Colored polymer-reinforced metal-organic framework microparticles with high charge-to-mass ratio for electrophoretic display

Brighter Screens That Sip Power

Most of todayfs phones and laptops rely on glowing screens that drain batteries and can strain our eyes. In contrast, e-readers use "electronic paper" that reflects ambient light, making them easy to read and very energy efficientbut mostly black and white. This paper explores a new class of colorful particles that could bring vivid, fast-changing color to electronic paper while keeping its low power and paper-like look.

Building Color from Crystals

The researchers start with a family of materials called metal-organic frameworks, or MOFs. These are highly porous crystals built from metal atoms linked by organic molecules, like scaffolds made of metal joints and carbon rods. By choosing different metalscopper, iron, nickel, or cobaltand the same organic linker (BTC), they created four kinds of MOF microparticles that are naturally blue, reddish-brown, green, and purple. These tiny crystals are lighter and more colorful than traditional inorganic pigment particles, and their structure and density can be tuned during synthesis, which is important for how they move in a liquid when an electric field is applied.

Giving Particles a Charge-Friendly Jacket

To work in an electrophoretic display, particles must carry a strong and stable electric charge so they respond quickly and do not clump. On their own, the MOF particles had only a weak negative charge. The team solved this by coating each MOF crystal with a very thin layer of a polymer called polyethyleneimine (PEI), which is rich in positively charged nitrogen groups. Rather than forming strong chemical bonds, the PEI chains attach through gentle interactions and hydrogen bonds, like a soft jacket around the crystal. This coating flips the surface charge from slightly negative to strongly positive and boosts the particlesf mobility in an electric field, all while leaving their shape, color, and internal crystal structure essentially unchanged.

Suspending Colors in a Clear, Gentle Liquid

The coated MOF particles then have to be dispersed in a nonpolar oil that will not damage the crystals. The researchers chose isododecane, a low-polarity liquid, and added a special additive (PIBSA) that acts as both a dispersant and a charge-control agent. PIBSA helps keep particles from sticking together by providing steric hindranceits long flexible chains create a buffer zone between particles. The result is a set of stable, vividly colored inks in which the MOF-PEI particles remain evenly suspended for extended periods. The team confirmed the colors with reflectance measurements and mapped them onto standard color charts, showing that the blue, brown, green, and purple tones are distinct and saturated enough for display use.

From Colored Inks to Working Electronic Paper

To demonstrate actual devices, the scientists combined each colored MOF-PEI ink with white titanium dioxide nanoparticles, creating two-color systems such as blue-white and brown-white. These mixtures were sealed between two transparent plates coated with electrodes, forming simple display cells. When a small direct voltage was applied, the positively charged colored particles and the white particles migrated in opposite directions, switching the visible surface from white to color or back again. Tested at a very low field strength, all four color systems showed response times under about two seconds and recovery times under six seconds, which is competitive with many existing color electronic paper approaches. The blue-white and reddish-brownwhite combinations gave the best visual contrast and color separation from white, making them especially promising for readable text and graphics.

Why These Particles Matter

From a practical standpoint, these MOF-based particles offer a rare combination of advantages: strong charge relative to their mass, tunable density close to that of the host liquid, intense and stable colors, and relatively simple, low-cost preparation. Compared with common organic dyes and conventional inorganic pigments, they move faster under weaker electric fields, maintain their color after repeated switching, and can be customized through choice of metal and polymer coating. For a layperson, the bottom line is that this work outlines a credible path toward future color e-paper displays that are more vivid, respond more quickly, and consume very little powerpotentially enabling color-rich e-readers, signage, and low-energy gadgets that remain easy on both batteries and eyes.

Citation: Cheng, J., Qin, M., Wang, W. et al. Colored polymer-reinforced metal-organic framework microparticles with high charge-to-mass ratio for electrophoretic display. Light Sci Appl 15, 122 (2026). https://doi.org/10.1038/s41377-025-02095-3

Keywords: electrophoretic display, electronic paper, metal-organic framework, color e-ink, display materials