Nanostructured morphology of polymer films prepared by matrix assisted pulsed laser evaporation
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Nanostructured morphology of polymer films prepared by matrix assisted pulsed laser evaporation Kimberly B. Shepard · Yunlong Guo · Craig B. Arnold · Rodney D. Priestley
Received: 15 January 2012 / Accepted: 3 August 2012 / Published online: 5 September 2012 © Springer-Verlag 2012
Abstract As recently illustrated, nanostructured glassy polymer films with exceptional thermal and kinetic stability can be formed via Matrix Assisted Pulsed Laser Evaporation (MAPLE) (Guo et al. in Nat. Mater. 11:337, 2012). Relative to the standard poly(methyl methacrylate) glass formed on cooling at standard rates, glasses prepared by MAPLE can be 40 % less dense and have a 40 K higher glass transition temperature (Tg ). Furthermore, the kinetic stability in the glassy state can be enhanced by 2 orders-of-magnitude. Here, we examine the stability of the structured morphology. We show that nanostructured glasses may be formed even when the substrate is held at temperatures greater than the polymer Tg during deposition. In addition, we discuss the origin of the enhanced stability and the mechanism of nanostructured film formation within the framework of the Zhigilei model. Finally, we compare the nanostructured morphology to the surface morphology of other MAPLE-deposited films in the literature.
1 Introduction The development of Matrix Assisted Pulsed Laser Evaporation (MAPLE) has enabled the gentle deposition of K.B. Shepard · Y. Guo · R.D. Priestley () Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA e-mail: [email protected] C.B. Arnold Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA C.B. Arnold · R.D. Priestley Princeton Institute for the Science and Technology of Materials, Princeton University, Princeton, NJ 08544, USA
large macromolecules, where degradation can be avoided during laser processing. Since its inception, the deposition of a diverse array of materials has been reported: polysiloxane [1], poly(methyl methacrylate) [2–8], polythiophenes [9], poly(ethylene glycol) [4, 10–16], poly(9,9dioctylfluorene) [17–19], and polystyrene–poly(ethylene oxide) block copolymers [20]. In the MAPLE method, a pulsed laser ablates a frozen target solution under vacuum, forming a plume, which is collected on a temperaturecontrolled substrate. The originally proposed mechanism of film formation via MAPLE [1] implied that solute molecules were transported from the target as single polymer molecules within a solvent vapor plume that was pumped away during transport, leaving solute molecules to reach the substrate in isolation. However, recent simulations of the MAPLE process by Zhigilei and workers [21, 22] suggest that polymer molecules are ejected from the target within a polymer–solvent cluster. These clusters form due to explosive decomposition of the solvent molecules when the target is overheated by a short laser pulse. During the ejection process, a “foamy transient structure” of interconnected solvent and polymer molecules transfo
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