粘度法研究高分子溶液行为的实验改进(Ⅱ)

高分子在粘度计毛细管管壁上的吸附不仅会导致毛细管有效管径减小，而且可以导致毛细管界面性质发生显著改变，具体表现为测定高分子溶液流过时间t之前和之后纯溶剂的流过时间t0和t0′与高分子溶液流过时间t对浓度作图外推到浓度为零时的值t0^*并不一致。不同温度时聚乙烯吡咯烷酮（PVP）水溶液粘度测定结果表明，当吸附讷发子显著改变了毛细管界面性质时，需要将高分子溶液粘度测定方法由t/t0′改为t/t0^*。经过改进的粘度测定方法不仅更加普适合理，而且更加简单有效。     

表面张力对PEO稀溶液粘度行为的影响

测定了不同分子量聚氧化乙烯(PEO)在水和苯溶剂中的粘度,发现在低浓度区PEO水溶液的比浓粘度出现负偏离, PEO苯溶液比浓粘度与浓度之间依旧满足线性关系.表面张力测定结果表明, PEO分子显著降低了水的表面张力,而苯的表面张力则不受影响.PEO水溶液和纯溶剂水表面张力的不同干扰了高分子溶液和溶剂在粘度计中流过时间的测量,导致低浓度区PEO水溶液比浓粘度出现负偏离.利用PEO水溶液和水表面张力测定结果,结合乌式粘度计的几何尺寸,定量分析了PEO水溶液和纯溶剂水表面张力的差异对粘度测量结果的影响,计算结果与实验结果基本相符.如果用PEO水溶液流过时间对浓度作图的外推值t0*计算相对粘度,可以完全消除PEO水溶液和水表面张力差异对粘度测量的影响.     

粘度法测定聚乙烯醇相对分子质量的实验改进

对在25℃时测定聚乙烯醇(PVA)水溶液粘度的实验进行了改进,以高分子溶液流过时间对浓度作图的外推值t0*代替纯溶剂的流过时间t0计算PVA水溶液的相对粘度ηr,结果表明可以得到较好的实验结果。     

利用Poiseuille方程确定聚乙烯醇在粘度计毛细管管壁上吸附层的厚度

利用高分子溶液流过时间测量之前和之后纯溶剂流过时间的变化不仅再次证实了极低浓度区高分子溶液反常粘度行为的起源和校正方法，而且找到了定量研究粘度计毛细管管壁上高分子吸附层厚度的实验方法。研究结果表明，溶剂的性质对高分子吸附层厚度有着显著影响。     

极低浓度区高分子溶液异常粘度行为研究进展

极低浓度区高分子溶液粘度的测定涉及到外推法确定高分子溶液特性粘数的实验基础。综述了极低浓度区高分子溶液反常粘度行为的起源，探讨了粘度计毛细管管壁上高分子吸附层、界面效应、高分子溶液或溶剂在毛细管中流动模式的改变、高分子与毛细管管壁界面间相互作用、乌氏粘度计结构限制等对极稀高分子溶液粘度的影响，以及正确测定极低浓度区高分子溶液粘度的实验方法。     

粘度法测量高分子在玻璃表面上的吸附层厚度

高分子在固体表面上的吸附层厚度对了解其结构具有重要意义．厚度的测量通常采用椭圆偏振法、流体力学法和沉降法等几种方法来测量［１］．流体力学法始创于５０年代中期Ｏｈｒｎ［２］对极稀高分子溶液粘度异常行为的解释．由于高分子在粘度计的毛细管管壁上的吸附,致使...     

一组新的高分子溶液粘度与浓度关系函数式

<正> 粘度法是测定高聚物分子的大小与结构最简便、最常用的方法.在用粘度法测定高聚物分子大小与结构时,需求得极限粘数[η].为此,需确立高分子溶液粘度与浓度的关系,文献中有过种种不同的函数式.通常,将ηsp/c、logηsp/c、lnηr/c对c或ηsp/c对ηsp作图外推到c为零或ηsp为零得[η].Heller对各种外推方法进行了详细的研究,可是到目前为止,采用的成对外推公式不多,且有明显的缺陷.     

树状高分子溶液在粘度计毛细管表面的吸附现象

本文测定了树状高分子DAB(PA) n 水溶液和脂肪族超支化聚酯及其硅烷化衍生物溶液性质 .通过粘度测量 ,得到了吸附常数k ,半数吸附浓度ca,分子间缔合常数Km ,特性粘度 [η]等参数 ,解释了特性粘度的反常行为 ,重点研究了吸附现象 .发现树状高分子和超支化高分子溶液在粘度计毛细管表面形成了多层吸附 ,高分子之间的相互作用及高分子与溶剂分子间的氢键作用是形成多层吸附的重要原因     

离分子混合物溶液在极稀浓度区的粘度异常行为

上世纪50年代初人们就发现,高分子溶液的粘度在极稀浓度区往往表现出异常行为,即当浓度低于某一特定值后,比浓增比粘度浓度图偏离预计的线性关系,出现上弯或下弯的曲线.几十年来人们对此现象展开了大量研究,提出了一些互不协同的解释[1,2].最近,程时等[3,4]对该问题作了系统深入的研究,指出这种粘度异常是源于粘度测量中高分子溶液与毛细管内壁间的界面作用,并给出了消除界面作用干扰的理论改正公式.至此,单一高分子溶液粘度的异常问题得到了明确的解释.但是,关于高分子混合物在极稀浓度区的粘度行为的研究就比较稀少.80年代Ｄｏｎｄｏｓ…     

梳型聚合物在固液界面吸附形态的Monte Carlo模拟

采用Monte Carlo模拟方法对PAA/PEO梳型聚合物在固液界面吸附形态进行了模拟,得到了聚合物在液相中聚集形态以及在固液界面上吸附形态的瞬时构型,同时获得了聚合物的吸附层厚度、均方回转半径和吸附在固液界面的各种链段数等微观信息. 结果证实：随着聚合物的接枝数Np增大,聚合物在液相中的扩散系数逐渐降低、相对粘度逐渐增大;当Np≥6时,羧基阴离子基团置于吸附层最外围,吸附层厚度近似等于PEO侧链长度,聚合物在固体表面形成空间排斥为主、静电排斥为辅的吸附状态;吸附聚合物分子密度过低或过高均不能起到良好的空间屏蔽或阻隔效应;吸附在固体粒子表面聚合物应该具有适宜的吸附-脱附自平衡能力.     

Studies on the viscosity behavior of polymer solutions at low concentrations

Viscosity measurements had been made on poly(vinyl alcohol) (PVA), poly(N-vinyl-2-pyrrolidone) (PVP) and poly(ethylene oxide) (PEO) solutions down to low concentrations. It was found that defined as the flow time of the pure solvent in ideal conditions and obtained practically by extrapolating the flow time of polymer solution t to zero concentration, was not equal to the flow time of the pure solvent t₀ measured. The reduced viscosity η_sp/C determined by (t/t₀-1)/C exhibited either a drastic increase or a significant decrease with dilution, depending upon the polymer solution investigated. On the other hand, η_sp/C determined by was proportional to C even at low concentrations. The anomalous viscosity behavior of neutral polymer solutions at low concentrations, therefore, was due to the incorrect method by which η_sp/C was determined. The detailed experiments indicated that the effective diameter of the viscometer capillary, the surface property of the capillary wall and the additional pressure corresponding to the measurement of t and t₀ for PVA, PVP and PEO solutions were not the same. Taking into account the contact anger and the surface tension of the liquid, together with the geometric parameter of the viscometer, the influence of the additional pressure upon the flow time measurement could be studied quantitatively. The calculation was in a good agreement with the experimental result. According to the method presented in this paper, the thickness of the adsorbed polymer layers on the capillary walls could be determined. It was noted that the thickness of the adsorbed polymer layers on the capillary walls was closely related to the solvent in which the polymer molecules were dissolved. The polymer molecular weight, however, had little or no effect on the thickness of the adsorbed polymer layers on the walls of the viscometer capillary.     

A novel method for determining the viscosity of polymer solution

The relative viscosity η_r and, thus, the reduced viscosity η_sp/C of polymer solution could be obtained by recording the flow times of the polymer solution and the pure solvent in a capillary viscometer. Our experimental results indicated that the measurement of the flow time of the pure solvent was unnecessary. In particular, if the recorded flow time of the pure solvent was used to determine the viscosity of polymer solution, the reduced viscosity η_sp/C exhibited either a drastic increase or a significant decrease in an extremely dilute solution, depending upon the properties of the polymer solution investigated. In this research work, a new method for determining the viscosity of polymer solutions is reported. In the proposed method, the flow time of polymer solution at zero concentration, t₀^*, instead of the measured flow time of the pure solvent, was used to determine the viscosity of polymer solution. The reduced viscosity η_sp/C determined by the new method is proportional to concentration C even in an extremely dilute solution. The relative viscosity η_r vs. C plot also indicated clearly that t₀^*, instead of the measured flow time of the pure solvent, should be used for determining the viscosity of polymer solution. At low concentrations, the flow time of the polymer solution was proportional to C. As a result, t₀^* could be determined by extrapolating the flow time of the polymer solution to C=0.     

Effect of polyethylene oxide on the viscosity of dispersions of charged silica particles: interplay between rheology, adsorption, and surface charge

In this study a systematic investigation on the adsorption of polyethylene oxide (PEO) onto the surface of silica particles and the viscosity behavior of concentrated dispersions of silica particles with adsorbed PEO has been performed. The variation of shear viscosity with the adsorbed layer density, concentration of free polymer in the solution (depletion forces), polymer molecular weight, and adsorbed layer thickness at different salt concentrations (range of the electrostatic repulsion between particles) is presented and discussed. Adsorption and rheological studies were performed on suspensions of silica particles dispersed in solutions of 10⁻² M and 10⁻⁴ M NaNO₃ containing PEO of molecular weights 7,500 and 18,500 of different concentrations. Adsorption measurements gave evidence of a primary plateau in the adsorption density of 7,500 MW PEO at an electrolyte concentration of 10⁻² M NaNO₃. Results indicate that the range of the electrostatic repulsion between the suspended particles affects both adsorption density of the polymer onto the surface of the particles and the viscosity behavior of the system. The adsorbed layer thickness was estimated from the values of zeta potential in the presence and absence of the polymer and was found to decrease with decreasing the range of the electrostatic repulsive forces between the particles. Experimental results show that even though there is a direct relation between the viscosity of the suspension and the adsorption density of the polymer onto the surface of the particles, variation of viscosity with adsorption density, equilibrium concentration of the polymer, and range of the electrostatic repulsion cannot be explained just in term of the effective volume fraction of the particles and needs to be further investigated. Received: 15 February 2000/Accepted: 26 June 2000     

EFFECT OF ADSORPTION ON THE VISCOSITY OF DILUTE POLYMER SOLUTION*

Careful measurements of the dilute solution viscosities of polyethylene glycol and polyvinylalcohol in water were carried out. The reduced viscosities of both polymer solutions plot upward curves atextremely dilute concentration levels similar to the phenomena observed for many polymer solutions in theearly 1950's. Upon observation of the changes of the flow times of pure water in and the wall surfacewettability of the viscometer after measuring solution viscosity, a view was formed that the observed viscosityabnormality at extremely dilute concentration regions is solely due to the effect of adsorption of polymerchains onto the wall surface of viscometer. A theory of adsorption effect based on the Langmuir isothermswas proposed and a mathematical analysis for data treatment was performed. The theory could adequatelydescribe the existing viscosity data. It seems necessary to correct the viscosity result of dilute polymersolutions measured by glass capillary viscometer by taking into account the effect of adsorption in all cases.     

毛细管粘度计动能和残液改正的综合效应

对玻璃毛细管粘度计驱动静压的动能损耗和器壁粘附液体的残液效应作了统一的处理, 说明两者紧密相关, 不能分离。毛细管粘度计的工作方程具有η/ρt=A~*-B~*/t2-C~*/t4的形式, 其中A~*, B~*、C~*为仪器常数, 均与粘度计的尺寸和残液效应因子有关。理论指出, 在习惯用的Poiseuille-Hagenbach公式动能改正项中引进的数值因子m是由于液体粘附于球泡器壁引起的后果, 相当于m=1+C~*/B~(*t2), 从而解释了数值因子随Reynold数增加而增大的事实。列举了溶液相对粘度的计算公式和仪器常数的订定方法, 并给出了文献和实验的例证。     

Effects of polymer adsorption on the effective viscosity in microchannel flows: phenomenological slip layer model from molecular simulations

Molecular simulations (Dissipative Particle Dynamics - DPD) were used to quantify the effect of polymer adsorption on the effective shear viscosity of a semi-dilute polymer solution in microchannel Poseuille flow. It is well known that polymer depletion layers develop adjacent to solid walls due to hydrodynamic forces, causing an apparent wall slip and reduced effective viscosity (increased total flow rate). We found that depletion layers also developed in the presence of hydrodynamically rough adsorbed layers on the wall. Polymer-polymer (steric) repulsion between flowing and adsorbed polymer expanded the depletion layer compared to no-adsorption cases, and the effective viscosity was reduced further. Desorption occurred for higher shear rates, reducing the repulsion effect and shrinking the depletion layers. A phenomenological algebraic model for the depletion layer thickness, including a shear modified adsorption isotherm, was developed based on the simulation data. The depletion layer model can be used together with the effective viscosity model we developed earlier.     

Surface rheology of PEO-PPO-PEO triblock copolymers at the air-water interface: comparison of spread and adsorbed layers

The dilatational rheological properties of monolayers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-type block copolymers at the air-water interface have been investigated by employing an oscillating ring trough method. The properties of adsorbed monolayers were compared to spread layers over a range of surface concentrations. The studied polymers were PEO26-PPO39-PEO26 (P85), PEO103-PPO40-PEO103 (F88), and PEO99-PPO65-PEO99 (F127). Thus, two of the polymers have similar PPO block size and two of them have similar PEO block size, which allows us to draw conclusions about the relationship between molecular structure and surface dilatational rheology. The dilatational properties of adsorbed monolayers were investigated as a function of time and bulk solution concentration. The time dependence was found to be rather complex, reflecting structural changes in the layer. When the dilatational modulus measured at different concentrations was replotted as a function of surface pressure, one unique master curve was obtained for each polymer. It was found that the dilatational behavior of spread (Langmuir) and adsorbed (Gibbs) monolayers of the same polymer is close to identical up to surface concentrations of approximately 0.7 mg/m2. At higher coverage, the properties are qualitatively alike with respect to dilatational modulus, although some differences are noticeable. Relaxation processes take place mainly within the interfacial layers by a redistribution of polymer segments. Several conformational transitions were shown to occur as the area per molecule decreased. PEO desorbs significantly from the interface at segmental areas below 20 A(2), while at higher surface coverage, we propose that segments of PPO are forced to leave the interface to form a mixed sublayer in the aqueous region.     

聚丙烯酸/聚氧化乙烯高分子复合溶液的结构与粘度

通过溶液折光指数和粘度测定,研究了聚丙烯酸（ＰＡＡ）与聚氧化乙烯（ＰＥＯ）高分子链间在复合溶液中的相互作用和ＰＡＡ／ＰＥＯ高分子氢键复合溶液的结构与粘度,研究了复合溶液粘度随溶液ｐＨ值的变化规律及不同浓度时剪切速率对复合溶液粘度和复合增粘效果的影响。结果表明：ＰＡＡ／ＰＥＯ复合溶液结构不同于ＰＡＡ和ＰＥＯ两组分聚合物溶液结构,ＰＡＡ与ＰＥＯ高分子链间的氢键相互作用形成构象更为伸展、流体力学体积列大     

聚丙烯酸在纳米TiO2表面吸附行为的研究

讨论了聚丙烯酸在纳米TiO₂水悬浮体系中的吸附行为.红外光谱分析和吸附实验结果表明,纳米TiO₂通过氢键吸附PAA.PAA吸附量随着浓度的升高而增大直至饱和吸附量,且分子量越大,饱和吸附量越大.pH值增大,则饱和吸附量减小.在相同条件下,表面吸附层的厚度随PAA分子量、浓度和pH值增大而增大.这是由PAA在颗粒表面构型的变化所致.吸附PAA后的纳米TiO₂的表面电荷密度和ζ电位发生变化,pHiep值向低值方向移动.表面吸附自由能的计算结果说明,PAA在纳米TiO₂表面的吸附是自发过程.