What type of surfactants have a positive charge?

Cationic surfactants are characterized by their positive charge, which distinguishes them from other types of surfactants. This positive charge allows cationic surfactants to adsorb to negatively charged surfaces, including many types of plant membranes and soils. The interaction between cationic surfactants and these surfaces can enhance the effectiveness of herbicides by improving their adherence and penetration into plant tissues.

In contrast, nonionic surfactants lack a charge, which makes them versatile and effective in various applications without the interaction complexities of charged surfactants. Anionic surfactants carry a negative charge and are more common in applications where repulsion or emulsification is desired. Amphoteric surfactants can carry either a positive or negative charge depending on the pH of the environment, allowing them to function in diverse conditions but not specifically as positively charged agents. Thus, cationic surfactants are the correct answer as they are the only group consistently identified with a positive charge, making them unique in their application and function.