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sagebob
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Quote sagebob Replybullet Posted: 14 July 2006 at 10:03am

howdy

if you look through the various forums here, there are several different TiO2 solutions described.

--bob

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Khann
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Quote Khann Replybullet Posted: 16 August 2006 at 10:49am

Hello fellows:

I have TiO2 powder (particle size=100nm), i want to make a stable suspension of it. I would highly appreciate, if you tell me an easy hand preparation method.

Thanks..........

kahn
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Rafiki
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Quote Rafiki Replybullet Posted: 31 August 2006 at 2:56pm

Hi, is there anybody who did TiO2 film on polymer, for examle, polycarbonate by sol-gel? I am going to try, but i was told that the film tends to crack. Is that true? how to solve this problem? thank you.

 

Rafiki
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sagebob
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Quote sagebob Replybullet Posted: 31 August 2006 at 5:19pm

howdy Rafiki,

One issue is how you define a "TiO2 film".  You can certainly apply a nice looking film on plastics from a sol-gel solution.  The problem is removing the organic and carbon content of the film to leave substantially pure TiO2.

Vacuum coating is how I would do it. 

Hoever, the easiest approach for film curing is a high temperature bake.  Works for glass, etc. but not plastics.  I have done some work using lasers to cure the films on glass and plastic.  Easy on glass.  I had some spotty success doing this on plastic but it is tricky.  E-beam, and UV exposure made some improvement in coating properties but the plastic degraded faster thant he coating improved.  Oxygen plasma exposure in a vacuum chamber did something but again, the plastic degraded.  Probably a great area for experimentation.

If you had some kind of suspension of TiO2 particles, they could be put on plastic.  Again, need to remove solvent and then need to make particles adherent to the plastic and also each other.

Cracking of films is due to relatively poor adhesion on plastics.  By the way, this is a standard way to get an isolated piece of film.  If film stress is greater than adhesion, films crack and peel.

sorry I did not have a ready answer - bob

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Rafiki
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Quote Rafiki Replybullet Posted: 01 September 2006 at 9:55am
Hi Bob, thank you for your kind quikly reply and suggestion. So i think there is few people work on this field, TiO2 film on polymer. I want to get a dense continueous film but thin. It seems that there may be a long way for this work, just as you said.
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Quote lee_malone Replybullet Posted: 11 October 2006 at 6:05am
Hello, I am delighted to see there is this much information on TiO2 on this forum. However after reading a lot of topics, I still haven't found much about what I am doing.

Right now I am working on transparant TiO2-films with superhydrophilic properties. As a substrate I have to use Lexan PC. The deposition of the layers happens by dip- or washcoating. The maximum temperature in my synthesis is +/-135C, due to the thermal properties of PC.

Up untill now I have been searching on three different routes, all having their specific problems. I'll make a very short description of each method.


A. Starting from a dispersion of TiO2-nanomaterials in water. Occuring problems: thin film is not transparent and adhesion is terrible. After heat treatment at 135C I can easily scratch off the layer.

B. Starting from Ti-alkoxide (more specific Ti(OBU)4) in water, HNO3 and isopropanol. Here I do reach a clear starting solution, yet I don't get any wettability at all.

C. Starting from an inorganic titanium source ((NH4)2TiF6) in water + a few other chemicals. This method is supposed to give me some crystallinity, yet also here I don't get good wettability on my substrates.


These are the things I tried so far. I still have some other routes left, but I fear that I won't get any results at all. The main problems for me are obtaining a clear dispersion of TiO2-nanoparticles in method A and reaching better wettability in methods B and C.

I hope some of you have been working on these polymer-substrates or have ideas how to solve these problems. I read that Rafiki, Soni, Barrie and A-Dog 23 were working on this subject as well. Maybe it would be usefull for all if we shared our information.

Thank you for reading, and thank you even more if you can help me. You can also e-mail me when you dont want your post to be public. You find my address on my profile.


Nigel Van de Velde
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sagebob
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Quote sagebob Replybullet Posted: 11 October 2006 at 7:47am

Howdy Nigel,

I believe the wetting problem has been covered somewhere in these forums.  Basically, plastics do not "wet" as well as glass and adhesion to plastic is less than on glass.  A question to ask is; "if nanoparticles (or anything else) are put on a surface, why should they stick to it?".   You need a physical mechanism working for you.  I see no reason for TiO2 nano particles to stick particularly well to Lexan.  Especially since you can not apply any heat.

Can you get the coating applied during manufacturing??  Should be much easier to incorporate into the surface then.

Just to form a layer, either the surface needs treatment to make it more wettable or your coating solution needs to have better wetting characteristics.  Adhesion is a different problem.

Surface treatments can range from a simple prime coat to exposure to oxygen plasma.  Automobile headlight reflectors are coated with silicone and organic based materials.  Some research here might help you.  You might try coating some of the "hard coat" or antireflection coated plastic.  This is a silane based based coating on the surface that might act as a bonding layer.  It might also be worse.  Depends on the particular design specifications of hte hardcoat.

I do not believe the simple solutions you are trying will form a good coating.  I have had some success using organically modified SiO2 and TiO2 coatings.  these fall into the ormosil type coatings.  The inorganic material is there but an organic resin of some sort is also present.  In your case, maybe PMMA or a related compound.

Acrylic is much easier to coat since you can dissolve the surface with solvent adn promote a good bond.

You might try the TBT solution I posted previously.  (contain ethyl acetoacetate, etc.).  This was designed as a coating solution for production purposes.  It has much better wetting and adhesion properties than what you are using.  It might wet the Lexan, but I would not expect it to adhere to it well.  This coating was designed to be baked at 450C but can also be somewhat cured by exposure to intense UV or oxygen plasma.

As far as wettability goes, alot of surface area is good.  Frosted surface wet much better than glossy ones.  An inherently wetabble material is also useful.  Adding lithium to a solgel layer often provides "fogging" resistance.  I could not tell you how long this lasts since theoretically the lithium should dissolve out of the coating.  It is good for at least a couple of years of rooftop exposure.

-have fun - bob

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Quote lee_malone Replybullet Posted: 12 October 2006 at 6:13am
Thank you very much for your reaction.
It is no suprise to me that you advise me to use some more complex methods. I allready had the idea that a TiO2-coating on PC wasn't going to be as simple as on glass or something else.

One of the methods I still have in mind is based on an ormosil-type coating. So I think this will be the first thing to try out.

Considering your reply I have got some more questions. You tell me about coating during manufacturing. What exactly do you mean by this? Normal procedure here is dipcoating with an automated dipcoater, then a drying step and then the thermal treatment in a tubular furnace.

Later on you also spoke about adding Lithium to my layer. Do you mean to incorporate lithium into my sol, or do you mean to make an underlying layer based on lithium?


When getting any results I will let you know!

Thank you!

Nigel Van de Velde    
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sagebob
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Quote sagebob Replybullet Posted: 12 October 2006 at 7:14am

Howdy Nigel,

Place I worked at coated 4 x 5 foot sheets of glass with multilayer dip coatings of various types.  Antireflection, beamsplitter, cold mirror, hot mirror, laser windows, etc.  So we had big tanks with different types of solutions, cart and trolley system to move the glass around between dip solutions, big ovens, big furnaces, etc. and needed solutions and a coating process that had wide process windows and excellent performance.

Lithium in the solution is probably easier.

What is the purpose of the TiO2 coating on plastic??

--bob

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lee_malone
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Quote lee_malone Replybullet Posted: 12 October 2006 at 4:20pm
Impressive, but we haven't got these facilities here. Everything is still on laboratory-scale.

We are trying to get superhydrofilicity on PC. If successful this might be applied in helmetvisors, windshields, etc...
So all we need is a lower contact angle and a clear, well-adhered thin film. Sounds easy, seems tricky!
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