Surface Modification of Polyethylene with Multi-End-Functional Polyethylene Additives

We have prepared and characterized a series of multifluorocarbon end-functional polyethylene additives, which when blended with polyethylene matrices increase surface hydrophobicity and lipophobicity. Water contact angles of >112° were observed on spin-cast blended film surfaces containing less than 1% fluorocarbon in the bulk, compared to 98° in the absence of any additive. Crystallinity in these films gives rise to surface roughness that is an order of magnitude greater than is typical for amorphous spin-cast films but is too little to give rise to superhydrophobicity. X-ray photoelectron spectroscopy (XPS) confirms the enrichment of the multifluorocarbon additives at the air surface by up to 80 times the bulk concentration. Ion beam analysis was used to quantify the surface excess of the additives as a function of composition, functionality, and molecular weight of either blend component. In some cases, an excess of the additives was also found at the substrate interface, indicating phase separation into self-stratified layers. The combination of neutron reflectometry and ion beam analysis allowed the surface excess to be quantified above and below the melting point of the blended films. In these films, where the melting temperatures of the additive and matrix components are relatively similar (within 15 °C), the surface excess is almost independent of whether the blended film is semicrystalline or molten, suggesting that the additive undergoes cocrystallization with the matrix when the blended films are allowed to cool below the melting point

Espacialização da precipitação pluvial por meio de krigagem e cokrigagem

O objetivo deste trabalho foi avaliar a cokrigagem ordinária, com dados de altitude e distância do mar, em comparação à krigagem ordinária, na espacialização da precipitação pluvial dos períodos anual, seco e úmido, no Estado do Espírito Santo. Os dados de altitude e distância do mar foram obtidos de pontos de amostragem em grades regulares e irregulares. Foram utilizados dados de 108 postos pluviométricos. A avaliação dos métodos e das variáveis foi realizada com base na validação cruzada, tendo-se considerado os erros dos valores preditos e o ajuste dos modelos de regressão linear para valores observados e preditos. A grade regular para amostragem das covariáveis apresentou melhor acurácia de predição em comparação à grade irregular. A cokrigagem produziu resultados mais acurados do que a krigagem, verificados por pequenas diferenças nos erros médios absolutos, capazes de produzir mapas estatisticamente diferentes. A interpolação por cokrigagem e o uso de grades regulares para amostragem são preferíveis, principalmente se as covariáveis são de fácil obtenção e de baixo custo

Neutron reflectivity studies at liquid-liquid interfaces: Methodology and analysis

A protocol is described for measuring and analyzing neutron reflectivity data from a buried oil-water interface. A hexadecane-water interface is considered, and data from the bare interface and from films of polybutadiene-poly(ethylene oxide) Linear diblock copolymers with M-w similar to 60 000 g mol(-1) and containing similar to 50 mol % poly(ethylene oxide) spread (with interfacial concentrations of Gamma = 4 and 10 mg m(-2)) at the interface are reported. From the analysis, it emerges that the hexadecane-water interface is "rougher" than capillary wave theory based expectations. This could be attributable to the influence of molecular size and shape on the intrinsic thickness of the interface. When present, the amphiphilic copolymers segregate at the interface with the blocks occupying a concentrated region (similar to 20% polymer) with thickness similar to 20 Angstrom and a dilute region (much less than 10% polymer) of thickness similar to 50 Angstrom on either side of a nominal dividing surface. The amount of copolymer at the interface, determined using a Guinier-type analysis, is in line with the spread amount at the interface at a moderate (Gamma = 4 mg m(-2)) interfacial concentration but is consistent with a more expanded configuration at Gamma = 10 mg m(-2)

Structure of a spread film of a polybutadiene-poly(ethylene oxide) linear diblock copolymer at the air-water interface as determined by neutron reflectometry

The structure of a film of a linear diblock copolymer of polybutadiene-poly(ethylene oxide) with a molecular mass of similar to 60 000 g mol(-1) and containing similar to 50 mol % poly(ethylene oxide) PEO spread on water has been investigated using neutron reflectometry. The reflectivity data have been analyzed using the optical matrix method and the kinematic approximation. From the optical matrix analysis it is found that at low surface concentrations (Gamma = 0.45, 0.83 mg m(- 2)), the reflectivity data are well described using a two-layer model, indicating that even at low concentrations the blocks of the copolymer are segregated. According to this model the polybutadiene (PB) block resides in a thin similar to3-5 Angstrom layer containing similar to 50% (by volume) polymer and indeterminate quantities of water and PEG. The PEG is accommodated in a slightly thicker layer (similar to6-11 Angstrom), and this solvated layer contains similar to 30% PEG and a negligible amount of PB. The amount of material in these layers determined from the reflectivity data agrees well with the spread amount. At higher surface concentrations (Gamma = 2.06 mg m(-2)), however, st more complex model is required to represent the data. Superficially, the two-layer model is modified by accommodating similar to 13% of PB in the PEG- enriched layer and by adding a third similar to 100 Angstrom layer containing a mixture of PB (10%) and PEO (15%). From this model it can be inferred that at this surface concentration any PEO brushlike structure is accompanied by a higher-level structure containing "submerged" PB. It is feasible that surface aggregates of copolymer are incorporated into the region underlying the segregated monolayer structure; this is suggested by an inflection or "nonhorizontal" transition in the surface-pressure isotherm. This behavior is not dissimilar to that found for adsorbed films of polystyrene-b-poly(ethylene oxide) at the air-water interface. Analysis using the kinematic approximation supports and reinforces the observations supplied by the optical matrix fitting

Antimicrobial peptide-lipid binding interactions and binding selectivity

Surface pressure measurements, external reflection- Fourier transform infrared spectroscopy, and neutron re. flectivity have been used to investigate the lipid-binding behavior of three antimicrobial peptides: melittin, magainin II, and cecropin P1. As expected, all three cationic peptides were shown to interact more strongly with the anionic lipid, 1,2 dihexadecanoyl-sn-glycerol3-( phosphor-rac-( 1- glycerol)) ( DPPG), compared to the zwitterionic lipid, 1,2 dihexadecanoyl-sn-glycerol-3-phosphocholine ( DPPC). All three peptides have been shown to penetrate DPPC lipid layers by surface pressure, and this was confirmed for the melittin-DPPC interaction by neutron reflectivity measurements. Adsorption of peptide was, however, minimal, with a maximum of 0.4 mg m(-2) seen for melittin adsorption compared to 2.1 mg m(-2) for adsorption to DPPG ( from 0.7 mu M solution). The mode of binding to DPPG was shown to depend on the distribution of basic residues within the peptide alpha-helix, although in all cases adsorption below the lipid layer was shown to dominate over insertion within the layer. Melittin adsorption to DPPG altered the lipid layer structure observed through changes in the external reflection-Fourier transform infrared lipid spectra and neutron reflectivity. This lipid disruption was not observed for magainin or cecropin. In addition, melittin binding to both lipids was shown to be 50% greater than for either magainin or cecropin. Adsorption to the bare air-water interface was also investigated and surface activity followed the trend melittin. magainin. cecropin. External re. ection- Fourier transform infrared amide spectra revealed that melittin adopted a helical structure only in the presence of lipid, whereas magainin and cecropin adopted helical structure also at an airwater interface. This behavior has been related to the different charge distributions on the peptide amino acid sequences

Neutron reflectivity studies of critical adsorption behaviour of the surface scaling function

Neutron reflectometry has been employed to examine the nature of the critical adsorption surface scaling function for a near critical mixture of hexane d14 perfluorohexane adsorbing to a solid substrate from the liquid one phase region. The analysis method of Dietrich and Schack has been applied to examine the nature of the power law part of the critical adsorption surface scaling function, which has been found to behave as m z P0z amp; 8722;m as the critical point is approached. Values of m 0.514 0.018 and P0 0.90 0.04 have been obtained. These values are consistent with theoretical expectations mth 0.516 0.004; P0th 0.94 0.05 , the value determined from Monte Carlo simulations P0MC 0.866 , and other experimental determinations P0ex 0.955 0.0

Aggregation, adsorption, and surface properties of multiply end-functionalized polystyrenes

The properties of polystyrene blends containing deuteriopolystyrene, multiply end-functionalized with C8F17 fluorocarbon groups, are strikingly analogous to those of surfactants in solution. These materials, denoted FxdPSy, where x is the number of fluorocarbon groups and y is the molecular weight of the dPS chain in kg/mol, were blended with unfunctionalized polystyrene, hPS. Nuclear reaction analysis experiments show that FxdPSy polymers adsorb spontaneously to solution and blend surfaces, resulting in a reduction in surface energy inferred from contact angle analysis. Aggregation of functionalized polymers in the bulk was found to be sensitive to FxdPSy structure and closely related to surface properties. At low concentrations, the functionalized polymers are freely dispersed in the hPS matrix, and in this range, the surface excess concentration grows sharply with increasing bulk concentration. At higher concentrations, surface excess concentrations and contact angles reach a plateau, small-angle neutron scattering data indicate small micellar aggregates of six to seven F2dPS10 polymer chains and much larger aggregates of F4dPS10. Whereas F2dPS10 aggregates are miscible with the hPS matrix, F4dPS10 forms a separate phase of multilamellar vesicles. Using neutron reflectometry (NR), we found that the extent of the adsorbed layer was approximately half the lamellar spacing of the multilamellar vesicles. NR data were fitted using an error function profile to describe the concentration profile of the adsorbed layer, and reasonable agreement was found with concentration profiles predicted by the SCFT model. The thermodynamic sticking energy of the fluorocarbon-functionalized polymer chains to the blend surface increases from 5.3kBT for x = 2 to 6.6kBT for x = 4 but appears to be somewhat dependent upon the blend concentration