In a 750 W ultrasonicator, around 10-15 mins  at room temperature, would be enough to properly disperse the nanofibers. For MWCNT modification, it would be completely dependent on your solution/solvent for modification as well as the MWCNT properties. 

Thank you so much Priyanka, 

For MWCNT surface modification. I use 0.5 g of MWCNT with 100 ml of H2SO4/HNO3, 3:1, v/v using ultrasonic for 4 hour at 80ºC following other authors.

For cellulose nanofibre dispersion, 500 - 750 W ultrasonicator with sonication for 15-30 mins at room temperature would be enough

For Cellulose nanocrystal suspension (CNC), tip sonicator 500W used at 30% of max power, 4 min on 200mL, on ~ 2%wt suspension. so around 9000J/g_dry_matter.

Bruno Frka It is impossible for 2wt% suspension because my CNF gel is 1wt%. For my CNF, I dilute to 0.2wt% in water.

Is it 2wt% suspension you mentioned about is to make CNC using sonicator?

Anyway, thank you very much for your kind answer.

Nanofibers are much longer and thus gelation occurs at lower concentration. I actually work on cellulose nanocrystals (CNC), their length is around 100-150nm, up to 300nm max. for cotton source, and they are then still liquid. Very low ionic strength can as well induce a gel-like state (= a Wigner glass). This sonication step is optional to finalise the suspension preparation, but my CNCs are actually made by acid hydrolysis, not by the sonication itself. I hope this was useful.

Bruno: For cotton source, Did you performe with homogenizer ? How many passes at high pressure (600bar)? and the final step with sonicator, did you use the same parameter that you mentioned above? 

I am asking you because, in our case we used cotton to get CNF but it is still liquid even with TEMPO-oxidized 15 mmol.

Thank you very much for your kind reply.

For the first step I only use teflon-stick mediated mechanic stirring at moderate speed during the hydrolysis step in sulphuric acid. No high pressure homogenizer, no tip-sonication homogenizer, or rotor-stator mechanical homogenizer (as ultra-turrax), while the additional sonication I was referring to was tip-soniation.

Bruno: Thank you very much for your sharing.

Hi Makayara and Bruno,

What is the concentration of the nanofiber suspension and the water that should be used in the sonicator? Would 2% cellulose be to 200 ml of water? Does this also work for bacterial cellulose?

Hi Paula,

It works well with low concentration (0.1 - 0.2wt%), so would be 0.1g of CNF need 100 or 50 ml of water.

For bacterial cellulose, once it is formed a membrance, it is hard to disperse even at low concentration.

Obrigada Makara Lay!