Polymer films volume-fraction profiles

Apart from yielding information about the film thickness and the nature of the interface, it is also possible to determine the volume fraction profiles of components present in a particular layer. For example, in the case of an adsorbed polymer... 

Reflectometry, where only the intensity of the reflected light is measured, requires a thin film adsorbed onto a reflecting substrate. The thin film has a different refractive index than both the bulk solution and the substrate so interference occurs between the rays reflected from the substrate/fllm and film/bulk solution interfaces. By model fitting the refractive index-distance behavior, it is possible to extract the volume fraction profile of the adsorbed polymer layer (15). 

Zink et al. used a blend of polystyrene (hPS) and its deuterated counterpart (dPS), both of molecular weight 1.95 x 106 (abbreviated 1.95 M). The average volume fraction (4>dPS) of deuterated polystyrene was 30%. The polymers were dissolved in toluene and spin cast on thin silicon wafers (about 10 x 10 mm), the resulting film thickness being about 300 nm. The samples were annealed at 245°C for 8 days, and the measurement of the resulting depth profiles was conducted by NRA using a monoenergetic 700 keV 3He beam. The nuclear reaction employed can be written ... 

Fig.20. Order parameter profiles m(z)=([pA(z)-pB(z)])/([pA(z)+pB(z)]), where pA(z), pB(z) are densities of A-monomers or B-monomers at distance z from the left wall, for LxLx20 films confining a symmetric polymer mixture, polymers being described by the bond fluctuation model with N=32, ab=- aa=- bb=8 and interaction range 6. Four inverse temperatures are shown as indicated. In each case two choices of the linear dimension L parallel to the film are included. While for e/kBT>0.02 differences between L=48 and L=80 are small and only due to statistical errors (which typically are estimated to be of the size of the symbols), data for e/kBT=0.018 clearly suffer from finite size effects. Broken straight lines indicate the values of the bulk order parameters mb in each case [280]. Arrows show the gyration radius and its smallest component in the eigencoordinate system of the gyration tensor [215]. Average volume fraction of occupied sites was chosen as 0.5. From Rouault et al. [56].

Degree of ciystallinity of polymer films (a volume fraction of the crystal ordered areas in a material) in this research was defined by diffractograms Fig. 5.3 for a series of samples only semiquantitative (more/less). The essence of the method of crystallinity definition consists in analytical division of a diffractogram profile on the Bragg peaks from crystal areas and diffusion peak of an amorphous phase [20], as is shown in Fig. 5.4. 

Figure 13 Volume fraction composition profiles for a thin film of deuterated polystyrene star polymer diffusing into a hydrogenous polystyrene star polymer film. Reprinted with permission from Clarke, N. Colley, F. R. Collins, S. A. etal. Macromolecules 2906,39,1290. Copyright 2006 American...

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