Adhesive transfer of thin viscoelastic films

Micellar suspensions of acrylic diblock copolymers are excellent model materials for studying the adhesive transfer of viscoelastic solids. The micellar structure is maintained in films with a variety of thicknesses, giving films with a well-defined structure and viscoelastic character. Thin films were cast onto elastomeric silicone substrates from micellar suspensions in butanol, and the adhesive interactions between these coated elastomeric substrates and a rigid indenter were quantified. By controlling the adhesive properties of the film/indenter and film/substrate interfaces we were able to obtain very clean transfer of the film from the substrate to the portion of the glass indenter with which the film was in contact. Adhesive failure at the film/substrate interface occurs when the film/indenter interface is able to support an applied energy release rate that is sufficient to result in cavity nucleation at the film/substrate interface. Cavity formation is rapidly followed by delamination of the entire region under the indenter. The final stage in the transfer process involves the failure of the film that bridges the indenter and the elastomeric substrate. This film is remarkably robust and is extended to three times its original width prior to failure. Failure of this film occurs at the periphery of the indenter, giving a transferred film that conforms to the original contact area between the indenter and the coated substrate.     

Thermoresponsive nanostructures by self-assembly of a poly(N-isopropylacrylamide)-lipid conjugate

The synthesis and purification of a poly(N-isopropylacrylamide)-lipid conjugate and its use in the preparation of a thermoresponsive lipid mesophase is described. Specifically, poly(N-isopropylacrylamide) with a single carboxyl group at one end was activated with dicyclohexylcarbodiimide/N-hydroxysuccinimide to form an active ester. This N-hydroxysuccinimide ester was then used to form a dimyristoyl-sn-glycero-3-phosphoethanolamine conjugate with poly(N-isopropylacrylamide) via an amide bond, rendering the conjugate amphiphilic. Quaternary phases comprising the conjugate, a phosopholipid, dimyristoylphosphatidylcholine, and a cosurfactant, N,N-dimethyldodecylamine-N-oxide, dispersed in water were found to self-assemble at room temperature to form liquid crystalline gels, adopting an expanded lamellar structure. A modest increase in temperature triggered the reversible conversion of the aggregate to a collapsed lamellar structure, while a modest reduction in temperature resulted in its conversion to a nonlamellar phase. The phases were characterized by polarized optical microscopy and small-angle X-ray scattering (SAXS).     

Electroreduction of Aryldiazonium Ion at the Polar and Non-Polar Faces of ZnO: Characterisation of the Grafted Films and Their Influence on Near-Surface Band Bending

ZnO is a strong candidate for transparent electronic devices due to its wide band gap and earth-abundance, yet its practical use is limited by its surface metallicity arising from a surface electron accumulation layer (SEAL). The SEAL forms by hydroxylation of the surface under normal atmospheric conditions, and is present at all crystal faces of ZnO, although with differing hydroxyl structures. Multilayer aryl films grafted from aryldiazonium salts have previously been shown to decrease the downward bending at O-polar ZnO thin films, with Zn−O−C bonds anchoring the aryl films to the substrate. Herein we show that the Zn-polar (0001), O-polar (000 ), and non-polar m-plane (10 0) faces of ZnO single crystals, can also be successfully electrografted with nitrophenyl (NP) films. In all cases, X-ray photoelectron spectroscopy (XPS) measurements reveal that the downward surface band bending decreases after modification. XPS provides strong evidence for Zn−O−C bonding at each face. Electrochemical reduction of NP films on O-polar ZnO single crystals converts the film to a mainly aminophenyl layer, although with negligible further change in band bending. This contrasts with the large upward shifts in band bending caused by X-ray induced reduction.     

Helical tubulate inclusion compounds of ferrocene and squalene

The inclusion compounds of 2,8-dimethyltricyclo[5.3.1.1^3,9]dodecane-syn-2,syn-8-diol,3, with ferrocene and with squalene have been prepared. The crystal structures of these helical tubulate compounds: (3)₃·(ferrocene)_0.75 [P3₁21,a=b=13.7480(6),c=7.0312(5) Å,Z=1,R=0.038] and (3)₃·(squalene)_0.23 [P3₁21,a=b=13.677(1),c=7.0533(9) Å,Z=1,R=0.042] are described. Supplementary Data relating to this article are deposited with the British Library as supplementary publication No. SUP 82151 (16 pages).     

The detection of drugs of abuse in fingerprints using Raman spectroscopy I: latent fingerprints

This paper describes the application of Raman spectroscopy to the detection of exogenous substances in latent fingerprints. The scenario considered was that of an individual handling a substance and subsequently depositing a contaminated fingerprint. Five drugs of abuse (codeine phosphate, cocaine hydrochloride, amphetamine sulphate, barbital and nitrazepam) and five non-controlled substances of similar appearance, which may be used in the adulteration of drugs of abuse (caffeine, aspirin, paracetamol, starch and talc), were studied in both sweat-rich and sebum-rich latent fingerprints. The substances studied could be clearly distinguished using their Raman spectra and were all successfully detected in latent fingerprints. Photobleaching was necessary to reduce the fluorescence background in the spectra of some substances. Raman spectra obtained from the substances in sweat-rich latent fingerprints were of a similar quality to spectra that obtained from the substances under normal sampling conditions. Interfering Raman bands arising from latent fingerprint material were present in the spectra obtained from the substances in sebum-rich fingerprints. These bands did not prevent identification of the substances and could be successfully removed by spectral subtraction. The most difficult aspect of the detection of these substances in latent fingerprints was visually locating the substance in the fingerprint in order to obtain a Raman spectrum.     

Writing with DNA and protein using a nanopipet for controlled delivery

We present a new, general method for the controlled deposition of biological molecules on surfaces, based on a nanopipet operating in ionic solution. The potential applied to the pipet tip controls the flux of biological molecules from the pipet, allowing fine control of the delivery rate. We used the ion current to control the distance of the pipet from the surface of a glass slide and deposited the fluorescently labeled DNA or protein G at a defined location onto the surface. Features of 830 nm size were obtained by depositing the biotinylated DNA onto a streptavidin surface; 1.3 mum size spots were obtained by depositing protein G onto a positively charged glass surface.     

Theoretical results for the excited states of ozone

On the basis of ab initio calculations (configuration interaction and generalized valence bond), we find eight excited states of ozone with vertical excitation energies less than 7 eV. Using these results the various experimental transitions are assigned. One state has an equilateral triangle as the minimum energy geometry (1.5 eV above the ground state).     

The synthesis of anthracyclinones-ii : The synthesis of 7,9-bisdeoxycarminomycinone and -daunomycinone

7,9-Bisdeoxycarminomycinone has been synthesised from 5-hydroxyquinizarin by two annelation routes involving nitronate addition to C-2 and aldol condensation at C-3. 4-Demethoxy-7,9-bisdeoxydaunomycinone has been synthesised efficiently by similar methods.     

The effect of chain structure on the annealing and deformation behaviour of polymers

Summary In a tensile test ductile thermoplastics may give either uniform deformation or necking. Recently it has been found that those giving uniform deformation either, are known to have extended chain configurations in solution, or have chemical formulae with linear structures and relatively few flexible bonds. The observed differences in behaviour can be predicted from a viscosity retarded rubber elasticity model in which a constant related to chain flexibility is introduced, which quantifies the strain hardening of the material. It is argued that the early development of strain hardening generally interferes with the localization of plastic strain in shear bands or crazes (as well as in a neck) and correlates with the stress cracking performance of high density polythenes.There is now also some evidence that polymers with extended chain configurations have small values ofcp (the change in specific heat atTg) and that this figure has an apparent correlation with draw ratio for different polymers.In the case of P.V.C. however it is possible to cause a changeover from the normal necking behaviour to uniform deformation by quenching the hot material in ice water. This process is believed to eliminate a structure which develops slowly in P.V.C. and most other thermoplastics when they are annealed at temperatures near toTg. The elimination of this structure during yielding causes strain softening and also promotes plastic strain localisation.This physical ageing or annealing process is still not well understood. It almost certainly includes free volume effects but recent studies have shown that a redistribution of rotational isomers also occurs. These observation, if correct, have fundamental implications for the physics of glassy polymers.

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Zusammenfassung Beim Zug-Test erfolgt bei dehnbaren Thermoplasten entweder eine gleichmäßige Deformation oder eine Einschnürung. Erstere tritt auf bei Vorliegen ausgestreckter Kettenkonfigurationen in Lösung oder bei Makromolekülen linearer Struktur und relativ unbiegsamer Bindungen. Die beobachteten Unterschiede wurden anhand eines ViskositätsModells mit verminderter Gummi-Elastizität unter Zugrundelegung von Literaturdaten diskutiert. Die Kettensteifheit wird rechnerisch durch Einfügung einer Konstanten berücksichtigt; sie steht in Konkurrenz mit der Lokalisierung der plastischen Dehnung und korreliert mit dem Auftreten einer Spannungsriß-Bildung im Polyäthylen hoher Dichte. Es wird darauf hingewiesen, daß sich die spezifische Wärme von Polymeren mit ausgedehnter Kettenkonfiguration beiTg nur wenig ändert; dieser Effekt steht mit dem Dehnungsverhältnis verschiedener Polymerer in Einklang.Bei PVC kann jedoch durch Abschrecken des heißen Materials in Eiswasser ein Übergang vom normalen Einschnürungsverhalten zu einer gleichmäßigen Deformation erzielt werden; dieser Effekt ist durch die Unterdrückung einer speziellen Struktur bedingt und kann auch bei der Temperung anderer thermoplastischer Polymerer nahe beiTg auftreten.Die sich bei der physikalischen Alterung und bei der Temperung abspielenden Vorgänge lassen sich noch nicht erklären. Sie umfassen sicherlich Effekte des freien Volumens und die Rückverteilung von Rotations-Isomeren. Beobachtungen dieser Art sind von grundsätzlicher Bedeutung für die Physik glasartiger Polymerer.

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Dedicated to Prof. Dr. Rehage on the occasion of his 60th birthday.

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With 22 figures and 2 tables