Surface Morphology of Annealed Polystyrene and Poly(methyl methacrylate) Thin Film Blends and Bilayers

Abstract

Thin films of polystyrene (PS) and poly(methyl methacrylate) (PMMA) were spun-cast onto silicon substrates, annealed, and analyzed by atomic force microscopy (AFM), total electron yield (TEY), and partial electron yield (PEY) near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in order to resolve conflicting prior literature regarding the tendency of PS to form a wetting layer or overlayer on top of PMMA. From the comparison of the three methods of analysis and on the basis of the extraordinary surface sensitivity of PEY NEXAFS, we conclude that PS does not form an overlayer in samples with morphologies near thermodynamic equilibrium. The PS forms droplets of a large size range on top of a PMMA layer that wets the hydrophilic SiO x substrate. From our results, the maximum thickness of a continuous PS wetting layer would be about 0.25 nm. This is in contrast to recent experiments that imply an equivalent PS wetting layer of about 5−10 nm is forming during annealing.

A solution concentration dependent transition from self-stratification to lateral phase separation in spin-cast PS:d-PMMA thin films

“…This results in highly uniform films of controllable thickness under suitable experimental conditions. However, when blends of two or more polymers (rather than a single polymer solution) are used for spin casting phase separation into domains rich in each of the two constituent polymers often occurs [3][4][5][6][7][8][9]. Whether or not phase separation occurs is determined by the immiscibility of the constituent polymers in the starting solution, as determined by the FloryHuggins interaction parameter and the polymer chain length.…”

“…This self assembly into phase separated domains of a given size may be utilised to enhance devices [10] and can be controlled by patterning the substrate surface [11][12][13][14]. Therefore, there is considerable interest in understanding the physical mechanisms which govern the evolution of the complex phase separated morphologies [6][7][8][9]. Although phase separation during spin casting is a dynamic nonequilibrium process surprisingly little of the experimental research into spin casting has been done in situ.…”

Block Copolymers for DSA in the 100 ^|^Aring; Regime

“…In retrospect, this early success was due to a fortuitous characteristic of PS-b-PMMA. By chance, the surface tensions of PS and PMMA with air or vacuum are nearly identical at a temperature around 220 0 C. This has been known for some time [9]. Hence, annealing thin films of PS-b-PMMA on a neutral substrate results in perpendicular orientation of lamellae (and cylinders) since both the bottom and the top interface are neutral at that temperature.…”

Multi-jet electrospinning of polystyrene/polyamide 6 blend: thermal and mechanical properties

“…As the PA6 composition increased, SCA was decreased accordingly. It was because PA6 has higher surface energy (45.3 mN/m) (Gotoh 2004) than that of PS (40.7 mN/m) (Harris et al 2003). Also the phenomenon may be caused by the fact that PA6 fibers were finer and smoother, giving less surface roughness than PS fibers (Fig.…”