Comparative Inveatigation On Complexation Between Polymers And Anionic Surfactants

Polymer-surfactant systems having different self-assembled structures and exhibiting better performance in solubilization,foaming and interfacial adsorption,compared with single surfactants,are widely used in personal care,coatings,enhanced oil recovery,protein purification and simulation of biological processes.Many researchers have deeply conducted the weak interaction of neutral polymer-anionic surfactant systems and the strong electrostatic interaction of polycation-anionic surfactant systems,and revealed the double critical concentration phenomenon?c₁ and c₂?,polyelectrolyte properties,structures model,interaction mechanism and solution properties between the two types of systems and so on.Nevertheless,some problems remain unresolved between these two types of representative systems.It lacks of comparative investigation on the complexation between polymer and anionic surfactants with different head group.Due to the limitations of experimental conditions or research concerns,many researchers failed to summarize the key parameters which would characterize the complexation,so that systematic comparative studies could not be carried out directly.It is found that as the hydration radius of alkali metal counterions decreases,the complexation boundary in the systems is pre-positioned and the complexation strength is gradually weakened in the study of the neutral polymer-anionic surfactants systems.However,the influence of changes with the hydration radius of alkali metal counterions on the types of polyelectrolyte is also not clear.A large number of studies on polycation-anionic surfactant systems have shown that strong electrostatic interaction would lead to a large precipitation zone in the systems.It is generally believed that as the concentration of surfactant increases,precipitation would redissolve after"string of beads"structure are formed.At present,there are limited research methods for the structure of the association and its charge characteristics after the precipitation zone,also the influence of the molecular weight and charge density of the polycation on the charge characteristics after the precipitation zone is still unclear.Therefore,based on the above mentioned problems,the main research contents,main results and conclusions of this paper are as follows:1.Comparison on complexation between polyvinylpyrrolidone?PVP?and anionic surfactantsNeutral polymer PVP and four typical anionic surfactants sodium dodecyl sulfate?SDS?,sodium dodecyl benzene sulfonate?SDBS?,sodium dodecanoate?SD?,potassium dodecyl phosphonate?MLP?were comparative studied by tensiometry,conductometry,CE and isothermal titration microcalorimetry?ITC?.New proposed four parameters complexation effectiveness??C?,complexation efficiency?[?_?]?,the degree of bridging site?f?and surface charge density of pseudo-polyanions(??_e?_max),and combined with the binding constant?K_D?were used to comprehensively evaluate and compare different complexation between PVP-anionic surfactants systems.The results showed that:?1?The?C and[?_?]of PVP-SDS and PVP-SDBS systems were higer than those of weakly dissociated SD and MLP,indicating that more surfactant molecules bind on the polymer chains so that cmc would be reduced.?2?The strongly dissociated surfactants SDS and SDBS could bind on the PVP chains at a low concentration to form a pseudo-polyanion structure,due to their low cmc and c₁.The??_e?_max of the corresponding pseudo-polyanion was stronger when the systems was balanced.?3?The internal stability of different systems obtained by the K_D and the f are greatly affected by the surfactants head group in alkaline conditions;while the head-based barrier effect can be neglected under near-neutral conditions.Above all,the combination of aforementioned four parameters and K_D proposed in this dissertation would provide a new and direct comparison method for the complexation of neutral polymer-anionic surfactant systems,and provide guidance for researchers to choose experimental systems.2.Effect of hydration radiu of alkali metal counterions on the complexationCE proves that the association between neutral polymer interact with the alkali metal counterions by ion-dipole interaction has weak polycation without surfactants,and the association which was formed by an alkali metal counterions bridge between neutral polymer and anionic surfactants,has strong polyanionic properties independent of the hydration radius.So there is an essential difference between the two systems.In addition,the effect of hydration radius of alkali metal counterions on PVP-dodecyl sulfate systems were investigated through?C,[?_?],f??_e?_max and K_D.When the hydration radius of alkali metal ions decreased?Li⁺>Na⁺>K⁺?,the value of?C,[?_?],f and the absolute value of??_e?_max increased,but the internal stability?K_D?of the pseudo-polyanion decreases.It is confirmed that the feasibility of a comparative during similar systems by five parameters.3.Study the complexation between cationic cellulose-anionic surfactantsThe CE results of cationic cellulose and anionic surfactant SDBS systems showed that the precipitation zone formed by strong electrostatic attraction would be narrowed with the decrease of cationic cellulose concentration,and disappeared when SDBS was excess.Furthermore,the association formed after precipitation zone was pseudo-polyanions,and its polyelectrolyte strength is less influenced by the molecular weight and substitution degree of the cationic cellulose.The same conclusion was obtained between the cationic cellulose-SDS systems without UV absorption signals by using the benzophenone probe method,which further indicating that the results are universal.