The formation of crystalline hydrogel films by self-crosslinking microgels

Abstract

Monodisperse spheres composed of a copolymer of poly(N-isopropylacrylamide) (PNIPAM) and N-hydroxymethylacrylamide (NMA) were prepared and used as building blocks for a thin hydrogel film. A dilute dispersion of these microgels was allowed to dry in air, resulting in the formation of crystalline microgel structures at the air/dispersion interface. Taking advantage of self-crosslinking property of NMA, the neighboring PNIPAM-NMA microgels reacted to form covalent bonds to stabilize the crystalline structure after the water was completely evaporated from the particle dispersion at ambient temperature. After immersion in water, this film not only absorbed a large amount of water like a conventional hydrogel but also exhibited iridescent colors due to long range ordered microgel arrays. The thermally responsive properties and mechanical properties of this film were studied.

Preparation of microgel composite hydrogels by polymer post-crosslinking method

“…Effect of polymer water content on the MC hydrogels prepared by partly evaporated composite polymers When NMA was used as an efficient crosslinking agent, covalent cosslinking bonds could be formed by thermal activation at around 110°C after water was evaporated in the acrylate latex films [27][28][29]. After water was completely evaporated to form drying films, covalent cosslinking bonds could also be formed under ambient conditions [20]. It is suggested that decreasing the polymer water content is beneficial to the covalent bond formation when NMA is used as a crosslinking agent.…”

“…Reactive microgels have also been used as multifunctional crosslinkers for photopolymerized thin films or thermosets to improve their mechanical properties [16,17]. In addition to the direct polymerization method by adding the reactive microgels containing C=C double bonds, the crosslinked structure can also be obtained by postcrosslinking of the polymers through irradiation, peroxide, drying, heating, and so on [18][19][20][21]. Amide groups of acrylamide can react with other groups [22].…”

A novel two-level microstructured poly(N-isopropylacrylamide) hydrogel for controlled release

“…have been the focus of research because of their unique and important properties [1][2][3][4][5]. Chemically crosslinked poly(N-isopropylacrylamide) (PNIPAAm) hydrogel is a typical temperature-sensitive hydrogel which undergoes a reversible volume phase transition around a lower critical solution temperature (LCST) ($32-34°C) [6].…”

Photoactive composite films prepared from mixtures of polystyrene microgel dispersions and poly(3-hexylthiophene) solutions

“…There is only one report to our knowledge that provides any information about polystyrene microgel deformation. 17,18 Here, we explore microgel ordering in films by first investigating the morphology of spin coated polystyrene microgel films. The rules governing nonaqueous microgel film formation have not been established, especially in the context of composites.…”