| 1. |
- Hellström, Anna-Karin, 1974, et al.
(författare)
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Carbamate Chemistry at Interfaces: Practical Considerations and Challenges of Studying Amine Surfactants
- 2019
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Ingår i: Journal of Surfactants and Detergents. - : Wiley. - 1558-9293 .- 1097-3958. ; 22:5, s. 1109-1117
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- It is well known that CO2 reacts with primary and secondary amines in aqueous solutions and forms carbamates. This reaction can have consequences when studying the self-assembly of amines. In this article, we discuss the practical challenges when working with an alkyl Y-shaped amine (Y12-amine) and demonstrate how the formation of carbamate species influences the physicochemistry of the amine-based surfactant. A drift in dynamic surface tension was observed for Y12-amine at pH above pKa due to the reaction with the naturally occurring CO2 from the atmosphere. The drift in dynamic surface tension was more pronounced at pH above pKa, than at and below pKa. Furthermore, the drift in dynamic surface tension of Y12-amine at pH 12 also affected the surfactant's critical micelle concentration (CMC). CMC of Y12-amine determined by the pendant drop at the air/water interface was almost five times higher than at the N-2/water interface. The latter result was in agreement with the one determined by monitoring the change in chemical shift of H-1 NMR in a N-2 atmosphere. Moreover, it was also shown that the adsorption of the amine at different interfaces influences carbamate formation.
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| 2. |
- Hellström, Anna-Karin, 1974, et al.
(författare)
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Formation, physicochemical and interfacial study of carbamate surfactants
- 2018
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 511, s. 84-91
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide is commonly used as pH regulator in switchable surfactant systems and in the formation of alkyl ammonium-alkyl carbamate ion-pair. Its use to form a meta-stable anionic surfactant has been less explored and can impart a cleavable character to the amphiphile. The reaction between CO2 and an alkylamine, N,N-di(propylamino)dodecylamine (Y12-amine), under alkaline pH conditions, produced a stable anionic carbamate-based surfactant (Y12-carbamate). By heating and exposure to N-2, anionic Y12-carbamate could slowly be reverted into Y12-amine. The surface activity of Y12-amine and Y12-carbamate was investigated by surface tension measurements. To study the behavior of Y12-amine at the gas-water interface during CO2 exposure, we used the pendant drop technique with a sealed chamber where the gas composition could be controlled. The Y12-carbamate had a higher CMC than Y12-amine at pH 12, and was also less surface active. The ion pair Y12-ammonium- Y12-carbamate, obtained at neutral pH, exhibited the lowest CMC and the highest surface activity. The interfacial formation of anionic Y12-carbamate induced an increase in surface tension. When CO2 was exchanged to N-2, the migration from the bulk to the interface of Y12-amine induced a decrease in surface tension. The rate was dependent on the concentration of Y12-amine.
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| 3. |
- Hellström, Anna-Karin, 1974, et al.
(författare)
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Reversible flocculation of nanoparticles by a carbamate surfactant
- 2019
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 536, s. 722-727
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Tidskriftsartikel (refereegranskat)abstract
- Fatty alkyldiamine readily reacts with CO2 in aqueous solution at pH 12 to reversibly form surface active carbamate species. The carbamate can be reverted to the amine by exposure to N2 and heat. In this work, a carbamate-based surfactant (Y12-carbamate) has been used to disperse and stabilize hydrophobic nanoparticles. This state could be regarded as the “on” state of a series of cycle. The nanoparticles were then flocculated when the carbamate groups were cleaved by exposure to N2 and heating, corresponding to the “off” state. In a subsequent cycle, the nanoparticles were re-dispersed by exposure to CO2, while the pH remained at 12. This cycle of re-dispersion and flocculation could be repeated two times without impairing the particle size. However, further cycles increased the particle size, indicating that all particles could not be completely re-dispersed. In addition, we also investigated the effect of pH on the colloidal stability with sodium Y12-carbamate, by measuring particle size and electrophoretic mobility. The results showed that pH strongly influenced the stability of the nanoparticles. Sodium Y12-carbamate stabilized the particles with a negative electrophoretic mobility at pH well above pKa whereas at pH close to pKa of Y12-amine (pKa = 9.0), the particles quickly flocculated, as a result of an ion-pair formation between Y12-ammonium and Y12-carbamate.
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| 4. |
- Hellström, Anna-Karin, 1974
(författare)
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Use of Switchable Carbamate Surfactants for Design of Reversible Colouring of Cotton
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Circularity of materials is a global need. However, recycling of cotton often requires many steps involving chemical or mechanical treatments. According to the waste hierarchy, reuse is a more environmentally benign approach than recycling, giving extended lifecycles with only limited processing of materials. To facilitate recycling and reuse of cotton, in particular reuse, an important step to meet is the possibility of re-colouring of cotton fabrics. In this thesis, a new colouring method, with an embedded function for removal of the colour, has been designed. The colouring method is based on pigment nanoparticles, stabilized by a switchable surfactant that enables control of the pigment adsorption at the surface of the fibres through electrostatic interactions. The pigment desorbs from the surface upon exposure to an external trigger, resulting in de-colouring. The switchable surfactant is based on a Y-shaped diamine (denoted Y12-amine), which, by reaction with CO2 at a pH above the both pKa values of the Y12-ammonium (protonated Y12-amine), forms an anionic Y12-carbamate. The anionic Y12-carbamate reverts to the Y12-amine upon heating, imparted by the cleavable and switchable character of the surfactant. The work presented in this thesis is divided into three parts. In the first part, the physicochemical properties of the Y12-amine and its carbamates are determined. The formation and stability of the anionic Y12-carbamate were shown to be dependent on pH and temperature. The anionic Y12-carbamate exhibited a higher CMC and less surface activity than the Y12-amine at pH 12. Furthermore, the ion-pair Y12-ammonium-Y12-carbamate, which was formed at neutral pH, exhibited the lowest CMC and the highest surface activity. In the second part of this work, the anionic sodium Y12-carbamate surfactant was used to disperse and stabilize nanopigments. The effect of pH on the colloidal stability with the anionic Y12carbamate as surfactant was investigated by measuring particle size and electrophoretic mobility. It was found that the pH value strongly affected the stability of the nanopigments. Moreover, by exposing the pigment dispersion to N2/heat or CO2 at pH 12, flocculation and re-dispersion cycles could be achieved without significantly affecting the particle size. Finally, a hydrophobic pigment stabilized by the anionic Y12-carbamate was used to colour cationised cotton through adsorption. Desorption was triggered by acid hydrolysis of the carbamate groups, generating Y12-ammonium. The mechanical properties of the de-coloured cationised cotton were determined and the maximum tensile stress was found to increase by ~15% and the strain decrease by ~16% compared to cationised cotton. The de-coloured cationised cotton could also be re-coloured. The reversible colouring method on cotton, which is presented in this thesis, demonstrates that pigment-dyeing triggered by the Y12-carbamate surfactant enables reversible colouring of cotton fabric, which can benefit the reuse of cotton
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