Various parameters are involved to  convert  solution into  gel in the mentioned  sol-gel synthesis process, these are temperature of synthesis , molarity of the precursors or concentration of chemicals, solvent amount, Time of synthesis ,  and  lastly (external pressure  )exclusively.

Thank you Khusha Kumar Naik, I got the points,  my problem now has been solved and it was due to pH and off course! the parameters you just mentioned are of huge importance in converting sol into gel...

Acidic pH will give you gels that are are fairly translucent and soft (they will dry to glass hardness). Under basic pH gels are white and non-transparent because they contain nanoparticles. The authoritative source is Iler's book on silica.

http://www.wiley.com/WileyCDA/WileyTitle/productCd-047102404X.html

Thank you very much respected Sir Themis Matsoukas for treasure of knowledge.

I am highly obliged.

Best Regards

If some one want to determine Sol Gel of a network. Do we need to wash, remove impurities, dry and then determine it sol gel part OR We do not need to perform first step, i.e. Washing??? and dry it as such etc ....

Dear Haroon Rasheed: mostly by drying network collapse due to capillary pressure exerted by out going water vapors so try to avoid drying...

I'm facing almost the same problem as you were. When i mix solution A(TMOS + Methanol) to solution B(Ammonia hydroxide + Methanol) i didn't get gel. Trying with different ammonia hydroxide concentration, solution converts into milky white and once it solidified but didn't converted into gel. Can you please help me to sort out this problem.... Do i need to heat the solution? Do i need to use some other catalyst? Or any other suggestion....

Ammonia catalyzes the formation of particles, which produce a milky gel. The witness depends on the size of the particles: large particles from white/milky suspensions, small particles form bluish transparent suspensions, and very small particles form suspension that look clear like water. Have you tried HCl instead? Are you're following a recipe from the literature?

@Themis Matsoukas

Thank you very much sir for your response.

Yes I'm following a recipe from literature (http://www.aerogel.org/?p=1406) and no i haven't tried HCl yet. Untill now i have just tried ammonia hydroxide.

@Themis Matsoukas

Also sir i want to add that, solution is not converting into gel they remain in liquid state even if they change transparency to milky white.

You should experiment with the precise amounts.

The attached paper is a study of ammonia catalyzed hydrolysis of TEOS. In this case the goal was to make stable particles. In your case you want very small particles, and you want them unstable so that they can aggregate and form a gel. In my experience, replacing ammonia with HCL is a more reliable way to make a gel, but it will take longer (hours to days).

Article Dynamics of Growth of Silica Particles from Ammonia–Catalyze...

@Themis Matsoukas

Thank you very much sir.

I'll definitely consider your advice and yeah now i have some points to consider. your advice lead me towards the solution. Thank you very much.