Sorry sir i didn't get you.... If you are asking about cladding then it is made of silica....

What is the surface chemistry of your AgNPs? Citrate may not be attracted to silica hydrocyl groups, unless the pKa's match. Silica hydroxyl group PKa = 7.1, [1], so unlikely that citrate has a pKa to match the silica hydroxyl group.

Making you AgNPs positively charged may allow them to be attractive to the silica below pH 7: modify with thiocholine bromide, a thiol functionalized quaternary ammonium salt, [2]. The pKa of the quaternary ammonium should be high, (teh Web say >10), thus it may stick via H-bonding to the hydroxyl group on your silica, which can donate it's proton to the positively charged quaternary ammonium.

[1] http://pubs.acs.org/doi/abs/10.1021/j100696a016?journalCode=jpchax

[2]Simple preparation of positively charged silver nanoparticles for detection of anions by surface-enhanced Raman spectroscopy, Analyst, 2015,140, 2988-2994 

Michael -  Indeed I've messed up, oops.: quaternary ammonium cannot have a pKa.

Let's try again: The quaternary ammonium may attach to silica hydroxyl groups generated after cleaning by piranha solution. Above pH 7 the silica hydroxyl group will be negative charged, i.e.deprotonated hydroxyl groups (- O-), which may bind to the positively charged quaternary ammonium (-NR3+) on AgNPs? .

Sir what is the basic role of pirahna solution does it only used to generate hydroxyl group on fiber...and in some papers it is mentioned that after treating with piranha the fiber will be cleaned and then silanized what does it means and why it is necessary.

Thanking you

See link on details of silane chemical modification of silica. Cleaning with pirahna solution is the first step to clean and generate reactive hydroxyl groups - these react with silanes changing the chemical nature of the silica surface.

If your pirahna cleaned silica still cannot attach you AgNPs, then changing the surface chemistry of your silica with various chemical groups may allow them to attach your AgNPs. The exact silane chemical groups that may attach your AgNPs will depend on surface chemistry of the AgNPs. What type of AgNPs do you wish to attach to your silica fibres: do you know details of the AgNP surface chemistry? This info would really help in deciding which type of silane may help attach the AgNPs.

Article Chemical Modification of Silica Surface by Immobilization of...

Clarkson sir... really thankful for you link... surely it will help me in many aspects.....i have to study it befor to start.