Won-Soo Kim

Thermal and rheological properties of poly(ϵ-caprolactone) and polystyrene blends

Abstract The thermal and rheological properties of blends of poly(ϵ-caprolactone) (PCL) and polystyrene (PS) have been investigated by differential scanning calorimetry (DSC), scanning electron microscopy, and Advanced Rheometric Expansion System. Two different molecular weights of PS 1 ( M w =1000) and PS 2 ( M w =69,000) have been used in the PCL–PS blend. In the thermal analysis of the PCL–PS 1 blend by DSC, the Tc of PCL in the blend decreased by about 3–13 degrees with blend composition compared to the Tc of pure PCL. The decrease in Tc of PCL in the blend indicates that the crystallization of PCL in the PCL–PS 1 blend is deactivated by PS 1. The Tm of PCL in the blend decreased by about 2–6 degrees with blend composition compared to the Tm of pure PCL. From the results of Tc and Tm of PCL, it is suggested that the PCL–PS 1 blend is partially miscible. The Tc of PCL in the PCL–PS 2 blend increased by about 2–5 degrees in the PCL-rich compositions. The increase in Tc of PCL can be explained by the nucleating effect of PS 2 on the primary nucleation of PCL in the PCL–PS 2 blend. From the results of the rheological properties of the PCL–PS 2 blend, the storage modulus of the blend at low frequencies has a larger value than that of the simple mixing rule. The elasticity increase from the simple mixing rule is consistent with the emulsion model for a dispersed system.

Clustering in poly(methyl acrylate) ionomers

Abstract Dynamic mechanical properties of poly(methyl acrylate- co -sodium acrylate) ionomers were studied. It was found that the ‘ionic’ modulus of the poly(methyl acrylate) (PMA) ionomers was lower than that for the poly(styrene- co -sodium methacrylate) (PS) ionomers at the same ion content. This implies that the PMA ionomer is less clustered than the PS ionomer, which is explained in terms of the differences in the glass transition temperature and polarity of the polymer matrix. It was also found that the increasing rates in the matrix and cluster T g s of the PMA ionomers were similar to those of the PS ionomers. However, the difference in the matrix and cluster T g s was higher for the PS ionomer than for the PMA system because of the lower clustering of the PMA ionomers.

A new model approach for the near-critical point region: 1. Construction of the generalized van der Waals equation of state.

To date, it has been considered that all classical equations of state (EOS) have failed to describe the properties of fluids near the critical region, where the density fluctuations have a significant influence on fluid properties. In this paper, we suggest a newly constructed equation for fluid states, the generalized van der Waals (GvdW) EOS with the highly simplified Dietericis form P = [RT/(V - b)] - a(b/V)c by a new model potential construction describing intermolecular interactions. On the basis of the model potential construction, it is shown that the a, b, and c parameters have physical interpretations as an internal pressure, a void volume, and a dimensionless value that represents an inharmonic intermolecular cell potential, respectively. As an illustration of our model approach, we initially apply it to near the critical point (cp) region, where all classical EOS descriptions have been incorporated with experimental thermodynamic data, and we obtain a table of three parameters for 12 pure normal fluids, which precisely describes thermodynamic critical values. On the basis of the basic relations between pressure and volume at the critical point, we express the corresponding EOS in terms of the c parameter, and by this means, we also obtain a theoretical vapor-liquid equilibrium (VLE) line, which closely coincides with the experimental data for several pure normal fluids near the critical region. As a result, we show that thermodynamic properties near the critical region can be described analytically by only three parameters. In addition, to validate our EOS for the temperature-differential derivatives, we show that the calculated isochoric heat capacity (Cv) of saturated argon closely coincides with the experimental data. Moreover, the possibility of a precise description with respect to the entire fluid region is also argued, in terms of the physical cases from the triple point to the ideal gas region.

A prediction of the abnormal behavior in the viscosity of liquid water under pressure

A phenomenological theory of viscosity proposed by authors was applied to liquid water under high pressure. Thermodynamic properties used in the calculation were obtained by using the theory of liquid proposed by Pak [13]. The calculated viscosities decreased abnormally with increasing pressure. We found this behavior was due to the decrease of the absolute value of kinetic and internal pressure with the pressure increase near 273.15 K.

A calculation for the viscosity of fluids by using van der Waals equation of state

A new equation for the viscosity of fluid is presented by considering that the viscosity is equal to the product of the shear pressure and the shear relaxation time. The shear pressure and the shear relaxation time are calculated thermodynamically by applying the van der Waals model for fluids. The calculated viscosities for various simple substances are in good agreements with those of the observed values through liquid-critical point-gas region.

The Multilevel Analysis for Factors effecting on the Health-related Quality of Life in Dental Technicians

Abstract This study was conducted to provide the basic data for the prevention and management of health risk ofdental technicians by proposing the necessary data in the management of the health related quality of life of dentaltechnicians. The subjects of the survey were 141 dental technicians working in 30 dental technical laboratories and corresponding companies in Daejeon area. A structured self-entry type questionnaire survey was implemented by measuring the work environment from December 20, 2011 to January 31, 2012 at the same time. The total score ofhealth index showed a significant difference according to the working hours and smoking state as the a factor of theindividual level, the physical health index showed a significant difference according to the smoking state and the exercise habits as the factor of the individual level. The mental health index showed a significant difference accordingto the working hours and smoking state as the factor of the individual level. The significant variable did not appearin the predictor of the group level. In conclusion, the quality of life of dental technicians in relation to health appearedto have a larger effect on the factor of the individual level than the factor of the group level.