we purchased dried-multi-layer GO powder, and have problem with dispersing in water! How ever we try ultra sonication for 20 min, 100 watt after stirring at room temperature it settles in after a short time.
Are special conditions ( like pH, surfactant, and ...) needed?
You have identified a key way of deciding whether your material is nano - if it settles over a short period of time (< 2 weeks) then it's not < 100 nm. If your material wets in water, a surfactant is not needed. The stages in making a stable dispersion are wetting (accomplished by a surfactant; if wetting already occurs then no surfactant is needed. Surfactants do not carry out dispersion - they wet and sometimes in the case of anionic or cationic can act as stabilizers in the optimum concentration); separation (input of energy required; there are no magic chemicals for this stage), and stabilization (either charge or steric). The key stage, as you have identified, is the separation one. Your powder is a fused collection of sub and post-micron aggregates that cannot be disrupted by sonication. See (and the earlier webinars given on slide 3):
Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge and
November 3rd, 2015 Adhesion and cohesion http://tinyurl.com/zwb2wlh
Once you have a powder, it's close to impossible to recover the primary particles. Your sonication energy is mostly wasted but you may wish to try 800 W for 15 minutes with the beaker suspended in a block of ice to remove heat.
No magic chemicals exist for dispersion(but generally like prefers like' and if the material was produced with hydrophilic bonds on the surface, like oxides, it'll wet easily. A pH change may help too. An alternative aggressive solvent such as DMF or THF can also help with the lowered surface tension.
You may want to check this earlier thread, as it may possibly be found helpful: https://www.researchgate.net/post/What_are_the_factors_affecting_the_dispersion_of_graphene_in_water
You have identified a key way of deciding whether your material is nano - if it settles over a short period of time (< 2 weeks) then it's not < 100 nm. If your material wets in water, a surfactant is not needed. The stages in making a stable dispersion are wetting (accomplished by a surfactant; if wetting already occurs then no surfactant is needed. Surfactants do not carry out dispersion - they wet and sometimes in the case of anionic or cationic can act as stabilizers in the optimum concentration); separation (input of energy required; there are no magic chemicals for this stage), and stabilization (either charge or steric). The key stage, as you have identified, is the separation one. Your powder is a fused collection of sub and post-micron aggregates that cannot be disrupted by sonication. See (and the earlier webinars given on slide 3):
Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge and
November 3rd, 2015 Adhesion and cohesion http://tinyurl.com/zwb2wlh
Once you have a powder, it's close to impossible to recover the primary particles. Your sonication energy is mostly wasted but you may wish to try 800 W for 15 minutes with the beaker suspended in a block of ice to remove heat.
No magic chemicals exist for dispersion(but generally like prefers like' and if the material was produced with hydrophilic bonds on the surface, like oxides, it'll wet easily. A pH change may help too. An alternative aggressive solvent such as DMF or THF can also help with the lowered surface tension.
It is expected that you are dealing with nano level multilayer graphene oxide. Surfactants have to be used as the groups on graphene oxides are basically CO, CHO, COOH etc. pH>7 may also dissolve it.
in addition to previous comments - to compare energy input you should compare on basis of W*s/cm³ because intensity of treatment is proportional to power and time of treatment and reversed case for treated volume.
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