Biomedical subjects

J U Sommer

Publications and source records attributed to J U Sommer.

2 recordsLinked to original sources

PubMed2001

Direct visualization of random crystallization and melting in arrays of nanometer-size polymer crystals.

Using tapping mode atomic force microscopy, we visualized in direct space and time resolved the changes in viscoelastic properties during crystallization and melting of polyethyleneoxide in 12 nm spheres of a block copolymer mesophase. All spheres crystallized individually and independently, randomly distributed sphere by sphere. Melting of the confined crystals also proceeded in a stochastic manner. Not all spheres melted at the same temperature, indicating different degrees of order of the individual nanometer-size polymer crystals. The independence of the spheres opens the possibility to manipulate material properties of surfaces at the nanometer scale.

Journal Article↗

PubMed2001

Liquidlike morphological transformations in monolamellar polymer crystals.

We performed annealing experiments on monolamellar polyethyleneoxid crystals. Even well below the melting point, local relaxations of metastable folded states led to pronounced liquidlike morphological changes on a micron scale of shape and perimeter of the crystalline domains, similar to dewetting of liquids. First, a rim of less folded molecules was formed around the lamellae, making relaxations of the interior difficult. On longer time scales, hole formation within these domains was observed. Our experiments showed that, due to such spatial anisotropy in relaxations, polymer crystal morphology depends on the thermal pathway taken, implying that a time-temperature superposition principle does not apply.

Journal Article↗