  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 the
versatile properties of catechols. This research gives first detailed insights
into the influence of DMA on the swelling of PNIPAM microgels and the
correlation 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 hydrophobicity
when compared to NIPAM, while sharpening the transition. The cross-linking
ability of DMA decreases swelling ratios and mesh sizes of the microgels.
Microgels adsorbed at the solid surface are characterised by atomic force
microscopy (AFM): Scanning provides information about the microgel's shape on
the surface and force spectroscopy measurements determines their nanomechanical
properties ($E$ modulus). As the DMA content increases, microgels protrude more
from the surface, correlating with an increase of $E$ modulus and a stiffening
of the microgels - confirming the cross-linking ability of DMA. Force
spectroscopy measurements below and above the VPTT display a stiffening of the
microgels with the incorporation of DMA and upon heating across it's entire
cross-section. The affine network factor $\beta$, derived from the Flory-Rehner
theory describing the elasticity and swelling of the microgel network, is
linearly correlated with the $E$ moduli of the microgels for both - pure PNIPAM
and P(NIPAM-co-DMA) microgels. However, for large amounts of DMA, DMA appears
to hinder the microgel shrinking, while still ensuring mechanical stiffness,
possibly due to catechol interactions within the microgel network.
