Contrast variation SANS measurement of shell monomer density profiles of smart core-shell microgels.

The radial density profile of deuterated poly(N,n-propyl acrylamide) shell monomers within core-shell microgels has been studied by small-angle neutron scattering in order to shed light on the origin of their linear thermally-induced swelling. The poly(N-isopropyl methacrylamide) core monomers have been contrast-matched by the H2O/D2O solvent mixture, and the intensity thus provides a direct measurement of the spatial distribution of the shell monomers. Straightforward modelling shows that their structure does not correspond to the expected picture of a well-defined external shell.

Spatial distribution of core monomers in acrylamide-based core-shell microgels with linear swelling behaviour.

The peculiar linear temperature-dependent swelling of core-shell microgels has been conjectured to be linked to the core-shell architecture combining materials of different transition temperatures. Here the structure of pNIPMAM-core and pNNPAM-shell microgels in water is studied as a function of temperature using small-angle neutron scattering with selective deuteration. Photon correlation spectroscopy is used to scrutinize the swelling behaviour of the colloidal particles and reveals linear swelling.

Deuteration-Induced Volume Phase Transition Temperature Shift of PNIPMAM Microgels.

The effect of deuteration on the volume phase transition (VPT) temperature of poly (-isopropylmethacrylamide) (pNIPMAM) microgels in aqueous suspension is determined via IR spectroscopy and size measurements by photon correlation spectroscopy (PCS). We study the effect of a hydrogenated and a deuterated solvent (H₂O/D₂O), and of the hydrogenated and (partially) deuterated monomer. Deuteration of the monomer or copolymerization with deuterated monomers shifts the volume phase transition temperature (VPTT) by up to 8.

Swelling behaviour of core-shell microgels in HO, analysed by temperature-dependent FTIR spectroscopy.

Stimuli-responsive microgels are colloidal particles and promising candidates for applications such as targeted drug delivery, matrices for catalysts, nanoactuators and smart surface coatings. To tailor the response, the architecture of microgels is of paramount importance with respect to these applications. Statistical copolymer microgels based on N-isopropylmethacrylamide (NiPMAM) and N-n-propylacrylamide (NnPAM) show a cooperative phase transition leading to a collapse at a specific temperature.

Determination of Internal Density Profiles of Smart Acrylamide-Based Microgels by Small-Angle Neutron Scattering: A Multishell Reverse Monte Carlo Approach.

The internal structure of nanometric microgels in water has been studied as a function of temperature, cross-linker content, and level of deuteration. Small-angle neutron scattering from poly( N-isopropylmethacrylamide) (volume phase transition ≈ 44 °C) microgel particles of radius well below 100 nm in DO has been measured. The intensities have been analyzed with a combination of polymer chain scattering and form-free radial monomer volume fraction profiles defined over spherical shells, taking polydispersity in size of the particles determined by atomic force microscopy into account.

Core-Shell Microgel-Based Surface Coatings with Linear Thermoresponse.

We study the swelling and shrinking behavior of core-shell microgels adsorbed on silicon wafers. In these systems, the core is made of cross-linked poly(N-isopropylmethacrylamide) and the shell consists of cross-linked poly(N-n-propylacrylamide). In suspension, these particles exhibit an extended linear swelling behavior in the temperature interval between the lower critical solution temperatures of the two polymers.