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1. Single-shot transient absorption spectroscopy of an organic film

   https://doi.org/10.1557/adv.2018.402  

   Wilson, Kelly S.; Scott, Madelyn N.; Wong, Cathy Y. (January 2018, MRS Advances)

   ABSTRACT We report single-shot transient absorption (SSTA) measurements of an organic film of 3,3’-Diethyloxatricarbocyanine iodide (DOTCI). In SSTA, the pump-probe time delay is spatially encoded by using a tilted pump pulse. Translation of the sample during SSTA measurements averages over any spatial heterogeneity in the film. We demonstrate that exciton dynamics measured with the single-shot technique agrees with traditional transient absorption measurements of the same film. A signal-to-noise ratio of ∼40 is achieved in 10 s. The ability to measure exciton dynamics in organic films will enable future SSTA measurements of exciton dynamics during the molecular aggregation events that result in film formation. 

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2. The interplay of thermodynamics and kinetics: imparting hierarchical control over film formation of self-stratified blends

   https://doi.org/10.1039/c9sm01147a  

   Rinehart, Samantha J.; Yuan, Guangcui; Dadmun, Mark D. (February 2020, Soft Matter)

   Spin casting has become an attractive method to fabricate polymer thin films found in organic electronic devices such as field-effect transistors, and light emitting diodes. Many studies have shown that altering spin casting parameters can improve device performance, which has been directly correlated to the degree of polymer alignment, crystallinity, and morphology of the thin film. To provide a thorough understanding of the balance of thermodynamic and kinetic factors that influence the stratification of polymer blend thin films, we monitor stratified polymer blend thin films developed from poly(3-hexylthiophene-2,5-diyl) and poly(methyl methacrylate) blends at controlled loading ratios, relative molecular weights, and casting speed. The structures of these thin films were characterized via neutron reflectivity, and the results show that at the fastest casting speed, polymer–polymer interactions and surface energy of the polymers in the blend dictate the final film structure, and at the slowest casting speed, there is less control over the film layering due to the polymer–polymer interactions, surface energy, and entropy simultaneously driving stratification. As well, the relative solubility limits of the polymers in the pre-deposition solution play a role in the stratification process at the slowest casting speed. These results broaden the current understanding of the relationship between spin casting conditions and vertical phase separation in polymer blend thin films and provide a foundation for improved rational design of polymer thin film fabrication processes to attain targeted stratification, and thus performance. 

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3. Effect of processing conditions on the mechanical properties of bio-inspired mechanical gradient nanocmposites

   Zhang, Y.; Edelbrook, A.N.; Rowan, S. J. (March 2019, European Polymer Journal)

   Photo-induced thiol-ene crosslinking of allyl-functionalized cellulose nanocrystal (CNC)/polymer nanocomposites allows access to films that mimic the water-enhanced mechanical gradient characteristics of the squid beak. These films are prepared by mixing the functionalized CNCs and polymer in a solvent before solution casting and drying. The photocrosslinking agents are then imbibed into the film before UV exposure. Reported herein are studies aimed at better understanding the effect of the film preparation procedure, film thickness and the conditions under which the UV treatment is carried out. It was found that when the film is heated at a temperature higher than its glass transition temperature (Tg) during the UV irradiation step there is a greater enhancement in the mechanical properties of the films, presumably on account of more efficient crosslinking between the CNC fillers. Moreover, composite films that were compression molded (at 90°C) before the imbibing step displayed lower mechanical properties compared to the as-cast films, which is attributed to phase separation of the CNC fillers and polymer matrix during this additional processing step. Finally, the film thickness was also found to be a critical factor that affects the degree of crosslinking. For example, thinner films (50 µm) displayed a higher wet modulus ca. 130 MPa compared to ca. 80 MPa for the thicker films (150 µm). Understanding the processing conditions allows access to a larger range of mechanical properties which is important for the design of new bio-inspired mechanical gradient nanocomposites. 

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4. Laser printed metal halide perovskites

   https://doi.org/10.1088/2515-7639/ab9aac  

   Tyznik, Colin; Lamport, Zachary A.; Sorli, Jeni; Becker-Koch, David; Vaynzof, Yana; Loo, Yueh-Lin; Jurchescu, Oana D. (June 2020, Journal of Physics: Materials)

   Abstract Hybrid organic–inorganic perovskites enable the production of semiconductor devices at low cost from solution processing. Their remarkable structural versatility offers unique and diverse physical properties, leading to their incorporation in a wide variety of applications. One major limitation is the significant negative environmental impact associated with developing perovskite devices; common solvents used in perovskite film deposition are highly toxic, which represents a barrier to the transfer to an industrial setting of the perovskite technology. Here we report on the fabrication and characterisation of the first laser printed organic–inorganic perovskite films. The method is solvent-free, scalable and low-cost, allowing fast deposition over large areas and with minimal material waste. We show that the laser printed perovskite films are crystalline and exhibit electrical properties on par with single crystals, despite the fact that the microstructure consists of randomly oriented crystallites. The toner used during printing is designed for optimal film transfer and the vertical separation of its components results in a segregation of the perovskite film in the middle of the stack, therefore also encapsulating the perovskite layer, a process that yields a remarkable resilience to defect formation upon environmental exposure. 

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5. Eco-Friendly Cellulose Nanofiber Extraction from Sugarcane Bagasse and Film Fabrication

   https://doi.org/10.3390/su12156015  

   Shahi, Naresh; Min, Byungjin; Sapkota, Bedanga; Rangari, Vijaya K. (August 2020, Sustainability)

   null (Ed.)

   The development of cost-effective cellulose fibers by utilizing agricultural residues have been attracted by the scientific community in the past few years; however, a facile production route along with minimal processing steps and a significant reduction in harsh chemical use is still lacking. Here, we report a straightforward ultrasound-assisted method to extract cellulose nanofiber (CNF) from fibrous waste sugarcane bagasse. X-ray diffraction-based crystallinity calculation showed 25% increase in the crystallinity of the extracted CNF (61.1%) as compared to raw sugarcane bagasse (35.1%), which is coherent with Raman studies. Field emission scanning electron microscopy (FE-SEM) images revealed thread-like CNF structures. Furthermore, we prepared thin films of the CNF using hot press and solution casting method and compared their mechanical properties. Our experiments demonstrated that hot press is a more effective way to produce high strength CNF films; Young’s modulus of the thin films prepared from the hot press was ten times higher than the solution casting method. Our results suggest that a combination of ultrasound-based extraction and hot press-based film preparation is an efficient route of producing high strength CNF films. 

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