X-ray reflectivity study on the surface and bulk glass transition of polystyrene.

The surfaces of polystyrene (PS) films decorated with gold nanoclusters were investigated by x-ray reflectivity measurements. The thicknesses of the films are much larger than the radii of gyration of the different PS samples. By annealing the films above the glass transition temperature T(g) an embedding process of the clusters into the polymer is detected which is accompanied by a substantial increase in the cluster layer thickness due to Brownian motion. These processes start at a sufficiently low viscosity and may be regarded as a probe of the glass transition in the near surface region of the PS films. Simultaneously the thermal expansion of the entire film and hence its approximate bulk behavior were monitored. Two samples of different molecular weight do not show a significant difference between the surface and bulk T(g) values.

Extraocular muscle changes in experimental orbital venous stasis: some similarities to Graves' orbitopathy.

BACKGROUND: Graves' orbitopathy (GO) is generally considered to have an autoimmune etiology. Recently, however, it has been hypothesized that orbital venous obstruction may contribute significantly to the clinical manifestations. To determine whether such obstruction could induce histologic and clinical findings consistent with GO, we developed an animal model of orbital venous obstruction by ligating the draining ophthalmic veins of the right eyes of four cats. METHODS: The branches of the ophthalmic veins were isolated and ligated following a lateral orbitotomy. Weekly photographs and echographs were taken of the cats; one cat was killed at each of four time points, namely 1, 2, 3, and 4 weeks after surgery. Histologic stains were applied to isolated orbital tissues to characterize pathologic changes. RESULTS: Clinically, there was onset of marked proptosis, chemosis, and exotropia. Histological findings within the extraocular muscles included activation and the presence of acid mucopolysaccharides 1 week after ligation, increased collagen and the presence of lymphoid cells at 2 weeks after ligation, and persistent interstitial lymphocytic infiltrates the 3rd and 4th weeks after ligation. CONCLUSION: Without evoking a primary orbital inflammation or inducing a systemic autoimmune disease, an animal model has been developed that closely mimics many of the advanced clinical and histologic changes that occur in GO.