Surface Relaxations in Polymers

Liu, Y.; Russell, Thomas P.; Samant, Mahesh G.; Stöhr, J.; Brown, Hugh R.; Cossy-Favre, A.; Dı́az, J.

doi:10.1021/ma970869a

Cited by 169 publications

(197 citation statements)

References 29 publications

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“…9 In particular, good quantitative agreement between the change in T g 19 and the change in T 0 as the PS film thickness is decreased from 50 to 10 nm supports the viewpoint that T 0 is directly related to T g . 8,9 This result, consistent with the previous finding that T 0 has the same M w dependence as T g , 12 suggests that the ␣ relaxation may dominate the observed relaxations of the rubbed PS films near T g . Moreover, at thicknesses greater than 30 nm, the T 0 's of PS films on HOSi are lower than those on SiO 2 surfaces.…”

Section: Resultssupporting

confidence: 89%

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Rubbing‐induced molecular alignment and its relaxation in polystyrene thin films

Tsang

Xie

Tsui

et al. 2001

J Polym Sci B Polym Phys

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Rubbing-induced molecular alignment and its relaxation in polystyrene (PS) thin films are studied with optical birefringence. A novel relaxation of the alignment is observed that is distinctly different from the known relaxation processes of PS. First, it is not the Kohlrausch-Williams-Watts type but instead is characterized by two single exponentials plus a temperature-dependent constant. At temperatures several degrees or more below the glass-transition temperature (T g ), the relaxation time falls between that of the ␣ and ␤ relaxations. Second, the decay time constants are the same within 40% for PS with weight-average molecular weights (M w 's) of 13,700 -550,000 Da at temperatures well below the sample T g 's, indicating that the molecular relaxations involved are mostly local within the entanglement distance. Nonetheless, the temperature at which the rubbing-induced molecular alignment disappears (T 0 ) exhibits a strong M w dependence and closely approximates the T g of the sample. Furthermore, T 0 depends notably on the thickness of the polymer in much the same way as previously found for the T g of supported PS films. This suggests that the ␣ process becomes dominant near T g . Preliminary spectroscopic studies in the mid-infrared range show a significant degree of bending of the phenyl ring toward the sample surface, with the COC bond connecting the phenyl ring and the main chain tends to lie along the rubbing direction, which indicates that the relaxation is connected with the reorientation of this COC bond. We exclude the observed relaxation, as predominantly a near-surface one, because detailed studies on the effects of rubbing conditions on the degree of molecular alignment indicate that the alignment is not local to the polymer-air surface.

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Section: Resultssupporting

confidence: 89%

“…Similar behavior has been observed before. 8,9 For PS films on SiO 2 , T 0 becomes smaller for thinner films. For PS films on HOSi, however, T 0 remains the same for all thicknesses.…”

Section: Resultsmentioning

confidence: 99%

Rubbing‐induced molecular alignment and its relaxation in polystyrene thin films

Tsang

Xie

Tsui

et al. 2001

J Polym Sci B Polym Phys

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“…8,18 Experiments using near-edge X-ray absorption fine-structure (NEXAFS) on rubbed polystyrene films have shown almost no difference in the rate of relaxation between polymer chains within 1 nm of the surface and chains within 10 nm of the surface, again indicating a small influence of the surface on the system's dynamics. 18 On the other hand, Monte Carlo simulations have shown a higher mobility at polymer-air surfaces, due to a reduction in density. 17 However, this effect does not extend more than a few segmental diameters into the film.…”

Section: Introductionmentioning

confidence: 99%

Surface Dynamics in Rubbed Polymer Thin Films Probed with Optical Birefringence Measurements

et al. 2000

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Measurements of the optical birefringence were used to probe the relaxation of rubbed ultrathin polystyrene (PS) films on glass substrates. It was found that the glass transition temperature, T g, of the films dropped by 15-20 K as the film thickness decreased from 10 µm to 5.8 nm. Experiments on thick films (∼10 µm) revealed that molecules closer to the polymer-air interface relax more quickly than molecules farther from the interface. These results are explained in the context of past experimental studies of thermal properties of similar ultrathin polymer films.

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“…Other methods involve dilatometric measurements for the determination of the specific volume, mechanical property measurements (thermomechanical analysis, TMA, and dynamic mechanical analysis, DMA), and dielectric measurements [4]. Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy [12], x-rays diffraction [13], slow-positron-annihilation spectroscopy (SPAP) [14,15], brillouin light scattering (BLS) [16,17], photon correlation spectroscopy and quartz crystal microbalance techniques [18], spectroscopic ellipsometry (SE) [19], attenuated total reflection (ATR) [20], and scanning probe microscopy (SPM) [21][22][23][24][25][26][27] have all been employed to determine T g for thin polymer films.…”

Section: Macromolecular Probing Techniquesmentioning

confidence: 99%