(Nanowerk Spotlight) Developing materials that remain flexible in extreme cold represents one of materials science’s persistent challenges. Standard flexible materials become brittle below freezing temperatures because their molecular structures stiffen or water within them turns to ice. This limitation has blocked progress in cold-environment technologies, from polar research equipment to space exploration systems.
Hydrogels, materials that combine polymer networks with water, are particularly vulnerable to cold. Their high water content makes them excellent for creating flexible sensors and devices at room temperature, but ice crystal formation destroys their useful properties in cold conditions. Previous solutions focused on adding antifreeze compounds, but these weaken the material and leak out over time, or on complex molecular modifications that only work slightly below freezing.
Researchers at Fuzhou University have now developed a hydrogel that maintains flexibility and transparency even in liquid nitrogen at -196 °C. Their approach controls water behavior through precise structural engineering at the nanoscale, rather than chemical additives.
The team combined methyl methacrylate, which repels water, with hydroxyethyl acrylate, which attracts water. These molecules naturally separate during formation, creating a network of channels just 6 nanometers wide. At this scale, water molecules cannot organize into ice crystals because they are physically constrained and forced to interact with the channel walls rather than each other.
a) Schematic of the preparation process and structure of the hydrogel with phase-separated nanochannels. b) Photographs of M10H10 and PHEA hydrogels at different temperatures. c) SAXS curves ofMH and PHEA hydrogels. d) Periodic size and nanochannel diameter fitted by the Teubner-Streymodel through SAXS results. (Image: Reprinted with permission by Wiley-VCH Verlag)
The material’s performance exceeds previous cold-resistant materials by orders of magnitude. After 41 days in liquid nitrogen, it remained transparent and flexible while conventional hydrogels become completely rigid and opaque. At -45 °C, it stretches to 69% of its original length with a strength of 25.3 megapascals (equivalent to about 3,670 pounds per square inch). For comparison, typical hydrogels become brittle and snap at temperatures just below freezing.
When tested as a sensor at -20 °C, the material detected subtle movements and pressure changes with the same sensitivity and response time as room-temperature sensors. It transmitted over 85% of visible light even at very low temperatures, matching the optical clarity of glass. The material also maintained consistent properties when repeatedly stretched and compressed at low temperatures – crucial for real-world applications.
Unlike previous attempts at cold-resistant hydrogels, this material solves several practical problems simultaneously. It resists swelling when exposed to water, maintains stable dimensions and properties over time, and can be manufactured using standard industrial chemicals and processes. The approach works with several different molecular combinations, suggesting a general strategy rather than a single specialized material.
The hydrogel also exhibits “shape-memory” behavior: it can be temporarily deformed when warm, hold that shape when cold, and return to its original form when reheated. This property enables applications in deployable structures and adaptive devices for cold environments.
This development opens new possibilities in extreme-environment technologies. Flexible sensors could monitor the structural health of aircraft at high altitudes where temperatures drop below -50 °C. Medical devices could maintain flexibility during cryogenic procedures. Space equipment could incorporate flexible components without risk of brittleness in the cold vacuum of space.
However, challenges remain before widespread implementation. The manufacturing process needs scaling up while maintaining precise nanoscale control. The material’s long-term durability under repeated temperature cycling requires further testing. Cost considerations will affect which applications become commercially viable first.
The research provides a new framework for creating cold-resistant flexible materials. By controlling structure at the nanoscale rather than relying on chemical additives or complex molecular designs, this approach may extend beyond hydrogels to other materials that need to maintain flexibility in extreme cold.
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