Interactions Between Polysaccharide And Surfactant

An increasing interest is directed today towards polysaccharide biopolymer, both for the important properties of these materials, such as, extensive and natural sources, nontoxicity, continuable use, security, and for the relevance of polysaccharide in biology. In practical application of polysaccharide, surfactant often exists. Polysaccharide-surfactant system usually displays intriguing and fascinating features, which is different from polysaccharide or surfactant. A striking feature of many (but not all) polymer/surfactant pairs is their complexation in dilute aqueous solution. In recent years, researchers not only focus on the exploiture of polysaccharide-surfactant system for technical reasons, but also consider a number of theoretical aspects. With the development of modern instruments and computer simulation, deeper studies dealing with the interaction between polysaccharide and surfactant changes from macroscopical properties to microstructure, from summarization of empirical law to molecular level. The present dissertation will focus on the interaction between polysaccharide biopolymer (Xanthan, chitosan and cellulose derivative) and surfactant. Some important evidence for such complexation is obtained by methods such as mesoscopic simulation and some experimental techniques. These studies are of significance in making a good physical picture of the interaction between polysaccharide and surfactant. The present dissertation includes four topics.1. Interaction between polysaccharide and surfactantMesoscopic simulation has been paid more and more attention as they can provide important information in a larger time and length scale. There are two types of mesoscopic simulation: MesoDyn and dissipative particle dynamics (DPD). This part is divided into 3 subsections according to the type of polysaccharide. MesoDyn simulation has been used to carry out studies for systems on interaction of surfactants and xanthan (XC) or carboxymethylchitosan (CMCHS), as well as the shape of aggregates. In addition, the kinetics of surfactant binding, which is very difficult to observe experimentally, can be studied by MesoDyn.In Chapter 2, MesoDyn method is used to study the interaction between XC and cationic surfactant nonyphenyloxypropylβ-hydroxyltrimethylammonium bromide (C9phNBr) in aqueous solution. The effects of C₉phNBr concentration, XC concentration and temperature on the morphology of XC/C₉phNBr aggregates as well as surfactant binding kinetics are discussed. Surfactant with different hydrophobic chain, dodecyloxypropyl-β-hydroxyltrimethyl ammonium (C₁₂NBr), is compared with C₉phNBr on their interactions with XC. Simulation results show that the addition of C₉phNBr or C₁₂NBr do not destroy the advanced shape of XC, C₉phNBr/XC or C₁₂NBr/XC aggregates still preserve rod-like shape with double helix characteristic. The process of surfactant binding on XC chain can be divided into three stages: diffusion, binding and equilibrium stage. The higher XC or surfactant concentration does not favor the binding of surfactant. Comparing with C₁₂NBr, binding of C₉phNBr is more difficult because of the rigid phenyl in its hydrophobic chain. The standard evidence for such complexation is in terms of surfactant binding isotherms, obtained by the potentiometric titration method using a surfactant-selective electrode. The experiments of binding isotherms seem to confirm the viewpoint deduced from simulation. Detailed discussion is described in Chapter 2.In Chapter 4, the aggregation behavior between CMCHS and oppositely charged cetyltrimethylammonium bromide (CTAB) micelles in aqueous solution is focused on. MesoDyn simulation and various experimental techniques (viscosity, DLS, TEM) are used. The effect of CTAB concentration and temperature on such interaction is investigated. Simulation results show that at lower CTAB concentration, CTAB micelles act as bridges and make CMCHS chains forming cross-linked network structure. A progressive increase in CTAB concentration eventually results in ellipsoidal shape forming because of most of CMCHS chains wrapping around the surface of CTAB micelles at the moment. The results on the viscosity and hydrodynamic radius of the aggregates are then described and related to the aggregation behavior. Finally, we proposed a detailed picture for their aggregation mechanism.In Chapter 5, the effect of pH value on the interaction between sodium carboxymethyl cellulose (NaCMC) and C₁₄BE is studied by DPD simulations and surface tension measurements. In solution of different pH value, NaCMC and C₁₄BE display different forms because of the existence of carboxyl and amidocyanogen groups. Different forms lead to different interactions between them. The results of DPD simulation indicate that mixing energy between C₁₄BE and NaCMC at pH=2 is lower than that at pH=7. Accordingly, such an interaction at pH=2 is stronger. The structure of the formed NaCMC/C₁₄BE complexes can be displayed by DPD simulation as well as its time evolution. Surface tension measurements further confirm the simulation results above. There are two inflexions in the surface tension isotherm of C14BE at pH=2, implying that NaCMC/C₁₄BE complexes are formed via hydrophobic interactions; while only one inflexion at pH=7 and the cmc andγcmc are decreased for the presence of NaCMC.2. Interaction between XC and hydrated polyacrylamide(HPAM)As a viscosity modifier mixed polymer solution has been the focus of intense fundamental an applied research, as it is often applied in a wide range of fields. The viscoelasticity of XC and HPAM mixed solution have been studied in Chapter 3, for the purpose of exploiting a new polymer flooding with strong heat resistance and salts tolerance for EOR. The effects of mixed ratio, inorganic salt and temperature on viscoelasticity of XC/HPAM system are focused on. Experimental results show that at 1:5 mixed ratio of XC/HPAM, apparent viscosity of the solution is higher than both XC and HPAM solution. The heat resistance and salts tolerance of 1:5 XC/HPAM systems are improved markedly. The end-to-end distance of HPAM in mixed solution is captured using DPD simulation, which provides interaction mechanism on the improved efficiency of enhancing viscosity.3. The surface dilational viscoelasticity of HPMC/CnTABThe dilational surface modulus is an appropriate function for the characterization of surface properties of HPMC/CnTAB system. The oscillating barriers method is used to study the dilational rheological properties of adsorbed layers during a narrow frequency (0.005 0.1 Hz). The evaluation of such measurements shows that the viscoelasticity of adsorbed layers is influenced markedly by oscillation frequency, bulk concentration and surfactant structure. The presence of HPMC results in the weaker dependence of dilational viscoelasticity on oscillation frequency comparing with pure CnTAB solution. The elasticity and strength of surface layer for HPMC/CnTAB solution is lower than that of pure HPMC solution in the presence of CTAB and DTAB, but it is higher for TTAB. This seems to be caused by the surface tension for CTAB, TTAB and DTAB concentrations is higher or not than surface tension of pure surfactant solution. Detailed discussion is described in Chapter 6.4. Quantitative structure-properties relationship (QSPR) of surfactant: Krafft point or cloud point Applying quantum chemistry, statistical method in molecular mechanics, thermodynamic method, the best QSPR equations between the Krafft point (cloud point) of surfactant and microstructure are obtained using the correlation parameter and F-test according to the structure of surfactant. The calculated results approach experimental values. The Krafft point or cloud point of some new surfactant can be forecasted according to such QSPR equations.The descriptors used in these QSPR equations are simple and can be obtained only running some half-empirical programs in quantum chemistry. This is meaningful for forecasting the Krafft point or cloud point of some new surfactant, as well as some other properties. In addition, these studies provide a new idea for forecasting other physicochemical properties. From QSPR equation. we can get some information on surfactants only depending on calculations, so this work can shorten working time and reduce experimental materials.The novelty of this dissertation:1. In the references dealing with MesoDyn, it is only used to simulate properties of block copolymer or polymer blend system. However, in this paper MesoDyn simulation is used to study interactions between polysaccharide and surfactant. A new and simple approach for studying such a system is found. This study enlarges the application of MesoDyn method in colloid chemistry and provides a new idea for investigating interactions between other type of polymer and surfactant.2. The second novelty of this dissertation is mesoscopic simulation and experiments are combined to study physicochemical properties of system. Simulation and experimental results illustrate the interaction mechanism between polysaccharide and surfactant from macro and micro viewpoint, respectively. Simulation results are consistent with experimental results. Simulation results can provide guidance for new experimental design.3. The QSPR equations between Krafft point and structure reported in references only focus on conventional hydrocarbon surfactant. So its application is limited. In this paper, a QSPR equation for Krafft point of a series of fluorocarbon surfactant is established for the first time. The effect of counterions on Krafft point is also considered in such equation.