FT-IR study of structure and properties of adsorbed monolayers of surfactants at the air/water interface.
Item
-
Title
-
FT-IR study of structure and properties of adsorbed monolayers of surfactants at the air/water interface.
-
Identifier
-
AAI9417463
-
identifier
-
9417463
-
Creator
-
Gao, Tao.
-
Contributor
-
Adviser: Milton J. Rosen
-
Date
-
1994
-
Language
-
English
-
Publisher
-
City University of New York.
-
Subject
-
Chemistry, Physical | Chemistry, Analytical
-
Abstract
-
A new technique--External Reflection-Absorption (RA) FTIR spectroscopy--has been applied to investigate the structure and properties of adsorbed monolayers of individual surfactants: sodium dodecanesulfonate (C{dollar}\sb{12}{dollar}SNa), sodium dodecylsulfate (C{dollar}\sb{12}{dollar}HS), deuterated sodium dodecylsulfate (C{dollar}\sb{12}{dollar}DS), dodecyltrimethylammonium bromide (C{dollar}\sb{12}{dollar}N), and their mixtures: C{dollar}\sb{12}{dollar}HS-C{dollar}\sb{12}{dollar}N and C{dollar}\sb{12}{dollar}DS-C{dollar}\sb{12}{dollar}N at the aqueous solution/air interface. A new method has been developed for the simultaneous determination of methylene chain orientation {dollar}(\chi){dollar} and surface concentration parameter {dollar}(\rm k\sb{lcub}max{rcub}){dollar} in adsorbed monolayers. The average chain orientation angle, {dollar}\chi,{dollar} and the surface concentration parameter, {dollar}\rm k\sb{lcub}max{rcub},{dollar} of adsorbed monolayers of C{dollar}\sb{12}{dollar}SNa at the air/water interface are found to be: {dollar}\chi = 38.4 \pm 3.3\sp\circ{dollar} (from the normal to the interface) and {dollar}\rm k\sb{lcub}max{rcub} = 0.53 \pm 0.04{dollar} at saturated adsorption from pure water solution. It is found that the chain orientation angle {dollar}(38.4 \pm 3.3\sp\circ){dollar} at the interface is very close to the chain tilt angle {dollar}(41\sp\circ){dollar} in crystalline solid. This indicates that the adsorbed monolayer of C{dollar}\sb{12}{dollar}SNa at the air/water interface has a molecular structure similar to that in the crystalline solid.;The phase transition (from LE to G) concentrations determined from RA spectra are in good agreement with those calculated from surface tension measurements for surfactants C{dollar}\sb{12}{dollar}SNa, C{dollar}\sb{12}{dollar}HS, and C{dollar}\sb{12}{dollar}DS in pure water and in salt solution. It is observed that saturated adsorbed monolayers of individual surfactants or equimolar cationic-anionic surfactant mixtures at the air/water interface have high-ordered all- trans conformation of methylene chains only in pure water solution. Adsorbed monolayers below saturation coverage in pure water or in salt solution and saturated adsorbed monolayers in salt solution have partial gauche conformers in their methylene chains.;The experimental data show that C{dollar}\sb{12}{dollar}DS has the same surface properties as C{dollar}\sb{12}{dollar}HS. This has provided a good basis by using C{dollar}\sb{12}{dollar}DS instead of C{dollar}\sb{12}{dollar}HS in surfactant mixtures containing C{dollar}\sb{12}{dollar}HS for spectroscopic studies (FTIR, NMR).;The composition of adsorbed mixed monolayers of C{dollar}\sb{12}{dollar}HS-C{dollar}\sb{12}{dollar}N and C{dollar}\sb{12}{dollar}DS-C{dollar}\sb{12}{dollar}N at the air/water interface with different bulk compositions are determined from RA Intensities, and are in good agreement with those calculated by use of the non-ideal mixing model. The FTIR study has provided new evidence that the surface composition in these mixed monolayers remains at a constant molar ratio of 1:1 at the interface over a large range of molar ratio in the solution phase.
-
Type
-
dissertation
-
Source
-
PQT Legacy CUNY.xlsx
-
degree
-
Ph.D.
