Polymer grafting from 10-nm individual particles: proving control by neutron scattering.

The core-shell structure of nanoparticles (5 nm radius) of silica grafted with polymer growing from the particle ("grafting from") is characterized by small angle neutron scattering (SANS), to our knowledge for the first time. This is made possible by a good control of the colloidal dispersion at each step of the synthesis. With this aim, we have improved our chemical procedure based on atom transfer radical polymerization (ATRP), which allows a good control of kinetics and polydispersity: the reaction takes place in a polar solvent, and the reaction medium remains always crystal clear. For such small particles, in contrary to direct space imaging, SANS is appropriate for characterization of the polymer corona as well as of the silica core using contrast matching provided by mixing normal and deuterated solvent. This allows checking of the level of aggregation at the nanoscale, which is found to be limited to a few percent of the particles in the reaction batch. After an initial slight increase, it is reduced by further polymerization, while the polymer layer grows progressively. After purification, grafted silica can be characterized accurately: its scattering can be fitted by a model of a silica core containing three to five particles surrounded by a polymer shell of thickness 7 nm. This is in good agreement with chain length and grafting density (214 sites per particle) evaluated by chemical analysis; hence SANS provides quantitative insight on chemical synthesis.

[Retrospective study of anorexia nervosa: reduced mortality and stable recovery rates]. / Diminution de la mortalité et stabilité du taux de guérison dans le suivi de l'anorexie mentale.

OBJECTIVES: Anorexia nervosa is an eating disorder that combines malnutrition, amenorrhea, and distorted body image. To learn more about the course of this disease we undertook a retrospective study of girls diagnosed with anorexia nervosa in the Saint Etienne Endocrinology Department between 1979 and 2004. METHODS: Patients were diagnosed according to DSMIV criteria. Data collected to complete the Morgan-Russell outcome assessment schedule included chronology of illness, patients' morphological features, anorexia type, treatment choice, patient's gynecological history, and social status. RESULTS: The study included 206 cases. The average follow-up period was 8.3 +/- 5.3 years. Defining recovery as stable BMI>17.5 kg/m2 for at least one year and recovery of normal menstruation, full recovery was observed in 55.8% and partial recovery in 25.7%, while 18.5% remained chronically ill. Early onset (i.e., during adolescence) was associated with good prognosis, and advanced emaciation and delayed or insufficient medical care with poor prognosis. CONCLUSIONS: The seriousness of this disease is due more to the incidence of cases that become chronic than to the mortality rate. Prediction of severity would be improved by taking into account underlying personality traits, such as addictive tendencies and depression.