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Tuning the solubility of fuzzy polymer microgels by external triggers, such as temperature or pH, provides a unique mechanism for controlling the porosity and size of colloidal particles on the nanoscale. As a consequence, these smart microgel particles are being considered for applications ranging from viscosity modifiers and sensing to drug delivery and as models for the glass and the jamming transition. Despite their widespread use, little is known about how these soft particles adapt their shape and size under strong mechanical compression. We use a combination of precise labeling protocols and two-color superresolution microscopy to unravel the behavior of tracer microgels inside densely packed soft solids. We find that interpenetration and shape deformation are dominant until, in the highly overpacked state, this mechanism saturates and the only remaining way to further densify the system is by isotropic compression.

Biological membranes do not only occur as planar bilayer structures, but depending on the lipid composition, can also curve into intriguing three-dimensional structures. In order to fully understand the biological implications as well as to reveal the full potential for applications, e.g. for drug delivery and other biomedical devices, of such structures, well-defined model systems are required. Here, we discuss the formation of lipid non-lamellar liquid crystalline (LC) surface layers spin-coated from the constituting lipids followed by hydration of the lipid layer. We demonstrate that hybrid lipid polymer films can be formed with different properties compared with the neat lipid LC layers. The nanostructure and morphologies of the lipid films formed reflect those in the bulk. Most notably, mixed lipid layers, which are composed of glycerol monooleate and diglycerol monooleate with poly(N-isopropylacrylamide) nanogels, can form films of reverse cubic phases that are capable of responding to temperature stimulus. Owing to the presence of the nanogel particles, changing the temperature not only regulates the hydration of the cubic phase lipid films, but also the lateral organization of the lipid domains within the lipid self-assembled film. This opens up the possibility for new nanostructured materials based on lipid-polymer responsive layers.

Hierarchical polymer structures such as pNIPAM microgels have been extensively studied for their ability to undergo structural and physical transformations that can be controlled by external stimuli such as temperature, pH or solvent composition. However, a direct three-dimensional visualization of individual particles in-situ has so far been hindered by insufficient resolution, with optical microscopy, or contrast, with electron microscopy. In recent years superresolution microscopy techniques have emerged that can provide nanoscopic optical resolution. Here we report on the in-situ superresolution microscopy of dye-labelled submicron sized pNIPAM microgels revealing the internal density profile during swelling and collapse of individual particles. Using direct STochastic Optical Reconstruction Microscopy (dSTORM) we demonstrate a lateral optical resolution of 30 nm and an axial resolution of 60 nm.

Populärvetenskaplig sammanfattning Microgelpartiklar är runda partiklar som har förmågan att ändra storlek beroende på olika yttre påverkan. I detta projekt har vi tittat på partiklar som blir upp till 10 gånger mindre när temperaturen höjs från 15˚C till 39˚C. Detta beror på att det nätverk som partiklarna är uppbyggda börjar ogilla lösningsmedlet när temperaturen höjs och hellre vill vara nära sig själva vilket medför att de drar ihop sig. Eftersom microgeler kan ändra storlek under kontrollerade former vill man titta på hur de beter sig om man ökar antalet partiklar. Detta kan man sedan jämföra med mer komplicerade system så som proteiner och hur de beter sig i närheten av varandra. För att titta på detta har vi använt oss av neutroner och en metod som gör det möjligt att titta på enbart ett fåtal microgelpartiklar i en lösning med väldigt många. Neutroner stålas på provet, microgelpartiklarna, och beroende på hur stora partiklarna i provet är kommer neutronerna efter kollisionen med partiklarna att böja av åt olika håll. Det går sedan att räkna hur många neutroner som har böjt av i olika vinklar och utifrån det få reda på hur stora partiklarna i provet är och vilken form de har. Det är av olika anledningar komplicerat att räkna ut storleken på partiklar i prover med hög koncentration. För att komma runt det har vi använt en metod som går ut på att proverna blandas på ett visst sätt så att information om enskilda microgelpartklar är det ända som mäts. På så vis kan storleken mätas utan att mängden partiklar stör mätningen. Det visade sig att metoden fungerade bra och information om de enskilda partiklarna kunde erhållas. En storleksminskning med ökad temperatur påvisades vilket var väntat då partiklarna drar ihop sig när temperaturen höjs. Det visades även att storleken inte påverkades mycket när antalet partiklar ökades. Detta bevisar att partiklarna gå in i varandra eftersom deras yttersta skal är väldigt fluffigt., Microgel particles have been widely investigated for their ability to undergo a volume phase transition due to different stimuli such as solvent quality, pH or salt addition. Their ability to reversibly change their size and thus the volume fraction makes them suitable to perform thorough studies on intra and inter‐particle interactions and various phase transitions. In this research work we show how the particle interactions were affected with changing temperature, and thereby volume fraction, in highly concentrated suspensions. For this purpose, the zero average contrast method (ZAC) has been employed, which allows canceling the effects of interparticle interactions in the scattering data, thus giving information about the form factor of the particles even at very high volume fractions. The results show that at low temperatures, i.e. in the fully expanded state, the microgel size appears almost independent of volume fraction, with a small decrease of the outer fuzzy shell only at concentrations far above close packing. With increasing temperature we find a shift in the form factor to higher q, which was expected due to a decrease in particle size: particles collapse when water starts to act as a poorer solvent at temperatures above the LCST (Lower Critical Solution Temperature). This temperature‐induced collapse of the particle size is found to be independent of the effective volume fraction eff even at ultrahigh densities up to eff = 1.7, i.e., far above close packing. These results clearly demonstrate that the temperature‐responsive behavior of the microgels is not altered by the interpenetration of the particles at high densities, and that the effective volume fraction of the microgels is a function of the temperature only.

Hierarchical polymer structures such as pNIPAM microgels have been extensively studied for their ability to undergo structural and physical transformations that can be controlled by external stimuli such as temperature, pH or solvent composition. However, a direct three-dimensional visualization of individual particles in-situ has so far been hindered by insufficient resolution, with optical microscopy, or contrast, with electron microscopy. In recent years superresolution microscopy techniques have emerged that can provide nanoscopic optical resolution. Here we report on the in-situ superresolution microscopy of dye-labelled submicron sized pNIPAM microgels revealing the internal density profile during swelling and collapse of individual particles. Using direct STochastic Optical Reconstruction Microscopy (dSTORM) we demonstrate a lateral optical resolution of 30 nm and an axial resolution of 60 nm.

Tuning the solubility of fuzzy polymer microgels by external triggers, such as temperature or pH, provides a unique mechanism for controlling the porosity and size of colloidal particles on the nanoscale. As a consequence, these smart microgel particles are being considered for applications ranging from viscosity modifiers and sensing to drug delivery and as models for the glass and the jamming transition. Despite their widespread use, little is known about how these soft particles adapt their shape and size under strong mechanical compression. We use a combination of precise labeling protocols and two-color superresolution microscopy to unravel the behavior of tracer microgels inside densely packed soft solids. We find that interpenetration and shape deformation are dominant until, in the highly overpacked state, this mechanism saturates and the only remaining way to further densify the system is by isotropic compression.