Advanced Materials Research Group at North Dakota State University, Fargo
Multiscale Modeling and Evaluation of Nanomaterials
Natural and synthetic nanomaterials both exhibit unique and extraordinary properties that could be of tremendous interest for applications in engineering, medicine etc. The relationship between molecular interactions, microstructure and macroscale properties and thus the understanding of mechanisms leading to the properties are key to effective use and design of such materials. Our research group has made major strides in exploring and unearthing key mechanisms responsible for the extraordinary properties exhibited by nanomaterials such as nacre (the inner layer of seashells) and polymer clay nanocomposites (PCNs). We have identified the vital role of molecular interactions on properties of nanomaterials such as bone, nacre, polymer clay nanocomposites, hydroxyapatite polymer nanocomposites for tissue engineering and smectite clays.
Using a combination of computational modeling and complimentary experimental techniques at various length scales spanning molecular scale to macro-scale, relationship between molecular interactions, microstructure and mechanical properties are evaluated.
Finite element modeling of nano and microstructure of nacre was conducted to evaluate mechanical properties of the nanoscale organic phase and to identify role of specific components of the nano-architecture. Electron microscopy was used to study failure mechanisms. Steered molecular dynamics (SMD) simulations, FTIR spectroscopy, AFM imaging and protein pulling and nano-indentation experiments revealed the influence of mineral phase on nacre protein.
Molecular dynamics simulations of PCNs provided maps of interaction energies between clay-modifier-polymer. Experimental techniques such as FTIR spectroscopy, X-ray diffraction, nano-indentation and differential scanning calorimetry provided an insight into how interaction energies influence physical and mechanical properties. Using a multi-scale modeling approach, key mechanism for property enhancement in PCN was described.SMD simulations of clay-water interactions were conducted to evaluate mechanical behavior of clay interlayer. A modified discrete element approach was developed to study role of particle “breakdown” on swelling behavior. A new permeameter was designed to study role of molecular interactions between clay and fluids with a range of polarities on fluid flow and mechanical properties.
Ab-initio calculations and SMD simulations of mineral-polymer and mineral-collagen interactions in bone complimented by various experimental techniques were used to study materials for tissue engineering and bone. Mechanics of cell-scaffold interactions is being conducted using nano-indentation.
Proximity of minerals to proteins in biological nanocomposites has a large influence on unfolding and mechanical behavior of proteins. Platelet interlocks in nacre are key to the high fracture toughness exhibited by nacre. The fundamental mechanism of property enhancement in PCNs with nanoclays is the result of ‘altered phase’ of polymer resulting from molecular interactions between clay-modifier and polymer. Permeability, mechanical properties, and evolution of microstructure in swelling clays are greatly influenced by molecular interactions between clays and fluids.
Molecular interactions in nanomaterials play a vital role on their mechanics and are critical for accurate modeling of these materials for robust simulation based design of next generation materials.
1. Sikdar, D., Pradhan, S. M., Katti, D.R., Katti, K. S., and Mohanty, B., (2008), Altered Phase Model for Polymer Clay Nanocomposites, Langmuir, 24, 5599-5607
2. Amarasinghe, P. M., Katti, K. S., and Katti, D. R., (2009), Nature of Organic Fluid-Montmorillonite Interactions: An FTIR Spectroscopic Study, J. of Colloid and Interf. Sci, 337, 97-105.
3. Bhowmik, R.; Katti, K. S.; and Katti, D.R., (2009), Mechanisms of Load-Deformation Behavior of Molecular Collagen in Hydroxyapatite-Tropocollagen Molecular System: Steered Molecular Dynamics Study, ASCE J. of Eng. Mechanics, Vol. 135, n. 5, 413-421.
4. Katti, D. R., Matar, M. I., Katti, K. S., Amarasinghe, P. M., (2009), Multiscale Modeling of Swelling Clays: A Computational and Experimental Approach, KSCE J of Civil Engineering, 13(4), 243-255.
5. Katti, D. R., Schmidt, S. R., Ghosh, P., Katti, K. S., (2007) Molecular Modeling of the Mechanical Behavior and Interactions in Dry and Slightly Hydrated Sodium Montmorillonite Interlayer, Can. Geotech. J.,44,425-435.
6. Ghosh, P.; Katti, D. R.; and Katti, K. S., (2007) “Mineral Proximity Influences Mechanical Response of Proteins in Biological Mineral-Protein Hybrid Systems” Biomacromolecules., 8, 851-856.
7. Katti, K. S., Katti, D. R., Pradhan, S.M., and Bhosle, A.,(2005), Platelet Interlocks are the Key to Toughness and Strength in Nacre, J. of Mater. Res. 20, 1097-1100.