Home         ►

Paul Podsiadlo
Ph.D. Student, Hertz Fellow
apodsiad(at)umich(dot)edu

M.S. ChE, University of Michigan, 2006
B.S. ChE, University of Michigan, 2002

 

Research Projects

I am studying layer-by-layer (LBL) assembled nanocomposites from montmorillonite clay nanosheets and cellulose nanocrystals for optical, biomedical, automotive, and space applications.

Clay Nanocomposites

I am pursuing development of ultra-strong and tough polymeric nanocomposites and I am also trying to develop fundamental understanding of the underlying composite mechanics. Previously, our group has reported preparation of a thin film nanostructured composite from montmorillonite clay nanosheets and poly(diallyldimethyl ammonium chloride) (PDDA) (Tang et al., Nature Materials, 2003, 2, 413) using the layer-by-layer assembly technique (LBL). The structure, deformation mechanism, and mechanical properties (ultimate tensile strength (σ_UTS) ~100 MPa and Young’s modulus (E) ~11 GPa) of the material were found to be very similar to those of natural nacre and lamellar bones. More importantly, the nanocomposite was composed of nearly 50 vol.% of well organized and dispersed nanosheets of the montmorillonite (E’ ~260 GPa), which have received substantial interest in the development of reinforced polymeric composites. These results were encouraging for generation of new class of biomimmetic materials and ultra-strong nanocomposites at very high loadings of the reinforcing nanoparticles. I have expanded on this work by exploring different strategies of preparation of the nanocomposites with an ultimate goal of developing ultra-strong and stiff nanocomposites. Some of the approaches I have taken were: replacement of the PDDA with a macroscopically stronger polycation, using a biomimmetic polymer incorporating highly adhesive groups, and covalent and ionic cross-linking of the polymeric matrix to increase the load transfer between the polymer and the filler. All of this research has recently led to the development of a clay nanocomposite with record-high strength and stiffness: σ_UTS ~400 MPa and E’ ~110 GPa.

Images: Idealized internal architecture of a clay-polymer nanocomposite composed of 5.5 bilayers (1 bilayer corresponds to a polymer and clay pair). The ultra-strong, 300-bilayer, free-standing poly(vinyl alcohol)-clay films showing flexibility and transparency.

Images: Scanning electron microscopy images of a cross-section of the 300-bilayer free-standing poly(vinyl alcohol)-clay film showing exceptionally well defined, stratified architecture.

References:

Paul Podsiadlo, Amit K. Kaushik, Ellen M. Arruda, Anthony M. Waas, Bong Sup Shim, Jiadi Xu, Himabindu Nandivada, Benjamin G. Pumplin, Joerg Lahann, Ayyalusamy Ramomoorthy, Nicholas A. Kotov, “Ultra-Strong and Stiff Layered Polymer Nanocomposites”, Science, 318, 80-83, 2007.

Paul Podsiadlo, Nicholas A. Kotov, “Can One Improve Nature’s Design? High-Strength, Transparent, Nacre-Like Nanocomposites from Montmorillonite”, Journal of the American Chemical Society, (in preparation)

Paul Podsiadlo, Zhiyong Tang, Bong Sup Shim, Nicholas A. Kotov, “Counterintuitive Effect of Molecular Strength and Role of Molecular Rigidity on Mechanical Properties of Layer-by-Layer Assembled Nanocomposites”, Nano Letters, 7 (5), 1224-1231, 2007.

Paul Podsiadlo, Zhongqiang Liu, David Paterson, Phillip B. Messersmith, Nicholas A. Kotov, “Fusion of Seashell Nacre and Marine Bioadhesive Analogs: High Strength Nanocomposite by LBL of Clay and DOPA-Polymer”, Advanced Materials, 19, 949-955, 2007.

Paul Podsiadlo, Stephen Paternel, Zhengfei Zhang, Jean-Marie Rouillard, Jungwoo Lee, Erdogan Gulari, Nicholas A. Kotov “Layer-by-Layer Assembly of Nacre-Like Nanostructured Composites with Antimicrobial Properties”, Langmuir, 21 (25), 11915-11921, 2005.

Back to Top ↑
 

Cellulose Nanocrystals Nanocomposites

Cellulose nanocrystals (NCs) are emerging as a new class of reinforcing material for the preparation of high performance nanostructured composites. The combination of their natural and renewable origins with exceptional mechanical properties: bending strength ≈ 10 GPa and E ≈ 150 GPa, make them an attractive nanomaterial for the preparation of low cost, light-weight, and ultra-strong hybrid composites for multitude of applications. Unlike carbon nanotubes (CNTs), their exceptional properties (only 6-7 times lower then those of single walled CNTs) are thus far largely unexplored and currently described nanocrystal reinforced composites possess far lower properties then theoretically achievable. In this project, I am taking a synergistic approach to that with clay nanosheets with the end goal of developing light weight and ultra-strong nanocomposites from cheap and renewable resources. I am also interested in developing novel applications for these thin films.

I am researching preparation of thin film composites from cotton (100-300 nm long) and/or tunicate (a marine animal, several microns long) NCs with different polyelectrolytes using the LBL technique. LBL assembly of the NCs with PDDA polymer results in a nanocomposite with σ_UTS ≈ 40 MPa and E ≈ 2 GPa (as high as 10 GPa from Brillouin light scattering). Post-assembly thermal-treatment increases σ_UTS to ≈ 130 MPa without a change in E.

LBL assemblies of tunicate NCs also show strong antireflection (AR) properties having an origin in a novel highly porous architecture reminiscent of a “flattened matchsticks pile”, created by randomly-oriented and overlapping NCs. At an optimum number of LBL deposition cycles, light transmittance reaches nearly 100% (λ ~400 nm) when deposited on a microscope glass slide and the refractive index is ~1.28 at λ = 532 nm. This first example of LBL layers of tunicate NCs can be seen as an exemplary structure for any rigid axial nanocolloids, for which given the refractive index match, AR properties are expected to be a common property. Similarly, the films exhibit exceptional mechanical properties with E reaching as high as 30 GPa.

Images: A free-standing, 200-bilayer, PDDA-Cotton NCs film with a scanning electron microscopy image of a top surface topography.

Images: Atomic force microscopy images of a single layer of tunicate NCs adsorbed onto a poly(ethylene imine) (PEI) coated silicon wafer.

Images: Scanning electron microscopy image of a porous structure of a 12-bilayer PEI-tunicate NCs LBL film deposited on top of a microscope glass-slide. Light transmittance spectra evolution for a microscope glass slide coated with 0 è 12 bilayers of PEI-NCs.

Images: A photograph of a microscope glass slide partially coated with 12 bilayers of PEI-NCs. 

References:

Paul Podsiadlo, Lang Sui, John Kieffer, Nicholas A. Kotov, “High Speed LBL Assembly of High-Strength Nanocomposites from Cellulose Nanocrystals”, (in preparation)

Paul Podsiadlo, Lang Sui, Yaseen Elkasabi, Peter Burgardt, Jeabeom Lee, Winardi Kusumaatmaja, Ashwini Miryala, Max Shtein, Joerg Lahann, John Kieffer, Nicholas A. Kotov, “Layer-by-Layer Assembled Films of Cellulose Nanowires with Antireflective Properties”, Langmuir, 23 (15), 7901-7906, 2007.

Paul Podsiadlo, Seok-Youl Choi, Bongsup Shim, Jungwoo Lee, Meghan Cuddihy, Nicholas A. Kotov “Molecularly Engineered Nanocomposites: Layer-by-Layer Assembly of Cellulose Nanocrystals”, Biomacromolecules, 6 (6), 2914-2918, 2005.
 

Back to Top ↑