posted on 2023-12-26, 06:43authored bySandra Forg, Xuhong Guo, Regine von Klitzing
The combination of the catechol-containing comonomer
dopamine methacrylamide
(DMA) with stimuli-responsive poly(N-isopropylacrylamide)
(PNIPAM) microgels bears a huge potential in research and for applications
due to the versatile properties of catechols. This research gives
the first detailed insights into the influence of DMA on the swelling
of PNIPAM microgels and their nanomechanical properties. Dynamic light
scattering measurements showed that DMA decreases the volume phase
transition temperature and completion temperature due to its higher
hydrophobicity when compared to NIPAM, while sharpening the transition.
The cross-linking ability of DMA decreases the swelling ratios and
mesh sizes of the microgels. Microgels adsorbed at the solid surface
are characterized by atomic force microscopyas the DMA content
increases, microgels protrude more from the surface. Force spectroscopy
measurements below and above the volume phase transition temperature
display a stiffening of the microgels with the incorporation of DMA
and upon heating across its entire cross section as evidenced by an
increase in the E modulus. This confirms the cross-linking
ability of DMA. The affine network factor β, derived from the
Flory–Rehner theory, is linearly correlated with the E moduli of both pure PNIPAM and P(NIPAM-co-DMA) microgels. However, large DMA amounts hinder the microgel shrinking
while maintaining mechanical stiffness, possibly due to catechol interactions
within the microgel network.