Ivan Haller

On the Measurement of Indices of Refraction of Nematic Liquids

Abstract We wish to report on a simple method for measuring the birefringence and indices of refraction of nematic liquids with an accuracy comparable with or superior to previously reported means.(1–3) The method is exemplified in measurement of the temperature dependences of the indices of refraction of p-methoxybenzylidene p-butylaniline (MBBA) at two wavelengths.

Elastic Constants of the Nematic Liquid Crystalline Phase of p‐Methoxybenzylidene‐p‐n‐Butylaniline (MBBA)

The bend and splay elastic constants of MBBA were measured over its nematic temperature range. The ratio of the two constants is 1.25± 0.05. The temperature dependence of the elastic constants is found to be adequately described by the simple mean‐field models. A comparison is made between viscosity coefficients obtained from the elastic constants and light scattering spectra and from classical viscosity measurements. A method proposed for the measurement of twist elastic constants is evaluated and an upper limit of this constant of MBBA as a function of temperature is reported.

Ionic species in a silane plasma

The abundances Aj of groups of higher silane ions SijH+k were measured mass spectrometrically in an rf glow discharge in SiH4 under conditions used for preparation of hydrogenated amorphous silicon. The ratio Aj/Aj−1 is about 0.3 nearly independently of j, of pressure, of degree of ionization, and of rf power. The mean hydrogen to silicon ratio for j⩾3 is 1.5±0.1 and pressure independent in the 0.017–0.100‐Torr range. A mechanism postulating charge or hydride ion transfer and the addition of SiH4 as the most rapid reactions of silane ions is consistent with the observations.

Alignment and wetting properties of nematic liquids

Contrary to recent claims, no correlation of useful predicting power exists between the tendency of a nematic liquid to align transverse to a solid surface and the difference between the surface free energies of the nematic liquid and of the substrate. Observations that lead to this conclusion are reported for systems in which (i) the composition but not the surface tension of the nematic liquid, (ii) the adsorbed layer and hence the surface free energy of the substrate, and (iii) the temperature is varied.

Raman spectroscopy of reactive ion etching induced subsurface damage

Raman spectroscopy has been used to characterize the surface modifications introduced into Si(100) by reactive ion etching with a CF4/H2 plasma. Both Raman scattering due to the destruction of crystalline long range order by lattice damage and the stretching modes of protons bonded to Si atoms have been observed without any special sample preparation. Our results are consistent with backscattering and nuclear reaction profiling studies of similarly prepared samples and Raman studies of Si(100) bombarded by low‐energy protons and Ar ions.

Graded-index AR surfaces produced by ion implantation on plastic materials.

The damage tracks of high energy ions in dielectric materials can be etched until overlapping conical etch pits are obtained. If the depth of the pits is >lambda/2, an effective graded-index layer with very low reflectivity is obtained. Broadband antireflection treatment achieving reflectivities of <10(-4) has been applied to plastics like Lexan and Mylar.

Preparation and thermodynamics of Some Homologous Nitrones, a New Group of Liquid Crystals

Abstract To investigate the mesomorphic behavior of aldonitrones, a series of 13 homologs of N-(p-alkoxyphenyl)-α-anisylnitrones was prepared and characterized. Although most of these substances exhibit normal nematic or smectic mesophases, the trend in nematic-isotropic transition temperatures to increase as a function of alkoxy chain length is an exceptional occurrence. Comparison of our data with that of analogous compounds previously reported indicates that thermal persistence of the nematic phase of these compounds increases in the following order : 4, 4′-dialkoxybenzylideneaniline, 4, 4′-dialkoxyazobenzene, N,α-di-(4-alkoxyphenyl)-nitrone, 4, 4′-dialkoxyazoxybenzene. In addition, the phase transitions were investigated by means of differential scanning calorimetry. The entropies of the mesophase-isotropic transitions of the nitrones imply that the long alkoxy chains, in contrast to a widely held belief, are not restricted to a single conformation in the mesophase.

Vibrational Spectra and Molecular Structure of Bicyclo[1.1.0]butane

The infrared and Raman spectra of bicyclo[1.1.0]butane and the infrared spectrum of its deuterated analogue were observed. The rotational structure of some infrared bands were partially resolved. If the numerical values occurring in cyclopropane and its derivatives are adopted for the related structural parameters of bicyclobutane, the spectrum is found consistent with a C2v structure with an angle between the planes of the rings of 126°±3° and a bridgehead C–C distance of 1.54±0.02 A. A complete assignment of the fundamental vibrational frequencies of the light isotope is given.

Photochemistry of 1,3‐Butadiene : Details of the Primary Processes and Mechanism of Photopolymerization

The photolysis of 1,3‐butadiene in the vapor phase was studied in the presence of inert gases such as krypton, diethyl ether, and cyclohexane. In every instance, an increase in the pressure of the added gas led to a decrease in all of the volatile products. The behavior of 1,2‐butadiene and 2‐butyne were exceptional in that they showed a slight increase in yield when a small quantity of an inert gas was added. But at higher pressures, even in these cases, the yields decreased. A consideration of the radiative lifetime of the first‐singlet excited state of 1,3‐butadiene suggests that the observed pressure dependence cannot be attributed to a quenching reaction from that state. It seems likely that all of the volatile products in the vapor phase photolysis arise from a vibrationally excited ground state molecule of 1,3‐butadiene that is formed by the internal conversion of the electronically excited singlet state. Photolysis of 1,3‐butadiene in solution, which is equivalent to photolysis at very high pressu...

Mesomorphism in the 4,4′-Dialkoxy-trans-Stilbenes

Abstract In order to ascertain the effect of linkage groups (X[dbnd]Y) in mesomorphic substances of the general formula a homologus series of stilbenes has been prepared, where R[dbnd]Cn, H2n+1O—, X[dbnd]Y[dbnd]CH. The lower members of the series (1 ≤ n ≤ 10) are monotropic nematic, while the higher members (12 ≤ n ≤ 16) are monotropic smectic substances. The mesophase-isotropic transition temperatures are higher than those reported for the related nitrones (X[dbnd]CH, Y[dbnd]N → O) and Schiff Bases (X[dbnd]CH, Y[dbnd]N). Also the entropies of the nematic-isotropic transitions, as measured by differential scanning calorimetry, are nearly the same in the stilbenes and the nitrones. These results suggest that the permanenet dipole associated with the linkage group plays a relatively unimportant role in enhancing the intermolecular attractions which are responsible for mesomorphic alignment.