Multifunctional, Light-Weight and Ultra-Strong Nano-Structured Clay/Polymer Composite Thin Films Prepared by Layer-by-Layer Assembly: from Ultra-Low Thermal Conductivity to Antibacterial Coatings

摘要

Nature has evolved highly complex and elegant mechanisms for materials design and synthesis with physical properties that still surpass those of analogous synthetic materials with similar phase composition. Nacre ("the mother of pearl") is one of the best examples of a bottom-up fabricated natural nanocomposite material that exhibits structural robustness, strength, and toughness, despite the brittle nature of its constituents: inorganic CaCC_3 and organic biopolymer. Finding a synthetic pathway to artificial analogs of such materials represents a fundamental milestone in the development of composites. Recently we have reported synthesis of a new composite material produced by sequential deposition of poly(diallyldimethylammonium chloride) (PDDA) and Na~+-Montmorillonite clay nanometer size platelets using layer-by-layer deposition technique (LBL), which closely mimics properties of the nacre. With it's light weight and high mechanical properties: ultimate strength, σ_μ = 100±10 MPa and the Young's modulus, E = 11±2 GPa, nacre analogs possess high potential for applications ranging from the biomedical sciences to space technologies. Given the simplicity of LBL technique and a wide range of polyelectrolytes and nanocolloids available, we set out to further refine and improve the properties of the nacre. We have envisioned further improvement of its mechanical properties by replacing PDDA (σ_μ =1-2 MPa) with a much stronger polymer, e.g. Chitosan (σ_μ = 60-67 MPa) or polysulfones (σ_μ = 70-80 MPa), We have also envisioned imparting additional properties to the composite through inclusion of additional components in the deposition sequence, e.g. Ag nanoparticles for antibacterial properties. Recent investigation into thermo-insulating properties of layered W/A1O_3 composite has also shown that sequential nano-layering results in drastically lowered effective thermal conductivity (k_(effective) = ~0.6 W/mK). With these results, we have realized that our composite has potentially ultra-low thermal conductivity, since it is composed of polymeric and ceramic nanometer size alternating layers. We report here the synthesis of new, potentially even stronger Chitosan/clay and Quaternary Chitosan/clay composites. We also report synthesis and bactericidal properties of novel, ultra-strong antimicrobial thin films from starch stabilized Ag nanoparticles and clay nanosheets. Lastly, we report preliminary results from our investigation into thermo-insulating properties of our clay polymer nanocomposites.