Amphiphilic Silicones with Modern Utility for Marine and Medical Applications
Melissa A. Grunlan, Ph.D.
Charles H. and Bettye Barclay Professor in Engineering
Departments of Biomedical Engineering, Materials Science & Engineering, and Chemistry
Texas A&M University, College Station, Texas, USA
Silicones are extensively used in broad applications, particularly for non-toxic, foul-releasing marine coatings as well as for medical devices such as intraocular lenses (IOLs) and catheters. The utility of silicones stems from unique elastomeric mechanical properties, oxygen permeability, and resistance to degradation. However, the hydrophobicity of silicone surfaces limits their antifouling character. As a result, silicone marine coatings are prone to accumulate a variety marine organism, particularly under static conditions. Silicone IOLs do not inhibit ongrowth of lens epithelial cells (LECs) which leads subsequent posterior capsule opacification (PCO). Silicone catheters are prone to infection and to thrombosis due to the accumulation of bacteria, proteins, and platelets. Thus, we have developed amphiphilic surface modifying additives (SMAs) for facile modification of silicones, including dimethyl- and diphenyl-type silicones. These SMAs are comprised of a hydrophobic siloxane tether (of varying lengths) and a hydrophilic poly(ethylene oxide) (PEO) segment [HSi-ODMSm-block-PEO8-OCH3]. SMA-modified silicones coatings exhibitred a dramatic increase in water-driven surface hydrophilicity, leading to a resistance to biofouling with as little as 1 weight % of SMA. Such coatings were able to dramatically decrease fouling by marine organisms in both lab assays and ocean tests. Resistance to LEC ongrowth was also observed with the incorporation of SMAs into a diphenyl silicone, and improved with longer tether lengths. SMA-modified silicones also showed resistance to bacterial adhesion and thrombus formation, including under flow conditions.
Sustainable Polyelectrolyte Coatings for Flame Retardancy, Food Protection, and High Voltage Insulation
Jaime C. Grunlan
Leland T. Jordan ’29 Chair Professor
Department of Mechanical Eng., Materials Science & Eng. and Chemistry
Texas A&M University, College Station, TX 77840
Abstract
Layer-by-layer (LbL) assembly is a conformal coating “platform” technology capable of imparting a multiplicity of functionalities on nearly any type of surface in a relatively environmentally friendly way. At its core, LbL is a solution deposition technique in which layers of cationic and anionic materials (e.g. nanoparticles, polymers and even biological molecules) are built up via electrostatic attractions in an alternating fashion, while controlling process variables such as pH, coating time, and concentration. Here we are producing nanocomposite multilayers (50 – 1000 nm thick), having 10 – 96 wt% clay, that can be completely transparent, stop gas permeation, impart extreme heat shielding to carbon fiber reinforced polymer composites. Similar films exhibit very high dielectric breakdown strength. In an effort to impart flame retardant behavior to fabric using fewer processing steps, a water-soluble polyelectrolyte complex (PEC) was developed. This nanocoating is comprised of polyethylenimine and poly(sodium phosphate) and imparts self-extinguishing behavior to cotton fabric in just a single coating step. Adding a melamine solution to the coating procedure as a second step renders nylon-cotton blends self-extinguishing. A PEC of PEI and polyacrylic acid is able to achieve an oxygen transmission rate below 0.005 cm3/m2/day at 100%RH and a thickness of just 2 mm. These coating techniques can be deposited using roll-to-roll processing (e.g., flexographic printing, dip-coating, or spray-coating). Opportunities and challenges will be discussed. Our work in these areas has been highlighted in C&EN, ScienceNews, Nature, Smithsonian Magazine, Chemistry World and various scientific news outlets worldwide. For more information, please visit my website: http://nanocomposites.tamu.edu
