Multifunctional Silica-Modified Hybrid Microgels Templated from Inverse Pickering Emulsions

Interfacial Electrokinetic Phenomena of Thermoresponsive Microgels with a Spatial Gradient of Charged Groups

When functional microgels are synthesized via radical copolymerization, spatial gradients of functional groups often form due to a difference in reactivity ratios between monomer and comonomer. In this study, we systematically investigated the effect of a decreasing gradient of charged groups from the core to the shell of microgels on their surface properties, which are crucial for colloidal particles, through the analysis of interfacial electrokinetic phenomena using Ohshima's equation. A series of electrophoretic analyses combined with dynamic light scattering revealed that the surface of the microgels undergoes a multistep collapse during the particle-size reduction due to dehydration upon increasing the temperature. Furthermore, the more complicated hierarchical gradient of charged groups within the microgels was elucidated by quantitatively evaluating changes in surface properties during precipitation polymerization based on interfacial electrokinetic phenomena.

Modulating the conformation of microgels by complexation with inorganic nanoparticles

HYPOTHESIS

The complexation of microgels with rigid nanoparticles is an effective way to impart novel properties and functions to the resulting hybrid particles for applications such as in optics, catalysis, or for the stabilization of foams/emulsions. The nanoparticles affect the conformation of the polymer network, both in bulk aqueous environments and when the microgels are adsorbed at a fluid interface, in a non-trivial manner by modulating the microgel size, stiffness and apparent contact angle.

EXPERIMENTS

Here, we provide a detailed investigation, using light scattering, in-situ atomic force microscopy and nano-indentation experiments, of the interaction between poly(N-isopropylacrylamide) microgels and hydrophobized silica nanoparticles after mixing in aqueous suspension to shed light on the network reorganization upon nanoparticle incorporation.

FINDINGS

The addition of nanoparticles decreases the microgels' bulk swelling and thermal response. When adsorbed at an oil-water interface, a higher ratio of nanoparticles influences the microgel's stiffness as well as their hydrophobic/hydrophilic character by increasing their effective contact angle, consequently modulating the monolayer response upon interfacial compression. Overall, these results provide fundamental understanding on the complex conformation of hybrid microgels in different environments and give inspiration to design new materials where the combination of a soft polymer network and nanoparticles might result in additional functionalities.

Durable gelfoams stabilized by compressible nanocomposite microgels

Compressible nanocomposite microgels can stabilize the air/water interfaces of gas bubbles for several months, which affords durable gelfoams.