On the Thermoresponsivity and Scalability of N,N‐Dimethylacrylamide Modified NIPAM Microgels

Abstract

versa. [1a,2a] The deswelling/swelling temperature is then referred to as volume phase transition temperature (VPTT), as opposed to an LCST. This reflects the fact that the particles undergo a volume collapse at the transition temperature, as opposed to the nearly complete desolvation observed in the case of linear homopolymer.The prime technique to synthesize such colloidal thermoresponsive microgels is precipitation polymerization (PP). [1c,h] Here, monomer, initiator, and optionally surfactant are all molecularly dissolved in the initially homogeneous reaction solution, which makes this process rather simple to conduct. Once a critical degree of polymerization is reached and the polymerization is performed above the LCST of the targeted polymer, the polymer chains become insoluble while the charges obtained from the initiator prevent particle precipitation. The precipitating chains agglomerate and serve as nuclei that are grown by further conversion of monomer and oligoradicals, leading to near-monodisperse particles in the range of 100 nm to ≈1 µm. Considering the simplicity of PP, it is hardly surprising that the body of proposed applications is vast: it ranges from waste water treatment, [3] enhanced oil recovery, [4] and thickening, [5] to more sophisticated technologies such as drug delivery, tissue engineering, sensing, and liquid chromatography (i.e., used as temperature-sensitive stationary phases for size exclusion, hydrophobic, ionic, and affinity chromatography), which are summarized in recent reviews. [1h,6] In addition to these proposed fields of application, colloidal microgels are valuable model systems in fundamental research to study soft matter physics. [1g] In this context, the usage of near-monodisperse particles of well controllable size and dispersity is essential to study effects on the microscopic scale (or less), which is perfectly fulfilled by particles obtained by PP.With this article, we want to present our contribution on the synthesis of thermoresponsive microgels. For a collaborative project, we were requiring significant amounts of such particles supposed to be embedded in films (or foams) for the reversible release/absorption of water at a critical temperature. More specifically, the following criteria were defined for the system to be used as the responsive material:1. The synthetic method to be used is scalable and provides at least 250 g pure thermoresponsive microgels per batch. N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMAAm) are prepared using either precipitation polymerization (PP) or inverse emulsion polymerization (IEP). The comparison of the volume phase transition temperature (VPTT) for PNIPAM n -co-PDMAAm m copolymer microgels prepared by PP or IEP reveals significant differences. Empirically, PP leads to lower VPTTs than IEP for identical monomer composition, whereby the observed difference in the VPTT becomes greater the higher the DMAAm content of the monomer mixture is. Presumably this is because IEP confers a higher homogeneity of the cros...

Surface‐Bound Microgels for Separation, Sensing, and Biomedical Applications

“…LCST-type microgels are much more widely employed and rely on the amphiphilic character of monomers like vinyl caprolactam (NVCL) and various N(alkyl)acrylamides, chiefly N(ethyl)-(NEAm), N(isopropyl)-(NIPAm), and N,N'(dimethyl)acrylamides. [123] Tagit et al studied the phase transition of surface-bound PNIPAm microgels via AFM by monitoring the concurrent decrease in volume and increase in the height of single microgels while heating the surrounding aqueous solution. [121] Wiedemair et al evaluated the deformability of analogous systems, discovering a 15-fold increase in Young's modulus as the surrounding temperature crossed the LCST boundary.…”

“…[32,58] Responsive monomers can also be included to reversibly alter the morphology of the microgels upon exposure to specific environmental stimuli. [27,[122][123][124] Other monomers providing residues such as amine, carboxylic acid, epoxide, azide, or alkyne can also be incorporated to enable post-synthetic modification. [125][126][127][128] This section presents an overview of the monomers that have been utilized in microgel fabrication and their contribution to the functionality of the microgel-coated surface.…”

Equilibrium swelling of thermo-responsive copolymer microgels

“…To show that even a small number of observations ensures sufficient accuracy in determination of this parameter, we study experimental data on P(NIPAm-DMAAm) gels prepared by free-radical polymerization at room temperature of an aqueous solution of monomers (0.7 M) by using BIS (3.2 mol% with respect to monomers) as a cross- To compare the thermo-mechanical responses of macroscopic gels and microgels, we analyze observations on P(NIPAm-DMAAm) microgels synthesized by free-radical polymerization (6 h at 75 C) of an aqueous solution of NIPAm and DMAAm monomers (170 mM) by using BIS (1.4 mol% with respect to monomers) as a cross-linker, SDS (0.75 mol% with respect to monomers) as a surfactant, and KPS as an initiator. 64 Experimental data on microgels with c co ¼ 0 and 0.18 are plotted in Fig. 6A and those on microgels with c co ¼ 0.06, 0.10, 0.14 and 0.16 are depicted in Fig.…”

A Short Review on the N,N-Dimethylacrylamide-Based Hydrogels

“…The heavy metal ions removal properties of copolymers of DMAA with 2-acrylamido-2-methylpropane sulfonic acid (AMPS) was also examined in many studies [ 23 , 24 , 25 ]. Furthermore, because its volume phase transition temperature (304–307 K) is near that of poly(N-isopropylacrylamide), N,N-dimethylacrylamide is a strong candidate for replacing poly(N-isopropylacrylamide) (307 K) [ 26 ].…”