Bending and Stretching Actuation of Soft Materials through Surface‐Initiated Polymerization

Abstract

Rotschopf: Hydrophile oberflächengebundene Polymerbürsten (siehe Bild) mit hohem Molekulargewicht und hoher Pfropfdichte verursachen ein reversibles Biegen und Dehnen weicher Polymerträger auf der Makroskala. Die Formänderung des Trägers wird durch Reaktion auf verschiedene Reize wie Feuchtigkeit, Temperatur und pH‐Wert gesteuert.

Chain Length and Grafting Density Dependent Enhancement in the Hydrolysis of Ester-Linked Polymer Brushes

“…1 In the experiments described here, we determined the rate of hydrolysis of end-tethered polymers at grafting densities that are associated with high lateral forces within the brush layer. 4 At these high grafting densities, the cleavage rate was found to be enhanced by an order of magnitude relative to the rate in less dense brushes, an increase that we propose is due to mechanical stress within the highly crowded hydrated brushes.…”

“…4 As shown in Table 1, brush B3, with the smallest R g , has the lowest hydrolysis rates (Table 1). This leads to questions about the hydrolysis within polydisperse brushes and the possibility that the longer chains are cleaved more rapidly than the shorter chains.…”

“…35 For high molecular weight PDMA brushes similar to those described here the lateral force has been reported to be relatively high (12−74 N/m; increases with grafting density), sufficient to cause buckling of soft substrates, or to stretch the substrates if the brush has been produced on both the top and bottom surfaces. 4 If we assume a width equal to twice the R g for the polymer chains, then we have a force per chain in the 100 nN range (sample calculation: 74 N/m × 2 × 10 −9 m = 148 nN). This compressive force is considerably higher than the stretching forces predicted to enhance the hydrolysis of ester groups.…”

Mechanics of polymer brush based soft active materials– theory and experiments

“…Polymer brushes (PB) (Milner, 1991;Edmondson et al, 2004) (see Fig. 1) are soft active materials (SAMs) that produce reversible deformation (Zou et al, 2011) in response to external stimuli, such as a change in temperature, pH, light, electromagnetic fields, among others. Other examples of SAMs include, stimuli-responsive gels (Ahn et al, 2008;White et al, 2013), electroactive polymers (Scrosati et al, 1993;Wang et al, 2016), liquid crystal elastomers (Küpfer and Finkelmann, 1991;White and Broer, 2015) and shape memory polymers (Lendlein and Kelch, 2002;Hager et al, 2015).…”

“…Stimuli response originating from surface modification, a unique feature of PB-SAMs, is advantageous due to minimal trade-off with other bulk material properties. Polymer brushes have been used as programmable material (Kelby et al, 2011) for sensing and actuation (Abu-Lail et al, 2006;Klushin et al, 2014), as microcantilever coatings in glucose sensing (Chen et al, 2010), selective metallic ion sensing (Peng et al, 2017), microcantilever actuation (Zhou et al, 2006, and as macroscale bending stretching actuators (Zou et al, 2011) exhibiting large elastic deformations. A comprehensive overview of polymer brushes and their applications is available in Stuart et al (2010) and Azzaroni (2012).…”