Polystyrene films temperature

Figure 2. Time dependence for 600K MW polystyrene films spin cast at 8,000 rpm and annealed at different temperatures.

Transmission and scanning electron microscopy, differential scanning calorimetry and minimum film temperature analysis supports a core/shell morphology for the two-stage latex polymers, consisting predominantly of a polystyrene rich core surrounded by a soft acrylic rich shell. 

The polystyrene films were irradiated with the ions in a vacuum chamber ( < 10 6 Torr) at room temperature. The sample holder had a hole 2 mm or 7 mm in diameter (Fig. lb). The ion beam currents used in this experiment were very low ( < 1 nA). 

Abstract Thin polystyrene films are prepared by spin-coating and annealed above the calorimetric glass transition temperature Tg alternatively in vacuum, in a pure nitrogen atmosphere, in the presence of water vapor or in ambient air. 

Fig. 7 Dielectric loss vs. temperature at different frequencies, as indicated, for a thin polystyrene film of 89 nm, before and after 24 hours of annealing at 180 °C in a pure nitrogen atmosphere...

For thin polystyrene films annealed for 12 hours at 150 °C in high vacuum (10-6 mbar) and measured in a pure nitrogen atmosphere the dynamic glass transition was characterized using two experimental techniques capacitive scanning dilatometry and Broadband Dielectric Spectroscopy. Data from the first method are presented in Fig. 15a, showing the real part of the complex capacity at 1 MHz as a function of temperature for a thin PS film of 33 nm. 

Fig. 2. Temperature dependence of intensity of fluorescence of auramine O in polystyrene film open circles, heating from room temperature to the melting point filled circles, cooling and solidifying the melt (70)...

The results of early flash studies were irreproducible and led to various conclusions concerning the nature of the primary photoproduct. For example, flash photolysis of Cr(CO)g in room temperature degassed cyclohexane solutions and in polystyrene film was reported to produce a transient having a maximum absorbance in the visible at 450 nm and which decayed with second-order (equal concentration) kinetics (83). The following scheme was proposed for the overall mechanism ... 

In terms of their dielectric response, thin polymer films turn out to be thermally stable if kept in an inert atmosphere (i.e., flow of pure nitrogen), even for long times at temperatures well above the glass transition. An example is given in Fig. 3 for a thin polystyrene film of 89 nm After 24 hours at 180°C in a pure nitrogen atmosphere, the sample was measured again and no changes in the dielectric response were detected. 

Figure 8. Temperature dependence of integrated resolved emission for a polystyrene film.

Figure 10. Temperature dependence of fluorescence decay lifetimes of a polystyrene film.

The multiphoton absorption cycle was confirmed by a comparison of the temporal profile of the fluorescence of anthracene-doped polystyrene films with computational results based on the cyclic process [97]. In the computational studies, the ground state, first excited singlet state, and lowest triplet state have been included. The calculated temperature rise during the laser pulse depends nonlinearly on the laser intensity. Rapid internal conversion within the triplet manifold is the most effective mechanism for depositing heat at the irradiated surface. 

Browning et ai (60) observed a broad singlet spectrum at g = 2 after irradiation of polystyrene at —196° C and attributed this spectrum tentatively to phenyl radicals. Selivanov et al. (87) also observed a similar singlet spectrum with a width of about 20 oersted at —196° C (Fig. 11a). When this sample was warmed to room temperature in the presence of air, the spectrum changed into an asymmetric singlet spectrum with a width of about 16 oersted (Fig. lib). This spectrum disappeared after several seconds at room temperature. Figure 11c shows the spectrum erf free radicals produced after irradiation of the polystyrene film at room temperature in the presence of air. The spectrum is a symmetric singlet... 

Excimer formation has been studied in polystyrene and poly(a-alkylstyrenes)189 (PS), poly(vinylcarbazole),139>140 poly-(2-vinylnaphthalene), and poly-(4-vinyl-biphenyl).141 For polystyrene films, David et a/.189 showed that the fluorescence yield increased with increasing crystallinity, at both ambient temperature and 77 K. The contribution of excimer fluorescence yield increased in the sequence atactic (0.7) < atactic oriented (0.60) < isotactic amorphous (0.28) < isotactic crystallized (0.01), with normal yields relative to excimer given in parentheses. Similar results were obtained for poly(vinylcarbazole), PVCZ, although the contribution of excimer fluorescence at 77 was independent of crystallinity. The results can be interpreted in terms of electronic energy migration to low-energy defect sites from which excimer emission can occur. In PVCZ copolymers with fumaronitrile (10), diethyl fumarate (11), and diethyl maleate (12) (Scheme 6),... 

Figure 11.6 The glass transition temperature as a function of film thickness of polystyrene films on silicon, gold, and SAM surfaces. (Reprinted with permission from Ref. 50. 2004 Elsevier.)...

Dewetting Experiments Using a Visco-Elastic Fluid Polystyrene Films Slightly Above the Glass Transition Temperature... 

Hutcheson, S. A., and McKenna, G. B., Comment on the properties of free polymer surfaces and their influence on the glass transition temperature of thin polystyrene films by J.S. Sharp, J. H. Teichroeb and J. A. Forrest, Eur. Phys. J. E, 22, 281-286 (2007). 

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