Kohzoh Shiokawa

Simulations of the shape of a regularly branched polymer as a model of a polymacromonomer

Computer simulations were performed to examine the effects of the main (backbone) and side (branch) chain size on the shape and dimensions of a polymacromonomer using the bond fluctuation model in which bond cutting is allowed. The polymacromonomer was treated as a self-avoiding chain having N bonds in the main chain and n bonds in the side chains which are attached to every main chain element. In the simulation N and n were varied up to 64. A power law relation, 〈S2〉m∼N2νm, was obtained for each value of n, where 〈S2〉m is the mean-square radius of gyration of the main chain. The exponent 2νm increased monotonically from 1.24±0.02 at n=1 to 1.95±0.05 at n=64, indicating that the shape of the main chain gradually varied with increasing n, from a self-avoiding coil-like structure to an extended rod-like form. The mean-square radius of gyration of the side chain moiety, 〈S2〉s was independent both of N and also of the position of the branching point along the main chain for every value of n. A power law relat...

Simultaneous determination of the heat capacity and the heat of the transitions for long-chain compounds with a heat-flux type DSC

Abstract The heat capacity method of DSC measurements, for which sapphire was used as a standard, was applied to determine simultaneously the heat of the transitions and the heat capacity for long-chain compounds. A heat-flux DSC was used because of its relatively high sensitivity at slow scanning rates. The data were analyzed with a computer system. Measurements on indium were performed to obtain information about factors affecting the accuracy. Fairly satisfactory results were obtained for the heat of melting and the heat capacity at heating rates of 0.5 and 2 K min −1 . Long-chain symmetrical ketones were also used to test the reliability of the measurement because their thermal behavior is very simple. Solution-grown crystals of henpentacontane and dopentacontane clearly showed high-temperature modifications with a high heat capacity. Analysis by the present method indicates that the heat capacities of these modifications have a relatively large contribution to the overall change in enthalpy from the stable crystal at room temperature to the liquid.

A New Type of Refractometer for High-Temperature Use

A new type of refractometer is proposed. Its design is based on the method of critical angles. Instead of visually detecting the position of the critical boundary, the refractometer measures the intensity of scattered light from a sample layer. The temperatures of the sample and the prism were controlled over a range up to 300°C. The apparent critical angle θc could be determined from the relationship between the scattering intensity and incident angle. Reliable data were obtained for a simple liquid. When the sample size was limited due to temperature homogeneity, the effect of the sample thickness on θc had to be taken into consideration. High-temperature measurements on polycarbonate were satisfactorily obtained.