Studies On The Rheological Behaviors And Dynamic Scaling Theory Of Opposite Charged Surfactant And Polyelectrolyte Complex Solution

The polyelectrolyte and surfactant system with opposite charges has attractedgreat attention both in academic research and commercial application. However, toour knowledge, there were few studies concerning the polyelectrolyte-surfactantinteractions in entangled polyelectrolyte solutions. It is well known that rheologicalbehaviors of multiphase and multicomponent polymer systems are related to thecomponents and phase morphologies. In this dissertation, the rheological behavior ofentangled semidilute solution of anionic polyelectrolyte poly (acrylic acid) (PAA) andsodium carboxymethyl cellulose (NaCMC) containing cationic surfactant wasinvestigated, as a function of surfactant concentration, tail length, polyelectrolyteconcentration, charge density and temperature. Moreover, on the basis of "StickyReptation Model", we modified the polyelectrolyte scaling expression in entangledsemidilute solution. It is found that the relationship between rheological response andstructure of the opposite charged polyelectrolyte and surfactant system can bedescribed by using the modified model.On the other hand, The interactions between anionic polyelectrolyte, poly(acrylicacid) (PAA), and cationic surfactant, alkyltrimethylammonium bromide (C_nTAB),were investigated by rheological measurements in PAA entangled semidilute solution.The results reveal that addition of both dodecyl and cetyltrimethylammoniumbromides (C₁₂TAB and C₁₆TAB) into PAA solution could increase its viscosity whenthe surfactant amounts surpassed a critical surfactant concentration (C_c). The increaseof viscosity is attributed to the surfactant micelles bridging of the polymer chains andconfine the mobility PAA chain. On the other hand, the viscosity increases rapidlywith the adding surfactant into PAA solution with lower neutralization extent, due tolower neutralization extent PAA-C_nTAB complex having more hydrogen bondings.The steady and dynamic rheological behaviors of NaCMC entangled semidilutesolution filled with C₁₂TAB were investigated. Both steady and dynamic rheologicalresults present that the rheological parameters (zero shear rate viscosity (η₀), relaxation time (Ï„) and dynamic storage modules (G′)) increase with surfactantconcentration (c_surf), and can be divided in three scaling regions by two criticalC₁₂TAB concentrations (C₁, C₂; c₁, c₂; and C₁′, C₂′are from curves ofη₀～c_surf,τ～c_surfand G′～c_surf, respectively). The presence of two critical C₁₂TAB concentrationsimplies that the structures evolution of NaCMC-C₁₂TAB complex could be exposed tothree states with increase of c_surf, i.e. no network formation, network extentprogressive formation and perfect network formation, respectively. Moreover, c₁, c₂approach C₁′, C₂′, while a little lower than C₁, C₂, indicating that the relaxation timeand dynamic module are more sensitive to detect the structure change of the complex.Both C₁(c₁, C₁′) and C₂(c₂, C₂′) increase with NaCMC concentration increasing andcharge density decreasing. Meanwhile, the dynamic rheological results also revealedthat the decrease of G′at critical strain amplitude, i.e., the so called "Payne Effect", isprominently enhanced upon increasing c_surf. Apart from this phenomenon, as c_surfincreases, the slopes of plotting log G′～logωand log G″～logωdecrease, revealingthat the network extent of NaCMC-C₁₂TAB systems progressively increases as c_surfincreases. It is also found that G′of NaCMC-C₁₂TAB is much more sensitive to c_surfthan that of G″.The experimental results show that the viscosity, relaxation time and moduleincrease with c_surf increasing, which is ascribed to the surfactant micelles bridging ofthe polymer chains and confining of the mobility of polymer chain in entangledsemi-dilute solution. Hence, based on "Sticky Reptation Model", we modify thepolyelectrolyte scaling expression in entangled semidilute solution. And the modelcan be used to explain our experimental results. It is also applied to predict anincrease in viscosity of PAA/C₁₂TAB systems reported in literature. The results are ingood agreement with experimental data, proving our model can be used for examinethe relationship between rheological response and structure of the opposite chargedpolyelectrolyte and surfactant system.