Freely standing film

Experimental. Films of B-staged BCB were coated on salt substrates by spray deposition and cured in air at 250°C for one hour. This cure period was determined from the minimum time necessary for the elimination of the reaction exotherm as measured by DSC. After the cure cycle the films were removed by dissolving the substrate in a water bath. The freely standing films so obtained were between 25 mm and 50 mm thick. 

Samples for dielectric spectroscopy were prepared by sputtering 100 nm of Au in an Ar plasma onto both sides of the freely standing films. Disks 9.5 mm in diameter were punched out of the metallized films. These disks were used to measure both the dielectric permittivity with an HP 4192 Impedance Analyzer and the dissipation factor with a GenRad 1615-A Capacitance Bridge. 

Stacked thin films exhibit glass transition dynamics that are similar to those observed for single thin films. The Tg of as-stacked thin films is lower than that of the single thin supported films with the same thickness as that of a single layer in the stacked thin films, and is higher than that of freely standing films. 

Roth CB, Dutcher JR (2003) Glass transition temperature of freely-standing films of atactic poly(methyl methacrylate). Eur Phys J E 12 S103-S107... 

A major advancement in the study of nanometer-thick films came when Dutcher and co-workers [Forrest et al., 1996, 1997, 1998] developed a capability to perform ellipsometry or Brillouin scattering measurements on freely standing films. One... 

Fig. 13 Tg of PS film as a function of its thickness, (a) Freely standing films with two different molecular weights. The experiments were ctirried out using Brillouin light scattering (BLS) and ellipsometry [35,37]. (b) Films on the native oxide covered silicon surface (eUipsometry measurements) [31]. PS samples with Afw = 1.2 x 10 , 5 x 10 , and 2.9 x 10 were taken...

Dielectric Breakdown Measurements. The dielectric breakdown strength was measured on the freely standing BCB-2 films as described above. The breakdown strength was 2.5 x 10 v/cm for 22 mm thick films. This value is -50% of the breakdown strength measured for 1.5 mm polyimide films on Si (8). However, the breakdown strength does not vary proportionally to the film thickness. The breakdown strength was also measured for 1.7 mm BCB-2 films deposited on a Si substrate. The value obtained from this measurement was 4.0 x 106 v/cm. The latter value was much closer to breakdown strengths observed in polyimide films of comparable thickness. 

C. A. Murray, S. W. Kamp, J. M. Thomas, and J. R. Dutcher, Onset and manipulation of self-assembled morphology in freely standing polymer trilayer films. Phys. Rev. E 69, 061612... 

Napolitano S, Wiibbenhorst M (2010) Structural relaxation and dynamic fragility of freely standing polymer films. Polymer 51 5309-5312... 

Dalnoki-Veress, K., Forrest, J. A., Murray, C., Gigault, C., andDutcher, J. R., Molecular weight dependence of reductions in the glass transition temperature of thin freely standing polymer films, Phys. Rev. E, 63, 031801 (2001). 

Roth, C. B., and Dutcher, J. R., Hole growth in freely standing polystyrene films probed using a differential pressure experiment, Phys. Rev. Lett., 72, 021803-1 to 021803-4 (2005b). 

In spin-coated or free-standing films, the smectic layers are aligned parallel to the surface [163, 164]. In such a homeotropic arrangement the tilt direction is not defined and the polar axis of different domains is randomly distributed over the film. If the substrate is water-soluble, it can be dissolved and freely suspended films can be obtained [165]. 

Beginning from the pioneer works of McKenna [28,29], Keddie [30,31], van Zanten [32-34], and Forrest with co-workers [35-37], a very large series of experimental studies of dynamics has been performed for polymers in ultrathin films, adsorbed on solid substrates, or in the freely standing state, and for polymers and low-molecular-weight substances confined to nanovolumes (nanopores, nanoslits, and so on) [38-65]. The results of these studies have been summarized in particular in the reviews [40,52,53],... 

Figure 13a shows the Tg values of freely standing PS films measured by ellipsometry and BLS techniques [35,37]. Its dramatic decrease, from 100°C to 30-40°C, was observed for the 30-50 nm thick films the critical film thickness (bend in the... 

Ngai, K.L., Rizos, A.K., Plazek, D.J. Reduction of the glass temperature of thin freely standing polymer films caused by the decrease of the coupling parameter in the coupling model. J. Non-CtysL Solids 235, 435 (1998)... 

Napolitano, S., WuebbenhOTSt, M. Stmctural relaxation and dynamic fingility of freely standing polymer films. Polymra 51(23), 5309-5312 (2010)... 

Hsuan-Yi Chen and D. Jasnow, Layer dynamics of freely standing smectic-A films, Phys. Rev. E, 61, 493-503 (2000). 

THE GLASS TRANSITION IN FREELY-STANDING POLYMER FILMS... 

Figure 1 Tg versus film thickness h for freely-standing PS films of different M values (7).

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