Bulk Linear Triblock (linearTriblock.pre)


phase diagram, triblock, multiblock, copolymer, morphologies, bulk behavior

Problem description

This simulation can be performed with a PSimBase license.

This example shows how to simulate copolymer chains with multiple blocks using PSim by modeling a 2-component linear triblock (ABA). Since there are two distinct blocks with the same monomer species, this example also shows how to separately track the contributions to the monomer density different blocks.

Input File Features

Files: linearTriblock.pre.

The variables in the Setup tab are

  • NX (Number of cells in the x-dir)
  • NY (Number of cells in the y-dir)
  • NZ (Number of cells in the z-dir)
  • fA1 (Length fraction of ‘head A’ block)
  • fB (Length fraction of ‘B’ block)
  • fA2 (Length fraction of ‘end A’ block)
  • chiNAB (Flory \(\chi N\) parameter between the two chemically distinct blocks”
Note, the two block lengths controled by ‘fA1’ and ‘fA2’ consist of the same
monomer species.

The parameters ‘fA1’, ‘fA2’, and ‘fB’ refer to the triblock length fractions of the two outer blocks and one middle block respectively of the ABA triblock being simulated. When changing these parameters note that \(f_{A1} + f_{B} + f_{A2} = 1\). To separately track the contributions from the two ‘A’ blocks there are two extra physical field blocks specified

<PhysField s1BlockDens>
  kind = monomerDens
  type = fieldD3R

<PhysField s2BlockDens>
  kind = monomerDens
  type = fieldD3R

These blocks are refered to by an optional parameter, ‘blockfield’, in the input blocks specifying the triblock model

<Block blockA>
  kind = flexPseudoSpec
  scfield = totStyrDens
  blockfield = s1BlockDens
  ds = DS
  lengthfrac = fA1
  headjoined = [freeEnd]
  tailjoined = [blockB]

<Block blockC>
  kind = flexPseudoSpec
  scfield = totStyrDens
  blockfield = s2BlockDens
  ds = DS
  lengthfrac = fA2
  headjoined = [blockB]
  tailjoined = [freeEnd]

Creating the run space

The Linear Triblock example is accessed from within PSimComposer by the following actions:

  • Select the New from Template menu item in the File menu.
  • In the resulting New from Template window, select PSimBase and then press the arrow button to the left.
  • Select “Linear Triblock” and press the Choose button.
  • In the resulting dialog, press the Save button to create a copy of this example in your run area.

The basic variables of this problem should now be settable in text boxes in the right pane of the “Setup” window, as shown in Fig. 64.


Figure 64: Setup window for the Linear Triblock example.

Running the simulation

After performing the above actions, continue as follows:

  • Press the Save And Setup button in the upper right corner.
  • Proceed to the run window as instructed by pressing the Run button in the left column of buttons.
  • Note: because the initial random state depends on the number of processors, the final simulation state can depend on the number of processors chosen if running in parallel. The results in this example are produced by running on two processors. The parallel run options can be accessed by going to the ‘MPI’ tab on the left side of the Run button window.
  • To run the file, click on the Run button in the upper right corner. of the window. You will see the output of the run in the right pane. The run has completed when you see the output, “Engine completed successfully.” This is shown in Fig. 65.

Figure 65: The Run window at the end of execution.

Visualizing the results

After performing the above actions, continue as follows:

  • Proceed to the Visualize window as instructed by pressing the Visualize button in the left column of buttons.
  • Press the “Open” button to begin visualizing.
  • Go to the Scalar Data Variable in the CONTROLS panel on the left and press the arrow to the left
  • Check one of the MonomerDensity boxes (try the totEthyDens database) This selects all of the datafiles for this physical field ‘totEthyDens’. This first *h5 file will be shown first.
  • Move the Dump slider at the bottom of the window to the last position to see the final simulation state.
  • Click on the Colors button in the Visualization pane. Different coloring schemes can be selected from here as well as scaling the colors between minimum and maximum values. As the monomer density fractions take on values between [0, 1], set the min/max values accordingly. This is shown in the following figure

Figure 66: Visualization of Linear Triblock as a color contour plot.

Further Experiments

Change the length fraction of the end blocks and re-run simulation. Visualize the separate block density fractions ‘s1BlockDens’ and ‘s2BlockDens’ to see how the distinct end blocks contribute to the overall monomer density ‘totStyrDens’

Note, the image on the Setup window is generated by accessing the full VisIt capability by right clicking on the Visualization pane and starting the VisIt GUI.