Single crystals of linear polyethylene crystallized from the glass.

Isolated single crystals of polyethylene have been crystallized from the glassy state by annealing uniformly thick films of amorphous linear polyethylene just above their glass transition temperature. In agreement with previous results for polycarbonate, substantial molecular mobility at the glass transition temperature is.

Ultrastructural deformation studies on biological membranes.

The ultrastructural deformation technique has been used to study various membranes, including several claimed to show subunit structure. With localized deformation fibers ca. 100-300 A in diameter and up to 4,000 A long were found extending across the cracks parallel to the draw direction in all membranes. Lipid extraction and proteolytic enzyme (papain) treatment of membranes has shown that the fibers are protein in nature. Deformation of membranes while still wet showed no significant change in the appearance of the fibers compared with those obtained from deformation of membranes after air drying, indicating that formation of fibers is not an artifact due to dehydration. There must be extensive interaction between the protein molecules and thus we indicate that the results do not agree with current suggestions that membranes are composed of individual protein subunits immersed in a lipid bilayer.

Surface Films on Poly(oxymethylene) Single Crystals.

The deformation of single crystals of poly(oxymethylene) grown from 0.01 percent bromobenzene solution has been studied by deposition on a deformable substrate. Slight decoration of the crystal surfaces with gold prior to mechanical deformation of the composite reveals breaks in the gold which are displaced with respect to cracks in the underlying polymer crystals. These observations are interpreted to imply the existence of a very thin discrete film on the surface of the polymer crystals which can slip during deformation. Such a film might arise from polymer molecules adsorbed on the crystal surface.

Spinning of a random copolypeptide composed of gamma-benzyl-L-glutamate and L-alanine.

The solution spinning of a random copolypeptide of gamma-benzyl-L-glutamate polymerized with L-alanine at a mole ratio of 1 to 4 has been examined. Good fibers were obtained by using dichloroacetic acid and water as solvent and coagulation reagent respectively. The mechanical properties of the fibers are comparable with those of natural fibers.

Small angle x-ray diffraction studies of mucopolysaccharides in collagen.

Small angle X-ray diffraction (SAXD) was used to locate mucopolysaccharides (MPS) at regular intervals along the collagen axis under physiological conditions. Ruthenium red was used to stain the MPS specifically. The difference in electron density between ruthenium red-stained and unstained moist native rat tail tendon should correspond to the position of the MPS. This difference was calculated from the SAXD intensity data by using difference Fourier transform calculations. Phases calculated independently from the amino acid sequence of collagen by two laboratories were used in this calculation, and the results were compared. At least four to seven bands of MPS per 660 A were found at regular intervals along the collagen axis. Some of these bands match in position to the cross-striations observed by freeze-etching. Electron micrographs of ruthenium red-stained native fibrils also showed bands close in position to the ones calculated.

Ultrastructural deformation of collagen.

Ultrastructure deformation studies of reconstituted and native rat tail tendon collagen revealed that deformation occurs primarily in the non-staining and presumably non-polar proline rich regions for all ages examined. At low deformation (tension and compression) the deformation occurs somewhat more between the a2 and b1 and b2 and c2 bands than within the rest of the d period. At moderate elongations (greater than 40%), the deformation becomes localized between the c2 and d bands, with subfibrils on the order of 3-15 nm being drawn across the openings between the c2 and d bands. At high elongations (100% or greater) d period splitting occur on a regular basis between the c2 and d bands, along with a retraction of the 64 nm repeat period into 60 nm segments. It is in this deformation region that the effects of molecular slip and the apparent association of the acid mucopolysaccharides can be noted. These results suggest that crosslinking, if increasing as a function of age, does not affect the deformation characteristics of the individual fibrils and that changes with age in mechanical properties should be sought in changes in the fibril size and their interaction with the surrounding matrix.