Multi-responsive microgels: Synthesis, characterization, and applications.

摘要

Carboxylic acid-functionalized poly(N-isopropylacrylamide) (PNIPAM) microgels exhibit "smart", rapid, and reversible responses to changes in temperature, pH and ionic strength. To achieve a targeted set of physical properties and optimize microgel morphologies for particular applications, both the bulk content and the radial and intrachain distributions of functional groups within microgels must be understood and controlled.;In this work, methods are developed for controlling functional group distributions in PNIPAM-based microgels by tuning the hydrophobicity and copolymerization kinetics of the functional comonomer(s). The resulting functionalized microgels are extensively characterized, both directly via electron microscopy and indirectly using electrophoresis, potentiometric and isothermal calorimetric titration, differential scanning calorimetry, light scattering, and rheology. Novel dimensionless plotting strategies allow direct comparisons to be made between the microscale and macroscale development of the thermal and pH-induced phase transitions, giving insight into both the functional group distributions within the microgels and the underlying mechanisms of microgel swelling. The experimentally-observed functional group distributions can be predicted theoretically using a novel copolymerization kinetics model which permits the estimation of the local functional monomer and crosslinker densities within microgels. A comprehensive thermodynamic gel swelling model is further employed to exploit this local compositional information to predict local water contents and crosslinking efficiencies and understand the impact of compositional gradients on microgel swelling.;The structure-property-application relationships identified through this work are applied to engineer microgels for specific technological end uses. The impact of the radial and chain functional group distributions on the application performance of microgels is illustrated by testing the microgels as drug uptake/delivery vehicles, heavy metal uptake sponges, and bioactive molecular conjugation supports. Phenylboronic acid-functionalized microgels are also designed which can swell or deswell in response to changes in the environmental glucose concentration under physiological conditions. The potential application of these novel microgels as linear glucose sensors, self-regulating insulin release vehicles, and cell-specific flocculants is demonstrated.