Abstract
Abstract. Porous poly(N-isopropylacrylamide) (PNIPAAm) hydrogels with pore diameters in the nanometer and the micrometer range were synthesized using two variations of the surfactant-based template method. We showed that smaller pore diameters lead to faster swelling and deswelling. A graphic representation of a model describing the swelling kinetics explains the assumption that the release and the uptake of water is faster for a larger specific surface area, that is smaller pore diameters. Additionally, the open-porous channel structure benefits the water transport compared to a nonporous PNIPAAm hydrogel. Sensor measurements result in response times between 36 s and 4 min also showing the importance of mechanical stability of porous hydrogels.
Highlights
Responsive hydrogels are swellable three-dimensional polymer networks
A change of the pH value, the concentration of analytes or the temperature of a surrounding aqueous medium leads to a volume change of these networks (Dušek and Patterson, 1968; Tanaka, 1978; Saito et al, 1993; Orakdogen and Okay, 2006) making them suitable for applications as transducers in sensors and as actuators (Guenther and Gerlach, 2009; Richter, 2009; Kuckling et al, 2003; Guenther et al, 2007; Richter et al, 2009; Richter and Paschew, 2009)
The so-called lower critical solution temperature (LCST = 32 ◦C), poly(N -isopropylacrylamide) (PNIPAAm) chains are dissolved in water due to predominant polymer–solvent interactions as described in Nayak and Lyon (2005) and pictured in Scheme 1a
Summary
Responsive hydrogels are swellable three-dimensional polymer networks. A change of the pH value, the concentration of analytes or the temperature of a surrounding aqueous medium leads to a volume change of these networks (Dušek and Patterson, 1968; Tanaka, 1978; Saito et al, 1993; Orakdogen and Okay, 2006) making them suitable for applications as transducers in sensors and as actuators (Guenther and Gerlach, 2009; Richter, 2009; Kuckling et al, 2003; Guenther et al, 2007; Richter et al, 2009; Richter and Paschew, 2009).A major disadvantage of hydrogels is the slow swelling process possibly lasting for hours or even days depending on sample size and geometry. Responsive hydrogels are swellable three-dimensional polymer networks. The so-called lower critical solution temperature (LCST = 32 ◦C), PNIPAAm chains are dissolved in water due to predominant polymer–solvent interactions as described in Nayak and Lyon (2005) and pictured in Scheme 1a. The PNIPAAm chains collapse to form insoluble globules and the polymer precipitates (Nayak and Lyon, 2005; Scheme 1a). This characteristic of PNIPAAm chains translates into hydrogels as pictured in Scheme 1b. 32 ◦C, the predominant polymer–solvent interactions attract water molecules inside the three-dimensional crosslinked polymer network. 32 ◦C, coiling of the PNIPAAm chains in the hydrogel occurs due to predominant polymer–polymer interactions. The volume of the hydrogel collapses, which leads to a deswollen state
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