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<p>Interactions between dyes and surfactants play a crucial role in numerous physicochemical and industrial processes. Crystal violet (CV), a widely used industrial dye, was selected to investigate its interaction with the nonionic surfactant Triton X-100 (TX-100). The clouding behavior of the TX-100&#xa0;+&#xa0;CV system was examined by the cloud point (CP) method in presence of organic additives (methanol (MeOH), ethanol (EtOH), 1-propanol (1-PrOH), 2-propanol (2-PrOH), 1-butanol (1-BuOH) and 2-butanol (2-BuOH)) and hydrotrope (urea). The concentrations of TX-100 (77.27 mmol kg<sup>-1</sup>) and CV (0.01 mmol kg<sup>-1</sup>) were kept constant throughout the study. Short-chain alcohols (MeOH, EtOH, 1-PrOH, and 2-PrOH) and urea increased the CP values, whereas long-chain alcohols (1-BuOH and 2-BuOH) decreased the CP. Thus, lower alcohols and urea acted as CP enhancers, while higher alcohols served as CP suppressors. With the further increment of the content of organic additives, the following CP values were noted down as series: CP (H<sub>2</sub>O + EtOH) &gt; CP (H<sub>2</sub>O + Urea) &gt; CP (H<sub>2</sub>O + 2-PrOH) &gt; CP (H<sub>2</sub>O + MeOH) &gt; CP (H<sub>2</sub>O + 1-PrOH) &gt; CP (H<sub>2</sub>O + 2-BuOH) &gt; CP (H<sub>2</sub>O + 1-BuOH). The observed positive standard free-energy changes (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\:{\varDelta\:G}_{c}^{o}\)</EquationSource> </InlineEquation>) values of TX-100 + CV mixture indicate that the clouding is nonspontaneous under the studied conditions but becomes more favorable (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\:{\varDelta\:G}_{c}^{o}\)</EquationSource> </InlineEquation> values decrease) with increasing additive concentration. The observed changes in enthalpy (<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\:{\varDelta\:H}_{c}^{o})\)</EquationSource> </InlineEquation> and entropy (<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\:{\varDelta\:S}_{c}^{o})\)</EquationSource> </InlineEquation> suggest that hydrophobic and ion–dipole interactions are the main forces governing the clouding of TX&#xa0;+&#xa0;100–CV dye system. The findings offer quantitative insight into how small organic molecules and urea modulate the phase separation of nonionic surfactants, providing useful guidance for optimizing formulations in dyeing and separation processes. </p> Graphical Abstract <p></p>

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Effect of monohydroxy alcohol and urea on phase separation and thermodynamics of triton X-100 in the presence of crystal Violet dye

  • 期刊论文

  • 发表日期：

    2025年11月15日

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  • Tania Ferdous,
  • Mohammad Anwar Parvez,
  • Md. Rafikul Islam,
  • Bulbul Ahmed,
  • Malik Abdul Rub,
  • Khalid A. Alzahrani,
  • Md. Anamul Hoque,
  • Shariff E. Kabir

摘要

Interactions between dyes and surfactants play a crucial role in numerous physicochemical and industrial processes. Crystal violet (CV), a widely used industrial dye, was selected to investigate its interaction with the nonionic surfactant Triton X-100 (TX-100). The clouding behavior of the TX-100 + CV system was examined by the cloud point (CP) method in presence of organic additives (methanol (MeOH), ethanol (EtOH), 1-propanol (1-PrOH), 2-propanol (2-PrOH), 1-butanol (1-BuOH) and 2-butanol (2-BuOH)) and hydrotrope (urea). The concentrations of TX-100 (77.27 mmol kg-1) and CV (0.01 mmol kg-1) were kept constant throughout the study. Short-chain alcohols (MeOH, EtOH, 1-PrOH, and 2-PrOH) and urea increased the CP values, whereas long-chain alcohols (1-BuOH and 2-BuOH) decreased the CP. Thus, lower alcohols and urea acted as CP enhancers, while higher alcohols served as CP suppressors. With the further increment of the content of organic additives, the following CP values were noted down as series: CP (H2O + EtOH) > CP (H2O + Urea) > CP (H2O + 2-PrOH) > CP (H2O + MeOH) > CP (H2O + 1-PrOH) > CP (H2O + 2-BuOH) > CP (H2O + 1-BuOH). The observed positive standard free-energy changes ( \(\:{\varDelta\:G}_{c}^{o}\) ) values of TX-100 + CV mixture indicate that the clouding is nonspontaneous under the studied conditions but becomes more favorable ( \(\:{\varDelta\:G}_{c}^{o}\) values decrease) with increasing additive concentration. The observed changes in enthalpy ( \(\:{\varDelta\:H}_{c}^{o})\) and entropy ( \(\:{\varDelta\:S}_{c}^{o})\) suggest that hydrophobic and ion–dipole interactions are the main forces governing the clouding of TX + 100–CV dye system. The findings offer quantitative insight into how small organic molecules and urea modulate the phase separation of nonionic surfactants, providing useful guidance for optimizing formulations in dyeing and separation processes.

Graphical Abstract