Glass transition of polystyrene near the surface studied by slow-positron-annihilation spectroscopy

Jean, Y. C.; Zhang, Renwu; Cao, Hui; Yuan, Jen-Pwu; Huang, Chun‐Kai; Nielsen, B.; Asoka‐Kumar, P.

doi:10.1103/physrevb.56.r8459

Cited by 176 publications

(166 citation statements)

References 16 publications

Supporting

Mentioning

148

Contrasting

Order By: Relevance

“…15 Recently, it has been observed that a significant depression of T g near a polymer thinfilm surface occurs as deep as several tens of nanometers, up to 100 nm, into the bulk region. [34][35][36] It is crucial to understand the mechanisms of why the existence of the high-mobility interfacial region might affect the overall polymer chain dynamics. The glass transition behavior was explained with a percolation mechanism by Hunt [37][38][39][40] in the early 1990s.…”

Section: T Gmentioning

confidence: 99%

Pore structure and glass transition temperature of nanoporous poly(ether imide)

Liu

Ozisik

Siegel

2006

J Polym Sci B Polym Phys

View full text Add to dashboard Cite

The effect of nanopores on the glass transition temperature (T g ) of poly (ether imide) was studied with differential scanning calorimetry. Nanoporous poly (ether imide) samples were obtained through the phase separation of immiscible blends of poly(ether imide) and polycaprolactone diol and by the removal of the dispersed minor phase domains with a selective solvent. Microscopy and statistical methods were used to characterize the pore structure and obtain the pore structure parameters. The pore size was found to depend on the processing time and the initial blend composition, mainly because of phase-coarsening kinetics. A decrease in T g was observed in the nanoporous poly(ether imide) in comparison with the bulk samples. The change in T g was strongly influenced by the pore structure and was explained by the percolation theory.

show abstract

Section: T Gmentioning

confidence: 99%

Pore structure and glass transition temperature of nanoporous poly(ether imide)

Liu

Ozisik

Siegel

2006

J Polym Sci B Polym Phys

View full text Add to dashboard Cite

show abstract

“…The positron annihilation technique was used to estimate the free volume in the surface region, and indicated that the effective T g of PS was T g (bulk)-25 C and T g (bulk)-43 C for the surface region to a depth of 5 nm and 2 nm, respectively. 5,6 Scanning viscoelasticity microscopy 7 showed enhanced mobility on the PS surface, and subsequent atomic force microscopy measurements confirmed a soft surface region 3-4 nm thick with low T g . 8 Regarding thermodynamical considerations, concentration of the ends of molecules in the surface region was pointed out, 9 suggesting a decrease in polymer density on the surface, subsequently confirmed by simulations.…”

mentioning

confidence: 99%

Thickness Anomalies in Supported Polystyrene Films with Thicknesses Comparable to the Radius of Gyration

2009

View full text Add to dashboard Cite

We report on X-ray reflectivity of ultrathin polystyrene films with thickness h, which is comparable to the radius of gyration R g . Tiny jumps in thickness, accompanying an increase in surface roughness and decrease in electron density, are reproductively observed at around 80 C and 92 C only with increasing temperature. For films thinner than R g , the jump at 92 C disappears. However, films of 2R g thick, the jump at 80 C is hardly observed with a faint trace in slope at this temperature. For much thicker films, neither jump appears in heating experiments. The thickness dependent complex behavior observed in non-equilibrium condition is considered to be some indication of surface and confined effects, because the characteristic film thicknesses coincide with the order of R g .KEY WORDS: Ultrathin Polystyrene Film / Glass Transition / Thickness Jump / X-Ray Reflectivity / Physical properties of systems are strongly affected by symmetry, dimensionality, and the number of constituent particles. Part of such dependences comprises an interesting field of physics, widely known as confined effects. Numerous experimental and theoretical studies have reported many intriguing confined effects on the glass transition of polymeric materials, and therefore glass-forming polymers are recognized to be an excellent example of such systems. As reproducible experimental results are easily obtained, polystyrene (PS) thin films with atomically flat surfaces have been used as standard glass-forming polymer films. For substrate-supported PS films, a large reduction in the glass transition temperature (T g ) dependent on the film thickness is observed for films less than 40 nm thick.1,2 More interestingly, the so-called free-standing PS films showed T g reduction much larger than those of supported films.3,4 Since the free-standing PS films are free from the interaction between the solid substrates, the strong reduction in T g is considered to reflect enhanced mobility inherent in the surface region exposed to air. The positron annihilation technique was used to estimate the free volume in the surface region, and indicated that the effective T g of PS was T g (bulk)-25 C and T g (bulk)-43 C for the surface region to a depth of 5 nm and 2 nm, respectively.5,6 Scanning viscoelasticity microscopy 7 showed enhanced mobility on the PS surface, and subsequent atomic force microscopy measurements confirmed a soft surface region 3-4 nm thick with low T g . 8 Regarding thermodynamical considerations, concentration of the ends of molecules in the surface region was pointed out, 9 suggesting a decrease in polymer density on the surface, subsequently confirmed by simulations. 10,11 Since the reduced density naturally leads to an increase in the free-volume and enhanced mobility of chain segments, several experimental studies on the surface glass transition of PS successfully employed a two-layer 1 or three-layer 5 model where the surface layer is characterized by constant thickness and peculiar physical properties (e.g., density, and viscosity...

show abstract

“…Although the AFM response vs. T curve is strictly speaking different from this curve due to the finite creep rate for the tip to penetrate the rubbery layer, one may envision that the position of the intercept would still be very close to T g (∞) due to the theoretical divergence of the rubbery layer thereat. Given the vast number of recent experiments showing the surface dynamics of PS to be enhanced, 29,44,45,49 the scenario portrayed in Fig. 11 is probable.…”

Section: Atomic Force Microscopymentioning

confidence: 99%

“…22,28,29,36−50 These experiments involved a large number of measurement techniques, which include angle-dependent x-ray photoelectron spectroscopy, 28 various kinds of atomic force microscopy (AFM), 37−42 near-edge x-ray absorption fine structure, 43,44 positron annihilation lifetime spectroscopy, 22,45 optical birefringence measurement, 46 melting of a topographic structure, 49,50 and local T g probe by fluorescence labeling. 29 Although some of the results are conflicting, the majority holds that the mobility of PS, for which the thin film T g shows the biggest reduction, is enhanced near the free surface.…”

Section: Experimental Search For Enhanced Mobility At the Polymer-airmentioning

confidence: 99%

Anomalous Dynamics of Polymer Films

Tsui

2008

Series in Soft Condensed Matter

View full text Add to dashboard Cite

This chapter reviews the recent experiments involving the dynamics of polymer films with thickness comparable to the gyration radius of the polymer, which overwhelmingly show that their glass transition temperature, T g , depends on the film thickness and can sometimes differ significant from that of the bulk. The greatest mystery is the onset film thickness of this phenomenon being ~50 nm, much larger than the typical cooperativity size (~3 nm) of glass transition. While the sliding chain model [De Gennes, Eur. Phys. J. E (2000)] can qualitatively explain the results of the high molecular weight (M w ) freely-standing films, it fails to account for those of the low-M w freely-standing films and the supported films. For the latter two, at least two theories, i.e., the percolation theory [Long et al., ibid (2001)] and surface capillary wave theory [Herminghaus et al., ibid (2001)] have been proposed that can account for the observed thickness dependence of thin film T g . However, experimental data available at this time do not allow the theories to be distinguished. We briefly outline the physical ideas of these theories, and delineate how dynamical measurements of nanometer thick films may provide important insights about the problem.

show abstract

Glass transition of polystyrene near the surface studied by slow-positron-annihilation spectroscopy

Cited by 176 publications

References 16 publications

Pore structure and glass transition temperature of nanoporous poly(ether imide)

Pore structure and glass transition temperature of nanoporous poly(ether imide)

Thickness Anomalies in Supported Polystyrene Films with Thicknesses Comparable to the Radius of Gyration

Anomalous Dynamics of Polymer Films

Contact Info

Product

Resources

About