Single interface, polymers

MIM or SIM [82-84] diodes to the PPV/A1 interface provides a good qualitative understanding of the device operation in terms of Schottky diodes for high impurity densities (typically 2> 1017 cm-3) and rigid band diodes for low impurity densities (typically<1017 cm-3). Figure 15-14a and b schematically show the two models for the different impurity concentrations. However, these models do not allow a quantitative description of the open circuit voltage or the spectral resolved photocurrent spectrum. The transport properties of single-layer polymer diodes with asymmetric metal electrodes are well described by the double-carrier current flow equation (Eq. (15.4)) where the holes show a field dependent mobility and the electrons of the holes show a temperature-dependent trap distribution. 

Yoon TH, Arnold CA, McGrath JE (1989) Titanium 6/4 single lap shear adhesive performance of polyimide homopolymers and poly(siloxane imide) segmented copolymers. Mater Res Soc Symp Proc 153 (Interfaces Polym Met Ceram) 211... 

The generation of photoexcited species at a particular position in the film structure has been shown in (6.19) and (6.20) to be proportional to the product of the modulus squared of the electric field, the refractive index, and the absorption coefficient. The optical electric field is strongly influenced by the mirror electrode. In order to illustrate the difference between single (ITO/polymer/Al) and bilayer (ITO/polymer/Ceo/Al) devices, hypothetical distributions of the optical field inside the device are indicated by the gray dashed line in Fig. 6.1. Simulation of a bilayer diode (Fig. 6.1b) clearly demonstrates that geometries may now be chosen to optimize the device, by moving the dissociation region from the node at the metal contact to the heterojunction. Since the exciton dissociation in bilayer devices occurs near the interface of the photoactive materials with distinct electroaffinity values, the boundary condition imposed by the mirror electrode can be used to maximize the optical electric field E 2 at this interface [17]. 

Next, results for a nonbridging polymer at c = 0.1 M, M = 4,000 provide a comparison with the more widely studied case of polymer adsorption at a single interface [9], The results are given in Table 12.6. In this case, it is clear that the fractionation factor/is approximately constant, with an average value of 0.95. This means that the polymer is roughly equally divided between the two phases. 

The overall performance of single-layer polymer LEDs can be drastically improved if hole- and/or electron-transport layers are inserted at the interface between the polymer and the electrodes (see Fig. 8.15).107,108 The working principle of singlelayer and multilayer LEDs, which is outlined in Refs. 56 and 109, can be well described in various models.110-112... 

Structure formation of polymer CM with low polymer content in the PE-P1 melt apparently takes the following path. Equilibrium phases a and (3 are nucleated during melt crystallization, although do not stratify fully with formation of a single interface because of high viscosity of the pol3uner system. Thus enriched by the polymer, the /3-phase approaches a solid body in its properties and forms a continuous porous matrix with the pol3uner-depleted a-phase. As a result, a gel structure typical of the biphasic polymer with characteristic deformation properties and inclination to syneresis is formed [70]. 

The second study (Meghala and Ranganathaiah 2012) was dedicated to the evaluation of interfaces in poly(styrene-co-acrylonitrile) (SAN)-based ternary polymer blends using also positron lifetime spectroscopy. The method successfully applied for binary blends (single interface), mentioned above, was theoretically modified for ternary blends and experimentally verified by measuring free volume content in blends and their constituents. They tested the efficacy of this method in two ternary blends S AN/PVC/PMMA and SAN/EVA/PVC at different compositions. The effective hydrodynamic parameter evaluated using individual values turned out to be handy in predicting the overall miscibility level of a ternary blend. 

One approach to obtain the energy to break single chains involves placing them across a polymer blend interface. Polymer interfaces between two polymers, however well annealed, are often weak see Chapter 12. One way to strengthen an interface is to put small quantities of block copolymers at the interface. Usually the two blocks are identical to or at least soluble in their... 

Wang W, Haung Z, Laird ED, Wang S, Li CY. Single-waUed carbon nanotube nanoring induces polymer crystallization at liquid/liquid interface. Polymer 2015 54(24) l-9. 

Figure B3.6.2. Local mterface position in a binary polymer blend. After averaging the interfacial profile over small lateral patches, the interface can be described by a single-valued function u r. (Monge representation). Thennal fluctuations of the local interface position are clearly visible. From Wemer et al [49].

Fig. 24. Experimental set-up of Harding and Berg for testing the single-particle composites. The digital video image shows an example of a failed interface for a silane-treated glass bead in polymer matrix. Redrawn from ref. [166].

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