Chain Diffusion and Microstructure at a Glassy−Rubbery Polymer Interface by SIMS

Abstract

The microstructure and chain diffusion behavior at a rubbery/glassy polymer interface (PS/ PPO) were studied using the depth-resolved technique of secondary ion mass spectroscopy (SIMS). Unlike the typical rubbery-rubbery interface, the microstructure of the miscible glassy-rubbery interface demonstrated a very sharp symmetric profile with a thickness around 25 nm before annealing. As chain diffusion took place, the glassy-rubbery interface moved toward the PPO region, the interface broadened asymmetrically, and the chains diffused across the interface showing both the Fickean and the case II characteristics simultaneously. For the purpose of analysis, the interfacial layer can be divided into a rubbery region and a glassy region according to the local T g calculated from the local polymer concentration using the Flory-Fox equation. The case II characteristic dominated on the glassy side of the interface, where chain mass flow required plasticization of the glassy polymers by the neighboring rubbery chains. The Fickean characteristic, on the other hand, prevailed on the rubbery side of the interface, where polymers at both sides of the interface were rubbery chains. The effect of temperature on the interdiffusion was in good agreement with that predicted by the WLF equation. The average velocity of the interface decreased with the PS molecular weight following a negative power law. The power of the dependence, however, was different for the two molecular weight regimes above and below the critical molecular weight of PS (M c ) 38K). The mutual diffusion coefficient and the tracer diffusion coefficients were determined from the SIMS data. The results were in good agreement with the slow theory predictions.

Cluster secondary ion mass spectrometry of polymers and related materials

“…In addition, the sputter rate is significantly reduced when employing atomic beams, such that only dynamic SIMS instruments are typically used. There are several examples of polymeric depth profiling with atomic beams including PS (Whitlow & Wool, 1989, 1991Zhao et al, 1991;Shwarz et al, 1992;Liu et al, 1995;Zheng et al, 1995;Strzhemechny et al, 1997;Rysz et al, 1999;Yokoyama et al, 1999;Shin et al, 2001;Hu et al, 2003;Lin et al, 2003;Harton, Stevie, & Ade, 2006a,b,c;Harton et al, 2006d), PAMA (Valenty et al, 1984), PBMA (Verhoeven et al, 2004), PEVA (Verhoeven et al, 2004), PC (Valenty et al, 1984), PVDF (Chujo, 1991), PEO (Mattsson et al, 2000;Huang et al, 2001), PMMA (Chujo, 1991;Huang et al, 2001;Hu et al, 2003;Harton, Stevie, & Ade, 2006a,b,c;Harton et al, 2006d), polydimethyl phenylene oxide (PDPO) (Lin et al, 2003), PVP (Zheng et al, 1995;Pinto, Novak, & Nicholas, 1999;Yokoyama et al, 1999;Harton, Stevie, & Ade, 2006a,b;Harton et al, 2006d), PPV and other polymer based LED materials Bulle-Lieuwma & van de Weijer, 2006), solar cell materials (Bulle-Lieuwma et al, 2003), conducting polymers (Gray et al, 1992), video tapes (Chujo, 1991), silicones …”

Diffusion Kinetics at Liquid‐Glassy Polymer Interphases

“…Figure 3 summarizes similar results plotted in Fickean fashion, as functions of the square root of the elapsed diffusion time. In these experiments and differently from previous reports,5,10 we have taken particular care in examining not only an extended range of diffusion temperatures, but also a wide range of diffusion times. In this way, diffusion data are extended over time scales large enough to make sure whether the evolution is linear or other.…”

“…Some authors have extended the concept of Case‐II to explain the diffusion mechanism at the liquid/glassy polymer interphase, claiming that the process is controlled by the mechanical response of the glassy polymer 5–7. This idea has been predominant in many papers published about this topic, including some very recent ones 10. Other authors have questioned this view pointing out that large molecules, such as liquid polymers, are associated with extremely low osmotic pressures, insufficient to trigger a mechanism of mechanically controlled penetration 9.…”

“…We focused our investigation on two miscible polymer pairs: a) liquid poly(vinyl methyl ether)‐glassy polystyrene ( l ‐PVME/PS); and b) liquid PS‐glassy poly(phenylene oxide) ( l ‐PS/PPO). For these systems, the diffusion mechanisms reported in the literature are contradictory,9,10 or based on studies not systematic enough to be convincing 5,6,10. We also wanted to investigate whether the observed mechanism is a general or a particular one (e.g., osmotic pressure effects are only dependent on molecular sizes).…”

Neutron Reflectometry on Interfacial Structures of the Thin Films of Polymer and Lipid

“…At the end, almost uniform ðAEb i Þ was attained along the depth direction reflecting homogeneous composition, though the film surface was still kept enriched with the PTMSS with lower surface energy. This complicated interfacial behavior does not simply obey the Fickian diffusion process, but can be explained by an asymmetric diffusion 40 due to the difference in molecular mobility between glassy PTMSS and rubbery PI at 90 C. …”