Copolymers, surface composition

Magonov, S.N., Elings, V., Cleveland, J., Denley, D., and Whangbo, M.-H., Tapping-mode atomic force microscopy study of the near-surface composition of a styrene-butadiene-styrene triblock copolymer film, Surf. Sci., 389, 201, 1997. 

Table V. Influence of Siloxane Graft Molecular Weight and Composition on Surface Composition of PMMA-g-PSX Copolymers by Variable Angle XPS (ESCA) (Copolymers 5 wt.% PSX)...

Xu C, Barnes SE, Wu T, Eischer DA, DeLongchamp DM, Batteas JD, Beers KL (2006) Solution and surface composition gradients via microfluidic confinement fabrication of a statistical-copolymer-brush composition gradient. Adv Mater 18 1427-1430... 

Chen, Gardella and Kumler106 have studied a series of polydimethylsiloxane-polystyrene block copolymers and examined the surface composition by ATR-FTIR and XPS. For AB-type PS-PDMS diblock copolymers (26) with siloxane block molecular weights of between 38,000 and 99,000, the surface was found to be exclusively polydimethylsiloxane down to a depth of 10 nm by XPS. ATR-FTIR, which samples... 

A laser beam was used for graft polymerization of AAc onto a tetrafluo-roethylene-perfluoroalkyl vinyl ether copolymer film [81]. The film placed in contact with AAc solution was irradiated with KrF laser through the film to excite the film/solution interface. Surface composition of the grafted film determined by XPS revealed an extensive loss of fluorine atom and an increase of oxygen atom in addition to the presence of a Cls line shape, similar to that of AAc monomer. Mirzadeh et al. [82] used pulsed laser beam for the graft polymerization of AAm on a rubber surface in the presence of a photosensitizer, ben-zophenone, or AIBN. 

Colloid characterization is not the classical application of Th-FFF. Nevertheless, Th-FFF was first applied to silica particles suspended in toluene testing a correlation between thermal diffusion and thermal conductivity [397]. Although a weak retention was achieved, no further studies were carried out until the work of Liu and Giddings [398] who fractionated polystyrene latex beads ranging from 90 to 430 nm in acetonitrile applying a low AT of only 17 K. More recently, polystyrene and polybutadiene latexes with particle sizes between 50 pm and 10 pm were also fractionated in aqueous suspensions despite the weak thermal diffusion [215] (see Fig. 30). Th-FFF is also sensitive to the surface composition of colloids (see the work on block copolymer micelles), recent effort in this area has been devoted to analyzing surfaces of colloidal particles [399,400]. 

Films of the three block copolymers were cast from chloroform, a mutual solvent for PS and PEO,( ) and the measured and 0. core level spectra are shown in Figure 2. The spectra show the characteristic peak of PEO, the shake-up satellite of PS, and an easily deconvoluted doublet for the core levels in PS and PEO. It is apparent from the spectra that he PS concentration at the copolymer surface increases as the PS in the copolymer increases. More importantly, however, an analysis of the spectral data clearly shows that the surface compositions are significantly richer in PS than would be predicted based on a knowledge of the bulk compositions of the block copolymers. In Figure 3 is shown a plot of the surface-vs-bulk compositions for the diblock copolymers. ... 

An example of a random multiblock copolymer is found in the study of HMS/DMS copolymers where the DMS bulk content was varied from 27%, to 57.2% to 72.5% by weight. XPS ( 0 ) studies established that trends in the surface composition and morphology were similar in nature to both the PS/PEO diblock and triblock systems. In other words, the polymer components are segregated into isolated domains and the lower surface energy component dominates the immediate surface. By plotting the results from the XPS ( 6 ) studies on compositional variations with depth and extrapolating to an angle of 0 = 90, or just the immediate outer surface... 

The combined use of continuous-glass-strand mat as a core material and uniformly and monoaxially aligned continuous-glass fiber as the surface material has also been proposed (5, 25). The incorporation of expanded polystyrene copolymers into composites was proposed for shock-absorbing composites, such as bumper beam cores, knee bolsters, etc. (17, 18). 

Block copolymers of PDMS are amphiphiles and behave as surfactants. At low concentrations they accumulate at the surface, at intermediate concentrations they may form micelles, and at high concentrations and in the bulk they segregate into domains of one block in a continuum of the other. Thus one would expect the surface composition and morphology to be quite different from that in the bulk. 

The arrangement of molecular elements of a polymeric material at a blood-polymer interface generally is not known in detail x-ray photoelectron spectroscopy (XPS, also called ESCA) indicates that for block copolymers, polymers having large side groups of differing polarity and polyelectrolytes, the surface composition may be quite different from the bulk, stoichiometric composition (2). 

XPS was used to evaluate the surface composition of these copolymers in relation to the bulk composition (fractions of methyl acrylate and styrene). Surface composition was essentially identical to the bulk composition. Thus, for example, when the bulk composition is 40 mol % styrene, the surface percentage of styrene is about 40. Such a surface appears to be as active as polystyrene homopolymer. 

Four polymers with different surface compositions were used in this study—polystyrene (PS), poly(methyl methacrylate) (PMMA), polyacrylamide (PAM), and a poly(vinylidene chloride) (PVeC) copolymer (containing 20% polyacrylonitrile). Polystyrene has essentially a hydrocarbon surface, whereas the surfaces of poly (methyl methacrylate) and polyacrylamide contain ester and amide groups, respectively. The surface of the poly(vinylidene chloride) copolymer on the other hand will contain a relatively large number of chlorine atoms. The presence of acrylonitrile in the poly(vinylidene chloride) copolymer improved the solubility characteristics of the polymer for the purposes of this study, but did not appreciably alter, its critical surface tension of wetting. Values of y of these polymers ranged from 30 to 33 dynes per cm. for polystyrene to approximately 40 dynes per cm. for the poly(vinylidene chloride) copolymer. No attempt was made to determine e crystallinity of the polymer samples, or to correlate crystallinity with adsorption of the fluorocarbon additives. 

Fig. 18.7 Al peel strength of Al-plasma copolymer-PP composites as a function of functional group density at the plasma polymer surface (squares COOH half-filled squares COOH circles OH triangles NHj copolymers ethylene and butadiene).

Fig. 34. Surface PS fractions (symbols) for PS-PEO copolymer films prepared by dipping (dip) and by spin coating (spin) from solutions in CCI4 and tetrahydrofurim (THF) on two different substrates silicon wafer covered by its native oxide (denoted SiC>2) and silanized silicon wafer (denoted Silane) for nonannealed (empty squares) and annealed films (full squares). The gray line represents copolymer stoichiometric composition. Stoichiometric composition corresponds to a PS fraction of 0.09. Horizontal lines represent average values for annealed (----) and non-annealed (-----) films.

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