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Phase Studies of Complex Polyelectrolyte Mixtures

Axenstrand, Magdalena LU (2019) KLGM15 20182
Food Technology and Nutrition (M.Sc.)
Abstract
Complex coacervation is a type of liquid-liquid phase separation, that occurs when oppositely charged macroions are mixed in aqueous solution under certain conditions. It has been proven to have applications within many different industries including the food and pharmaceutical industries. For example, protein/polysaccharide coacervates have been used for their emulsifying and foaming properties. Additionally, complex coacervate can be utilized for encapsulation of sensitive compounds such as flavors. In pharmaceutics, this phenomenon has also successfully been used to encapsulate therapeutic agents such as proteins and lipophilic substances, in an attempt to improve their efficiency and delivery. Other application areas include production... (More)
Complex coacervation is a type of liquid-liquid phase separation, that occurs when oppositely charged macroions are mixed in aqueous solution under certain conditions. It has been proven to have applications within many different industries including the food and pharmaceutical industries. For example, protein/polysaccharide coacervates have been used for their emulsifying and foaming properties. Additionally, complex coacervate can be utilized for encapsulation of sensitive compounds such as flavors. In pharmaceutics, this phenomenon has also successfully been used to encapsulate therapeutic agents such as proteins and lipophilic substances, in an attempt to improve their efficiency and delivery. Other application areas include production of carbonless copy paper and fragrance samples.
Despite the interest in complex coacervation within many different fields, the phenomenon and its underlying driving forces are still poorly understood. The most common theory is that the process is initially driven by electrostatic attractions between opposite charges on the macroions, followed by an entropic gain from release of counterions and rearrangement of water molecules.
The purpose of this study was to better understand the concept of complex coacervation and how it is affected by different parameters. A model system comprising polyacrylic acid (pAA) and ε-poly-L-lysine was used to investigate the impact of salt concentration, pH and degree of polymerization on coacervate formation and composition. Water content was analyzed by freeze drying, a nitrogen and protein analyzer was used to measure the EPL content and salt ion levels were measured with potentiometry. Since pAA could not be analyzed, a mass balance was required to determine the composition of the two phases created upon phase separation.
It was found that all three parameters influenced phase composition. Increasing the salt concentration led to higher water content; presumably due to a loosening of the polymer network. It also resulted in lower concentration of both polymers in the coacervate. However, interestingly, the molar ratio between the polymers remained relatively constant over all salt concentrations. A similar decrease in polymer concentration was observed as the limits of the pH window for coacervation were approached. Furthermore, higher degree of polymerization generated more viscous coacervates with lower water content and resulted in a higher critical salt concentration. Unfortunately, the reason for many of the observations were difficult to explain, which is why further research is necessary. It would be of particular interest to investigate how these parameters influence the structure of the coacervate. Additionally, more research on the thermodynamics of complex coacervation is crucial for increasing the understanding of this complex phenomenon. (Less)
Popular Abstract (Swedish)
Polymerer är långa molekyler bestående av identiska repeterande enheter som antingen produceras på konstgjord väg eller naturligt av exempelvis bakterier. Plast, socker och cellulosa är exempel på polymerer som man kommer i kontakt med i sin vardag.
Fortsättningsvis, kan polymerer bära positiva eller negativa laddningar och kallas då istället för polyelektrolyter. Om sådana molekyler av motsatt laddning blandas i en lösning under rätt förhållande, kan de klumpas ihop och bilda olösliga komplex. Denna olöslighet resulterar i att två separata faser bildas, där den undre fasen är trögflytande och väldig rik på polyelektrolyter och den övre är väldigt fattig på polymerer, se figuren nedan. Vidare, har tidigare studier visat att denna typen... (More)
Polymerer är långa molekyler bestående av identiska repeterande enheter som antingen produceras på konstgjord väg eller naturligt av exempelvis bakterier. Plast, socker och cellulosa är exempel på polymerer som man kommer i kontakt med i sin vardag.
Fortsättningsvis, kan polymerer bära positiva eller negativa laddningar och kallas då istället för polyelektrolyter. Om sådana molekyler av motsatt laddning blandas i en lösning under rätt förhållande, kan de klumpas ihop och bilda olösliga komplex. Denna olöslighet resulterar i att två separata faser bildas, där den undre fasen är trögflytande och väldig rik på polyelektrolyter och den övre är väldigt fattig på polymerer, se figuren nedan. Vidare, har tidigare studier visat att denna typen av fasseparation är starkt beroende på ett flertal parametrar, exempelvis, pH, koncentrationen av polyelektrolyter i lösningen, tillsats av salt och längd på polelektrolyterna.
Intressant nog, har fasseparationen i fråga applikationer inom ett flertal industrier, bland annat livsmedels- och läkemedelsindustrin där den kan användas till att inkapsla aktiva substanser eller andra känsliga ämnen i den trögflytande undre fasen. Trots dess många applikationer är det väldigt lite man vet om fasseparationen vilket försvårar optimering av dess användning.
Således var syftet med arbetet i fråga, att öka förståelsen för detta fenomen och hur det påverkas av olika parametrar. För att uppnå målet, studerades ett modellsystem bestående av två polyelektrolyter av motsatt laddning. Tre olika parametrar justerades; saltkoncentration, polyelektrolytlängd och pH, och därefter undersöktes den resulterande effekten på kompositionen av de två faserna som bildas.
Resultaten visade att de tre parametrarna som justerades, hade en signifikant inverkan på kompositionen av de båda faserna som bildas vid fasseparationen. Vattenhalten i den tjocka underfasen steg när saltkoncentrationen ökades, medan halten av polyelektrolyterna minskade. Däremot, förblev förhållandet mellan polyelektrolyterna relativt konstant. Användning av längre polyelektrolyter resulterade däremot i längre vattenhalt i underfasen som därmed blev ännu mer trögflytande. Trots att många intressanta trender observerades, kunde inte alla förklaras. Fortsatta studier inom detta forskningsområde krävs därför för att öka förståelsen för vad som ligger bakom de iakttagna effekterna av justering en av de utvalda parametrarna. (Less)
Please use this url to cite or link to this publication:
author
Axenstrand, Magdalena LU
supervisor
organization
course
KLGM15 20182
year
type
H2 - Master's Degree (Two Years)
subject
keywords
coacervate, coacervation, phase separation, polyelectrolytes, pharmaceutical technology, läkemedelsteknologi
language
English
id
8994778
date added to LUP
2019-10-22 10:45:49
date last changed
2019-10-22 10:45:49
@misc{8994778,
  abstract     = {Complex coacervation is a type of liquid-liquid phase separation, that occurs when oppositely charged macroions are mixed in aqueous solution under certain conditions. It has been proven to have applications within many different industries including the food and pharmaceutical industries. For example, protein/polysaccharide coacervates have been used for their emulsifying and foaming properties. Additionally, complex coacervate can be utilized for encapsulation of sensitive compounds such as flavors. In pharmaceutics, this phenomenon has also successfully been used to encapsulate therapeutic agents such as proteins and lipophilic substances, in an attempt to improve their efficiency and delivery. Other application areas include production of carbonless copy paper and fragrance samples. 
Despite the interest in complex coacervation within many different fields, the phenomenon and its underlying driving forces are still poorly understood. The most common theory is that the process is initially driven by electrostatic attractions between opposite charges on the macroions, followed by an entropic gain from release of counterions and rearrangement of water molecules. 
The purpose of this study was to better understand the concept of complex coacervation and how it is affected by different parameters. A model system comprising polyacrylic acid (pAA) and ε-poly-L-lysine was used to investigate the impact of salt concentration, pH and degree of polymerization on coacervate formation and composition. Water content was analyzed by freeze drying, a nitrogen and protein analyzer was used to measure the EPL content and salt ion levels were measured with potentiometry. Since pAA could not be analyzed, a mass balance was required to determine the composition of the two phases created upon phase separation. 
It was found that all three parameters influenced phase composition. Increasing the salt concentration led to higher water content; presumably due to a loosening of the polymer network. It also resulted in lower concentration of both polymers in the coacervate. However, interestingly, the molar ratio between the polymers remained relatively constant over all salt concentrations. A similar decrease in polymer concentration was observed as the limits of the pH window for coacervation were approached. Furthermore, higher degree of polymerization generated more viscous coacervates with lower water content and resulted in a higher critical salt concentration. Unfortunately, the reason for many of the observations were difficult to explain, which is why further research is necessary. It would be of particular interest to investigate how these parameters influence the structure of the coacervate. Additionally, more research on the thermodynamics of complex coacervation is crucial for increasing the understanding of this complex phenomenon.},
  author       = {Axenstrand, Magdalena},
  keyword      = {coacervate,coacervation,phase separation,polyelectrolytes,pharmaceutical technology,läkemedelsteknologi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Phase Studies of Complex Polyelectrolyte Mixtures},
  year         = {2019},
}