Difference between revisions of "Main Page"

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(→‎Plan for Paper: Numbered the points in the paper)
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====Plan for Paper====
 
====Plan for Paper====
−
* Main points of paper:
+
# Main points of paper:
 
## We have a valid strategy for simulating BCP thin films.
 
## We have a valid strategy for simulating BCP thin films.
 
## We can reproduce many expected results for BCP thin films (islands and/or holes, L0 vs. T, etc.).
 
## We can reproduce many expected results for BCP thin films (islands and/or holes, L0 vs. T, etc.).
 
## We have identified internal film pressures/tensions/stresses as having a significant role in controlling film behavior (morphology orientation, L0, islands and holes... and also defect density, ordering kinetics, etc.):
 
## We have identified internal film pressures/tensions/stresses as having a significant role in controlling film behavior (morphology orientation, L0, islands and holes... and also defect density, ordering kinetics, etc.):
−
*** A "happy" (stable, low-energy) film has a low internal tension. The formation of an island or hole is one place to "pay the energy penalty" of having incommensurate thickness. Internal film stresses is another.
+
### A "happy" (stable, low-energy) film has a low internal tension. The formation of an island or hole is one place to "pay the energy penalty" of having incommensurate thickness. Internal film stresses is another.
−
**** ''Currently speculative:'' The tradeoff between forming islands-and-holes versus building up internal stress depends on the bending energy (chain stiffness).
+
#### ''Currently speculative:'' The tradeoff between forming islands-and-holes versus building up internal stress depends on the bending energy (chain stiffness).
−
**** ''Currently speculative:'' Tension builds up to a critical level before being released ("pop") with the formation of an island or hole (e.g. as T is changed and thus L0 changes).
+
#### ''Currently speculative:'' Tension builds up to a critical level before being released ("pop") with the formation of an island or hole (e.g. as T is changed and thus L0 changes).
−
*** ''Currently speculative:'' The vertical state is low-energy than horizontal on neutral surfaces, because a tension mismatch between the two blocks (slightly different cohesive energy) creates an energy penalty in horizontal configuration, which can be relieved (slightly) in the vertical configuration via surface "puckering". (We have experimental data showing the puckering.)
+
### ''Currently speculative:'' The vertical state is low-energy than horizontal on neutral surfaces, because a tension mismatch between the two blocks (slightly different cohesive energy) creates an energy penalty in horizontal configuration, which can be relieved (slightly) in the vertical configuration via surface "puckering". (We have experimental data showing the puckering.)
−
**** ''Currently speculative:'' A perfectly vertical state (rather than vertical with tilt) should be preferred because this can minimize chain perturbation at the film surface (and also minimizes surface area?). Thus a perfectly vertical state should appear when the bending energy is increased (and the surface tensions increase?).
+
#### ''Currently speculative:'' A perfectly vertical state (rather than vertical with tilt) should be preferred because this can minimize chain perturbation at the film surface (and also minimizes surface area?). Thus a perfectly vertical state should appear when the bending energy is increased (and the surface tensions increase?).
−
* Figures: (tentative, of course)
+
# Figures: (tentative, of course)
 
## A graph of T vs. time to explain our general simulation protocol. Sub-panels show generic image of a spin-cast starting state, and a final state (with an expected morphology; e.g. commensurate horizontal on a strongly wetting substrate). This justifies our methodology.
 
## A graph of T vs. time to explain our general simulation protocol. Sub-panels show generic image of a spin-cast starting state, and a final state (with an expected morphology; e.g. commensurate horizontal on a strongly wetting substrate). This justifies our methodology.
 
## A few "boring" results (e.g. morphology vs. composition?), mostly to justify that our protocol is "getting the right answer".
 
## A few "boring" results (e.g. morphology vs. composition?), mostly to justify that our protocol is "getting the right answer".

Revision as of 10:52, 13 November 2009

This is a wiki for collaborating on research projects.

Current Projects

Molecular Dynamics of Block-copolymers (MDBCP)

Recent Results

  • MDBCP:Log_2009_Nov_12: Larger system size simulation for LAM of higher bending energy (kbend=2), neutral surface (g=0.5), and intermediate temperature (T=1.4).
  • MDBCP:Log_2009_Nov_12-cylinders: Small box size (7x16x2), for CYL (Na=3 Nb=7), for various temperatures (1.1 to 1.6) and surface energy (g = 0.2, 0.5, 0.8).

Progress

  • Done:
    • Temperature (T) and surface energy (g) phase diagram for LAM (chains 5+5 ??). T1.357, T1.38, T1.403, T1.426, T1.45, T1.473, T1.497, T1.520, T1.543 and gamma 0.2, 0.5, 0.8. See MDBCP:Log_2009_Nov_10.
  • Running:
    • TBD
  • To be done:
    • Composition and surface energy phase diagram (at a particular T, like 1.4?)

Plan for Paper

  1. Main points of paper:
    1. We have a valid strategy for simulating BCP thin films.
    2. We can reproduce many expected results for BCP thin films (islands and/or holes, L0 vs. T, etc.).
    3. We have identified internal film pressures/tensions/stresses as having a significant role in controlling film behavior (morphology orientation, L0, islands and holes... and also defect density, ordering kinetics, etc.):
      1. A "happy" (stable, low-energy) film has a low internal tension. The formation of an island or hole is one place to "pay the energy penalty" of having incommensurate thickness. Internal film stresses is another.
        1. Currently speculative: The tradeoff between forming islands-and-holes versus building up internal stress depends on the bending energy (chain stiffness).
        2. Currently speculative: Tension builds up to a critical level before being released ("pop") with the formation of an island or hole (e.g. as T is changed and thus L0 changes).
      2. Currently speculative: The vertical state is low-energy than horizontal on neutral surfaces, because a tension mismatch between the two blocks (slightly different cohesive energy) creates an energy penalty in horizontal configuration, which can be relieved (slightly) in the vertical configuration via surface "puckering". (We have experimental data showing the puckering.)
        1. Currently speculative: A perfectly vertical state (rather than vertical with tilt) should be preferred because this can minimize chain perturbation at the film surface (and also minimizes surface area?). Thus a perfectly vertical state should appear when the bending energy is increased (and the surface tensions increase?).
  2. Figures: (tentative, of course)
    1. A graph of T vs. time to explain our general simulation protocol. Sub-panels show generic image of a spin-cast starting state, and a final state (with an expected morphology; e.g. commensurate horizontal on a strongly wetting substrate). This justifies our methodology.
    2. A few "boring" results (e.g. morphology vs. composition?), mostly to justify that our protocol is "getting the right answer".
    3. phase diagram (images) of gamma and T for LAM. This will show many expected trends (horizontal vs. vertical), and we will point out some interesting features (islands and holes, tilt angles, etc.)
    4. L0 vs. T (and corresponding pressure vs. T?); trend is in expected direction (L0 decreases as T increases for the usual reasons) but exact scaling is informative.
    5. phase diagram of tensions for the gamma vs. T images. We can show the "residual final tension" or the "tension in z direction" or the "tension along LAM normal" or whatever best makes our point: that internal stress and tension mismatch between the blocks drives behavior.
    6. And some more...

Future Directions

  • Explore role of substrate topography (roughness, channels).
  • Combine MD simulations with scattering modeling, to compare with experimental data. (Possibly fit experimental data by adding an energetic bias in LAMMPS based on fit quality?)

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