Session BB05: V: Experimental Advances in Polymer Physics

Electroabsorption in the Nonconjugated Conductive Polymer Iodine-doped Polyethylene Terephthalate, an example of Organic Metallic Quantum Dots of Subnanometer Dimensions

Quadratic electro-optic effect in iodine-doped polyethylene terephthalate (PET) has been recently reported along with the magnitudes of the real part of its Kerr coefficients.¹ In this report, we will discuss results of electroabsorption measurements providing values of the imaginary part of Kerr coefficients for different doping levels of iodine. The measurements have been made using ac fields at 4 kHz at 633 nm wavelength which is near the onset of the surface plasmon resonance of PET quantum dots. The magnitude of the imaginary part of Kerr coefficient as we have measured at a low doping level of iodine is ~ 2.3x10^-12 m/V². This is a large magnitude consistent with the subnanometer dimensions of these quantum dots.

 

1. Mrinal Thakur & Justin Van Cleave (2023) Quadratic electro-optic effect in the nonconjugated conductive polymer iodine-doped polyethylene terephthalate, Journal of Macromolecular Science, Part A, 60:2, 92-96, DOI: 10.1080/10601325.2023.2174443   

On-Demand Wearable Piezoelectric Textiles Enabled by Lead-Free Perovskite and Conducting Polymer

In recent years, the demand for smart textiles has been increasing day by day in healthcare devices and wearable sensor applications. In this regard, we introduce a novel approach to create a three-layer wearable textile piezoelectric nanogenerator (t-PENG) using a continuous electrospinning process. The central layer is the active component, composed of Cs₃Bi₂I₉-PVDF (PVDF-CBI) nanofiber, while the outer layers consist of conducting electrode nanofiber mats (PVDF-PEDOT) with a high electrical conductivity of ~2.2 S m^-1. By incorporating perovskite Cs₃Bi₂I₉ nanofillers, we have successfully induced a 100% yield of the electroactive β-phase within the PVDF matrix. Our PENG exhibits outstanding performance metrics, including a remarkable open circuit voltage of ~12 V, a short circuit current of 7 µA, and a power density of 3 µW cm^-2. Furthermore, it boasts exceptional breathability (~1.13 kg m^-2 day^-1), flexibility, water-resistant properties (as indicated by a water contact angle of ~138⁰), and impressive mechanoacoustic sensitivity (with a sensitivity value of Sm ~5 V Pa^-1). These functionalities make t-PENG suitable for use in robust wearable devices, enabling efficient monitoring of human physiological motions and simultaneous harvesting of biomechanical energy.   

Electrostatic Force Mediated Work Function Modulation of Polyvinylidene crystalline Phases

We studied how the polarity of different phases of polyvinylidene fluoride (PVDF), a flexible and sensitive ferroelectric polymer, affects its work function. This is important for designing new flexible electronics and healthcare devices. We used Fourier transform infrared spectroscopy (FTIR) to identify the non-polar (α) and electroactive (γ and β) phases. We measured the water contact angle and surface potential to see how the phases changed the surface properties. We also used atomic and Kelvin probe microscopy (AFM and KPFM) to map the spherulite and surface potential variation of each phase. We used ultraviolet photoelectron spectroscopy (UPS) to measure the valence bands spectrum and work function of PVDF phases. We showed that the surface potential variation can enhance the charge generation by contact electrification in single material based multi-interfaces (αα < γγ < αγ).   

Origins of Ultrahigh Electromechanical Response in a New Class of Relaxor Ferroelectric Polymers

Due to their high pliability, easy fabrication into complicated shapes and large areas, light weight, and low cost, ferroelectric polymers are attractive for a broad range of electromechanical (EM) applications. On the other hand, the low EM properties of polymers, compared with inorganic counterparts, limit device performance. Recently, we reported a new class of relaxor ferroelectric polymers, poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene-fluorinated alkyne) (PVDF-TrFE-CFE-FA) tetrapolymer (Science, 2022, 375, 1418) that, at FA content near 2 mol%, generates giant electrostriction at ultralow electric fields. Moreover, the tetrapolymer exhibits electromechanical coupling factor and piezoelectric fields at low DC bias much higher than those of PZT ceramics, the most widely used piezoelectrics. Here, we study the phase transition behavior of the tetrapolymer as a function of FA content. Increasing FA content weakens the relaxor behavior, and at high FA content (4 mol% FA), the tetrapolymers exhibit normal ferroelectric response. A diffused critical endpoint transition region at compositions near 2 mol% FA is observed, at which the energy barriers between the weak relaxor and polar phase almost vanish; thus, a small electric field can induce a large EM response.   

Spectroscopic Analysis on Polyethylene Oxide Loaded with Fullerenes

A broad spectroscopic investigation to better understand the structure and interactions between polyethylene oxide (PEO) and fullerenes (C60) is reported. PEO-C60 nanocomposites (PEO-C60NC) were obtained by dissolving PEO and C60 in water, mixing, and homogenization these dispersions by stirring, and water evaporation. This path exploited the insolubility of C60 in water, thus resulting in a standard polymer nanocomposite. The molecular dispersion of C60 in PEO (PEO-C60MD) was obtained by dissolving PEO and C60 in a common solvent (toluene, chloroform), mixing the two solutions, and evaporating the solvent. The outcome was a polymer within which C60 is molecularly dispersed, (PEO-C60MD). PEO-C60NC and PEO-C60MD containing various weight fractions of C60 were prepared.

Spectroscopic studies by X-ray diffraction (using a Bruker Discovery 8 spectrometer), Raman spectroscopy (using a Renishaw InVia Raman confocal microscope operating at 785 nm), FTIR (using a Bruker Tensor 27 coupled with a Hyperion FTIR confocal microscope), UV-Vis spectroscopy, and Electron Spin Resonance (using an EPR Elexsys spectrometer operating in the X-band) have been carried out on both PEO-C60MD and PEO-C60NC.

The modifications of the structural properties of PEO upon the addition of C60, either as a nanofiller or as a molecularly dispersed component, are investigated and reported in detail, with emphasis on the differences between the nanocomposite and the molecularly dispersed sample.   

Surface Potential Modulation in 3D Printed Thermoelectret for Improved Mechanical Energy Harvesting and Physiological Sensing

Self-powered devices capable of physiological signal detection are the primary demand in the healthcare sector. Recently, PVDF-based sensors have shown potential in human health care monitoring. However, the simultaneous (piezo- and pyro-electric) response of the PVDF-based pressure sensor might generate a lack of accuracy. In addition, the composites-based pressure sensor is cost-intensive and less biocompatible due to toxic parts from inorganic counterparts. It is not advisable in wearable electronics since it has direct contact with the human body.

The present research demonstrates a 3D-printed biopolymer-based thermoelectret (3D-TNG) utilized to operate in self-power mode and can collect energy from mechanical motions and bone-joint motion. Additionally, the 3D-TNG is utilized to monitor coughing and other movements of bone joints, including hinge, condyloid, and ball and socket joints (without any physical contact from the volunteer). Furthermore, the use of 3D-TNG is made to capture the distribution of human foot pressure, which may be used to analyze the physiological signals linked to body balance. The 3D printed self-powered 3D-TNG can monitor precise biomechanical signals, and it envisions the utility in on-spot patient-specific bone fracture due to the ability of instant fabrication of complicated structure by 3D printing technology and charge generation properties of thermoelectret, where PLA-like biopolymer may also be used.

    

Phase Behavior of Polyethylene Oxide-Fullerene

Phase transitions (glass, melting, crystallization) are important features of materials. The dispersion of (nano)particles within homopolymers results in complex modifications of their thermal properties. A study focused on two materials with the same composition: polyethylene oxide (PEO) and fullerene (C60) is reported. PEO-C60 nanocomposites (PEO-C60NC) were obtained by dissolving PEO in water, dispersing fullerene in water, homogenizing these dispersions, mixing them, homogenizing the obtained mixture, and removing the water. Because C60 is insoluble in water, a standard nanocomposite (PEO-C60NC) was obtained. Molecular dispersions of C60 in PEO (PEO-C60MD) were obtained by dissolving the polymer in toluene, the fullerenes in toluene, homogenizing each solution, mixing the two solutions, and removing the solvent. With a diameter of about 1.1 nm, fullerene provides a huge surface area that affects the phase transitions of PEO. Thermal features of PEO-C60NC and PEO-C60MD have been measured by Differential Scanning Calorimetry by using the Netzsche instrument. Thermograms were recorded at various heating/cooling rates in the range of 5 to 50 oC/min. The effect of cooling and heating rate as well as the effect of the loading by fullerene on glass, melting, and crystallization of PEO is reported. The differences between PEO-C60NC and PEO-C60MD are analyzed in detail.   

Observation of ferroelectric programmability in 3D printed metamaterials

Architected materials can break the limit of what is possible compared to natural materials, however, once

fabricated they retain fixed properties. A growing trend in research is devoted to materials with properties that

can be tuned post fabrication in a programmable manner. Such tunability can be achieved through magnetic,

electric, or thermal stimuli to responsive elements within the metamaterial’s architecture. In this paper, we

present the first demonstration of ferroelectric programmability of 3D printed polymeric metamaterials. We

harness electric poling effects to change the mechanical properties of polyvinylidene fluoride (PVDF). We

utilize the poling-induced softening to reverse metamaterials behavior from attenuating waves to propagating

them and vice versa. We demonstrate the utility of the proposed platform to program a desired set of pixels

within the metamaterials to open a path for waves to propagate in a waveguide. Our findings introduce a

methodology for elastic wave guiding by electrical poling, which can open the door for numerous applications

in various fields such as vibration isolation, wave guiding, and energy harvesting.   

Investigation of the Bound Layer in Thin Films of Hydrophilic Polymer and their Nanocomposites

The conformation of polymer chains is strongly affected in proximity to a solid, impenetrable surface. Depending on the interactions between the polymer and the surface, a distinct layer forms as the chains adsorb to the surface. Such a bound layer is known to significantly influence the structural and dynamic properties of polymer thin films and nanocomposites. In recent work, we introduced a novel approach for determining the thickness and density of this bound layer by measuring the swelling kinetics of polymer thin films exposed to solvent vapour. In this study, we have investigated the properties of the bound layer in annealed thin films of the hydrophilic polymer, Poly(vinyl alcohol) (PVA) further, and also in PVA/SiO₂ nanocomposites. The thickness of the bound layer (ds) obtained by analyzing the swelling kinetics was compared to that obtained using Guiselin's approach. The swelling kinetics of the films on exposure to water vapour was measured by in-situ spectroscopic ellipsometry and X-ray reflectivity. Intriguingly, Guiselin's approach revealed a noteworthy finding: the obtained ds values were essentially independent of the initial thickness of the films. These ds values were similar to those obtained using the swelling kinetics. In addition, the physical properties of the bound layer, as observed in PVA/SiO₂ nanocomposite films will be presented.    

Modifying thermal properties of polyesters by incorporating additional groups

Sustainable polyesters are promising materials to replace petroleum-based non-degradable polymers. Unfortunately, the high crystallinity degree of some polyesters limits their applications due to poor mechanical properties and low melting temperatures. A suitable strategy to broaden their applications is introducing functional groups into their backbone to enhance intermolecular interactions which can impact the thermal properties of the material. Nevertheless, a comprehensive understanding of these interactions on the crystallization properties is still lacking. In this work, we have studied the impact of incorporating additional ester and amide groups into aliphatic polyesters with varying numbers of methylene groups between the functional groups. We show that functional groups that induce strong intermolecular interactions increase the melting and crystallization temperature. However, these groups slow down the crystallization kinetics. This work demonstrates how appropriately selecting the functional groups makes it possible to independently tune the thermal transition and the crystallization kinetics of the promising polyesters.