Faculty of Engineering and Natural Sciences
Pınar Kurt, PhD
Massachusetts Institute of Technology
PART-I: Biocidal Polymer Surfaces via Amphiphilic Polymeric Surface Modifiers (PSMs)
This work addresses a methodology for polymer surface functionalization by using polymeric surface modifiers (PSMs). By intelligent design at the molecular level, PSMs provide an antimicrobial functionality at the surface. Being inspired from naturally occurring polypeptides, novel amphiphilic telechelics were engineered for contact biocidal functionality by incorporation in polyurethanes. For this purpose, novel P(AB) telechelics having alkylammonium (B) and either fluorous or PEG-like (A) side chains were generated by oxetane ring opening polymerization. P(AB) telechelics were incorporated into polyurethanes to obtain alkylammonium side chains in 1,3-propylene oxide soft blocks. Six (C6) and twelve carbon (C12) alkylammonium chain lengths were used. An innovative test employing aerosol and other pathogen challenges showed high effectiveness against both Gram(-) (Pseudomonas aeruginosa, Escherichia coli) and Gram(+) (Staphylococcus aureus) bacteria. Later, these effective antimicrobial polyurethanes were used as polymer surface modifiers (PSM). They were coprocessed in 2wt% with conventional polyurethane (98%) and their surface concentration was examined by using XPS), ATR-IR spectroscopyDCA analysis, sessile drop measurement, and TM-AFM. Surface concentration of fluorous and alkylammonium side chains (C6 and C12) was observed. PEG-like PSM showed weak concentration of short alkyl ammonium side chains (C6). However, longer alkylammonium side chains (C12) can “self-chaperone” and surface concentrate better compared to shorter side chain analogs. 2wt% PSM modified polyurethane coatings were tested against aerosol challenges of the same bacteria strains. The 2wt% PSM with soft block containing trifluoroethoxy (A, 89mol%) and C-12 alkylammonium (B, 11mol%) side chains gave the highest biocidal effectiveness against all bacteria strains in 30 min (100% kill, 3.6-4.4 log reduction).
PART-II: Development of Structural Color Based on Layer-by-Layer Assembly of Nanoparticles
Multilayer thin film coatings containing different types of nanoparticles can be used to create variety of functionality with high durability. Functional coatings created by layer-by-layer assembly techniques can exhibit anti-fogging, anti-reflection, self-cleaning properties or combination of them. Additionally, structural colors and optical filters can be designed by using alternating layers of high and low refractive index nanoparticles. The presented project describes methods to obtain different colors with high reflectance. By matrix transfer method, we have created simulation program to optimize optical thicknesses. In order to achieve the designed multilayer thin films, titania nanoparticles with 7 nm mean size were synthesized. Titania and silica nanoparticles were assembled into durable Bragg stacks with <90% reflectance using aqueous layer-by-layer assembly method following high temperature calcination. To have more insight into nanoparticle assembly, growth trend of nanoparticles on various substrates and optical properties were investigated by using TM-AFM, UV-Vis, profilometer and spectroscopic ellipsometer. Effect roughness and intermixing layers were studied by using simulation programs. To widen the palette of nanoparticle types, ceria nanoparticles were synthesized (8nm). Optical properties of ceria thin films were investigated.
June 18, 2008, 10:00, FENS G032