The boundary between different phases of matter is commonly referred to as an interface, including gas/liquid, gas/solid, liquid/liquid, solid/solid, and solid/liquid interfaces. Among these, interfaces containing a gas phase are termed surfaces, which include both liquid and solid surfaces. Surfactants can alter the chemical properties of surfaces/interfaces by forming adsorption films through adsorption, thereby reducing surface tension. Thus, surfactants are functionally sophisticated chemical products that can induce significant changes in the state of surfaces/interfaces with a small amount added, thereby providing functions such as wetting, penetration, foaming, emulsification, and sterilization.
So, how are these functions of surfactants applied to enhance the disinfection effect? Let's explore how wetting and penetration functions contribute to improving the disinfection effect.
Most pathogenic microorganisms grow along with the formation of biofilms. Initially, planktonic microorganisms weakly adhere to surfaces/interfaces through van der Waals forces, hydrophobic interactions, electrostatic forces, etc. At this stage, pathogenic microorganisms have not formed stable, firm biofilms, which can be easily removed. As adherent pathogens grow and reproduce, they continuously secrete gelatinous extracellular polysaccharide matrix, making their adhesion to surfaces/interfaces more secure, forming microbial colonies. The biofilm formed becomes thicker from thin, making it difficult to remove.
The formation of biofilms can confer resistance to disinfectants. The polymer structure of the extracellular polysaccharides and proteins in biofilms can create resistance, delaying the penetration of disinfectants and other substances into the biofilm matrix. Compared to directly acting on planktonic microorganisms, the presence of biofilms reduces the accessibility of disinfectants to microorganisms adhering to surfaces/interfaces.
Research comparing the resistance of bacteria in biofilms and planktonic bacteria to disinfectants found that using disinfectants containing 800mg/L of peracetic acid, the average killing rates of planktonic Pseudomonas aeruginosa, Staphylococcus aureus, and Pseudomonas aeruginosa were 90.53%, 87.64%, and 83.16%, respectively, while the average killing rates of the same bacteria in biofilms were only 82.56%, 84.81%, and 82.85%, respectively. Using disinfectants containing 150mg/L of chlorine dioxide for 1 minute, the average killing rates of planktonic Pseudomonas aeruginosa, Staphylococcus aureus, and Pseudomonas aeruginosa were 96.95%, 96.18%, and 96.05%, respectively, while the average killing rates of the same bacteria in biofilms were only 86.37%, 89.54%, and 91.20%, respectively. It can be seen that bacteria forming biofilms exhibit stronger resistance to disinfectants than planktonic bacteria.
In addition, some components of biofilm structure can react with certain disinfectants, leading to partial consumption of disinfectants, thereby reducing their disinfection effect. Moreover, the wetting coverage of disinfectants on surfaces/interfaces also affects the disinfection effect. Only when droplets completely cover the surface/interface can the possibility of missed disinfection be truly avoided.
Based on the effects of biofilms and surface/interface wetting on the disinfection effect, the wetting and penetration functions of surfactants, when combined with disinfectant components, can enhance the disinfection effect:
Correlation between contact angle size and degree of wetting
(1) Enhancement of wetting performance on the disinfection effect: The wetting function of surfactants can enhance the wetting of disinfectants on surfaces/interfaces, especially in cracks, corners, and other areas where pathogenic microbial colonies are prone to accumulate and difficult to clean. This ensures complete coverage and eliminates blind spots for disinfection on surfaces/interfaces. On the other hand, the wetting function also accelerates the contact between disinfectants and surfaces/interfaces. The combination of the two enhances the disinfection effect. The wetting degree of droplets on surfaces/interfaces can be assessed using the Dataphysics OCA15EC Video Optical Contact Angle Measurement Instrument (equipment in the Surface Active Agent Research Center Laboratory of Chengdu Kehongda).
Disruption of biofilms by surfactant penetration functions
(2) Enhancement of penetration performance on the disinfection effect: The penetration function of surfactants allows disinfectants to more quickly destroy microbial biofilms and penetrate into the interior of biofilms, increasing the contact between disinfectants and pathogenic microorganisms. At the same time, it also assists disinfectants in more easily and rapidly destroying and penetrating the cell membrane structures of pathogenic microorganisms, thereby enhancing the disinfection effect.
In summary, surfactants, with their unique wetting and penetration functions, can be combined with disinfectant components to effectively increase the contact between disinfectants and pathogenic microorganisms, thereby enhancing the disinfection effect.
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