nozzle was used, with the substrate maintained at a constant temperature of 60°C. Carrier gas flow rate and printing speed were adjusted in a stepwise manner to compare the forming differences between two types of ink.

Pattern Printing: Single‑line patterns, multi‑layer stacked three‑dimensional microcolumns, hierarchical partitioned arrays, hollow columnar structures, and planar–microcolumn composite electrodes—multiple sets of samples were prepared.

Annealing and curing: The temperature is ramped up at 2°C/min, held at 70°C to remove solvents, and then subjected to high‑temperature decomposition at 325°C to eliminate organic additives, thereby preserving the pristine graphene conductive network.

Characterization and Testing: Optical profilometry is used to measure line width and pillar height; SEM is employed to examine the three-dimensional morphology; wetting angle measurements and electrochemical performance tests are conducted to verify the functionality of the microdevices.

III. Five Core Advantages of Aerosol Systems Compatible with Phase-Change Inks

High-speed printing meets high precision, so you no longer have to choose between speed and accuracy.

The droplets gel prematurely during the flight phase, eliminating material overflow even at high deposition rates; continuous printing requires no drying time, reducing cycle times by more than 50%.

Ultra-high aspect ratio 2.5D three-dimensional microstructures can be fabricated.

Conventional ink-based multilayer stacks are highly prone to collapse; in this system, the aspect ratio of the fabricated micropillars can reach as high as 10, and both hollow and gradient‑height arrays can be stably fabricated.

Wide process window and low equipment‑setup threshold.

Print speed and airflow fluctuations have a negligible impact on line width, significantly improving dimensional consistency during mass production and reducing the scrap rate.

Universal for multiple types of nanomaterials, with a reusable formulation approach.

Both graphene and metal oxide nanoparticles can be fabricated using a glycerol‑based phase‑transition approach, enabling the development of carbon‑ and ceramic‑based functional devices within a single process.

Compatible with low-temperature substrates; no high-temperature pre-drying required.

It relies on the ink’s intrinsic rheological transformation to control its shape, eliminating the need to raise the substrate temperature and making it compatible with heat‑sensitive flexible substrates such as PET and PI.

IV. Five Core Technological Innovations of This Study

Innovation 1: A Novel Ink Design Approach Based on In-Situ Phase-Transition Gels in the Fog Channel

By leveraging solvent evaporation‑induced phase separation during aerosol jetting, this approach eliminates the need for substrate heating and staged drying to address spreading issues, thereby pioneering an innovative pathway for rheological control of inks.

Innovative 2-Rate – Resolution-Decoupled Quantization Framework

Quantitatively compare the linewidth fluctuations with and without glycerol‑based ink, clarify that glycerol suppresses the Marangoni spreading effect, and establish a high‑speed, high‑precision, universally applicable printing window.

Innovative 3‑axis continuous 2.5D additive manufacturing process

Eliminating the interlayer drying step, hundreds of micro‑pillar layers can be stacked in a single pass, streamlining the 2.5D device‑fabrication process and significantly boosting processing efficiency.

Innovative 4-Gradient Controllable Three-Dimensional Microarray Fabrication Method

The process employs partitioned regulation to control the number of printing layers, enabling the fabrication of graphene microstructures with distinct topographical features on a single substrate, thereby achieving customizable wettability and electrochemical interfaces.

Innovative 5-Carbon/Metal Oxide Dual-Material Universal Formulation Paradigm

The phase-transition mechanism is not limited to graphene; it has been successfully extended to copper oxide inks, providing a standardized approach for the development of various colloidal nanoscale aerosol inks.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: The faster the aerosol printing speed, the more severe the ink spreading, leading to a sharp drop in line accuracy.

✅ Glycerol induces droplet gelation, causing a sharp drop in viscosity upon landing and significantly suppressing lateral spreading, while enabling high-speed printing that still produces narrow, crisp lines.

Challenge 2: In multilayer stacking, the 2.5‑μm microcolumns are highly prone to collapse, necessitating prolonged interlayer drying, which results in extremely low efficiency.

✅ Continuous, uninterrupted stacking fabrication—no need to wait for solvents to evaporate; the microcolumn structures remain intact and undeformed after annealing.

Challenge 3: Conventional shape‑control methods rely on high‑temperature substrates, making flexible thin films prone to thermal deformation.

✅ It relies on the ink’s intrinsic phase transition for shaping, operates at a low substrate temperature of only 60°C, and is compatible with various thermally sensitive flexible substrates.

Challenge 4: Different functional nano‑inks require individually developed shape‑control formulations, resulting in lengthy R&D cycles.

✅ Standardize the design logic for glycerol-based phase transitions, enabling direct reuse of carbon and metal oxide materials and shortening the ink development cycle.

Challenge 5: Even slight variations in printing parameters can lead to dimensional deviations, resulting in poor production‑run consistency.

✅ The phase-change ink process features a wide tolerance window, with minimal impact of air velocity and printing speed variations on line width, thereby enhancing batch‑to‑batch manufacturing stability.

VI. Future Diversified Industrial Application Scenarios

1 High-Density Bio-Microelectrode Array

Graphene microcolumns with a high specific surface area, serving as sensing electrodes for neural signal detection and in vitro organ‑on‑a‑chip applications, enhance the sensitivity of signal acquisition.

2 Microelectrochemical/Biochemical Sensors

Three-dimensional columnar reaction interface, microfluidic detection, and rapid antigen‑screening chip, reducing the detection limit.

3 Current collector for micro-supercapacitors

High-aspect-ratio graphene arrays increase the active surface area, enabling the mass production of lightweight, flexible energy-storage devices.

4 Microfluidic Controllable Wetting Chip

Partitioned gradient microstructures enable precise control of droplet spreading and contraction, supporting single-cell isolation and microfluidic reagent partitioning.

5 High-Throughput R&D Platform for New Materials

Rapid prototyping of two types of three-dimensional functional structures—carbon-based and metal oxide-based—accelerates the screening of ink formulations for sensing and energy storage applications.

Image and Text Guide

• (a) Principle : After deposition, glycerol‑based inks suppress liquid‑phase spreading through polymer phase transformation (gelation), thereby preserving feature integrity and preventing the spreading and resolution loss typical of conventional inks.
• (b,c) Resolution vs Deposition Rate : For glycerol-free inks, the linewidth increases significantly with increasing deposition rate/feed rate (with a range exceeding 215 μm); in contrast, quaternary inks containing glycerol exhibit much smaller variations (with a range of only about 38 μm).
• (d,e) Multi-layer line profile : After heat treatment, the quaternary ink forms higher, narrower features with a high aspect ratio (resolution ~60 μm), significantly outperforming the gly‑free formulation (~100 μm).

• (a) Process The print head moves along a circular path (diameter d), continuously depositing graphene ink and allowing it to dry, thereby building up the support structure layer by layer.
• (b) SEM : Pillars with diameters of 100 μm and 200 μm were post‑annealed at heating rates of 5 °C/min and 2 °C/min, respectively (both subjected to 40 layers).
• Key : A slow heating rate of 2 °C/min preserves the original shape; a rapid heating rate of 5 °C/min causes partial collapse of the pillars. All samples were prepared using a quaternary ink and glycerol‑induced gelation.

• (a,b) Optical Profile : The maximum height of the 40-layer pillars is 54.2 ± 2.6 μm (59 pillars in the image); the top-view and 3D surface plots exhibit geometric consistency.
• (c,d) SEM : Top-down view (scale bar 100 μm) and cross-sectional view (scale bar 50 μm) confirm that the hollow cylindrical structure retains its integrity during subsequent processing.
• Reducing the carrier gas flow rate to 8 sccm enables the printing of hollow cylindrical structures, with material aggregation at the base of the struts resulting from liquid-phase phase transformation (distinct from aerosol overspray).

• A pillar with a nominal diameter of 100 μm, with a base diameter of approximately 105 μm; The aspect ratios of the 50-, 100-, 150-, and 200-layer configurations are approximately 2.4, 4.3, 7.5, and 10.5, respectively. 。
• The diameter of the 300-layer pillars has increased to approximately 160 μm, and the aspect ratio has decreased to about 6.6—under the current printing/drying/curing conditions, an aspect-ratio limit exists.
• Slower heating (1 °C/min) results in a lower overall height but greater uniformity, enabling up to 500 layers; the cured material is denser and exhibits improved mechanical stability.

• (a,b) Electrodes + PMMA dielectric layer : (a) AJP precisely deposits PMMA between the pillars, exposing only the pillar sidewalls for chemical functionalization; (b) The crack in the middle is due to sample preparation cutting and does not reflect the true morphology of the sample.
• (c) Column-free area : Guiding droplet wetting behavior through engineered air gaps (Cassie–Baxter surface regulation).
• (d) Non-uniform column height : Implement a gradient of column height tapering toward the center, without requiring any additional processing steps.

• (a,b) : Electrode array fabrication pathway and printed final product (Kapton, scale bar 2 mm).
• (c) : The surface topography reveals that the central electrode is the lowest—corresponding to different neuronal planes, for neural‑interface monitoring.
• Thanks to its ability to maintain a high aspect ratio in the wet state, it exhibits minimal inter‑pillar overspray and eliminates the need for an additional focused ion beam removal step, enabling an efficient process that supports electrical isolation of electrodes.