I am trying to create a simple o/w emulsion, ideally staying together ~8 hours, to study the oil in the emulsion. My emulsions, one mix of emulsifiers to get a HLB of 7 and one with an HLB of 16 both at 1% of emulsion, did not stay together for an hour
Obviously, it much depends on dispersing intensity. If you shake only by hand or use magnetic stirrer or similar droplet size will be relatively large. For both emulsifiers using high intensity ultrasonication with a tip stability will be much higher.
Depending on stability obtained you may use analysis of separation process at earth gravity or in centrifugal field with continuous optical detection.
The settling could be due to larger droplet size or due to lack of stabilizing entities. if the size of droplets are too large the droplets settle faster due to gravitational pull, Coalescence due to lack of stabilizing moieties would increase the floc size and settling.
You may look at the size of the droplets under a microscope or use DLS based size measurements. DLS can also be used to follow the evolution of droplet size or stability.
If the size is too large, try to bring it down by choosing appropriate emulsification parameters (higher sonic power, stirrer speed etc.)
oil itself should have lower density than water, i.e. oil droplets will cream not sediment no matter how large they are.
Depending on further application, the stability of emulsion could be improved by addition of some polymers into water phase (i.e. alginate, pectin, PVA, etc). This must be combined with high speed homogenization.
Obviously, the oil droplet in your emulsions are two big. Emulsion stability does not depend very much on HLB. More important are properties of the emulsifier adsorption layer and its surface concentration on oil droplets. Important is also shear viscosity and dilatation modulus. If the emulsifier concentration in the continuous phase is bellow CMC then Gibbs Marangoni effect is of importance, as well. If you add polymers you can induce depletion flocculation or bridging.
You might check that your emulsion does not destabilize due to Ostwald ripening that typically arises in the early stages of the emulsion life. Due to interfacial tension that makes smaller droplets less stable than bigger droplets, the dispersed phase subsequently diffuses from smaller to larger droplets through the continuous phase. This results in an increase in the mean droplet size with time. For more information and applications please refer to: http://www.lsinstruments.ch/applications/application_notes_dws/aging_of_an_emulsion_ostwald_ripening_mechanism/
http://www.lsinstruments.ch/applications/application_notes_dws/aging_of_an_emulsion_ostwald_ripening_mechanism/
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