Modelling and impact of tensiometer plate geometry and sample volume on biosurfactant surface activity assessment

Biosurfactants are molecules with hydrophilic and hydrophobic moieties with the capacity to reduce the surface tension of water. Given the limited quantity of biosurfactant extracts in laboratories, it is recommended to use equipment that requires minimal sample quantities for detecting the presence of biosurfactants. In this work, commercial glycolipids biosurfactants (rhamnolipids or sophorolipids) were diluted in water and subjected to different analyses to obtain their minimum surface tension (ST) reduction and their critical micellar concentration (CMC). The independent variables of the study were: the geometry of platinum plate (rectangular or cylindrical), the sample volume (2, 4 and 20 mL) and the container material consisting of either glass or polytetrafluoroethylene (PTFE). The variation of ST with biosurfactant concentration was studied based on the isotherm model proposed by Li & Lu. It was observed that the profile of ST values did not vary so much using the different independent variables described, observing that platinum rectangular plate can be used for volumes of 4 mL biosurfactants instead of cylindrical plate usually recommended for volumes lower than 20 mL, the container material was also not significant based on the Pearson and Spearman statistical treatment. Moreover, well-fitting regression model results were obtained for a non-commercial biosurfactant extract obtained from a residual stream of the dairy industry, predicting values close to the observed data.

A comprehensive review on sustainable surfactants from CNSL: chemistry, key applications and research perspectives

Surfactants, a group of amphiphilic molecules (i.e. with hydrophobic(water insoluble) as well as hydrophilic(water soluble) properties) can modulate interfacial tension. Currently, the majority of surfactants depend on petrochemical feedstocks (such as oil and gas). However, deployment of these petrochemical surfactants produces high toxicity and also has poor biodegradability which can cause more environmental issues. To address these concerns, the current research is moving toward natural resources to produce sustainable surfactants. Among the available natural resources, Cashew Nut Shell Liquid (CNSL) is the preferred choice for industrial scenarios to meet their goals of sustainability. CNSL is an oil extracted from non-edible cashew nut shells, which doesn't affect the food supply chain. The unique structural properties and diverse range of use cases of CNSL are key to developing eco-friendly surfactants that replace petro-based surfactants. Against this backdrop, this article discusses various state-of-the-art developments in key cardanol-based surfactants such as anionic, cationic, non-ionic, and zwitterionic. In addition to this, the efficiency and characteristics of these surfactants are also analyzed and compared with those of the synthetic surfactants (petro-based). Furthermore, the present paper also focuses on various market aspects and different applications in various industries. Finally, this article describes various future research perspectives including Artificial Intelligence technology which, of late, is having a huge impact on society.

Temperature-Driven Structural Evolution during Preparation of MCM-41 Mesoporous Silica

This study explores the influence of micelles on the evolution of MCM-41's pore structure via 24 h hydrothermal treatments in a range of temperatures from 100 °C to 200 °C. MCM-41 was characterized using BET, SAXD, FTIR, TEM, and TG-DSC. The findings demonstrate that with temperature elevation from 100 °C to 160 °C, the micelles undergo expansion, leading to an enhanced lattice constant from 4.50 nm to 4.96 nm and an increase in pore diameter from 3.17 nm to 3.45 nm, while maintaining the structural orderliness of the pore channels. Upon cooling, the reversible contraction of micelles and the strategic addition of water glass contribute to a reduction in pore size. However, at a threshold of 180 °C, the SAXD (100) peak's half-peak width surges by approximately 40% relative to that at 160 °C, illustrating a progressive disruption of the hexagonal configuration of MCM-41. Coupled with elevated silica dissolution at higher temperatures in an alkaline solution, a total disintegration of the ordered pore structure at 200 °C results in a drastic reduction in the specific surface area to 307 m2/g. These results are beneficial to developing structural transformation mechanisms of MCM-41 materials and designing mesoporous materials via temperature modulation innovatively.

Experimental Investigation of Cavitation Bulk Nanobubbles Characteristics: Effects of pH and Surface-Active Agents

Nanobubbles (NBs) have a widespread application in antimicrobial activity, wastewater treatment, and ecological restoration due to numerous peculiar characteristics, such as small diameter, long-term stability, and ability to produce hydroxyl radicals. Despite significant applications, only limited comprehensive investigations are available on the role of surfactants and pH in NBs characteristics. Therefore, this study examines the effects of different surfactants (i.e., anionic, cationic, and nonionic) and pH medium on bulk NB formation, diameter, concentration, bubble size distribution (BSD), ζ-potential, and stability. The effect of surfactant at concentrations above and below the critical micelle concentration was investigated. NBs were generated in deionized (DI) water using a piezoelectric transducer. The stability of NBs was assessed by tracking the variation in diameter and concentration over time. In a neutral medium, the diameter of NBs is smaller than in other surfactant or pH mediums. The diameter, concentration, BSD, and stability of NBs are strongly influenced by the ζ-potential rather than the solution medium. BSD curve shifts to a smaller bubble diameter when the magnitude of ζ-potential is high in any solution. In pure water, surfactant, and pH mediums, NBs have existed for a long time. NBs have a shorter life span in environments with a pH ≤ 3. Surfactant adsorption on the surface of NBs increases with increasing surfactant concentration up to a certain limit, beyond which it declines substantially. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to interpret the NBs stability, resulting in a total potential energy barrier that is positive and greater than 45.55 k_BT for 6 ≤ pH ≤ 11, whereas for pH < 6, the potential energy barrier essentially vanishes. Moreover, an effort has also been made to explicate the plausible prospect of ion distribution and its alignment surrounding NBs in cationic and anionic surfactants. This study will extend the in-depth investigation of NBs for industrial applications involving NBs.

CNSL, a Promising Building Blocks for Sustainable Molecular Design of Surfactants: A Critical Review

Surfactants are crystallizing a certain focus for consumer interest, and their market is still expected to grow by 4 to 5% each year. Most of the time these surfactants are of petroleum origin and are not often biodegradable. Cashew Nut Shell Liquid (CNSL) is a promising non-edible renewable resource, directly extracted from the shell of the cashew nut. The interesting structure of CNSL and its components (cardanol, anacardic acid and cardol) lead to the synthesis of biobased surfactants. Indeed, non-ionic, anionic, cationic and zwitterionic surfactants based on CNSL have been reported in the literature. Even now, CNSL is absent or barely mentioned in specialized review or chapters talking about synthetic biobased surfactants. Thus, this review focuses on CNSL as a building block for the synthesis of surfactants. In the first part, it describes and criticizes the synthesis of molecules and in the second part, it compares the efficiency and the properties (CMC, surface tension, kraft temperature, biodegradability) of the obtained products with each other and with commercial ones.

Tuning the Surface Plasmon Resonance of Gold Dumbbell Nanorods

Gold has always fascinated humans, occupying an important functional and symbolic role in civilization. In earlier times, gold was predominantly used in jewelry; today, this noble metal's surface properties are taken advantage of in catalysis and plasmonics. In this article, the plasmon resonance of gold dumbbell nanorods is investigated. This unusual morphology was obtained by a seed-mediated growth method. The concentration of chemical precursors such as cetyltrimethylammonium bromide and silver nitrate plays a significant role in controlling the shape of the nanorods. Indeed, the aspect ratio of dumbbell nanostructures was varied from 2.6 to 4. UV-visible absorption spectra revealed a shift of the longitudinal surface plasmon resonance peak from 669 to 789 nm. Having the plasmon resonance in the near infrared region helps to use those nanostructures as photothermal agents.