UNIT_3_PHYSICAL_PHARMACEUTICS_1st PDF

# Unit - III: Surface & Interfacial Phenomenon ## Surface & Interface - The outer boundary of any matter is called surface. - The contact phase of any two immiscible matters is called interface. - All the surface is also an interface but all interface is not a surface. - When any matter comes in co...

# Unit - III: Surface & Interfacial Phenomenon ## Surface & Interface - The outer boundary of any matter is called surface. - The contact phase of any two immiscible matters is called interface. - All the surface is also an interface but all interface is not a surface. - When any matter comes in contact with another matter and they are immiscible it is called interface. - And when any matter make interface with air then it is called surface. ## Interface may be of following type: | Interface | Type | |---|---| | Air-Oil | L-L Interface | | Oil-Water | L-L Interface | | Air-Ball | G-S Interface | | Ball-Water | S-L Interface | | Air-Water | L-G Interface | | Water-Ball | S-S Interface | ## Surface Tension - Surface tension is the property of liquid. - This force is exist b/w the liquid and gas interface. - Surface tension of any liquid is defined as the perpendicular force applying on the surface of liquid in below direction due to the cohesive force of attraction is called surface tension of liquid. - When any liquid particle is present in the middle of the container then it feels van der Waal force of attraction in four directions, so the net force becomes zero. - But the liquid particles present upper surface of liquid feels the attraction force from three directions so the below layers of liquid pulls the liquid of upper layer in up, and this is called surface tension. - It is represented by Y. - $Y = F/L$ - Where: - Y = Surface tension - F = Perpendicular force - L = length of surface. - The SI unit of surface tension is N/m and CGS unit is dyne/cm. - Ex: Surface tension as 20°C - Water - 72.075 - Ethanol - 27.50 - Chloroform - 27.10 - Hexane - 18.4 - Benzene - 28.88 - Ethyl Alcohol - 22.4 ## Surface Free Energy - Any liquid wants to require the minimum surface area to increase their surface tension. - Liquids require the spherical shape due to the surface area sphere is very less. - The energy required for any liquid to reduce their surface area is called surface free energy of that liquid. - In an experiment take an immovable frame. A,B,C,D which is closed from three sides, and from bottom a movable wire is attached. - Now, place this frame is soap solution then a film of soap is made over the frame. - Due to surface tension, the movable wire moves upward up to distance (d) - So the work done by the film will be equal to: - $W = Fxd$ - Where: - W = Work - F = force. - d: displacement. - $W=Fxd$ (i) - $Y = F/2L$ - $F = Y x 2L$ (ii) - Put the value of equation no ii into main equation i - $W: Y x2LXd$ - We know that 2LXd = A - So the new equation is: - W = YxA - $W = 4G = YxA$ - Y = W/A - Where - 4G = Free Energy - Y = Surface tension - A = Area. ## Method to determine Surface free Energy: - Here is three method to determine the surface free energy: - 1) Dyne Pen Method - 2) Contact Angle Method. - 3) Interfacial Transmitter Method. ## Method to determine surface tension - The surface tension of any liquid can be determine by following free method - - 1) Capillary Rise Method. - 2) Drop count method. - 3) Drop weight Method. - 4) Wilhelmy plate method. - 5) Ring detachment Method (DU Nory Method) ## 1) Capillary Rise Method: - This is the capillary based method in which the liquid reaches into a certain height and the surface tension is measured by using height of liquid in capillary. - When liquid rise into capillary then two force is acting on liquid, surface tension and the potential energy due to gravity. - Then: - $Y_{caso} = ^1/2 x rx Y$ (i) - $F: mgh + Wl$ (ii) - Where: - $Y_{caso}$ = Surface tension - $F = mgh + Wl$ - Where - m = mass of liquid - g = gravity. - h = height of liquid - Wl = weight of liquid - We know that $m = pV = pxπr²$ - Put the value in equation (ii) - $F= erx πr² gh + Wl$ - So we compare both force. - $2 x πrY = erx πr²gh + Wl$ - $2Y = ergh + Wl$ - $Y = ^1/2 x ergh + Wl$ ## 2) Drop weight Method: - This is determine by using an apparatus "Stalagmometer" then the sample liquid is filled up to mark A in stalagmometer and allow to fall liquid dropwise then by using weight of the drop surface tension can be calculated. - $W= 2πrY$ - $Y = W / 2πr$ - $Y₁ = W₁ / 2πr$ - $Y₂ = W₂ / 2πr$ - $Y₁ / Y₂ = W₁ / W₂$ - Where - $Y₁$ : Surface tension of Water - $Y₂$ : Surface tension of Sample - $W₁$ : Weight of water - $W₂$ : weight of sample. ## Doopcount Method - In this method surface tension is determine by using stalagmometer. The same volume of water and sample is filled up to the mark, and allow to fall by counting the no of drops of sample and water surface tension is calculated - $W = 2πrY$ - $Y = W = mg$ (mass x g force) - $Y = M / 2πrM $ - $M = eV $ (mass = density x volume ) - $Y₁ = (ρ₁ x V x g) / 2πrM₁$ - $Y₂ = (ρ₂ x V x g) / 2πrM₂$ - $Y₁ / Y₂ = (ρ₁ x V x g) / 2πrM₁ / (ρ₂ x V x g) / 2πrM₂ $ - $Y₁ / Y₂ = (ρ₁ x M₂) / (ρ₂ x M₁)$ - Where - $Y₁$ : Surface tension of Water - $Y₂$ : Surface tension of sample - $ρ₁$ = Density of Water - $ρ₂$ = Density of sample - $M₁$ = No of drop of water - $M₂$ = No of drop of sample. ## 4) Wilhelmy Plate Method: - In wilhelmy plate method a light plate of aluminum or platinum is tied with a thread and placed on the upper surface of liquid. - Due to surface tension the plate is pulled downward and a force is applying from upward direction to detach the plate. - The fatal force required for detachment of plate will be equals to the surface tension applied by liquid. - $Y = F/Lcosθ$ - Where - Y = Surface tension - F= force - L= Length of plate. ## 5) Do Nouy Method / Ring detachment method: - This method is used to determine the surface tension as interfacial tension bath. - The liquid whose surface tension is measured is placed in a container and the platinum or Excidium is suspended in liquid. - And the ring is attached with a wire and try to detach. - The force required is recorded by the scale. - And then surface tension is calculated by using this formula: - $Y = F / 2π(γ1+γ2)$ - Where - Y = Surface tension. - F = Force - γ₁ = Radius of outer surface - γ₂ = Radius of inner surface. ## Spreading: - When any immiscible liquid is placed on the surface of another immiscible liquid then either it form a thin film or remain as a drop. - The property of any lipid is comes in contact with another immiscible liquid is called spreading - And the ability of spreading of any liquid into another immiscible liquid is called spreading coefficient. - There are two types of forces is applying during spreading - 1) Adhesive force: b/w immiscible liquid. - 2) Cohesive force: b/w the same liquid. - If the work done for adhesive force is greater than the work done for cohesive force, then spreading occur. - And vice versa - $WA > WC$ - $S = WA - WC$ - Where: - S = spreading - WA = work done for Adhesive - WC = Work done for cohesive. - $S = +V$ Spreading occur (film) - $S = -V$ No Spreading occur. (Drop) - The work done for adhesive and cohesive force can be expressed as: - $S = WA - WC$ (i) - $Wc = Y₁.4A+Y₁.4A$ - $Wc= 2Y₁.4A$ - If $4A = 1cm$ - $Wc = 2Y₁$ (ii) - $WA = Y₁.4A+Y₁.4A - Yes.4A$ - If $4A = 1cm²$ - $WA = Y₁ + VS + VLS$ (iii) - Put the value in equation (i) - $S = WA - WC$ - $S = Y₁+YS -YLS - 2Y₁$ - $S = Y₁+Ys -YLS$ ## Application - Spreading coefficient is used in the manufacturing of lotion, liniment, ointment & cream. - Ex: In dyne/cm - Benzene - 8.8 - Hexane - 3.4 - Octane - 0.2 - Paraffine - -13.4 ## Adsorption at liquid surface: - Adsorption is a process in which the drug particles, molecules, ions is disperse on the surface of liquid - When some molecules are ions are disperse in favour of interface only then it is called the adsorption and in the Adsoprtion surface tension is decrease. - When some molecules and ion are dispersed in liquid in the favour of bulk then it is called -ve adsorption and surface tension is increase. - **Adsorption** - +Ve Adsorption - -Ve Adsorption - **Adsorbdim** - **Absorption** ## Surfectant: - Surfectant are those agents which reduce the interfacial tension b/w two immiscible liquid and mix them in one another. - In the structure of surfectant, one end is present, which head is of hydrophilic nature and tail is of lycophilic in nature. - In liquid mixture, the head part is attached with water molecule and the tail is attached with oil molecule. - In any liquid mixture the surfectant molecule is attached on the surface of oil or water, and form a ball like structure which is KLa micelle. - And the minimum conc. of surfectant which is required for micelle formation is called CMC - Critical Micellar Concentration. - And the minimum temp. which is required for micelle formation is kraft temp. ## Types of Swifectant: On the basis of nature of surfectant it is of four types: - 1) Cationic - 2) Anionic - 3) Amphilynic - 4) Non ionic. - **1) Cationic Surfectant** - These organic surfectant have the charge on their head and they are mostly used as disinfectant, ambiseptic, and secondary emulsifying agent for external use. - Ex: Benzalkonium, Benzathoninom chloride, cesimide, Quartenary Ammonium compound. - **2) Anionic Surfe cient** - These surfectant contains anionic charge on their head. - They are not suitable for internal used due to irritating action. - Ex: Alkali Soap - Oleic Acid, Recinaleic Acid, Sodium Stearate, Metallic Soap: Calcium Stearate, Alumiminim stearate, Alkyl Sulphate and phosphate: Sadim lauryl sulphate, Frietiginal Amine sulphate, Sodium phosphate. - **3) Ampholylic surfectant**: - This surfectant depends upon pH value. - Before a certain pH it is cationic in nature and above the pH it is anionic in nature. - Ex - Lecithin, N-dodecyl Alanine. - **4) Non ionic swifecent**: - These surfectant do not dissociate ions in water. - They are mostly use in pharmaceuticals because it is compatible with both cation and anion and. No irritant action. - Ex: Paloxyl stearate, Span, Tween Eighty. ## HLB System (Hydrophilic lipophilic balance): - The nature of surfectant is depends upon total no of palar and nonpolar group present in the surfectant. - If more palar group is present then surfectant will be hydrophilic in nature and if more non palar group is present then the nature of surfectant is lycophilic in nature. - The main purpose of surfectant is to mix the two immiscible liquids ail and water. - HLB Scale gives the idea of nature of the surfectant. - The HLB scale was introduced by griffin in 1949. - And he devides the scale from one to twenty division. - If the value of HLB is high (12 to 20) then nature of surfectant is hydrophilic and if the value of HLB is low then the nature of surfectant is lipophilic. - From ( 0 to 20 ) Surfectant can be categorized into following nature: - 1) Antifoaming Agent - (0 to 3) - 2) W/O Emulsifying Agent (3 to 9) - 3) Wetting (Suspending Agent) (7 to 9) - 4) O/N Emulrifying Agent (8 to 16) - 5) Detergents (13 to 16) - 6) Solubilizing Agent (16 to 20) ## Solubilization: - When two immiscible liquids are mixed then they are not suterbelize in one another. - But after the use of surfectant they are sulubelize in one another and this is called suluubelization. - The mechanism of sulubelization is based on micelle formation. - The hydrophilic head of surfectant is bind with water and the liphophilic tail is bind with ail; so they comes closer and their interfacial tension is reduce and they solubilize easy. ## Detergency: - The process of removal of dust particles from any non linen surfaces is called detergency. - In the vaids of cloth the oily and water soluble dust particle are adhere and which is not removed by washing with water. - After applying detergent it makes micelle formation and the dust particles are removed. ## Adsorption - Adsorption is a surface phenomena in which the solid particles are adsorbed on the surface of solid or liquid. - In the process of Adsorption two component is present. - **1) Adabsorbont**: The surface in which particle adsorb. - **2) Adsorbate**: The particle which is adsorbed. - **Types of Adsorbtion** - **(A) Physirooption** - In Physisorption the force of Attraction b/w adsorbate and adsorbent molecule is weak physical attraction force like van der Waals force of attraction, hydrogen bonding. - **(B) Chemissoption** - In chemisorption, the force of Attraction b/w adsorbate and adsorbent molecule is strong chemical attraction force like, ionic bond, Electrostatic bond, and covalent bonding etc. - **Properties of Physisorption and chemisorption** - 1) **Force of Attraction**: - The force of Attraction for physisorption is weak and for chemisorption is strong. - 2) **Bond**: - In physisorption, the bond formation like van der Waals force of attraction and hydrogen bonding occur. - In chemisorption, the bond formation like ionic bond and covalent bond occur. - 3) **Surface Energy**: - Surface energy for physisorption is decrease and for chemisorption is increase. - 4) **Layer**: - In physisorption, multi layers are formed and in chemisorption, only single layer is formed. - 5) **Remove**: - In case of physisorption, it is easy to remove and in case chemisorption, it is not easy to remove. - 6) **Effect of fluid**: - Effect of fluid is low or decrease in the case of physisorption and high or increase in the case of chemisorption. ## Adsorption Isotherm - **(A)** When the pressure is increase then the rate of chemisorption is increase but the rate of physisorption is decrease. - **(B)** At constant temperature, for chemisorption process when the rate of adsorption and pressure is plotted on x and y axis then a straight line graph is obtain. This is called adsorption isotherm. - **(1) Frandlich Adsorption Theorum** - According to this theorum at constant temperature the rate of action of adsorption is directly proportional to the pressure it means when the pressure is increase then more adsorbent particle in the surface. - $x = Kp^{1/n}$ - where : - x = Mass of Adsorbate - m = Mass of adsorbent. - x/m = Fraction of Adsorption. - $log x = log k + log p^{¹/n}$ - **(2) Longmuir Theorum** - Longmuir theorum is based on physisorption process. - The adsorbent particle adsorb on the active sides of the adsorbate surface. - When particle adsorb in active side then this is called adsorption and when they left the active side this is called desorption. - The rate of adsorption and desorption is depends upon free sides as following. - **Adsorption** - $x₁ = K₁ x (1-0) xp$ - $x₁ = K₁ (1-0) xp$ - $x₁= K₁P - K₁0P$ - at eqauation: - $x₁ = x₂$ - $K₁P - K₁0P = 0$ - $K₁P = K₂0 +K₁0P$ - $K₁P = 0 ( K₂ + K₁P)$ - **Desorption** - $x₂= K₂0$ - $x₂= K₂0$