Poly(N-isopropylacrylamide) microgel particles were prepared via a ''classical'' surfactant-free precipitation polymerization and a continuous monomer feeding approach. It is anticipated that this yields microgel particles with different internal structures, namely a dense core with a fluffy shell for the classical approach and a more even crosslink distribution in the case of the continuous monomer feeding approach. A thorough structural investigation of the resulting microgels with dynamic light scattering, atomic force microscopy and small angle neutron scattering was conducted and related to neutron spin echo spectroscopy data. In this way a link between structural and dynamic features of the internal polymer network was made.Germany.

Phytochromes, found in plants, fungi, and bacteria, exploit light as a source of information to control physiological processes via photoswitching between two states of different physiological activity, i.e. a red-absorbing...

The continuous improvement of synthesis leads to a great variety in the internal architecture and functionality of colloidal hydrogels. A majority of envisioned applications use microgels as colloidal building blocks for layer formation at solid substrates. In this context, a fundamental understanding of the influence of these substrates on the internal structure and physical properties is essential. Especially, the nanomechanical properties of adsorbed poly­(N-isopropylacrylamide) microgel particles are important for their application in cell cultivation, functional surface coatings, and others. Furthermore, these properties are closely related to the swelling behavior and the internal structure and dynamics of these microgels. However, the number of methods that are able to probe the viscoelasticity of adsorbed microgels over the entire vertical particle profile is limited. Grazing incidence neutron scattering techniques are suited to probe soft-matter samples with limited sample volumes at planar solid substrates and allow a resolution in the z-direction. We used neutron spin echo spectroscopy under grazing incidence to access fast thermal fluctuations (10–9 s) over the entire vertical particle profile. Atomic force microscopy nanoindentation was used to characterize the nanomechanical properties of adsorbed microgel particles prepared by batch and continuous monomer feeding methods. The resulting force maps revealed that batch microgels were “hard” and heterogeneous in their Young’s moduli, while the microgels from the continuous method were “soft” and homogeneous. Finally, neutron spin echo spectroscopy under grazing incidence revealed major differences in the vertical dynamic profile of both types of microgels.

The structure and the dynamic properties of poly(N -isopropylacrylamide) brushes at solid planar surfaces under good solvent conditions are studied. Polymer brushes with grafting densities in the high density and semidilute regime are prepared via surfaceinitiated atom transfer radical polymerization. The polymer brushes were removed from the substrates to determine the molar mass and molecular dispersity via size exclusion chromatography to draw conclusions about the grafting density. The structure of the brushes was investigated with ellipsometry and neutron reflectometry measurements.We find an influence of the grafting density on the swelling properties of the poly(Nisopropylacrylamide) brushes. Furthermore, the brush dynamics at different neutron † A footnote for the title 1 penetration depths was analyzed with neutron spin echo spectroscopy under grazing incidence. The evanescent intensity distribution was modeled with the BornAgain software package, which uses the Distorted Wave Born Approximation.

The commercial availability of natural surfactants, e.g., alkyl-oligoglucosides and the solubilization of plant and food grade oils extends the field of applications for microemulsions. To study potential effects of the confinement on the structure and dynamics inside a microemulsion, neutron reflectometry and neutron spin echo spectroscopy under grazing incidence have been used. Measurements of the contact between a bicontinuous microemulsion and a hydrophilic and hydrophobic surface are compared and show a similar wetting behavior and near surface structuring.