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Agenda

Agenda. 9.00 - Welcome 9.15– Molecular simulations of soft materials; classical simulations of polymers and glasses 10.15 – Break 10.30 – Computational chemistry studies of hard materials; DFT, Monte-Carlo and classical Simulation studies of crystals, surfaces and zeolites.

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Agenda

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  1. Agenda • 9.00 - Welcome • 9.15– Molecular simulations of soft materials; classical simulations of polymers and glasses • 10.15 – Break • 10.30 – Computational chemistry studies of hard materials; DFT, Monte-Carlo and classical Simulation studies of crystals, surfaces and zeolites. • 11.30 – Open Session: Q&A and software demonstration • 12.00 - Lunch • 13.15 – Using the Materials Studio Environment– ‘Hands on session’ • 14.30 – Simple simulations using Molecular Mechanics – Talks and ‘Hands on session’ • 15.45 – QM methods in Materials Studio – Talk and ‘Hands on session’. • 17.00 – Closing remarks

  2. Molecular simulations of soft materials; Classical and mesoscale simulations of polymers and glasses Dr. Shyam Vyas

  3. Introduction What is simulations, what can you do with it, how does it work Polymer-Additive Miscibility Polymer – Diffusion Mesoscale Modeling Some basic concepts Studies of Pluronics Studies of Haldoperiodol Simulation of nanotube-polymer composites Simulations of Glasses Solid-Liquid Interactions Summary Overview

  4. Simulation: Unique Insights • Modeling strengths • Resolves time and space more finely than experiment • Allows discrete questions to be asked of a system • Provides information that is essentially unavailable through experimental approaches alone • Modeling complements experiment • Opportunity is to use modeling as an integral part of the design and optimization of catalysts

  5. Accelrys’ Simulation Technologies Simulation/Modeling Methods (Mathematical representations of the real material) Quantum Mechanics Atomistic Simulation Mesoscale Modeling Analytical Instrument Simulation Statistical Correlations Properties Structure Solubility Activity Diversity Adhesion Stability Morphology Adsorption Diffusion Mechanical Energies Spectra... Molecular Models Caffeine Aspirin Polyurethane Glass

  6. Materials Properties from Calculations - I • Thermodynamic Properties • DU, DH, DS, DG, Cp, Cv • Binding energies • Surface and interface energies - adhesion • Pressure induced phase transitions • Temperature induced phase transitions • Phase diagrams • Transport properties • Electrical conductivity • Thermal conductivity • Viscosity • Diffusion constants • Permeability • Structural properties • Geometries of molecules • Crystal structures (packing) • Density • Defect structures • Crystal morphology • Surface structures • (reconstructions, adsorption) • Interface structures • Mechanical Properties • Compressibility • Elastic moduli • Thermal expansion coefficients • Vibrational properties • Hardness & Fracture toughness

  7. Materials Properties from Calculations - II • Electrical, optical, and magnetic properties • Electron density distribution - electrical moments • Polarizabilities, hyperpolarizabilities • Ionization energies and electron affinities • Electrostatic potential, work function • Energy band structure - metal, semiconductor, insulator, superconductor • Band gaps, band offsets at hetero-junctions • Optical spectra • NMR chemical shifts • Dielectric response • Luminescence • Fluorescence • Chemical and other properties • Chemical reaction rates (catalytic properties, corrosion, electro- • chemistry) • Reactivity with surfaces • UV stability

  8. e.g. micelles CORRELATIVE METHODS e.g., crystallization, miscibility e.g., electronics, catalysis Accelrys Solutions for Materials Modeling

  9. Introduction What is simulations, what can you do with it, how does it work Polymer-Additive Miscibility Polymer – Diffusion Mesoscale Modeling – phase behaviour of soft materials Some basic concepts Studies of Pluronics Studies of Haldoperiodol Simulations of Glasses Solid-Liquid Interactions Summary Overview

  10. Molecular Mechanics • A molecule is described as a series of charged points (atoms) linked by springs (bonds). • A mathematical description of this system is known as a forcefield • The forcefield is used to calculate the relative potential energy of the molecule (relative to other conformations of the same molecule).

  11. Energy Expression Force Field Parameterization

  12. Estimating Miscibility Using d Ecoh = E(molecules in bulk) - E(molecules separated) Bulk estradiol (amorphous)

  13. Calculating Solubility Parameters to Rank Solubility of Drugs in Solvents benzyl alcohol isopropyl alcohol PEG 200 density = 1.045 g/cc density= 0.785 g/cc density = 1.156 g/cc sol. param. = 15.33 (J/cc)1/2 sol. param. = 23.35 (J/cc)1/2 sol. param. = 23.80 (J/cc)1/2

  14. Calculating Solubility Parameters to Rank Solubility of Drugs in Solvents Acetaminophen Amorphous state: density = 1.219 ± 0.010 g/cc sol. param. = 29.28 ± 0.14 (J/cc)1/2 Simulations allow the prediction of which solvent will mix with the drug. PEG and isopropyl alcohol have solubility parameters much closer to acetaminophen than benzyl alcohol.

  15. Calculating c from the energy of mixing: Amorphous Cell methods • Estimating compatibility through estimation of Solubility Parameters is fast. • However, it does not pick-up favourable or unfavourable interaction between the molecule; dipole-dipole interactions, hydrogen bonding etc • To address this we need to calculate the energies of mixing, Emix • Construct bulk amorphous models of polymer bulk or solutions and equilibrate using the Amorphous Cell module. • High precision pVT and cohesive energy prediction using Discover and COMPASS forcefield. • .

  16. Calculating c from the energy of mixing: Amorphous Cell methods

  17. GE and Accelrys studyUltem® • an amorphous engineering thermoplastic polyetherimide (PEI) with excellent properties such as heat resistance (high Tg ~500K), good hydrolytic and chemical stability and mechanical properties. • ideally suited for a broad range of applications, e.g. • Autoclavable medical equipment • Aircraft interiors • Automotive engine compartment parts

  18. Case study: Cohesive Properties of Ultem® • High performance polymer used in a variety of applications including telecomms and food packaging • Scientists at General Electric-CRD, NY, USA, and Accelrys Inc. have used Accelrys' Materials Studio to determine the cohesive properties of the polyether imide, Ultem™. • Dr J. Stein, General Electric-CRD, comments, "The calculations were undertaken in order to develop silicone adhesive formulations which could be used to bond Ultem to plastics and metals. Understanding the cohesive properties of the Ultem allowed the team to understand the fundamental interactions governing adhesion of Ultem to modified silicones". B. E. Eichinger, D. Rigby, and J. Stein, Polymer, 43, 599-607, 2002 http://www.accelrys.com/reference/cases/studies/ultem.html

  19. Issues in Ultem products and applications • Frequently require application of solvent-based adhesives or coatings • understand interaction of solvents with Ultem® substrate • design effective promoters which improve adhesion of otherwise incompatible coatings with the polymer. • Modeling was used to study interactions with solvents.

  20. Results: Densities and solubility parameters • solubility parameter of Ultem® ~22 MPa0.5 • Solvent densities and solubility parameters: • B. E. Eichinger, D. Rigby, and J. Stein, Polymer, 43, 599-607, 2002 • http://www.accelrys.com/reference/cases/studies/ultem.html

  21. Interaction energies correlated to solubility Approx. quadratic in difference between polymer and solvent solubility parameter

  22. Ultem-Solvent Interaction Studies - Conclusions • Materials Studio provides quantitative, predictive properties:densities, cohesion, adhesion. • Results are consistent with experimental data:solvents except for ethylene glycol are capable of wetting Ultem® • Stable and theoretically reasonable predictions are possible on the ‘MD time scale’ requiring few hours of CPU time. • For further details, see Polymer43, 599-607 (2002)

  23. Introduction What is simulations, what can you do with it, how does it work Polymer-Additive Miscibility Polymer – Diffusion Mesoscale Modeling – phase behaviour of soft materials Some basic concepts Studies of Pluronics Studies of Haldoperiodol Simulations of Glasses Solid-Liquid Interactions Summary Overview

  24. Diffusion in PEO membranes • PolyEthyleneOxide and its Sulfonic Acid derivatives are used as an electrolytes in Fuel Cell Applications • The charge carriers in the system are; • H+, H3O+ and the PEO sulfonic anions An understanding of the diffusive behavior of the charge carriers will enable us to design a more energy efficient fuel cell Polymer, 2000, Vol 41, Page 985, Ennari et al Ph.D. Thesis, University of Helsinki, 2000 - Ennari

  25. Diffusion in PEO membranes • Built and refined several amorphous cells of the polymer system using MD • Analysis shows that cations are strongly coordinated to anions in the anhydrous state. The opposite is true when water is present This has an effect on the diffusion coefficients and the conductivity of the material. Increasing the water concentration in the system improves the conductivity of the electrolyte

  26. Modeling transdermal adhesives • http://www.accelrys.com/cases/transdermal.html (National Starch) • The mechanism of drug diffusion through a transdermal polymer adhesive has been studied. The diffusion is seen to occur through a series of activated “hops”. • Quantitative agreement with experimental results is obtained, but a much deeper appreciation for the process is gained. Estradiol in Duro-tak

  27. Further properties ... • IR and scattering functions • Statistical mechanics data: Radial distribution functions and structure factors • For polymers: torsional distribution, radius of gyration, persistence lengths, etc. • Mechanical properties (e.g., Poisson’s ratio, Young’s modulus, Lame constants, etc.) • Shear and bulk viscosities • Diffusion coefficients and permeability

  28. Introduction What is simulations, what can you do with it, how does it work Polymer-Additive Miscibility Polymer – Diffusion Mesoscale Modeling – phase behaviour of soft materials Some basic concepts Studies of Pluronics Studies of Haldoperiodol Simulations of Glasses Solid-Liquid Interactions Summary Overview

  29. Mesoscale modeling • Material properties are often affected by structure and dynamics at scales considerably larger than atoms. • This is especially true for polymer based systems • Structured materials can have unique and highly desirable traits (e.g., controlled release) • Atomistic modeling is too fine grained (we would need too many atoms, and very long simulations) • We seek coarse-grained methods which capture the underlying physics • Accelrys has “mesoscale” tools (DPD and MesoDyn) which address this need.

  30. Atomistic Mesoscopic Length nm 100’s of nm (or more) Units atoms Beads representing many atoms Time ns as much as milli-seconds Dynamics F=ma Diffusion, hydrodynamics

  31. Methods MesoDynDensity fields of the various chemical components and substructures Evolves with stochastic diffusion equations driven by local gradients in chemical potential. DPDDissipative Particle Dynamics Beads represent groups of atoms with an effective interaction Dynamics is driven by noise, dissipations and conservative forces.

  32. MesoDyn - Pluronics modeling: BASF PEO-PPO-PEO block copolymers nonionic surfactant used in detergency, dispersion stabilisation, lubrication, drug delivery etc Parameterisation for MesoDyn of Pluronic L64:EO13 PO30 EO13A3 B8 A3

  33. Pluronic L64 structures as a function of concentration in aqueous solution: Predicted mesosphases:(a) (70% ) lamellar (b) (60%) bicontinuous(c) (55%) hexagonal(d) (50%) micellar Excellent agreement with experiments. Same parameters also give correct predictions for other Pluronics. B.A.C.van Vlimmeren, N.M.Maurits, A.V.Zvelindovsky, G.J.A.Sevink and J.G.E.M.Fraaije 1999 Macromolecules 32: 646-656

  34. Pluronic P85:Temperature dependence of morphology • Flory Huggins interaction parameter depends on temperature • For polymer-solvent systems: • Y M Lam and G Goldbeck-Wood determined a and b from experimental vapour pressure data of PEO and PPO by Malcolm & Rowlinson (1957) • PEO-Water: a = 2.85, b = -439K • PPO-Water: a = 2.023, b = -97.9K

  35. Pluronic P85: Morphology variation with Temp Temperature = 70 oC Rods Temperature = 15 oC Micelles Polymer Concentration = 0.27 • transition from micelles to rods • agrees with experimental phase diagram by K. Mortensen et al, 1993 Y M Lam, G Goldbeck-Wood 2000, Univ Cambridge,to be published

  36. Hydrophobic drugs in pluronic micelles Hydrophilic Hydrophobic Hydrophobic Drug At Temperature > CMT: • Hydrophobic drugs must be encapsulated to ensure adsorption • Pluronics (tri-block polymers of ethylene oxide and propylene oxide) are very useful delivery devices Core Corona With hydrophobic drugs • Pluronics self assemble in solution, providing a hydrophobic environment for drug uptake. • Relative chain lengths can be controlled to yield desired properties

  37. O F N Cl 35 nm 35 nm OH Effect of Drug on micelle size and shape • Pluronic F127 in water forms micellar phase • Size of Micelles increases with presence of drugs • Distribution of size increases as well • Micelles are less spherical 10%wt F127-No Drug Drug is Haloperidol. An anti-psychotic. Must cross blood-brain barrier. Control of micelle size distribution is important. 10%wt F127 with HAL

  38. Predicted effect of haldol, using MesoDyn • MesoDyn calculations of pluronic in water with and without Haldol present. 24 %wt PEO26PPO40PEO26 Without Haldol 24 %wt PEO26PPO40PEO26 With 0.1% Haldol 24 %wt PEO26PPO40PEO26 With 1% Haldol • MesoDyn calculations agree with experiment. Addition of drug distorts and swells micelles. • Rationale? Distribution of drug concentrations within micelles leads to different sizes and shapes

  39. Implications • Addition of small amounts of hydrophobic drug drastically changes morphology • To promote a homogeneous distribution of micelles, steps should be taken to distribute drug evenly, so that similar amounts of drug reside in each micelle. • Processing may be able to address this. Red points show position of Haldol. Some micelles are full of drug others are relatively empty.

  40. COMPASS-optimized structure of PmPV polymer on a (12, 7) chiral nanotube Polymer-Nanotube interaction • Important for: • Structural Nanocomposites • Solubilizing nanotubes • Interaction of small chains of PmPV polymer with chiral nanotubes was studied: • COMPASS forcefield in het Panhuis, Maiti, Coleman, Dalton, McCarthy, and Blau, J. Phys. Chem B 109, 478 (2003). To study composites you need many nanotubes In solution with a very long-chain polymers => Much longer length and time-scales

  41. Estimating Miscibility Using d Ecoh = E(molecules in bulk) - E(molecules separated)

  42. Solubility parameter (d) of nanotubes • d D-1/2 • d independent of chiral angle • Experimentally PmPV polymer is found to mix with tubes of diameters between 1.35-1.55 nm • Dalton et al., J. Phys. Chem. B 104, 10012.

  43. (10, 10) CNT DPD simulations of CNT-PMMA composites • Extra spring + angle-dependent terms • included to describe nanotubes • CNT-alignment as a function of Shear • No shear (top) • Shear (Bottom) A. Maiti, J. Wescott, P. Kung, Mol. Sim., in press (2004)

  44. (10,10) CNT in PMMA (small difference in )

  45. (15, 15) CNT DPD simulations of CNT-PMMA composites • Top – 15,15 is insoluble in PMMA • By functionalizing nanotube get better dispersion

  46. (15,15) CNT in PMMA (large difference in )

  47. Introduction What is simulations, what can you do with it, how does it work Polymer-Additive Miscibility Polymer – Diffusion Mesoscale Modeling – phase behaviour of soft materials Some basic concepts Studies of Pluronics Studies of Haldoperiodol Simulations of Glasses Solid-Liquid Interactions Summary Overview

  48. Modeling of glass: Bulk and Surface Studies S.Vyas, J. Dickinson, and E. Armstrong-Poston, Molecular Simulations, Vol 32, No 2, 2006, 135-143

  49. Introduction - Motivation • Glass is used as a support in various appplication; • DNA Microarrays, Optical applications • In such applications the glass is often coated with an organic molecule • Binding of the organic to the glass surface is improved via silane coupling agents

  50. Introduction - Silanes • Silanes couple organic components to surface of glass, via interaction of silane group with glass surface • The quality of the adhesion is very sensitive to the nature of the glass. • A Borosilicate glass seems to show better adhesion properties than traditional Sodalime glasses. • Sodalime is cheaper • WHY DOES ONE WORK BETTER? Step 1 - Understand the substrate

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