Roger S. Porter

Some Flow Characteristics of Mesophase Types

Characteristic flow properties for each of the three nominal mesophase types have been empirically established. Results are given for the nematic, smectic, and cholesteric types of mesophase. Discussion is centered on mesophases or liquid crystals exhibited by pure compounds within defined temperature intervals between the regular solid and the isotropic liquid. For nematic mesophases, the prominent flow orientation, consequent low viscosity, and the unusual flow behavior near the nematic—isotropic transition are discussed. The remarkably high and shear‐dependent viscosities of cholesteric mesophases are contrasted to the simple flow properties of these cholesterol derivatives at temperatures for their respective isotropic liquids. Descriptions of flow properties for smectic mesophases are based essentially upon data on a single compound, ethyl‐p‐azoxybenzoate. Viscosity data on this compound from several sources are intercompared for the first time. Some of the new empirical conclusions given here are at variance with those reported previously in several reviews.

Polymer degradation VI—Distribution changes on polyisobutene degradation in laminar flow

Abstract Precisely established polymer molecular weight distribution changes with variations in shear degradation history are extensively interpreted. The systems consist of solutions of polyisobutenes degraded in homogeneous, laminar-flow, shear fields. The polymer solutions studied were 9·6 volume per cent in n-hexadecane and 9·7 volume per cent in 1,2,4-trichlorobenzene. The procedure for preparing equilibrium shear degraded systems is described. A new computer programme is used to derive integral and differential distributions as well as molecular weight averages from number to Z +1. The programme also computed distribution inhomogeneities and standard deviations from the different molecular weight averages. It is found that the standard deviation, derived from number and weight average, changes linearly with weight average molecular weight. A predominantly random mechanism of degradation in laminar flow shear is postulated to explain the results. The efficiency of bond rupture due to storage of shear energy in polymer bonds is shown to be low. Equivalent results were obtained in the two solvents.

Gel Permeation Chromatography with Organic Solvents

Abstract Fractionation of polymers either as a means of determining molecular-weight distributions for the characterization of polymers or the preparation of fractions with defined molecular-weight distributions, for subsequent physical and chemical testing, is a valuable and widely used technique. There are many ways of performing fractionations and of measuring molecular-weight distributions; see, for example, the forthcoming book Polymer Fractionation [1]. Gel permeation chromatography is the newest of the fractionation methods and has already found widespread applications; see, for example, the forthcoming review by Altgelt and Moore [2]. Because of its speed and high resolving power and the possibility of a high degree of automation gel permeation chromatography is the most promising current technique for the fractionation of polymers on an analytical scale and, probably, on a preparative scale.

Recording High Shear Viscometer for Measurement at Shear Rates Near 106 Sec−1

An improved recording rotational high shear viscometer has been developed. The instrument employs concentric steel cylinders with unusually narrow and precisely defined shear clearances. Both shear rate and stress are continuously and independently recorded. Improved cylinders and other additional features have led to accurate viscosity measurements at shear rates from 5×102 to 2×106 sec−1. The temperature range is −20 to +150°C with a viscosity range which varies inversely with the desired shear rate for measurement. The shear rate range and the upper limit, 2×106 sec−1, exceed all previous reports of measurement at defined conditions in a homogeneous, isothermal shear field.