Novel Configurations of Ionic Polymer-Metal Composites (IPMCs) As Sensors, Actuators, and Energy Harvesters

This dissertation starts with describing the IPMC and defining its chemical structure and fundamental characteristics in Chapter 1. The application of these materials in the form of actuator, sensor, and energy harvester are reported through a literature review in Chapter 2. The literature review involves some electromechanical modeling approaches toward physics of the IPMC as well as some of the experimental results and test reports. This chapter also includes a short description of the manufacturing process of the IPMC. Chapter 3 presents the mechanical modeling of IPMC in actuation. For modeling, shear deformation expected not to be significant. Hence, the Euler-Bernoulli beam theory considered to be the approach defining the shape and critical points of the proposed IPMC elements. Description of modeling of IPMC in sensing mode is in Chapter 4. Since the material undergoes large deformation, large beam deformation is considered for both actuation and sensing model. Basic configurations of IPMC as sensor and actuator are introduced in Chapter 5. These basic configurations, based on a systematic approach, generate a large number of possible configurations. Based on the presented mechanisms, some parameters can be defined, but the selection of a proper arrangement remained as an unknown parameter. This mater is addressed by introducing a decision-making algorithm. A series of design for slit cylindrical/tubular/helical IPMC actuators and sensors are introduced in chapter 5. A consideration related to twisting of IPMCs in helical formations is reported through some experiments. Combinations of these IPMC actuators and sensors can be made to make biomimetic robotic devices as some of them are discussed in this chapter and the following Chapters 6 and 7. Another set of IPMC actuator/sensor configurations are introduced as a loop sensor and actuator that are presented subsequently in Chapter 6. These configurations may serve as haptic and tactile feedback sensors, particularly for robotic surgery. Both of these configurations (loop and slit cylindrical) of IPMCs are discussed in details, and some experimental measurements and results are also carried out and reported. The model for different inputs is studied, and report of the feedback is presented. Various designs of these configurations of IPMC are also presented in chapter 7, including their extension to mechanical metamaterials and soft robots

Synthesis and characterizations of pyridinium salts including poly(pyridinium salt)s and their applications

Pyridinium salts, both molecular and polymeric, are an interesting class of multifunctional materials that exhibit liquid-crystalline and light-emitting properties. Moreover, their properties can be easily tuned by introducing new types of anions or by modifying their chemical structures. This dissertation describes synthesis and characterization of poly(pyridinium salt)s containing macrocounterions and fluorene moieties in their backbones, synthesis and characterization of nanocomposites of poly(pyridinium salt)s with single-walled carbon nanotubes via non-covalent interactions, and synthesis and characterizations of pyridinium salts having different aliphatic linkages and their application in organic acid sensing. First, all of these ionic polymers were prepared by either ring-transmutation or by metathesis reaction. Their chemical structures were established by FTIR, 1H spectroscopy and elemental analysis. Some polymers containing macrocounterions had relatively low melting transitions above which they formed thermotropic liquid-crystalline phase; and other polymers were amorphous as determined by VTXRD studies. Ionic polymers containing fluorene moieties in their backbones exhibited lyotropic properties in both polar protic and aprotic solvents at various critical concentrations. Light emission properties of this class of polymers in common organic solvents as well as in water and in solid states were also studied. To explore the application of poly(pyridinium salt)s, we developed a method of preparation of nano-composites with a number of poly(pyridinium salt)s and single-walled carbon nanotubes. The single-walled carbon nanotubes were effectively dispersed with various poly(pyridinium salt)s resulting in nanocomposites. The optical and solution properties of these composites were examined by a number of experimental techniques. Finally, some of the synthesized dicationic salts exhibited ionic liquid properties, but all exhibited fluorescent properties in solution and solid states. Due to the presence of methyl orange counterions, pyridinium salts could serves as a pH sensor in organic solvents

The synthesis and development of novel, easily processable poly (n-isopropylacrylamide)-based hyrdogels.

This work describes the invention of a synthetic method which allows a fully-reacted PNIPAM/clay nanocomposite system to remain a watery liquid until it is cooled to a predetermined temperature. Beyond this temperature, the polymer/clay precursor hydrogel liquid (PCPH) spontaneously forms a cross-linked hydrogel that does not re-liquefy upon re-heating, but instead, possesses all of the highly utilisable stimuli-responsive properties typical of PNIPAM-based nanocomposite hydrogels synthesised in situ. This novel methodology simultaneously addresses issues including cytotoxicity, processability, injectability, cross-linking and mechanical stability. In addition, PCPH synthesis requires no specialist equipment, inexpensive and basic components typical of cross-linked hydrogels (water, monomer, clay and initiator), requires no purification steps and can be maintained as a fully-reacted liquid at evaluated temperatures for up to several weeks with no apparent loss of eventual functionality. The ability to create a fully polymerised hydrogel polymer with a liquid intermediate state has allowed the incorporation of biologically active dopants which can be dispersed and distributed homogeneously throughout the matrix prior to "phase transition triggered nanoparticle anchored gelation" (or PTTNAG) of the hydrogel.Human mesenchymal stem cells (MSCs), have been incorporated into the gel by i) placing them on the assembled gel surface - the cells responded by migrating and proliferating throughout the matrix of the gel, and more interestingly, ii) combining the MSCs with the PCPH in the liquid phase and allowing PTTNAG of the polymer matrix to occur around the cells. In both cases, cell viability was excellent throughout a series of 14-28 day experiments. The work was expanded by the exploration of PTTNAG temperature tailorability. This was achieved with the incorporation of the relatively polar comonomer dimethylacrylamide (DMAc), and non-polar comonomer glycedyl methacrylate (GMAc) which respectively increased and decreased the PTTNAG and lower-critical solution temperature (LCST) of the resulting gels. Crucially, it was found that the PTTNAG temperature can be tailored precisely and incorporation of DMAc did not affect cell viability. The process also opened several novel avenues for gel processing possibilities, including facile casting, extruding and electrospinning. Well defined and uniform electrospun fibres with diameters ~300nm are presented. The production of continuous, uniform flat PNIPAM/ clay sheets of 300pm -1000pm achieved using an industrial film extrusion line is detailed. This work represents an innovation in the way in which such hydrogels can be manufactured and produced safely and cleanly, with no additives, no energy input and no toxic by-products.Interactions between polymer and water are examined by monitoring the dehydration of 3 separate hydrogel formulations using ATR-FTIR. The pseudo diffusion coefficient (in this instance, the diffusion of water out of the polymer matrix) was not affected by dopant composition, but instead, the intercept of the slope was altered markedly. Cross-link type, cross-link density, initiation method and addition of dopants have a strong influence on the swelling/ deswelling behaviour of the hydrogels under study. PNIPAM/ clay gels exhibit much larger volume changes than those prepared with chemical cross-linking agent methylenebisacrylamide (BIS). Deswelling magnitude increases with decreasing cross-linker content for all gel types examined. Thermal deswelling is hindered in dopant-incorporated networks. The aqueous dilution of the nanocomposite in the liquid phase affects gel deswelling behaviour when clay concentration is low. De/reswelling of PNIPAM/ clay, PNIPAM/BIS and gelatine-doped PNIPAM/ clay gels can be induced by adjusting the alcohol volume fraction of the media. BIS cross-linked gels exert restricted swelling/deswelling behaviours compared to those cross-linked with clay. Cross-link density within systems does not have a significant impact on cononsolvency behaviour, although the incorporation of gelatine imposes some restriction on it, directly relative to gelatine concentration.X-ray diffraction (XRD) data proved the exfoliation of clay in the nanocomposite system post-PTTNAG. DMA data revealed that the viscoelasticity of the gels can be tailored with varying the nature and quantity of dopant materials. Gels doped with hyaluronic acid (HA) most closely resemble the mechanical properties of bovine NP tissue

The synthesis and development of novel, easily processable poly (n-isopropylacrylamide)-based hyrdogels.

This work describes the invention of a synthetic method which allows a fully-reacted PNIPAM/clay nanocomposite system to remain a watery liquid until it is cooled to a predetermined temperature. Beyond this temperature, the polymer/clay precursor hydrogel liquid (PCPH) spontaneously forms a cross-linked hydrogel that does not re-liquefy upon re-heating, but instead, possesses all of the highly utilisable stimuli-responsive properties typical of PNIPAM-based nanocomposite hydrogels synthesised in situ. This novel methodology simultaneously addresses issues including cytotoxicity, processability, injectability, cross-linking and mechanical stability. In addition, PCPH synthesis requires no specialist equipment, inexpensive and basic components typical of cross-linked hydrogels (water, monomer, clay and initiator), requires no purification steps and can be maintained as a fully-reacted liquid at evaluated temperatures for up to several weeks with no apparent loss of eventual functionality. The ability to create a fully polymerised hydrogel polymer with a liquid intermediate state has allowed the incorporation of biologically active dopants which can be dispersed and distributed homogeneously throughout the matrix prior to "phase transition triggered nanoparticle anchored gelation" (or PTTNAG) of the hydrogel.Human mesenchymal stem cells (MSCs), have been incorporated into the gel by i) placing them on the assembled gel surface - the cells responded by migrating and proliferating throughout the matrix of the gel, and more interestingly, ii) combining the MSCs with the PCPH in the liquid phase and allowing PTTNAG of the polymer matrix to occur around the cells. In both cases, cell viability was excellent throughout a series of 14-28 day experiments. The work was expanded by the exploration of PTTNAG temperature tailorability. This was achieved with the incorporation of the relatively polar comonomer dimethylacrylamide (DMAc), and non-polar comonomer glycedyl methacrylate (GMAc) which respectively increased and decreased the PTTNAG and lower-critical solution temperature (LCST) of the resulting gels. Crucially, it was found that the PTTNAG temperature can be tailored precisely and incorporation of DMAc did not affect cell viability. The process also opened several novel avenues for gel processing possibilities, including facile casting, extruding and electrospinning. Well defined and uniform electrospun fibres with diameters ~300nm are presented. The production of continuous, uniform flat PNIPAM/ clay sheets of 300pm -1000pm achieved using an industrial film extrusion line is detailed. This work represents an innovation in the way in which such hydrogels can be manufactured and produced safely and cleanly, with no additives, no energy input and no toxic by-products.Interactions between polymer and water are examined by monitoring the dehydration of 3 separate hydrogel formulations using ATR-FTIR. The pseudo diffusion coefficient (in this instance, the diffusion of water out of the polymer matrix) was not affected by dopant composition, but instead, the intercept of the slope was altered markedly. Cross-link type, cross-link density, initiation method and addition of dopants have a strong influence on the swelling/ deswelling behaviour of the hydrogels under study. PNIPAM/ clay gels exhibit much larger volume changes than those prepared with chemical cross-linking agent methylenebisacrylamide (BIS). Deswelling magnitude increases with decreasing cross-linker content for all gel types examined. Thermal deswelling is hindered in dopant-incorporated networks. The aqueous dilution of the nanocomposite in the liquid phase affects gel deswelling behaviour when clay concentration is low. De/reswelling of PNIPAM/ clay, PNIPAM/BIS and gelatine-doped PNIPAM/ clay gels can be induced by adjusting the alcohol volume fraction of the media. BIS cross-linked gels exert restricted swelling/deswelling behaviours compared to those cross-linked with clay. Cross-link density within systems does not have a significant impact on cononsolvency behaviour, although the incorporation of gelatine imposes some restriction on it, directly relative to gelatine concentration.X-ray diffraction (XRD) data proved the exfoliation of clay in the nanocomposite system post-PTTNAG. DMA data revealed that the viscoelasticity of the gels can be tailored with varying the nature and quantity of dopant materials. Gels doped with hyaluronic acid (HA) most closely resemble the mechanical properties of bovine NP tissue

Manufacturing conductive patterns on polymeric substrates : development of a microcontact printing process

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 215-233).The focus of this research was to develop a process suitable for creating very high resolution conductive patterns on polymer substrates, in a way that can be scaled to high volume manufacturing. The original motivation for this work came from the problem of manufacturing electrodes on microfluidic devices (which in volume production are commonly formed from polymers), but the findings of this work also have applications in flexible electronics, optics, surface patterning, organic micromanufacturing, and photovoltaics. After an initial exploration of various micromanufacturing processes, microcontact printing (μCP) was chosen as the most promising technique for further study. By using μCP to directly pattern conductive inks, this work has demonstrated previously unachievable printing: feature sizes down to 5μm, using liquid inks on polymer substrates, with a process that can be scaled to high-volume production. An understanding of the mechanisms of direct liquid ink transfer was used to identify relevant process input and output factors, and then the process sensitivities of those factors were investigated with a careful design of experiments. From the empirical data, a process model was built with generalized variables. This model was then used to successfully predict behavior of other inks and other substrates, thus validating the model and showing that it is extendable for future work. By developing an empirically verified model of ink transfer at the micron scale, this work has enabled a process for low cost, high volume microfeature patterning over large areas on polymer substrates.by Melinda Hale.Ph.D