Responsive Microgels at Surfaces and Interfaces

Abstract

Stimuli responsive surface structures attract increasing attention due to a large variety of envisioned applications. The controlled organization of poly(N-isopropyl acrylamid), PNIPAM microgel particles at solid surfaces inspired numerous research activities. In this review article, we briefly discuss the swelling/deswelling properties of adsorbed microgel particles in comparison to the behavior in the bulk phase. The presence of the solid interface highly influences and changes their behavior with respect to the properties in solution. Furthermore, the confinement on a solid substrate allows the direct and in-situ investigation of the mechanical properties of the microgel particles. Additionally, we briefly review the research on microgel particles at liquid interfaces. At these interfaces new interesting effects occur. Moreover, we discuss some interesting work on potential applications. In this context, microgel particles are often used as an active component for responsive coatings of various functionality envisioning applications, e.g. in medicine, biotechnology, and nanooptics.Zusammenfassung: Responsive Oberflächenmaterialien finden aufgrund der damit verbundenen potentiellen technischen Anwendungsmöglichkeiten große Beachtung in der aktuellen Forschung. Die Möglichkeit, kolloidale Gelpartikel aus poly(N-Isopropylacrylamid), PNIPAM an festen Oberflächen kontrolliert anzuordnen, inspirierte vielfältige Forschungsakivitäten. In diesem Übersichtsartikel diskutieren wir das Quellverhalten adsorbierter Mikrogelpartikel im Vergleich zu

Goosebumps‐Inspired Microgel Patterns with Switchable Adhesion and Friction

“…At pH 7, the particles on the surface became flatter (average height: 36.5 ± 15.7 nm, diameter: 787 ± 82 nm) than the particles at pH 3 (average height: 91.8 ± 9.5 nm, diameter: 527 ± 32 nm), indicating strong attractive forces between the brush and the particles with a stronger negative charge (Figure vs Figure a). Similar results have been reported previously . At pH 8, the particles were less flat (average height: 47.1 ± 7.8 nm, diameter: 744 ± 63 nm) than at pH 7 (Figure ).…”

The Next Generation of Colloidal Probes: A Universal Approach for Soft and Ultra‐Small Particles

“…PNIPAM‐based hydrogels are stimuli responsive with respect to the external temperature and undergo a volume phase transition (VPT). This behavior is caused by the lower critical solution temperature of PNIPAM in water at temperatures of 32–33 °C . Consequently, the thickness of the hydrogel shell of the core–shell particles in this study changes significantly when surpassing the VPT temperature (VPTT).…”

Microgels at fluid-fluid interfaces for food and drinks

“…In principal any type of gelling material could be made into a microgel particle, but the majority of systems studied to date are composed of either synthetic or natural polymers. By the far the most widely investigated synthetic microgels are based on poly-(N-isopropylacrylamide) (PNIPAM) (Wellert et al, 2015) or its derivatives. PNIPAM microgels have a volume phase transition temperature in the convenient region of 32 °C.…”

“…The effects of microgel particle deformability (Destribats et al, 2014a) and size (Destribats et al, 2011); (Murphy et al, 2016) on adsorption and the ability to stabilize and emulsions has been studied (Chevallier et al, 2018); (Kwok and Ngai, 2018a). The outer layers of microgels tend to be less crosslinked and are therefore capable of greater distortion, giving the 'fried egg' appearance of microgels adsorbed on solids (Style et al, 2015); (Destribats et al, 2011) where the interaction with the interface can be especially pronounced, as reviewed by Wellert (Wellert et al, 2015). The balance between the rates of adsorption, spreading and inter-particle interactions (Maldonado-Valderrama et al, 2017) is important to understand in order to control the structure and properties of dried films of microgels on solid substrates (Horigome and Suzuki, 2012).…”