R. M. Hooper

Indentation-size effects in single-crystal MgO

Abstract The microhardness values in many very hard materials need to be measured at low loads to prevent cracking from unduly affecting the measurement accuracy. However, the resultant indentation-size effect (ISE) means that it is difficult to compare the results obtained by different workers and for different specimens, particularly of small crystals or coatings. The purpose of this study is to obtain and analyse Knoop microhardness data for a well-characterized material, with a view to being able to interpret the results. Consequently microhardness indentations have been performed on single-crystal MgO(001) along {110} in air for loads between 0.125 and 1.001kg and temperatures between 20 and 600°C, investigating also the influence of interfacial coatings and lubricants. The main experimental findings were that the ISE decreased with increasing test temperature and was unaffected by coating or lubrication. The data fitted equally well either the power-law or the proportional specimen resistance models. It is proposed qualitatively herein that the ISE is controlled by the extent of elastic recovery occurring on removal of the load, and should thus correlate with the hardness-to-elastic modulus ratio H/E.

Synthesis of four n-alkanes with terminal dipolar substituents

Abstract 12-Nitrododecanol, 1,12-dinitrododecane, 1,24-dinitrotetracontane and 2,15-diaminohexadecan-1,16-dioioc acid were prepared from the common intermediate 12-bromododecanol. This bromoalcohol, being prepared from cyclododecanone, is free of homologous bifunctional impurities. The functionalised 24 carbon chain was prepared by a Wittig reaction of 12-bromododecanal with the triphenylphosphonium salt of 12-bromododecanal ethylene acetal using ‘naked’ carbonate anion to provide the base. The resulting bromoacetal was converted to 24-bromotetracont-12-enol, both this and the 12-bromododecanol were converted to the corresponding α,ω-di-iodides and then to the desired α,ω-dinitro compounds. The α-amino acid functionality can be introduced on an α,ω-dihalide with the anion of either diethyl 2-acetylaminopropan-1,3-dioate or benzylidene glycine ethyl ester. Also detailed is the previously unreported reduction of a carboxylic acid to an alcohol by borane-dimethyl sulphide in dichloromethane.

Conduction transients in single-crystal octadecane

Abstract Charge transients were measured in high-quality single-crystal octadecane after electron beam irradiation. The signals produced were of significantly greater duration than the ionization pulse but were not interpretable by conventional uniform field time-of-flight analysis. By assuming that the specimens contained a strong inbuilt polarization field, it was possible to predict the properties of the observed charge transients and obtain values for the positive and negative drift mobilities. The results indicated a positive species with a mobility of 0.7 × 10−4 m2 V−1 s−1 and a negative carrier value of 1.6 × 10−4 m2 V−1 s−1. The standard deviations observed in the data were large, being 0.3 × 10−4 m2 V−1 s−1 and 0.8 × 10−4 m2 V−1 s−1, respectively. This scatter was significantly in excess of the estimated experimental error.

Drift Mobilities in Single Crystal Normal Alkanes

Abstract The normal alkanes have been of interest for some time as model substances for saturated alkane polymers1. Theoretical estimates of the electron drift mobility have been made by several authors2,3,4 with results in the range 5X10−3 to 10−2 m2 v−1 s−1 and an associated lifetime of the order of 10−10 s. Measurements on n-alkanes have been mainly confined to the liquid phase where highly degassed samples yielded fast negative carrier drift mobilities in the range 10−6 to 10−4 m2 v−1 s−1 5,6,7,8.

Far-infrared anisotropy in polar end-substituted alkanes

Abstract This article examines the anisotropies in the long wavelength infrared spectra observed in strongly polar end-substituted straight chain alkanes. Comparison with the unsubstituted parent molecules suggest that dipole-dipole coupling is responsible for the anisotropies. A simple weak coupling analysis of the problem shows that the frequencies at which the anisotropies occur can be computed from an ab-initio analysis without recourse to fitting parameters.

Conformational behavior of polar endgroup substituted alkanes explored by simulation methods

Results from the Monte Carlo computational simulation of the equilibrium thermodynamics of terminally substituted linear alkanes are described. The molecules modeled have a linear alkyl backbone of the form -(CH/sub 2/)/sub n/-, where n=10, 12, or 14, bearing identical polar chain termini. The range of endgroup dipole moments investigated is 0.1 to 10 D. The analytical basis of the model and the assumptions and limitations inherent in it are fully discussed. For the purposes of comparison with the available experimental observations on 1,12-dinitrododecane, O/sub 2/N-(CH/sub 2/)/sub 12/-NO/sub 2/, which is a typical member of this class of molecules, the parameters of interest are the net dipole moment and the mean-square end-to-end separation. The temperature dependencies of these parameters with varying chain length and endgroup dipole moment are described and evaluated. >

Conformational properties of substituted alkanes in solution: terminal nitro functionalities

Measurements of the dielectric permittivity of nitrohexane and 1,12-dinitrododecane in nonpolar aromatic hydrocarbon solvents are presented. The measured dipole moment of nitrohexane is 3.31 D and that of 1,12-dinitrododecane is 4.5 D. The time-averaged equilibrium conformation of 1,12-dinitrododecane has an overall bend angle of approximately 100 degrees . Measurements were performed over the temperature range 25 to 50 degrees C. Details of the measurement technique are discussed. >