Conductance calculation of a long tube with equilateral triangle cross section

Using the stratified gas flow model for calculating the conductance of long tubes with constant cross section, an analytical expression for calculating the conductance of along tube with equilateral triangle cross section has been derived. The formula given is applicable to the full pressure range. A minimum in the conductance in the intermediate flow state is shown. 2002 American vacuum Society.

Laser-induced damage threshold of ZrO2 thin films prepared at different oxygen partial pressures by electron-beam evaporation

ZrO2, films were deposited by electron-beam evaporation with the oxygen partial pressure varying from 3 X 10(-3) Pa to I I X 10(-3) Pa. The phase structure of the samples was characterized by x-ray diffraction (XRD). The thermal absorption of the films was measured by the surface thermal lensing technique. A spectrophotometer was employed to measure the refractive indices of the samples. The laser-induced damage threshold (LIDT) was assessed using a 1064, nm Nd: yttritium-aluminium-garnet pulsed laser at pulse width of 12 ns. The influence of oxygen partial pressure on the microstructure and LIDT of ZrO2 films was investigated. XRD data revealed that the films changed from polycrystalline to amorphous as the oxygen partial pressure increased. The variation of refractive index at 550 nm wavelength indicated that the packing density of the films decreased gradually with increasing oxygen partial pressure. The absorptance of the samples decreased monotonically from 125.2 to 84.5 ppm with increasing oxygen partial pressure. The damage threshold, values increased from 18.5 to 26.7 J/cm(2) for oxygen partial pressures varying from 3 X 10(-3) Pa to 9 X 10(-3) Pa, but decreased to 17.3 J/cm(2) in the case of I I X 10(-3) Pa. (C) 2005 American Vacuum Society.

Laser-induced damage threshold of ZrO2 thin films prepared at different oxygen partial pressures by electron-beam evaporation

ZrO2, films were deposited by electron-beam evaporation with the oxygen partial pressure varying from 3 X 10(-3) Pa to I I X 10(-3) Pa. The phase structure of the samples was characterized by x-ray diffraction (XRD). The thermal absorption of the films was measured by the surface thermal lensing technique. A spectrophotometer was employed to measure the refractive indices of the samples. The laser-induced damage threshold (LIDT) was assessed using a 1064, nm Nd: yttritium-aluminium-garnet pulsed laser at pulse width of 12 ns. The influence of oxygen partial pressure on the microstructure and LIDT of ZrO2 films was investigated. XRD data revealed that the films changed from polycrystalline to amorphous as the oxygen partial pressure increased. The variation of refractive index at 550 nm wavelength indicated that the packing density of the films decreased gradually with increasing oxygen partial pressure. The absorptance of the samples decreased monotonically from 125.2 to 84.5 ppm with increasing oxygen partial pressure. The damage threshold, values increased from 18.5 to 26.7 J/cm(2) for oxygen partial pressures varying from 3 X 10(-3) Pa to 9 X 10(-3) Pa, but decreased to 17.3 J/cm(2) in the case of I I X 10(-3) Pa. (C) 2005 American Vacuum Society.

Thermal-mechanical modeling of nodular defect embedded within multilayer coatings

The initiation of laser damage within optical coatings can be better understood by thermal-mechanical modeling of coating defects. The result of this modeling shows that a high-temperature rise and thermal stress can be seen just inside the nodular defect compared to surrounding coating layers. The temperature rise and thermal stress tend to increase with seed diameter. Shallower seed tend to cause higher temperature rise and greater thermal stress. There is a critical seed depth at which thermal stress is largest. The composition of the seed resulting from different coating-material emission during evaporation can affect the temperature rise and thermal stress distribution.

醋酸乙烯酯辐射乳液聚合

用膨胀计连续记录法测定了VAC辐射乳液聚合的转化率～时间曲线，并由此得到各种反应条件下的聚合反应速度。发现聚合反应速度与各因素之间的依赖关系为：Rp∝I~(0.5)[SLS]~(0.12)[V_M/V_(H2O)]~(0.03)。用电子显微镜测定了聚合所得胶乳的粒子大小及数目，发现：N∝[SLS]~(0.48); Rp∝N~(0.24)。其他因素对N无明显影响，实验测定还表明，当转化率超过10%以后，N基本保持恒定。测得的总的反应活化能为5.7千卡/克分子。这些实验结果与化学法VAc乳液聚合得到的结果较相似，这说明两种聚合中存在着一些类似的规律。另外，也注意到两种聚合之间所存在的一些差别，例如，辐射聚合所得乳胶粒较细小，直径分布较窄，同样反应条件下N值较大，以及总反应活化能较低。修改了Friis提出的VAc乳液聚合动力学方程中的常数Kd'的经验表达式。同修改后的Kd'计算出的转化率～时间理论曲线与我们用化学法聚合得到的实验结果很吻合。然后进一步将该模型中的引发速度修改成适合辐射聚合的情况，计算引发速度时同时考虑水、单体和聚合物的辐解，这样得到的转化率～时间理论曲线和我们用辐射法聚合得到的实验结果也较一致。通过我们的和文献上的实验结果，以及通过理论上的分析，论证了我们对Friis模型中的Kd'经验式修改的合理性，同时还论证了我们在理论计算中所采用的各个参数的值或表达式是合理的。考察了各种因素对辐射乳液聚合PVAc的分子量，分子量分布及支化度的影响，发现和化学法聚合的情况类似，主要影响因素是温度，温度越高，分子量越小，支化度越大。和化学法聚合产物不同之处在于，辐射乳液聚合PVAc的分子量比前者高，支化度比前者小，分子量分布比前者窄。另外，前者的分子量分布在整个转化率范围都呈对数正态分布，而后者的分子量分布只是在低转化率下才是如此。Friis为VAc乳液聚合提出的分子量和支化度随转化率变化的理论公式也能适合辐射法聚合的结果，但必须修改K_(tnm)和K_(tnp)的表达式。我们用电子计算机迭出了一组能适合我们各个实验结果的各反应速率常数表达式，并对所得到的这些表达式进行了讨论。这些讨论表明，辐射乳液聚合所得PVAc的分子量较高，支化度较小是由于辐射聚合温度较低，以及K_(tnm)和K_(tnp)比化学法聚合中的相应常数要小些等原因造成的。测定了PVAc和PVA的立规结构，头一头结构，发现辐射乳液聚合的PVAc和PVA均属于典型无规聚合物，头一头结构含量均比化学法聚合产物低。还测定了PVAc和PVA的Tg, Tm, Td，结晶度，溶解度，断裂强度，伸长率，粘接性能，络合交换性能等。发现辐射法聚合产物的结晶度比化学法聚合产物大，而溶解度较小，Tg, Td, Tm较高。所得结果表明，影响溶解度的主要因素是结晶度，影响结晶度的主要因素是头一头结构含量，影响Tg的主要因素是支化度，影响断裂强度的主要因素是结晶度和头一头结构含量，影响剪切力的主要因素是分子量等等。最后，实验结果表明，辐射乳液聚合所得高分子量PVAc具有优良的粘接性能，高分子量PVA具有优良的络合交联性能，这些性能使得高分子量PVAc和PVA在实际应用上将会是很有前途的。

Miscibility and crystallization of poly(beta-hydroxybutyrate)/poly(vinyl acetate-co-vinyl alcohol) blends

Poly(vinyl acetate-co-vinyl alcohol) copolymers (P(VAc-co-VA)) were synthesized by hydrolysis-alcoholysis of PVAc. The miscibility, crystallization, and morphology of poly(P-hydroxybutyrate) (PHB) and P(VAc-co-VA) blends were studied by differential scanning calorimetry, optical microscopy (OM), and SAXS. It is found that the P(VAc-co-VA)s with vinyl alcohol content of 9, 15, and 22 mol % will form a miscible phase with the amorphous part of PHB in the solution-cast samples. The melting-quenched samples of PHB/P(VAc-co-VA) blends with different vinyl alcohol content show different phase behavior. PHB and P(VAc-co-VA9) with low vinyl alcohol content (9% mel) will form a miscible blend in the melt state. PHB and P(VAc-co-VA15) with 15 mol % vinyl alcohol will not form miscible blends while PHB/P(VAc-co-VA15) blend with 20/80 composition will form a partially miscible blend in the melt state. PHB and P(VAc-co-VA22) with 22 mol % vinyl alcohol are not miscible in the whole composition range. The single glass transition temperature of the blends within the whole composition range suggests that PHB and P(VAc-co-VA9) are totally miscible in the melt. The crystallization kinetics was studied from the whole crystallization and spherulite growth for the miscible blends. The equilibrium melting point of PHB in the PHB/P(VAc-co-VA9) blends, which was obtained from DSC results using the Hoffman-Weeks equation, decreases with the increase in P(VAc-co-VA9) content. The negative value of the interaction parameter determined from the equilibrium melting point depression supports the miscibility between the components. The kinetics of spherulitic crystallization of PHB in the blends was analyzed according to nucleation theory in the temperature range studied in this work. The best fit of the data to the kinetic theory is obtained by employing WLF parameters and the equilibrium melting points obtained by DSC. The addition of P(VAc-co-VA) did not affect the crystalline structure of PHB, as shown by the WAXD results. The long periods of blends obtained from SAXS increase with the increase in P(VAc-co-VA) content. It indicates that the amorphous P(VAc-co-VA) was rejected to interlamellar phase corporating with the amorphous part of PHB.

醋酸乙烯酯乳液聚合数学模型(Ⅰ) 阶段Ⅰ模型

研究了较大亲水性单体醋酸乙烯酯(VAc)乳液聚合的乳胶粒生成和生长过程,提出了VAc乳液聚合阶段Ⅰ数学模型.该模型既考虑到胶束成核机理,又考虑到水相中低聚物沉淀成核机理.研究了自由基解吸与吸附在单体珠滴上的乳化剂对VAc乳液聚合阶段Ⅰ动力学的影响,并对模型预计结果与实验数据进行了比较和讨论.

醋酸乙烯酯乳液聚合数学模型(Ⅱ) 阶段Ⅱ与阶段Ⅲ模型

研究了较大亲水性单体醋酸乙烯酯(VAc)乳液聚合动力学,着重剖析了自由基解吸的影响及水相中的聚合反应对总聚合反应速率的贡献,提出了阶段Ⅱ和阶段ⅢVAc乳液聚合数学模型,成功地预计了聚合反应速率、自由基在乳胶粒中的分布及乳胶粒中平均自由基数随转化率的变化规律.并将模型预计结果和实验数据进行了比较和讨论.

聚丙烯酸钠和丙烯酸钠-醋酸乙烯酯无规共聚物的防垢效果

本文研究了聚丙烯酸钠的防垢效果与其分子量的关系,发现防垢率随其分子量的降低而增加。合成了不同组成的丙烯酸钠-醋酸乙烯酯无规共聚物,并对其作了表征,给出了奇特的NMR谱。实验结果表明,所合成的NaA-VAc无规共聚物型双亲聚合物水溶性好,且具有优秀的防垢性能。

双组份网状共聚物的动态力学性质

本文研究了端乙烯基聚氨酯预聚物(VTPU)同乙烯类单体甲基丙烯酸甲酯(MMA)、苯乙烯(St)、醋酸乙烯酯(VAc)、和甲基丙烯酸丁酯(BMA)聚合得到的双组份网状共聚物(BCN′s)的动态力学性能及形态结构。四种BCN′s试样两组份在动态力学谱上均有半相容的特征。体系的交联密度增大,混合熵增加,相容性改善,试样中可溶性组份含量随BCN′s的组成而变化。溶胶组份可改善体系中两组份的相容性。

聚醋酸乙烯酯/聚丙烯酸甲酯互穿网络聚合物的研究——1.聚合条件对体系相容性的影响

用分步法合成了聚醋酸乙烯酯/聚丙烯酸甲酯互穿网络聚合物(PVAc/PMA-IPN),PVAc和PMA的交联剂分别是丁二酸二烯丙酯(DAS),和二乙烯基苯(DVB)。当DAS用量较小时,VAc聚合时的接枝反应较明显,PVAc网络的交联密度高于化学当量的计算值。动态力学的实验结果表明,丙烯酸甲酯的聚合温度和聚合过程中的溶胶-凝胶转变对PVAc/PMA-IPN体系的相容性有很大影响。