Title: Molecular gels-based controlled release devices for pheromones Authors
|Jadhav, Swapnil -|
|John, George -|
Submitted to: Soft Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 22, 2011
Publication Date: March 21, 2011
Citation: Jadhav, S.R., Chiou, B., Wood, D.F., Hoffman, G.D., Glenn, G.M., John, G. 2011. Molecular gels-based controlled release devices for pheromones. Soft Materials. 7:864-867. DOI: 10.1039/c0sm00878h. Interpretive Summary: Many important natural control agents for various agricultural pests are volatile and require some method of controlled release. Molecular gels find applications in the agricultural industry by demonstrating their capability in developing efficient controlled release devices for pheromones, which are potential biopesticides. Such new devices are readily biodegradable, exhibit high pheromone-loading capacity and deliver the pesticide uniformly at high concentration for a prolonged time.
Technical Abstract: 2-Heptanone is a volatile solvent that is effective in controlling parasitic mites (Varroa) in honeybee. Controlled-release of 2-heptanone is needed to avoid overdosing, minimize chemical usage, and provide a sustained release over a several week period. Control-release devices comprised of a reservoir of 2-heptanone and a biodegradable vapor barrier film can effectively control the rate of release. However, there is a need to develop a solid gel of 2-heptanone to ensure that the reservoir contents do not leak from the device in the event of a break in the vapor barrier. A solid gel was made of 2-heptanone by adding 3, 5, and 7% (w/w) of a mannose-based aryl glycolipid gelling agent. The materials were heated to 80C and cooled slowly to room temperature. Gelling temperature (ca. 70°C) was determined using differential scanning calorimetry. Light microscopy was used to show the crystallization properties of the mixture. Crystallization was initiated randomly in the mixture and individual crystals grew radially until they contacted adjacent crystals. The radial crystal structure was further documented by scanning electron microscopy (SEM). Close evaluation of the crystals by SEM revealed ribbon-like fibers with no branching. Compressive tests indicated a compressive strength of 1.3, 4.0, and 7.5 kPa for gels containing 3, 5, and 7% of the aryl glycolipid gelling agent, respectively. The compressive modulus was 6.8, 13.5, 23.6 kPa for the 3, 5, and 7% aryl glycolipid, respectively. The dynamic rheological properties of the gels indicated elastic (G’) and viscous moduli (G”) ranging from 6,000 rad/s for samples containing 3% glycolipid to more than 100,000 rad/s for samples containing 7% glycolipid. The release rate of 2-heptanone from liquid versus gel was monitored under controlled conditions. The gel structure had no significant effect on the volatilization rate of 2-heptanone. Control-release devices were made from beeswax (maximum 50% loading) and the 2-heptanone gel (maximum 97% loading). Both devices had similar percent release rates but the sample containing the 2-heptanone gel had a higher total sustained release of 2-heptanone. The results suggest that the use of the polymeric gel not only immobilizes the 2-heptanone in the reservoir but also provides way to load a very high percentage of 2-heptanone in the reservoir which will allow for smaller devices with equal or larger capacity than other devices.