Dispersion characteristics of nano bubbles: high stability and uniform distribution of "suspension advantage"

Dispersion characteristics of nano bubbles: high stability and uniform distribution of "suspension advantage"

Micro nano bubbles (MNBs) refer to bubbles with diameters ranging from micrometers (1-100 μ m) to nanometers (1-1000 nm). Their unique scale effect endows them with excellent dispersion and activation properties, which are also the core basis for their widespread applications in environmental protection, agriculture, medicine, industry, and other fields. The following provides a detailed analysis of characteristic definitions, formation mechanisms, key manifestations, and application associations:

1、 The dispersion characteristics of micro nano bubbles: the "suspension advantage" of high stability and uniform distribution

The core of the "dispersion characteristics" of micro nano bubbles refers to their ability to achieve long-term stable suspension and uniform distribution in liquids, as well as their resistance to coalescence and buoyancy, which distinguishes them from the shortcomings of traditional macroscopic bubbles (diameter>1 mm) such as "rapid buoyancy, easy rupture, and uneven distribution".

1. The core formation mechanism of dispersion characteristics

The dispersion stability of micro nano bubbles is mainly determined by three factors: interface mechanics, charge effects, and fluid mechanics

Balance between interfacial tension and buoyancy:

The upward velocity of bubbles follows Stokes' law (v=9 μ 2r2 (ρ l − ρ g) g, where r is the bubble radius, ρ l/ρ g is the liquid/gas density, and μ is the liquid viscosity).

The radius of micro nano bubbles is extremely small (for example, the radius of a 100 nm bubble is only 1/10000 of that of a 1 mm macro bubble), resulting in a very slow upward velocity: the upward velocity of a 10 μ m bubble in water is about 0.03 cm/s (which takes several hours to float to the surface), and the upward velocity of a 100 nm bubble is as low as 0.00003 cm/s (almost equivalent to "suspended stationary"), providing a time basis for uniform dispersion.

The "electrostatic repulsion" effect of surface charge:

The interface between micro nano bubbles and liquid will form a double layer structure due to ion adsorption (such as H+, OH -, electrolyte ions in water), and the surface of nano bubbles will be negatively charged (or positively charged, depending on the liquid medium), resulting in electrostatic repulsion between adjacent bubbles. This repulsive force can effectively prevent bubbles from approaching and merging with each other, maintain the independent dispersion of individual bubbles, and avoid the formation of large-sized bubble clusters.

The "anti settling" assistance of Brownian motion:

For nanoscale bubbles, the irregular thermal motion (Brownian motion) of liquid molecules will continuously collide with the bubbles, causing them to exhibit "irregular motion", further suppressing the settling or coalescence of bubbles, and enhancing dispersion uniformity.

2. Key manifestations and application value of dispersion characteristics

High specific surface area: The uniformly dispersed micro nano bubbles have a large total surface area (for example, if 1 L of water is filled with 100 nm bubbles, the total surface area can reach 6 × 104m2), greatly increasing the gas-liquid contact area - this is the core of their efficient role in "dissolved oxygen (aquaculture), air flotation (wastewater treatment), and gas reactions (chemical industry)":

Example: In aquaculture, micro nano bubbles can increase the dissolved oxygen efficiency of water by 3-5 times compared to traditional aeration, and the duration of dissolved oxygen is longer, avoiding local hypoxia.

Global permeability: Due to its extremely small size, micro nano bubbles can penetrate into the tiny pores of liquids (such as soil gaps and the interior of porous materials), achieving a "global uniform effect" - for example, in agricultural irrigation, micro nano bubble water can penetrate deep into crop roots, improving root oxygen supply efficiency; In soil remediation, oxidants/microorganisms can be carried and infiltrated into the contaminated soil to enhance the remediation effect.

Long term stability: Under no external interference, micro nano bubbles can exist stably in liquid for several hours to several days (traditional macro bubbles only last a few seconds to a few minutes), without frequent replenishment, reducing energy consumption - for example, in industrial circulating water, injecting micro nano bubbles at once can maintain the dissolved oxygen demand for several days, reducing the operating time of aeration equipment.

2、 Activation characteristics of micro nano bubbles: functional advantages of interface activity and free radical generation

The "activation characteristics" of micro nano bubbles refer to their functional effects such as "enhanced interfacial activity, free radical release, and optimized water properties" generated through interface energy accumulation and physical/chemical interactions during their formation, ascent, or rupture, endowing them with additional "active functions" in addition to "mass transfer".

1. Core formation mechanism of activation characteristics

The activation effect of micro nano bubbles mainly originates from the extreme environment of interface energy enrichment and bubble rupture:

Interface energy enrichment and surface activity:

The surface energy of bubbles is inversely proportional to their radius (E=4 π r2 γ, where γ is the surface tension). The small radius of micro nano bubbles makes their surface energy extremely high, and a large amount of energy and active molecules (such as surfactants, ions, and gas molecules) accumulate at the interface, forming a "highly active interfacial layer".

This highly active interfacial layer can reduce the gas-liquid interfacial tension and enhance the adsorption capacity for pollutants such as oils and organic compounds. For example, in wastewater treatment, the micro nano bubble interface can quickly adsorb oil droplets and suspended solids in water, improving the efficiency of air flotation separation; Meanwhile, highly active interfaces can promote the dissolution and reaction of gas molecules (such as the conversion of O2 to reactive oxygen species such as O2 − and H2O2).

The generation of hydroxyl radicals (· OH) during bubble rupture:

During the slow upward movement of micro nano bubbles, they gradually contract due to changes in liquid pressure or surface tension, and eventually rupture on the water surface or inside the liquid. At the moment of rupture, the gas inside the bubble is rapidly compressed, producing local high temperatures (up to 1000-3000 K) and high pressures (up to tens of atm). At the same time, water molecules (H2O) at the interface undergo "uniform cracking" under extreme conditions, generating a large number of hydroxyl radicals (· OH) - this is an active species with extremely strong oxidation ability (redox potential 2.8 V, second only to fluorine), which can selectively oxidize and decompose organic matter in water (such as pesticide residues, antibiotics, and difficult to degrade COD), and kill bacteria and viruses.

Regulation of water potential and pH value:

The double layer structure on the surface of micro nano bubbles can affect the ion distribution of the surrounding water, resulting in weak electronegativity (or electropositivity) of the water. At the same time, local reactions during bubble rupture (such as the decomposition of H2O to produce H+, OH -) can fine tune the pH value of the water (usually making neutral water slightly alkaline, increasing pH by 0.5-1.0) - this fine tuning can optimize the water environment, for example, weak alkaline water in agriculture can promote crop nutrient absorption; Aquatic products can neutralize the acidity of water and improve the breeding environment.

2. Key manifestations and application value of activation characteristics

Strong oxidative degradation ability: The generated · OH can directly oxidize and decompose difficult to degrade organic compounds without the need for chemical agents (or reducing the amount of agents used) - for example, in industrial wastewater treatment, micro nano bubbles can degrade toxic organic compounds such as phenol and aniline, increasing COD removal rate by 20% to 50%; In drinking water purification, algae toxins and disinfection by-products precursors can be removed from the water, improving water quality safety.

Efficient sterilization and disinfection: OH can destroy the cell walls/membranes of bacteria and viruses, while the small size of micro nano bubbles can penetrate the surface of microorganisms, enhancing the sterilization effect. For example, in food processing, micro nano bubble water can replace some chemical disinfectants (such as sodium hypochlorite) to kill Escherichia coli and Salmonella on the surface of fruits and vegetables, reducing chemical residues; In aquaculture, it can inhibit the reproduction of pathogenic bacteria such as Vibrio in water and reduce the incidence of diseases.

Interface adsorption and desorption enhancement: Highly active interfaces can enhance the adsorption capacity of heavy metal ions (such as Cu2+, Pb2+) and colloidal particles - for example, in heavy metal wastewater treatment, micro nano bubbles can adsorb heavy metal ions in water and then remove them through air flotation separation; In soil remediation, organic pollutants on the surface of soil particles can be desorbed to improve the efficiency of pollutant removal.

3、 The synergistic effect of dispersion characteristics and activation characteristics: application efficiency of 1+1>2

The two major characteristics of micro nano bubbles do not exist independently, but often form a "synergistic effect", further amplifying their application value:

In the treatment of odorous exhaust gas:

The dispersion characteristics enable micro nano bubbles to be uniformly dispersed in the absorbing liquid, forming a "gas-liquid solid" three-phase efficient contact system, ensuring that odorous gases (such as H2S, NH3) are fully captured;

The activated OH can oxidize and decompose the captured odorous gases into harmless substances (such as H2S → SO42 −, NH3 → N2), avoiding secondary pollution - the synergy of the two increases the odor removal rate to over 90%, and the treatment cost is lower than traditional adsorption methods.

In medical beauty:

The dispersion characteristic allows micro nano bubbles to be uniformly suspended in the care solution and can penetrate deep into the skin pores;

The activated OH can remove oil and bacteria from pores, while the interfacial activity can promote the absorption of nutrients in skincare products, achieving a dual effect of "cleaning+nourishing".

In summary, the dispersion characteristics of micro nano bubbles solve the problems of low gas-liquid mass transfer efficiency and uneven effects, while the activation characteristics endow them with additional functions of oxidation, sterilization, and interface regulation. Together, they constitute the core competitiveness of their efficient application in multiple fields.