Segregation layer

Figure 1.37 Top and side views taken 15 s after merging of two droplets, one being fluorescent and the other transparent. Having only the top view can lead to the erroneous conclusion that mixing is completed, while the side view shows that actually a segregated, layered fluid system exists [97] (by courtesy of RSC).

Figure 25.7 Schematic illustration of the microphase-segregated layered structure for the mixtures of hydroxyl-terminated mesogenic compounds 13 and 15 with ionic liquid 16.

The quantitative study of polymer surfaces and interfaces is about ten years old and so is a relatively recent subject. It is therefore not surprising that there are many possibilities for future research. Many of the phenomena that occur at polymer interfaces are related to self-assembly. Even the simplest example, that of surface segregation of one component of a polymer blend to an interface is self-assembly. This is because where we initially had a homogeneous film, we now have one with two layers, a bulk layer and a surface segregated layer. We have shown how even such a well-studied phenomenon as surface segregation can have a future because with it one can generate a surface which could provide an excellent precursor to an interface. 

The profile ( >(z) of the surface segregated layer is predicted by a mean field theory to follow the formula (obtained by integrating Eq. 25) ... 

Numerous trials for the mean field approach have been performed. Most of them have been focused on testing whether real profiles c )(z) of the surface segregated layer follow Eq. (30). Neutron reflectometry (NR, with a depth resolu-... 

Snoeck et al. (13) suggested that segregation is a fast process and that a segregation/dissolution equilibrium exists at the gas side of the nickel particle. A simple Langmuir equation (Eq. (2 and 3)) was used to estimate the concentration of carbon in the segregation layer (7) ... 

In Eq. (2) 6c is the surface coverage of carbon and Xb is the weight fraction of carbon in the segregation layer of Ni (g carbon/g Ni). The concentration of carbon dissolved in Ni at the support side of the particle equals the saturation concentration of filamentous carbon in Ni during steady-state carbon filament growth (CNi,r= C>at) (7, 13). 

Suz] Suzuki, S., Waseda, Y, Copper Segregated Layer and Oxide Layer Formed on flie Surface of an Fe-0.8 at.% Cu Alloy by Angle Resolved XPS , Scr. Mater., 36(8), 915-920 (1997) (Interface Phenomena, Experimental, 15)... 

In addition, we have to take into account that metal oxide-based nanocomposites have specific structure. Research on such a two-phase system, in which the concentration of the second oxide phase is much less than the concentration of the base oxide, has shown that the second phase, as a rule, is finely dispersed on the surface of the base oxide grains (Szezuko et al. 2001 Pagnier et al. 2000 Carreno et al. 2002). Possible versions of segregation layers of foreign cations on the surface of SnOj grains are shown in Fig. 14.4 (Varela et al. 1999 Carreno et al. 2002). It has been established... 

Fig. 14.4 Formation of segregation layer on the surface of SnOj grains as dependent on the nature of the doping elements (Reprinted with permission from Korotcenkov 2005, Copyright 2005 Elsevier)...

Figure 5. Depth profiles for segregated layers at grain boundaries showing single-atom-layer distribution [35].

All the work described above has established XPS firmly as a flexible method for the evaluation of the acid-base properties of homopolymers, but the technologically more important advantage of XPS is its ability to analyze thin modified or segregated layers not amenable to traditional forms of analysis [129]. The molecular probe technique has been used to good effect by Shahidzadeh et al. in the study of the plasma treatment of poly(propylene) film [130-132]. Their work identified the need to select basic probe molecules for the assessment of acidic surfaces, and dimethyl sulfoxide was shown to be a good choice, although the photoelectron cross section for sulfur is low, as it is for the Cl 2p core level used for trichloromethane this puts an effective limit on the detectability of the molecular probe, i.e., the number (but not the strength) of the acid-base pairs detectable. 

SEM indicated well-defined regions of segregated layers of montmorillonite and polymer. The bilayer thickness decreased respectively with montmorillonite content by 53, 31, 24, 17, and 11 nm. The modulus of the constructions increased from 0.025 0.005 GPa for the pure polymer to 3.6 GPa for the construction with 41 wt.% montmorillonite. The tensile strength increased from 13.2 0.9 MPa for the pure polymer and plateaued at approximately 39.4 3.0 to 41.2 3.8 MPa in the range of 13 to 21 wt.% montmorillonite content in the construction. The percent elongation to failure steadily decreased from 4.10 0.10 for the pure polymer to 0.008 0.003 for the construction with 41 wt. % montmorillonite. Apparently, the restriction of the polymer in the... 

As indicated above, the surface treatment process may be responsible for the removal of such material and exposing the bulk of the polymer underneath the segregated layer. Such a situation can be illustrated by the XPS spectra of Fig. 10.4 fi om PVC in its extruded form and after flame treatment. The extrudate is protected by a thin film of low density polyethylene (LDPE), and upon removal of this film the spectrum (O Fig. 10.4a) is dominated by carbon and oxygen with significant contributions from PVC-spedfic elements such as chlorine, lead, and zinc. On flame treatment (O Fig. 10.4b), the carbon level is reduced to a certain extent... 

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