Use of environmentally-responsive smart glasses in controlled release: Diffusion of molecules under applied stimuli

The use of organosilica sol-gels as environmentally-responsive materials for stimuli-controlled release of encapsulated molecules is reported. These sol-gels exhibit bulk volume changes with respect to applied stimuli such as pH, temperature, salt, and solvents. These volume changes result in expulsion/intake of solvent molecules which can be utilized as a means for externally-regulated release and delivery of dopant molecular entities. For these materials, which undergo a volume transition in response to environmental changes, the magnitude and response time of the material is related to diffusion of solvent molecules in and out of the material. The release of encapsulated molecules and diffusion of solvent accompanies the volume transitions, which can be initiated by changes in temperature or ionic concentration. The kinetics and mechanism of volume changes of organosilica network consisting of hydrophilic and hydrophobic segments are investigated which provide critical insights into the nature of underlying factors that influence release of encapsulated entities. The diffusion coefficient of water molecules in these gels is determined to be considerably faster as compared to organic polymer gels and silica gels indicating rapid volume responses which can be utilized as efficient trigger mechanisms for release of molecules. The results validate preliminary feasibility of stimuli-controlled release of molecules with these gels initiated by the diffusional flow of solvent established by the volume changes.