Atomic force microscopy microphase separation

Demonstier-Champagne et al. used atomic force microscopy (AFM) to observe microphase separation within cast films of PS-PMPS-PS/ PS-PMPS block copolymer mixtnre [43] that were nsed to compatibilize a blend of PMPS and PS. The fractnre snrface of blend films with the block copolymer incorporated show a far finer dispersion of particle sizes than those without. Matyjaszewski et al. studied PMPS-PS thin films by SFM (scanning force microscopy) and TEM (transmission electron microscopy) and Fig. 8 shows a TEM picture of a thin section of a film which was prepared by slow evaporation from THE, which is slightly selective for the polystyrene block [73]. 

Physical characterization of macromolecular systems strives to determine chemical structure/property relationships. This subfield includes study of thermomechanical performance viscoelastic properties surface properties, adhesion science thermal transitions morphological analysis, including semicrystalline, amorphous, liquid-crystalline, and microphase-separated structures. Structural analysis employs electron microscopy, con-focal microscopy, optical microscopy, x-ray photoelectron spectroscopy, atomic force microscopy, and x-ray and neutron scattering of macromolecular compositions. 

Figure 6.7 Atomic force microscopy phase images for thin films of mixtures of polystyrene-poly(methyl methacrylate) (PMMA) and PMMA-60 with various volume fractions (—H) (a) 0.18, (h) 0.33, (c) 0.55, and (d) 0.67. Panels a and h show only microphase separation, whereas panels c and d clearly exhibit macrophase separation of PMMA homopolymer.

The PUs microstructure can be also investigated by means of atomic force microscopy (AFM). Phase images obtained via AFM, enable visual representation of the PUs microphase separated morphology. AFM records the surface topography of materials by measuring attractive or repulsive forces between the probe and the sample. Vertical deflections caused by surface variations are monitored as a raster scan drugs a fine tip over the sample. A detailed description of different modes in AFM technology has been described in [195]. 

More recently, the same strategy was attempted to prepare isotactic/syndiotactic stereoblock polypropylene by using mixtures of rac-dimethylsilyl-bis(2-methyl-benz[e]-l-indenyl)ZrCl2 and diphenylcarbenyl(Cp)(9-fluorenyl)ZrCl2 in combination with MAO. Morphological studies by means of atomic force microscopy on such materials documented exclusive microphase separation between the isotactic and syndiotactic domains. This behavior is at odds with physical blends of isotactic and syndiotactic polypropylene, for which macrophase separation was observed. ... 

It has been well established by Cooper and Tobolsky that the unique properties of polyurethanes are strongly linked to its two-phase morphology [21], Characterization of microphase separation is performed using a variety of techniques including dynamic mechanical thermal analysis (DMTA), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and atomic force microscopy. Consideration of both the thermodynamic driving forces and the kinetics is needed to elucidate microstructure formation in polyurethanes [60-66],... 

Over the years, electron microscopies and scanning or atomic force microscopy were fonnd to be the most powerful analytical tools in block copolymer research because they are able to highlight the type, size, and arrangement of the different blocks indnced by microphase separation (Hasegawa and Hashimoto 1996). 

In order to verify that block copolymers are formed it is necessary to demonstrate a microphase separation of the respective blocks. This can be done e.g. by atomic force microscopy (AFM) as demonstrated in Figure 3. Figure 3 a shows the morphology of the triblock copolymer 49Tri38 after slow evaporation of tetrahydrofbran (THF). The phase contrast mode was employed. There is a microphase separation but the phases do not appear very well ordered. Also thermal annealing above the glass transition did not yield a more perfect structure. 

Precisely this latter situation arises if the confining solid surface is endowed with a chemical pattern that is both nanoscopic in size and hnite in extent. Such chemical patterns may be created by lithographic methods [179]. Atomic beams have been employed to produce hexagonal nemostruc-tures [180]. Other methods capable of creating cliemically nanostnictured substrate surfaces involve microphase separation in diblock copolymer films [181] or the use of forc( microscopy to locally oxidize silicon surfaces [182]. 

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