Thermoresponsive microgels at the air–water interface: the impact of the swelling state on interfacial conformation
- 11 July 2016
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Soft Matter
- Vol. 13 (1), 230-238
- https://doi.org/10.1039/c6sm01375a
Abstract
Poly(N-vinylcaprolactam) (PVCL) is a new temperature-responsive type of polymer microgel with improved biocompatibility as compared to more commonly used poly(N-isopropylacrylamide) (PNIPAM). Both polymers swell at low temperatures and collapse at high ones, showing a volume phase transition temperature (VPTT) around the physiological temperature. Exploring the interfacial characteristics of thermoresponsive microgels is important due to their potential application in emulsion based systems with tailored stabilities and controlled degradation profiles. In this work, we study the properties of charged PVCL particles at the air–water interface by a combination of adsorption, dilatational rheology and Langmuir monolayers. Although PVCL particles adsorb spontaneously at the air–water interface in both, swollen and collapsed conformations, the interfacial properties show significant differences depending on the swelling state. In particular, the total amount of adsorbed microgels and the rigidity of the monolayer increase as the temperature increases above the VPTT, which is connected to the more compact morphology of the microgels in this regime. Dilatational rheology data show the formation of a very loose adsorbed layer with low cohesivity. In addition, collapsed microgels yield a continuous increase of the surface pressure, whereas swollen microgels show a phase transition at intermediate compressions caused by the deformation of the loose external polymer shell of the particles. We also provide a qualitative interpretation for the surface pressure behavior in terms of microgel–microgel effective pair potentials, and correlate our experimental findings to recent rescaling models that take into account the importance of the internal polymer degrees of freedom in the rearrangement of the conformation of the microgel particles at the interface.This publication has 49 references indexed in Scilit:
- Interplay between internal structure and optical properties of thermosensitive nanogelsColloids and Surfaces A: Physicochemical and Engineering Aspects, 2015
- Effect of Salt on Swelling Behaviors of Thermosensitive Hydrogels: Applicability of the Nonrandom Contact ModelMacromolecules, 2015
- Computer simulations of thermo-sensitive microgels: Quantitative comparison with experimental swelling dataThe Journal of Chemical Physics, 2012
- Design and properties of supramolecular polymer gelsSoft Matter, 2012
- Temperature-sensitive nanogels: poly(N-vinylcaprolactam) versus poly(N-isopropylacrylamide)Polymer Chemistry, 2012
- Gel swelling theories: the classical formalism and recent approachesSoft Matter, 2011
- Soft nanoparticles (thermo-responsive nanogels and bicelles) with biotechnological applications: from synthesis to simulation through colloidal characterizationSoft Matter, 2011
- Reentrant swelling behavior of thermosensitive N-isopropylacrylamide nano-sized gel particlesPolymer, 2009
- Stimuli-responsive hydrogels: drugs take control.Nature Materials, 2008
- Temperature-sensitive aqueous microgelsAdvances in Colloid and Interface Science, 2000