Thin film blends

In a large part of what we have discussed above, we considered binary polymer mixtures. However, the situation is somewhat different, if instead of polymer blends, thin films of block copolymers are investigated. Due to the molecular connectivity of the different blocks, the inherent length scale is now determined by the size of the molecules. Early experiments focussed on the thin film morphology in symmetric diblock copolymers, where surface interactions tend to orient the block copolymer lamellae parallel to the boundary surfaces. In contrast to most bulk specimens, the planar interfaces lead to the formation... 

Using the standard TM-AFM procedures (3.2.1), the free surface of the blend thin films can be investigated. Owing to the softness and adherent properties of the PB phase, it is advisable to increase the rms amplitude of the free cantilever oscillation sufficiently. 

Babel, A., Wind, J.D. and Jenekhe, S.A., Ambipolar charge transport in air-stable polymer blend thin-film transistors, Adv. Func. Mater, 14, 891-898, 2004. 

Ogawa, H., Kanaya, T., Nishida, K., Matsuba, G. Phase separation and dewetting in polystyrene/poly(vinyl methyl ether) blend thin films in a wide thickness range. Polymer 49(1), 254-262 (2008)... 

Fig. 10.7 Three-dimensional AFM images (50x50 jim ) of PMMA/PS (50/50 w/w) blend thin films. Images on the left were...

H. Zhou, ). Fang, J. Yang and X. Xie, Effect of supercritical CO2 on the surface structure of PMMA/PS blend thin films, pp. 137-145, Copyright (2004), with permission from Elsevier). 

A. Car, C. Stropnik, W. Yave, K.-V. Peinemann, Pebax /polyethylene glycol blend thin film composite membranes for CO2 separation Performance with mixed gases, Sep. Purif. Tech., 62, 110-117 (2008). 

The phase separation in blend thin films also proceeds by the well-described bulk mode of nucleation and growth and spinodal decomposition. However, the conditions of phase separation during the formation of a blend thin film are significantly... 

Reproduced with permission from K.G. Yager, E. Lai, C.T. Black, Self-assembled phases of block copolymer blend thin films, ACS Nano 8 (2014) 10582-10588. 

Figure 6.13 Height-mode atomic force microscopy images of poly(styrene-b-2-vinyl pyridine)/poly(methyl methacrylate) (PMMA) blend thin films with different compositions of PMMA (a) 10wt%, (h) 20wt%, (c) 30 wt%, (d) 40wt%, and (e) 50wt% at a fixed polymer concentration of 0.6 wt%.

Sharma, S. Zhang, W. Schrag, E. Hsaio, B. Mather, P. T. Sokolov, J. Rafailovich, M. H. Gersappe, D. Luo, H., Polymer Blend Thin Films with POSS Compatibilization and Dewetting. Chicago Am. Chem. Soc. Meeting 2001. 

KaUas, L., Bertrand, P. (2006) End group effect on surface and interfadal segregation in PS-PMMA blend thin films. Appl. Surf. ScL,252,6648-6651. 

Fig. 28 (a) DUV-SNOM and (b) topographic images of a phase separation structure of a polystyrene/poly(methyl methaacrylate) blend thin film. The polystyrene is directly observed without any labeling procedure... 

LEDs were fabricated with TA-PPP as the emissive layer. Single-layer devices of ITO/PEDOT/TA-PPP/Ca/Al were fabricated. PEDOT, poly(3,4-ethylenedioxythiophene), was used to enhance hole injection from the anode. Charge injections of the single layer LEDs were clearly hole dominant The barrier for electron injection, around 1.0 eV, is too high. Electron dominant materials such as DO-PF and 2-(4-t-butylphenyl)-5-biphenyloxadiazole (t-PBD) were used to enhance electron injection. The thin film of a TA-PPP and PF blend (95 5 weight ratio) was phase separated. Atomic force microscopy (AFM) showed PF spheres, close to 1 pm in diameter, dispersed in the TA-PPP matrix (Figure 6). This type of phase separation is common in blends of stiff and soft polymers. The PL emission of die blend film was characteristic of TA-PPP. However, once thermally treated, the spectrum shifted bathochromically much like PF. The EL spectrum from LEDs based on the blend thin film contained much emission from PF in the 500-700 nm regime. The device efficiency was about 0.43 cd/A. TA-PPP/PF double layer LEDs were also fobricated. But the efficiency was not improved because when PF was spin coated onto TA-PPP, the PF solution washed out most of the TA-PPP layer. 

Collision crushing PE-PP blend Thin film formers 63... 

Figure 9.2 Typical ellipsometric cooling scan for PPO and PS blend thin films. The thicknesses of PP03/PS7, PP05/PS5, and PP07/ PS3 are 477, 464, and 457 A, respectively. The vertical arrow indicates Tg for the film. The...

In order to obtain more accurate spatial information on the polymer blend surface, a highly focused probe SIMS, namely NanoSIMS, can be used. Indeed, the lateral resolution (in the range of some tens of nanometers) of this technique would be expected to be sufficient for imaging the domains [8,9]. Due to dynamic SIMS conditions of the measurement, and to the limited thickness of the polymer blend thin films, it is possible to acquire only a few frames before reaching the substrate [10], NanoSIMS has been used with some success to study the surface morphology and composition of thin-film polymer systems [8-lOj. 

Polymer blend thin films are interesting both for their technological applications (e.g., coatings) and from an academic point of view. By confining a polymer (blend) in a thin film, both the air-polymer and the polymer-substrate interface can (significantly) influence its physical properties, in comparison with those observed in bulk [12]. 

Polymer blend thin films are interesting both for their technological applications (e.g., coatings), and from an academic point of view [12]. 

Although micron-scale lateral phase separation has been observed in F8BT TFB blend thin films, these phase-separated domains are not pure at the submicron length scale, and a nanoscale vertical phase segregation may occur with enrichment of the lower surface energy component (TFB) at both air and substrate interfaces. Imaging of the spatial uniformity of electroluminescence emission on the microscopic scale indicates a spatially localized charge-carrier recombination in LEDs fabricated with these blends [53]. 

At this point, a number of the critical and experimental issues associated with ToF-SIMS imaging will be discussed, and several recent applications of ToF-SIMS imaging to the study of polymer blend thin films [137] reviewed. 

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