Morphological Evolution in Dewetting Polystyrene/Polyhedral Oligomeric Silsesquioxane Thin Film Bilayers

Abstract

Morphological evolution in dewetting thin film bilayers of polystyrene (PS) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP), was studied as a function of annealing temperature and annealing time. The results demonstrate unique dewetting morphologies in PS/TPP bilayers at elevated temperatures that are significantly different from those typically observed in dewetting polymer/polymer bilayers. During temperature ramp studies by optical microscopy (OM) in the reflection mode, PS/TPP bilayers form cracks with a weak optical contrast at approximately 130 degrees C. The crack formation is attributed to tensile stresses within the upper TPP layer. The weak optical contrast of the cracks observed in the bilayers for annealing temperatures below approximately 160 degrees C is consistent with the cracking and dewetting of only the upper TPP layer from the underlying PS layer. The optical contrast of the morphological features is significantly enhanced at annealing temperatures of >160 degrees C. This observation suggests dewetting of both the upper TPP and the lower PS layers that results in the exposure of the silicon substrate. Upon annealing the PS/TPP bilayers at 200 degrees C in a temperature jump experiment, the upper TPP layer undergoes instantaneous cracking as observed by OM. These cracks in the upper TPP layer serve as nucleation sites for rapid dewetting and aggregation of the TPP layer, as revealed by OM and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) results indicated that dewetting of the lower PS layer ensued for annealing times >5 min and progressed up to 90 min. For annealing times >90 min, OM, AFM, and XPS results revealed complete dewetting of both the layers with the formation of TPP encapsulated PS droplets.

Polyhedral oligomeric silsesquioxane–polyphenylsulfone nanocomposites: Investigation of the melt‐flow enhancement, thermal behavior, and mechanical properties

“…Studies in our own and other research laboratories have demonstrated the propensity of POSS to segregate to the surface of a polymer matrix 26–32. The POSS surface‐enriched nanocomposites exhibit reduced friction and melt viscosity and improved surface hardness, abrasion resistance, and hydrophobicity.…”

POSS‐nylon 6 nanocomposites: Influence of POSS structure on surface and bulk properties

“…A high surface concentration of POSS (> fifty percent) was reported. Esker and coworkers25, 26 studied the phase separation behavior and morphological evolution in dewetting thin films of POSS/poly( tert ‐butyl acrylate) blends as a function of annealing temperature and time. Similarly, Takahara and coworkers27 reported the use of POSS nanofillers to control the surface dewetting characteristics of polystyrene.…”

POSS‐inducedrheological and dielectric modification of polyethersulfone

“…The effect of formation of a surface skin on the nanocomposite melt, enriched with the incorporated nanoparticles, has also been considered to contribute to melt processability enhancements by reducing the friction between the nanocomposite melt and the metal parts of the compounding equipment 13,30 . Studies in our own and other research groups have demonstrated the propensity of POSS to segregate to the surface of a polymer matrix, with concomitant reduction in surface friction 31–35 . Clearly, there is no consensus on the fundamental principles controlling the rheological modification, and the predominant processes vary with systems of different compositions.…”

“…13,30 Studies in our own and other research groups have demonstrated the propensity of POSS to segregate to the surface of a polymer matrix, with concomitant reduction in surface friction. [31][32][33][34][35] Clearly, there is no consensus on the fundamental principles controlling the rheological modification, and the predominant processes vary with systems of different compositions.…”