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The combination of the catechol-containing co-monomer dopamine methacrylamide(DMA) with stimuli-responsive microgels such as poly(N-isopropylacrylamide)(PNIPAM) bears a huge potential in research and for applications due to theversatile properties of catechols. This research gives first detailed insightsinto the influence of DMA on the swelling of PNIPAM microgels and thecorrelation with their nanomechanical properties. Dynamic light scattering(DLS) was used to analyse the swelling behaviour of microgels in bulk solution.The incorporation of DMA decreases the volume phase transition temperature(VPTT) and completion temperature (VPT CT) due to its higher hydrophobicitywhen compared to NIPAM, while sharpening the transition. The cross-linkingability of DMA decreases swelling ratios and mesh sizes of the microgels.Microgels adsorbed at the solid surface are characterised by atomic forcemicroscopy (AFM): Scanning provides information about the microgel's shape onthe surface and force spectroscopy measurements determines their nanomechanicalproperties ($E$ modulus). As the DMA content increases, microgels protrude morefrom the surface, correlating with an increase of $E$ modulus and a stiffeningof the microgels - confirming the cross-linking ability of DMA. Forcespectroscopy measurements below and above the VPTT display a stiffening of themicrogels with the incorporation of DMA and upon heating across it's entirecross-section. The affine network factor $\beta$, derived from the Flory-Rehnertheory describing the elasticity and swelling of the microgel network, islinearly correlated with the $E$ moduli of the microgels for both - pure PNIPAMand P(NIPAM-co-DMA) microgels. However, for large amounts of DMA, DMA appearsto hinder the microgel shrinking, while still ensuring mechanical stiffness,possibly due to catechol interactions within the microgel network.

Influence of Dopamine Methacrylamide on swelling behaviour and nanomechanical properties of PNIPAM microgels