Der beste Schaum kommt von der Statistik

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Thermoresponsive Core-Shell Nanoparticles: Does Core Size Matter?

Nanoparticles grafted with a dense brush of hydrophilic polymers exhibit high colloidal stability. However, reversible aggregation can be triggered by an increase in temperature if the polymer is thermoresponsive, as the polymer shell partly loses its hydration. We investigate the role of nanoparticle curvature on the critical solution temperature (CST) of grafted poly(2-isopropyl-2-oxazoline) (PiPOx) and critical flocculation temperature (CFT) of the core-shell nanoparticle dispersion. Cores with diameters ranging from 5 to 21 nm were studied by temperature-cycled dynamic light scattering and differential scanning calorimetry over a large range of concentrations. We show that core size and curvature only have a minor influence on particle aggregation (CFT and cluster size), while they have major influence on the CST of the polymer shell. The densely grafted shells exhibit three distinct solvation transitions, the relative contributions of each is controlled by the core curvature. We link these transitions to different polymer density regimes within the spherical brush and demonstrate that the CST of the innermost part of the brush coincides with the CFT of the particle dispersion

Multi-material ceramic material extrusion 3D printing with granulated injection molding feedstocks

Material Extrusion (MEX) is an advanced technology for polymer 3D printing and countless printers are commercially available. MEX has also been demonstrated for ceramics. For that purpose, thermoplastic binders are filled with high loads (>40 vol%) of a ceramic powder. The printed parts are subsequently debound and sintered. In contrast to most MEX printers, the ceramic printer presented herein works with granulated feedstock instead of filaments. Therefore, the development of novel feedstocks is faster and more straightforward since the challenges associated with filament production are omitted. Furthermore, commercial ceramic injection molding (CIM) feedstocks can be used which allows fast prototyping with the same material that is later used in high-quantity industrial production by CIM. In this study, a method to fabricate multi-material ceramic parts using a granulate-fed printer is presented. Examples of multi-material printing include colored ZrO2 parts as well as ceramic high-temperature heating elements in various shapes consisting of an electrically conductive and a non-conductive component. Light- and electron microscopy confirms that the layer adhesion before and after sintering is flawless, even between different materials if the material combination is chosen carefully. All feedstocks are based on a commercially available CIM binder filled with the desired ceramic powder. Consequently, the feedstock preparation as well as optimizing of debinding and sintering conditions are simple and reproducible

Stealth Nanoparticles Grafted with Dense Polymer Brushes Display Adsorption of Serum Protein Investigated by Isothermal Titration Calorimetry

Core–shell nanoparticles receive much attention for their current and potential applications in life sciences. Commonly, a dense shell of hydrated polymer, a polymer brush, is grafted to improve colloidal stability of functional nanoparticles and to prevent protein adsorption, aggregation, cell recognition, and uptake. Until recently, it was widely assumed that a polymer brush shell indeed prevents strong association of proteins and that this leads to their superior “stealth” properties in vitro and in vivo. We show using <i>T</i>-dependent isothermal titration calorimetry on well-characterized monodisperse superparamagnetic iron oxide nanoparticles with controlled dense stealth polymer brush shells that “stealth” core–shell nanoparticles display significant attractive exothermic and enthalpic interactions with serum proteins, despite having excellent colloidal stability and negligible nonspecific cell uptake. This observation is at room temperature shown to depend only weakly on variation of iron oxide core diameter and type of grafted stealth polymer: poly­(ethylene glycol), poly­(ethyl oxazoline), poly­(isopropyl oxazoline), and poly­(<i>N</i>-isopropyl acrylamide). Polymer brush shells with a critical solution temperature close to body temperature showed a strong temperature dependence in their interactions with proteins with a significant increase in protein binding energy with increased temperature. The stoichiometry of interaction is estimated to be near 1:1 for PEGylated nanoparticles and up to 10:1 for larger thermoresponsive nanoparticles, whereas the average free energy of interaction is enthalpically driven and comparable to a weak hydrogen bond

The Role of Chain Molecular Weight and Hofmeister Series Ions in Thermal Aggregation of Poly(2-Isopropyl-2-Oxazoline) Grafted Nanoparticles

Thermoresponsive nanoparticles are promising smart materials for many applications. However, a rational design for applications requires a deeper understanding and experimental verification of the various parameters that influence the thermoresponsiveness of the spherical polymer brushes that define most of such nanomaterials. Therefore, we investigate superparamagnetic iron oxide nanoparticles (SPION) grafted with poly(2-isopropyl-2-oxazoline) (6&ndash;33 kg mol&minus;1) by temperature-cycled dynamic light scattering and differential scanning calorimetry. The grafting of dense spherical polymer brushes leads to lower aggregation temperatures and transition enthalpies when compared with the free polymer. The transition enthalpy and temperature depend on the polymer shell size and structure. The addition of kosmotropic salts decreases the aggregation temperature following the Hofmeister series

Crystal structure of 2,6-diaminopyridinium chloride

The asymmetric unit of the title salt, C5H8N3+·Cl−, comprises one half of the 2,6-diaminopyridinium cation (the other half being completed by the application of mirror symmetry) and one Cl− counter-anion, also located on the mirror plane. The amino N atom shows a significant pyramidalization, with a dihedral angle of 30.4 (14)° between the least-squares planes of the amino group and the non-H atoms of the 2,6-diaminopyridinium moiety. In the crystal, the cationic molecules and Cl− counter-anions are arranged in sheets parallel to (001) consisting of alternating polar and non-polar parts associated with the the Cl− anions, pyridinium and amino moieties, and the pyridine rings, respectively. N—H...Cl interactions within the polar part, as well as slipped π–π interactions in the non-polar part, help to establish the three-dimensional network

Thermoresponsive Block Copolymer Grafted on Core-Shell Nanoparticles

Since 1966, when the poly(2-oxazolines) (POx) were discovered, they have undoubtedly been recognized as a polymer class with high synthetic versatility and good biocompatibility, giving access to highly functional and adaptable materials. The poly(2-oxazolines) are prepared through cationic ring-opening polymerization (CROP), which allow for simple control of the reaction condition, mainly due to the absence of undesired termination and even chain transfer are suppressed. Furthermore, the large available number of monomers with different side chain modifications opens the path towards the fabrication of innovative smart materials with a manifold of applications. Taking into account such observations, we envisage the possibility of designing and synthesizing a block-copolymer featured by: (i) a polar side chain (Fragment A), able to trap organic and/or inorganic compounds (e.g. heavy metal in wastewater or active principles for drug delivery applications); (ii) a thermoresponsive scaffold (Fragment B), able to change the interaction with the media by tuning the temperature. Subsequently, we intend to graft these polymers onto iron oxide nanoparticles (high grafting density) or on organic cores. Pursuing this research, herein we report our results involving the synthesis of the two Fragments (A and B) and the consequent grafting system to the nanoparticles. Finally, we point out the test for heavy metal binding in combination with the thermoresponsive behaviour of our products

Influence of Grafted Block Copolymer Structure on Thermoresponsiveness of Superparamagnetic Core–Shell Nanoparticles

The morphology and topology of thermoresponsive polymers have a strong impact on their responsive properties. Grafting onto spherical particles has been shown to reduce responsiveness and transition temperatures; grafting of block copolymers has shown that switchable or retained wettability of a surface or particle during desolvation of one block can take place. Here, doubly thermoresponsive block copolymers were grafted onto spherical, monodisperse, and superparamagnetic iron oxide nanoparticles to investigate the effect of thermal desolvation on spherical brushes of block copolymers. By inverting the block order, the influence of core proximity on the responsive properties of the individual blocks could be studied as well as their relative influence on the nanoparticle colloidal stability. The inner block was shown to experience a stronger reduction in transition temperature and transition enthalpy compared to the outer block. Still, the outer block also experiences a significant reduction in responsiveness due to the restricted environment in the nanoparticle shell compared to that of the free polymer state. The demonstrated pronounced distance dependence importantly implies the possibility, but also the necessity, to radially tailor polymer hydration transitions for applications such as drug delivery, hyperthermia, and biotechnological separation for which thermally responsive nanoparticles are being developed

Polymer Topology Determines the Formation of Protein Corona on Core-Shell Nanoparticles

Linear and cyclic poly(2-ethyl-2-oxazoline) (PEOXA) adsorbates provide excellent colloidal stability to superparamagnetic iron oxide nanoparticles (FexOy NPs) within protein-rich media. However, dense shells of linear PEOXA brushes cannot prevent weak but significant attractive interactions with human serum albumin. In contrast, their cyclic PEOXA counterparts quantitatively hinder protein adsorption, as demonstrated by a combination of dynamic light scattering and isothermal titration calorimetry. The cyclic PEOXA brushes generate NP shells that are denser and more compact than their linear counterparts, entirely preventing the formation of a protein corona as well as aggregation, even when the lower critical solution temperature of PEOXA in a physiological buffer is reached.ISSN:1936-0851ISSN:1936-086