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Reološko obnašanje površinsko aktivnih snovi
Lokar, Pavlina (Author), Šarac, Bojan (Mentor) More about this mentor... This link opens in a new window

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Abstract
Površinsko aktivne snovi (PAS) so snovi sestavljene iz hidrofilne glave in hidrofobnega repa, imajo amfifilno naravo in se orientirajo na površini med dvema različnima snovema (fazna meja). S tem zmanjšajo površinsko napetost fazne meje, ki pa je lahko različna, npr. meja trdo – tekoče, tekoče – tekoče in tekoče – plin. PAS delimo glede na naboj polarne glave, in sicer na anionske, kationske, neionske ter obojestranskoionske. PAS lahko tvorijo tudi micele; to so skupki več unimerov PAS. Micele se začnejo tvoriti, ko je dosežena kritična micelna koncentracija (CMC). PAS se v raztopinah združujejo v sferične, cilindrične, reverzne micele ter vezikle. Reologija je veda o deformaciji materiala in njegovem tokovnem obnašanju ter se ukvarja z odzivnostjo snovi na deformacijo. Poznamo elastično in plastično deformacijo. Newtonske tekočine (voda, olje, med, polimerne raztopine,…) so idealne tekočine, neodvisne od jakosti, smeri in časa delovanja sile, ki deluje na sistem. Pri teh tekočinah je strižna napetost premo sorazmerna strižni hitrosti. Viskoznost je pri ne-newtonskih tekočinah odvisna od strižne napetosti. Viskoelastičnost lahko opišemo s porazdelitvijo energije med delovanjem obremenitve, del energije se zaradi trenja viskoznosti pretvori v toploto, del energije pa je namenjeno temu, da vrne snov nazaj v prvotno obliko. Reološko obnašanje viskoelastičnih raztopin lahko ponazorimo z mehanskim Maxwellovim modelom, ki predvideva, da so po linearnem odnosu med napetostjo in hitrostjo elastične lastnosti podane po Hookovem zakonu in viskozne lastnosti po Newtonovem zakonu. S pomočjo tega modela lahko opišemo ne-newtonske lastnosti vodnih raztopin površinsko aktivnih snovi, ki vsebujejo določene aditive. Tak primer je na primer raztopina cetilpiridinijevega klorida z natrijevim salicilatom ali mešanica natrijevega lavrileter sulfata in kokamidopropil betaina z dodano oktanojsko kislino.

Language:Slovenian
Keywords:Površinsko aktivne snovi, reologija, viskoznost, reometrija
Work type:Bachelor thesis/paper (mb11)
Tipology:2.11 - Undergraduate Thesis
Organization:FKKT - Faculty of Chemistry and Chemical Technology
Year:2020
COBISS.SI-ID:15906563 This link opens in a new window
Views:534
Downloads:207
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Secondary language

Language:English
Title:Rheological behaviour of surface active agent solution
Abstract:
Surface active agents or surfactants are substances that bind to the surface substances or between the contacts of two substances and decrease surface tension. Surfactants are adsorbed on different types of contact between substances (solid - liquid state, liquid - liquid state, liquid - gas state). They are amphiphilic, meaning they contain both hydrophilic heads and hydrophobic tails. Surfactants are divided by the charge of the polar head in anionic, cationic, nonionic and zwitterionic. Surfactants can also form micelles, which are aggregates of several surfactant unimers. Micelles begin to form when critical micelle concentration (CMC) is reached. Surfactants can be combined into spherical micelles, worm-like micelles, inverted micelles, lamellar phase, continuous structure and vesicles. Rheology is the study of the deformation of the material and deals with the response of a substance to deformation. We know elastic and plastic deformation. Newtonian fluids (water, oil, honey, polymer solutions…) are ideal liquids, independent of the strength, direction and time of the force acting on the system. For these liquids, the shear stress is proportional to the shear rate. Non-newtonian fluids are real fluids. Viscosity depends on the shear stress. Viscoelasticity can be described by the distribution of energy during loading. Part of the energy is converted into heat due to the viscosity friction; the other part of the energy is used to return the substance back to its original form. The rheological behaviour of viscoelastic solutions is manifested in time-dependent functions, such as transient viscosity or relaxation model. The rheological properties of viscoelastic substances are shown by a mechanical model, which assumes that, by the linear relationship between stress and velocity, the elastic properties are given by Hooke's law and viscous properties by Newton's law. Such a model is Maxwell's substance, which describes the viscosity of surfactant solutions. Non-newtonian behaviour is reflected in solutions where viscosity decreases and the shear increases. For example, a solution of cetylpyridinium chloride with sodium salicylate or a mixture of sodium lauryl ether sulphate and cocamidopropyl betaine with added octanoic acid.

Keywords:Surface active agents, rheology, viscosity, reometry

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