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The rheological behaviors of fresh cement paste with polycarboxylate superplasticizer were systematically investigated. Infl uential factors including superplasticizer to cement ratio (Sp/C), water to cement ratio (w/c), temperature, and time were discussed. Fresh cement pastes with Sp/Cs in the range of 0 to 2.0% and varied W/Cs from 0.25 to 0.5 were prepared and tested at 0, 20 and 40 °C, respectively. Flowability and rheological tests on cement pastes were conducted to characterize the development of the rheological behavior of fresh cement pastes over time. The exprimental results indicate that the initial fl owability and flowability retention over shelf time increase with the growth in superplasticizer dosage due to the plasticizing effect and retardation effect of superplasticizer. Higher temperature usually leads to a sharper drop in initial fl owability and fl owability retention. However, for the cement paste with high Sp/C or w/c, the fl owability is slightly affected by temperature. Yield stress and plastic viscosity show similar variation trends to the flowability under the abovementioned infl uential factors at low Sp/C. In the case of high Sp/C, yield stress and plastic viscosity start to decline over shelf time and the decreasing rate descends at elevated temperature. Moreover, two equations to roughly predict yield stress and plastic viscosity of the fresh cement pastes incorporating Sp/C, w/c, temperature and time are developed on the basis of the existing models, in which experimental constants can be extracted from a database created by the rheological test results. [Download]

The influences of triethanolamine (TEA) on the portlandite in hardened cement pastes (HCPs) were systematically investigated. Results show that the addition of TEA in cement pastes leads to a visible reduction of Ca(OH)2 (CH) content and considerably alters themorphology of CH crystals fromlarge and parallel-stacked lamellar shape to smaller and distorted actinomorphic one. For the first time, the CH micro-crystals and even noncrystalline CH in HCPs were observed in the presence of TEA. Due to integration of CH micro-crystals in C–S–H phase, remarkable higher Ca/Si ratio of C–S–H phase was found. The formation of TEA-Ca2+complex via the interaction between Ca2+ and the oxygen atoms in TEA moleculewas evidenced by the results ofNMR and UV. It is believed that TEA can be introduced into the crystallization process of portlandite and thus significantly alters the morphology of CH crystals and even the content of the crystalline CH phase.[Download]

This paper proposes a novel approach to achieve self-healing property of cement sheath in the oil well triggered by oil leakage through cracks. An oil swellable polymer (OSP) with oil absorptivity as high as 700% was synthesized through emulsion polymerization. The OSP dispersion was added into the Portland cement paste. It is found that the oil absorption and the linear expansion of the OSP modified hardened cement paste (MHCP) are greatly increased compared to the blank hardened cement paste (BHCP). Pore structure measurements by Nadsorption show that the addition of OSP decreases the total porosity of MHCP which confirms that the formation of the polymeric film in MHCP. The self-healing ability of MHCP was evaluated by the oil flow test through a single crack in the cylindrical specimen. The oil flow tests indicate that the leakage of oil through the crack is gradually mitigated due to the expansion of the MHCP and thus the self-healing ability is successfully achieved.[Download]

The effects of polymer latexes on cement hydration were investigated by the combination of isothermal calorimetry, in-situ XRD and Cryo-SEM. Two model latexes with varied amounts of anionic charges were used for measurements after cleaned by dialysis to remove the serum components. This study confirms that in-situ XRD technique can be successfully adapted to hydrating cementitious systems in the presences of polymer latexes to quantitatively follow evolution of mineral phases involved in cement hydration. Results show that both polymers retard aluminate reaction and depress silicate reaction, by delaying the dissolution of C3A, anhydrite and gypsum and consequently the formation of ettringite, and reducing the dissolution of C3S and the formation of C-S-H. The anionic colloidal polymers exhibit more pronounced retardation effect on aluminate reaction than on silicate reaction due to stronger electrostatic interaction between the polymer particles and the positively charged aluminate phases. The more charged latex shows stronger retardation.[Download]

A microrheology analyzer was adapted to in-situ follow the development of viscoelastic properties of fresh cement pastes (FCPs) for the first time. It enables a non-disturbing measurement on the FCPs through monitoring the mean square displacement of cement particles, which gives an insight into the elastic and viscous properties of materials from a microstructural point of view. Various parameters including elastic index, macroscopic viscosity index, storage modulus, loss modulus and Maxwell parameters were obtained to quantitatively analyze the viscoelastic properties of FCPs. Results indicate that these parameters show a progressive increase with time at first and then stay stable. The incorporation of superplasticizer significantly decreases these parameters and their growth rates. Moreover, superplasticizer could evidently weaken the elastic feature of the FCP due to its effects of improving the dispersion of cement grains and retarding cement hydration. The effects of superplasticizer are more pronounced at lower water to cement ratio.[Download]

The influences of three types of silane (tetraethoxysilane (TEOS), 3-aminopropyltriethoxysilane (APTES), N-2-aminoethyl-3-aminopropyltrimethoxysilane (AEAPTMS)) on flowability, strength development and hydration kinetics of cement pastes and mortars are systematically investigated. Results show that: 1) three silanes exhibit a dispersing effect on cement pastes indicated by the increased flowability of fresh cement pastes, among which AEAPTMS shows the strongest dispersing power; 2) AEAPTMS and APTES retard cement hydration by extending the induction period and reducing the hydration degree at certain ages determined by isothermal calorimetry, measurements of non-evaporable water amount and portlandite content in hydration products at ages before 90 days; 3) AEAPTMS and APTES show positive effect on the toughness of mortars after 7 day curing; and 4) three silanes act differently on strength growth at various ages, which should be a result that is counterbalanced by their influences on hydration kinetics, pore structure, composition and morphology of hydration products.[Download]

Interactions between styrene-acrylate latexes and cement are investigated with emphasis of the charge properties of the polymer particles by means of calorimetry, adsorption measurement, and confocal laser scanning microscope. Three latexes with varied surface charges of polymer particles were prepared by respectively using methacrylic acid (MAA), sodium styrene sulfonate (SSS) and methyl poly(ethylene glycol) methacrylate (MPEGMA) as water soluble monomers during synthesis. It is found that the polymer latexes retard cement hydration in two manners, namely the delaying effect represented by a delayed hydration peak and the slowing down effect characterized by a reduced main hydration peak during the acceleration period. The delaying effect is closely related to the concentration of carboxylic groups existing in the latex,while the depression effect of hydration rate is majorly caused by the adsorption of polymer particles on surface of cement grains and proportional to the total charge density of polymer particles.[Download]

A series of amphoteric polycarboxylate (PC) polymers were synthesized by radical copolymerization of acrylic acid (AA), [3-(methacryloylamino) propyl] trimethylammonium chloride (MAPTAC) and x-methoxypolyoxyethylene methacrylate ester (MPEGMA). Cationic groups were introduced in to PC molecules with expectation of less retardation effect on cement hydration compared to the traditional anionic PC superplasticizers. The content of cationic groups in polymer was varied by changing the monomer ratio of MAPTAC to AA in the synthesis recipes. The structure of the synthesized amphoteric PCs was verified by gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FTIR). The performances of the amphoteric PCs were evaluated by measurement of flowability and zeta-potential of cement pastes and adsorption amount of PC in cement pastes. Impacts of the PCs on cement hydration were studied by isothermal calorimetry. It is concluded that both anionic and cationic PC polymers can be effectively adsorbed onto the surface of cement particles and thus change the zeta potential of cement pastes. The adsorption amounts of the amphoteric PCs decrease with increasing content of cationic units. A proper incorporation of cationic units into PC polymers may lead to a higher fluidizing performance in fresh cement pastes. The amphoteric PC polymers with higher content of cationic units show less retardation effect on cement hydration and hence higher early strength of cementitious materials may be achieved by using amphoteric PCs with appropriated content of cationic units without losing their plasticizing efficiency.[Download]

Comparative study of NSF and PCE superplasticizerswas carried out aiming at correlating the adsorption in fresh cement pastes (fcps)with their dispersing capability and the impacts on cement hydration. Results showthat the adsorption of NSF follows a typical Langmuir monolayer adsorption model while PCE exhibits a multi-layer adsorption. The fluidity of fcps containing NSF and the retardation effect of NSF on hydration are directly proportional to the surface coverage of NSF on cement grains. As full coverage is achieved, the fluidity enhancement and the retardation effect reach maximum by addition of NSF. By contrast, the fluidity of fcps with PCE is related to the coverage of the first adsorbed layer and the secondary adsorbed layer does not contribute to the enhancement of fluidity. Both the adsorbed PCE and the PCE remaining in aqueous phase participate in retarding cement hydration because of the complexation effect of \COO− with Ca2+.[Download]

The traditional polycarboxylate (PC) superplasticizers are usually negatively charged polymers, inwhich the carboxylate functionalities are responsible for their adsorption on cement surface driven by electrostatic interaction. This paper investigates the impacts of the charge characteristics of PC co-polymers on their adsorption behaviors and the retardation effects on cement hydration. PC co-polymers with variation of their charge specieswere synthesized by co-polymerizing the macro-monomerwith selected anionic and cationic monomers. Adsorption and impacts on cement hydration of the monomers, their homo-polymers and the PC co-polymers were studied in cement pastes by total organic carbon tests and calorimetry respectively. Results show that in cement pastes, no adsorption and retardation were observed for the monomers while for their corresponding homo-polymers, different extents of adsorption and retardation were found. Charge characteristics of PC co-polymers strongly determine their adsorption behaviors and retardation effects, in the order of \COO− N \SO3 − N `N+\.[Download]

The influences of three types of silane (tetraethoxysilane (TEOS), 3-aminopropyltriethoxysilane (APTES), N-2- aminoethyl-3-aminopropyltrimethoxysilane (AEAPTMS)) on flowability, strength development and hydration kinetics of cement pastes and mortars are systematically investigated. Results showthat: 1) three silanes exhibit a dispersing effect on cement pastes indicated by the increased flowability of fresh cement pastes, among which AEAPTMS shows the strongest dispersing power; 2) AEAPTMS and APTES retard cement hydration by extending the induction period and reducing the hydration degree at certain ages determined by isothermal calorimetry, measurements of non-evaporable water amount and portlandite content in hydration products at ages before 90 days; 3) AEAPTMS and APTES show positive effect on the toughness of mortars after 7 day curing; and 4) three silanes act differently on strength growth at various ages,which should be a result that is counterbalanced by their influences on hydration kinetics, pore structure, composition and morphology of hydration products.[Download]

Three types of polymers commonly used in concrete and mortar (polycarboxylate superplasticizer, polyacrylate latexes and asphalt emulsions) which differ in molecular/particle size from nanometer to micron were employed to investigate their effects on the pore structure of hardened cement pastes and the impermeability of hardened mortars. The pore structure and the impermeability of the hardened ones cured for 7 days and 28 days were measured by mercury intrusion porosimetry and alternating current impedance, respectively. Results show the incorporation of superplasticizer obviously reduces the average pore size and enhances the impermeability. The polyacrylate latexes also lead to the decline in pore size and consequently the enhanced impermeability at dosage higher than 3%. At the same dosage, latex with smaller polymer particle size is more effective in reducing the average pore size and enhancing the impermeability than that with larger particle size due to its better plasticizing effect. Similarly, asphalt emulsions also facilitate the enhancement in impermeability, and the anionic asphalt emulsion with better plasticizing effects brings about stronger impermeability than the cationic one. It is believed that for superplasticizer, the plasticizing effect is the main controlling factor for the finer pore structure and the enhanced impermeability. In the case of polymer latexes and asphalt emulsions, the plasticizing effect contributes actively at low dosage and the filling effect is dominant at high dosage in terms of declining pore size and augmenting impermeability.[Download]

Pre-soaked super-absorbent polymer (SAP) was incorporated into high-strength concrete (HSC) as an internal curing agent to study its effects on early-age shrinkage and mechanical properties. On the basis of the capillary stress based model for shrinkage prediction of concrete, together with the experimental results of cement hydration kinetics, evolution of internal temperature and humidity, development of pore structure and mechanical properties, the working mechanism of SAP was discussed. Results indicate that the addition of pre-soaked SAP significantly reduces the autogenous shrinkage as well as the early-age shrinkage of HSC under drying condition. In sealed HSC specimens, the drop of internal humidity caused by the self-desiccation effect is notably postponed by addition of pre-soaked SAP. The addition of presoaked SAP slightly reduces the compressive strength of HSCs and this effect is more pronounced in earlyage concrete. Furthermore, an insightful comparison of the behaviours of the internal curing water introduced by the pre-soaked SAP and the additional free mixing water in concrete was made. Results indicate that the internal curing water behaves differently from the additional mixing water in influencing the cement hydration kinetics, pore structure of hardened cement pastes and the mechanical strength of concrete, due to the different spatial distribution of the two types of water in the concrete bodies. The shrinkage-reducing effect on HSC due to the addition of extra internal curing water incorporated by pre-soaked SAP is much stronger than that of the additional mixing water. Besides, the internal curing water shows much less strength-reducing effect than the additional mixing water. In virtue of the shrinkage prediction model, the working mechanism of pre-soaked SAP in reducing autogenous shrinkage of HSC is proposed on the basis of the following two aspects. The participation of internal curing water in cement hydration process leads to a total volume gain of the hardening cement pastes. Meanwhile, the release of internal curing water from the pre-soaked SAP postpones the drop of internal humidity. The synergistic effect of these two factors effectively reduces the autogenous shrinkage of HSC.[Download]

Silica aerogels were prepared from a mixture of tetraethylorthosilicate and organo- alkoxysilanes. The effects of organo-alkoxysilanes on the mechanical properties of the silica aerogels were studied. The fl exibility of silica aerogels was signifi cantly improved by incorporation of organo-alkoxysilanes. When MTES and TEOS were combined as precursors of silica areogels, with the increased amount of MTES, the apparent elastic modulus and apparent compressive strength monotonously rose. At the same organo- alkoxysilanes to TEOS ratio, the size of alkyl groups of the organo-alkoxysilanes had little effect on the mechanical properties. In series of MTES and TEOS, the lowest elastic modulus of silica skeleton and the highest compressive strength of silica skeleton were observed at MTES to TEOS ratio of around 50:50. At a certain organo-alkoxysilanes to TEOS ratio, the elastic modulus of silica skeleton increased and the compressive strength of silica skeleton decreased with the size increase of the alkyl groups.[Download]

Polymer nano-particles (PNPs) with particle size range of 29.4鈥52.7 nm were synthesized via emulsion polymerization. The mini-cone tests were conducted to evaluate the dispersion capability of PNPs in fresh cement pastes (fcps). Interactions of PNPs with cement were studied by measurements of total organic carbon, zeta potential, transmission electron microscopy, calorimetry and mercury intrusion porosimetry. Results show that the prepared PNPs can be adsorbed on to cement surface and improve fluidity of fcps effectively. The addition of PNPs leads to lesser retardation effect on cement hydration than popularly used polycarboxylate superplasticizers and reduces pore connectivity of micro-pores in hardened cement pastes.[Download]

Static and dynamic mechanical properties of cement-asphalt composites with various contents of asphalt incorporated were studied. Uniaxial compressive stress-strain curves of different cement-asphalt mortars (CAMs) with cement mass ratio (A/C) in the range of 0.2 to 1.0 were obtained by the Materials Testing System (MTS) under different testing temperatures ranging from 鈥40 to 80掳C. Two typical CAMs, one with A/C of 0.2 denoted by LAC and the other with A/C of 0.9 denoted by HAC, were chosen to be tested at varied deformation rates over a range of 0.3 to 30mm/min at room temperature. The correlation between mechanical properties, e.g.,peak stress or elastic modulus, and temperature or loading rate was, respectively, acquired. As a result, temperature sensitivity and loading rate dependence for mechanical behavior of different CAMs were analyzed. Dynamic mechanical analysis (DMA) on three cement-asphalt binders (CABs) with A/Cs from 0.2 to 1.0 was carried out, and temperature spectra and frequency spectra were obtained. The Burger model was u[Download]

The influence of triethanolamine (TEA) at varying dosages on the strength development of pure cement (PC) and fly ash cement (FAC) pastes was systematically investigated. Techniques including mercury intrusion porosimetry, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy were employed to characterise the microstructure of hardened cement pastes and to monitor the cement hydration process with the aim of correlating strength variations with microstructural changes caused by TEA addition. The results showed that 0.03-0.10% addition of TEA visibly enhances the early strength but decreases the compressive strength after 3 d for PC pastes. A high dosage of TEA (1%) leads to a sharp decrease in 28-d strength for both PC and FAC pastes. Mechanistic explanations regarding why TEA affects the strength development differently at different dosages and ages are discussed by considering the impacts of TEA on the hydration degree, pore structure, composition and morphology of hydration products.[Download]

The coupling effects of temperature and time on the fluidity of fresh cement mixtures were investigated. Mini-cone tests on cement mortars and rheological tests on cement pastes under different temperatures (0 to 60 掳C) were conducted to characterize the development of the fluidity of fresh cement mixtures over time. In addition, total organic carbon tests were performed to quantify the adsorption amount of superplasticizers on the cement surface. The amount of free water in cement pastes was determined via centrifugation. Isothermal calorimetry was employed to characterize the hydration kinetics of cement under different temperatures. Results show that the spread diameter of mortars decreases in a roughly linear fashion over elapsed time. Higher temperature facilitates a sharper decrease in fluidity with time, although the initial fluidity of fresh mortars is not significantly affected by temperature. Higher temperature results in a greater amount of adsorbed polycarboxylate ester/ether on the cement surface and a lower amount of free water in fresh cement pastes, which is believed to result from the higher hydration rate of cement. The evolution of rheological properties over time can be attributed to the development of hydration degree. Relative hydration degree is introduced to indicate the development of rheological properties with time. Two models to describe the evolution of yield stress and plastic viscosity for fresh cement pastes were developed.[Download]

The compressive mechanical properties of cement asphalt mortars ( CAMs ) with varied bitumen-cement ratio (B/C) were studied under different temperatures, in order to reveal the susceptibility of mechanical properties to temperature. Results indicate that the compressive strength and the elastic modulus generally increase with a decrease in temperature for all tested CAMs . The quantitative evaluation of the temperature dependence of the strength and the elastic modulus using defined temper[Download]

The rheological properties of fresh cement asphalt paste (CA paste) were investigated, in which influencing factors such as type of asphalt emulsion, temperature, and time were discussed. CA pastes with two types of asphalt emulsions and varied asphalt contents were prepared at 0, 20 and 40℃. The initial yield stress and its development over shelf time were tested to characterize the rheological properties of the pastes. The measurement of semi-adiabatic temperature development during hydration and optical microscopic observation were carried out to determine the hydration kinetics and microstructure evolution of the pastes. Results indicate that the initial flowability and flowability retention over shelf time of the pastes visibly improve because of the plasticizing effect of the asphalt emulsion and its retardation effect on cement hydration. The anionic asphalt emulsion is more effective... more The rheological properties of fresh cement asphalt paste (CA paste) were investigated, in which influencing factors such as type of asphalt emulsion, temperature, and time were discussed. CA pastes with two types of asphalt emulsions and varied asphalt contents were prepared at 0, 20 and 40℃. The initial yield stress and its development over shelf time were tested to characterize the rheological properties of the pastes. The measurement of semi-adiabatic temperature development during hydration and optical microscopic observation were carried out to determine the hydrat.[Download]

The hydration and hardening mechanism of cement asphalt binder (CAB) was studied. The early hydration process, hydration products and paste microstructure of CAB made by Portland cement and anionic asphalt emulsion were investigated by calorimetry, X-ray diffraction, and environmental scanning electron microscopy. The early hydration process of CAB can be characterized as 5 stages similar to those of Portland cement. There is no chemical reaction detected between cement and asphalt, hence no new hydration products other than those of Portland cement are produced. The hardening of CAB begins with the hydration of cement. When the hydration of cement comes into the acceleration period and its exothermic rate comes to the maximum, the coalescence of asphalt particles in asphalt emulsion is triggered. In the hardened system of CAB, it was found that the hydration products of cement form the skeleton and are covered by the continuous asphalt film. They formed an interpenetrating network system. The emulsifiers in the asphalt emulsion may retard the hydration process of cement.[Download]

The compressive strength developing process and the microstructure of cement-asphalt mortar (CA mortar) were investigated. The fl uidity of CA mortar has a great infl uence on its strength. The optimum value of spread diameter of slump fl ow test is in the range of 300 to 400 mm. The compressive strength of CA mortar keeps a relatively high growth rate in 56 days and grows slowly afterwards. The residual water of hydration in CA mortar freezes under minus environmental temperature which can lead to a signifi cant reduction of the strength of CA mortar. Increasing A/C retards asphalt emulsion splitting and thus prolongs the setting process of CA mortar. The hydration products of cement form the major structural framework of hardened CA mortar and asphalt is a weak phase in the framework but improves the viscoelastic behavior of CA mortar. Therefore, asphalt emulsion should be used as much as possible on the condition that essential performance criterions of CA mortar are satisfi ed. [Download]

Silica gels prepared by copolymerizing tetraethylorthosilicate with 3-aminopropyltriethoxy-silane were modified using polymer derived from toluene diisocyanate and dried under ambient pressure. The successful preparation of silica aerogels depended on the effective control of shrinkage during drying. The resulting material, polymer-modified silica aerogel, was then characterized by thermogravimetric analysis and uniaxial compression tests. Results indicated that the apparent elastic modulus and compressive strength of the polymer-modified silica aerogels decreased with increasing amounts of incorporated polymer because of decreasing shrinkage and density, while the strains at the surface cracking point and the final failure point increased significantly during compression tests. The strength and modulus of the silica skeleton could be calculated from the apparent strength and modulus of the silica aerogels respectively. It was interestingly shown that the elastic modulus of the silica skeleton of the silica aerogels increased because of the incorporated polymers, while the polymers had no effects on the compressive strength of the silica skeleton. In addition, the relationships between the apparent elastic modulus or the apparent compressive strength of the polymer-modified silica aerogels and their shrinkage were quantitatively expressed.[Download]

In order to overcome the low conversion and complex post-treatment, four different polymerization procedures were adopted to prepare the magnetic polymer latexes. The results clearly show that the strategy using magnetic emulsion template-dosage is the most effective and feasible. Based on the optimized procedure, various factors including the type of initiators such as oil soluble initiator, water soluble initiator, redox initiator system, crosslinking agent, functional monomers etc. were systematically studied. Magnetic polymer latex with high monomer conversion of 83% and high magnet content of 31.8% was successfully obtained. Besides, core鈥搒hell structured magnetic polymer latex with good film forming property was also prepared, which is promising for potential applications such as magnetic coatings and modification of cementitious materials with controlled polymer location.[Download]

The strength mechanisms of two kinds of cement-asphalt (CA) mortar, which vary principally in their strength and elastic modulus, were investigated by environmental scanning electron microscopy, calorimetry, and strength tests. The results showed that the asphalt emulsion delayed the early hydration of the cement and the asphalt membrane had a negative effect on the further hydration of the cement, to some extent. The cement products could impale the asphalt membrane, and the cement could hydrate adequately because of the sufficient water supply in the CA mortar. The framework formed by the hardened cement paste was the primary structure skeleton in the CA mortar with a high elastic modulus and the asphalt phase, exhibiting as a filling phase, increased the weak phase of the structure system. For CA mortar with a low elastic modulus, the asphalt phase exhibited as a dominant phase. Two weak structure skeletons, formed by the asphalt membrane and the hardened cement paste, respectively, were responsible for the strength together.[Download]

以不同分子量的甲氧基聚乙二醇 甲基丙烯酸酯(mPEG1000MA或mPEG2000MA)为大单体,与丙烯酸(AA)、甲基烯丙基磺酸钠(SMAS)等单体通过自由基聚合反应合成了 一系列具有不同分子量、不同侧链长度、不同侧链密度的聚(丙烯酸-co-甲氧基聚乙二醇甲基丙烯酸酯)梳状高分子.用乌氏黏度计测定梳状高分子的特性黏数 以表征其分子量大小.采用示差扫描量热法(DSC)测量梳状高分子中甲氧基聚乙二醇(mPEG)侧链的结晶温度和熔点.分析认为,当mPEG1000MA 与AA共聚后,处于玻璃态的PAA主链对mPEG侧链的物理限制作用很大程度上影响了mPEG侧链的结晶行为.这种在受限环境中mPEG的结晶温度和结晶 熔点均发生明显漂移,低于PEG在本体中的结晶.结晶温度和熔点的偏移受到主链长度、侧链疏密、侧链长度、磺酸侧基含量等诸多分子结构和组成因素的影响. 研究结果表明:共聚物中侧链越稀疏,侧链结晶受限作用越明显;mPEG侧链分子量越大,其结晶受到主链的限制作用越弱;在梳状高分子主链上引入磺酸侧基官 能团后,侧链的结晶的受限程度增加,并且由于非晶侧链的增多,表现出明显的侧链玻璃化转变.[Download]

The changes of free solution amount,fluidity and the time-depended fluidity loss of cement paste were examined by varying the water-cement ratio and the dosages of superplasticizer. The distribution of solution and flocculation microstructure in fresh cement paste was observed with optical microscope. The change of free solution amount and its effect on the fluidity and bleeding of cement paste was studied. The results show that the adsorbed solution amount has a great influence on the compatibility of cement-superplasticizer system,including the bleeding degree,the fluidity and the time-depended fluidity loss of cement paste. Superplasticizer increases the fluidity of cement paste by destroying the flocculated cement particle structure and increasing the amount of adsorbed solution. Polycarboxylate superplasticizer shows higher ability of adsorption than naphthalene superplasticizer. Over dosage of superplasticizer is not the primary cause of bleeding. The principle reason of bleeding is the high water-cement ratio and the insufficient enhancing ability of water adsorption of superplasticizer.[Download]

An efficient method using a polymer dispersion (PD) based on a copolymer of styrene and butyl acrylate to prepare TiO2 electrodes for dye-sensitized solar cells (DSCs) was introduced. The obtained TiO2 nanoporous film was investigated by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. A porous structure with pore size distribution from tens of nanometers to several hundred nanometers or even micrometers was characterized. This offered the film a feature of high haze factor and porosity. When using the film as photoanode, a quasi-solid-state DSC was successfully fabricated. The device showed an improved per-weight-efficiency by a factor of 2.7, resulting from the reduced interfacial resistance and the enhanced light scattering effect revealed by electrochemical impedance spectroscopy and transmittance spectroscopy, respectively. The developed PD-based colloid is promising to be applied in production on a large scale as a result of its simple prescription and stability during storage. A proposal to further improve the porous film is also introduced at the end of the paper.[Download]

A polymer dispersion consisting of soft latex spheres with a diameter of 135 nm was used to produce a crystalline film with face-centered cubic (fcc) packing of the spheres. Different from conventional small-molecule and hard-sphere colloidal crystals, the crystalline latex film in the present case is soft (i.e., easily deformable). The structural evolution of this soft colloidal latex film under stretching was investigated by in-situ synchrotron ultra-small-angle X-ray scattering. The film exhibits polycrystalline scattering behavior corresponding to fcc structure. Stretching results not only in a large deformation of the crystallographic structure but also in considerable nonaffine deformation at high draw ratios. The unexpected nonaffine deformation was attributed to slippage between rows of particles and crystalline grain boundaries. The crystalline structure remains intact even at high deformation, suggesting that directional anisotropic colloidal crystallites can be easily produced.[Download]

The coarsening process of the droplets in a two-phase polymer blend (PP/EVAc) was studied under two-dimensional and three-dimensional conditions using a phase contrast microscope and computer image analyzer. The results showed that under three-dimensional conditions the growth of the droplet's radius with time follows r(3) approximately t(1.01), corresponding to the evaporation-condensation theory of Lifshitz-Slyozov, r(3) approximately t, while under two-dimensional conditions the growth law is r(3) approximately t(1.31). The growth rate of the droplets under two-dimensional conditions is faster than that under three-dimensional conditions. This difference is caused by an interfacial interaction (wetting effects) between the substrates and polymer blend. The existence of the interface promoted the coarsening process of the polymer blend under two-dimensional conditions. Copyright 2001 Academic Press.[Download]