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Morphology of evaporated multiblock copolymer membranes studied by molecular dynamics simulations

Macromolecules

Tsige, Mesfin T.; Mattsson, Thomas M.; Grest, Gary S.

We present extensive simulations modeling the casting of multiblock polymer films by evaporation. The domain structure of the resulting film is strongly affected by varying the relative stiffness of the coblocks. The morphology changes from a bicontinuous lamellar phase when both blocks are flexible to a small-scale phase-separated phase with isolated domains as the stiffness of one of the blocks increases. As the relative stiffness of the blocks changes, the rate of evaporation, interfacial width, and morphology of the system changes. The findings can be used to tailor membrane morphology of interest to fuel-cell applications where the morphology is important for proton conduction.

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TYPE Journal Article YEAR 2004
ScopusOSTI

Equation of state and electrical conductivity of stainless steel

Mattsson, Thomas M.; Desjarlais, Michael P.

Warm dense matter is the region in phase space of density and temperature where the thermal, Fermi, and Coulomb energies are approximately equal. The lack of a dominating scale and physical behavior makes it challenging to model the physics to high fidelity. For Sandia, a fundamental understanding of the region is of importance because of the needs of our experimental HEDP programs for high fidelity descriptive and predictive modeling. We show that multi-scale simulations of macroscopic physical phenomena now have predictive capability also for difficult but ubiquitous materials such as stainless steel, a transition metal alloy.

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TYPE SAND Report YEAR 2004
OSTIDOI

Mechanisms for radiation dose-rate sensitivity of bipolar transistors

Hjalmarson, Harold P.; Hjalmarson, Harold P.; Shaneyfelt, Marty R.; Schwank, James R.; Edwards, Arthur H.; Hembree, Charles E.; Mattsson, Thomas M.

Mechanisms for enhanced low-dose-rate sensitivity are described. In these mechanisms, bimolecular reactions dominate the kinetics at high dose rates thereby causing a sub-linear dependence on total dose, and this leads to a dose-rate dependence. These bimolecular mechanisms include electron-hole recombination, hydrogen recapture at hydrogen source sites, and hydrogen dimerization to form hydrogen molecules. The essence of each of these mechanisms is the dominance of the bimolecular reactions over the radiolysis reaction at high dose rates. However, at low dose rates, the radiolysis reaction dominates leading to a maximum effect of the radiation.

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TYPE Conference YEAR 2003
OSTI

Electric field effects on surface dynamics: Si ad-dimer diffusion and rotation on Si(001)

Surface Science

Mattsson, Thomas M.; Mattsson, Thomas M.; Swartzentruber, Brian S.; Stumpf, Roland R.; Feibelman, Peter J.

Density functional calculations show that the electric field effect on Si ad-dimer diffusion on Si(0 0 1) is largely a reflection of the position dependence of the ad-dimer’s dipole moment. We can use surface diffusion barriers’ dependence on perpendicular electric fields to discriminate between diffusion mechanisms. Since the previously accepted mechanism for ad-dimer diffusion on Si(0 0 1) has the opposite field dependence to what is observed, it cannot be the one that dominates mass-transport. Here, we identify an alternate process, with a similar barrier at zero electric field and field dependence in agreement with measurements. For rotation, calculations to date show linear field dependence, in contrast to experiments.

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TYPE Journal Article YEAR 2003
OSTIDOI
Results 151–175 of 178
Results 151–175 of 178