Literature Review on Conjugated Polymers as Light-Sensitive Materials for Photovoltaic and Light-Emitting Devices in Photonic Biomaterial Applications

Due to their extended p-orbital delocalization, conjugated polymers absorb light in the range of visible-NIR frequencies. We attempt to exploit this property to create materials that compete with inorganic semiconductors in photovoltaic and light-emitting materials. Beyond competing for applications in photonic devices, organic conjugated compounds, polymers, and small molecules have also been extended to biomedical applications like phototherapy and biodetection. Recent research on conjugated polymers has focused on bioapplications based on the absorbed light energy conversions in electric impulses, chemical energy, heat, and light emission. In this review, we describe the working principles of those photonic devices that have been applied and researched in the field of biomaterials.

Influence of the Print Envelope Temperature on the Morphology and Tensile Properties of Thermoplastic Polyolefins Fabricated by Material Extrusion and Material Jetting Additive Manufacturing

Additive manufacturing (AM) nowadays has become a supportive method of traditional manufacturing. In particular, the medical and healthcare industry can profit from these developments in terms of personalized design and batches ranging from one to five specimens overall. In terms of polymers, polyolefins are always an interesting topic due to their low prices, inert chemistry, and crystalline structure resulting in preferable mechanical properties. Their semi-crystalline nature has some advantages but are challenging for AM due to their shrinkage and warping, resulting in geometrical inaccuracies or even layer detaching during the process. To tackle these issues, process parameter optimization is vital, with one important parameter to be studied more in detail, the print envelope temperature. It is well known that higher print envelope temperatures lead to better layer adhesion overall, but this investigation focuses on the mechanical properties and resulting morphology of a semi-crystalline thermoplastic polyolefin. Further, two different AM technologies, namely material jetting (ARBURG plastic freeforming-APF) and filament-based material extrusion, were studied and compared in detail. It was shown that higher print envelope temperatures lead to more isotropic behavior based on an evenly distributed morphology but results in geometrical inaccuracies since the material is kept in a molten state during printing. This phenomenon especially could be seen in the stress and strain values at break at high elongations. Furthermore, a different crystal structure can be achieved by setting a specific temperature and printing time, also resulting in peak values of certain mechanical properties. In comparison, better results could be archived by the APF technology in terms of mechanical properties and homogeneous morphology. Nevertheless, real isotropic part behavior could not be managed which was shown by the specimen printed vertically. Hence, a sweet spot between geometrical and mechanical properties still has to be found.

Influence of microstructural alterations of liquid metal and its interfacial interactions with rubber on multifunctional properties of soft composite materials

Liquid metal (LM)-based polymer composites are currently new breakthrough and emerging classes of soft multifunctional materials (SMMs) having immense transformative potential for soft technological applications. Currently, room-temperature LMs, mostly eutectic gallium‑indium and Galinstan alloys are used to integrate with soft polymer due to their outstanding properties such as high conductivity, fluidity, low adhesion, high surface tension, low cytotoxicity, etc. The microstructural alterations and interfacial interactions controlling the efficient integration of LMs with rubber are the most critical aspects for successful implementation of multifunctionality in the resulting material. In this review article, a fundamental understanding of microstructural alterations of LMs to the formation of well-defined percolating networks inside an insulating rubber matrix has been established by exploiting several existing theoretical and experimental studies. Furthermore, effects of the chemical modifications of an LM surface and its interfacial interactions on the compatibility between solid rubber and fluid filler phase have been discussed. The presence of thin oxide layer on the LM surface and the effects and challenges it poses to the adequate functionalization of these materials have been discussed. Plausible applications of SMMs in different soft matter technologies, like soft robotics, flexible electronics, soft actuators, sensors, etc. have been provided. Finally, the current technical challenges and further prospective to the development of SMMs using non‑silicone rubbers have been critically discussed. This review is anticipated to infuse a new impetus to the associated research communities for the development of next generation SMMs.

"May the Force Be with You!" Force-Volume Mapping with Atomic Force Microscopy

Information of the chemical, mechanical, and electrical properties of materials can be obtained using force volume mapping (FVM), a measurement mode of scanning probe microscopy (SPM). Protocols have been developed with FVM for a broad range of materials, including polymers, organic films, inorganic materials, and biological samples. Multiple force measurements are acquired with the FVM mode within a defined 3D volume of the sample to map interactions (i.e., chemical, electrical, or physical) between the probe and the sample. Forces of adhesion, elasticity, stiffness, deformation, chemical binding interactions, viscoelasticity, and electrical properties have all been mapped at the nanoscale with FVM. Subsequently, force maps can be correlated with features of topographic images for identifying certain chemical groups presented at a sample interface. The SPM tip can be coated to investigate-specific reactions; for example, biological interactions can be probed when the tip is coated with biomolecules such as for recognition of ligand-receptor pairs or antigen-antibody interactions. This review highlights the versatility and diverse measurement protocols that have emerged for studies applying FVM for the analysis of material properties at the nanoscale.

The Quantitative Nanomechanical Mapping of Starch/Kaolin Film Surfaces by Peak Force AFM

Starch films modified with additives are materials increasingly being used in the production of packaging. These types of biopolymers can, to a considerable degree, replace plastic, contributing to the reduction in both production and waste management costs. However, they should be characterised by specific mechanical and surface parameters which determine their application. In the presented work, the PeakForce Quantitative Nanomechanics Mapping (PFQNM) method was applied to analyse a starch-based biopolymer modified with two different kaolin clay contents (5% and 10%). The technique used facilitates the assessment of the correlation of Atomic Force Microscope AFM height parameters with nanomechanical ones which provide the definitions of mutual interactions and allow the possibility to analyse materials in respect of various details. The investigated material was mapped in the Derjaguin-Muller-Toporov (DMT) modulus, adhesion and height domains. The results obtained indicated the impact of additives on the determined parameters. Increases in the DMT modulus and the adhesion force, along with the kaolin content, were observed. The enhancement of starch films with kaolin clay also induced growth in the surface roughness parameters.

Ionic Liquids Grafted Cellulose Nanocrystals for High-Strength and Toughness PVA Nanocomposite

The surface functionalization of cellulose nanocrystals (CNCs) is of significant importance for promoting its diverse applications. However, the efficient strategy reported so far for cation functionalization of CNCs remains limited owing to the electrostatic attraction between cationic modifiers and electronegative CNCs. Herein, a cationized CNC (CNC-LA-IL) has been successfully prepared in aqueous media by grafting the [VBIm][BF₄], a kind of ionic liquid (IL), on the surface of a sulfated CNC using lactic acid (LA) as a linker molecule. This surface functionalization not only converts the negative charge of CNC suspensions to a positive charge (zeta potential reversed from -35 to +40 mV) but also leads to enhanced thermal stability and redispersibility of the dried CNC. To examine the reinforcing effect of IL-modified CNCs, poly(vinyl alcohol) (PVA)/CNC-LA-IL nanocomposite films were further prepared by the solution casting method. To one's surprise, the as-prepared PVA/CNC-LA-IL films exhibit extraordinary improvement in both the tensile strength (92%) and the toughness (166%) with only a 0.3 wt % CNC loading. This study provides a green and facile method to achieve ionic liquids grafted CNCs for high-performance nanocomposites.

3D-Printable PP/SEBS Thermoplastic Elastomeric Blends: Preparation and Properties

Currently, material extrusion 3D printing (ME3DP) based on fused deposition modeling (FDM) is considered a highly adaptable and efficient additive manufacturing technique to develop components with complex geometries using computer-aided design. While the 3D printing process for a number of thermoplastic materials using FDM technology has been well demonstrated, there still exists a significant challenge to develop new polymeric materials compatible with ME3DP. The present work reports the development of ME3DP compatible thermoplastic elastomeric (TPE) materials from polypropylene (PP) and styrene-(ethylene-butylene)-styrene (SEBS) block copolymers using a straightforward blending approach, which enables the creation of tailorable materials. Properties of the 3D printed TPEs were compared with traditional injection molded samples. The tensile strength and Young’s modulus of the 3D printed sample were lower than the injection molded samples. However, no significant differences could be found in the melt rheological properties at higher frequency ranges or in the dynamic mechanical behavior. The phase morphologies of the 3D printed and injection molded TPEs were correlated with their respective properties. Reinforcing carbon black was used to increase the mechanical performance of the 3D printed TPE, and the balancing of thermoplastic elastomeric and mechanical properties were achieved at a lower carbon black loading. The preferential location of carbon black in the blend phases was theoretically predicted from wetting parameters. This study was made in order to get an insight to the relationship between morphology and properties of the ME3DP compatible PP/SEBS blends.

Probing nanomechanical properties with AFM to understand the structure and behavior of polymer blends compatibilized with ionic liquids

The PeakForce QNM AFM mode was used to investigate the nanoscale mechanical properties of poly(butylene-adipate-co-terephthalate)/poly(lactic acid) (PBAT/PLA) blends successfully compatibilized with phosphonium-based ionic liquids (ILs).