Results for “Solvent casting” — Page 5

DOE OSTI2021

Controlling the Morphology of PEDOT:PSS Blend Films with Pre-Deposition Solution Composition and Deposition Technique

Understanding the relationships between morphology, fabrication processes, and thermoelectric performance in conducting polymers is essential to the development of high- efficiency organic thermoelectrics as an alternative to commonly used rare metals. Altering the film fabrication process of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with the addition of high boiling solvents to the precast solution improves the electrical conductivity and significantly increases its Seebeck value. Neutron scattering monitors the changes in the atomic, nanoscale, and mesoscale morphologies of PEDOT:PSS thin films with the addition of dimethyl sulfoxide (DMSO) to the aqueous solution prior to film formation and with varying fabrication procedures. The neutron scattering results show a decrease in the deuterated PSS domain size along with systematic variations in PEDOT fibril assemblies in the final blend film with the addition of DMSO to the pre-deposition solution. These structural modifications indicate that the increase in conductivity of PEDOT:PSS blends with addition of DMSO reported in the literature can be ascribed to the disruption of solvated PEDOT assemblies by the DMSO, forming smaller PSS domains in the pre-deposition solution and allowing smoother film formation. These improvements are observed significantly with the addition of just 1% DMSO but continue to modestly improve with the addition of up to 5% DMSO to the PEDOT:PSS blend pre-deposition solution. The fact that the variations in the measured morphology are independent of whether the films were deposited by spin or ultrasonic spray casting methods emphasizes the crucial importance of the structure of the blend in the pre-deposition solution in determining the final thin film blend morphology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Preshaping clear glass at low temperatures

Advances in available glass chemistries and glass processing methods have accompanied and enabled some of the biggest technology revolutions, from the development and mass production of light bulbs to low-loss fiber optics and durable smartphone touchscreens. An emerging generation of low-temperature processing technologies aims to continue this important trend and make a broader array of glass components mass producible. In the issue, Mader et al. (1) describe one such innovation in glass processing—the use of low-temperature injection molding to preshape silica particle–filled composites that can later be transformed into transparent fused silica glass objects. Traditionally, transparent glass objects are manufactured in high volume from molten or softened glass, which is floated, drawn, blown, cast, or blow-molded to a desired shape (see the figure, top). The glass composition and processing technique dictate the working temperature, which is usually quite high (near 1000°C) and often restricts the choice of compatible equipment or limits the choice of glass composition. Because geometry-specific capital investment is required for production, drastic or frequent component design changes or small batches may be cost prohibitive. Alternatively, transparent glass components can also be shaped at ambient temperature from solid glass by a series of subtractive processes, including cutting or multiple stages of grinding, followed by slower processing steps, such as polishing or etching. This approach is somewhat less amenable to mass production, and certain geometries containing tool-inaccessible regions cannot be fabricated in this way. Several emerging glass-shaping technologies aim to reduce the required manufacturing temperatures and still provide access to a broader range of glass compositions and component geometries (see the figure). These approaches use a three-step process. First, a desired shape is preformed at low temperature from a glass-forming, organic-inorganic composite. Next, the preform is dried, and organic materials used to bind particles are removed. Finally, the preform is heated (sintered) well below the glass-melting temperature to densify to transparent glass. Although the second and third steps do occur at increased temperatures, only standard, geometry-agnostic driers and furnaces are required. This strategy builds on the well-studied sol-gel approach to forming monolithic glass, where silica network–forming chemical solutions are poured into molds, slowly dried, and condensed into dense glass without melting (2). In a departure from the sol-gel process, these new technologies use solvents, cross-linkers, and polymers to formulate organic-inorganic composites tuned for compatibility with a particular shaping process, with formats ranging from photocurable liquids to shear-thickening pastes to solids. The composite inorganic loadings are also typically higher than those in the pure sol-gel approach, which drastically reduces shrinkage in comparison.

36 MATERIALS SCIENCE↗