The compression of deformed microgels at an air/water interface

Abstract

The compression of microgels at air/water interfaces was investigated using a Langmuir–Blodgett trough with in situ fluorescent microscopy. The relationship between the structure of the microgel arrays and the compression behavior was clarified.

Softness matters: effects of compression on the behavior of adsorbed microgels at interfaces

“…16 In this framework, mechanical and visco-elastic properties of air–water and oil–water microgel-covered interfaces have been investigated by means of interfacial rheology and surface pressure measurements to determine how microgel conformation, packing and film stability change in response to compression. 17–22…”

“…Furthermore, the transfer of a microgel monolayer from a fluid interface to a solid substrate might introduce artifacts, raising concerns about the reliability of observed solid-to-solid isostructural phase transitions. 21,44…”

“…16 In this framework, mechanical and visco-elastic properties of air-water and oil-water microgel-covered interfaces have been investigated by means of interfacial rheology and surface pressure measurements to determine how microgel conformation, packing and film stability change in response to compression. [17][18][19][20][21][22] Softness is known to strongly affect the properties of microgels at interfaces, such as the formation of crystalline lattice, the contact angle they form and the final architecture they assume once adsorbed. 12 The softest pNIPAM-based microgels that can be synthesized by precipitation polymerization [23][24][25][26] are the so-called ultra-low crosslinked (ULC) microgels.…”

“…Furthermore, the transfer of a microgel monolayer from a fluid interface to a solid substrate might introduce artifacts, raising concerns about the reliability of observed solid-to-solid isostructural phase transitions. 21,44 Among surface-sensitive techniques, neutron reflectometry (NR) can be used to determine the out-of-plane profile of the microgels orthogonal to the interface and to assess their volume fraction in situ. 13,45 In this work, by combining NR, surface pressure measurements, and computer simulations, we comprehensively describe the out-of-plane behavior of pNIPAM-based microgel monolayers under compression at the air-water interface.…”

Interfacial Fluid Rheology of Soft Particles

“…Several recent ex situ experimental observations have reported that microgels crystallize in hexagonal lattices and undergo a solid-to-solid transition with increasing concentration [25,26]. The structure of the monolayer has also been addressed in situ [27,28], where important differences have been observed with respect to ex situ measurements. It thus appears fundamental to address the properties of the monolayer by in situ techniques [29,30] and by appropriate theoretical modeling [22,31,32].…”