J. T. Koberstein

The determination of interfacial tension by video image processing of pendant fluid drops

Abstract A novel technique is presented for the determination of interfacial tension by analysis of axisymmetric fluid drop profiles. The technique couples recent developments in digital image acquisition and processing with modern methods for robust shape comparison. The entire algorithm for drop profile acquisition and analysis is executable on a personal computer and includes a facility for rotationally resistant smoothing of the drop profile. The general performance of the robust shape comparison algorithm and improvement in accuracy resulting from smoothing is illustrated by analysis of simulated pendant drop profiles. The overall performance of the image acquisition hardware and profile analysis software is assessed by evaluating the surface tension of glycerin. The resultant value of 62.6 ± 0.3 dyn/cm (at 24.2 ± 0.2°C) agrees well with the literature data for glycerin.

Light and neutron scattering studies of excess low-angle scattering in moderately concentrated polystyrene solutions

Abstract The light scattering (LS) and small-angle neutron scattering (SANS) behaviour of semi-dilute solutions of polystyrene has been determined in both ‘good’ and ‘theta’ solvents. Above a critical concentration related to chain overlap, an excess small-angle scattering component is in evidence for scattering vectors, q, such that qRg

The measurement of polymer surface tension by drop image processing: Application to PDMS and comparison with theory

Digital image processing techniques are applied toward the determination of polymer surface tension by pendant drop measurements. Experimental values for poly(dimethylsiloxane) as a function of molecular weight and temperature correspond well with previous measurements of poly(dimethylsiloxane) surface tension, testifying to the applicability of the new technique. Current thermodynamic treatments are found to provide excellent predictions of poly(dimethylsiloxane) surface tension for molecular weights of 3900 and 75,000 at temperatures ranging from 20 to 120°C. Theories developed by K. M. Hong and J. Noolandi (Macromolecules, 14, 1223, 1981) and Y. Rabin (J. Polym. Sci. Polym. Lett. Ed. 22, 335, 1984) yield predictions within 5% of t he experimental results for the materials and conditions studied. The proposed relation of Sanchez

Small-angle light scattering studies of macrophase separation in segmented polyurethane block copolymers

Abstract Quantitative small-angle light scattering (SALS) analysis is carried out on two similar segmented polyurethane block copolymers. The polyurethane prepared from toluene diisocyanate, is optically transparent, while a polyurethane prepared using the same soft segment, but with 4-4′ diphenyl methane diisocyanate, scatters light appreciably. SALS investigation of the latter sample shows clearly that the scattering arises from the presence of long-range density fluctuations. Analysis of the density fluctuations is accomplished with the Debye-Bueche theory for random two-phase systems, incorporating a correction for the effects of multiple scattering. Application of this procedure leads to a correlation length of 4200 nm; corresponding well with the structure observed in optical photo-micrographs. The occurrence of phase separation during polymerization is discussed as a possible origin for the observed macrophase structure.

Static screening length behaviour in polystyrene solutions

Abstract The concentration dependence of screening lengths in polystyrene solutions is determined by light and neutron scattering measurements. The data support the existence of a marginal regime in the temperature-concentration diagram, inside which mean field behaviour is observed. In addition, it is found that polymer solutions conforming to either semidilute good or marginal behaviour can be described universally in terms of two common variables: a reduced correlation length, and a reduced concentration. Experimentally determined concentrations for crossovers between various regimes of solution behaviour are reported, and compared with quantitative predictions from a recent theory of Schaefer.