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Composites made of polymer brushes with inclusions of gold nanoparticles (AuNPs) combine the responsive nature of polymer brushes with the optical properties of the AuNPs, which offers the possibility to be used as colorimetric sensors. To this end, it is crucial to know how AuNPs are distributed inside the brush. Here, this distribution was elucidated by neutron reflectometry with contrast variation and a self-consistent reflectivity analysis based on the analytical parameterization of the volume fraction profiles of all chemical components. In contrast to former studies, this analysis allows the determination of the spatial distribution of components separately from each other: polyelectrolyte, AuNP, and water. Cationic poly-[2-(Methacryloyloxy) ethyl] trimethylammonium chloride (PMETAC) brushes were loaded with 5 nm AuNPs, which were coated with a pH-sensitive capping. The pH was varied during the incubation of the brush in the AuNP suspension. At a lower pH, AuNPs form aggregates in suspension and are attached to the brush periphery. They adsorb into the brush but do not fully penetrate it due to their bulkiness. At a higher pH, AuNP suspensions are electrostatically stabilized and the AuNPs penetrate the brush entirely. However, the AuNP distribution over the brush is not homogeneous but decreases gradually toward the substrate. Penetration of the AuNPs leads to a more extended conformation of the brush. According to the results of the detailed analysis of all components, an increase in water content could be excluded as a reason for brush swelling but replacement of water by the AuNP was observed.
To prepare nanoparticles, was used the gold precursor solution (HAuCl4 with 2,5x10-4 M) and as reducer agent the resin lyophilized of Virola oleifera (1mg/mL), both dillueted in distilled water. Based on the experimental design, the solution of the reducing agent was added to the gold solution and stirred for predefined times.
WORCESTER -- Women's Rowing saw its varsity eight turn in a gold medal-winning performance Saturday as the Engineers hosted the Quinsigamond Snake Regatta on Lake Quinsigamond. The Crimson and Gray saw five boats participate in their lone home meet of the fall season.
Yesterday's loss to Canada provided the U.S. Winter Olympians with silver bookends: two silvers on the first day of competition, one on the last. There was plenty of gold in between, along with more silver and bronze, as the United States finished with a record 34 medals.
While the Americans and Canadian hockey teams were winning medals, the biggest doping scandal of the games saw cross-country skiers Johann Muehlegg of Spain and Larissa Lazutina of Russia stripped of their most recent gold medals after drug positives.
On Thursday, she was disqualified before the relay for having high levels of performance-boosting hemoglobin, a blood molecule that helps carry oxygen to muscles. She was permitted to race yesterday morning, but the medal was taken back after she tested positive. Gabriella Paruzzi of Italy, who finished second, was awarded the gold.
Meuhlegg, a triple gold medalist, tested positive, as did cross-country skier Olga Danilova of Russia. Meuhlegg must surrender his gold in the 50K race, but can keep his medals in the 30K freestyle and the 10K pursuit events.
There are women who have put their stamp on Olympic history, like for example Charlotte Cooper of Great Britain, gold medallist at the 1900 Paris Olympics, in singles tennis; the great Dutch athlete Fanny Blankers-Koen who became the first woman to win four medals in a single games and Larissa Latynina a Soviet Union gymnast, whose nine gold, five silver and four bronze medals, over the course of three Olympiads and between the births of two children, remains a record... 041b061a72