However, as recently reported by Ushikubo, nanobubbles of inert gases do possess similar lifetimes and are formed from helium, neon, and argon, and since the only intermolecular forces of note they experience are van der Waal’s forces of attraction, Lifshitz forces and dipole-dipole interactions, it can be assumed that these are also strong enough, and the gases sufficiently inert, for the same mechanism as well as the steric hindrance of the hydroxide ions to apply to the same case. Considering the formation of a 1 μm micro-bubble which eventually shrinks into a nanobubble, the number of ions available to it for stabilisation from the water it displaces upon formation, at pH 7, is approximately 33 ions, which if all the ions were adsorbed, does not agree with the zeta potentials reported by Takahashi et. al. for micro-bubbles of comparable size, which by equation is given to be approximately 495 ions. It follows that the ions which are adsorbed diffuse toward the nanobubble surface from the surrounding bulk fluid, which can explain the apparent generation of free radicals observed by Takahashi et. al., since there is now a minuscule concentration difference present to drive the diffusion. The availability of hydroxide ions also depends on the pH, and at pH 7 it is thus possible for stable nanobubbles to form as is reported by Ushikubo, as well providing a mathematical treatment for their stabilization and the calculation of their surface charge. At lower pH, in the absence of other ions, the concentration of stabilized ions would be lower due to the lower availability of hydroxide ions and the increased time needed for them to diffuse to the surface of the nanobubble, allowing it more time to shrink. The dependence of the size of the bulk nanobubble on external pressure is given by equation . Of the external pressure, the proportion of the atmospheric pressure to the total value of the actual pressure, the rest being the pressure exerted by the fluid. However, the major component to the force contributing to the shrinkage of the nanobubble is the surface tension,dutch buckets system which also increase with the size of the nanobubble. Thus, for higher external pressures and given that a limited amount of gas is dissolved in the fluid, the equation gives a trend of increasing nanobubble size with increasing external pressure.

However, due to the limited amount of gas available, it is expected that the number of nanobubbles formed, i.e. concentration will decrease, while still giving higher particle size. This is confirmed by Tuziuti and co-workers through their observations of air nanobubbles in water. The temperature term appears only in the term that describes the internal pressure, causing a linear increase with temperature, not taking into account the increase in molecular motion due to heat, as well the increased energy of the surface ions. Thus, it also shows that the internal pressure will increase with the increase in temperature. This will, in turn, cause a reduction in the radius if all other terms are kept the same. Thus, we can say that given a limited amount of gas dissolved in the solvent, an increase in temperature will give smaller nanobubbles, but will also cause an increase in concentration of the nanobubbles in the solvent. It is also possible that zeta potentials may decrease, as thermally agitated hydroxide ions may be more susceptible to de-adsorption and may return to solution more easily. Conversely, as lower temperatures, larger bubbles may form, especially by the method of collapsing micro-bubbles, and larger numbers of hydroxide ions may be adsorbed on the surface of the nanobubble, giving longer lifetimes. Bulk nanobubbles are, in essence, minuscule voids of gas carried in a fluid medium, with the ability to carry objects of the appropriate nature, that is, positively charged for a length of time that is significant, if the nanobubble is left alone, yet is also controllable, since the bubbles can be made to collapse with ultrasonic vibration, or magnetic fields. The applications, then, seem to be limited only by how we can manipulate and design systems that make use of these properties for new technology in several fields. As mentioned before, thus far technology has made use of the uncontrolled collapse and generation of bulk nanobubbles, in the fields of hydroponics, pisciculture, shrimp breeding, and algal growth, while the property of emission of hydroxide ions during collapse has been applied to wastewater treatment.

Here and there, there are indications of greater possibilities, as evidenced by research into their ability to remove microbial films from metals, to remove calcium carbonate and ferrous deposits from corroded metal, the use of hydrogen nanobubbles in gasoline to improve fuel efficiency, and the potential application for to serve as nucleation sites for crystals of dissolved salts. The following sections elaborate on further applications which are possible in the near future. Proton exchange membrane fuel cells, are finding wide application in several fields due to the ease of their deployment, the low start-up times, and the convenience of their size and operating temperatures . However, significant limitations exist for their wider application, which can broadly be classed under the headings of catalysis, ohmic losses, activation losses, and mass transfer losses. The first of these is due to the rate of catalysis of the splitting of hydrogen, which cannot be pushed beyond a certain limit due to the constraints of temperature. But the larger issue is the cost of the catalyst itself, which is a combination of platinum nanoparticles and graphite powder, which provides the electrical conductivity. The inclusion of platinum presents a significant cost disadvantage, and while efforts are ongoing to reduce or replace platinum as a catalyst, these are still experimental and much research is ongoing in this field. The second limitation is due to ohmic losses, which accumulate due the proton exchange membranes, also termed the electrolyte, and can only be reduced by reducing the thickness of the membrane. Current popularly used membranes are usually made of Nafion, a sulphonate-grafted derivative of polytetrafluoroethylene marketed by DuPont, but experimental membranes include the use of graphene, aromatic polymers, and other similar materials which possess a high selective conductivity toward protons [ref]. However, beyond a certain thickness the membranes are unable to mechanically support themselves, and often mechanical failure of the membrane will cause a break in operations.The third limitation is due to the start-up conditions of the fuel cell, and are a matter of the mechanics of operation of the fuel cell itself. The last limitation is due to the transport of hydrogen and oxygen to the triple phase boundaries around the catalyst and the transport of water away from them, and is a significant concern for the operation and efficiency of PEMFCs.

However, the current PEMFCs depend on gaseous hydrogen and oxygen, which are released from a compressed source and derived from air respectively. This necessitates a mechanically strong membrane and construction to resist the operating pressures. However, the inclusion of the gas as a nanobubble dissolved in water presents new possibilities, used in combination with microfluidic technology. It becomes possible to also replace both membranes and catalysts with materials that have been hitherto discarded fro being too mechanically weak, such as graphene, and the possibility of using graphene as a combined catalyst and proton exchange membrane, as nanobubbles of hydrogen and air, dissolved in water, to act as the reservoirs for the fuel and oxidant. Such as system would operate on the basis that nanobubbles are negatively charged,dutch buckets and would hence be attracted to the graphene through which current would be passed in order to activate the process. Air and hydrogen nanobubbles would be separated by the graphene membrane, and be adsorbed to opposite sides of it. The graphene membrane would also have a potential difference applied across it in the plane of the graphene layer. This would, in turn, permit the hydrogen to be catalyzed to protons [ref], and hence be conducted across the graphene [ref], allowing it react with the oxygen to form more water, which would be carriedaway with the flow. Microfluidic bipolar plates would enable the construction of such a device, and such fuel cells could become the future source of energy for several applications. The advantages of such a system would be numerous. Firstly, graphene is far cheaper than platinum, and can be used as a catalyst of almost comparable quality, in addition to also being the conductor for the removal of electrons released during catalysis. Secondly, the thickness of a graphene sheet is in the range of nanometers, which would mean that ohmic losses would, quite possibly, be nearly eliminated. Additionally, due to the flow of water as a solvent, the losses due to the mass transport of water away from the triple phase boundary, and that due to transport of hydrogen and oxygen to the triple phase boundary, would also be significantly reduced. The last, but not the least advantage would be the reduction in the size of one fuel cell. The voltage generated by fuel cells is independent of the size they are, which would mean that a much larger number of fuel cells can fit in the same area as currently applied fuel cells, which will provide a much larger voltage. Polymeric foams have been a staple of several products since their inception, and pore size is one of the key properties of the foam that determines its performance. In general, the larger the pore size, and more the pore count, the lighter the foam is. However, both can come at the cost of reduced wall thickness of the pores, which makes the whole foam less able to deform elastically and more susceptible to tearing and heat damage, while substantially reducing fatigue resistance and creep resistance. In general, therefore, the standard practice is to achieve a balance between pore size and pore count, measured in pores per volume, so as to achieve the desired properties. However, the voids rarely go below the size of one micron, and this in turn places a limit on the number of pores per volume, thus limiting the number of pores it is possible to introduce, as well as the amount of gas that can be introduced into the foam system. While there are several methods of foam manufacturing, including in-situ foam molding, and pre-mixed foam molding, none of these offer pore sizes lower than a few microns reliably and controllably. Furthermore, many of the polymers used in the construction of these foams can either be dispersed or dissolved into water, such as polyamides, polystyrene, polyesters, and polyurethanes. This offers a unique opportunity to introduce nanobubbles into the system, by first dispersing the gas into solution by means of a micro-bubble generator, and then dispersing the polymer, either in dilute solution form or as a monomer, and then either coagulating the dispersion, or polymerizing it, or cross linking the chains in solution to create a foam with pore sizes in the nanometer range. At standard pore counts, this would offer a very high wall thickness, which necessitates a large increase in the concentration of nanobubbles which should be introduced to return wall thickness to the same levels as a microporous foam. The pores can then be opened, if so desired, by a microneedle array, or by other methods such as guided bursts of ultrasound, creating such structures as channels only nanometers in width through the foam, and presenting new possibilities for water filtration and purification, as well as for testing and for further application in water quality testing and other similar applications. As of now, there are several applications for such open-celled foams, such as the production of nanopure water, which are expensive due to the filtration equipment needed. Thus, opencelled polymeric foams have direct application to these areas, where as closed-celled foams are potentially lighter and stronger, as well as tougher than other foams with larger pores and lower pore counts. Thus, it is reasonable to suggest that nanobubble technology will find widespread use in this particular application, especially when the cost factor is taken into account.