Graphene dispersions in alkanes: toward fast drying conducting inks.

Graphene inks are becoming widely popular. However the vast majority of these inks are formulated in polar solvents with high-boiling points. Their slow evaporation is a bottleneck factor in roll-to-roll printing processes. Here, we developed a highly-conductive fast-drying graphene ink in isooctane, a non-polar and low-boiling solvent. For this purpose, a diblock copolymer containing pendant cholesterol groups was used during the exfoliation of natural graphite in isooctane. The polymer develops non-covalent supramolecular interactions with the graphene conjugated system, resulting in the formation of stable graphene dispersions (up to c = 4 mg mL-1). These dispersions were used for direct writing on a variety of substrates, and were shown to dry instantly after application. The influence of polymer concentration on graphene characteristics, on colloidal stability and on electrochemical characteristics has been studied. The lowest sheet resistance (80 Ω â–¡-1) was obtained when 23% of the graphene surface was covered by the polymer. In this case, the flakes were constituted of 2-5 graphene layers. More extensive exfoliation, down to single-layer graphene, was achieved at greater surface coverage, but led to inks with higher sheet resistance. Thus, by combining a tailored polymeric dispersant, a smooth exfoliation process and a low-boiling non-polar ink solvent, we were able to prepare highly-conductive fast-drying graphene inks which should have a high potentital for the development of roll-to-roll printed electronics.

[Post-traumatic cerebral fat embolism]. / Embolie graisseuse cérébrale post-traumatique.

A seventeen year old boy sustained pelvic, femoral shaft and malleolar fractures in a road traffic accident. Six hours after admission, the patient became comatose (Glasgow coma score = 7); the coma worsened such that, 24 h later, the coma score was 4. Petechiae were present on the conjunctiva and anterior chest wall. Computed tomography revealed diffuse brain swelling. The diagnosis of cerebral fat embolism was made. There were multiple episodes of severe intracranial hypertension. After 23 days of traction, the femoral fracture was internally fixed. The patient returned home after five months of hospital, with just a few memory and writing problems. Ten months after the accident, magnetic resonance imaging showed a small ventricular dilatation due to subcortical atrophy. Residual ischaemic lesions and demyelination could be seen in the right centrum ovale and temporal lobe. The cerebral lesions contrast with the reversibility of the clinical state.