A research team from the University of Pennsylvania and the University of Notre Dame has published a paper entitled Aerosol-based combinatorial printing of cholesteric liquid crystal elastomers with tunable and pixelated structural colors in the ScienceDirect edition of the journal Matter, marking a groundbreaking advance in the field of printing technology.

Focusing on the advanced preparation technology and application breakthroughs of cholesteric liquid crystal elastomers (CLCEs), the paper corely proposes the Combinatorial Aerosol Printing (CAP) strategy—a multi-ink additive manufacturing method based on Aerosol Jet Printing (AJP). This strategy addresses the key challenges in traditional CLCEs fabrication, such as low resolution, single color output, and poor adaptability to curved surfaces, laying a solid foundation for the multifunctional and high-precision applications of soft photonic materials.

https://www.sciencedirect.com/science/article/abs/pii/S2590238525005387

Core Research Background and Breakthroughs

CLCEs possess a helical nano-lamellar structure, endowing them with unique structural colors and mechanochromic properties (the helical pitch changes upon stretching/compression, enabling reversible color switching). These characteristics make them highly promising for applications in displays, camouflage, sensors and other fields. However, conventional fabrication methods including solution casting, spin coating, and inkjet printing suffer from notable limitations: they are only capable of producing single-color films, yield pixel resolution mostly at the millimeter scale, fail to realize gradient control of color and mechanical properties, and cannot achieve high-precision printing on complex curved surfaces.

In contrast, the CAP technology enables CLCEs printing with a line resolution of ≈15 μm and a thickness of 1.1 μm by real-time regulation of the mixing ratio of multiple aerosolized inks. It supports conformal deposition on 3D curved surfaces with continuously varying curvatures (e.g., human facial surfaces) and simultaneously achieves programmable gradients of both color and Young’s modulus, breaking through multiple limitations of traditional technologies.

The Key Role of CHEMFISH’s LC756

The chiral dopant used in this study—(3R,3aS,6aS)-hexahydrofuro[3,2-b]furan-3,6-diyl bis(4-(4-((4-(acryloyloxy)butoxy)-carbonyloxy)benzoyloxy)benzoate (LC756, 82% purity), supplied by CHEMFISH (Tokyo), is the core functional material enabling the tunability of CLCEs’ structural colors. Its mechanism of action and technical value are embodied in the following aspects:

1. A Core Variable for Structural Color Regulation

The reflection peak wavelength (λ) of CLCEs follows the Bragg condition (λ = n·p·cosθ, where n is the average refractive index, p is the helical pitch, and θ is the incident angle), and the concentration of LC756 directly determines the helical pitch (p). An increase in LC756 concentration reduces the helical pitch, causing a blue shift of the structural color toward shorter wavelengths; a decrease in concentration enlarges the helical pitch, leading to a red shift toward longer wavelengths. This property forms the foundation for precise color regulation.

2. Material Support for Gradient Colors and Pixelation

The core advantage of CAP technology lies in "on-the-fly ink mixing". Precisely adjusting the mixing ratio of two CLCE precursor inks with different LC756 concentrations enables continuous gradient changes in the chiral dopant concentration within a single pixel, thereby generating high-saturation gradient structural colors. Meanwhile, it synchronously modulates the mechanical properties (e.g., Young’s modulus) of the material, providing critical material support for fabricating pixelated, multifunctional CLCEs patterns such as micron-scale colored QR codes and dynamic camouflage patterns.

3. An Important Guarantee for Maintaining Mechanochromic Properties

The chemical structure of LC756 exhibits excellent compatibility with CLCE precursors (e.g., liquid crystal monomer RM257 and nematic liquid crystal 5CB). During its participation in the self-assembly and photopolymerization of CLCEs, it does not damage the stability of the helical structure or the mechanical response characteristics, ensuring that the printed CLCEs retain the reversible mechanochromic ability of traditional materials. This provides performance support for subsequent applications in wearable strain sensors, interactive displays and other scenarios.

Research Significance and Application Prospects

Through the optimization of material formulations (including the development of LC756-compatible inks) and the innovation of printing processes, this technology applies CAP to CLCEs fabrication for the first time, realizing structural color printing with high resolution, gradient tunability and curved surface compatibility. Its potential applications span encrypted displays, biomimetic camouflage, secure data storage, human-machine interfaces and other fields.

As the core chiral dopant, CHEMFISH’s LC756 provides an indispensable material foundation for the core performances of this technology (color tunability and gradient controllability), serving as a key link connecting material formulation and process innovation.

In addition to LC756, related materials supplied by CHEMFISH include RM257, LC242, C6BAPE, 5CB and others, all of which deliver outstanding performance in various research fields.