Method of obtaining anisotropic crystalline films and devices for implementation of the method
The invention pertains to methods of obtaining anisotropic crystalline films and to devices for carrying out the methods. A colloidal system with anisometric particles is applied as a film onto the surface of a substrate while the viscosity of the colloidal system is lowered. The particles of the colloidal system with lowered viscosity are oriented and the original viscosity of the colloidal system is restored. The film is then dried. The drying is carried out under controlled conditions. Zones of the dried film may be progressively heated to improve the film characteristics.
1. A method of fabricating anisotropic crystalline films comprising the steps of:
applying a layer of a colloidal system with anisometric particles onto a substrate, externally impacting the colloidal system to lower the viscosity of the applied layer of the colloidal system,
applying external orienting action on the colloidal system to provide dominant orientation of particles of the colloidal system,
allowing the deposited colloidal system with dominant orientation of the particles to return to at least its initial value of viscosity, and
drying the deposited layer.
2. The method according to claim 1 wherein the external impact on the colloidal system and the external orienting action on the system are carried out simultaneously.
3. The method according to claim 1 wherein the external impact on the colloidal system further comprises heating the colloidal system to lower its viscosity prior to applying the external orienting action.
4. The method according to claim 2 wherein the external impact on the system is performed via mechanical action on the layer of colloidal system as it is applied onto the substrate.
5. The method according to claim 1 wherein during the drying of the deposited layer, humidity gradients are created in tangential or normal direction above the surface of layer.
6. The method according to claim 5 wherein the finite volume over the surface of the deposited layer is created by performing the drying operation in a shell encasing at least a part of the surface of the layer and humidity gradient above the surface of the deposited layer is created via at least a single shifting of the shell along the surface of layer in at least one direction.
7. The method according to claim 1 wherein the drying of the deposited layer is performed at a temperature in the interval 0° to 50° C. and humidity in the interval from 60 to 90% with a forced slowing of the drying rate by performing the process in a finite volume which is configured to resist deflection of solvent fumes from the surface of the deposited layer.
8. The method according to any of claim 1 or 7 , which further comprises a thermally processing the deposited layer via at least a single directional pass of the temperature zone along the layer.
9. The method according to claim 8 , wherein the temperature zone is created via a local heating of the substrate on the side opposite to that on which the deposited layer is formed.
10. The method according to claim 8 , wherein simultaneously with the local heating in the temperature zone, the rest of the substrate is cooled.
11. The method according to claim 8 , wherein the temperature of the temperature zone is chosen to be no less than 10% higher than the substrate temperature and no less than 10° less than the decomposition temperature of the crystalline film.
12. The method according to claim 8 , wherein the direction of pass of the temperature zone is chosen to coincide with the direction of the orientation.
13. The method according to claim 8 , wherein the multiple passes of the temperature zone are performed with the direction of each subsequent pass chosen at an angle from 0° to 180° to the previous one.
14. The method according to claim 8 wherein for at least a part of the time during fabricating of the anisotropic crystalline film the deposited layer is under constant electric and/or magnetic field.
15. The method according to claim 7 wherein the finite volume is created by a shell, at least part of which is implemented in the form of porous membrane having pore diameter from 4 nm to 2 mm and porosity no less than 5%.
16. The method according to claim 7 wherein the drying step is performed at a temperature lower than the temperature of deposition and orientation of the colloidal system, and humidity higher than the humidity of deposition and orientation of the colloidal system.
17. The method according to claim 7 wherein a microporous membrane is used as the substrate for the application of the colloidal system.
18. The method according to claim 7 wherein the drying is performed until a solvent content in the film is 2 to 15%.
19. The method according to claim 7 wherein, after completion of the drying, the crystalline film is aged at temperature from 60° to 150° and normal humidity.
20. A method of fabricating anisotropic crystalline films comprising the steps of:
external impacting a colloidal system with anisometric particles situated in a reservoir to lower the viscosity,
external orienting action on the colloidal system to provide a dominant orientation of particles of the colloidal system via running it through a slot-die under pressure,
formation of a film with raised viscosity upon exiting from the the slot-die due to cession of the external impact or application of an additional external impact to provide restoration of at least the initial value of viscosity of the colloid system,
application of the said formed film onto a substrate, and
drying the deposited layer.
21. The method according to claim 20 wherein the external impact on the colloidal system is performed via heating the colloid system placed in the reservoir.
22. The method according to claim 20 wherein the external orienting action is performed using the slot-die, inner walls of which feature the orienting relief.
23. The method according to claim 20 wherein a lyotropic liquid crystal is used in the capacity of the colloid system.
24. The method according to claim 20 wherein the external action is chosen such as to ensure phase transition in the colloid system.
25. The methods according to claim 20 wherein sol or gel is used in the capacity of the colloid system.
26. The method according to claim 20 wherein the anisometric particles in the colloid system are crystalline.
27. The method according to claim 20 wherein one uses the colloid system, concentration of dispersion phase in which is chosen such as to provide thixotropy of the system.
28. The method according to claim 20 wherein the anisometric particles in the system carry charge.
29. A device for fabricating a crystalline film on a substrate comprising:
a substrate holder,
means mounted on a selected distance above the substrate for applying a layer of a colloidal system with anisotropic particles of predetermined thickness onto the substrate carried by the substrate holder,
an orienting tool for applying an orienting action on the colloidal system applied to the substrate, and
means for heating the colloidal system applied to the substrate.
30. The device according to claim 29 wherein the means for heating the colloidal system heats at least part of the substrate holder.
31. A device for fabricating a crystalline film on a substrate comprising:
a reservoir for placing a colloid system, supplied with heating elements and means of creating extra pressure in a reservoir,
a substrate holder, installed at a controlled distance under the reservoir with possibility of movement relative to the reservoir in the horizontal plane;
wherein the lower part of the reservoir has an opening in the shape of a slot-die, dictating conditions of an orienting impact.
32. The device according to claim 31 wherein under the substrate holder there is a thermo-element implemented such that it allows maintaining certain temperature over at least a part of the substrate holder surface.
33. The device according to claim 31 wherein at least a part of the slot-die surface features a relief.
34. The device according to claim 31 wherein at least a part of the slot-die surface features hydrophilic or hydrophobic coating.