Fully (99+ %) hydrolyzed poly(vinyl alcohol) (PVA) was electrospun from water using Triton X-100 surfactant to lower the surface tension. The diameter of the electrospun PVA fibers ranged from 100 to 700 nm. Treatment of the PVA fiber mats with methanol for 8 h stabilized the fibers against disintegration in contact with water. In addition, the mats showed increased mechanical strength due to increased crystallinity following post-spinning treatment with methanol. We suggest that methanol treatment serves to increase the degree of crystallinity, and hence the number of physical cross-links in the electrospun PVA fibers. This may occur by removal of residual water within the fibers by the alcohol, allowing PVA-water hydrogen bonding to be replaced by intermolecular polymer hydrogen bonding resulting in additional crystallization. Potential applications of electrospun PVA include filters, precursors to graphitic fibers, and biomedical materials.

Biodegradation of plant biomass is a slow process in nature, and hydrolysis of cellulose is also widely considered to be a rate-limiting step in the proposed industrial process of converting lignocellulosic materials to biofuels. It is generally known that a team of enzymes including endo- and exocellulases as well as cellobiases are required to act synergistically to hydrolyze cellulose to glucose. The detailed molecular mechanisms of these enzymes have yet to be convincingly elucidated. In this report, atomic force microscopy (AFM) is used to image in real-time the structural changes in Valonia cellulose crystals acted upon by the exocellulase cellobiohydrolase I (CBH I) from Trichoderma reesei. Under AFM, single enzyme molecules could be observed binding only to one face of the cellulose crystal, apparently the hydrophobic face. The surface roughness of cellulose began increasing after adding CBH I, and the overall size of cellulose crystals decreased during an 11-h period. Interestingly, this size reduction apparently occurred only in the width of the crystal, whereas the height remained relatively constant. In addition, the measured cross-section shape of cellulose crystal changed from asymmetric to nearly symmetric. These observed changes brought about by CBH I action may constitute the first direct visualization supporting the idea that the exocellulase selectively hydrolyzes the hydrophobic faces of cellulose. The limited accessibility of the hydrophobic faces in native cellulose may contribute significantly to the rate-limiting slowness of cellulose hydrolysis.

We present a real-rock micromodel approach whereby microfluidic channels are fabricated in a naturally occurring mineral substrate. The method is applied to quantify calcite dissolution which is relevant to oil/gas recovery, CO2 sequestration, and wastewater disposal in carbonate formations - ubiquitous worldwide. The key advantage of this method is the inclusion of both the relevant substrate chemistry (not possible with conventional microfluidics) and real-time pore-scale resolution (not possible with core samples). Here, microchannels are etched into a natural calcite crystal and sealed with a glass slide. The approach is applied to study acidified brine flow through a single channel and a two-dimensional micromodel. The single-channel case conforms roughly to a 1-D analytical description, with crystal orientation influencing the local dissolution rate an additional 25%. The two-dimensional experiments show highly flow-directed dissolution and associated positive feedback wherein acid preferentially invades high conductivity flow paths, resulting in higher dissolution rates ('wormholing'). These experiments demonstrate and validate the approach of microfabricating fluid structures within natural minerals for transport and geochemical studies. More broadly, real-rock microfluidics open the door to a vast array of lab-on-a-chip opportunities in geology, reservoir engineering, and earth sciences.

The effects of shear stress on the crystallization kinetics and morphology of linear polyethylene and polybutene‐1 were studied with the aid of a specially designed apparatus. With this equipment, it was possible to heat a thin polymer sample between glass slides to a melt temperature, quench the sample to a crystallization temperature, and then deform the sample in shear by applying a constant load to one of the glass slides. During the deformation, the crystallization process was observed and photographed under a polarizing microscope. Also, the displacement of the glass slide was simultaneously recorded which made possible a determination of the shear strain as a function of time. The results demonstrate that two phenomena may occur in the initially supercooled polymer samples in response to the applied shear stress. In one case, the sample deformed until it fractured, generally exhibiting no evidene of crystallization; in the other, the sample deformed until an inflection point was reached after which the sample became rigid. This latter phenomenon was attributed to crystallization. At low shear stresses, the inflection point was associated with the growth of spherulites which simply became large enough to bridge the glass slides and prevent further deformation of the sample. This generally occurred prior to the completion of the radial growth of the lamellae. At high shear stresses, however, no evidence of crystallization was seen in the microscope until the inflection point was reached. At this point, birefringence was observed in the sample. The resulting structure generally could not be resolved in the microscope, thereby indicating very profuse nucleation. The results obtained clearly demonstrate that the application of a sufficiently high shear stress to an initially supercooled melt has a substantial effect on the rates of crystallization of both polyethylene and polybutene‐1. This was shown most dramatically at temperatures close to the melting point, e.g., both polyethylene at 130°C and polybutene‐1 at 113°C, which require over 104 sec to crystallize under quiescent conditions, crystallized at approximately 0.05 seconds. The application of a shear stress to a polymer melt is envisaged as resulting in molecular orientation. In accord with the theories of Flory, and Krigbaum and Roe, the associated decrease in entropy of the melt may be considered to increase the supercooling. Under high stresses at which large increases in supercooling result, crystallization occurs more rapidy at the high temperatures and with polymers of lower molecular weight. At low shear stresses, the influence of temperature and molecular weight on the crystallization kinetics is essentially the same as that obseved under quiescent conditions. Observations through the microscope have shown that the application of a shear stress to a polymer melt leads to large increases in the number of crystalline structures formed and to the formation of oriented morphologies. This latter phenomenon arises due to nucleation lines form...