Ahmet Giz

A New Model for the Evolution of the Molecular Weight Distribution of Polymers During Ultrasonic Chain Scission

A new model for ultrasonic scission of polymer chains has been developed. The model takes the coiled nature of the polymer chains into consideration. The time evolution of the molecular weight distribution for several values of the solvent quality parameter is obtained using the new model. It is seen that the model leads to higher scission rates and lower final molecular weights for better solvents in accord with the experiments. Simulated gel permeation chromatography results are also in line with the experiments.

Dielectric spectroscopy study of EMA-EGDM crosslinking system at sol-gel transition

Ethyl methacrylate, ethylene glycol dimethacrylate free radical crosslinking co-polymerization reaction is studied by dielectric spectroscopy at various temperatures. A maximum in the dielectric constant was observed during the gelation reaction. At the same point, the dielectric loss switched from a linear decrease to a relatively constant behavior. Parallel experiments, performed with a magnetic stirrer, showed that this maximum is consistent with the gel-point. In the ethyl methacrylate homopolymerization reactions the dielectric constant did not go through a maximum but decreased monotonically. The evolution of the dielectric constant is found to depend on the extent of the reaction, but not on time and temperature separately.

An error-in-variables method for use when the reactivity ratios in copolymerization are close to one

Two new error-in-variables methods to estimate the reactivity ratios are developed. These are based on variants of the Skeist solution of the copolymerization equation. One method is suitable when one of the reactivity ratios is close to one and the other is for use when both ratios are close to one. In simulations, the latter is compared with an error-in-variables method based on the original Skeist solution. The results of the two error-in-variables methods and the extended Kelen-Tudos method are given for a wide selection of reactivity ratios and error magnitudes.

Dielectric investigation of the sol-gel transition in the acrylamide/N,N′ methylenebisacrylamide system

The acrylamide/N,N′-methylenebisacrylamide gelation process was studied by time dependent measurement of real ϵI and imaginary ϵII parts of the complex dielectric permittivity. The measurements were carried out in the frequency interval 500 Hz to 13 MHz. Strong relaxation behavior of ϵI and ϵII was observed in all dielectric spectra during the transformation from the sol to the gel state. At all frequencies a maximum in the imaginary part of dielectric constant ϵII was observed. The gel point was found by extrapolating this maximum to zero frequency. The behavior of ϵI and ϵII related to the gelation mechanism is discussed.

Online Viscometric Monitoring of Ultrasonic Sodium Poly (Styrene Sulfonate) Scission

Ultrasonic chain scission (degradation) of a polyelectrolyte, sodium poly(styrene sulfonate) is investigated in saline solutions by online continuous viscometric monitoring. Ultrasound intensity and the polymer concentration are kept constant while the solvent quality is varied by varying the salt concentration between 0.68 and 7.65 mM. The scission rate is found to depend strongly on the solvent quality. As the salt concentration is increased, hydrodynamic volume of the polymer is decreased. This effect is reflected in the scission rate which also shows a steep decrease. During sonication, the molecular weight approaches a limit value, beyond which no degradation takes place. This limit molecular weight, is observed to be relatively insensitive to salt concentration.

Ultrasonic Chain Scission of Polyacrylamide in Solution: Online Monitoring Results and Comparison with Theoretical Models

Abstract Ultrasonic processing of a water soluble polymer, polyacrylamide, is investigated and molecular weight evolution during ultrasonic degradation was monitored online by light scattering and viscometry. The resulting Data were compared to various theoretical models. Initially the scission was very rapid but as the limiting molecular weight was approached it slowed down. This slowing down was too pronounced to be described by a first order model. Only the Giz, Ovenall/Harrington/Madras and Tang models, adequately accounted for this slowing down and gave good fits to the data.

Simulation of Direct Electronic Energy Transfer between Donors and Acceptors Embedded in a Rubbery Phase Network in Glassy Particles

Abstract By direct electronic energy transfer fluorescence technique the temporal behavior of donors in the presence of acceptors when both types of molecules are embedded in a rubbery phase PIB forming an interconnected network within glassy PMMA spheres is studied. The experimental results are compared with simulations of the decay curves in (i) bag of marbles geometry where the PMMA particles are formed of glassy marbles, and the PIB fills the intervening spaces, (ii) the rubbery phase forms channels in the otherwise solid glassy PMMA sphere. For the latter case we analyzed both parallel and perpendicular PIB channels. The experimental and simulated data are compared by both the fractal analysis method and by obtaining the Klafter-Blumen dimension from the derivative of the ln(InI) with respect to Int. On the basis of our results we give preference to the rubbery PIB channels within solid glassy PMMA model over the bag of marbles model.