Weting of solid surfaces has been a subject of huge involvement since last few decennaries maintaining in position of the broad scopes of applications. It refers to a phenomenon affecting spreading of a liquid bed on a solid surface ensuing from coincident action of interfacial forces between solid, liquid and gas stage. A big figure of industrial Fieldss such as froth floatation ( Al-Otoom et al. , 2009 ) , oil recovery, ( Fuerstenau et al. , 1991 ) oil agglomeration ( Garcia et al. , 1998 ) , solid-liquid separation in wetting medium ( Cournil et al. , 2006 ) , surface cleansing, dust suspension ( Ulusoy and Yekeler, 2004 ) coating, adhesion, printing and detergence ( Neumann and Good,1979, Adamson, 1991, Janczuk et al. , 1999 ) demand a basic apprehension of the wetting procedure, and the parametric quantities impacting procedure. If wetting and dewetting belongingss of surfaces are known, so van der Waals interactions, interfacial free energy, distributing and capillary flow phenomena can be easy explained. ( Xia et al. , 2001 ) .
Wetting of a solid surface
Wettability of a solid surface is quantitatively measured in footings of contact angle. Contact angle is the angle between the solid-liquid and liquid-air interface. When contact angle is 180 & A ; deg ; , the surface is said to hold zero affinity towards the liquid or non wetting. When the angle is 0 & A ; deg ; , the surface is said to hold the affinity towards that liquid or complete wetting of the surface by the liquid. Both of these are the utmost instances, whereas in the existent instances, the contact angle between a solid and liquid varies between 0 & A ; deg ; and 180 & A ; deg ; .
During distributing procedure the liquid molecules are arranged on the solid surface so as to minimise the information and do the system stable. So while organizing a bead of a liquid, the free energy of the molecules exposed on the liquid air interface is really the minimal possible sum of energy of the corresponding system of solid and liquid.
The solid surfaces are loosely categorized as hydrophobic or hydrophilic depending upon the extent to which the wetting of the surface is facilitated.
As the name itself implies, hydrophilic surface means surfaces holding affinity to water.. Since contact angle is less, the open country of liquid to air is less. Water spreads really good on these surfaces giving a contact angle less than 90 & A ; deg ; . Glass is an illustration of this type of surfaces.
On the other manus, on hydrophobic surfaces, H2O does non distribute good. The H2O drops formed on these surfaces have higher surface energy because of higher surface country. Contact angle formed is ever more than 90 & A ; deg ; .
Consequence of wetting agents on wettability
As illustrated before, rather a good figure of applications are at that place so far as wetting of a solid is concerned. Wettability sweetening of hydrophobic surfaces as per our demand is possible utilizing aqueous solution of assorted surface active agents with mention to pure H2O. When surfactant molecules are introduced to the liquid, the surfactant molecules along with the dissolver molecules are oriented in a mode so as to minimise the information. More is the unsimilarity between constructions of wetting agent and a solvent molecule more is the inclination to diminish the information.
Decreasing the wettability is peculiarly of import in instance of those stuffs which may damage in contact with H2O, for illustration, in nutrient industries where nutrient coming in contact with wet is non desirable, in order to keep the freshness, cut downing wettability is desirable. In picture and coating applications non wetting is desirable. Increasing wettability is of import in instances where complete contact of a solid surface with a liquid is desirable. In fabric industries, increasing the wettability of fibers is desirable for effectual dyeing and cleansing.
Surfactant surface assimilation:
A wetting agent or surface active agent alters the belongings of the liquid which affects the wettability of the solid surface for the corresponding liquid. To alter the wettability of hydrophobic surfaces, different wetting agents are used which acquire adsorbed at the solid liquid interface.
In instance of surfactant surface assimilation, surfactant molecules get adsorbed on the solid-liquid interface and lower the overall free energy of the system. Adding more and more surfactant molecules to the dissolver increases the surfactant concentration at the interface and surface tenseness goes on diminishing boulder clay CMC.
Types of wetting agents
The wetting agents are loosely classified into cationic, anionic, non-ionic and zwitterionic depending upon the charge of caput group attached to the surfactant molecule. When the caput group is negatively charged, the wetting agent is called anionic and if positively charged it is called cationic wetting agent. Head group is impersonal in instance of non-ionic 1s. Zwitterionic wetting agents carry both the charges and act as cationic, anionic and non-ionic depending upon pH of dissolver, temperature, concentration and other conditions.
Mixed wetting agent system
Properties wetting agents of different or the same type were assorted and their belongingss were studied extensively. The function of a assorted system of wetting agents in heightening wetting belongingss was investigated by different research workers. Assorted system of wetting agents normally has a critical micelle concentration which may be greater than or less than that of single 1s depending upon the interaction between single wetting agent molecules, the effects being named as hostility or synergy severally. In the instances where a lower CMC value is achieved, a more economical manner of altering surface belongingss is provided. The assorted wetting agent system is relatively undiscovered country with regard to that of individual wetting agent.
Application of assorted wetting agent system
Industrial application of surfactant mixtures include dispersion/flocculation, floatation, emulsification, corrosion suppression, cosmetics, drug bringing, chemical mechanical shining, enhanced oil recovery ( Zhang and Somasundaran, 2006 ) industrial cleansing and degreasing of metals surface ( Davis et al.,2003 ) . Mixture of wetting agents shows better consequence in bettering wetting features than pure 1s in most of the practical applications. In fact, the commercial wetting agents designated as pure wetting agents in some instances are mixtures of wetting agents due to nonhomogeneous natural stuffs, presence of unreacted natural stuffs or formation of by merchandises. ( Zdziennicka et al. , 2003 ) .
2.1. Single wetting agent system
Broad scope of research has been performed on solution behavior and contact angle surveies for individual surfactant systems. The consequence of SDS concentration on contact angle was studied by Serrano-Salda & A ; ntilde ; a et Al. ( 2004 ) with an aim to analyze the consequence of ionic strength and wetting agent concentration which is given in figure-2.1.
Figure-2.1 Contact angles ( ? ) of solid/n-C12/brine systems as a map of: ( I ) ionic strength ; ( two ) CSDS ; and ( three ) CNaCl + CSDS. ( Serrano-Salda & A ; ntilde ; a et al. , 2004 )
Dutschk et Al. ( 2003 ) studied the wetting behavior of non-ionic and ionic wetting agents on Teflon surface and the undermentioned tendency was found to be followed.
Figure-2.2 Contact angle relationship with clip of C12E5 on Teflon AF surface ( Dutschk et al. , 2003 )
Figure-2.3 Contact angle relationship with concentration of SDS ( Dutschk et al. , 2003 )
In order to analyse the equilibrium province, an algorithm to rectify the contact angle taking vaporization into history is presented in this survey done by Dutschk et Al. ( 2003 ) .
To set up relation between solution behavior of individual surfactant solutions with concentration, utilizing Na dodecylsulfate ( SDS ) and sodium dioctylsulfosuccinate ( SDOSS ) and a non-ionic surfactant Triton X 100 ( TX100 ) SimonA?iA? and Rozman, 2007 produced the experimental consequences which when plotted followed the tendency shown in figure-2.4.
Figure-2.4 Surface tenseness, ?L, of surfactant solutions vs. the logarithm of surfactant concentration, log Ms ( – ) SDS, ( – ) SDOSS, ( ) TX100 ( SimonA?iA? and Rozman, 2007 )
The tendency followed by surface tenseness and contact angle due to add-on of cationic wetting agent on Teflon surface was studied by Harkot and Janczuk ( 2009 ) which is shown in figure-2.5.
Fig-2.5 The relationship between the values of the surface tenseness ( ?LV ) of aqueous C12 ( EDMAB ) ( – ) and BDDAB ( – ) solutions and the values of the contact angle ( ? ) of aqueous C12 ( EDMAB ) ( – ) and BDDAB ( – ) solutions for the PTFE surface and the concentration of the wetting agents ( log C ) . ( Harkot and Janczuk, 2009 )
Weting belongings of non-ionic wetting agents studied by Kim and Hsieh ( 2001 ) gave the tendency shown in figure-2.6 of changing surface tenseness with altering concentration of wetting agent.
Fig-2.6 Gibbs ‘ surface assimilation isotherms for Span 20 ( ) and Tween 20 ( • ) . ( Kim and Hsieh, 2001 )
2.2. Mixture of wetting agents
Mixtures of two wetting agents showed divergence from the additive dependance between the contact angle and mixture composing, nevertheless, no synergy in the wettability was observed. Synergy in the wettability of low-energetic hydrophobic solids should be expected if a mixture of ionic and non-ionic wetting agents is added to H2O. ( Rosen, 2004 ; Gharibi et al. , 2000 ; Li et al. , 1998 ) . The plants done on mixture of wetting agents altering the contact angle can be summarised as given in table no. 2.1
The alteration in contact angle with mole fraction of a peculiar wetting agent in a mixture of two cationic wetting agents is given by Szymczyk et Al. ( 2006 ) which is presented in figure-2. 7
Fig-2.7. The relationship between the contact angle, ? , and logC ( where C is the entire concentration of the mixture ) for different values of the monomer mole fraction of CTAB, ? , in CPyB and CTAB mixture ( for PTFE ) . ( Szymczyk et al. , 2006 )
Similarly the behavior of a cationic-nonionic mixture was studied by Szymczyk and Janczuk ( 2006 ) for which the tendency as given in figure-2.8 was followed.
Fig-2.8. The relationship between the contact angle, ? , and monomer mole fraction of CTAB, ? , in TX100 and CTAB mixture ( for PTFE ) at changeless entire mixture concentration, C, equal to 10?6 ( swerve 1 ) , 10?5 ( swerve 2 ) , 5-10?5 ( swerve 3 ) 10?4 ( swerve 4 ) and 2-10?4 M ( swerve 5 ) . ( Szymczyk and Janczuk, 2006 )
Zdziennicka et Al. ( 2003 ) studied wettability of Teflon by aqueous solutions of two anionic wetting agent mixtures and the relationship between contact angle with logC was plotted for different ratios.
Fig-2.9 the relationship between cos? ( ?-contact angle ) and logarithm C for different values of the mole fraction ( ? ) of SHDSs in SDDS+SHDSs mixture ( Zdziennicka et al. , 2003 )
Table 2.1 Previous surveies on assorted wetting agent system
Wetting agents used
Sodium dodecyl sulphate and Sodium hexadecyl sulfonate
Zdziennicka et al. , 2003
Dodecylethyldimethylammonium bromide and Benzyldimethyldodecylammonium bromide
PTFE and PMMAe
Harkot and Janczuk, 2009
Cetyltrimethylammonium bromide and Cetylpyridinium bromide
PTFE and PMMAe
Szymczyk et al. , 2006
Non-ionic + Non-ionic
Triton X-100 and Triton X-165
Szymczyk and Janczuk, 2008
Triton X-100 and Triton X-165
Szymczyk and Janczuk, 2007
Triton X-100 and Cetyl trimethylammoniumbromide
Szymczyk and Janczuk, 2006
n-dodecyl trimethylammonium chloride, n-dodecyl trimethylammonium bromide, sodium 1-decanesulfonate and sodium dodecyl sulphate
Polyethylene ( PE )
Wu and Rosen, 2005
2.3. Effectss of additives
In many industrial applications additives are used along with wetting agents to better wetting belongings. Presence of additives greatly influences assorted wetting parametric quantities therefore supplying a more effectual manner of accomplishing the coveted wettability. Largely the additives used include intoxicants and electrolytes.
2.3.1. Consequence of Alcohols
Great trade of research done by Rosen ( 2004 ) , Zana ( 1995 ) , Forland et Al. ( 1994 ) , Forland et Al. ( 1998 ) , Attwood et Al. ( 1994 ) , Zana et Al. ( 1981 ) , Rao and Ruckenstein ( 1986 ) , Castedo et Al. ( 1997 ) and Leung and Shah ( 1986 ) have been presented on the solution behavior of intoxicant and surfactant mixture in altering wetting features. The alteration of contact angle with concentration of intoxicant was presented by Zdziennicka and Janczuk ( 2008 ) which is shown in figure-2.10
Fig-2.10 Dependence between the mensural values of the contact angle ( ? ) and the propanol concentration. Curves 1, 2, 3 and 4 correspond to the changeless values of CTAB equal to 1-10?5, 1-10?4, 6-10?4 and 1-10?3 M, severally. ( Zdziennicka and Janczuk, 2008 )
The solution belongings observed by intoxicant surfactant mixture as given by Tomi et Al. ( 2009 ) is presented in figure-2.11.the alteration of CMC with concentration of intoxicant can be noticed.
Figure-2.11 Dependence of cmc of DTAB solutions on intoxicant content. Open Markss denote the experimental consequences and solid Markss denote the deliberate values ( Tomi et al. )
2.3.2 Effect of electrolytes
The application of electrolytes as additives has been besides studied late. When we add electrolyte to a peculiar Attic surfactant solution it has been observed that surface tenseness and contact angle values are reduced. This happens because presence of electrolyte decreases the repulsive force between the caput groups. As the repulsive force is decreased, the CMC is decreased. So the add-on of electrolyte can give a more economical manner of utilizing the wetting agents for diminishing the contact angle and changing the wetting belongings. ( Chaudhuri and Paria, 2009 )
Figure 2.12. Plot of progressing contact angle ( ?A ) for different electrolytes ( NaCl, CaCl2, Na2SO4 ) in the presence of SDBS and CTAB solution on the Teflon surface. ( Chaudhuri and Paria, 2009 )
The above graph was obtained by Chadhuri and Paria ( 2009 ) for consequence of electrolyte on contact angle of pure wetting agents. Dependence of contact angle on concentration and valency of electrolyte is shown in the graph.
The wetting agents used were IGEPAL- 630 ( molecular weight 617gm/mole from Sigma Aldrich, catalogue no-542334 ) and CTAB ( molecular weight 364.46gm/mole from Fluka analytical of 99 % pureness ) . Electrolyte used was NaCl with 99.9 % pureness taken from Ranbaxy Fine Chemicals Ltd. No farther purification technique was adopted for wetting agents or electrolytes.
For mensurating surface tenseness a surface tensiometer, Data Physics, Germany ( DCAT-11EC ) was used. Platinum sheet is used for surface tenseness measuring in Wilhelmy home base technique. Three readings for a peculiar solution were taken and for the concluding computations, the norm of the three is taken. To avoid the surface assimilation of wetting agent on the home base it was cleaned decently with H2O and propanone and was besides burned to guarantee a clean surface. During the experiment, the temperature was maintained changeless at a 250c with the aid of a circulator.
Figure-3.1: Photograph of Surface tensiometer
For mensurating contact angle, contact angle metre, Data Physics, Germany ( OCA30 ) was used. Goniometric technique is used to cipher the contact angle. In Hamilton syringe solution is taken and forced out bead wise with droplets of a fixed volume which can be adjusted with aid of package. Press of the Piston are motion of the base home base are besides done by the instrument itself.
Figure-3.2: Photograph of picture based optical contact angle metre
The Teflon sheets used for the experimental work were available in signifier of involute sheets due to which even a really little part of a sheet was non found to be wholly consecutive which could take to deviation in contact angle consequences. So to avoid the job, an agreement of keeping the sheet really tightly with aid of a base home base and four prison guard was made. To avoid surface assimilation of wetting agent on the surface Teflon sheet is washed with H2O propanone and Chromic acid
RESULT AND DISCUSSION
4.1. Solution behavior of pure wetting agents
Surface tenseness measurings were done for different concentrations of both the cationic and non-ionic individual wetting agents to acquire the CMCs every bit good as minimal surface tenseness values. Apart from the CMC values minimal surface tenseness is besides really of import in any interfacial phenomena. The surface tenseness values obtained were plotted against log C in Figure 4.1. From the figure it is really clear that the CMC value of Igepal — 630 is much lower than CTAB with a lower minimal surface tenseness value. Then, quantitatively to acquire an thought about the surface assimilation of wetting agents at the airaˆ‘water interface, Gibb ‘s surface extra equation is used to cipher the surface extra values every bit good as minimal surface country occupied per molecule ( Chaudhuri and Paria, 2009 ) :
Figure- 4.1: Change of surface tenseness with log C for CTAB and Igepal-aˆ‘630
( 4.1 )
( 4.2 )
where i?‡ is the surface surplus in mole/m2, Amin is surface country per molecule in nm2, R is cosmopolitan gas invariable ( 8314 M3 Pa/kg mole K ) , T is absolute temperature, and NA is Avogadro figure ( 6.023 – 1023 ) .The value of surface surplus and Amin are calculated from the experimental informations given in table 4.1
Table-4.1: surface surplus and minimal surface country values
CMC ( millimeter )
( mN/m )
Exp. ?max ( mole/m2 ) – 106
( nm2 )
Lit. ?max ( mole/m2 ) – 106
( nm2 )
1.8 ( at 30 & A ; deg ; C )
( Rosen, 2004 )
( Rosen, 2004 )
Igepal — 630
The value obtained by experimentation was close to the value obtained from literature, the little difference with the reported value may be due to the difference in temperature of 5 & A ; deg ; C, as higher temperature surface assimilation denseness decreases, and eventually ensuing in higher Amin. From Amin we can acquire an thought about the wadding of surfactant molecules at the airaˆ‘liquid interface. Amin is lower in the instance of Iepal-630 which implies more surface assimilation denseness than CTAB being a non-ionic wetting agent.
4.2 Weting behavior of pure wetting agents
After analyzing the solution behavior wettability of two pure wetting agents was studied. Figure 4.2 shows change in contact angle on PTFE surface with the alteration in surfactant concentration at the aqueous solution.
Figure-4.2 Change in contact angle with alteration in log C for CTAB and Igepal — 630
A relationship sing Young and Gibbs equation gives the equation
( 4.3 )
Taking ?SV =0, from the equation ( 4.3 ) it can be explained that the graph between
surface tenseness and adhesional tenseness besides gives the ratio between surface surplus of solid-liquid and liquid-air interface.
Figure-4.3 Variation of adhesional tenseness with surface tenseness for CTAB and Igepal — 630
From figure-4.3, the incline is -1.0731 for IGEPAL- 630 which on seting in equation ( 7 ) , the value of ?SL= 2.395810-6 ( mole/m2 ) while for CTAB the incline is -1.003 and ?SL=1.55410-6 ( mole/m2 ) which implies surface assimilation denseness is more for IGEPAL- 630 on solid-liquid interface than CTAB. There is no equal surface assimilation at solid-liquid and liquid-air interface which is apparent from ?SL and ?LV values.
4.3. Solution behavior of the assorted wetting agent system
Harmonizing to Rubingh ‘s regular solution theory for assorted micelles, the assorted CMC ( C12 ) for system obtained by blending two wetting agents is given by the Eq. ( 4.4 ) ( Rubingh, 1979 ) ,
( 4.4 )
where C1 and C2 are the CMC of first and 2nd single wetting agent, C12 is that of the mixture, f1 and f2 are the activity coefficients value of which are taken as 1 in instance of ideal behavior. Therefore presuming ideal behavior, equation ( 4.4 ) becomes
( 4.5 )
For different values of ?1 the by experimentation found CMC and mathematically calculated CMC from equation ( 4.5 ) are plotted in figure-4.4. The divergence of experimental value from the deliberate value shows the divergence of the solution from ideal behavior.
Figure -4.4.Variation of CMC of assorted surfactant system with changing micellar mole fraction
To acquire a quantitative thought about divergence from ideal behavior as a consequence of interaction between two wetting agents, interaction parametric quantity ? is defined. Rubingh defined a relation
( 4.6 )
Using the value of x1 from equation ( 4.6 ) , ? is calculated
( 4.7 )
From the dealingss given in equation ( 4.6 ) and ( 4.7 ) ? value is calculated for the four mixtures with different ratios which are given in table 4.2.
Table 4.2 ( value of interaction parametric quantity for different micellar mole fractions of Igepal — 630 )
Value of ? is going more and more negative demoing negative divergence increasing with mole fraction of IGEPAL- 630. These theoretical values back up the graphical illations drawn from figure 4.3, therefore corroborating and giving a quantitative step of nonideality of the mixture.
4.4. Wettability of assorted wetting agent system
The mensural values of the Cos ? for aqueous solution of Igepal — 630 and CTAB mixtures on the PTFE surface is presented in figure 4.5. The figure shows the dependance of cos ? on Log C for different ratios of concentration of Igepal — 630 and CTAB. It is observed in the graph that with addition in Log C from -3 to -0.5 ( 9:1 ) , from -3 to -0.25 ( 7:3 ) , from -3 to -0.75 ( 1:1 ) and from -3 to -1.20 ( 1:4 ) ? lessenings and so becomes changeless for any farther addition in value of Log C. Change in contact angle is maximal in the lower concentration part. The maximal alterations of the contact angle happening in the concentration scope of solutions correspond to the addition of surfactant monomer concentration with surfactant add-on to the liquid. The part where with addition in concentration no farther lessening of contact angle is observed is the part matching to formation of micelles and increasing concentration in micelle.
Figure 4.5 alteration of contact angle ? with regard to altering concentration C of wetting agent.
The mensural values of the Cos CA ( ? ) for aqueous solution of IGEPAL- 630 and CTAB mixtures on the PTFE surface is presented in figure 4.5. The figure shows the dependance of cos ? on Log C for different ratios of concentration of IGEPAL- 630 and CTAB. It is observed in the graph that with addition in Log C from -3 to -0.5 ( 9:1 ) , from -3 to -0.25 ( 7:3 ) , from -3 to -0.75 ( 1:1 ) and from -3 to -1.20 ( 1:4 ) ? lessenings and so becomes changeless for any farther addition in value of Log C. Change in contact angle is maximal in the lower concentration part. The maximal alterations of the contact angle happening in the concentration scope of solutions correspond to the addition of surfactant monomer concentration with surfactant add-on to the liquid. The part where with addition in concentration no farther lessening of contact angle is observed is the part matching to formation of micelles and increasing concentration in micelle.
4.4.1. Adsorption at solid-liquid and liquid-air interface
Harmonizing to Bargeman et al. , 1973 that there is a additive relationship between the adhesion tenseness and surface tenseness of aqueous solutions of wetting agents ( cos ? = a + B ; a and B are invariables ) both for single wetting agents and besides for mixtures. But for all the ratios value of a and B in additive equations were near the same for a given polymeric solid. So to depict the relation between adhesional tenseness and surface tenseness on Teflon surface we have ( Szymczyk et al. , 2005 ) ,
cos ? = ? + 46.88 ( 4.8 )
utilizing the relationship between adhesional tenseness and surface tenseness the relation between surface free surplus at solid-liquid and liquid-air interface can be obtained as in instance of pure wetting agents from equation ( 4.3 )
Figure 4.6. Variation of adhesional tenseness with changing surface tenseness
The relationship between the values of cos ? and the surface tenseness ( ) of aqueous solution of IGEPAL- 630 and CTAB mixture on PTFE are shown in the above figure.
Generalizing the consecutive additive dependance given by equation ( 4.8 ) to the point where cos ?=1, i.e ?=0, ?c can be calculated, the liquid surface tenseness required to give zero degree contact angles, which is known as critical surface tenseness. ( Szymczyk et al. , 2006 )
In figure 4.7, the relation between ?-1 and cos ? is observed. In this secret plan if we extrapolate the graph to the point at which value of cos ? is equal to 1, the matching value of surface tenseness will give critical surface tenseness. Critical surface tenseness is the surface tenseness value at which complete wetting of a solid surface is at that place i.e. ?=0.
Figure- 4.7 relationship between opposite of surface tenseness with cos ?
4.4.2. Critical surface tenseness
From Young ‘s equation ( 4.9 )
It is possible to cipher the solid-solution interfacial tenseness from Eq. ( 4.9 ) on the premise that both = ? and = . For computation of the values of aqueous solutions of IGEPAL- 630 and CTAB mixtures, the surface tenseness of PTFE ( 20.34 mN/m ) was taken. For different ratios of concentration of CTAB and IGEPAL- 630, the alteration of interfacial tenseness with Log C is shown in figure 4.4. Rapid lessening in interfacial tenseness is observed in between the scope -3 to -1 or -0.5 and so it becomes changeless for any longer addition in Log C. There is besides a lessening in the value of Log C at which impregnation is reached for the four ratios with the addition in per centum of IGEPAL- 630 in the mixture.
Figure-4.8 Change in interfacial tenseness with alteration in log C therefore finding critical surface tenseness
4.4.3. One-dimensionality of relation between surface tenseness and interfacial tenseness
In figure-4.9 additive relationship between surface tenseness and interfacial tenseness is shown. Interfacial tenseness additions with addition in surface tenseness which once more implies an opposite relationship between concentrations of wetting agent. It can besides be observed that the incline or the intercept does non alter much with the four ratios. So this relationship is non dependent upon the micellar mole fraction ? .
Figure-4.9 additive relation between surface tenseness and interfacial tenseness
4.4.4. Work of adhesion on Teflon surface
Dependence between the adhesion work ( WA ) of the aqueous solutions of wetting agents to PTFE surface and log C is shown in figure – 4.6. The solid-solution interfacial tenseness fulfils the status
= + ?WA ( 4.10 )
where WA is the work of adhesion of the liquid to solid surface, which can be treated as the amount of two constituents, apolar ( Lifshitz-van derWaals ) , WA ( apolar ) , and polar, WA ( polar ) , interactions across solid-liquid interface. ( Szymczyk et al. , 2006 )
Using Young ‘s equation another relation can be established as
WA = ( cos ? +1 ) ( 4.11 ) .
This work of adhesion calculated from equation ( 4.11 ) is plotted against Log C in figure-4.10. The ascertained alteration implies that work of adhesion lessenings and so attains a impregnation value with addition in Log C for the ratio 1:1 and 1:4 for concentration of CTAB and IGEPAL- 630. But for ratios 9:1 and 7:3 for these two wetting agents, work of adhesion lessenings, increases a spot and so becomes constant which may be because of prevailing consequence of non-ionic wetting agent in the former two ratios which was non at that place in the ulterior two ratios.
Figure – 4.10 Change of work of adhesion with concentration
4.5. Electrolyte consequence on assorted wetting agent system
4.5.1. Solution behaviour assorted surfactant system with electrolyte
Consequence of presence of electrolyte NaCl in presence of assorted surfactant system with 90 % CTAB and 10 % Igepal-630 was studied first doing surfactant concentration invariable and changing electrolyte concentration boulder clay impregnation value of surface tenseness and contact angel were achieved and so the same process was repeated with two more concentrations of the same wetting agent system.
Presence of electrolyte decreases the repulsive force between caput groups of ionic wetting agents and therefore bettering adhesion and wettability. However, non-ionic wetting agents are non much affected by the electrolyte. So the mixture with ratio 9:1 of cationic and non-ionic wetting agents severally was chosen to analyze the consequence of electrolyte.
Figure 4.11 alteration of surface tenseness with concentration of wetting agent for a peculiar value of concentration of electrolyte
In figure-4.11 alteration of surface tenseness with surfactant concentration for four different concentration of electrolyte is plotted. All the four graphs follow the same tendency in diminishing the surface tenseness. But with increasing electrolyte concentration, for the same concentration of wetting agent, value of surface tenseness reduces. This provides an effectual manner of cut downing surfactant ingestion. Taking a closer expression at the secret plan besides reveals that an add-on of 100mM of electrolyte is efficient of cut downing ingestion of wetting agent by about 10 times
The difference in surface tenseness value is more between pure wetting agent and 50mM of electrolyte with surfactant. With increasing electrolyte concentration, the difference reduces. This implies that at low salt concentration, electrolyte consequence is more and after that, for a peculiar wetting agent concentration, surface tenseness attains a impregnation value which does non alter for any farther alteration in electrolyte concentration.
4.5.2. Wettability of assorted surfactant system with electrolyte
In figure-4.12 the fluctuation of contact angle with concentration of wetting agent is shown for four different concentrations of electrolyte. In similar ways as in figure-4.8, the contact angle decreases with increasing concentration of electrolyte at a peculiar surfactant concentration. The difference between contact angle with add-on of electrolyte lessenings at higher concentration of wetting agent. In fact, after adding 100mM of electrolyte, farther addition in electrolyte concentration makes about no alteration in contact angle except for at really low concentration of wetting agent of the order 0.0001.
Figure 4.12 Change of contact angle with concentration of wetting agent for a peculiar value of concentration of electrolyte
Now adhesional tenseness, interfacial tenseness and work of adhesion are calculated for the assorted surfactant system of CTAB and IGEPAL- 630 in the ratio 9:1 in presence of electrolyte NaCl and the undermentioned graphs are plotted.
Figure-4.13 alteration of adhesional tenseness with surface tenseness for 9:1 ratio of CTAB and IGEPAL- 630 assorted surfactant system with 4 different concentrations of electrolyte NaCl
Figure-4.14 Relation between opposite of surface tenseness and cos ? for 9:1 ratio of CTAB and IGEPAL- 630 assorted surfactant system with 4 different concentrations of electrolyte NaCl
Figure-4.15 Change in interfacial tenseness for 9:1 ratio of CTAB and IGEPAL- 630 assorted surfactant system with 4 different concentrations of electrolyte NaCl with alteration in log C
Figure-4.15 Relation between interfacial tenseness and surface tenseness for 9:1 ratio of CTAB and IGEPAL- 630 assorted surfactant system with 4 different concentrations of electrolyte NaCl
Figure-4.16 Change in work of adhesion for 9:1 ratio of CTAB and IGEPAL- 630 assorted surfactant system with 4 different concentrations of electrolyte NaCl with alteration in log C
Addition in cos ? value with addition in Log C and eventually attainment of a impregnation value.
Linear relationship between surface tenseness and adhesional tenseness with a negative incline.
Inverse of surface tenseness keeping additive relation with cos ? .
Decreasing interfacial tenseness with increasing Log C and eventually making impregnation value and the value of Log C matching to saturation value diminishing with addition in per centum of IGEPAL- 630 concentration in mixture.
Decrease in work of adhesion to a impregnation value for higher concentration of non-ionic wetting agent
Decrease in work of adhesion followed by addition and so eventually achieving impregnation value for lower concentration of non-ionic wetting agent.
The nonideality of assorted surfactant system additions with increasing concentration of non-ionic wetting agents.
Addition of 100mM solution of salt decreases the surface tenseness and contact angle value of a peculiar concentration to the surface tenseness and contact angle matching to concentration 10 times the former concentration without electrolyte.
Table-5.1 Final consequences
Igepal — 630
CTAB: Igepal — 630
CTAB: Igepal — 630 = 9:1 ( 0.01 ) + NaCl
CMC ( millimeter )