Limiting conditions for applying the spherical section assumption in contact angle estimation

The shape of liquid drops on solid surfaces deviates from the spherical as tension decreases and gravity effects start affecting the drop shape. This paper attempts to define this deviation and estimates the dimensionless Eotvos number limits above which the deviation becomes "significant." The use of these limiting values can facilitate estimation of contact angle in the following manner. It is well known that the equilibrium contact angle made by a liquid drop on a solid surface can be estimated from measurements of two drop parameters. These parameters can be any two chosen from the drop volume, height, and wetted radius. In case the effect of gravity on the drop shape is negligible, simple algebraic relations derived from the spherical section assumption exist, from which the contact angle can be estimated. In systems where the "spherical section" assumption is invalid, the Laplace equation for the drop shape has been solved numerically with any two of the above parameters as the constraints, to obtain the contact angle. In this paper, Eotvos numbers at which the deviation of the drop profile from the spherical is significant enough to result in contact angle deviation of 1 degrees are estimated. The limiting values of Eotvos number, expressed as a function of the original contact angle made by the spherical profile, are obtained by solving the Laplace equation for the drop shape with the drop volume and wetted radius constraints for decreasing values of Interfacial tension. These limiting values are also estimated for different drop sizes and for cases where the drop phase is heavier (sessile) and lighter (buoyant) than the surrounding fluid. The independence of the Eotvos number estimates from the sign of the density difference as well as the drop size is shown. These Eotvos number limits can be used to check if the spherical section assumption, with the resulting simple algebraic relations, can be used for contact angle estimation and other shape-related analysis for a system.     

Kinetics of heterogeneous cellulose reactions. I. Cyanoethylation of cotton cellulose

Sakurada's equation and fundamental kinetic laws were applied to the heterogeneous cyanoethylation of cellulose, performed by reacting fiber with liquid acrylonitrile, with sodium hydroxide as the catalyst. The data fit Sakurada's equation better at higher temperatures; deviation occurs at the initial stage, and the rate of reaction falls abruptly at a later stage. The degree of substitution at which the abrupt rate change occurred decreased as the temperature increased from 31 to 60°C. and also as the crystallinity of the fiber decreased. Diluting the reagent with different solvents decreased the rate of reaction and changed its transition points, but did not change the essential nature of the reaction, each segment of which fits Sakurada's equation very well. A uniform distribution of the catalyst (sodium hydroxide) throughout the fiber was attempted, and then the reaction was studied at 50°C. Diffractograms of the samples provided further evidence that the position of the rate change is associated with the change of cellulose (I) crystalline structure. Approximate energy of activation has been calculated, from the specific rate constants, between 31 and 40°C. as 10.6 kcal. and between 45 and 50°C. as 16.7 kcal. At other temperatures the determination was handicapped, due to temperature dependence of the order of reaction. An empirical relation between the constants of Sakurada's equation and the reaction temperature has been sought and correlated with the Arrhenius equation. Energies of activation, determined from this relationship, have been found to be very close to the above values. The change of order of reaction with temperature suggests that the reaction is affected by diffusion and the mechanism is interpreted as a diffusion-controlled reaction where hydrogen bonds play a significant role in diffusion.     

Aquation of α-cis-chloroaquoethylenediamine-N,N'-diacetatocobalt(III) in aqueous and in mixed solvents: A mechanistic study

Summary The displacement of chloride ligands from -cis-chloro-aquoethylenediamine-N,N-diacetatocobalt(III) in nonacidic aqueous solutions was followed conductimetrically at 30–45° and the products of aquation were characterised by conductance, spectral and ion-exchange techniques. The rate constants for aquation in aqueous media and in 1 : 4 v : v mixed solvents at 25° are: 4.0 × 10^–5 s^–1 in H₂O, 2.71 × 10^–5 s^–1 in MeOH : H₂O, 2.74 × 10^–5 s^–1 in EtOH: H₂,O and 2.58 × 10^–5 s^–1 n in Me₂CO : H₂O. The corresponding H* and S* values have also been evaluated. Solvent polarity has a marked influence on the rate of chloride ion release. The aquation rate constants and the activation parameters have been correlated with solvent parameters,e.g. D, Y-values, Dimroth's E_T and Kosower's Z-values and, based on these correlations, a dissociative interchange (I_d) mechanism is proposed rather than dissociative as observed for some other cobalt(III) complexes.Senior author.     

A Sensitive Spectrophotometric Determination of Nitrite in Water and Soil

A highly sensitive spectrophotometric method for the determination of nitrite in water and soil has been developed. The reaction of nitrite with acidified potassium iodide to liberate iodine which oxidizes leuco‐crystal violet (LCV) to form crystal violet having absorption maxima at 590 nm forms the bases of this method. In aqueous medium the system obeys Beer's law in the range of 0.1 to 1.0 μg per 25 mL (0.004–0.04 ppm), while in an extractive system the range is 0.025–0.25 μg in 100 mL (0.00025–0.0025 ppm). The molar absorptivity and Sandell's sensitivity were found to be 1.54 × 10⁶ 1 mol^?1 cm^?1 and 44 pg cm^?2, respectively.     

Honeycomb nets with interpenetrating frameworks involving iminodiacetato-copper(II) blocks and bipyridine spacers: syntheses, characterization, and magnetic studies

Three coordination polymers of copper(II), viz. ([Cu(ida)(4,4'-bipyH)]ClO(4))( proportional, variant ) (1), ([Cu(2)(ida)(2)(micro-4,4'-bipy)].2H(2)O)( proportional, variant ) (2), and [Cu(2)(ida)(2)(bpa)]( proportional, variant ) (3) have been synthesized by the process of self-assembly using Cu(ida) [ida = iminodiacetate(2-)] as the building block and 4,4'-bipyridyl and 1,2-bis(4-pyridyl)ethane (bpa) as linkers. Crystals of 1 are orthorhombic, of space group Pna2(1), with a = 13.8956(12) A, b = 16.3362(16) A, c = 7.3340(12), and Z = 4. Both compounds 2 and 3 crystallize in monoclinic space group P2(1)/a with a = 10.1887(8) A (9.6779(10) A for 3), b = 8.0008(11) A (9.1718(10) A), c = 11.6684(9) A (12.9144(12) A), beta = 98.307(11) degrees (102.796(18) degrees ), and Z = 2 (2). Compound 1 has a zigzag chain structure with an extensive hydrogen-bonded network while compounds 2 and 3 are honeycomb (6,3) nets with interpenetrating structures. Variable temperature (2-300 K) magnetic study indicates the presence of weak antiferromagnetic interactions (J = 0.82 +/- 0.01 cm(-)(1)) in 1 and ferromagnetic in 2 (J = -0.45 +/- 0.05 cm(-)(1)) and 3 (J = -0.21 +/- 0.02 cm(-)(1)). The extent of planarity of the bridging "Cu-O-C-O-Cu" moiety, acting as the super-exchange pathway between the neighboring copper centers, probably controls the sign of the magnetic exchange coupling in these compounds.     

Preparation of Enantiopure trans‐1,2‐Cyclohexanediol and trans‐2‐Aminocyclohexanol

Trans‐1,2‐cyclohexanediol and trans‐2‐aminocycloxexanol are useful chiral auxiliaries. Simple chemical resolution procedures for these molecules are presented.     

Effect of Structure on Titration Curves of p-Bromoaniline-Formaldehyde-p-Cresol Copolymers in Nonaqueous Media

Copolymers obtained by the condensation of p-bromoaniline, formaldehyde, and p-cresol have been separated into five fractions by a fractional precipitation method. Some of these copolymers showed characteristic titration curves in non-aqueous media. The titration curves indicated a series of breaks which bear integral relations to each other. These features have been interpreted in terms of homoconjugation, intramolecular hydrogen bonding, and composition of the copolymers.