Internal nanoparticle structure of temperature-responsive self-assembled PNIPAM-b-PEG-b-PNIPAM triblock copolymers in aqueous solutions: NMR, SANS and light scattering studies

In this study we report detailed information on the internal structure of PNIPAM-b-PEG-b-PNIPAM nanoparticles formed from self-assembly in aqueous solutions upon increase in temperature. NMR spectroscopy, light scattering and small-angle neutron scattering (SANS) were used to monitor different stages of nanoparticle formation as a function of temperature, providing insight into the fundamental processes involved. The presence of PEG in a copolymer structure significantly affects the formation of nanoparticles, making their transition to occur over a broader temperature range. The crucial parameter that controls the transition is the ratio of PEG/PNIPAM. For pure PNIPAM, the transition is sharp; the higher the PEG/PNIPAM ratio results in a broader transition. This behavior is explained by different mechanisms of PNIPAM block incorporation during nanoparticle formation at different PEG/PNIPAM ratios. Contrast variation experiments using SANS show that the structure of nanoparticles above cloud point temperatures for PNIPAM-b-PEG-b-PNIPAM copolymers is drastically different from the structure of PNIPAM mesoglobules. In contrast with pure PNIPAM mesoglobules, where solid-like particles and chain network with a mesh size of 1-3 nm are present; nanoparticles formed from PNIPAM-b-PEG-b-PNIPAM copolymers have non-uniform structure with “frozen” areas interconnected by single chains in Gaussian conformation. SANS data with deuterated “invisible” PEG blocks imply that PEG is uniformly distributed inside of a nanoparticle. It is kinetically flexible PEG blocks which affect the nanoparticle formation by prevention of PNIPAM microphase separation

Block and gradient copoly(2-oxazoline) micelles : strikingly different on the inside

Herein, we provide a direct proof for differences in the micellar structure of amphiphilic diblock and gradient copolymers, thereby unambiguously demonstrating the influence of monomer distribution along the polymer chains on the micellization behavior. The internal structure of amphiphilic block and gradient co poly(2-oxazolines) based on the hydrophilic poly(2-methyl-2-oxazoline) (PMeOx) and the hydrophobic poly(2-phenyl-2-oxazoline) (PPhOx) was studied in water and water ethanol mixtures by small-angle X-ray scattering (SAXS), small angle neutron scattering (SANS), static and dynamic light scattering (SLS/DLS), and H-1 NMR spectroscopy. Contrast matching SANS experiments revealed that block copolymers form micelles with a uniform density profile of the core. In contrast to popular assumption, the outer part of the core of the gradient copolymer micelles has a distinctly higher density than the middle of the core. We attribute the latter finding to back-folding of chains resulting from hydrophilic hydrophobic interactions, leading to a new type of micelles that we refer to as micelles with a "bitterball-core" structure

Phase separation in aqueous solutions of thermoresponsive polymers as studied by spectroscopic methods.

In this thesis NMR and FTIR spectroscopy is used for investigation of structural and dynamic changes in polymer chains and water during temperature-induced phase separation in D2O solutions. We have investigated one-component D2O solutions of uncharged and negatively charged poly(N-isopropylmethacrylamide) and solutions of random copolymers of poly(N-isopropylmethacrylamide/N-isopropylacrylamide). Two-component D2O solutions of mixtures of poly(N-isopropylmethacrylamide)/poly(vinyl methyl ether) and poly(N-isopropylmethacrylamide)/N-isopropylacrylamide were also studied.Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi

Growth of Nd:Gd3Ga5O12 Thin Films by Pulsed Laser Deposition for Planar Waveguide Laser

Pulsed laser radiation of a KrF excimer laser was used for the deposition of thin Nd 3+ doped Gd 3 Ga 5 O 12 (Nd:GGG) films on yttrium aluminium garnet (YAG) and sapphire single crystal substrates. By variation of PLD-parameters such as temperature and processing gas pressure, amorphous and single crystalline thin films were produced. The morphology and the composition of the grown films were investigated by optical microscopy, scanning electron microscopy and electron dispersive X-ray spectroscopy. Thickness and structural properties of the deposited films were determined by optical reflection spectroscopy and X-ray diffraction, respectively. The optical properties of grown films on different substrates were compared. An amorphous Nd:Gd 3 Ga 5 O 12 thin film on yttrium aluminium garnet was used for demonstration of an infrared waveguide laser. A planar wave guiding structure was formed in deposited film between two parallel grooves micromachined using laser radiation delivered by a femtosecond CPA-Laser-System. The resulting waveguides were polished and provided with resonator mirrors. With a 5% output coupler at 1064 nm, a laser threshold of 1080 mW and 0.2% slope efficiency were obtained

ATRP of POSS Monomers Revisited: Toward High-Molecular Weight Methacrylate–POSS (Co)Polymers

For the first time, ATRP was successfully employed for homopolymerization of a commercial methacrylate-functionalized polyhedral oligomeric silsesquioxane (POSS) monomer, iBuPOSSMA, to high molecular weights. It was found that iBuPOSSMA has a low ceiling temperature (<i>T</i>_c); therefore, low temperatures and/or high initial monomer concentrations need to be used in order to avoid low degrees of polymerization that had been observed previously. The values of <i>T</i>_c, as well as of the polymerization enthalpy Δ<i>H</i>_p and entropy Δ<i>S</i>_p were determined to be 130 °C (at [M]₀ = 1 M), −41 kJ mol^–1, and −101 J mol^–1 K^–1, respectively. Under optimized conditions, poly­(iBuPOSSMA) homopolymers having low dispersity and high <i>M</i>_n, ranging from 23 000 to 460 000, were obtained in a well-controlled ATRP process. Moreover, various block copolymers having high-<i>M</i>_n poly­(iBuPOSSMA) blocks were prepared by copolymerization of iBuPOSSMA with methyl methacrylate and styrene