Fluolab【JACS】15°C温差精准调控！光编程非接触式热力学超材料，实现高分辨率智能软体机器人新突破
文章标题：Light-Programmable Morphology in Photothermal Polyurethanes Based on Stenhouse Salt as Photothermal Agent
通讯作者：Christopher M. Bates, Craig J. Hawker, Javier Read de Alaniz
文章概要
引言
远程精准递送热量在生物医药、软体机器人以及可穿戴设备等前沿领域展现出巨大的应用潜力。传统光热材料通常依赖于物理掺杂金纳米棒或碳纳米管等外加助剂，但这往往会破坏材料原有的透明度与机械性能，且复杂的空间多步加工极大地限制了图形化的分辨率。为了打破这一瓶颈，加州大学圣芭芭拉分校的科研团队提出了一种颠覆性的单步光刻图案化策略。研究人员巧妙地将供体-受体斯坦豪斯盐发色团直接共价构建到半结晶热塑性聚氨酯的主链中，利用该发色团特有的光化学异构化特性，在无需任何添加剂重新分布的情况下，实现了微米级的高分辨率光编程空间控温与各向异性力学调控。
Figure 1. Photopatterning enables spatially resolved photothermal heating. Top: White light irradiation through a photomask permanently bleaches exposed regions via cyclopentenone rearrangement, preserving photothermal activity in masked areas. Bottom: Subsequent green light irradiation selectively heats the colored (unbleached) regions, while bleached regions remain near ambient temperature (∼25 °C), as visualized by thermal imaging.
主要实验及结论
这种全新设计的核心在于斯坦豪斯盐独特的非平衡态光化学行为。在黑暗条件下，发色团呈现出具有强可见光吸收的深色开环三烯结构，能够高效地进行非辐射弛豫并将光能转化为热能。当暴露在温和加热环境下的白光照中时，材料会发生不可逆的环戊烯酮重排，导致共轭体系彻底断裂，从而永久性地褪色并丧失光热活性。
Figure 2. Stenhouse salt exists in three forms: the colored, switchable ionic triene form (middle) undergoes reversible photoisomerization to the colorless 4,5-cyclopentenone (left); with combined light and heat, irreversible rearrangement produces permanently closed colorless 2,3- and 2,4-cyclopentenone tautomers (right)─the basis for permanent photopatterning under white light.
为了将这种精妙的分子开关转化为宏观功能材料，团队开发出了一种三氟甲磺酸催化的逐步增长聚合新工艺。该工艺成功克服了离子型发色团对传统锡催化剂的毒化效应，实现了大尺寸的高分子量聚氨酯共聚物一锅法放大合成。实验表明，共价骨架集成不仅完美保留了基体高达三百兆帕的杨氏模量和硬段结晶度，还彻底消除了染料聚集与相分离的隐患，显著增强了发色团与聚合物基质之间的热耦合效率。
Figure 3. Acid-catalyzed copolymerization of the Stenhouse salt diol (StS) with a diisocyanate and diol chain extender to form a polyurethane in 10 g scale (white: no Stenhouse salt; magenta: 0.07 wt %; burgundy: 0.4 wt %).
Figure 4. Thermal and mechanical properties of polyurethanes are preserved with incorporation of Stenhouse salts. (a) UV–Vis spectra of polyurethane films (0.2 mm thickness) showing characteristic absorption at λmax = 530 nm that is proportional to chromophore loading. Insets are photographs of films (0.25 mm × 3 mm × 3 mm). (b) DSC traces showing similar melting transitions (_T_m = 50 °C) regardless of chromophore loading, with crystallinity (_X_c) decreasing only slightly from 60 to 54%. (c) All compositions exhibit a three-orders-of-magnitude drop in modulus (E′ > 100 MPa to E′ < 1 MPa) across the melt transition.
在高分辨率光刻测试中，研究人员透过掩膜板对聚氨酯薄膜进行照射，成功在宏观尺度上烙印出清晰度接近一百微米的复杂几何图形乃至可扫描的二维码。随后在均匀的绿色发光二极管连续照射下，未曝光的着色区域在短短一分钟内便迅速升温并跨越了五十摄氏度的熔融转变温度，转变为高弹性的无定形软橡胶状态；而永久褪色的曝光区域则保持在转变温度以下，依然维持着坚硬的半结晶固态。这种由单束光激发的十五摄氏度局部温差，使得同一种材料在拉伸载荷下展现出极其罕见的逐级屈服机械行为，着色区与褪色区交替响应，完美实现了力学超材料的数字化编程。
Figure 5. Direct photopatterning of Stenhouse salt-containing polyurethanes. (a) Schematic of photomask lithography process: melt-processed polyurethane film (∼0.2 mm thickness) was irradiated with a halogen lamp (200 mW cm–2, 45 °C, 15 min) through a photomask, producing permanent patterns where exposed regions bleach irreversibly. (b) Photographs demonstrate patterning versatility with micron-scale resolution.
Figure 6. Spatially resolved photothermal heating. (a) Mean temperature profiles under green LED irradiation (525 nm, 130 mW cm–2) show distinct heating behavior: pristine 0.07 wt % Stenhouse salt containing films heat rapidly above 55 °C (exceeding melting transition indicated by plateau), bleached films show reduced heating (<45 °C), and control films without Stenhouse salt exhibit minimal response. Crystallization exotherm is visible upon light removal. (b) Schematic of a photopatterned film under uniform green-light irradiation: photobleached regions remain below _T_m and retain semicrystalline, stiff character (T < _T_m), while colored regions photothermally heat above _T_m and become amorphous and soft (T > _T_m). (c) Photograph and corresponding thermal image of QR code pattern after 10 s green light irradiation. Colored regions selectively heat (bright in thermal image) while bleached regions remain cool, creating ∼15 °C spatially resolved temperature differential across the 25 mm × 25 mm sample.
Figure 7. Spatial control over the photothermal effect enables the patterning of mechanical properties. (a) Schematic showing patterned materials heated under green light exhibit different moduli related to the presence of semicrystalline or amorphous morphologies in photobleached and nonphotobleached regions, respectively. (b) Tensile measurements of patterned polyurethanes in the presence and absence of green light.
总结及展望
该项研究成功攻克了光热软材料在空间热流控制与工业级聚合物加工相兼容方面的核心挑战。通过将智能有机分子机器与大宗商品聚氨酯完美融合，不仅实现了高分辨率的 persistent 光编程功能，更开辟了无需复杂多层装配即可构建自适应器件的新途径。基于这种不可逆漂白反应的剂量依赖性特征，团队目前正在深入探索利用空间渐变辐照来实现灰度光热梯度的精准调控。这一兼具高力学鲁棒性与空间可控性的设计平台，未来有望在软体机器人智能驱动、仿生自适应结构以及高安全性信息加密等诸多前沿工业领域催生出革命性的应用成果。