Polymer/Substrate Interfaces: Simulation of Structure ... · Polymer/Substrate Interfaces:...
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Polymer/Substrate Interfaces: Simulation of Structure, Properties and Behavior Dhiraj K. Mahajan, a Anatoly V. Berezkin, b P. Ulrich Biedermann, b Fathollah Varnik, a Alexander Hartmaier a a ICAMS, Ruhr-Universität Bochum, b Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf Role of Substrate Roughness Linear/cross-linked polyurethane film on the ZnO surface • ZnO(0001)-Zn-O/OH single crystal surface: well characterized by experiment, stable at ambient conditions. • Polyurethane. The behavior of some typical molecules and polymer fragments are considered to extend existing OPLS-AA force filed to the polyurethane case. water methyl acetate methyl isocyanate N-methyl-acetamide , , , … LEED images obtained at 63 eV Polyurethane Network: Curing, Structure and Properties + n PPO = 2, 5, 8 H 3 C CH 2 CH 2 CH 2 O O O CH 2 CH 2 CH 2 C H C H C H CH 3 OH CH 3 OH CH 3 OH k l m branched polypropylene ether triol (Desmophen 1380 BT) <k + l + m> = 5.3 n PPO n PPO n PPO N N C C O O 4,4'-methylene diphenyl diisocyanate + + + Coarse-Grain Network model All-atom network model Conversion vs. time Network properties Curing kinetics Branching degree 3 2 3 2 2 s s s BD + = Glass transition temperature Stress-strain curves Young modulus Objective • Metals are usually coated with polymers against corrosion. The objective of this project is to develop an atomistic understanding of the interphase/interface structure of polymer/metal oxide contacts and the diffusion mechanism of ions and small molecules (H 2 O, O 2 ) along the interface as a guide for future material design. • Multiscale computer simulation • Kinetics of curing during polymer coating formation; • Interfacial structure of coating; • Permeability of coating and mechanisms of substrate corrosion. DFT calculations - structure, charge, and conformation of small molecules; - molecule-surface interactions Atomistic simulation (MD) - adsorption phenomena; - diffusivity, viscoity, density, cohesion energy of components; Calibration of atomistic force-field (OPLS) Coarse-grained level (MD) - kinetics of curing; - coating strucutre; - corrosion mechanisms; Parameterization of coarse-grained model back-mapping to atomistic details Method Main Questions Materials Adsorption of Small Organic Molecules (Density Functional Theory + Classical Simulations) Water, methyl acetate, methyl isocyanate. Adsorbed configurations and energies of adsroprtion Ads. energy OPLS-AA Ads. energy DFT Adsorbed configurations Correction of force field Iterative improvement of FF Adsorption energy of H 2 0 (test molecule) Adsorption energy of methyl acetate Comparison of classical and DFT adsorption simulations ≠ Polyurethane Structure at ZnO Interface Objective • Polymer/substrate coating systems are generally characterized by rough substrate surfaces with undulations ranging from few nanometers to several micrometers. It is known that the surface roughness strengthens the polymer/substrate bonding either by increasing the effective contact area or by mechanical interlocking of polymer between surface undulations. However, little is known regarding the role of relative dimensions of polymer chains with respect to surface undulations in effecting the polymer bonding. Such information can be used in substrate surface engineering for improving bonding without changing the interface chemistry, which forms the objective of this part of the project. Bonded interaction Non-bonded interaction Coarse-grained Polymer molecule Molecular Dynamics Simulation Details Effect of Substrate Roughness • An ideal coating system is obtained by equilibrating the coarse-grained polymer molecules between thin atomic layer at the top and planar atomic substrate at the bottom. • After polymer equilibration, coating systems with varying substrate roughness is obtained by removing atoms from the planar substrate in regular pattern with dimensions of the order of R g . • Polymer molecules interacts with the atomic substrate and top layer using non-bonded Lennard-Jones potential. • Zero pressure initial configuration of different coating systems is obtained by allowing motion of top layer atoms in z-direction. Various rough substrates studied Polymer/substrate system Statistical dimensions of polymer molecule cm x y z Failed configuration of various coating systems at similar strain under Mode I loading Mode I loading applied to coating system B C A Rough substrate Deformation behavior of various coating systems under Mode I loading with different substrate roughness. Work of separation versus roughness factor for different substrate roughness samples shows a vital role of mechanical interlocking in strengthening the interface in contrast to the contribution of increased effective area of contact as shown by a linear fit. x y z Method • Coarse-grained Molecular Dynamics simulations Rough surfaces strengthen the interface by increasing the effective contact area Mechanical interlocking is another mechanism responsible for strengthening the interface http://www.specialch em4adhesives.com/re sources/adhesionguid e/index.aspx?id=theo ry4 R. Van Tijum, PhD thesis, University of Groningen, 2006 Polymer/substrate interactions play an important role in coatings and composite materials, applications of which includes renewable energy production structures, sandwich panels used in automobiles and packaging. Desired properties of these materials include high adhesion strength of polymer with substrate and corrosion resistance of the substrate, among others. Polymer/substrate interfaces are essentially characterized by the network structure of the polymer and substrate roughness that plays a vital role in imparting the desired properties to these materials. The objective of the present project is to understand the mechanism(s) responsible for adhesion of polymer on substrates and to quantify the role of substrate roughness as well as polymer network structure on the desired properties of the coating system. At this stage of the project, the individual roles of substrate roughness and network structure are studied separately using multi-scale simulation methodology. The outcome of these complementary studies will improve our understanding of polymer/substrate interface structure, properties and behavior and may be used as guide for future material design. Introduction Polymer/Solid interfaces finds several technological applications such as renewable energy production structures, sandwich panel for automobiles and packaging. http://www.thyssenkrupp.com/en/bildstrecke/17/ http://www.thyssenkrupp.com/de/produkte/energie.html Measure of roughness References • F. Varnik and K. Binder, Multiscale modeling of polymers at interfaces, Int. J. Mat Res, 100, 1494-1502, (2009). • J. Rottler and M.O. Robbins, Molecular simulations of deformation and failure in bonds formed by glassy polymer adhesives. J. Adh. Sc. Tech. 17, 369-381, (2003). • A. V. Berezkin, P. U. Biedermann and A. A. Auer, Mesoscale simulation of network formation and structure, combining molecular dynamics and kinetic Monte Carlo approaches, In proceeding: European Polymer Congress 2011, 1378.
Transcript of Polymer/Substrate Interfaces: Simulation of Structure ... · Polymer/Substrate Interfaces:...
Polymer/Substrate Interfaces: Simulation of Structure, Properties and Behavior
Dhiraj K. Mahajan,a Anatoly V. Berezkin,b P. Ulrich Biedermann, b Fathollah Varnik,a
Alexander Hartmaier a
a ICAMS, Ruhr-Universität Bochum, b Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf
Role of Substrate Roughness
Linear/cross-linked polyurethane film on the ZnO surface • ZnO(0001)-Zn-O/OH single crystal surface: well
characterized by experiment, stable at ambient conditions. • Polyurethane. The behavior of some typical molecules and
polymer fragments are considered to extend existing OPLS-AA force filed to the polyurethane case.
water methyl acetate methyl isocyanate N-methyl-acetamide
, , , …
LEED images obtained at 63 eV
Polyurethane Network: Curing, Structure and Properties
+
nPPO = 2, 5, 8
H3C
CH2
CH2
CH2
O
O
O
CH2
CH2
CH2
CH
CH
CH
CH3
OH
CH3
OH
CH3
OHk
l
m
branched polypropylene ether triol(Desmophen 1380 BT)
<k + l + m> = 5.3
nPPO
nPPO
nPPO
NNCC
O O
4,4'-methylene diphenyl diisocyanate
+
+
+
Coarse-Grain Network model
All-atom network model
Conversion vs. time
Network properties
Curing kinetics Branching degree
32
3
22
sssBD+
=
Glass transition temperature Stress-strain curves Young modulus
Objective • Metals are usually coated with polymers against corrosion.
The objective of this project is to develop an atomistic understanding of the interphase/interface structure of polymer/metal oxide contacts and the diffusion mechanism of ions and small molecules (H2O, O2) along the interface as a guide for future material design.
• Multiscale computer simulation • Kinetics of curing during polymer coating formation; • Interfacial structure of coating; • Permeability of coating and mechanisms of substrate
corrosion.
DFT calculations - structure, charge, and conformation of small molecules; - molecule-surface interactions
Atomistic simulation (MD) - adsorption phenomena; - diffusivity, viscoity, density, cohesion energy of components;
Calibration of atomistic force-field (OPLS)
Coarse-grained level (MD) - kinetics of curing; - coating strucutre; - corrosion mechanisms;
Parameterization of coarse-grained model
back
-map
ping
to
ato
mis
tic d
etai
ls Method
Main Questions
Materials
Adsorption of Small Organic Molecules (Density Functional Theory + Classical Simulations)
Water, methyl acetate, methyl isocyanate.
Adsorbed configurations and energies of adsroprtion
Ads. energy OPLS-AA
Ads. energy DFT
Adsorbed configurations
Correction of force field
Iterative improvement of FF
Adsorption energy of H20 (test molecule)
Adsorption energy of methyl acetate
Comparison of classical and DFT adsorption simulations
≠
Polyurethane Structure at ZnO Interface
Objective • Polymer/substrate coating systems are generally characterized
by rough substrate surfaces with undulations ranging from few nanometers to several micrometers. It is known that the surface roughness strengthens the polymer/substrate bonding either by increasing the effective contact area or by mechanical interlocking of polymer between surface undulations. However, little is known regarding the role of relative dimensions of polymer chains with respect to surface undulations in effecting the polymer bonding. Such information can be used in substrate surface engineering for improving bonding without changing the interface chemistry, which forms the objective of this part of the project.
Bonded interaction
Non-bonded interaction
Coarse-grained Polymer molecule
Molecular Dynamics Simulation Details
Effect of Substrate Roughness
• An ideal coating system is obtained by equilibrating the coarse-grained polymer molecules between thin atomic layer at the top and planar atomic substrate at the bottom.
• After polymer equilibration, coating systems with varying substrate roughness is obtained by removing atoms from the planar substrate in regular pattern with dimensions of the order of Rg.
• Polymer molecules interacts with the atomic substrate and top layer using non-bonded Lennard-Jones potential.
• Zero pressure initial configuration of different coating systems is obtained by allowing motion of top layer atoms in z-direction.
Various rough substrates studied
Polymer/substrate system
Statistical dimensions of polymer molecule
cm
x
y z
Failed configuration of various coating systems at similar strain under Mode I loading
Mode I loading applied to coating system
B
C
A
Rough substrate
Deformation behavior of various coating systems under Mode I loading with different substrate roughness.
Work of separation versus roughness factor for different substrate roughness samples shows a vital role of mechanical interlocking in strengthening the interface in contrast to the contribution of increased effective area of contact as shown by a linear fit.
x
y z
Method • Coarse-grained Molecular Dynamics simulations
Rough surfaces strengthen the interface by increasing the effective contact area
Mechanical interlocking is another mechanism responsible for strengthening the interface
http://www.specialchem4adhesives.com/resources/adhesionguide/index.aspx?id=theory4
R. Van Tijum, PhD thesis, University of Groningen, 2006
Polymer/substrate interactions play an important role in coatings and composite materials, applications of which includes renewable energy production structures, sandwich panels used in automobiles and packaging. Desired properties of these materials include high adhesion strength of polymer with substrate and corrosion resistance of the substrate, among others. Polymer/substrate interfaces are essentially characterized by the network structure of the polymer and substrate roughness that plays a vital role in imparting the desired properties to these materials. The objective of the present project is to understand the mechanism(s) responsible for adhesion of polymer on substrates and to quantify the role of substrate roughness as well as polymer network structure on the desired properties of the coating system. At this stage of the project, the individual roles of substrate roughness and network structure are studied separately using multi-scale simulation methodology. The outcome of these complementary studies will improve our understanding of polymer/substrate interface structure, properties and behavior and may be used as guide for future material design.
Introduction
Polymer/Solid interfaces finds several technological applications such as renewable energy production structures, sandwich panel for automobiles and packaging.
http://www.thyssenkrupp.com/en/bildstrecke/17/ http://www.thyssenkrupp.com/de/produkte/energie.html
Measure of roughness
References
• F. Varnik and K. Binder, Multiscale modeling of polymers at interfaces, Int. J. Mat Res, 100, 1494-1502, (2009).
• J. Rottler and M.O. Robbins, Molecular simulations of deformation and failure in bonds formed by glassy polymer adhesives. J. Adh. Sc. Tech. 17, 369-381, (2003).
• A. V. Berezkin, P. U. Biedermann and A. A. Auer, Mesoscale simulation of network formation and structure, combining molecular dynamics and kinetic Monte Carlo approaches, In proceeding: European Polymer Congress 2011, 1378.
