Synthesis and Characterizations of Lightweight, Highly Flexible Porous Polydimethylsiloxane (PDMS) Structures with Piezoresistive Strain Sensing Capabilities Using Solvent Evaporation Technique

Considering their specific structure, porous polymers have high adsorptive capacity, high flexibility, and high surface area compared to solid material. Highly flexible, deformable, and ultralightweight structures are required for advanced sensing applications such as wearable electronics and robotics. Hence, porous conductive polymer nanocomposites (CPNCs) have attracted significant attention for developing flexible piezoresistive sensors. In the first part of this dissertation, the application of solvent evaporation-induced phase separation (EIPS) as a promising technique to create porous polymer structures is investigated. The ternary polymer solution consisting of polymer/solvent/nonsolvent is explored. The ternary phase diagram is constructed, showing the thermodynamic equilibrium state for polymeric solutions consisting of Polydimethylsiloxane (PDMS)/Water/Tetrahydrofuran (THF). The possible composition path during the heat treatment and phase separation procedure is obtained. Moreover, the fabrication and characterization of porous PDMS structures developed by the EIPS technique are explored. The porous PDMS structures are formed by phase separation induced by removing the solvent, leading to water enriched droplets formation and removal during the stepping heat treatment procedure. The results show that the isolated pores with the adjustable pore size ranging from 330 µm to 1900 µm are obtained by tuning the water to the THF ratio. A wide range of elastic modulus ranging between 0.49-1.05 MPa was achieved without affecting the density of the porous sample by adjusting the solvent and non-solvent content in the solution. The second part of the dissertation proposes a two-step phase separation synthesis protocol based on a ternary polymer solution. THF and Toluene with various mixing ratios are utilized as the solvent phase. Two distinct pore size distributions were observed in the cast PDMS sheets. The large pores with an average of 509 µm are formed during the first step of the phase separation after THF is evaporated. The second phase separation occurs later at higher temperatures by the evaporation of Toluene, resulting in much smaller pores with an average size of 28 µm. The experiments reveal that raising the THF/solvent ratio increases the large pore concentration, and the small pore density is reduced. The elastic modulus is varied between 0.64-0.95 MPa, indicating that the proposed method can create porous structures with a wide range of flexibility while keeping the density constant. In the third part of the dissertation, a novel approach to synthesizing highly flexible and ultralightweight piezoresistive sensors is developed by combining the direct ink writing (DIW) and EIPS method. CPNC is prepared by dispersing carbon nanotubes (CNTs) at various concentrations in PDMS polymer, followed by mixing with solvent and nonsolvent phases to achieve a homogenous solution. Macroscale pores are established by designing structural printing patterns with adjustable infill densities, while the microscale pores are developed by EIPS of the deposited CPNC solution ink. Silica nanoparticles are utilized to modify the rheological properties of the DIW, evaluated by rheology experiments. A tunable porosity of up to 84% is achieved by controlling macroscale (infill density) and microscale porosity (polymer weight). The effect of macroscale/microscale porosity and printing nozzle sizes on the mechanical and piezoresistive behavior of the CPNC structures is explored. The electrical and mechanical testing demonstrate a durable, extremely deformable, and sensitive piezoresistive response without sacrificing mechanical performance. The flexibility and sensitivity of the CPNC structure are enhanced up to 900% and 67% with the development of dual-scale porosity. The application of the developed porous piezoresistive sensor for detecting human motion is also evaluated

Critique and Analysis of Moniru Ravanipour’s Ecological Story “Ahle Ghargh” with a Look at the Discourse of Power

Ecological critique is the study of the relationship between literature and the natural world, the origins of which are the emergence of new ideas in anthropology and environmental issues that humanist discourses play an important role in their emergence. In the story of Moniru Ravanipour’s Ahle Ghargh, the relationships of the characters such as Kheyjo, Zayer Ahmad Hakim, Mah Jamal, Madine, and Mobor men with the environment are examined in this article to show how power relations at different levels of this story are effective based on Foucault's ideas. In this story, Kheyjo, Mah Jamal, Madine, and Zayer Ahmad Hakim have a close relationship with nature as well as a transcendental view of the earth that challenges the dominant discourse of the age, philosophical humanism; the humanism in which more attention is paid to human thought and looks at man and nature through the eyes of an element or object. This is why Foucault in the age of modernity sees the presence of man in the scene of the illustration of thought and consciousness, and argues that empirical combinations should be applied in a place other than the absolute rule of "I think". In this article, considering the importance and impact of discourses in the production of the literary text, the aim was to examine the story in question with a descriptive-analytical method of the human relationship with the environment and the impact of different discourses that play an effective role in exercising power to inform man about his behavior with the environment and to reveal his relationship with nature

Highly sensitive compression sensors using three-dimensional printed polydimethylsiloxane/carbon nanotube nanocomposites

This article presents three-dimensional printed and highly sensitive polydimethylsiloxane/multi-walled carbon nanotube sensors for compressive strain and pressure measurements. An electrically conductive polydimethylsiloxane/multi-walled carbon nanotube nanocomposite is developed to three-dimensional print compression sensors in a freestanding and layer-by-layer manner. The dispersion of multi-walled carbon nanotubes in polydimethylsiloxane allows the uncured nanocomposite to stand freely without any support throughout the printing process. The cross section of the compression sensors is examined under scanning electron microscope to identify the microstructure of nanocomposites, revealing good dispersion of multi-walled carbon nanotubes within the polydimethylsiloxane matrix. The sensor’s sensitivity was characterized under cyclic compression loading at various max strains, showing an especially high sensitivity at lower strains. The sensing capability of the three-dimensional printed nanocomposites shows minimum variation at various applied strain rates, indicating its versatile potential in a wide range of applications. Cyclic tests under compressive loading for over 8 h demonstrate that the long-term sensing performance is consistent. Finally, in situ micromechanical compressive tests under scanning electron microscope validated the sensor’s piezoresistive mechanism, showing the rearrangement, reorientation, and bending of the multi-walled carbon nanotubes under compressive loads, were the main reasons that lead to the piezoresistive sensing capabilities in the three-dimensional printed nanocomposites. </jats:p