SiO2/聚乙二醇非牛顿流体流变性能研究

利用应力控制流变仪考察了SiO₂/聚乙二醇分散体系稳态和动态的流变性能. 实验结果表明, 该体系具有剪切变稀和可逆的剪切增稠现象. 稳态应力实验中, 当应力较小时, 体系具有剪切变稀现象, 而在剪切应力(σ)大于临界剪切应力(σ_c^s, σ_c^s=9.99 Pa)后, 体系粘度急剧增大. 在动态实验中, 剪切应力小于临界剪切应力(σ_c^o, σ_c^o=15.85 Pa)时, 储能模量G′减小, 耗能模量G″与复合粘度η*基本不变, 但σ＞15.85 Pa后, G′、G″及η*同步增大, 且在所研究的应力范围内, G″均大于G′. 同时还考察了测试频率、分散相含量以及分散介质平均分子量的差别对流变性的影响. σ_c^o随测试频率的增大而变大; SiO₂质量分数越大, σ_c^o基本不变, 但增稠现象变得更明显; 与平均分子量小的PEG200体系相比, 平均分子量大的PEG400体系, σ_c^o并未发生改变, 但在增稠之前体系的粘度较低, 增稠之后体系粘度增大的幅度较大.     

低固相含量SiO2分散体系流变性研究

以甘油(GL)和聚乙二醇(PEG)为分散介质, 研究了低体积分数(Φ＜8%)的SiO₂分散体系的稳态和动态的流变性能, 发现体系都具有可逆的剪切变稀和剪切增稠现象. 在剪切速率大于临界剪切速率(γ^_.＞γ_^.c)时, 体系具有明显的剪切增稠现象, 而当γ^_.＜γ_^.c, GL体系只有轻微的剪切变稀现象, PEG体系剪切变稀现象却很明显. 在动态试验中考察了模量以及损耗角正切tg δ随剪切应力(σ)的变化. 在所研究的应力范围内, 体系中耗能模量G"都大于储能模量G', tg δ大于1, 体系主要表现为粘性. 用“粒子簇”生成机理能较好地解释这种剪切变稀和剪切增稠现象, 即剪切变稀是由于连续的空间网络结构被破坏, PEG体系剪切变稀现象较GL体系明显应该与PEG高分子链的松弛以及体系中较少的氢键有关; 剪切增稠是由于粒子簇的生成引起的.     

SiO2/PEG分散体系动态剪切流变行为

在动态应变条件下, SiO2/PEG200(聚乙二醇, 平均分子量为200)分散体系出现了剪切增稠现象. 剪切流变实验表明, 在两种情况下都出现了剪切增稠: 一种是在不同的恒定频率下应变扫描, 在临界应力γc出现的剪切增稠; 另一种是恒定的应变(γ0=500%)条件下频率扫描, 在临界频率棕c抑10 rad·s-1出现的剪切增稠. 在不同的恒定频率应变扫描条件下, 实验研究了储能模量(G’)和耗能模量(G’’)与应变的关系, 同时初步探讨了应变与不同恒定频率的函数关系. 在线性粘弹性区域内, G’和G’’满足G’∝ω0.57和G’’∝ω0.7指数关系. 在恒定的应变条件下, 发现模量和复数粘度与扫描频率具有强烈的依赖关系, 这些现象可以定性地通过“粒子簇”理论来解释.“粒子簇”理论认为这种剪切增稠的发生是由于形成了亚稳定、流动所导致的“粒子簇”, 使得粘度上升.     

低固相含量SiO2分散体系流变性研究

以甘油(GL)和聚乙二醇(PEG)为分散介质, 研究了低体积分数(Φ＜8%)的SiO₂分散体系的稳态和动态的流变性能, 发现体系都具有可逆的剪切变稀和剪切增稠现象. 在剪切速率大于临界剪切速率(γ^_.＞γ_^.c)时, 体系具有明显的剪切增稠现象, 而当γ^_.＜γ_^.c, GL体系只有轻微的剪切变稀现象, PEG体系剪切变稀现象却很明显. 在动态试验中考察了模量以及损耗角正切tg δ随剪切应力(σ)的变化. 在所研究的应力范围内, 体系中耗能模量G"都大于储能模量G', tg δ大于1, 体系主要表现为粘性. 用“粒子簇”生成机理能较好地解释这种剪切变稀和剪切增稠现象, 即剪切变稀是由于连续的空间网络结构被破坏, PEG体系剪切变稀现象较GL体系明显应该与PEG高分子链的松弛以及体系中较少的氢键有关; 剪切增稠是由于粒子簇的生成引起的.     

剪切作用下纳米粘土对LDPE熔体粘弹响应的影响

以LDPE/EVA/纳米粘土复合体系为研究模型,考察了剪切作用下,分散良好的纳米粘土对聚合物基体熔体稳态及瞬态粘弹响应的影响.发现剪切作用下,纳米粘土增加了聚合物熔体粘弹特性对剪切速率、剪切应变及剪切作用史的依赖性,改变了相应的依赖关系.稳态剪切时,纳米粘土的加入使体系第一法向应力差(N1)在低剪切速率区变为负值,而在高剪切速率区N1与粘土的含量无关;同时就瞬态剪切应力及N1的应变依赖关系而言,复合体系明显不同于聚合物基体;预剪切对聚合物基体瞬态粘弹响应几乎没有影响,而当纳米粘土的加入量大于3wt%后,与未经预剪切的样品相比较,经预剪切的复合体系的瞬态剪切应力值、应力过冲程度以及稳态剪切应力值均明显下降,且预剪切前后复合体系达到稳态时其瞬态剪切应力差值随纳米粘土含量的增高而线性增加.此外,纳米粘土的添加对聚合物熔体受剪切作用的非线性粘弹响应存在影响.复合体系熔体呈现特异非线性粘弹响应,其缘由被认为是由于纳米粘土在聚合物基体中剥离分散,或聚合物分子链插层于粘土片层间,形成局部有序结构,受剪切作用而排列取向.     

抗冲聚丙烯共聚物熔体结构演化的动态流变学表征

用动态流变学方法研究了抗冲聚丙烯共聚物(IPC)熔体的流变行为.通过探讨温度、抗氧剂、氧气的存在对其熔体动态粘弹响应的影响,对IPC熔体结构的演化过程进行了描述.随温度的升高,IPC熔体的动态粘弹响应明显改变,低频率(ω)区域动态储能模量(G′)与ω的对数关系lgG′-lgω呈现平台特征;加入复合抗氧剂B215或在N2气氛下,在一定的时间范围内,IPC的特征粘弹行为完全消失,呈现均相体系的流变响应特征.低ω区域粘弹函数对IPC的结构变化存在敏感响应.通过改变温度、添加抗氧剂以及N2保护,获得了IPC熔体因降解与交联反应所引起的结构改变的信息.     

十二烷基聚氧乙烯硫酸钠胶束体系的流变性质研究

用流变学方法研究了无机电解质KBr存在时,阴离子表面活性剂十二烷基聚氧乙烯(3)硫酸钠(SDES)水溶液中胶束的生长和结构。通过测量体系的稳态剪切粘度(η)和应力(σ)关系,得到零剪切粘度(η0)、复合粘度(|η^*|)、动态模量[储能模量(G')和损耗模量(G")、平台模量(G0)、结构松驰时间(τ)等流变学参数,并应用Cox-Merz规则和Cole-Cole图,发现在SDES/KBr体系中可以形成蠕虫状胶束网络结构,体系为假塑性流体,偏离Maxwell模型,具有非线性粘弹性,没有单一的结构松驰时间。     

十二烷基聚氧乙烯硫酸钠胶束体系的流变性质研究

用流变学方法研究了无机电解质KBr存在时,阴离子表面活性剂十二烷基聚氧乙烯(3)硫酸钠(SDES)水溶液中胶束的生长和结构。通过测量体系的稳态剪切粘度(η)和应力(σ)关系,得到零剪切粘度(η0)、复合粘度(|η^*|)、动态模量[储能模量(G')和损耗模量(G")、平台模量(G0)、结构松驰时间(τ)等流变学参数,并应用Cox-Merz规则和Cole-Cole图,发现在SDES/KBr体系中可以形成蠕虫状胶束网络结构,体系为假塑性流体,偏离Maxwell模型,具有非线性粘弹性,没有单一的结构松驰时间。     

泥鳅体表黏液的流变行为

研究了无鳞鱼———泥鳅的体表黏液流变行为,发现黏液的稳态流动存在着3个不同区域:第一区域内,黏度随剪切速率(γ)变化不显著,呈现牛顿流动行为;第二区域内,随γ增大,黏度下降,呈现非牛顿行为;第三区域内,随γ继续增大,黏度又基本保持不变.黏液表观黏度(ηa)与γ的关系可用Carreau模型很好地拟合,其增比黏度(ηsp)与浓度(c)的关系为ηsp∝c1.5,表明黏液处于亚浓缠结区域.在测试频率(ω)范围内,黏液的动态储能模量(G′)大于动态损耗模量(G″),表明与黏性相比较,弹性占优,且G′及G″随ω变化不显著.存在一临界温度(35℃),当低于35℃时,黏液黏度随温度变化不显著,当高于35℃时,黏液变性,表现出不同的流变行为.     

聚丙烯/多壁碳纳米管复合材料的热性能和流变性能

用熔融共混法制备了聚丙烯多壁碳纳米管(PP MWNTs)复合材料,TGA研究表明在氮气气氛下碳纳米管显著增加了聚丙烯基体的热稳定性.3wt%MWNTs可使PP热分解起始温度提高44℃.非等温结晶研究表明MWNTs对PP基体的结晶行为没有明显的影响.流变测试结果表明PP MWNTs复合材料的储能模量G′和损耗模量G″随着MWNTs含量增加逐渐增大.1wt%MWNTs的PP聚合物的零剪切粘度最低,5wt%MWNTs的PP聚合物的零剪切粘度最高,PP和3wt%MWNTs的PP纳米聚合物的零剪切粘度居于二者之间,随着频率的增加,剪切稀化作用越来越明显,呈现出假塑性流体行为.含5wt%MWNTs的PP复合材料的体积和表面电阻率与纯PP相比分别下降了9个和4个数量级,表明少量的MWNTs可以显著改变PP的电学性能.     

Non-linear Viscoelastic Rheological Properties of PCC/PEG Suspensions

The shear thinning and shear thickening rheological properties of PCC/PEG suspension were investigated with the increase of oscillatory amplitude stress at different constant frequencies. The results show that the complex viscosity was initially independent of stress amplitude and obvious shear thinning occurred, then dramatic shear thickening took place after reaching the minimum viscosity. Typically, in a constant frequency of 5 rad/s, the elastic modulus, viscous modulus, and tanδ （δ is the out-of-phase angle） vs. the stress amplitude was investigated. It is found that the elastic modulus initially appeared to be independent of stress amplitude and then exhibited a rapid decrease, but the viscous modulus was independent of amplitude stress at lower amplitude stress. After reaching the minimum value the viscous modulus showed a rapid increase. On the other hand, tanδ increased from 0.6 to 92, which indicates that the transition from elastic to viscous had taken place and tanδ showed a steep increase when shear thickening occurred. Lissajous plots are shown for the dissipated energy vs. different maximum stress amplitude in the shear thinning and shear thickening regions. The relationship of dissipated energy vs. maximum stress amplitude was determined, which follows a power law. In the shear thinning region the exponent was 1.91, but it steeply increases to 3.97 in the shear thickening region.     

PMVS/SiO2复合体系中粒子表面处理对动态粘弹特性的影响

粘弹性是高分子材料最本质的特征,其与高分子结构的关系一直是多组分高分子材料研究的热点。目前,对于填料增强聚硅氧烷体系的研究主要集中于填料在聚合物中的分散以及增强机理等方面,而有关不同填料表面特性体系的粘弹响应的研究报道尚不多见．在前文报道未经表面处理的超细SiO2填充聚甲基乙烯基硅氧烷(Polymethylvinylsiloxane,PMVS)的粘弹性研究的基础上,本文采用双(γ-三乙氧基硅基丙基)四硫化物IBis(3-triethoxysilyl)tetrasul{ane,TESPT]对SiO2进行表面处理,并采用溶液共混法制备样品,研究了经表面处理的SiO2填充PMVS体系的动态粘弹行为,并探讨了其结构变化与粘弹响应的关系。     

超细SiO2填充聚甲基乙烯基硅氧烷的动态流变特性

研究粒子填充类聚合物体系的动态粘弹响应，可在较宽应变、温度、频率范围内获得有关体系分散状态及相互作用等结构信息。用粒径小、比表面积大的二氧化硅(SiO2)增强聚硅氧烷时，其独特的化学结构和表面特性对填充体系的静态和动态流变特性有显著影响，Payne等研究了碳黑增强硫化橡胶的动态粘弹性，迄今关于SiO2增强聚硅氧烷，尤其对未硫化体系动态流变特性研究很少报道。本文以超细、高比表面积且具多孔结构的SiO2填充聚甲基乙烯基硅氧烷(Polymethylvinylsiloxane，PMVS)，对室温下不同SiO2含量的SiO2/PMVS体系动态流变特性进行了研究。     

Sol–gel transition and rheological properties of silica nanoparticle dispersions

Possible variants of the rheological behavior of silica model dispersions have been analyzed. Different types of interaction between the particles and a dispersion medium make it possible to obtain different systems from low-viscosity sols to gels. Proton-donor (water) and aprotic (dimethyl sulfoxide) media have been used for comparison. Dispersions in the aprotic medium behave as non-Newtonian viscous fluids exhibiting shear thinning or shear thickening depending on deformation rate. Aqueous dispersions are viscoelastic and viscoplastic objects that exhibit the shear thickening at stresses higher than the yield stress. The introduction of small amounts of poly(ethylene oxide) into the organic dispersion medium initiates gelation. An increase in the polymer content in the dispersion medium above the concentration corresponding to the formation of a macromolecular network promotes an increase in stiffness and strength of the gels. The rheological behavior of gels is influenced by the polymer molecular mass and its affinity for a solvent.     

Study of a shear thickening fluid: the suspensions of monodisperse polystyrene microspheres in polyethylene glycol

The monodisperse polystyrene (PS) microspheres were prepared by dispersion polymerization. The rheological properties of shear thickening fluid (STF) based on PS microspheres dispersing in polyethylene glycol with different concentrations were studied through the steady and oscillatory shear at different temperatures, respectively. All suspensions successively present the first shear thinning, the shear thickening, and the second shear thinning. The experimental results indicate that the shear thickening behavior of STF is controlled by the concentration of PS microspheres and temperature, as changed from continuous shear thickening (CST) to discontinuous shear thickening (DST) with increasing solid content or decreasing temperature. The STF is affected by shear rate, temperature, and the viscosity of the dispersed medium, and it is reversible absolutely and presents transient response ability. Both CST and DST behave as dilatancy. The PS microsphere aggregations formed under shear stress may result in the shear thickening in STFs.     

Rheology and Structure of Cornstarch Suspensions in Water-Poly(propylene glycol) Mixtures

Concentrated aqueous cornstarch (CS) suspensions are often used to demonstrate an extreme example of shear thickening rheological behavior. Here, we describe the increased rheological complexity that occurs on the addition of poly(propylene glycol) (PPG) to an aqueous CS suspension. The appearance of shear thickening/jamming, shear thinning, yield stress and near-Newtonian behaviors is dependent on the PPG:water ratio. Rheological measurements have been complemented by dielectric measurements and optical microscopy. The complex behavior is interpreted in terms of reduced electrostatic stabilization of the CS particles with increased poly(propylene glycol) concentration. The analysis also suggests why cornstarch suspensions in water exhibit particularly good shear thickening characteristics.     

聚合物多元醇分散体的流变特性

聚合物多元醇分散体(以下简称分散体)是接枝聚醚多元醇、聚醚多元醇和乙烯基单体聚合物的混合物,直接用于制备高回弹、高负载和阻燃的软质和半软质聚氨酯泡沫体,是新一代聚醚多元醇产品[1].分散体用于聚氨酯工业中各种产品的生产,除要求有良好的稳定性外,其最为重要的指标是粘度应小于3000mPa·s和乙烯基单体聚合物的含量(固含量)应大于40%.但分散体的粘度,随固含量的增加呈指数性增加[2].近年来,已有既具高固含量和良好稳定性,又有较低粘度的分散体的研究报道[3].本文在不同的反应条件下,合成了分散体,测定了其流变特性和体系中微粒的大小…     

Theory of rheology of colloidal dispersions

This brief review contains a survey of recent literature on theory of rheology of colloidal dispersions. Areas of active research are highlighted, such as approximations for many body interactions in weakly sheared dispersions and the flow-induced microstructural distortions in more strongly sheared dispersions. The former approach seeks to capture the viscosity increase on increasing particle concentration, whereas the latter explains shear thinning and shear thickening.     

Investigating the effect of hydrophobic structural parameters on the thickening properties of HEUR associative copolymers

Hydrophobically modified ethoxylated urethanes (HEUR) associative copolymers are prepared through the hydrophobic modification of polyethylene glycol based polyurethanes. These types of thickeners are categorized as anionic associative thickeners. To investigate the effect of structure of the hydrophobic groups on the thickening properties, three different hydrophobic groups were selected. These groups were comprised of cetyl alcohol (16 carbons), dodecyl alcohol (12 carbons) and a cyclic group such as cyclo hexanol. These functional groups were substituted on the identical prepolymers made from H₁₂MDI and polyethylene glycol. Here, three different urethane associative polymers containing hydrophobic segments and different hydrophobic groups were synthesized. The viscoelastic characteristics of all the samples were determined using a cone and plate rheometer. The viscosities of the examined HEUR samples showed both Newtonian and non-Newtonian behaviours (shear thinning and thickening) for the explored shear rates window. The steady shear viscosity results were interpreted using the theories by Raspaud [Macromolecules 27 (1994) 2956] and Semenov [Macromolecules 28 (1995) 1066]. The Cox-Merz rule happened to be applicable to these systems for the various hydrophobic ends and concentrations at lower shear rates indicating typical associative polymer behaviour. The cyclic end groups did not show viscoelasticity for the frequencies window explored. The zero shear viscosity increased by almost two orders of magnitude from HEUR-cyc to HEUR-dod and by four orders of magnitude from HEUR-cyc to HEUR-cet. The intermediate shear thickening was only observed for the concentrated HEUR-cet samples.