Abstract
The present study focuses on the development of multiresponsive core-shell microgels and the manipulation of their swelling properties by copolymerization of different acrylamides—especially N-isopropylacrylamide (NIPAM), N-isopropylmethacrylamide (NIPMAM), and NNPAM—and acrylic acid. We use atomic force microscopy for the dry-state characterization of the microgel particles and photon correlation spectroscopy to investigate the swelling behavior at neutral (pH 7) and acidic (pH 4) conditions. A transition between an interpenetrating network structure for microgels with a pure poly-N,n-propylacrylamide (PNNPAM) shell and a distinct core-shell morphology for microgels with a pure poly-N-isopropylmethacrylamide (PNIPMAM) shell is observable. The PNIPMAM molfraction of the shell also has an important influence on the particle rigidity because of the decreasing degree of interpenetration. Furthermore, the swelling behavior of the microgels is tunable by adjustment of the pH-value between a single-step volume phase transition and a linear swelling region at temperatures corresponding to the copolymer ratios of the shell. This flexibility makes the multiresponsive copolymer microgels interesting candidates for many applications, e.g., as membrane material with tunable permeability.
Highlights
In soft matter research, stimuli-responsive core-shell microgels have become a strongly investigated field in recent years [1,2,3]
All core-shell microgels synthesized in this work comprise the same core material, consisting of a PNIPAM–co–AAc core with an nominal acrylic acid content of 5 mol % and a nominal cross-linker content of 10 mol %
Nominal shell monomer composition and sample names of all PNIPAM–co–AAc@PNNPAM–co–PNIPMAM core-shell microgels investigated in the present study
Summary
Stimuli-responsive core-shell microgels have become a strongly investigated field in recent years [1,2,3]. Different particle architectures have been examined in this context, ranging from dual-responsive networks [4,5,6,7], amphiphilic self-assembled systems [8], colloidally supported nanoreactors [9,10], nanoparticle containers [11,12], interpenetrating networks [13,14], and hollow spheres [15,16] to core-shell microgels with natural materials (e.g., starch) [17]. One of the most prominent examples for stimuli-responsive microgels are thermoresponsive particles based on poly-N-isopropylacrylamide (PNIPAM). One of the most advantageous properties of PNIPAM based microgels is the possibility to tailor their stimuli-responsive behavior by copolymerization [22,23]. It is possible to add Polymers 2019, 11, 1269; doi:10.3390/polym11081269 www.mdpi.com/journal/polymers
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
