Font Size: a A A

Study On The PH Response Of Gemini Ester Quaternary Ammonium Salt Surfactant Or Amino Acid Type Surfactant Mixed Systems

Posted on:2021-10-03Degree:MasterType:Thesis
Country:ChinaCandidate:S S ZhangFull Text:PDF
GTID:2491306095498344Subject:Physical chemistry
Abstract/Summary:PDF Full Text Request
In this thesis,the p H-responsive micellar systems have been constructed by(green)surfactants and p H-sensitive additives.The methods,such as steady-state rheology,dynamic rheology,dynamic light scattering,UV-vis spectrophotometry,nuclear magnetic resonance spectroscopy,transmission electron microscopy(TEM)and molecular dynamics simulation(MD)were used to explore the mechanism of the microstructural transition of p H-induced micellar systems and the construction mechanism of p H-responsive micelles.(1)Using phthalic acid(PA)as additive,the p H-responsive mixed micellar systems have been constructed by cetyltrimethylammonium bromide(CTAB)or N,N’-bis(2-(dodecanoyloxy)ethyl)-N,N,N’,N’-tetramethyl-1,3-propane diammonium dibromide(C12DEG3).The experimental results show that both the two mixed micellar systems exhibit high p H sensitivity and good cyclic reversibility.The molecular dynamics simulation method was used to explore the reason why the CTAB/PA/H2O mixed micellar system exhibits p H sensitivity.PA molecules can be quickly solubilized into the pre-assembled rodlike micelles,the micelles maintain as short rodlike morphology due to the hydrophobic interaction between the benzene ring of PA and the hydrocarbon tail of CTAB.However,when the p H value of the mixed system increases,PA molecule is deprotonated to form hydrogen phthalate(OPA),which can effectively shield the electrostatic repulsion between the ionic head groups of CTAB,the hydrophobic interaction between the benzene ring and the hydrocarbon tail is also beneficial for the participation of OPA in the self-assembly of CTAB to form long straight rodlike micelles.With the further increase of p H,OPA can be further deprotonated to form phthalate disodium salt(DOPA).The two carboxylate ions lead to enhanced hydrophilicity of DOPA and weaker hydrophobic interaction between the benzene ring of DOPA and the hydrocarbon tail of CTAB,resulting in the microstructural transition from long rodlike micelles to spherical(short rodlike)micelles.(2)CTAB and sodium lauroyl glutamate(LAG-Na)have been used to construct p H-responsive mixed micellar systems.The CTAB/LAG-Na/H2O mixed systems with the total molality of 0.1mol·kg-1are transparent isotropic single-phase systems in the whole composition range.The viscosities of the mixed systems increase first and then decreases with the increase of x CTAB(the mole fraction of CTAB in the total surfactant).Since the degree of dissociation of LAG-Na varies with the p H of the mixed system,resulting in its different combination ability with CTAB in the mixed micelles.The addition of acetic acid or Na OH into the CTAB/LAG-Na/H2O mixed system with x CTAB=0.667leads to decrease in viscosity,and the mixed system shows good p H sensitivity.(3)CTAB or N(α)-palmitoyl-L-lysine methyl ester hydrochloride(PLM)and sodium N-lauroylsarcosinate(SLS)have been used to construct p H-responsive mixed micellar systems.When x CTABchanges from 0 to 1,the CTAB/SLS/H2O mixed micellar system exhibit complicated phase behaviors:the phase change behaviors from single phase to two-aqueous phases and then to single phase have been observed.For the CTAB/SLS/H2O mixed micellar system with x CTAB=0.667,when the p H value is decreased from 2.97 to 2.67,the viscosity decreases by 3orders of magnitude.For the PLM/SLS/H2O mixed micellar system,when the p H value decreases from 3.48 to 2.40,the viscosity decreases by nearly 5 orders of magnitude.The reason is that the degree of dissociation of SLS changes with the p H of the mixed system,leading to its different combination ability with cationic surfactant,which induces the mixed system showing good p H sensitivity.
Keywords/Search Tags:anionic and cationic surfactants, pH responsive micelles, rheological property, phase behavior, wormlike micelles
PDF Full Text Request
Related items