Influence of Solution pH on Stability of Fumed Silica–Polyacrylic Acid Systems

The influence of polyacrlic acid (PAA) adsorption on fumed silica (SiO2) surface on suspension stability has been studied. Сhanges in the suspension stability were monitored using a Turbiscan LabExpert with a TLAb Cooler cooling module at 25oC. PAA is an anionic polymer containing carboxyl groups; therefore all the measurements were carried out at different pH 3, 6 and 9. Analysis of obtained transmission and backscattering curves and Turbiscan Stability Indexes (TSI) allowed determination of the most probable mechanism of the system stability.Вивчено вплив адсорбції поліакрилової кислоти (ПAК) на поверхні високодисперсного кремнезему (SiO2) на стабільність суспензії. Зміни стабільності суспензії спостерігались за допомогою приладу Turbiscan LabExpert із охолоджуючим модулем TLAb Cooler при 25oC. ПAК є аніонним полімером, що містить карбоксильні групи, тому всі вимірювання проводились при різних рН (3, 6 та 9). Аналіз одержаних кривих перенесення та зворотнього розсіяння, а також індексів стабільності (Turbiscan Stability Indexes (TSI)) дозволив визначити найбільш вірогідний механізм стабілізації вивчених систем.Изучено влияние адсорбции полиакриловой кислоты (ПAA) на поверхности высокодисперсного кремнезема (SiO2) на стабильность суспензии. Изменения стабильности суспензии наблюдались с помощью прибора Turbiscan LabExpert с охлаждающим модулем TLAb Cooler при 25oC. PAA является анионным полимером, содержащим карбоксильные группы, поэтому все измерения проводились при различных рН (3, 6 и 9). Анализ полученных кривых переноса и обратного рассеяния, а также индексов стабильности (Turbiscan Stability Indexes (TSI)) позволил определить наиболее вероятный механизм стабилизации изученных систем

The temperature effect on electrokinetic properties of the silica–polyvinyl alcohol (PVA) system

The influence of polyvinyl alcohol (PVA) adsorption on the structure of the diffuse layer of silica (SiO2) in the temperature range 15–35 °C was examined. The microelectrophoresis method was used in the experiments to determine the zeta potential of the solid particles in the absence and presence of the polymer. The adsorption of PVA macromolecules causes the zeta potential decrease in all investigated SiO2 systems. Moreover this, decrease is the most pronounced at the highest examined temperature. Obtained results indicate that the conformational changes of adsorbed polymer chains are responsible for changes in electrokinetic properties of silica particles. Moreover, the structure of diffuse layer on the solid surface with adsorbed polymer results from the following effects: the presence of acetate groups in PVA chains, the blockade of silica surface groups by adsorbed polymer and the shift of slipping plane due to macromolecules adsorption

Determination of relevance between surface free energy and adsorption capacity of cement particles

ABSTRACT The compatibility between superplasticizer and cement was influenced by the adsorption capacity of cement particles. This study investigated the relevance between the adsorption capability and surface free energy. Adsorption capacity and surface free energy of both sulphoaluminate cement and portland cement were measured. The adsorption capacity of cement particles was measured by ultraviolet spectrophotometry. The test showed that particles of sulphoaluminate cement adsorbed more molecules of superplasticizer than portland cement particles. The weight of superplasticizer adsorbed by 2g of sulphoaluminate cement and portland cement were 0.28mg and 0.159mg respectively. Surface free energy of cement particles was calculated by contact angle and the contact angles were determined by the thin-layer wicking technique and washburn equation which is theoretical basis of thin-layer wiching technique presented by Chibowski E. The sulphoaluminate cement, portland cement's surface free energy were 51.46 mJ·m-2 and 49.36 mJ·m-2 respectively. The results showed that the higher adsorption capacity of particles was usual accompanied by higher surface free energy. The fluidity of cement paste was influenced by the adsorption capacity of cement particles because the more molecules of superplasticizer was adsorbed by cement particles there were lacking superplasticizer in the paste. The macro-behaviour of higher adsorption capacity is that the cement paste need more superplasticizer to reach the needed fluidity