Emulsion is a colloid where the two non-miscible liquid stages are present ; it is a suspension where one of the liquid phases is dispersed in the other. Here the liquid which is dispersed as all right atoms in called as spread stage and the liquid medium which holds the spread stage is known as uninterrupted stage.
There are ways to scatter a liquid in another liquid stage which could besides be achieved by mechanical agitation which breaks a liquid stage into all right droplets which gets dispersed into the uninterrupted stage ( e.g. oil in H2O ) . But the stableness of such emulsion would be really low as the spread stage coalesces together and divide out into non-miscible liquid stage with a distinguishable boundary.
The stableness of an emulsion depends on assorted factors and the constituents which help in stabilising are known as emulsifiers. The amphiphilic substances such as wetting agents and polymers are by and large used to stabilise the emulsion. Goodwin, Pashly-b
1.2 Emulsions in pattern: –
( Foams and emulsions as soft affair in general particularly in nutrient systems, Aim of this survey )
Some of the emulsions in pattern are nutrient systems such as mayonnaise, milk, salad dressings and ice pick, etc. The other systems are picks in cosmetics and unctions in pharmaceuticals, etc. In all the instances stable emulsions which contain non-miscible liquid stages are necessary which drive us to analyze more about the factors act uponing their stableness.
The nutrient emulsions are frequently really complicated by their composing due to presence assorted substances which makes it difficult to analyze and understand the influence of all those factors. One attack to such systems would be to analyze good defined simpler systems and use this cognition to turn to the jobs in the complex systems.
So the purpose of this survey is to understand the implicit in rules of interfacial scientific discipline and to analyze the behavior of protein/surfactant mixtures adsorbed at the water/oil interface. E.dickinsen ( Adv in nutrient colloids ) -b
1.3. Role of proteins and wetting agents in emulsions: – ( in general description of surfactant categories, few words of protein folding and different types of proteins, beginning of amphiphilicity, interactions ) ; besides a few more words about the used wetting agent.
The wetting agent is a molecule which is amphiphilic in nature ( i.e. which has both hydrophilic and hydrophobic portion ) and adsorbs at interface of two non-miscible stages and therefore cut downing the interfacial tenseness.
The interfacial tenseness or surface tenseness is net imbalanced cohesive forces of bed of molecules at the surface of the majority liquid stage. It is measured in dynes.cm-1 or N/m. The interfacial energy is indistinguishable parametric quantity but it is measured in J/m2. For illustration the interfacial tenseness of water/oil is 30 to 40 mN/m and interfacial energy is 30 to 40 mJ/m2.
So at water/oil interface the hydrocarbon in oil stage East in such a manner to avoid the H2O molecules as they can non interact strongly with each other. This is why they are non mixable but when disrupted automatically the oil signifiers droplets which coalesce rapidly and phase out. A stable emulsion could be formed by take downing the surface energy which is possible by add-on of polymers or proteins and wetting agents. There are besides other factors which stabilize the emulsions such as electrostatic repulsive force of ionic wetting agents wetting agents, increased interfacial viscousness due to proteins or polymers which give mechanical strength to the droplets and prevent liquid drainage between the movies. ( pashley ) -b
Add here in more item the function of the two compounds:
Harmonizing to a good accepted hypothesis the little surfactant molecules in a assorted protein/surfactant system adsorb more speedy, cut down the interfacial tenseness expeditiously and lend in this manner to the optimal formation of an emulsion. The proteins are non really efficient in cut downing the interfacial tenseness, but they provide the several behaviour to the emulsion movies, and cut down drainage and stabilise the movies against coalescency.
Following the chief thoughts of emulsion stabilisation, the protein provides a steric stabilisation of liquid movies but gives besides elastic and syrupy belongingss to the movie, which can be tuned via the composing of the protein/surfactant mixture.
Therefore, probes of the interfacial behaviour, including the dilational and shear rheology, of such assorted beds is in the focal point of involvement soon.
There are many applications of protein/surfactant mixtures such as in nutrient industries for stabilising emulsions and froths ( eric.dickinson ) and many other biological systems.
1.4. Interfacial surveies of adsorbed beds
( in general dynamic interfacial surveies – interfacial tenseness, interfacial rheology – different sort of distortion, surface assimilation phenomena, construction formation, turn uping -unfolding )
Note in peculiar: The rheological belongingss are really of import for many applications. There are two types of distortion, shear and dilational. While shear alterations the form of the interface by maintaining the size, in dilation the form is kept changeless and the size is changed. Therefore, shear rheology is basically sensitive to construction formation in the interfacial beds.
1.5. Importance of shear rheology: –
The interfacial shear rheology is survey of distortion of adsorbed bed construction with emphasiss applied on it. It gives the step of rigidness and mechanical stableness ( better to compose flow behavior and mechanical belongingss of interfacial beds ) of the adsorbed beds. The rate of formation of construction can besides be studied with this technique.
Note here, that the figure of surveies of the shear rheology of beds between two non-miscible liquids is really little and executable merely since late due to the handiness of the needed experimental tools.
2. MATERIALS AND METHODS
2.1. Model systems under probe: –
Here & amp ; szlig ; -Lactoglobulin with anionic wetting agent SDS was chosen to analyze with hexane and Medium Chain Triglycerides ( MCT ) as oil stage. & A ; szlig ; -Lactoglobulin is a protein nowadays in the bovine milk. It is a ball-shaped protein with molecular weight 18.4 kDa and isoelectric point of 5.3. Sodium dodecyl-sulphate ( SDS ) is an anionic wetting agent of molecular weight 288.38 g/mol.
2.2. Materials used.-
& A ; szlig ; -Lactoglobulin purified with 90 % agarose gel cataphoresis was purchased from Sigma-Aldrich. Sodium dodecyl sulfate ( SDS ) was purchased from Sigma-Aldrich. The solutions were prepared with 10mM Na phosphate buffer, pH 7, prepared by blending appropriate stock solutions of Na2HPO4 and NaH2PO4 with Milli-Q H2O. Hexane was purchased from Aldrich and purified with aluminum oxide. The interfacial tenseness of NaH2PO4/Na2HPO4 buffer was 72.5 and 49 mN/m at the water/air and water/hexane interface, severally. The medium concatenation triglycerides ( MCT ) oil was purchased from Danisco and interfacial tenseness measured against NaH2PO4/Na2HPO4 buffer was 26 mN/m.
All the glassworks used were flushed with H2O and so immersed in concentrated sulfuric acid for 2 hours. Subsequently, they were flushed good with H2O and rinsed with Milli Q H2O and so dried and stored in clean topographic point.
2.3. Instruments used and their on the job rule: –
2.3.1. Profile Analysis Tensiometer ( PAT1 ) : –
The dynamicss of surface assimilation for & A ; szlig ; -Lactoglobulin and SDS mixtures were measured utilizing profile analysis tensiometer PAT1 ( SINTECH/Germany ) . The rule of this method is to find the surface tenseness of liquid from the form of a pendant bead. This form is determined by Gauss-Laplace equation, which gives a relationship between the curvature of semilunar cartilage and the surface tenseness i?§ .
Y ( 1/R1+1R2 ) = delta.P0 + delta.ro.gz
R1 and R2 are the radii of curvature, i?„P0 is the force per unit area difference in mention plane, i?„i?? is the denseness difference, g is the acceleration due to gravitation, and omega is the perpendicular tallness of the bead measured from the mention plane.
The surface tenseness can be obtained from fitted the Gauss-Laplace equation to the coordinates of a bead, utilizing i?§ as the adjustment parametric quantity. The form of the bead is captured by CCD camera and the volume of the bead is kept changeless by active control cringle of the instrument.
The bead profile tensiometry can besides be applied for surveies of the dilational rheology of interfacial beds. For this intent, the bead is generated to harmonic volume oscillations and the ensuing country alterations lead to compactions and enlargements of the adsorbed bed. The relation behaviour of the interfacial bed as response to these disturbances can be obtained by mensurating the interfacial tenseness during the oscillations. The dilational snap and viscousness are obtained eventually via a Fourier analysis of the harmonic interfacial tenseness response.
2.3.2. Forced oscillation interfacial shear rheometer ( MCR301 ) : –
The MCR 301 rheometer equipped with the interfacial cell IRS from Anton Paar ( Germany ) was used to mensurate the shear elastic and loss modulus of & A ; szlig ; -lactoglobulin and SDS mixtures. This instrument performs the oscillations at controlled emphasis or controlled strain conditions and the parametric quantities which determine the construction of adsorbed beds such as shear snap, shear viscousness were calculated. The experimental informations presented below are based on controlled strain conditions where the sum distortion of the interfacial bed is kept changeless at same frequence of oscillation. Thus the dynamicss of construction formation at the interface can be recorded over defined length of clip. This instrument can mensurate really stiff beds but less sensitive to weak beds.
The instrument has high declaration optical detector for place control of shear rate and strain. The EC motor for warp is magnetic non contact thrust motor which is sensitive to little torsions. A biconical disc is fixed to the EC motor thrust and its crisp border is placed at the interface of fluids. The measurement cell is fitted to the thermoregulator for keeping the changeless temperature. ( this is incorrect! The temperature is controlled by a Peltier component – which needs a ain chilling )
[ few more words about the measurement geometry and measurement rules ( amplitude, frequence and clip sweep manners ) ]
2.3.3. Damped oscillation interfacial shear rheometer ( ISR1 ) : –
ISR 1 interfacial shear rheometer from Sinterface works on the rule of muffling of hovering pendulum suspended by a tortuosity wire. The setup consists of a thrust comprising of a stepper motor, transmittal and motor accountant for the warp. The tortuosity wire is fixed to the thrust and a biconical disc is suspended to it which is a mensurating organic structure. The vas keeping the system under probe is surrounded by H2O jacket for temperature control. The biconical disc is immersed in the liquid by puting knife borders precisely at the interface. The angular place of the biconical disc is recorded by a mini optical maser and position-sensitive photosensor. Due to the sensitiveness of the photodiode and, the round gesture of the border can be measured with an truth of f 0.01 Hz and warp angle of 2′.This should be improved! The frequence is given by the tortuosity wire parametric quantity ; the maximum desertion angle due to the placement of PSD – an of import parametric quantity is the declaration of detector which limits the smallest desertion angle. More inside informations mensurating rule, geometry etc.
2.4. Preparation of stock solutions: –
10 milliliter of 1e-4 M & A ; szlig ; -Lactoglobulin stock solution was prepared by fade outing 0.018g of & A ; szlig ; -lactoglobulin crystals in 10 milliliter of NaH2PO4/Na2HPO4 buffer at pH 7 with 1-2 ppm Na azide to forestall microbic debasement of stock solution and stored in icebox.
A new stock solution is prepared one time in every 10-12 yearss.
100 milliliter of 1e-3 M SDS stock solution is prepared by fade outing 0.028g pure SDS in 100ml of NaH2PO4/Na2HPO4 buffer at pH 7 and stored in icebox.
The coveted concentration of & A ; szlig ; -lactoglobulin and SDS mixtures were attained by farther dilution with NaH2PO4/Na2HPO4 buffer solution.
2.5. Mold of surface assimilation beds
2.5.1. Surfactant surface assimilation beds
2.5.2. Protein surface assimilation beds
2.5.3. Assorted protein/surfactant surface assimilation beds
3.1. & A ; szlig ; -lactoglobulin and SDS mixtures adsorbed at water/hexane interface: –
3.1.1. Pendent bead measuring of dynamic interfacial tenseness.
Fig 3.1.1. ( a ) The isotherm comprising of interfacial tenseness values at the water/hexane interface matching to concentration of & A ; szlig ; -lactoglobulin after the equilibrium has been reached.
Fig 3.1.1. ( B ) The isotherm comprising of interfacial tenseness values matching
to concentration of SDS assorted with 1e-6 mol/l & A ; szlig ; -lactoglobulin after the equilibrium has been reached.
Do we hold besides such informations at the water/MCT interface?
3.1.2. Shear rheology consequences: –
Fig 3.1.2. ( a ) Addition in shear viscousness of 3e-7M & A ; szlig ; -lactoglobulin mixed with different concentrations of SDS adsorbed bed at water/hexane interface and measured under controlled strain forced oscillations performed by MCR 301 Anton Paar shear rheometer at 0.2 % distortion and 0.7 Hz frequence at pH 7 and temperature 20o C.
Do we hold any surveies with both rheometers and can compare the consequences?
Fig 3.1.3. ( B ) Tendency of entire addition in the shear viscousness observed in the fig.3.1.2. ( a )
Show besides the job of repeatability and discuss possible grounds.
3.2. & A ; szlig ; -lactoglobulin and SDS mixtures adsorbed at water/MCT interface: –
3.2.1. Pendent bead measuring of dynamic interfacial tenseness.
Fig 3.2.1. ( a ) Adsorption isotherm for 3e-7M & A ; szlig ; -lactoglobulin
Dwelling of dynamic interfacial tenseness at Water/MCT interface
at pH 7 and temperature 20 C.
3.2.2. Shear rheology consequences: –
Fig 3.2.2 ( a ) Addition in shear viscousness of 3e-7M & A ; szlig ; -lactoglobulin mixed with different concentrations of SDS adsorbed bed which is aged for 18 hours at water/MCT interface and measured under controlled strain forced oscillations performed by MCR 301 Anton Paar shear rheometer at 0.2 % distortion and 0.7 Hz frequence at pH 7 and temperature 20o C.
Do we hold any surveies with both rheometers and can compare the consequences?
Fig 3.2.2 ( B ) Addition in shear viscousness of 3e-7M & A ; szlig ; -lactoglobulin mixed with different concentrations of SDS adsorbed bed at water/MCT interface and measured by damped oscillations performed by ISR 1 shear rheometer at an angle 0.75 at pH 7 and temperature 20o C.
Fig 3.2.2 ( degree Celsius ) Increase in shear viscousness of 3e-7M & A ; szlig ; -lactoglobulin with different concentrations of Monolein in oil stage, adsorbed bed at water/MCT interface and measured by damped oscillations performed by ISR 1 shear rheometer at an angle 0.75 at pH 7 and temperature 20o C.
Do we hold any surveies with both rheometers and can compare the consequences?
The surface assimilation dynamicss studied by bead profile analysis gives good information about the adsorbed bed at the interface. The fig 3.1.1. ( a ) Shows that adsorbed bed is saturated with & A ; szlig ; -lactoglobulin molecules at a concentration 2e-7 M or more. There is formation of 2nd bed of & A ; szlig ; -lactoglobulin at a concentration of more than 1e-6 M which is obtained from surface force per unit area informations ( Vincent ) . So to analyze the rheology of adsorbed monolayer the concentration of 3e-7M is chosen.
The fig 3.1.1. ( B ) tells us that wetting agents dominate the interface by replacing the protein, so higher the concentration of surfactant greater the laterality over the protein which is shown in surface tenseness isotherm. It is besides of import to observe that at low concentrations of ionic wetting agent, composites are formed with protein which has about similar surface tenseness value compared to & A ; szlig ; -lactoglobulin without any wetting agent.
The consequence of low concentrations of SDS mixed with & A ; szlig ; -lactoglobulin is seeable in the fig 3.1.2. ( B ) . The tendency in addition of the shear viscousness ab initio and so lessening with increasing surfactant concentration was seen, nevertheless the duplicability of interfacial shear rheology informations is bad so no literature is published on this subject at water/oil interface. Therefore rheological informations obtained can non be analyzed quantitatively but important difference with assorted ratios of protein/surfactant mixtures can be analyzed qualitatively. The higher shear viscousness at lower ratios of & A ; szlig ; -lactoglobulin/SDS mixtures could be due to ionic interaction and flowering of the protein molecule and so binding of more SDS molecules via hydrophobic interaction with more open protein. The interaction between the protein-surfactant composites becomes more due to increase in more bonding sites, therefore increasing the rigidness of the two-dimensional construction formed at the interface. ( R.Miller )
The dynamicss of construction formation at water/MCT interface was really slow compared to that of water/hexane. So the adsorbed bed was aged for approximately 18 hours before running the experiment with MCR 301 as the construction has to make visco-elastic government at that mensurating conditions. In both instances ( hexane and MCT ) the protein-surfactant composite formed more stiff beds than the protein. The water/MCT system showed better duplicability than the water/hexane system.
The scheme should be: Show that
– BLG has its peculiar shear rheology at the water/oil interface
– there are differences at water/hexane and water/MCT interfaces
– all this gives in general the same image like at the water/air interface, but on the other manus besides quantitative differences
– consecutive add-on of surfactant alterations the shear rheology such that we can presume the protein is step by measure removed from the interface
– this is in equality to the water/air interface
– the surface assimilation informations ( isotherm and dynamicss, and possibly besides dilational rheology ) support this image
– usage eventually a sketch that demonstrates the chief thought ( from either of the recent documents by Alahverdjieva, or Kotsmar, or Pradines )