Maria Celeste R. Tria

Antimicrobial graphene polymer (PVK-GO) nanocomposite films

The first report on the fabrication and application of a nanocomposite containing poly-N-vinyl carbazole (PVK) polymer and graphene oxide (GO) as an antimicrobial film was demonstrated. The antimicrobial film was 90% more effective in preventing bacterial colonization relative to the unmodified surface. More importantly, the nanocomposite thin film showed higher bacterial toxicity than pure GO-modified surface.

Antimicrobial applications of electroactive PVK-SWNT nanocomposites.

The antibacterial properties of a nanocomposite containing an electroactive polymer, polyvinyl-N-carbazole (PVK) (97 wt %), and single-walled carbon nanotubes (SWNT) (3 wt %) was investigated as suspensions in water and as thin film coatings. The toxic effects of four different PVK-SWNT (97:3 wt %) nanocomposite concentrations (1, 0.5, 0.05, and 0.01 mg/mL) containing 0.03, 0.015, 0.0015, and 0.0003 mg/mL of SWNT, respectively, were determined for planktonic cells and biofilms of Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). The results showed that the nanocomposite PVK-SWNT had antibacterial activity on planktonic cells and biofilms at all concentration levels. Higher bacterial inactivation (94% for E. coli and 90% for B. subtilis) were achieved in planktonic cells at a PVK-SWNT concentration of 1 mg/mL. Atomic force microscopy (AFM) imaging showed significant reduction of biofilm growth on PVK-SWNT coated surfaces. This study established for the first time that the improved dispersion of SWNTs in aqueous solutions in the presence of PVK enhances the antimicrobial effects of SWNTs at very low concentrations. Furthermore, PVK-SWNT can be used as an effective thin film coating material to resist biofilm formation.

Electrochemical Deposition and Surface-Initiated RAFT Polymerization: Protein and Cell-Resistant PPEGMEMA Polymer Brushes

This paper introduces a novel and versatile method of grafting protein and cell-resistant poly(poly ethylene glycol methyl ether methacrylate) (PPEGMEMA) brushes on conducting Au surface. The process started with the electrochemical deposition and full characterization of an electro-active chain transfer agent (CTA) on the Au surface. The electrochemical behavior of the CTA was investigated by cyclic voltammetry (CV) while the deposition and stability of the CTA on the surface were confirmed by ellipsometry, contact angle, and X-ray photoelectron spectroscopy (XPS). The capability of the electrodeposited CTA to mediate surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization on both the polymethyl methacrylate (PMMA; model polymer) and PPEGMEMA brushes was demonstrated by the increase in thicknesses of the films after polymerization. Contact angles also decreased with the incorporation of the more hydrophilic brushes. Significant changes in the morphologies of the films before and after polymerization were also observed with atomic force microscopy (AFM) analyses. Furthermore, XPS results showed an increase in the O 1s peak intensity relative to C 1s after polymerizations, which confirmed the grafting of polyethyleneglycol (PEG) bearing brushes. The ability of the PPEGMEMA-modified Au surface to resist nonspecific adhesion of proteins and cells was monitored and confirmed by XPS, ellipsometry, contact angle, AFM, and fluorescence imaging. The new method presented has potential application as robust protein and cell-resistant coatings for electrically conducting electrodes and biomedical devices.

Hydrodynamic Transformation of a Freestanding Polymer Nanosheet Induced by a Thermoresponsive Surface

Freestanding quasi-two-dimensional ultrathin films (e.g., 41 nm thick polymer nanosheets) were produced, on which stimuli-responsive 47 nm thick polymer brushes were constructed by atom transfer radical polymerization (ATRP) of poly(N-isopropylacrylamide). The resulting surfaces of the multilayered polysaccharide ultrathin films were evaluated by ellipsometry, IR imaging, in situ variable-temperature atomic force microscopy (AFM), and contact angle measurements. The morphological transformation of the freestanding polymer nanosheet bearing thermoresponsive polymer brushes was observed macroscopically through reversible structural color changes at the air-water interface. The dynamic shape change of the nanosheet was also monitored with the addition of a surfactant such as sodium n-dodecylsulfate to reduce the hydrophobicity of the surface. It was then demonstrated that the highly flexible freestanding polymer nanosheet is capable of acting as a unique platform for inducing stimuli-responsive behavior in nanomaterials.

PVK/MWNT Electrodeposited Conjugated Polymer Network Nanocomposite Films

The facile preparation of poly (N-vinyl carbazole) (PVK) and multiwalled carbon nanotubes (MWNTs) solution and conjugated polymer network (CPN) nanocomposite film is described. The stable solutions of PVK/MWNT were prepared in mixed solvents by simple sonication method, which enabled successful deaggregation of the MWNTs with the polymer matrix. MWNT was most effectively dissolved in N-cyclohexyl-2-pyrrolidone (CHP) compared to other solvents like N-methyl pyrrolidone (NMP), dimethyl formamide, and dimethyl sulfoxide (DMSO). The composite solution was relatively stable for months with no observable precipitation of the MWNTs. Thermogravimmetric analysis (TGA) revealed the thermal stability of the nanocomposite while the differential scanning calorimetry (DSC) showed an increasing melting (T(m)) and glass transition (T(g)) temperatures as the fraction of the MWNTs in the nanocomposite was increased. Cyclic voltammetry (CV) allowed the electrodeposition of the nanocomposite film on indium tin oxide (ITO) substrates and subsequent cross-linking of the carbazole pendant group of the PVK to form CPN films. Ultraviolet-visible (UV-vis), fluorescence, and Fourier transform infrared (FTIR) confirmed film composition while atomic force microscopy (AFM) revealed its surface morphology. Four-point probe measurements revealed an increase in the electrical conductivity of the CPN nanocomposite film as the composition of the MWNTs was increased: 5.53 × 10(-4) (3% MWNTs), 0.53 (5%), and 1.79 S cm(-1) (7%). Finally, the interfacial charge transfer resistance and ion transport on the CPN nanocomposite film was analyzed by electrochemical impedance spectroscopy (EIS) with a measured real impedance value of ∼48.10 Ω for the 97% PVK and 3% MWNT ratio of the CPN nanocomposite film.

Electrochemically crosslinked surface-grafted PVK polymer brushes as a hole transport layer for organic photovoltaics

Electrochemically crosslinked surface-grafted poly(N-vinylcarbazole) (PVK) brushes as hole transport layers (HTLs) on a photovoltaic device have been demonstrated using SI-RAFT polymerization. Comparable performance to PEDOT:PSS/P3HT:PCBM based devices was achieved. A main advantage is strong adhesion to ITO with a possible long-term stability against acid dopants and oxygen.

Polymer catenanes via a supramolecularly templated ATRP initiator

Synthesis of polymer catenanes via a living radical polymerization and supramolecular template approach are demonstrated. The ring closure was performed via atom transfer radical cross coupling (ATRC) to obtain polymer catenanes from the linear polymer metal complex precursor.

Electropatterning of Binary Polymer Brushes by Surface-initiated RAFT and ATRP

A new, simple, and effective method for preparing binary patterned brushes by electrodeposition and self-assembly is presented. The technique involves the use of electrochemistry to immobilize a chain transfer agent (CTA) on a patterned conducting substrate that mediate surface-initiated polymerization (SIP) through a reversible addition-fragmentation chain transfer (RAFT) process. The non-electropatterned surfaces were then backfilled with self-assembly of an atom transfer radical polymerization (ATRP) silane initiator where the polymerization of the next brush was initiated. The use of techniques such as RAFT and ATRP is well known to give a controlled polymerization mechanism, which would be of great advantage in generating binary patterned brushes. FT-IR imaging was used to analyze these films.

Permeability of anti-fouling PEGylated surfaces probed by fluorescence correlation spectroscopy

The present work reports on in situ observations of the interaction of organic dye probe molecules and dye-labeled protein with different poly(ethylene glycol) (PEG) architectures (linear, dendron, and bottle brush). Fluorescence correlation spectroscopy (FCS) and single molecule event analysis were used to examine the nature and extent of probe-PEG interactions. The data support a sieve-like model in which size-exclusion principles determine the extent of probe-PEG interactions. Small probes are trapped by more dense PEG architectures and large probes interact more with less dense PEG surfaces. These results, and the tunable pore structure of the PEG dendrons employed in this work, suggest the viability of electrochemically-active materials for tunable surfaces.

RAFT “grafting-through” approach to surface-anchored polymers: Electrodeposition of an electroactive methacrylate monomer

Abstract.The synthesis of homopolymer and diblock copolymers on surfaces was demonstrated using electrodeposition of a methacrylate-functionalized carbazole dendron and subsequent reversible addition-fragmentation chain transfer (RAFT) “grafting-through” polymerization. First, the anodically electroactive carbazole dendron with methacrylate moiety (G1CzMA) was electrodeposited over a conducting surface (i.e. gold or indium tin oxide (ITO)) using cyclic voltammetry (CV). The electrodeposition process formed a crosslinked layer of carbazole units bearing exposed methacrylate moieties. This film was then used as the surface for RAFT polymerization process of methyl methacrylate (MMA), styrene (S), and tert-butyl acrylate (TBA) in the presence of a free RAFT agent and a free radical initiator, resulting in grafted polymer chains. The molecular weights and the polydispersity indices (PDI) of the sacrificial polymers were determined by gel permeation chromatography (GPC). The stages of surface modification were investigated using X-ray photoelectron spectroscopy (XPS), ellipsometry, and atomic force microscopy (AFM) to confirm the surface composition, thickness, and film morphology, respectively. UV-Vis spectroscopy also confirmed the formation of an electro-optically active crosslinked carbazole film with a