Surface Modification of Nitrile Rubber by Plasma Polymerization

Radio frequency plasma polymerization of vinylidene fluoride was used to modify the surface properties of nitrile rubber. The chemistry and frictional properties of the plasma films were characterized. FTIR transmission spectra and EDX analysis of plasma polymer films deposited on NaCl windows showed that the degree of fluorination of the plasma polymers increased as plasma power was increased from 25 to 50 W, and then decreased monotonically at higher powers. An estimation of the actual F/C ratio from EDX data indicated that the plasma polymer films contained approximately one fluorine atom for every 2–5 carbon atoms. Sliding friction tests on a Delrin countersurface showed that the coefficient of friction of the plasma treated rubbers was lower than untreated rubber, but slighly higher than rubber coated with silicone oil. Repetitive sliding friction testing showed that silicone oil treated samples had a longer lubricating lifetime than plasma treated samples. However, cyclic friction tests conducted with nitrile rubber o-rings yielded similar frictional behavior and lubricating lifetimes for silicone oil and plasma treatments. There was no correlation between chemical composition and the frictional and wear properties of the plasma films. Environmental scanning electron micrographs showed that the plasma films were brittle and tended to crack and flake off during wear testing.     

Reorganization of the structures,morphologies, and conformations of bulk polymers via coalescence from polymer–cyclodextrin inclusion compounds

Bulk poly(ethylene terephthalate) (PET) and bisphenol A polycarbonate (PC) samples have been produced by the coalescence of their segregated, extended chains from the narrow channels of the crystalline inclusion compounds (ICs) formed between the γ‐cyclodextrin (CD) host and PET and PC guests, which are reported for the first time. Differential scanning calorimetry, Fourier transform infrared, and X‐ray observations of PET and PC samples coalesced from their crystalline γ‐CD‐ICs suggest structures and morphologies that are different from those of samples obtained by ordinary solution and melt processing techniques. For example, as‐received PC is generally amorphous with a glass‐transition temperature (T_g) of about 150 °C; when cast from tetrahydrofuran solutions, PC is semicrystalline with a melting temperature (T_m) of about 230 °C; and after PC/γ‐CD‐IC is washed with hot water for the removal of the host γ‐CD and for the coalescence of the guest PC chains, it is semicrystalline but has an elevated T_m value of about 245 °C. PC crystals formed upon the coalescence of highly extended and segregated PC chains from the narrow channels in the γ‐CD host lattice are possibly more chain‐extended and certainly more stable than chain‐folded PC crystals grown from solution. Melting the PC crystals formed by coalescence from PC/γ‐CD‐IC produces a normal amorphous PC melt that, upon cooling, results in typical glassy PC. PET coalesced from its γ‐CD‐IC crystals, although also semicrystalline, displays a T_m value only marginally elevated from that of typical bulk or solution‐crystallized PET samples. However, after the melting of γ‐CD‐IC‐coalesced PET crystals, it is difficult to quench the resultant PET melt into the usual amorphous PET glass, characterized by a T_g value of about 80 °C. Instead, the coalesced PET melt rapidly recrystallizes during the attempted quench, and so upon reheating, it displays neither a T_g nor a crystallization exotherm but simply remelts at the as‐coalesced T_m. This behavior is unaffected by the coalesced PET sample being held above T_m for 2 h, indicating that the extended, unentangled nature of the chains in the noncrystalline regions of the coalesced PET are not easily converted into the completely disordered, randomly coiled, entangled melt. Apparently, the highly extended, unentangled characters of the PC and PET chains in their γ‐CD‐ICs are at least partially retained after they are coalesced. Initial differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared, and X‐ray observations are described here. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 992–1012, 2002     

Surface modification of chlorobutyl rubber by plasma polymerization

Radio frequency (r.f.) plasma polymerization of vinylidene fluoride (CH₂CF₂) has been used to modify the surface properties of chlorobutyl rubber. FTIR-ATR spectra of the treated rubbers and transmission spectra of plasma polymer films on NaCl windows indicated that as power increased the F/H ratio decreased. SIMS tests supported the FTIR results, and showed that the decrease in the F/H ratio was due to a decrease in the amount of F and an increase in the amount of H in the plasma polymer. Sliding friction measurements showed a reduction in the coefficient of friction (μ) from 3.7 for the untreated rubber to values ranging between 0.4 and 1.9 for the plasma-treated rubbers. There did not appear to be any correlation between the coefficient of friction and plasma power or monomer flow rate, and the average coefficient of friction for the plasma-treated samples was 0.9, which was lower than a commercially used silicone oil treatment (μ = 1.1–1.3). Repetitive sliding friction tests showed that the plasma- and silicone oil treated-chlorobutyl rubbers had the similar lubricating lifetimes. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1651–1660, 1997     

X-ray microscopy of novel thermoplastic/liquid crystalline polymer blends by mechanical alloying

Incorporation of liquid crystalline polymers (LCPs) into commodity polymers remains a challenge in the design of high-performance, low-cost polymeric blends. Blends of a thermoplastic polymer and a nematic LCP are produced here by mechanical alloying. Functionality sensitive X-ray microscopy reveals LCP dispersions as small as 100 nm in diameter. Intimate mixing remains upon subsequent melt processing, indicating that mechanical alloying is suited for applications such as recycling.     

XPS study of silver and copper nanoparticles demonstrated selective anticancer,proapoptotic, and antibacterial properties

Silver and copper nanoparticles were produced by an ecologically safe metal vapor synthesis (MVS) method using acetone as an organic dispersion medium. Transmission electron microscopy (TEM) showed that the specimens are spherical and polydisperse, and their average size is 2.5 nm for silver nanoparticles (Ag NPs) and 2.6 nm for copper nanoparticles (Cu NPs). X-ray photoelectron spectroscopy analyses showed that the state of silver in the nanoparticles is close to that of silver in the Ag⁰ state, whereas copper black contains two oxidized states of the metal—Cu⁺ and Cu²⁺. Biological in vitro studies demonstrated that the nanoparticles have antibacterial activity against Gram-positive and Gram-negative bacterial species. Cu NPs exhibited more prominent antibacterial effects and induced significant growth inhibition of Bacillus cereus and Escherichia coli. Both types of nanoparticles showed anticancer properties in vitro. Cu NPs induced intense cytotoxicity in cancer and normal fibroblasts in vitro cultures, but their inhibitory effect against noncancerous cells was milder compared with cancer cell lines. Ag NPs demonstrated selective cytotoxicity against human lung and cervical adenocarcinoma cell lines. Further in vitro studies indicated that the mechanism of Ag NPs and Cu NPs anticancer effects involves induction of apoptosis. The present study describes a green synthesis approach for production of biologically active silver and copper nanoparticles and highlights their potential for medical application.     

The Nano-threading of Polymers

When guest polymers are threaded by host cyclodextrins (CDs) to form crystalline inclusion compounds (ICs), the included polymer chains are highly extended and separated from neighboring chains. This is a consequence of the stacking of the cyclic oligosaccharides, α-, β-, or γ-CD containing 6, 7, or 8 glucose units, respectively, which produces continuous narrow channels (~0.5–1.0 nm diameters), where the guest polymers are included and confined. Observations that illuminate several important aspects of the nano-threading of polymers to form polymer-CD-ICs are described. These include (i) the competitive CD threading of polymers with different chemical structures and molecular weights from their solutions containing suspended solid or dissolved CDs, (ii) the threading and insertion of undiluted liquid polymers into solid CDs, and (iii) suspension of polymer A or B-CD-IC crystals in a solution of polymer B or A and observation of the transfer of polymer B or A from solution to displace polymer A or B and form polymer B or A-CD-ICs, without dissolution of the CD-ICs. In addition, we report observations of polyolefins adsorbed on zeolites, where we believe the adsorbed polyolefin chains are actually threaded and absorbed into the interiors of the zeolite nano-pores, rather than adsorbed on the zeolite surfaces. All of the above observations were made to assist in answering the question “Why do randomly-coiling polymer chains in solution or the melt become threaded or thread into the nano-pores of dissolved or solid CDs and solid zeolites, where they are highly extended and segregated from other polymer chains?” Though still not fully able to answer this question, we are able to assess the importance of several factors that have been previously suggested to be important in the formation of CD-ICs with both polymer and small-molecule guests and to the nano-threading of polymers in general. In particular, the value in observations of the inclusion of guest polymers, as well as small-molecule guests, into solid CDs suspended in their solutions and in neat guest liquids were made apparent, because interactions between host CDs, between CDs and solvents, and between quests and solvents, which complicate and make understanding the formation of polymer-CD-ICs difficult, are either eliminated or can be independently varied in these experiments.     

Epitaxial morphologies of polyoxymethylene. II. Deposition energetics on alkali halide (001) surfaces

Molecular mechanics energy calculations have been used to assess the relative affinities that an iodobenzene solvent molecule and a segment of a polyoxymethylene chain have for five different alkali halide (001) surfaces. Dispersive-repulsive and coulombic contributions to the interaction energy have been included. The calculated interaction deposition energy correlates well with the nucleation density of rodlike epitaxial crystals formed on these substrates in epitaxial crystallization experiments from solution. Substrates which have a higher preference for solvent (LiF and NaF) than for polymer exhibit relatively low polymer nucleation densities. As the degree of solvent preference decreases, and polymer preference increases, higher nucleation densities are observed (KCI and KI). These results suggest that preferential solvent adsorption may account for the low nucleation densities observed on some substrates in polymer epitaxial crystallization experiments from solution.     

High-energy ion implantation of polymers: Poly(ethylene terephthalate)

The effect of high-energy ion implantation of oxygen into a thin film of poly(ethylene terephthalate) (PET) was studied by Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC). Mylar samples 13 μm thick were implanted with 6-MeV oxygen ions at fluences ranging from 5 × 10¹² to 2 × 10¹⁴ ions/cm². The DSC data showed a substantial loss of crystallinity, even at the lowest fluence, which extended deeper into the polymer film than the predicted range for oxygen deceleration in PET. Solubility measurements indicated the presence of cross-linking, especially at the highest fluence, but bands due to cross-linking could not be detected in the infrared. The trans/gauche ratio for the glycol group conformation was measured by a pair of conformationally sensitive infrared bands. Surprisingly, the conformation of the glycol segments did not change appreciably with increasing fluence, although crystallinity decreased and degree of cross-linking increased. The implications these results have on possible mechanisms of chemical and physical alterations of the polymer structure by ion implantation are discussed.     

Formation of crystalline inclusion compounds of poly (vinyl chloride) of different stereoregularity with γ-cyclodextrin

This work reports the formation and detailed characterization of the γ-cyclodextrin (γ-CD) inclusion compounds (ICs) formed with two poly (vinyl chloride) samples with different isotactic content. The ICs were characterized by X-ray diffraction, solid state ¹³C-NMR, solution ¹H-NMR, FT-infrared, differential scanning calorimetry, and thermogravimetric analysis. Experimental evidence of the inclusion of the guest polymer chains into the narrow channels created by the γ-CD crystalline host lattice has been obtained. Examination of coalesced poly (vinyl chlorides) (PVCs) obtained after the host γ-CD is removed reveals different characteristics specifically for the coalesced PVC sample with higher isotactic content. An increase in T_g was observed by DSC for this PVC. To the contrary, the T_g of the coalesced PVC sample with lower isotactic content is almost the same as that of the as-synthesized sample. Thermogravimetric analysis indicated that coalesced PVC with higher isotactic content acquires a degree of stabilization after modification by threading into and being extracted from its γ-CD IC. The results suggest that an irreversible conformational change takes place when PVC forms ICs with a solid host lattice like γ-CD. The PVC molecules extend and reorganize into a more stable conformation in the IC, consequently improving the properties of the coalesced sample. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2503–2513, 2007