藍相液晶(blue phase liquid crystal, BPLC)具有由局部雙扭轉圓柱(double-twist cylinders, DTCs)所構成的三維週期性晶格，展現出高度幾何對稱性與宏觀近光學等向性。不同於具備明確導軸排列與方向偏好之向列型或膽固醇型液晶彈性體能有效產生光致彎曲響應，藍相液晶因其高對稱性，能否將外部光刺激轉化為具方向性的宏觀機械形變，至今仍是一個懸而未決且缺乏深入研究的課題。為此，本研究設計並製備了摻混偶氮苯分子之藍相液晶聚合物網絡薄膜，詳細探討其動態光致彎曲行為，並進一步揭示微觀藍相網絡結構與宏觀異向性形變之間的深層物理機制。
實驗首先透過偏光顯微鏡、反射光譜與科索圖案量測，確認藍相液晶混合物為(110)晶面的BPI相態，並具備三個特徵溫區，分別為：第一特徵溫區(dλBP/dT < 0)、第二特徵溫區(dλBP/dT ≅ 0)及第三特徵溫區(dλBP/dT > 0)。以此為基礎，將藍相液晶樣品分別於此三個溫區進行光聚合，成功製備出於縱向(厚度方向)具有不同結構梯度特徵之藍相液晶聚合物網絡(BPLCN)薄膜。研究發現，於第一及第三特徵溫區聚合之薄膜，在紫外光照射下均展現顯著的光致彎曲，且彎曲方向與光源方向無關，此特性完全不同於傳統向列相與膽固醇相液晶聚合物薄膜「朝向光源彎曲」的行為；反觀於第二特徵溫區聚合之薄膜，則無光致彎曲現象。結果顯示，雖然BPLCN薄膜縱向晶格梯度所對應的最大與最小反射波長差僅有數奈米，但此極微小的結構差異，即可於紫外光驅動下轉換為宏觀的顯著形變。
綜合上述結果，本薄膜獨特的光致彎曲行為歸因於兩大主因：偶氮苯交聯分子光異構化引發的液晶有序結構擾動，以及缺陷線聚合網絡密度差異造成的應變放大效應。紫外光照射時， DTCs內部的CR2分子發生trans cis光異構化，干擾液晶排列並降低秩序參數，進而產生體積膨脹，於光譜上記錄為反射峰紅移(晶格膨脹)。根據等效雙層模型，大晶格側(晶格常數為aL)疏鬆的聚合缺陷網絡能有效緩衝DTC膨脹，傳遞至宏觀晶格的應變較小(ΔaL/aL較小)；反之，小晶格側(晶格常數為aS)的高密度網絡形成較強空間約束，使DTCs膨脹直接轉化為宏觀晶格擴張，產生較大的應變(ΔaS/aS較大)。此「小晶格高膨脹與大晶格低膨脹」的應變不匹配(ΔaS/aS > ΔaL/aL)經層間力學耦合，驅使薄膜向應變較小的大晶格側(凹面)彎曲。
在光致驅動性能方面，BPLCN薄膜於紫外光照射下的最大彎曲角度可達約 90°，顯示其具有顯著的光驅動形變能力。進一步透過分區聚合設計，使薄膜不同區域具有不同的梯度結構與光致形變行為，可實現選擇性及局部彎曲，展現BPLCN薄膜在智慧型材料、光驅動元件及仿生機械等領域之應用潛力。本研究首次展示BPLCN薄膜可實現顯著且可控制的光致彎曲行為，並揭示微小厚度方向兩側結構的微小差異可透過光致異構化效應轉換為顯著的宏觀彎曲形變，為三維液晶光子結構與光驅動軟材料之結合提供新的研究方向。

This study investigates the fabrication and photo-actuated bending behavior of blue phase liquid crystal polymer network (BPLCN) films, along with their underlying deformation mechanism. The phase properties of the BPLC mixture were characterized using polarized optical microscopy, reflection spectroscopy, and Kossel pattern measurements. We identified three characteristic temperature zones from the temperature dependence of the reflection wavelength (dλc/dT < 0, dλc/dT ≅ 0, and dλc/dT > 0). Consequently, BPLCNZ1, BPLCNZ2, and BPLCNZ3 films were obtained via complete photopolymerization at 55.4, 54.8, and 54.5 °C, corresponding to the first, second, and third zones, respectively. The photo-actuated bending behaviors of the films were strongly dictated by the polymerization temperature. The BPLCNZ1 and BPLCNZ3 films demonstrated striking bidirectional bending, reaching maximum angles of ~66° and ~90°, respectively; in contrast, the BPLCNZ2 film remained nearly inactive. Distinct from typical photoinduced bending that relies on the irradiation side, BPLCNZ1 consistently warped toward the top surface, whereas BPLCNZ3 deformed toward the bottom surface, irrespective of the UV exposure side. These findings confirm that the bending direction is primarily ruled by the film’s internal structural asymmetry. Reflection spectroscopy of the BPLCN films in silicone oil confirmed asymmetrical lattice expansion between the film's top and bottom surfaces. The surface with a smaller initial lattice showed greater photoinduced expansion than the larger one, a behavior linked to variations in disclination-line density and local network constraints. This photoinduced deformation was fully reversible under green light irradiation. Moreover, spatially regulating the polymerization temperature produced an S-shaped deformation within a single BPLCN film, validating temperature control as a powerful strategy for spatially controlled photoactuation.

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