Hybrid Micellar Network Hydrogels of Thermosensitive Hydrophilic Triblock Copolymers and Thermosensitive Hairy Nanoparticles

Hybrid micellar network hydrogels, composed of thermosensitive hydrophilic triblock copolymers and thermosensitive polymer brush-grafted nanoparticles (hairy NPs), exhibit intriguing rheological properties. This dissertation work studies thermosensitive hybrid hydrogels with NPs positioned either inside or outside the core of block copolymer micelles.

Chapter 1 is an introduction. Chapter 2 examines the effect of NP’s location on properties of hybrid hydrogels of a thermosensitive ABA triblock copolymer and hairy NPs. Two batches of thermoresponsive polymer brush-grafted silica NPs and an ABA triblock copolymer with thermosensitive outer blocks were prepared. When the lower critical solution temperature (LCST) of hairy NPs was similar to that of the ABA copolymer, the NPs were located in the core of micelles and both the sol-gel transition temperature (T_sol-gel) and dynamic storage modulus G¢ did not change much with increasing NP-to-polymer mass ratio. In contrast, when the LCST of hairy NPs was much higher, the NPs were located outside the micelles; T_sol-gel increased slightly while G¢ decreased significantly with the increase of NP-to-polymer mass ratio. Chapter 3 presents a follow-up work to further study the LCST effect of hairy NPs on rheological properties of hybrid hydrogels which the NPs being initially outside the core of micelles. Four batches of hairy NPs with different LCSTs were synthesized and for all hybrid hydrogels, a significant increase in G' was observed from heating ramps around the LCST of hairy NPs.

Chapter 4 describes a study of hybrid hydrogels of a doubly thermosensitive hydrophilic ABC triblock copolymer and thermoresponsive hairy NPs. With the incorporation of hairy NPs having a LCST similar to that of the higher LCST C block of the ABC copolymer, the gelation efficiency was increased substantially. No such benefit was observed when the LCST of hairy NPs was much higher than that of the C block. Chapter 5 presents a method to synthesize polymer brush-grafted mesoporous silica NPs (MSNs) with a silica NP size of 30-40 nm by “grafting from”. The hairy MSNs are an excellent candidate for the preparation of next generation hybrid hydrogels. Conclusions and future work are provided in Chapter 6.