A. Evren Özçam

Generation of functional PET microfibers through surface-initiated polymerization

In this study, we report on a facile and robust method by which poly(ethylene terephthalate) (PET) surfaces can be chemically modified with functional polymer brushes while avoiding chemical degradation. The surface of electrospun PET microfibers has been functionalized by growing poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(2-hydroxyethyl methacrylate) (PHEMA) brushes through a multi-step chemical sequence that ensures retention of mechanically robust microfibers. Polymer brushes are grown via “grafting from” atom-transfer radical polymerization after activation of the PET surface with 3-aminopropyltriethoxysilane. Spectroscopic analyses confirm the expected reactions at each reaction step, as well as the ultimate growth of brushes on the PET microfibers. Post-polymerization modification reactions have likewise been conducted to further functionalize the brushes and impart surface properties of biomedical interest on the PET microfibers. Antibacterial activity and protein resistance of PET microfibers functionalized with PDMAEMA and PHEMA brushes, respectively, are demonstrated, thereby making these surface-modified PET microfibers suitable for filtration media, tissue scaffolds, delivery vehicles, and sensors requiring mechanically robust support media.

Generation of functional coatings on hydrophobic surfaces through deposition of denatured proteins followed by grafting from polymerization.

Hydrophilic coatings were produced on flat hydrophobic substrates featuring n-octadecyltrichlorosilane (ODTS) and synthetic polypropylene (PP) nonwoven surfaces through the adsorption of denatured proteins. Specifically, physisorption from aqueous solutions of α-lactalbumin, lysozyme, fibrinogen, and two soy globulin proteins (glycinin and β-conglycinin) after chemical (urea) and thermal denaturation endowed the hydrophobic surfaces with amino and hydroxyl functionalities, yielding enhanced wettability. Proteins adsorbed strongly onto ODTS and PP through nonspecific interactions. The thickness of adsorbed heat-denatured proteins was adjusted by varying the pH, protein concentration in solution, and adsorption time. In addition, the stability of the immobilized protein layer was improved significantly after interfacial cross-linking with glutaraldehyde in the presence of sodium borohydride. The amino and hydroxyl groups present on the protein-modified surfaces served as reactive sites for the attachment of polymerization initiators from which polymer brushes were grown by surface-initiated atom-transfer radical polymerization of 2-hydroxyethyl methacrylate. Protein denaturation and adsorption as well as the grafting of polymeric brushes were characterized by circular dichroism, ellipsometry, contact angle, and Fourier transform infrared spectroscopy in the attenuated total reflection mode.

Photochromic materials with tunable color and mechanical flexibility

Florescence switches based on photochromic compounds have been fabricated previously and identified as potential candidates for information technology. Recently, optically responsive materials with tunable color have been prepared by dissolving photochromic compounds, such as spiropyran (SP), into solutions of various pH or embedding them into sol–gel matrices with adjusted chemical compositions. Here we report on fabricating flexible rubbers with tunable color by embedding SP molecules inside silicone elastomer networks (SENs) based on poly(vinylmethylsiloxane) (PVMS). SP-containing PVMS networks have been further modified either physically by exposing them to ultraviolet/ozone treatment or chemically by attaching functional thiols to the vinyl bonds in PVMS via UV-activated thiol–ene addition. The color hue of the SP–PVMS SENs after exposing to UV light depends on either the UVO dose or the chemical end-functionality of the thiol modifier, respectively. We also present simple methodologies enabling patterning regions in SP-doped SENs with various shapes and colors.

Fermentation of hydrolysate detoxified by pervaporation through block copolymer membranes

The large-scale use of lignocellulosic hydrolysate as a fermentation broth has been impeded due to its high concentration of organic inhibitors to fermentation. In this study, pervaporation with polystyrene-block-polydimethylsiloxane-block-polystyrene (SDS) block copolymer membranes was shown to be an effective method for separating volatile inhibitors from dilute acid pretreated hydrolysate, thus detoxifying hydrolysate for subsequent fermentation. We report the separation of inhibitors from hydrolysate thermodynamically and quantitatively by detailing their concentrations in the hydrolysate before and after detoxification by pervaporation. Specifically, we report >99% removal of furfural and 27% removal of acetic acid with this method. Additionally, we quantitatively report that the membrane is selective for organic inhibitor compounds over water, despite waters smaller molecular size. Because its inhibitors were removed but its sugars left intact, pervaporation-detoxified hydrolysate was suitable for fermentation. In our fermentation experiments, Saccharomyces cerevisiae strain SA-1 consumed the glucose in pervaporation-detoxified hydrolysate, producing ethanol. In contrast, under the same conditions, a control hydrolysate was unsuitable for fermentation; no ethanol was produced and no glucose was consumed. This work demonstrates progress toward economical lignocellulosic hydrolysate fermentation.

Toward the Development of a Versatile Functionalized Silicone Coating

The development of a versatile silicone copolymer coating prepared by the chemical coupling of trichlorosilane (TCS) to the vinyl groups of poly(vinylmethylsiloxane) (PVMS) is reported. The resultant PVMS-TCS copolymer can be deposited as a functional organic layer on a hydrophobic poly(dimethylsiloxane) substrate and its mechanical modulus can be regulated by varying the TCS coupling ratio. In this paper, several case studies demonstrating the versatile properties of these PVMS-TCS functional coatings on PDMS elastomer substrates are presented. Numerous experimental probes, including optical microscopy, Fourier-transform infrared spectroscopy, surface contact angle, ellipsometry, and nanoindentation, are utilized to interrogate the physical and chemical characteristics of these PVMS-TCS coatings.

Multipurpose Polymeric Coating for Functionalizing Inert Polymer Surfaces.

In this work, we report on the development of a highly functionalizable polymer coating prepared by the chemical coupling of trichlorosilane (TCS) to the vinyl groups of poly(vinylmethyl siloxane) (PVMS). The resultant PVMS-TCS copolymer can be coated as a functional organic primer layer on a variety of polymeric substrates, ranging from hydrophilic to hydrophobic. Several case studies demonstrating the remarkable and versatile properties of PVMS-TCS coatings are presented. In particular, PVMS-TCS is found to serve as a convenient precursor for the deposition of organosilanes and the subsequent growth of polymer brushes, even on hydrophobic surfaces, such as poly(ethylene terephthalate) and polypropylene. In this study, the physical and chemical characteristics of these versatile PVMS-TCS coatings are interrogated by an arsenal of experimental probes, including scanning electron microscopy, water contact-angle measurements, ellipsometry, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy.