Swelling Behavior of Organogels Containing Two Unique Block Copolymers

Organogels based on styrenic block copolymers are good candidates for many applications including transdermal drug delivery since their transport and mechanical properties can be easily tuned through formulation changes. Understanding the swelling behavior of such organogels is helpful in relating formulation changes to gels’ microscopic structure. In this work, the equilibrium swelling ratios of two series of styrenic block copolymer gels are investigated. The first series consists of a triblock copolymer (triblock1: 248 kg/mole, ƒ_PS=0.297), a diblock copolymer (136 kg/mole, ƒ_PS=0.334) and mineral oil (MO). The second series consists of two different triblock copolymers (triblock1 and triblock2: 76 kg/mole, ƒ_PS=0.658) and MO. In each series, triblock1 is fixed at three levels (10, 20, and 30 wt%) while the diblock, or triblock2, is varied from 0 wt% to 30 wt%. For a fixed amount of triblock1, it is observed that an increase in diblock (Series 1) amount leads to increased swelling until a total copolymer concentration of 35 wt% whereas swelling monotonically decreases with increasing triblock2 (Series 2) concentration. The cause of these trends will be discussed.