Fabrication processes and molecular organization in organic thin films: theory and simulation meet experiments
- Guido Raos (Politecnico di Milano, Italy)
- Claudio Zannoni (Universita' di Bologna, Dipartimento di Chimica Industriale "Toso Montanari", Italy)
- Giuseppe Milano (Dept. Of Organic Materials Science, Yamagata University, Italy)
The computational study and design of soft, functional organic materials, has made huge progresses in the last twenty years. Single molecule properties can now be calculated reliably and routinely by quantum chemical methods. The application of force-field-based Monte Carlo (MC) and Molecular Dynamics (MD) simulations is not so straightforward, but nonetheless they have progressed to a point where they can predict some basic properties of bulk condensed phases (e.g., the structure and transition temperatures of liquid crystals ). However, many technologically relevant applications of functional organic materials do not involve bulk phases but micro- or nano-thick films. Examples range from Organic Solar Cells (OSC) [3,4,5], Organic Field Effect Transistors (OFET) [7,8,9], Organic Light Emitting Diodes (OLED)  to Liquid Crystal Displays (LCD) [11,12] and polymeric films for optical applications, non-wetting surfaces, sensors and stimuli-responsive surfaces[14,15].
The computational study and design of these organic thin-films is much more complex than that of bulk phases, for a number of reasons:
(1) surfaces and interfaces (also within the organic film) play a key role. A realistic model of molecular organization on a solid substrate may have to include its chemical composition, morphology and roughness. Modelling the delicate balance of intermolecular interactions may be a problem, especially for organic-inorganic interfaces.
(2) there is generally a significant change in properties of organic materials (structure, morphology, melting, glass transition, etc.) from the bulk to the nano-scale level relevant for modern applications[17,18];
(3) the molecular organization within a film may strongly depend on its history and fabrication technology. Actually, the purpose of some fabrication processes (e.g. shearing) may be to generate and stabilize specific out-of-equilibrium structures with favorable properties (e.g., charge transport[19,20]).
A further source of complication resides in the variety of technologically relevant organic materials that range from low molar mass to polymeric, and moreover are often employed as multi-component mixtures. The preparation processes are also different. For low molar mass molecules, vapor deposition and molecular beam epitaxy are often preferred.[21,22] Thin films of polymers and block copolymers are instead usually produced by wet deposition techniques, including spin-coating, inkjet or roll-to-roll printing.[23,24,25] In all cases, the process parameters and post-deposition treatments (e.g., solvent evaporation and annealing) can have a major effect on the final structure and properties of the films and should be accounted for by simulations.[26,27]
The aim of the workshop is to bring together computational scientists, theorists and experimentalists, to define the state of the art and push forward the boundaries in the field of organic thin films. The theme is broad and ambitious. Speakers and participants will be encouraged to address key questions, including:
• What are the criteria for validating a simulation of an organic thin film, when the film itself may be in some non-equilibrium metastable state and information about its structure incomplete?
• What level of coarse-graining and scale-bridging strategies can make the simulations of organic thin film production processes feasible and closer to experiment?
• How can simulations be made more relevant to the interpretation of experiments? How can experimental information be used to constrain the outcome of the numerical simulations?
• What level of detail in a model is required to reproduce or predict specific properties of the films (e.g., charge transport)?
• What are the best techniques for extending simulations from the study of equilibrium molecular organizations to that of nonequilibrium ones produced by the processing techniques practically used in technology?
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