Nondestructive evaluation of polymer materials by solid state NMR imaging

Many polymer products are heterogeneous. Examples of heterogeneities are the chemical composition, distributions of mechanical stress, and variations in flexibility or molecular orientation. Applications of NMR imaging to polymers are summarized and investigations of the aging of rubber are reported as well as novel deuteron NMR techniques to image molecular order and mobility of polymers below the glass transition temperature.     

Thermal analysis of polymer layered silicate nanocomposites

It has been shown, for three different polymer layered silicate (PLS) nanocomposite systems, how differential scanning calorimetry (DSC) can identify the different reactions of homopolymerisation and of crosslinking that occur in the intra- and extra-gallery regions of these nanocomposites, respectively, and hence how DSC can be used to assess the cure conditions for optimising their nanostructure. The PLS nanocomposites are based upon: (i) diglycidyl ether of bisphenol-A (DGEBA) cured with a polyoxypropylene diamine; (ii) DGEBA cured with an –NH₂ terminated hyperbranched polymer (HBP); and (iii) tri-glycidyl p-amino phenol (TGAP) cured with a diamine. In each case, the existence of both intra- and extra-gallery reactions in the DSC cure curves, and whether they occur simultaneously or sequentially, and in what order, are identified and correlated with the nanostructure as observed by small angle X-ray scattering and transmission electron microscopy. In particular, it is shown that the intra-gallery reaction must precede the extra-gallery for significant exfoliation to occur. In accordance with this scenario, the TGAP/diamine system displays the greatest degree of exfoliation, the DGEBA/diamine system the least, with the DGEBA/HBP system intermediate. For those systems in which significant exfoliation occurs, the DSC cure curves also allow the optimum cure conditions, such as the isothermal cure temperature, to be determined.     

Nondestructive characterization of nanoscale layered samples

Multilayered samples consisting of Al, Co and Ni nanolayers were produced by MBE and characterized nondestructively by means of SRXRF, μ-XRF, WDXRF, RBS, XRR, and destructively with SIMS. The main aims were to identify the elements, to determine their purity and their sequence, and also to examine the roughness, density, homogeneity and thickness of each layer. Most of these important properties could be determined by XRF methods, e.g., on commercial devices. For the thickness, it was found that all of the results obtained via XRR, RBS, SIMS and various XRF methods (SRXRF, μ-XRF, WDXRF) agreed with each other within the limits of uncertainty, and a constant deviation from the presets used in the MBE production method was observed. Some serious preliminary discrepancies in the results from the XRF methods were examined, but all deviations could be explained by introducing various corrections into the evaluation methods and/or redetermining some fundamental parameters.     

Using protochirons for three-dimensional coding of certain chemical structures

For three-dimensional coding (including enantiomerism) of staggered paths and circuits on the diamond lattice, or paths/circuits with angles 90 degrees or 180 degrees on the cubic lattice, use is made of the previously defined paths-3 (paths of length three bonds defining two intersecting planes). The two cases mentioned above are examined and exemplified. In the diamond lattice there are three kinds of diamond-paths-3: one is achiral (Z) and two are chiral and enantiomeric (R and S). In the cubic lattice there are six kinds of orthopaths-3, of which only two are chiral and enantiomeric (R and S) and four are achiral (I, L, U, and Z). The chiral paths-3 are the previously defined protochirons in the respective lattice. Coding ascribes to each bond the letter that would characterize it if it were the central bond of an isolated path-3. To obtain a unique code out of several equally correct ones it is proposed to use the convention of inverse alphabetic priority in the above system of letters.     

Upperbound procedures for the identification of similar three-dimensional chemical structures

Summary This paper describes techniques for calculating the degree of similarity between an input query molecule and each of the molecules in a database of 3-D chemical structures. The inter-molecular similarity measure used is the number of atoms in the 3-D common substructure (CS) between the two molecules which are being compared. The identification of 3-D CSs is very demanding of computational resources, even when an efficient clique detection algorithm is used for this purpose. Two types of upperbound calculation are described which allow reductions in the number of exact CS searches which need to be carried out to identify those molecules from a database which are similar to a 3-D target molecule.     

Yttrium coordination polymers with layered structures

A hydrothermal reaction of a mixture of Y(NO₃)₃·xH₂O, phthalic and isophthalic acid, and phthalic acid and terephthalic acid in the presence of 1,10-phenonthroline gave rise two new two-dimensional coordination polymer, Y₂(C₁₂N₂H₈)₂[(1,2-BDC)₂(1,3-BDC)], I, Y₂(C₁₂N₂H₈)₂[(1,2-BDC)₂(1,4-BDC)], II, respectively. Both structures were solved using single crystal X-ray diffraction studies. I and II consist of a one-dimensional chain formed by the connectivity between Y³⁺ and 1,2-BDC anion, and cross-linked by 1,3-BDC and 1,4-BDC anions to form the layer structure. The 1,10-phenonthroline molecule, bound to yttrium, project into the interlayer space and contribute to the structural stability through favorable π…π interactions. Room temperature photoluminescence studies indicate that both I and II show strong emission, with bathochromic and hypsochromic shifts with respect the acid and 1,10-phenonthroline.     

Imaging with chemical analysis: adsorbed structures formed during surface chemical reactions

Imaging surfaces and interfaces with structural and chemical specificity has been essential for understanding a variety of phenomena occurring in adsorbed layers during surface chemical reactions. A recent achievement of chemical imaging with spectroscopic analysis is the experimental proof of theoretically predicted spontaneous formation of regular patterns of metal adatoms during surface chemical reactions. An attractive feature of this finding is that the reaction rate and adlayer coverage can be employed to precisely control the morphology of the structures. The mechanisms of these self-organisation phenomena, driven by the interplay between energetic principles and kinetics, opens a conceptually novel route to creating a wide range of surface-supported functional structures at the micro- and nanometre length scales.     

Two-photon excitation of fluorescence for three-dimensional optical imaging of biological structures

Techniques based on two-photon excitation (TPE) allow three-dimensional (3D) imaging in highly localized volumes, of the order of magnitude of a fraction of a femtolitre up to single-molecule detection. In TPE microscopy a fundamental advantage over conventional widefield or confocal 3D fluorescence microscopy is given by the use of infrared (IR) instead of ultraviolet (UV) radiation to excite those fluorophores requiring UV excitation, hence causing little damage to the specimen or to fluorescent molecules outside the volume of the TPE event and allowing a deeper penetration within the sample compared with conventional one-photon excitation of fluorescence. In our laboratory, within the framework of a national INFM project, we have realized a TPE fluorescence microscope, part of a multipurpose architecture also including lifetime imaging and fluorescence correlation spectroscopy modules. The core of the architecture is a mode-locked Ti:sapphire infrared pulsed laser pumped by a high-power (5 W, 532 nm) solid-state laser and coupled to an ultracompact scanning head. For the source we have measured a pulse width from 65 to 95 fs as a function of wavelength (690-830 nm). The scanning head allows conventional and two-photon confocal imaging. Point spread function measurements are reported with examples of applications to the study of biological systems.     

Organically templated vanadyl selenites with layered structures

Two layered vanadyl selenites with the compositions, [DABCOH2]0.5[(VIVO)(HSeO3)(SeO3)].H2O,I, and [enH2][(VivO)2-(VVO)O2(SeO3)3]-.1.25H2O, II, have been prepared by the reaction of NaVO3 with SeO2 or H2SeO4 under hydrothermal conditions in the presence of organic amines. Crystal data: I, orthorhombic, space group Pbcn (No. 60), a = 6.3152(3) A, b = 18.1918(8) A, c = 17.7172(8) A, V = 2035.4(2) A3, Z = 8, R1 (all data) = 0.0368; II, triclinic, space group P1 (No.2), a = 6.3406(2) A, b = 10.2085(3) A, c = 13.2551(10) A, alpha = 101.238(2) degrees, beta = 96.503(2) degrees, gamma = 104.332(2) degrees, V = 803.47(4) A3, Z = 2, R1 (all data) = 0.0814. While I contains the ladder motif, commonly found in open-framework metal phosphates, II is formed by a secondary building unit composed of a V4O18 cluster along with SeO3 and VO5 groups. The study demonstrates that the selenite unit can be fruitfully exploited to design interesting open-framework structures.     

Nondestructive examination of polymethacrylimide composite structures with terahertz time-domain spectroscopy

THz reflective time domain spectroscopy (THz-RTDS) has been considered as an effective method to detect hidden objects with potential for supplementing other NDE technologies for foam composite adhesive structure debonding defects. PMI (Polymethacrylimide) is a heat-resistant foam material, with the highest strength and stiffness to weight ratio. It is widely used in various parts of airplanes, especially the wing leading edge and rudder, landing gear doors, wing-body/wingtip fairings and so on. We analyzed the features of adhesive debonding defect based mainly on the variation of the time-domain wave form and compared with the inclusion defect. The quantification of degrees of adhesive debonding can be readily achieved with THz-RTDS images based on the delay of the wave front and the main reflection time-domain waveforms. Typical accuracy of about 100 μm was achieved.     

New titanium and nickel gallophosphates with layered structures

Two new transition-metal gallophosphates, (H(2)C(4)H(10)N(2))(3)[(Ti(2.5)(H(2)O)(4)Ga(5.5)(PO(4))(10)].2H(2)O (TGP-1) and [H(3.5)(C(4)H(13)N(3))(2)][(Ni(0.5)(OH)(4)Ga(5.5)(PO(4))(3)(HPO(4))(4)].2H(2)O (NGP-1), have been synthesized under mild hydrothermal conditions and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, electron paramagnetic resonance, electron probe microanalysis, and magnetic susceptibility data. TGP-1 exhibits a unique two-dimensional structure consisting of tetrahedral and octahedral metals centers and is the foremost paramagnetic TiGaPO material ever prepared. NGP-1 as well represents the first NiGaPO compound and adopts a layer structure that is constructed from hexameric M-O clusters of trigonal bipyramids and octahedra. In both compounds, the transition metals incorporate with gallium into octahedral sites only, while the four- and five-coordinated metals centers are only Ga(3+) ions. The unique sites for Ti(3+) and Ni(2+) ions have been initially elucidated from single-crystal structure refinements and further confirmed by bond-valence-sum calculations, EPR, and magnetic susceptibility studies. Crystal data: TGP-1, monoclinic, P2(1)/c; a = 25.692(2) A, b = 9.6552(8) A, c = 9.8418(8) A, beta = 96.737(2)(o) , V = 2424.5(3) A(3), and Z = 2; NGP-1, monoclinic, C2/c, a = 20.8363(12) A, b = 11.9546(7) A, c = 16.4577(9) A, beta = 117.285(1)(o) , V = 3643.3(1) A(3), Z = 4.     

Rheology of polymer layered silicate nanocomposites

Layered silicate based polymer nanocomposites have gained significant technological interest because of the recent commercialization of nylon 6 and polypropylene based materials. Aside from the natural interests in understanding and improving the processing of these hybrids, viscoelastic measurements have also proven to be a sensitive tool to probe the mesoscale structure and the strength of polymer–nanoparticle interactions.     

Lanthanide oxalatophosphonates with two- and three-dimensional structures

Reactions of lanthanide nitrate, oxalate sodium and 2-pyridylmethylphosphonic acid (2-pmpH₂) under hydrothermal conditions result in five new lanthanide oxalatophosphonates with two types of structures. Compounds [Ln₄(ox)₅(2-pmpH)₂(H₂O)₇]·5H₂O [Ln³⁺=Gd (1), Tb (2), Dy (3); ox²⁻=C₂O₄²⁻] exhibit a double layer structure, made up of net-like {Ln₄(ox)₅}_n layers containing Ln₁₀(ox)₁₀ rings which are connected by 2-pmpH^‐. While compounds [Ln₄(ox)₅(2-pmpH)₂(H₂O)₆]·6H₂O [Ln³⁺=Ho (4), Yb (5)] display a three-dimensional framework structure in which the {Ln₄(ox)₅}_n layers are cross-linked by 2-pmpH. The solid state luminescent and magnetic properties are investigated.     

A lanthanum pyromellitate coordination polymer with three-dimensional structure

A new three-dimensional metal-organic coordination polymer, [La₂(H₂O)₂(H₂BTEC)(BTEC)], 1, was hydrothermally synthesized and characterized by single crystal X-ray diffraction. The three-dimensional framework is built up from La₂O₁₆ dimers connected by carboxylate anions. The polymer exhibits strong photoluminescence at room temperature with the main emission band at 390 nm (λ_ex = 338 nm). Crystal data: triclinic, space group P(−1),a = 6.4486(3),b = 9.4525(5),c = 9.6238(5) ?, α= 88.24(1), β = 74.67(2), γ= 76.76(1)°,V = 550.45(5)     

Metal aminocarboxylate coordination polymers with chain and layered structures

The synthesis and structures of metal aminocarboxylates prepared in acidic, neutral, or alkaline media have been explored with the purpose of isolating coordination polymers with linear chain and two-dimensional layered structures. Metal glycinates of the formulae [CoCl2(H2O)2(CO2CH2NH3)] (I), [MnCl2(CO2CH2NH3)2] (II), and [Cd3Cl6(CO2CH2NH3)4] (III) with one-dimensional chain structures have been obtained by the reaction of the metal salts with glycine in an acidic medium under hydro/solvothermal conditions. These chain compounds contain glycine in the zwitterionic form. 4-Aminobutyric acid transforms to a cyclic amide under such reaction conditions, and the amide forms a chain compound of the formula [CdBr2(C4H7NO)2] (IV). Glycine in the zwitterionic form also forms a two-dimensional layered compound of the formula [Mn(H2O)2(CO2CH2NH3)2]Br2 (V). 6-Aminocaproic acid under alkaline conditions forms layered compounds with metals at room temperature, the metal being coordinated both by the amino nitrogen and the carboxyl oxygen atoms. Of the two layered compounds [Cd{CO2(CH2)5NH2}2]2 H2O (VI) and [Cu{CO2(CH2)5NH2}2]2 H2O (VII), the latter has voids in which water molecules reside.     

IR spectra of manganese oxides with either layered or tunnel structures

Four kinds of manganese oxides with either layered or tunnel structures were prepared by different methods. The structural features of the prepared materials were characterized by power X-ray diffraction, IR spectra and SEM observation. A compare analysis of IR spectra for these materials before and after the acid treatment was carried out. Band around 761 cm(-1) could be assigned to a characteristic adsorbent band of tunnel-type manganese oxides; while it was not observed in layer-type manganese oxides. After the acid treatment, the position and relative intensity of the bands in 300-1200 cm(-1) region showed an obvious change for layered manganese oxides in compare with tunnel-type manganese oxides. The variation of IR spectra could be used to distinguish layered manganese oxides from tunnel manganese oxides.