Long-term sustained release of small molecular surfactants using microcapsules

The controlled manipulation of surfactant concentration is essential for optimizing performance in numerous industrial applications, such as enhanced oil recovery in oil industry. However, encapsulating surfactants has proven challenging due to their propensity to localize at interfaces. In this study, we use microfluidic technology to fabricate poly(ethylene glycol) diacrylate-based microcapsules for encapsulating small molecular cargoes through finely tuning the relationships among the interfacial tensions of inner, middle and outer phases. These microcapsules show excellent retention by regulating the shell thickness and monomer content, releasing less than 47.2% over 49 d at 20 °C. Upon oil contact, surfactant release is indicated by a contact angle decrease of 7.2° at 20 °C and 21.8° at 50 °C within 48 h. The releases of nonionic Tween 80 and zwitterionic Betaine 1 calculated via surface tension in saline solutions at 80 °C are reduced to as low as 8.2% within 48 h and 1.1% within 8 h. The pressure-induced release reaches 22.7% within 24 h under 15 MPa, significantly exceeding the impacts of temperature and salinity. Notably, even microcapsules with reduced eccentricity still demonstrate sustained-release behavior. Mechanical and degradation tests show that the sustained release is driven by the increase in pore size of the shell due to its gradual degradation. This tunable system offers a versatile platform for encapsulating and controlling the release of surfactants or other sensitive agents, ideal for harsh environmental applications requiring sustained functionality.