• 한국세라믹학회지
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• 제40권11호
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• pp.1127-1131
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• 2003

인삼염유리는 전자부품분야에서 저온소성유리로 그 활용범위가 넓은 편이나 높은 열팽창계수로 알칼리 산화물 등을 첨가하여 그 특성을 조정하고 있다. 본 연구에서는 P$_2$O$_{5}$-SnO-ZnO-SiO$_2$/B$_2$O$_3$ 유리계에 대하여 열적특성으로 선팽창계수와 유리전이온도, 용융온도 등을 측정하여 그들 값의 상관관계를 고찰하였다. 이러한 결과는 다른 인삼염 유리와 비교하였을때 선팽창계수와 유리전이온도의 곱이 일정한 값으로 나타나서 이들 중의 하나의 값으로부터 간접적으로 다른 변수를 측정 할 수 있는 한 방법이 될 수 있다.

• Bulletin of the Korean Chemical Society
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• 제29권6호
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• pp.1167-1172
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• 2008

We investigated the glass transition temperatures ($T_g$) of dendrons consisting of conformationally mobile aliphatic polyether dendritic cores plus glassy peripheral polystyrenes (PSs), and linear PSs in the molecular weight range of 1000-8500 g/mol. We compared their $T_g$ behavior depending on their polymeric architecture. The linear PSs show a typical growth of $T_g$ up to 92.5 ${^{\circ}C}$ as the molecular weight increases to 8300 g/mol, while the dendrons display nearly constant $T_g$ values of 58-61 ${^{\circ}C}$, despite the increase of molecular weight with each generation. The striking contrast of Tg behavior would be mainly attributed to the fact that the dendrons keep the ratio of $N_e$/M ($N_e$: number of peripheral chain ends, M: molecular weight) over all the generations. Additionally, for the influence of dendritic spacers on glass transition temperature we prepared dimeric PSs with different linkage groups such as aliphatic ether, ester and amide bonds. We found that the dimer with the ether spacer exhibited the lowest glass transition at 55.4 ${^{\circ}C}$, while the amide linked dimer showed the highest glass transition temperature at 74.2 ${^{\circ}C}$. This indicates that the peripheral PS chains are effectively decoupled by the conformationally flexible ether spacer. The results from this study demonstrated that polymeric architecture and dendritic core structures play a crucial role in the determination of glass transition behavior, providing a strategy for the systematic engineering of polymer chain mobility.

• 전기학회논문지
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• 제62권5호
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• pp.649-656
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• 2013

A conventional epoxy-microsilica composite (EMC) and an epoxy-microsilica-nanosilicate composite (EMNC) were prepared in order to apply them to mold-type transformers, current transformers (CT) and potential transformers (PT). Nanosilicate was exfoliated in a epoxy resin using our electric field dispersion process and AC insulation breakdown strength at $30{\sim}150^{\circ}C$, glass transition temperature and viscoelasticity were studied. AC insulation breakdown strength of EMNC was higher than that of EMC and that value of EMNC was far higher at high temperature. Glass transition temperature and viscoelasticity property of EMNC was higher than those of EMC at high temperature. These results was due to the even dispersion of nanosilicates among the nanosilicas, which could be observed using transmission electron microscopy (TEM). That is, the nanosilicates interrupt the electron transfer and restrict the mobility of the epoxy chains.

• 전기학회논문지
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• 제65권9호
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• pp.1504-1510
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• 2016

The aim of this study is to improve properties both glass transition temperature($T_g$) and coefficient of thermal expansion(CTE) using epoxy/micro-nano alumina composites with adding glycerol diglycidyl ether (GDE:1,2,3,5g). This paper deals with the effects of GDE addition for epoxy/micro alumina contents (40, 50, 60wt%)+surface modified nano alumina(1_phr) composites. 20 kinds specimen were prepared with containing micro, nano alumina and GDE as a micro composites(10, 20, 30, 40, 50, 60, 70wt%) or a nano/micro alumina composites(1phr/40, 50, 60wt%). Average particle size of nano and micro alumina used were 30nm and $1{\sim}2{\mu}m$, respectively. The micro alumina used were alpha phase with Heterogeneous and nano alumina were gamma phase particles of spherical shape. The glass transition temperature and coefficients of thermal expansion was evaluated by DSC and TMA. The glass transition temperature decreased and coefficients of thermal expansion become smaller with filled contents of epoxy/micro alumina composites. On the other hand, $T_g$ and CTE as GDE addition variation(1,2,3,5g) of epoxy/micro-nano alumina composites decreased and increased respectively.

• 한국초전도ㆍ저온공학회논문지
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• 제15권2호
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• pp.16-19
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• 2013

The magneto-resistivity and electric field-current density (E-J) curves were investigated up to a magnetic field 9 T in the optimally doped $BaFe_{1.8}Co_{0.2}As_2$ single crystal with a superconducting temperature ($T_c$) of 24.6 K. The E-J Scaling behaviors below and above vortex glass transition temperature ($T_g$) were found, confirming the existence of the vortex glass phase transition. The critical exponents for the diverging spatial and time correlations at $T_g$, were obtained as v = $1.1{\pm}0.1$ and z = $4.5{\pm}0.3$, respectively. The obtained critical exponents are in good agreement with the predicted values of v ~ 1 - 2 and z > 4 within the 3D vortex glass theory.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.421-426
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• 2007

A parametric study to investigate the effects of composition variables on the glass transition and mechanical properties of CNT-based nanocomposites was performed using molecular dynamics simulations. In this study, matrix chain length and CNT length were chosen as the candidate characteristic parameters. In order to understand the effect of both parameters in detail, three sample sets having different chain lengths with the same CNT configuration and two sample sets having different CNT lengths with same chain length were prepared. Other parameters such as volume fraction and density were fixed to enable rigorous comparisons. Amorphous polyethylene is used as matrix polymer and (10,0) zigzag CNT is embedded into the matrix to reinforce polymer matrix. As a result, longer polymer chain length of matrix solely increased glass transition temperature but no reinforcing enhancement was observed. CNT length showed similar increase with little enhancement of elastic modulus. In addition to this, nanocomposites showed temperature-dependent elastic modulus jump passing thorough the glass transition region agrees well with experimental results.

• Preventive Nutrition and Food Science
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• 제15권4호
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• pp.356-359
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• 2010

Glass transition phenomena in nine Korean pure honeys (moisture content 18.3~20.1%) and honey-water mixtures by different water contents (0, 2, 5, and 10% w/w) were investigated with modulated different scanning calorimetry (MDSC). The total, reversing, and non-reversing heat flows were quantified during heating using MDSC. Glass transition was observed from reversing heat flow separated from the total heat flow. The glass transition temperatures ($T_g$) of pure honeys, which are in the range of $-42.7^{\circ}C$ to $-50.0^{\circ}C$, varied a lot with low determination coefficient ($R^2$=0.63), whereas those of honey-water mixtures decreased with a decrease in honey content. The $T_g$ values were also more significantly different among honey-water mixtures when compared to pure honeys, indicating that in the honey-water mixture system the $T_g$ values appear to be greatly dependent on moisture content. The measured heat capacity change (${\Delta}C_p$) was not influenced by moisture content.

• 분석과학
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• 제5권3호
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• pp.309-317
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• 1992

졸-겔법에 의해 무기-유기 복합체를 합성하였으며, 복합체의 결합특성을 알아보기 위하여 DMTA(Dynamic Mechanical Thermal Analyzer)를 이용하여 유리전이 온돈(Tg)를 측정하였다. HCl 과 물의 양이 증가될수록 Tg는 고운으로 진행됨으로부터 복합화가 더 잘 일어남을 알 수 있었다. 그러나 반응시간에 따른 Tg의 변화는 관찰되지 않았다.

• 한국재료학회지
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• 제32권12호
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• pp.560-564
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• 2022

In this study, lanthanum boron silicate glasses were prepared with a composition of x Li₂O-(60-x)B₂O₃-5CaO-5BaO-7ZnO-10SiO₂-10La₂O₃-3Y₂O₃ where x = 1,3,5,7, and 9 mol%. Each composition was melted in a platinum crucible under atmospheric conditions at 1,400 ℃ for 2 h. Clear glasses with a transmittance exceeding 85 % were fabricated. Their optical, thermal, and physical properties, such as refractive index, Abbe number, density, glass transition (T_g) and Knoop hardness were studied. The results demonstrated that refractive index was between 1.6859 and 1.6953 at 589.3 nm. The Abbe number was calculated using an equation for 589.3 nm (nd), 656.3 nm (nf) and 486.1 nm (nc) and was observed to be in the range from 57.5 to 62.6. As the Li₂O content increased, the glass transition temperature of the optical glass decreased from 608 ℃ to 564 ℃. If glass mold pressing is performed using a material with a low transition temperature and high mechanical strength, then the optical glasses developed in this study can be completely commercialized.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.1011-1016
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• 2001

The purpose of this study is to find out the effect of polymer glass transition temperature on mechanical properties of polymer latex-modified mortars in comparison with ordinary cement mortar. The Polymer latex-modified mortars are prepared with 5, 10, 15 and 20% of polymer cement ratio respectively, and properties of modified mortars such as air content, compressive, flexural and tensile strengths are tested. The test results indicate that the types of polymer dispersion and the polymer-cement ratio are very important factors to characterize the properties of polymer-modified mortars, and also the glass transition temperature of polymer dispersions has an important effect on the performance of polymer-modified mortars. The modifying effects of two kinds of polymer dispersion, St/BA-1 and SBR, are evaluated.