Fizikalno-kemijske raziskave mešanic neionskih in ionskih surfaktantov

Štenkler, Jana (author), Šarac, Bojan (mentor)

Površinska kemija se osredotoča na proučevanje fizikalno-kemijskih procesov, ki potekajo na mejah med različnimi fazami, kar predstavlja pomembno raziskovalno področje v sodobni farmacevtski industriji. Površinsko aktivne snovi (PAS), tudi surfaktanti, so snovi, ki znižujejo medfazno napetost oz. površinsko napetost v primeru fazne meje tekočina/zrak. Merjenje površinske napetosti ima pomembno vlogo pri razumevanju obnašanja snovi na površinah, pri čemer kombinacija različnih PAS predstavlja velik izziv pri interpretaciji rezultatov merjenj. V diplomskem delu smo se posvetili meritvam površinske napetosti in kalorimetričnim meritvam vodnih raztopin čistega natrijevega dodecilsulfata (SDS) ter raztopin površinske napetosti SDS z dodatkom površinsko aktivne snovi 1-dodekanola (DOH). Na ta način smo želeli preveriti, kako DOH vpliva na površinsko napetost oz. če se v krivulji pojavi minimum, kar v literaturi pogosto povezujejo s pojavom DOH v vzorcih SDS. V teoretičnem delu smo naprej definirali pojem površinske napetosti ter pojasnili njen pomen in vpliv površinsko aktivnih snovi na micelizacijo in CMC. Za eksperimentalni del smo uporabili tenziometrično metodo po du Noüyju, ki temelji na uporabi kovinskega obroča za merjenje sile, potrebne za odtrganje obroča od površine tekočine. Gre za pogosto uporabljeno in zanesljivo metodo, ki omogoča natančno določanje površinske napetosti. Prav tako smo definirali osnovne termodinamske količine ter njihovo povezavo s kalorimetrijo oz. izotermno titracijsko kalorimetrijo (ITC). V eksperimentalnem delu diplomske naloge smo naprej izmerili površinsko napetost raztopin natrijevega dodecilsulfata (SDS), nato pa nadaljevali z meritvami raztopin SDS z dodatkom DOH. Opazili smo, da se ob dodatku DOH v krivuljah površinske napetosti pojavi izrazit minimum, ki se s koncentracijo DOH znižuje. Prav tako smo opazili, da se v okolici kritične micelne koncentracije (CMC) surfaktanta SDS pojavi prelom pri merjenju gostote in ITC krivuljah. Ugotovili smo, da prisotnost dolgoverižnega alkohola DOH vpliva na organizacijo molekul SDS v raztopini in posledično tudi na površinsko napetost in energijske spremembe v sistemu. Zaradi večje površinske aktivnosti DOH ta na površini bolj zniža površinsko napetost pred CMC kot SDS, kar povzroči minimum v površinski napetosti, pod CMC pa se del molekule DOH vgradijo v micele, kar povšinsko napetosti potem zviša. S pomočjo ITC smo ugotovili, da se pred CMC tvorijo manjši agregati oz. se micele tvorijo bolj postopno kot pri čistem SDS.

• Language: Slovenian
• Keywords: površinska napetost, tenziometrija, natrijev dodecilsulfat, 1-dodekanol, kalorimetrija
• Work type: Bachelor thesis/paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Year: 2025
• PID: 20.500.12556/RUL-171859
• COBISS.SI-ID: 253396995
• Publication date in RUL: 03.09.2025

Secondary language

• Language: English
• Title: Physico-chemical research on mixtures of nonionic and ionic surfactants

Abstract

Surface chemistry focuses on the study of the physicochemical processes that take place at interfacial boundaries and is one of the most important research areas in the modern pharmaceutical industry. Surface tension plays a key role in understanding the behaviour of substances at these interfaces. Due to the increasing interest in the study of solutions in pharmaceutics, the thesis focused on the measurement of surface tension and calorimetric properties of sodium dodecyl sulfate(SDS) solutions at different concentrations, both without and with the addition of the surfactant 1-dodecanol. In the theoretical part, the concept of surface tension was further defined and its meaning and the influence of surfactants on its value were explained. For the experimental part, the du Noüy tensiometric method was used, which is based on the use of a metal ring to measure the force required to detach the ring from the liquid surface. This is a widely used and reliable method which, if performed correctly, allows accurate determination of the surface tension. In the experimental part of the thesis, we first measured the surface tension of sodium dodecyl sulphate (SDS) solutions and then proceeded to measure SDS solutions with 1-dodecanol added. The results of the measurements of the various parameters are shown graphically and accompanied by the corresponding comments. The surface tension values of the pure water measured in the framework of the study are comparable with literature data, confirming the reliability of the methods used. In the conclusion of the thesis, the results obtained are summarised, analysed and evaluated. In addition to surface tension measurements, isothermal titration calorimetry (ITC) was performed to monitor the thermal changes when SDS molecules aggregate into micellar structures. The purpose of these measurements was to determine thermodynamic parameters of micellar formation, such as the enthalpy change (ΔH), and thus to complement the understanding of the effect of 1-dodecanol on SDS in aqueous solution.

• Keywords: surface tension, tensiometric measurements, sodium dodecyl sulfate, 1-dodecanol, calorimetry