共查询到19条相似文献,搜索用时 93 毫秒
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聚二甲基硅氧烷分子尺寸的温度依赖性,文献报导出入甚大.Ciferri测定了一个试样在二甲基硅油中30—150℃的特性粘数.Mark、Flory测定了两个级份(M_w=2.5×10~6,4.3×10~5)在二甲基硅油中30—105℃的特性粘数,从所得良溶剂内[η]值依据稀溶液理论外推;钱人元、余世诚、高玉书采用乙苯-邻苯二甲酸二乙酯混合溶剂体系,在 相似文献
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在不同外加水压下作者等用毛细管粘度计测定了聚甲基丙烯酸甲酯五个分级试样的苯溶液粘度,并用光散射法在丙酮溶液中测定了重均分子量,得到下列特性粘数、分子量关系式(25°)。不加外压时:[η]=3.80×10~(-3)M~(0.79)毫升/克S_R=55达因/厘米~2:[η]_s=12.6×10~(-3)M~(0.70)D_R=5000秒~(-1):[η]_D=8.37×10~(-3)M~(0.73) 适用于分子量范围0.2—4.5×10~6。并指出用实验数据验证性粘数理论时,α值的切变速度依赖性有重要的影响。粘度数据中斜度系数 k′或β值,无论对 S_R 或 D_R 都没有显著的影响,与前人的结果有不同。对光散射测定所用仪器加以叙述并从光散射数据得到了试样的 A_2和<~2>_z 的数值。 相似文献
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高分子溶液性质依赖于在溶液中的形态,高分子-良溶剂溶液由于高分子链段与溶剂分子间相互作用使末端矩h~2~(1/2)大于θ-条件下末端矩h_0~2~(1/2),一维扩张因子α以下式表示 相似文献
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对低温聚合丁苯橡膠一个级分(M=1.0×10~6)的甲苯溶液在切变速度 D=10—20,000秒~(-1)范国内测定了五种浓度溶液的粘度数据(25.0℃)。粘度计采用 Tsuda 的水平毛细管水平流出体积计量管的设计,且在全部切变速度范围内都从同一毛细管流出,使不同范围内的数据很好衔接。实验结果证明在低切变速度区域牛顿粘度η(?)(0)的存在。并且从lnη(?)—ln D 曲线的反曲点(?)值不依赖于浓度和对反曲点的对称性估计η(?)(∞)值和整个切变速度范国内的粘度行为。取几个等 D 值时的 lnη(?)按(lnη(?)/C)-C 的线性外推得到[η]_D,明确表示在低切变速度区域[η](?)的存在。两种牛顿流动间转变区域的实难数据可以采用下列两公式线性化:x(D)=(1/2)[1-erf(kln(?))],x(D)=(1/1+(?))~n,式中x=(lnη(?)-lnη(?)(∞)/lnη(?)(0)-lnη(?)(∞)),erf(z)=(?)-u~2du,k 和 n 是依赖于浓度的参数,但在较高浓度时均趋向一恒定值。([η]_D/[η]_0)-ln D 曲线相当符合于刚性橢球轴比 p=4—5间的理论曲线,这样得到的转动扩散系数(?)_(rot)=6.6×10~2秒~(-1),但是从(?)_(rot)和[η]_0值按 Scheraga-Mandelkern 方法计算得到的分子量值与实际不符,所以丁苯橡膠分子线团不是刚性结构;而以1/(?)值作为高分子线团弹性变形的松弛时间,按 Bueche 理论计算得到的分子量值与实际极相一致。 相似文献
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(1)聚己內醯胺試樣在85%甲酸溶液中加水分級沉澱,得到分子量不同的級份,經羧基滴定,並於40%硫酸溶液中,在25°時测定粘度,得到下面的特性粘數分子量關係式: [η]=5.92×10~(-4) M~(0.686)或 [η]=2.44×10~(-5) M+0.080濃度單位是克/分升,分子量範圍是3000-13000。 (2)聚己內醯胺的40%硫酸溶液的粘度數據,試用了三種外推公式: lnη_r/c=[η]-β[η]~(2)c (1) η_(sp)/c=[η]+k′[η]~(2)c (2) logη_(sp)/c=log[η]+k[η]c (3) 用式(1)和式(3)得到的[η]值相同,式(2)得到的略小1-2%。β和k′值隨分子量的减小而顯著地增大,這和一般的高聚物——溶劑體系的行為相反。當高分子與溶劑分子間的氫鍵作用是高聚物溶解的主要因素時,用k′值來做溶劑能力的估計,是完全沒有意義的。 (3) 聚己內醯胺在40%硫酸裏,溶液粘度的切變速度依賴性是可以忽略的。我們認為40%硫酸是測定聚己內醯胺的粘均分子量的最合適溶劑。 (4) 從粘度數據依照Debye和Bueche的特性粘數理論,算出聚己內醯胺分子在40%硫酸裏的等效Stokes半徑,說明聚己內醯胺分子在40%硫酸溶液裏的形態,可以看作是無規則的線團。 相似文献
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聚N,N-二乙基丙烯酰胺溶液粘度的温度依赖性 总被引:2,自引:0,他引:2
通过自由基聚合,合成了线型聚N,N-二乙基丙烯酰胺(PDEA),用乌氏粘度计测定并考察了该聚合物在四氢呋喃(THF)、H2O以及THF-H2O混合溶剂中粘度的温度依赖性.实验结果表明,PDEA 在上述三种溶剂中粘度的温度依赖性不同,PDEA-THF体系的相对粘度随温度升高而增大;PDEA-H2O体系以及PDEA-THF-H2O体系的相对粘度随温度升高而减小,且THF体积分数φTHF < 0.7时具有透明-白浊转变现象;对PDEA-THF-H2O体系,φTHF增加,透明-白浊转变温度升高,而当φTHF=0.7时,则观察不到透明-白浊转变现象. 相似文献
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本文用激光小角散射光度计,测定了聚苯乙烯甲苯溶液的第二维利系数的分子量依赖性,重均分子量在3×104θ/M值为7.1 8×10-18厘米2/克(0为无扰均方半径,M为分子量),与文献测定值相近.在4×103相似文献
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前文已报导了具有较好抗凝血性能的新型聚电解质,聚甲基丙烯酸己磺酸钠(PSSH-MA)的合成,用统计方法对盐存在时PSSHMA溶液的粘性研究及用小角激光光散射法测定的PSSHMA体系的特性粘数和重均分子量的关系。本文进一步用KNAUER膜渗透计测定了该体系的特性粘数与数均分子量的关系[6],并进一步探讨聚电解质水溶液渗透压测定中的一些问题。 相似文献
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A DETAILED investigation of the temperature dependence of the fluorescence quantum yield φf can yield–directly or indirectly–significant information about behavior of excited states of organic molecules, such as the temperature effect on radiationless transitions and on photochemical reactivity. Variation of the temperature changes the viscosity of the solvent and, in conjunction with measurements of φf ( T ), allows investigations of diffusion-controlled processes. For example, energy transfer and quenching processes as well as excimer or exciplex formation fall into this category. Recent review articles by Weller (1962) and Birks (1970) deal with this topic. Moreover, Huber and Mantulin (1972) have suggested that restraints placed upon geometric modifications of the excited molecule by temperature-induced changes in the solvent cage (variation of site structure) are reflected in a varying φf .
The purpose of this note is to describe and verify a simple procedure, accurate to about ± 5%, for measuring the relative fluorescence quantum yield as a function of temperature. A quantum yield study of 9,10-diphenylanthracene between room temperature and 77°K is employed to demonstrate the capabilities of this method. In addition, we consider an example of diffusion-controlled quenching by oxygen measured over a wide temperature range. 相似文献
The purpose of this note is to describe and verify a simple procedure, accurate to about ± 5%, for measuring the relative fluorescence quantum yield as a function of temperature. A quantum yield study of 9,10-diphenylanthracene between room temperature and 77°K is employed to demonstrate the capabilities of this method. In addition, we consider an example of diffusion-controlled quenching by oxygen measured over a wide temperature range. 相似文献
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聚N—异丙基丙烯酰胺溶液的温度依赖关系 总被引:5,自引:0,他引:5
用自由基聚合法合成了聚N-异丙基丙烯酰胺(PNIPAAM)样品,用乌氏粘度计考查了该聚合物的四氢呋喃(THF)溶液和水溶液的粘度与温度的依赖关系。发现PNIPAAM-THF体系的特性粘数随温度升高而增大,PNIPAAM-H2O体系的特性粘数-温度曲线表现出较为复杂的变化规律。并用实验确定的特性粘数对合成样品的分子量进行了表征Mn=8.44×10^5g·mol^-1。 相似文献
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THE TEMPERATURE DEPENDENCE OF PHYTOCHROME TRANSFORMATIONS 总被引:4,自引:0,他引:4
Abstract— The kinetics of phytochrome transformation were examined over a 30°C temperature range (+5° to–25°C) in 75% glycerol. Two new intermediate reaction stages are described for the transformation of the red-absorbing form, P r to the far-red absorbing form, P fr The free energies, enthalpies and entropies of activation were obtained for five of the six reaction stages observed in the transformation of P r to P fr and for the two reaction stages observed in the reverse process. All exhibited positive entropies of activation with the maximum being 25 entropy units. The results suggest that the phototransformations between P r and P fr consist of relaxation processes beginning with the intermediate produced immediately upon absorption of a quantum of light and ending with either P r or P fr . 相似文献
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THE TEMPERATURE DEPENDENCE OF Pfr ACTION GOVERNS THE UPPER TEMPERATURE LIMIT FOR GERMINATION IN LETTUCE 总被引:1,自引:0,他引:1
In most cultivars of lettuce (Lactuca saliva L,), red light acting through the red/far-red reversible phytochrome system promotes full germination within the20–30°C range, but at progressively higher temperatures germination declines sharply. The relationship between this upper ternperature limit for germination and the temperature dependence of phytochrome action was investigated in Grand Rapids lettuce. In fresh seeds the GT50 (temperature giving half maximal germination) was ca 29–30°C. In these seeds, escape from far-red reversibility did not occur at 35°C, a temperature above the GT50, but occurred rapidly at 27°C, a temperature below the upper limit. Increasing periods of dark pretreatment at high temperature (35°C) or increasing concentrations of the germination inhibitor coumarin caused a progressive decline in the GT50, Escape from photoreversibility did not occur at 27°C in seeds in which the GT50 had been reduced to less than 25°C by coumarin or by prolonged high temperature pretreatment. These results indicate that there is a close correlation between the position of the upper temperature limit for germination, and the temperature dependence of phytochrome action. We conclude that factors that alter the upper temperature limit for germination do so by changing the temperature dependence of phytochrome action. 相似文献
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Abstract— A counting procedure is described for determining the polarization characteristics of very weak emission. The degree of polarization of weak emission of DNA bases in aqueous solution at room temperature is found to he high and positive, and shows an inverse correlation with their emission quantum yields which can be understood in terms of a competition between emission lifetimes and rotational relaxation times. For 5-methylcytosine the emission quantum yield can be changed by varying the acidity and the corresponding degrees of polarization show the behavior expected from Perrin's relation. The ratio τo/τrot is discussed in terms of anisotropic relaxation and calculations of τ0. 相似文献
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非晶聚氯乙烯玻璃化转变过程弛豫时间的温度依赖性研究 总被引:1,自引:0,他引:1
通过对非晶聚氯乙烯α内耗峰峰温与测量频率的实验结果的拟合,提出了一种新的玻璃化转变附近弛豫时间的表达式,不仅很好地拟合了实验结果,给出调节参量合理的物理意义,而且为Kauzmann疑题(paradox)提供了一个合理的解决. 相似文献