New Method for Gelation Temperature Measurement without Disturbing the Crystal Network

Designing thermoreversible gels for extended release of mosquito repellent

Mosquito-borne diseases are responsible for 700 000 deaths annually. Current outdoor protective strategies primarily focus on direct skin application of commercial repellents (i.e., aerosol sprays or topical lotions) which are typically limited to efficacy times of ≤10 hours due to rapid evaporation and dermal absorption. Consequently, frequent reapplication for continuous protection can increase associated health hazards and cause noncompliance. This study utilizes Hansen solubility parameter modeling to design physical gels composed of insect-repelling N,N-diethyl-meta-toluamide (DEET) and modacrylic copolymer poly(acrylonitrile-co-vinyl chloride) (P(AN-VC)). The P(AN-VC)/DEET composites exhibit tunable and reversible sol-gel transition temperatures that can meet the thermomechanical stability demands of the intended application and permit facile transition to commercial melt processing techniques such as injection molding, filament spinning, or film casting. P(AN-VC)/DEET gel films demonstrate mosquito repellency for more than half a year-performing longer than any other known material to date-due to the high reservoir of repellent and its desorption hindrance from the polymer matrix. Therefore, P(AN-VC)/DEET gels hold significant potential for extended protection against mosquitos and other biting arthropods.

Experimental and Numerical Investigation of the Degelation Behavior and Non-Isothermal Flow Restart of a Waxy Oil Pipeline

Flow assurance challenges associated with waxy crude oil precipitation at low ambient conditions are significant concerns for oil industries during production, transportation, and storage. Numerous methods have been employed to mitigate wax deposition and gelation issues. Since wax precipitation is temperature-sensitive, heating has emerged as a promising method to enhance oil flowability. The present work intends to examine the degelation behavior of waxy oil using rheometry, differential scanning calorimetry, and microscopy techniques. In addition, a non-isothermal flow restart simulation is performed using an in-house numerical simulator consisting of a rheological model of sol-gel transition developed in the current work. A numerical simulation of a preheated gelled pipeline demonstrates the significance of the degelation temperature. The effects of the wax concentration, initial gel temperature, and aging period on the degelation temperature are examined. The observed degelation temperature is higher than the gelation temperature, leading to thermal hysteresis. The extent of thermal hysteresis reduces with a decrease in the heating rate. The numerical simulation uses the finite volume method with variables placed on a staggered grid. The gel heated above and below the degelation temperature shows a significant variation in axial velocity profiles. However, further heating does not affect the velocity profiles. A shear banding type of effect is observed in the axial velocity profile above the degelation temperature. Heating the gelled oil to the degelation temperature instead of the wax disappearance temperature saves excessive heating energy during storage and transport operations.