Doctor blade techniques

The basic poly(phenylene vinylene) (PPV) polymer is commonly prepared by the sufonium prepolymer route developed by WessUng and Zimmerman in 1968 but much modified by subsequent workers. The synthesis starts from 1,4-bis(chloromethyl)benzene, via the bis-sulfonium salt formed by reaction with tetrahydrothiophene, and then polymerisation is effected to give the prepolymer by reaction with lithium hydroxide (Figure 3.39). Because of the inherent insolubility of PPV it is this prepolymer that is used to form the film coating on the substrate, for example by using a doctor blade technique. The prepolymer is converted into PPV on the substrate by heating in an oven under vacuum at 200 °C for 8-10 h. 

The application of non-crosslinkable LC siloxanes is very simple The material can be applied by contacting a hot (90°C < T <150°C) substrate and subsequent shearing with a doctor blade or with a second substrate layer, e g., glass. The application can also be done with the doctor blade technique starting from the melt. 

In this technique, a film of the solution containing the soluble polymer is spread with uniform thickness over the substrate using a precision doctor blade. 53 In contrast to spin-coating, the doctor-blade technique is very useful for fabricating relatively thick films, but does not enable the fabrication of films < 100 nm thick, which are commonly used in OLEDs. 

Polymeric thin films in this thickness range can easily be prepared from solution by spin coating or doctor blading techniques. Drying the films at elevated temperatures under high vacuum or under inert atmosphere is necessary to remove residual solvent traces, which cause softening of the material and contribute to fast relaxation of the oriented chromophores to an isotropic state. 

Organic materials can be processed easily by spin-coating, by doctor blade techniques, or by evaporation through a mask. 

Padinger, F., et al. 2000. Fabrication of large area photovoltaic devices containing various blends of polymer and fullerene derivatives by using the doctor blade technique. Opto-Electron Rev 8 280. 

The method used for the preparation of thin films of PPV or its derivatives depends on the specific potymer. For those that present high solubility in common organic solvents, very simple procedures, such as casting, doctor-blade technique [98], or spin-coating of the polymer solution with further solvent evaporation can be used. In the case of spin-coating, the film morphology is sensitive to the solvent evaporation rate, density, viscosity, polarity, and solubility during the process [99]. 

Spread the catalyst ink/paste onto a GDL (with the MPL on wet-proofed carbon paper) using the doctor blade technique or by spraying, painting, screen printing, etc. ... 

Aside from the above process, a decal transfer method has also been developed to make a thin-film electrode [81-83]. The catalyst ink is first coated onto a decal substrate (such as PTFE film or Kapton film) by spraying or by using the doctor blade technique. The catalyst ink is then transferred to a Nafion membrane by a hot-pressing process to form a catalyzed membrane. This decal transfer method is presented schematically in Fig. 2.15 [83]. 

---