Amphoteric (ampholytic) surfactants - compounds that, in aqueous solutions depending on the pH value of the medium, ionize differently and act - in an acidic solution exhibit the properties of cationic surfactants, and in an alkaline solution - anionic surfactants. [1] .
Content
General Information
At pH values, called the isoelectric point , amphoteric surfactant molecules exist in the form of dipolar balanced ions. At the isoelectric point, the charges are equal, and the amphoteric surfactant molecule is a zwitterion . The most common are cationic and anionic-oriented zwitterionic amphoteric surfactants. http://www.ngpedia.ru/id407917p1.html Primary, secondary or tertiary amino groups , pyridine or imidazoline groups usually serve as cationic groups. Instead of nitrogen, there can be sulfur, phosphorus, arsenic, etc. Carboxyl , sulphonate, sulfoester and phosphate groups are used as anionic groups. In general, amphoteric surfactants can be represented by the formula:
K - -RO + , where R is a hydrocarbon radical, usually C 9 -C 19 ; O + is the main group; K - - acid group.
Classification
According to the chemical structure, ampholytic surfactants are divided into five main types. [2] :
1.Alkylaminocarboxylic acids (AAAA):
- RNH (CH 2 ) nCOOH - the alkyl radical of an amine usually has a linear structure, the radical between the amine carboxyl groups sometimes has a branched character;
- alkylaminophenylcarboxylic acids - RNHC 6 H 4 COOH;
2.Alkylbetaine (AB) is the most common type of ampholytic surfactants:
- C- and N-alkyl betaines - RCH (N + (CH 3 ) 3 ) COO - RN + (CH 3 ) 2 CH 2 COO - ;
- sulfobetaines - RC 6 H 4 CH 2 N + (CH 3 ) 2 CH 2 CH 2 OSO 3 - ;
- sulfite betaine - RN + (CH 3 ) 2 CH 2 CH 2 OSO 2 ;
- phosphate betaines RN + (CH 3 ) 2 CH 2 CH (OH) CH 2 OPO 3 ;
- amidobetaines RCONH (CH 2 ) 3 N + (CH 3 ) 2 COO - ;
- ethoxylated betaines RN + (CH 2 CH 2 O) CH 2 COO - .
3. Derivatives of alkyl imidazolines. In the structure of imidazoline ampholytic surfactants, anionic and cationic groups are approximately equivalent. By structure, they can be divided into two main classes - non-beta and beta:
here, R is a C 7 -C 17 hydrocarbon radical.
4. Alkylaminoalkanesulfonates and sulfates. The ionization constant of the acid group of these surfactants is much larger than the main one, therefore they are used in an alkaline medium. Depending on the ionization constants, salts can be distinguished:
- alkylaminoalkanesulfonate salt RN (R ') - R: βSO 3 M;
- alkylaminoalkanesulfate salt RN (R ') - R: - OSO 3 M;
- aromatic amino sulfonic acid derivatives RR'N β Ar β SO 3 M, where R and R'are long and short hydrocarbon radicals, R: is a short divalent radical
5. Polymer ampholytic surfactants:
- natural (proteins, nucleic acids, etc.);
- stepwise condensation products of amines, formaldehyde, albumin, fatty acids;
- cellulose derivatives obtained by the introduction of carboxyl and ethanol aminoethyl groups;
- synthetic, in whose molecules the structural features of all the above amphoteric surfactant groups are combined.
Application
Amphoteric surfactants in combination with anionic surfactants improve foaming ability and increase the harmlessness of detergent formulations, and when combined with cationic polymers they increase the positive effect of silicones and polymers on hair and skin. These derivatives are derived from natural raw materials, so they are quite expensive components. The most commonly used derivatives are betaine (cocamopropyl betaine). The chemical structure of ampholytic surfactants provides for the presence in their structure of many diverse functional groups and the possibility of constructing them in various combinations. Therefore, with the emergence of new directions in the use of surfactants and the study of the possibilities of obtaining drugs with given properties, ampholytic surfactants are the most promising [3] .
Literature
- Rebinder P. A. Selected Works. Surface phenomena in dispersed systems. Physico-chemical mechanics of dispersed systems. M., 1979.
- Voyutsky S.S. Course of colloid chemistry. M.: Chemistry, 1975.
- Summ B. D., Goryunov Yu. V. Physical and chemical bases of wetting and spreading. M.: Chemistry, 1976
- A. Simon. Fluid adhesion and wetting. - M .: Chemistry, 1974.
- Volkov V. Π. Surface-active substances. Synthesis and properties. -M.1989
- Abramzon A. A. Surface-active substances. Properties and application, 2nd ed., L., 1981
- Taubman A. B., Markina Z. N. Physico-chemical basis for the use of surfactants, Tashkent, 1977