Morphology of polypropylene films treated in CO2 plasma

One of the most important claims for the plasma technique as a surface treatment is that it modifies only a few atomic layers of materials. However, with polymers, this assumption must be carefully verified to keep the bulk mechanical properties constant. Besides the oxidation of the film, with specific plasma conditions such as high power and duration, the polypropylene film structure is also modified in the bulk through vacuum ultraviolet absorption and thermal relaxation. This change is associated with smectic- and amorphous-phase transformation into an α-monoclinic phase, with a rapid rate for the smectic transformation and a slower rate for the amorphous transformation. At the same time, the crystallite size increases, and the polypropylene film texture is planar and moderated (1.7 mrd at the maximum of the distribution, with a discharge power of 100 W and a treatment duration of 10 min). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2007–2013, 2004     

Use of a dye‐labeled ethylene‐butene copolymer as a tracer in laser scanning confocal fluorescence microscopy studies of thermoplastic olefins

A benzothioxanthene‐labeled ethylene‐butene rubber has been synthesized and tested as a potential fluorescent tracer for the impact modifier (IM) phase in laser scanning confocal fluorescence microscopy (LSCFM) studies of thermoplastic olefin (TPO) morphology. The amino‐functional Hostasol Yellow derivative HY‐DP reacts with maleated EBR‐28 to give a good labeling yield (ca. 70%) and a dye concentration of 0.051 mmol/g, when the maleated rubber is first refluxed over molecular sieves and the reaction purged with N₂. Without pretreatment of the rubber and N₂ purging, a lower labeling yield (0.036 mmol dye/g) is obtained and the labeled product tends to undergo crosslinking at 240 °C and subsequent dye detachment when the crosslinked gel is hydrolyzed. LSCFM studies reveal HY‐labeled EBR to be completely miscible and evenly dispersed in the unlabeled EBR‐9 of model TPO blends. Moreover, the HY‐labeled EBR provides good fluorescence contrast between the IM droplets and the PP matrix in the TPO blend PP/EBR (80/20) (w/w) + 3 wt % labeled polymer with respect to EBR. Imaging of IM droplets down to 40 μm below the film surface of this blend has been demonstrated. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 239–252, 2001     

Internalization of PLGA nanoparticles coated with poloxamer 188 in glioma cells: A confocal laser scanning microscopy study

Internalization of poloxamer 188-coated PLGA nanoparticles (NPs) in GL261 murine glioma cells was studied using confocal laser scanning microscopy. For visualization, both poloxamer 188 (P188) and PLGA were labeled covalently with fluorescent dyes Rhodamine B and Cyanine5, respectively. The results indicated that the PLGA NPs coated with poloxamer 188 enter a cell as an integral core–shell structure, which can be helpful for gaining further insight into the in vivo performance of surfactant-coated polymeric NPs as core–shell delivery systems     

Stretched polymer surfaces: Atomic force microscopy measurement of the surface deformation and surface elastic properties of stretched polyethylene

The surface structure and surface mechanical properties of low‐ and high‐density polyethylene were characterized by atomic force microscopy (AFM) as the polymers were stretched. The surfaces of both materials roughened as they were stretched. The roughening effect is attributed to deformation of nodular structures, related to bulk spherulites, at the surface. The surface‐roughening effect is completely reversible at tensile strains in the elastic regime and partially reversible at tensile strains in the plastic regime until the polymers are irreversibly drawn into fibers. AFM force versus distance interaction curves, used to measure changes in the stiffness of the surface and the surface elastic modulus as a function of elongation, show that the surfaces become softer as the polymers are drawn into fibers at high strains. At low elastic strains, however, the surface elastic modulus of HDPE increases—attributed to elastic energy stored by the amorphous regions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2263–2274, 2001     

Investigations of the microscopic structure of poly(vinyl alcohol) hydrogels by confocal laser scanning microscopy

The fluorescence mode confocal laser scanning microscopy (CLSM) is introduced as an alternative method to investigate the bulk structure of poly(vinyl alcohol) (PVA) hydrogel. Investigations of the bulk structure of hydrogel samples, prepared by freezing and controlled thawing of aqueous PVA solutions followed by fluorochrome conjugation, were possible in the native state because with this technique water does not need to be removed prior to examination. This is of advantage to other methods, such as scanning electron microscopy, requiring dehydration by critical-point drying or freeze-etching, because both may result in a significant alteration of the gel structure. CLSM images of the hydrogel bulk structure were taken at several successive intervals from the surface into the hydrogel (up to 60 μm) without freeze-fracturing or cutting the sample. Detailed morphological characterization is achievable by superimposing series of images taken at successive intervals and by magnifying special regions of interest. Images of hydrogel bulk structures revealed a continuous, three-dimensional network that originates from phase-separation (spinodal decomposition) during the freezing period. The pore or mesh size in the cryogel increased, from about 2–7 μm, with decreasing PVA concentration. The surface layer was only a few microns thick, and the bulk structure underneath showed neither porosity gradients nor structural orientations. Received: 29 April 2000/Accepted: 18 August 2000     

Detection of protein coatings on nanoparticles surfaces by ToF‐SIMS and advanced electron microscopy

In this study, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and advanced electron microscopy (scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM)) were applied to detect and analyse different nano‐scaled protein coatings on gold nanoparticles (NP). The NP were coated with collagen type I and fibronectin as well as different combinations of these proteins. These two main proteins in human cell organization and tissue formation were identified with the aid of ToF‐SIMS by typical amino acid mass peak detection. In addition, the protein‐coated particles were investigated by TEM and SEM to get information about the protein structure, the protein layer thickness on the particle surfaces and the reaction of NP in different protein solutions. In this study, a differentiation of diverse protein induced particle agglomeration was proven. The investigations of this study were part of the Specific Targeted Research Project CellNanoTox (project no. NMP4‐CT‐2006‐032731) funded by the European Commission under the 6th EU Framework Programme for Research and Technological Development. Copyright © 2013 John Wiley & Sons, Ltd.     

Formation of an intact liposome layer adsorbed on oxidized gold confirmed by three complementary techniques: QCM‐D,AFM and confocal fluorescence microscopy

Supported layers of vesicles of dimyristoyl and dipalmitoyl phosphatidylcholine (DMPC and DPPC) containing cholesterol (CHOL) are adequate models for eukaryotic plasma membranes. Among the possible substrates to support these layers, gold offers the possibility of being used as an electrode for application in sensors. However, the formation of intact liposome layers on gold is not completely understood and several authors use more or less complex strategies to bind the liposomes. In this work we investigate the adsorption of unilamellar vesicles of DMPC, DMPC/CHOL and DMPC/DPPC/CHOL on the surface of oxidized gold using a quartz crystal microbalance with dissipation, atomic force microscopy and laser scanning confocal fluorescence microscopy. The results of all techniques indicate that for lipid concentrations ≥ 0.7 mg?mL^–1 a dense layer of intact liposomes irreversibly adsorbs on the gold surface. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface characterization of plasma‐modified poly(ethylene terephthalate) film surfaces

Poly(ethylene terephthalate) (PET) film surfaces were modified by argon (Ar), oxygen (O₂), hydrogen (H₂), nitrogen (N₂), and ammonia (NH₃) plasmas, and the plasma‐modified PET surfaces were investigated with scanning probe microscopy, contact‐angle measurements, and X‐ray photoelectron spectroscopy to characterize the surfaces. The exposure of the PET film surfaces to the plasmas led to the etching process on the surfaces and to changes in the topography of the surfaces. The etching rate and surface roughness were closely related to what kind of plasma was used and how high the radio frequency (RF) power was that was input into the plasmas. The etching rate was in the order of O₂ plasma > H₂ plasma > N₂ plasma > Ar plasma > NH₃ plasma, and the surface roughness was in the order of NH₃ plasma > N₂ plasma > H₂ plasma > Ar plasma > O₂ plasma. Heavy etching reactions did not always lead to large increases in the surface roughness. The plasmas also led to changes in the surface properties of the PET surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surfaces decreased. Modification reactions occurring on the PET surfaces depended on what plasma had been used for the modification. The O₂, Ar, H₂, and N₂ plasmas modified mainly CH₂ or phenyl rings rather than ester groups in the PET polymer chains to form C? O groups. On the other hand, the NH₃ plasma modified ester groups to form C? O groups. Aging effects of the plasma‐modified PET film surfaces continued as long as 15 days after the modification was finished. The aging effects were related to the movement of C?O groups in ester residues toward the topmost layer and to the movement of C? O groups away from the topmost layer. Such movement of the C?O groups could occur within at least 3 nm from the surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3727–3740, 2004     

Vector potential photoelectron microscopy: hyperspectral image processing and super‐resolution applied to images of a Ca–Al alloy intermetallic phase distribution

Vector potential photoelectron microscopy (VPPEM) produces four dimensional hyper‐spectral data, and image processing is an integral part of the experimental technique. VPPEM is a new class of instrument, and this is the first discussion of some of the data reduction techniques that have been found effective. The point spread function of VPPEM is multidimensional with a high‐frequency component. Although this high‐frequency component is a small fraction of the total spatial response, images with good signal‐to‐noise can be spatially deconvolved to give super resolution images. The VPPEM data reduction process is illustrated by the analysis of the multiple intermetallic phases in a Ca–Al alloy. These phases have been imaged with better than 0.5‐μ spatial resolution. Not all the problems with the data reduction process have been satisfactorily dealt with, and lessons from this work will influence the design of future instruments. Copyright © 2014 John Wiley & Sons, Ltd.     

Melt‐extensional properties and orientation behaviors of polypropylene‐layered silicate nanocomposites

Polypropylene‐layered silicate nanocomposites consisting of three components—pure polypropylene, maleated polypropylene, and organically modified silicate—were prepared by the melt‐intercalation method to investigate melt‐extensional properties such as melt strength, neck‐in test, and orientation behavior. The nanocomposites showed an enhanced tensile modulus, enhanced storage modulus, much enhanced melt tension, and reduced neck‐in during the melt processing as compared with neat polymer. The uniaxial drawing induced the silicate surface to align parallel to the sheet surface. The c and a* axes of the polypropylene crystals were bimodally oriented to the flow direction, and the b axes were oriented to the thickness direction. The bimodal orientation of the polypropylene crystal was enhanced with the concentration of silicates. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 158–167, 2005     

Molecular orientation and mechanical anisotropy of polypropylene sheet containing N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide

Effect of mixing and processing conditions at T‐die extrusion on the structure and mechanical properties is studied for isotactic polypropylene (PP) containing a small amount of β‐form nucleating agent, N,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide. It is found that trigonal β crystals are predominantly formed in the extruded samples containing the nucleating agent irrespective of the mixing and processing conditions, leading to the marked mechanical toughness. On the contrary, the molecular orientation is significantly affected by the mixing and processing conditions. In particular, it should be noted that PP molecules in the extruded sheet which was mixed at high temperature (260 °C) and extruded at low temperature (200 °C) orient perpendicular to the applied flow direction. As a result, the sheet shows anomalous mechanical anisotropy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 424–433, 2009     

Shear‐induced change of exfoliation and orientation in polypropylene/montmorillonite nanocomposites

For the improved dispersion of montmorillonite (MMT) in a polypropylene (PP) matrix, PP/MMT nanocomposites prepared via direct melt intercalation were further subjected to oscillating stress achieved by dynamic packing injection molding. The shear‐induced morphological changes were investigated with an Instron machine, wide‐angle X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The original nanocomposites possessed a partly intercalated and partly exfoliated morphology. A transformation of the intercalated structure into an exfoliated structure occurred after shearing, and a more homogeneous dispersion of MMT in the PP matrix was obtained. However, the increase of the exfoliated structure was accompanied by the scarifying of the orientation of MMT layers along the shear direction. Some bended or curved MMT layers were found for the first time by TEM after shearing. However, the orientation of PP chains in the PP/MMT nanocomposites became very difficult under an external shear force; this indicated that the molecular motion of PP chains intercalated between MMT layers was highly confined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1–10, 2003     

Directly Fabricating Monolayer Nanoparticles on a Polymer Surface by UV‐Induced MMA/DVB Microemulsion Graft Polymerization

Summary: A sequential two‐step method was successfully used for the photografting of methyl methacrylate/1,2‐divinylbenzene (MMA/DVB) microemulsion onto the surface of a poly(propylene) (PP) film. Atomic force microscopy (AFM) images showed that nanoparticles with a cross‐section diameter of 60 nm were directly grafted onto the substrate's surface. Environment scanning electron microscope (ESEM) images proved that the particles formed just a single layer on the surface. The dormant groups on the nanoparticles' surface were a potential factor in the evolution of single layer into multilayer nanoparticles.

The surface morphology of a PP film after being grafted with a MMA/DVB microemulsion. Nanoparticles (about 60 nm in size) are clearly tethered onto the substrate's surface with just one layer.     

Surface‐initiated atom transfer radical polymerization grafting of poly(2,2,2‐trifluoroethyl methacrylate) from flat silicon wafer surfaces

Poly(2,2,2‐trifluoroethyl methacrylate) (PTFEMA), a partially fluorinated polymer, was directly grafted from silicon wafer surfaces by a surface‐initiated atom‐transfer radical polymerization (ATRP). The polymer layer thickness increased linearly with monomer conversion and molecular weight of free polymers in solution. The thickness was mainly determined by the experimental conditions such as activator/deactivator ratio, monomer/catalyst ratio, and monomer concentration. PTFEMA layers of more than 100‐nm thick were obtained. The grafted PTFEMA chains were “living” and allowed the extension of a second block of PMMA. X‐ray photoelectron spectroscopy study showed that the chemical compositions at the surfaces agreed well with their theoretical values. A novel surface‐attachable difunctional initiator was also synthesized and applied to the grafting of PTFEMA. The grafting density was doubled using this difunctional initiator, from 0.48 to 0.86 chains/nm². © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1252–1262, 2006     

Quantitative analysis of near surfaces three‐dimensional orientation of polymer chains in PET and PEN films using polarized ATR FTIR spectroscopy

Polarized attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy was utilized to characterize the three‐dimensional orientation of polymer chains near highly anisotropic surfaces generated by uniaxial drawing. A versatile method was proposed to analyze the molecular orientation of the polymers by combining the experimental refractive indices and optimized contact pressure by an anvil for solving the optical contact problem. This method is effective even when changes in the molecular orientation along the thickness direction caused by drawing are remarkable. In addition, this method enables quantitative comparison of the molecular orientation among different polymers in the same coordinate system. From the molecular orientation analysis of poly (ethylene terephthalate) (PET) and poly (ethylene naphthalate) (PEN), it was revealed that this method has a broader range of applications with high accuracy in estimating the molecular orientation of polymers compared with the conventional methods. The significant changes in the molecular orientation caused by uniaxial and biaxial drawing of PET and PEN films were quantitatively analyzed, and the reasons for the significant in‐plane orientation of PEN chains on the film plane are discussed. In addition, the difference in the molecular orientation between both sides of the films was also demonstrated. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 870–879, 2010     

Surface oxidation process of a diamond‐like carbon film analyzed by difference X‐ray photoelectron spectroscopy

Difference X‐ray photoelectron spectroscopy (D‐XPS) revealed the surface oxidation process of a diamond‐like carbon (DLC) film. Evaluation of surface functional groups on DLC solely by the C 1s spectrum is difficult because the spectrum is broad and has a secondary asymmetric lineshape. D‐XPS clarified the subtle but critical changes at the DLC surface caused by wet oxidation. The hydroxyl (C―OH) group was dominant at the oxidized surface. Further oxidized carbonyl (C?O) and carboxyl (including carboxylate) (COO) groups were also obtained; however, the oxidation of C?O to COO was suppressed to some extent because the reaction required C―C bond cleavage. Wet oxidation cleaved the aliphatic hydrogenated and non‐hydrogenated sp² carbon bonds (C―H sp² and C―C sp²) to create a pair of C―OH and hydrogenated sp³ carbon (C―H sp³) bonds. The reaction yield for C―H sp² was superior at the surface, suggesting that the DLC film was hydrogen rich at the surface. Oxidation of aromatic sp² rings or polycyclic aromatic hydrocarbons such as nanographite to phenols did not occur because of their resonance stabilization with electron delocalization. Non‐hydrogenated sp³ carbon (C―C sp³) bonds were not affected by oxidation, suggesting that these bonds are chemically inert. Copyright © 2014 John Wiley & Sons, Ltd.     

Fabrication and Characterization of an Organic‐Inorganic Gradient Surface made by Polymethylsilsesquioxane (PMSQ)

Summary: A simple method for the fabrication of a chemical composition gradient from organic to inorganic by the pyrolysis of a polymethylsilsesquioxane (PMSQ) thin film in a gradient temperature field is reported. The resultant chemical gradient surface demonstrates gradual changes in wettability, and slight microstructural changes are observed along the substrate.

FT‐IR spectra of gradient PMSQ surface along the length from the unheated side to the heated side.     

Morphology of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) assemblies in diluted aqueous solution and gel studied by atomic force microscopy

Morphologies of poly(ε‐caprolactone)‐b‐poly(ethylene glycol)‐b‐poly(ε‐caprolactone) (PCL‐PEG‐PCL) triblock copolymer self‐assemblies in the diluted solution and in gel were studied by atomic force microscopy (AFM). The copolymer self‐assembled into wormlike aggregates, of uniform diameter, in water. The wormlike aggregates arranged in order to form separate clusters in the diluted copolymer solution; at a higher copolymer concentration, the clusters became bigger and bigger, and packed together to form gel. Copyright © 2008 John Wiley & Sons, Ltd.     

End‐grafting copolymers of styrene and 4‐vinylpyridine on an interacting solid surface

Copolymers of styrene and 4‐vinylpyridine with a styrene fraction f varying from 1 to 0 were grafted onto a silicon substrate in the melt. The grafting reaction and the stability of the grafted chains were investigated by Fourier transform infrared and X‐ray photoelectron spectroscopy. The thickness and surface morphology of the grafted copolymer layers were characterized with ellipsometry and atomic force microscopy (AFM). The copolymer chains were successfully grafted to the surface of the silicon substrate by a reaction between the hydroxyl groups of the nitroxide moiety at the end of the copolymers and the silanol groups on the surface of the silicon wafer. A measurement of the thickness of the grafted copolymer layers showed that the ratio of grafted‐layer thickness to the unperturbed chain radius of gyration decreased with the increasing fraction of 4‐vinylpyridine in the copolymer; this indicated that the grafted layer was strongly attracted to the substrate. In addition, an accelerated grafting process was observed at grafting times ranging from 48 to 72 h for pure poly(4‐vinylpyridine) and copolymers with f values of 0.3 and 0.5. AFM observation revealed that the grafted layers densely and homogeneously covered the silicon substrate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1332‐1343, 2005