【作者】 疏瑞文；

【导师】 童真；

【作者基本信息】 华南理工大学 ， 高分子化学与物理， 2014， 博士

【摘要】 胶体粒子与分子相比具有较大的尺寸（几个纳米到几个微米尺度）且粒子间的相互作用可在较宽范围内进行调节，因此胶体悬浮体系被广泛当作模型实验体系来研究基本的凝聚态物理问题，如凝胶化和玻璃化转变等。本研究采用三种结构比较清楚的胶体模型体系：锂藻土填充的油包水乳液、温敏性聚N-异丙基丙烯酰胺（Poly (N-isopropylacrylamide)，PNIPAm）微凝胶和锂藻土水分散液。研究工作的基本思路是：首先选择合适的方法制备三种胶体模型体系；然后通过改变胶体粒子的质量百分数（cw）、温度（T）、添加的无机电解质NaCl的摩尔浓度（cs）和聚乙二醇（poly(ethylene glycol)，PEG）的质量百分数（cw）等参数来调节胶体粒子间的相互作用势能U(h)，再通过振荡剪切流变学方法分别研究不同成分的油包水乳液、PNIPAm微凝胶悬浮液和锂藻土分散液的玻璃化转变和物理凝胶化过程，探讨其线性粘弹性与非线性粘弹性与粒子的微观结构之间的关系。本工作的主要内容和结果如下：1、采用高速分散乳化法制备了两种不同水油两相体积比的油包水乳液：E（液滴相为水）和E-L2S6（液滴相为锂藻土水分散液L2S6），分别通过小振幅振荡剪切（smallamplitude oscillatory shear，SAOS）和大振幅振荡剪切（large amplitude oscillatory shear，LAOS）流变学方法考察液滴弹性对油包水乳液的线性和非线性粘弹性的影响。通过光学显微镜观测了乳液中液滴的微观形貌，结果发现，随的增加，乳液中液滴由孤立分散状态逐渐变为堵塞状态。SAOS频率扫描结果发现，液滴弹性对堵塞状态的油包水乳液的线性粘弹性有非常显著的影响：乳液E-L2S6较乳液E具有更高的动态储能模量G’。堵塞状态下的油包水乳液是一种典型的屈服应力流体，在LAOS流场下呈典型的矩形Lissajous曲线。通过高次谐波的相对强度In/1和Lissajous曲线及其定量参数GM、GL和GK等对两种油包水乳液在稳定屈服流动状态的非线性粘弹性进行了表征，发现液滴弹性对堵塞状态的油包水乳液的非线性粘弹性有非常显著的影响。2、采用无皂乳液聚合法制备了一系列不同粒子质量百分数的温敏性PNIPAm微凝胶悬浮液。通过振荡剪切流变学考察温度T、微凝胶粒子的质量百分数w和剪切应力三个变量对PNIPAm微凝胶悬浮液的堵塞-去堵塞转变的影响。微凝胶粒子的有效体积分数eff同时依赖T和w。SAOS频率扫描结果表明，不同T和w的堵塞状态下PNIPAm微凝胶悬浮液的平台模量G’p随有效体积分数eff均呈幂律变化，表明粒子间的相互作用势能随温度变化不大。SAOS温度扫描结果发现，悬浮液发生去堵塞转变的临界温度Tc随w的增加而升高，但临界有效体积分数c随w的增加而减小，表明微凝胶粒子受到了压缩。LAOS应变扫描结果表明，当剪切应力超过试样的屈服应力时，悬浮液发生去堵塞转变。以T、w-1和σRh3/(kBθ)三个独立变量为坐标轴，构建了PNIPAm微凝胶的堵塞相图。3、制备了质量百分数cw=2.9~3.5wt%的锂藻土水分散液。离子电导率和pH值测试结果，表明未经透析或离子交换处理的锂藻土分散液，静置老化后形成的软固体是RLCA胶体凝胶，且不是“卡片屋”凝胶。固定预剪切条件，通过SAOS时间扫描实验跟踪锂藻土分散液在不同温度下的物理凝胶化转变过程。不同温度的SAOS时间扫描曲线可以通过水平平移叠加得到一条主曲线，表明锂藻土分散液的凝胶化过程具有普适的动力学路径，升高温度仅仅加速了分散液的凝胶化过程。本研究从粒子间的相互作用势能U(h)出发，根据胶体凝聚理论，建立了平移因子aT与U(h)之间的定量关系。通过SAOS频率扫描和LAOS应变扫描实验分别考察了温度对锂藻土凝胶试样的线性和非线性粘弹性的影响。结果发现，温度越高，锂藻土凝胶的线性弹性模量G’越大，且试样在大应变剪切流场下发生屈服流动时的“应变过冲峰”的强度越大，屈服应力的数值越大。4、制备了不同锂藻土粒子质量百分数和NaCl浓度的锂藻土水分散液，通过SAOS时间分辨粘弹谱方法，得到了同一锂藻土分散液试样的凝胶化过程中不同时刻的频率扫描曲线，发现不同时刻的结果可沿频率坐标平移叠加成主曲线。平移因子at反映了试样的结构松弛时间随实验观测时间tw的变化关系。结果表明，对于试样L1Scs，不同NaCl浓度的锂藻土分散液的G’、G”随tw的变化曲线可以通过水平平移叠加成一条主曲线，即“老化时间-盐浓度叠加”成立，表明锂藻土分散液的物理凝胶化过程具有普适的动力学路径，增加NaCl浓度仅仅加速锂藻土分散液的凝胶化速率。试样L3.5在不同观测时间tw下的G’、G’’vs曲线沿频率坐标水平平移可以得到一条叠加主曲线，平移因子at随tw的增加呈典型“两步老化”特征，表明锂藻土分散液的结构松弛动力学随tw的增加逐渐变慢，且物理凝胶化过程分为两个阶段：第一阶段为胶体凝胶的形成阶段，试样的松弛时间随实验时间呈指数增长；第二阶段为凝胶状态下的试样中网络结构逐渐完善的阶段，试样的松弛时间随实验时间呈幂律增长。5、制备了锂藻土的质量百分数cw=3.0wt%，不同PEG质量百分数cp的锂藻土/PEG分散液。利用稳态和动态剪切流变学方法考察了PEG的质量百分数对锂藻土/PEG分散体系的线性和非线性粘弹性的影响。通过SAOS频率扫描，首次在实验上观察到锂藻土/PEG分散体系由PEG分子链导致的排空力造成的再进入凝胶化行为。稳态剪切粘度和大振幅剪切动态模量结果表明，PEG质量百分数对锂藻土/PEG分散体系的屈服行为也有类似的影响。更多还原

【Abstract】 Colloidal particles have a larger size compared with molecules (several nanometer toseveral micron scale) and the interaction between the particles can be adjusted in a wide range,so it is widely used as a model experimental system to study the fundamental problems incondensed matter physics, such as gelation and glass transition, and so on. In the present work,three colloidal model systems with a rather clearly structure were used, including hectoriteclay-filled water-in-oil emulsion, temperature-sensitive Poly(N-isopropylacrylamide)(PNIPAm) microgel suspension and aqueous dispersion of hectorite clay. The basic idea of theresearch work were: firstly, we selected the appropriate method to prepare three colloidalmodel system. Later, a series of parameters, such as the mass percentage of colloidal particles,temperature, the mole concentration of inorganic electrolytes NaCl and the mass percentageof polyethylene glycol (poly (ethylene glycol), PEG) were modified to modulate theinteraction U(h) between colloidal particles. Lastly, the glass transition and physical gelationprocess in water-in-oil emulsion, PNIPAm microgel suspension and aqueous dispersion ofhectorite clay with different composition were studied by oscillatory shear rheology, in orderto relate the linear and nonlinear viscoelasticity behavior with the microscopic structure of thesample. The main works and results were as following:1. Two types of water-in-oil emulsion: E (pure water as droplet phase) and E-L2S6(asuspension of hectorite clay as droplet phase, L2S6) with different water-to-oil phase volumeratio were prepared and the effect of droplet elasticity on the linear and nonlinearviscoelasticity of water-in-oil emulsions was investigated by small amplitude oscillatory shear(SAOS) and large amplitude oscillatory shear (LAOS) rheological methods. The microscopicmorphology of the emulsions was observed with an optical microscope. The emulsiondroplets changed from isolated dispersed state to the jammed state with increasingwater-to-oil phase volume ratio was observed. SAOS frequency sweep experiments found thateffect of droplet elasticity was most significant in jammed state, where the clay-filledemulsion E-L2S6showed a much higher dynamic storage modulus G’ than the clay-free one.Water-in-oil emulsion in jammed state is a typical yield stress fluid, which showed a typicallyrectangular Lissajous curve under LAOS flow field. The nonlinear viscoelastic understationary flow state was measured by In/1and quantitative Lissajous curve parameters GM, GLand GK.The droplet elasticity was found to contribute to the nonlinear viscoelasticity ofwater-in-oil emulsions in jammed state.2. A series of PNIPAm microgel suspensions with different particle mass percentage wwere prepared by surfactant-free emulsion polymerization. The jamming and unjammingtransition in thermo-sensitive PNIPAm microgel suspensions was observed by rheology with three independent variables of temperature T, microgel weight fraction w, and the shear stressσ. The effective volume fraction φeff, depending on both T and w, was adopted to interpret thistransition. In the jamming state, the plateau modulus G’pmeasured by SAOS frequencysweep tests behaved the same power law to φeffwith varying T and w, indicating that thechange of interaction potential with temperature was insignificant. SAOS temperatures testsshowed that the critical temperature Tcincreased with increasing w but the critical volumefraction cdecreased with increasing w at the jamming transition because higherconcentration of particles lead to strong repulsive interaction. The shear-unjamming transitionoccurred as the shear stress exceeded the yield stress σy. A jamming phase diagram for themicrogel suspensions was established in a (1/w, σ, T) coordinate system.3. The aqueous dispersion of cw=2.9~3.5wt%hectorite clay were prepared. Theconductivity and pH values tests at different temperatures combined with calculationdemonstrated that the nature of aging aqueous dispersion of hectorite clay was RLCAcolloidal gel. With constant preshear condition, the higher the temperature of the sample, thefaster the rate of gelation was found. The G’, G’’ versus twcurves from samples with differenttemperature could be shifted into a mastercurve (G’, G’’ versus tw/at), the shift factor reflectingthe effect of temperature on the gelation rate. Therefore, increase in temperature couldaccelerate the physical gelation process, but couldn’t change the kinetics route of gelation.Considering the van der Waals attraction and electric double layer repulsion interactionbetween Laponite particle, a quantitative relationship between the shift factor aTand theinterparticle interaction potential U(h) was found with the help of the colloidal coagulationkinetic theory. We investigated the effect of temperature on the linear and nonlinearviscoelastic of hectorite clay gel samples by SAOS frequency sweep and LAOS strain sweepteasts. The results showed that the higher the temperature, the larger the linear elastic modulusG’, the higher the strength of “overshoot peak of strain” under yielding and the larger theyield stress value.4. Aqueous dispersion of hectorite clay with different hectorite clay mass percentageand NaCl concentration were prepared. G’, G’’ versus frequency ω results of the same sampleat different observation time during the gelation process was obtained by SAOS time-resolvedviscoelastic spectrum technique. Results of different times can be shifted along the frequencyaxis into a mastercurve (G’, G’’ versus at at). The shifting factor atreflects the dependence ofrelaxation time τ of the sample on observation time twin the gelation process. For sampleL1Scs, the G’, G’’ versus twcurves from samples of different NaCl concentration could beshifted into a mastercurve (G’, G’’ versus tw/at), that is,“aging time-salt concentrationsuperposition” was established, the shift factor reflecting the effect of salt contration on the gelation rate. Therefore, increase in NaCl concentration could accelerate the gelation process,but couldn’t change the kinetics route of gelation. For sample L3.5, results of different agingtimes can be shifted along the frequency axis into a mastercurve. It shows a two-step agingfeature, indicating that the structural relaxation dynamics for aqueous dispersion of hectoriteclay gradually slower with increasing tw, and the physical gelation process could be dividedinto two stages: In the first step, a colloidal gel was formed and the relaxation time increaseexponentially with observation time; in the second step, the gel network structure graduallyimproved and the relaxation time increase with observation time in a power-law form.5. The aqueous dispersion of3.0wt%hectorite clay with different PEG masspercentages were prepared. The effect of mass percentage of PEG on the linear and nonlinearviscoelasticity for hectorite clay/PEG dispersion was investigated by steady state and dynamicshear rheological methods. The re-entrant gelation behavior due to depletion force from freePEG chains was firstly observed in hectorite clay/PEG dispersion system by SAOS frequencysweep tests. Steady shear viscosity and LAOS dynamic moduli results suggested that PEGmass percentage had a similar effect on the yield behavior of hectorite clay/PEG dispersionsystem.更多还原