Multilayers Of Poly Research Articles

Determination of Molecular Orientation in Biaxially Oriented Ultrathin Films

Biaxial orientation in ultrathin films is characterized by a preferential orientation of the main molecular axis in the plane of the film in addition to its orientation with respect to the normal of the film. In this paper, analytical expressions allowing the calculation of the molecular orientation in biaxially oriented films from their anisotropic optical constants are presented for the first time. These expressions have been used to calculate the molecular orientation in multilayers of poly(γ-benzyl-l-glutamate) and to determine the angles between the main molecular axis and the different transition moments used (α angles). Using the optical constants determined by Buffeteau et al.1 for PBG multilayers, we have found that the tilt angle of the PBG helices with respect to the monolayer normal is 89° and that the azimuthal angle in the plane is 57°. The calculated α angles for the carbonyl stretching mode of the ester group and the amide I and amide II modes of the amide group are 49, 34 and 74°, respect...

Advances in the Raman depth profiling of polymer laminates.

The use of Raman microspectroscopy to depth profile multi-layered polymer laminates is becoming increasingly popular. However, the results are generally degraded by aberrations introduced by the change in refractive index at the air/sample interface. Recent research has suggested that the use of an immersion oil and suitable objective can reduce this effect. This study evaluates this proposal by comparing depth profiling results on a multi-layer poly(styrene)/poly(methylmethacrylate) (PS/PMMA) laminate polymer from both dry metallurgical objectives and immersion objectives (used in combination with an oil of suitable refractive index). The immersion technique enabled successful depth profiling to the full working distance of the objective (100 microm), showing clear and distinct variations in 11 different layers within the laminate; a dry metallurgical objective used for comparison achieved poor resolution of only two layers. This is the first demonstration of depth profiling within a polymer laminate to this depth. The depth profiling results are compared to results obtained by sectioning the PS/PMMA sample after setting it in resin.

Electrostatic Layer-by-Layer Assembly of Poly(amido amine) Dendrimer/Conducting Sulfonated Polyaniline: Structure and Properties of Multilayer Films

The multilayers of poly(amido amine) dendrimer (fourth generation amine-terminated, G4NH2) and conducting sulfonated polyaniline (SPANI) were successfully deposited onto solid substrates by alternatively dipping in SPANI and G4NH2 solutions. Multilayer growth was monitored by ultraviolet−visible absorption spectroscopy and Fourier transform infrared-reflection absorption spectroscopy, which revealed an adsorption−desorption phenomenon, although it was sensitive to the concentration and pH of solutions. The average thickness of the SPANI/G4NH2 bilayer obtained from X-ray reflectivity is much smaller than the diameter of G4NH2 with an ideal spherical structure, suggesting that the dendrimer molecules in multilayers are highly compressed along the surface normal. Electron density profiles indicate that the multilayers are highly interpenetrated, and the thickness and molecular arrangement in the multilayers depend on the pH of G4NH2 solutions. Cyclic voltammograms of the multilayers in acidic and neutral ele...

Formation of Uniform Polyaniline Thin Shells and Hollow Capsules Using Polyelectrolyte-Coated Microspheres as Templates

Multilayers of poly(diallyldimethylammonium chloride) and poly(sodium 4-styrenesulfonate) precoated onto melamine formaldehyde (MF) particles via the layer-by-layer (LbL) self-assembly procedure were used as templates for the subsequent deposition of polyaniline (PANI). Transmission electron microscopic (TEM) and scanning electron microscopic (SEM) images reveal that the as-prepared PANI-containing polyelectrolyte (PE)−MF core−shell particles are narrowly dispersed and possess uniform surface morphology. Intact hollow PANI/PE capsules can also be produced by extracting the MF cores in an acidic solution. FTIR spectra of the hollow capsules indicate that PANI and PE are both present and suggest that the PANI exists in the emeraldine form. The incorporation of PANI in the shells was found to enhance the rigidity of these composite materials, and the PANI/PE-coated MF core−shell particles have comparable conductivities with other PANI-coated colloidal particles. The amount of PANI incorporation was also foun...

Effects of self-assembled multilayers on the evolution of surface physical properties of indium-tin-oxide

Using layer-by-layer self-assembly technique, we have deposited multilayers of poly(diallydimethylammonium) (PDDA) and nickel phthalocyanine (NiPc) onto indium-tin-oxide (ITO) coated glass substrate. To determine how self-assembled multilayers affect charge transfer properties of conductive ITO surface, Kelvin probe and surface photovoltage measurements have been carried out. The results showed an oscillation of the surface potential as the top layer was alternated between PDDA and NiPc. The changes in surface potential of ITO induced by the growth of PDDA or NiPc monolayers are attributed to the modulation in electron affinity.

Effect of graft polymer on the formation of micron-sized, monodisperse, "onion-like" alternately multilayered poly(methyl methacrylate)/polystyrene composite particles by reconstruction of morphology with the solvent-absorbing/releasing method

Some factors contributing to the formation of an alternately multilayered structure of micron-sized, monodisperse poly(methyl methacrylate) (PMMA)/polystyrene (PS) (1/1, w/w) composite particles by reconstruction of the morphology with the solvent-absorbing/releasing method (SARM) were discussed. The original composite particles, which were produced by seeded dispersion polymerization (SDP) of styrene, had a core–shell structure. When PS/PMMA (1/1, w/w) composite particles produced by SDP of methyl methacrylate were treated by the SARM with toluene, the reconstructed morphology of the composite particles was not the multilayered structure but a hemisphere (or core–shell). The PS/PMMA composite particle contained less than 10 wt% PMMA-g-PS. On the other hand, the PMMA/PS composite particles contained about 40 wt% graft polymer. The graft polymer would exist at the interfaces of the alternate multilayers and decrease their interfacial energy. This was the main reason why the alternately multilayered structure was constructed by the SARM, though the total interfacial area between PMMA and PS layers in the multilayered particle is much larger than that of the hemisphere (or core–shell).

Nanoporous Thin Films Formed by Salt-Induced Structural Changes in Multilayers of Poly(acrylic acid) and Poly(allylamine)

We report here on the influence of changes in the solution salt concentration on the structure of multilayers of weak polyelectrolytes. For poly(acrylic acid) (PAA) and poly(allylamine) (PAH) multilayers assembled by the layer-by-layer process in the presence of sodium chloride, washing with pure water after deposition of each layer produces films with considerable surface roughness (root-mean-squared (rms) roughness ∼17 nm for a 10 layer film), as assessed by scanning force microscopy. In contrast, relatively smooth (rms roughness ∼1 nm) and homogeneous PAH/PAA multilayer films are formed when the salt concentration is kept constant both during the assembly process and in the washing steps. For such smooth films, subsequent exposure to pure water leads to the introduction of regular, discrete, nanometer-sized pores, thus providing a means of introducing lateral structure into the PAH/PAA multilayer films. Electrochemical measurements revealed that the pores formed in less than 10 min. The sensitivity of the multilayer films to salt as well as the subsequent creation of nanopores potentially makes them attractive candidates for use in controlled-release applications where defined permeability characteristics are desired.

Preparation of micron-sized, monodispersed, "onion-like" multilayered poly(methyl methacrylate)/polysterene composite particles by reconstruction of morphology with the solvent-absorbing /releasing method

Micron-sized, monodispersed, “onion-like” multilayered poly(methyl methacrylate) (PMMA)/polystyrene (PS) (1/1, w/w) composite particles were prepared by the solvent-absorbing/releasing method (SARM). The viscosity within toluene-swollen composite particles, the release rate of toluene therefrom, the PMMA/PS ratio, and the kind of solvent had great influences on the reconstruction of the morphology of the PMMA/PS composite particles by the SARM. From these results, the conditions for the preparation of the multilayered composite particles by the SARM are clarified.

Piezochromic Effect and Orientational Order in Monolayers and LB Multilayers of Poly(p-phenylenesulfonate)− Dioctadecyldimethylammonium Bromide Complexes

By spreading dioctadecyldimethylammonium bromide (DODA) on a subphase containing rigid-rod-like poly(p-phenylenesulfonate)s (PPPS), polyelectrolyte complexes are formed in situ at the air−water interface. These complex monolayers are investigated by recording surface pressure/area isotherms, UV/vis spectroscopy, and, after transfer onto a solid substrate, X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XR). XPS and XR measurements indicate that although the polyelectrolytes are aggregated in aqueous solution, the complexes are stoichiometric. The isotherms show that the area per amphiphile in the complex monolayer is significantly higher than in the monolayer of pure DODA. This is due to the distance of the ionic sites along the rigid-rod-like polymer chain and results in a more tilted arrangement of the alkyl chains as confirmed by the XR measurements. UV/vis spectroscopy reveals that the A-band of the PPPS is red-shifted in the complex, and a further red shift of the A-band upon compression of the complex monolayer is observed. This two-dimensional piezochromic effect is discussed to be a result of the electronic interaction of the π-systems, which improves with decreasing distance during compression. Upon transfer to solid substrates the rigid-rod-like polyelectrolytes are oriented to be parallel to the dipping direction as evidenced by polarized UV/vis spectroscopy. The degree of order in the LB film shows a linear dependence on the axial ratio of the rigid-rod-like PPPS.

Evolutionary optimization of the electron-beam lithography process for gate fabrication of high electron mobility transistors

An electron-beam lithography simulation tool was realized. This tool models the development of multilayered poly(methylmethacrylate) resist structures after exposure with an electron beam. A development front propagates inside the resist stack as a function of time and the local solubility. The local solubility was experimentally measured versus the electron dose for different types of resist. The efficiency of incident and backscattered electrons was determined using doughnut-shaped structures. The ratio of the backscattered to incident electron efficiencies η was found to be 1.35 for an acceleration voltage of 30 kV on InP substrates. We used genetic algorithms to optimize the electron dose necessary for the realization of a given resist profile. This tool was applied to fabricate T-gates and asymmetric gate recesses.

Alternate sign reversal in the ζ potential and synchronous expansion and contraction in the absorbed multi-layers of poly(4-vinyl- N - n -butylpyridinium bromide) cations and poly(styrene sulfonate) anions on colloidal silica spheres

Alternative multiple absorbed layers of up to ten macrocations [poly(4-vinyl-N-n-butylpyridinium bromide)] and macroanions [sodium poly(styrene sulfonate)] are formed on colloidal silica spheres above the critical concentration of macroions, m*. The m* value is the minimum number of macroions required to reverse the sign of the ζ potential of the spheres in the first absorption step. Alternative sign reversal in the ζ potential and expansive–contractive thickness changes are observed by the repeated and alternate addition of macrocations first and macroanions next. During multiple absorption, the pH and conductivity values decrease and increase continuously as the number of absorbed layers increases. When the macroanions are added first, sign reversal in the ζ potential and reversible expansion and contraction do not occur. Breaking of the alternate multiple-type absorption occurs when equivalency in the number of dissociative groups of macrocations and macroanions is broken. Synchronous conformational changes of macrocations and macroanions in the multiple- absorbed layers, where balancing of the conformational rigidities with the multiple electrostatic attraction and repulsion between macrocations and anions occurs, are supported strongly.

Accumulation of Hg(II) by adsorbed polyuridylic acid: differentiation of coordinated Hg(II) and covalently mercurated species

Abstract The voltammetric behavior of polyuridylic acid+mercuric acetate solutions at hanging mercury drop electrodes has been studied in neutral aqueous solution. Adsorbed polyuridylic acid (poly(U)) efficiently accumulates mercury, resulting in a peak voltammogram at ca. −0.6 V vs. SCE for the reduction of Hg(II) coordinated to the poly(U) film. The size of this wave was markedly dependent on the accumulation time. The magnitude of the charge associated with the peak voltammogram indicated formation of multilayer poly(U)–Hg(II) electroactive films. This voltammetric current could be distinguished from the reduction of covalent carbon–mercury bonds in mercurated poly(U), poly(U–Hg), prepared by treating the former with mercury(II)acetate at elevated temperature. Analysis of the surface voltammetry of poly(U–Hg) gave an estimate of the extent of mercuration.

Influence of shear stress treatment on stress-strain properties of methyl methacrylate-crosslinked butyl acrylate core-shell polymers

The incorporation of multilayer toughness modifiers to glassy polymers proceeds frequently by kneading the polymers in a molten state. This process influences the primary structure of the modifier and the properties of the blend in dependence on a shear stress intensity. In this article, we compare the properties of polymer materials prepared from a multilayer poly(methyl methacrylate) core, butyl acrylate copolymer interlayer, and methyl methacrylate copolymer shell particles {P[MMA-(BAC-co)-(MMA-co)]} by press-molding from powder and from polymer obtained by stirring a melt of this powder in the chamber of a Brabender mixer (200°C, 60 rpm, 10 min). The powder is obtained from a latex by coagulation after polymer synthesis in emulsion. Tensile testing shows different responses of the particle polymers when crosslinked in the middle layer by diallylphthalate (DAP) or by triallylcyanurate (TAC). Although many of the properties of the samples with DAP are improved by kneading, the presence of TAC in polymer particles led mostly to less desirable properties. The maximum percent strain in the polymer with 4.2 wt % of DAP upon shearing increases from 27% to 50%. In the samples with 4.5% TAC the maximum percent strain falls from 39% to 7%. Comparison of Young's modulus E for identical samples shows an analogous effect: a shift from 429 MPa to 638 MPa and from 624 MPa to 548 MPa. The design of the polymer particles used in this work leads to the conclusion that stress during kneading induces a partial desintegration of the crosslinked cage around the particle core. Thus, the varied behaviors of polymers used in this study are connected with the BAC-co network structure and its transformations during the shear stress treatment of the initial polymer material. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 493–501, 1999

Poly(4-methyl-1-pentene)-Supported Polyelectrolyte Multilayer Films: Preparation and Gas Permeability

Spontaneous sequential adsorption of poly(allylamine hydrochloride) and poly(sodium styrene sulfonate) (layer-by-layer deposition) onto surface-oxidized poly(4-methyl-1-pentene) film was studied with the objective of creating an asymmetric gas separation membrane consisting of a thin multilayer barrier layer on a more permeable polymer film. Poly(4-methyl-1-pentene) film was first surface-oxidized with chromic acid solution to introduce carboxylic acid functionality to the surface for depositing the first layer. By alternating the poly(allylamine hydrochloride) and poly(sodium styrene sulfonate) depositions, multilayered structures were prepared with the total number of layers up to 104. Gas permeabilities of composite membranes prepared by this layer-by-layer deposition technique were determined for hydrogen, oxygen, and nitrogen. The depressed gas permeabilities of the composite membranes are explained by dense and rigid packing of the polyelectrolytes in stratified layers. The multilayered poly(allylamine hydrochloride) and poly(sodium styrene sulfonate) structures were shown to be 18 000 times better barriers to nitrogen than poly(4-methyl-1-pentene). Alternating deposition of polyaniline and poly(sodium styrene sulfonate) into stratified multilayers on surface-oxidized poly(4-methyl-1-pentene), on the other hand, did not change the permeability properties of the film, suggesting a loose packing of molecules in the layers.

Structural Study of Langmuir-Blodgett Mono- and Multilayers of Poly(.beta.-hydroxybutyrate)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStructural Study of Langmuir-Blodgett Mono- and Multilayers of Poly(.beta.-hydroxybutyrate)G. Lambeek, E. J. Vorenkamp, and A. J. SchoutenCite this: Macromolecules 1995, 28, 6, 2023–2032Publication Date (Print):March 1, 1995Publication History Published online1 May 2002Published inissue 1 March 1995https://doi.org/10.1021/ma00110a041RIGHTS & PERMISSIONSArticle Views163Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 MB) Get e-Alerts Get e-Alerts

Mixed mono- and multilayers of poly(isocyanide)s with non-linear optically active side chains

The properties and structure of Langmuir-Blodgett mono- and multilayers of several poly(isocyanide)s with non-linear optically active side-chains were studied. These polymers formed very rigid layers or layers which appeared to be unstable. To circumvent this problem they were mixed with other poly(isocyanide)s or with amylose-butyrate. Transmission electron microscopy studies of the polymeric mixtures revealed that phase separation occured in all cases and that only poly(isocyanide)s substituted with hydrophilic side chains formed monomolecular layers. Depending on the nature of the polymer which was used for mixing, the dye polymers could be deposited with Y- or Z-type transfer. Second-harmonic intensities generated from these films were small in the case of the Y-type multilayered films and moderately high in the case of the Z-type films.

Anisotropic properties of high-temperature polyimide thin films: Dielectric and thermal-expansion behaviors

Multilayer poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) polyimide films of 172 μm total thickness (11.4 μm per layer) were prepared from the poly(amic acid) precursor solution through repetition of a spin-coat/softbake/cure process. Wide-angle x-ray diffraction results indicate that the polyimide molecules in the multilayer films are highly ordered along the chain axes as well as in the lateral direction and furthermore are highly oriented in the film plane as observed in a single-layer film of 11.4 μm thickness. The multilayer films showed the same dynamic mechanical properties and glass transition behavior (Tg = 330 °C) as a single-layer film. For the multilayer films both the in-plane dielectric constant (ε′XY) and out-of-plane thermal-expansion coefficient (αZ) were measured using time-domain spectroscopy and conventional thermal mechanical analysis, respectively. The ε′XY at room temperature was 3.69 (±0.08) over a frequency range of 0.35–2.50 THz. A similar ε′XY is predicted at frequencies of ≤0.35 THz. In contrast to the ε′XY, a relatively lower out-of-plane dielectric constant (ε′Z) was observed: ε′Z = 2.96–3.03 (±0.02) at 1 MHz, depending on moisture content in the film. The dielectric loss ε″Z at 1 MHz was 0.011–0.014 (±0.001), depending on moisture content. The measured αZ was 74 ppm/°C over the temperature range of 25–150 °C, which was much higher than αXY = 2.6–5 ppm/°C. Consequently, large anisotropic ε′ and α have been observed in the in plane and out of plane of the thermally imidized BPDA-PDA films. The anisotropic ε′ and α were caused by high in-plane orientation of the polyimide molecules highly ordered along the chain axes in the films.

New generation biodegradable plate for fracture fixation: Comparison of bending strengths of mandibular osteotomies fixed with absorbable self-reinforced multi-layer poly- l-lactide plates and metallic plates — an experimental study in sheep

Eighteen osteotomies of sheep's mandibular corpus were fixed: nine with self-reinforced multi-layer poly- l-lactide (SR-PLLA) plates and nine with metallic plates. Both plates were fixed with similar metallic screws. The right corpus of each sheep acted as a control. Radiographic analysis was carried out at 3 weeks and at sacrifice (6, 12 or 24 weeks) when the bending force needed to break the osteotomy site was measured. At 6 and 12 weeks of follow-up the osteotomy fixed with the PLA-plate seemed to tolerate the bending force better but no significant differences were detected at 3 or 24 weeks. The results have been satisfactory and have led the authors to continue with the development of a SR-PLLA plate-and-screw device for fracture fixation.

Langmuir-Blodgett mono- and multilayers of poly(isocyanides)s with different sidechains

In this study poly(isocyanide)s, [RNC] n with different sidechains R are used as spreading material to form LB monolayers at the water-air interface. Poly(isocyanide)s are rigid-rod polymers with a stable, helical conformation. One of the aims of this study was to ascertain whether this rigid conformation is sufficient to enable the formation of a stable monolayer on the water surface. We find that different poly(isocyanide)s with non-polar aliphatic substituents are unable to form such stable monolayers. On the other hand, poly(( S)-1-acetoxymethylethyl-isocyanide), a polymer which has polar substituents, does form a stable monolayer. This monolayer can be transferred onto all kinds of substrates by Z-type transfer. Multilayer formation is possible with transfer ratios remaining constant up to at least 40 layers. From IR measurements it follows that the polymer helices are preferentially oriented with their main axis parallel to the transfer direction.

Preparation and characterization of poly(amide-imide) multilayer films

Multilayer films of poly(amide-imide)s were prepared as follows: (1) monolayers of long alkyl amine salts of poly(amide-amic acid) were prepared at the air- water interface; (2) these monolayers were deposited on an appropriate plate by the Langmuir-Blodgett method; (3) the multilayers of poly(amide-amic acid) salts on the solid support were treated with acetic anhydride to afford poly(amide-imide) multilayer films. The monolayer thickness of the poly(amide-imide) multilayer films were 0.43–0.55 nm.