Studies on Ionic Polymer Membranes for Improvement of Electromechanical Performance in Ionic Polymer Actuators

Abstract

본 연구에서는 여러 형태의 이온 고분자 막을 제조하여 이를 액추에이터에 적용하였을 때에 액추에이터의 전자기계적 성능을 향상시킬 수 있는 방법을 제시하였다. 본 연구에서 제조된 이온 고분자 막 및 그 액추에이터들은 변위, 반응 속도 및 발생되는 힘에서 독특하면서도 우수한 특성을 나타내었다. 또한, 기존 Nafion이온 고분자 막에서 발견되던 치명적인 단점들 또한 없거나 적은 편으로, 이러한 결과를 통해 이온 고분자 액추에이터의 실질적이고 구체적인 응용을 기대할 수 있다.

1장에서는 이온 고분자 액추에이터의 구조 및 작동 메커니즘에 대하여 서술하고 있다. 이온 고분자 액추에이터의 작동 원리에서 이온 고분자 막이 액추에이터의 성능 개선에 가장 중요한 부분을 차지하고 있으므로 가장 유명한 이온 고분자인 Nafion을 예로 설명하였으며, Nafion이 가지는 한계점을 극복하기 위해 진행된 연구들을 통해 본 연구의 목표와 의미를 부여하고 있다.

2장에서는 음이온 교환 고분자를 이용한 이온 고분자 액추에이터를 제작하였다. Ether 결합으로 연결된 폴리벤지미다졸 고분자를 간단한 메틸화 과정을 거쳐 부분적으로 메틸화시키고 이온 전도도의 조절을 위햐여 음이온 교환 과정을 수행하였다. 음이온이 가지는 느린 이온 확산 속도에 따른 낮은 이온 전도도를 나타냈으나, 제작된 이온 고분자 액추에이터에서는 상대적으로 낮은 변위임에도 불구하고 사용된 전하 대비 높은 힘을 만들 수 있는 점을 확인하였다.

3장에서는 나노 구조를 가지는 술폰화된 스티렌계 5블록 공중합체와 술폰화된 산화 그래핀을 이용하여 고분자 나노복합체를 제조하였다. 이 고분자 나노복합체에서는 기존 Nafion 고분자에 비해 더 큰 이온 교환 영역을 가지고 있어 이온성 액체를 이용하여 공기 중에서 재현성이 높은 이온 고분자 액추에이터 제작이 가능하였다. 고분자 나노복합체를 이용한 액추에이터는 공기 중에서도 큰 변위와 빠른 초기 변형률을 확인하였다.

4장에서는 무기물을 이용한 복합체가 아닌 프탈로시아닌계 유기 물질을 이용하여 고분자 나노복합체를 제조하였다. 술폰화된 폴리술폰계 고분자와 술폰화된 프탈로시아닌계 유기 화합물을 사용한 이온 고분자 액추에이터에서 이온 전도도나 기계적 안정성이 우수함을 확인하였고, 또한 액추에이터 성능에서도 큰 변위, 빠른 초기 반응 속도 및 높은 힘 밀도를 가지고 있어 우수한 성능을 보이는 것을 확인하였다.|This thesis investigates ionic polymer membranes in ionic polymer actuators. Different types of ionic polymer membranes were developed for improvement of electromechanical performance in ionic polymer actuators. Ionic polymer actuators fabricated with those ionic polymers exhibit high and unique performance in the aspect of displacement, response rate, and force generation. Furthermore, they show less or no fatal drawbacks of typical ionic polymer actuators with Nafion membranes. These results are hopeful for practical and specific applications of ionic polymer actuators.

In Chapter 1, structure and actuation mechanism of ionic polymer actuators are described. It is obvious that ionic polymer membrane is most important part for enhancement of actuation performance due to their actuation mechanism. Therefore, the explanation is concentrated on ionic polymer and Nafion, the most popular ionic polymer for actuator. Because of the critical disadvantages of Nafion, there have been many researches to replace Nafion membrane, which is related to the aim and meaning of this study.

In Chapter 2, anion-conducting polymer for the use of ionic polymer actuators is suggested. Partially methylated ether-linked polybenzimidazole (PBI-OO) was prepared with simple methylation process and anion exchange process to control of ionic conductivity. Despite the much lower ionic conductivity due to slow ion diffusion of anion species, ionic polymer actuators with methylated PBI-OO membranes exhibited acceptable displacement with no back relaxation and large force generation with lower consumption of electrical charge.

In Chapter 3, nanocomposite polymer is fabricated with nanostructured block copolymer and functionalized inorganic filler. Ionic polymer membrane based on sulfonated styrenic pentablock copolymer (SSPB) and sulfonated graphene oxide (sGO) shows much larger ionic domain size than typical Nafion membrane. This structure is favorable for the impregnation of ionic liquid (IL) to make reproducible ionic polymer actuators in ambient condition. SSPB/sGO/IL actuators revealed excellent electromechanical performance with large deformation, initial strain rate, and charge-specific displacement. Furthermore, ion transport behavior in the polymer is suggested by tracking ion species during actuation.

In Chapter 4, another type of nanocomposite polymer is described. Instead of typical inorganic fillers, Copper(II) phthalocyanine tetrasulfonic acid (CuPCSA) is introduced as ion-conducting filler in sulfonated poly(arylene ether sulfone) polymer matrix. Ionic polymer actuator with SPAES/CuPCSA membrane shows not only outstanding membrane properties such as ion conductivity and mechanical robustness but also remarkable actuation performance in the aspect of large displacement, fast initial response rate, and high power density.; This thesis investigates ionic polymer membranes in ionic polymer actuators. Different types of ionic polymer membranes were developed for improvement of electromechanical performance in ionic polymer actuators. Ionic polymer actuators fabricated with those ionic polymers exhibit high and unique performance in the aspect of displacement, response rate, and force generation. Furthermore, they show less or no fatal drawbacks of typical ionic polymer actuators with Nafion membranes. These results are hopeful for practical and specific applications of ionic polymer actuators.

In Chapter 1, structure and actuation mechanism of ionic polymer actuators are described. It is obvious that ionic polymer membrane is most important part for enhancement of actuation performance due to their actuation mechanism. Therefore, the explanation is concentrated on ionic polymer and Nafion, the most popular ionic polymer for actuator. Because of the critical disadvantages of Nafion, there have been many researches to replace Nafion membrane, which is related to the aim and meaning of this study.

In Chapter 2, anion-conducting polymer for the use of ionic polymer actuators is suggested. Partially methylated ether-linked polybenzimidazole (PBI-OO) was prepared with simple methylation process and anion exchange process to control of ionic conductivity. Despite the much lower ionic conductivity due to slow ion diffusion of anion species, ionic polymer actuators with methylated PBI-OO membranes exhibited acceptable displacement with no back relaxation and large force generation with lower consumption of electrical charge.

In Chapter 3, nanocomposite polymer is fabricated with nanostructured block copolymer and functionalized inorganic filler. Ionic polymer membrane based on sulfonated styrenic pentablock copolymer (SSPB) and sulfonated graphene oxide (sGO) shows much larger ionic domain size than typical Nafion membrane. This structure is favorable for the impregnation of ionic liquid (IL) to make reproducible ionic polymer actuators in ambient condition. SSPB/sGO/IL actuators revealed excellent electromechanical performance with large deformation, initial strain rate, and charge-specific displacement. Furthermore, ion transport behavior in the polymer is suggested by tracking ion species during actuation.

In Chapter 4, another type of nanocomposite polymer is described. Instead of typical inorganic fillers, Copper(II) phthalocyanine tetrasulfonic acid (CuPCSA) is introduced as ion-conducting filler in sulfonated poly(arylene ether sulfone) polymer matrix. Ionic polymer actuator with SPAES/CuPCSA membrane shows not only outstanding membrane properties such as ion conductivity and mechanical robustness but also remarkable actuation performance in the aspect of large displacement, fast initial response rate, and high power density.