Absorption Wetting Crystal growth mechanism

Information about Absorption Wetting Crystal growth mechanism

Published on July 17, 2014

Author: amballa.sridivya

Source: authorstream.com


PowerPoint Presentation: ADSORPTION, WETTING, CRYSTAL GROWTH MECHANISM BY A SRI DIVYA PowerPoint Presentation: ADSORPTION AT SOLID INTERFACES: Adsorption is surface phenomenon ,when a solid surface exposed to a gas (or) , the molecules from gas or liquid accumulate at the surface ,this phenomenon is called as adsorption. Adsorption mainly depends upon chemical nature of adsorbate and adsorbent, Pressure and surface area of adsorbent. TYPES : PHYSICAL ADSORPTION: It is reversible ,mainly due to vanderwaals forces, commonly occurred at low temperature. PowerPoint Presentation: Eg : Adsorption of gases on charcoal CHEMICAL ADSORPTION: It is irreversible , mainly due to strong chemical bonds, occurred at high temperatures. E g : adsorption of oxygen on silver or gold. APPLICATIONS: For removal of objectional odours from room and food. Measurement of particle size in powders. Decolourising the solution. Detergency and wetting. C hromatography- To separate substances To purify a particles To remove calcium and magnesium ions from hard water Activated charcoal used as antidote in the poisoning. PowerPoint Presentation: ADSORPTION OF SOLID-GAS INTERFACE: The adsorption of gas on solid is depends on, chemical nature of a dsorbate and adsorbent, surface area of adsorbent, temperature and Partial pressure of gas. The amount of gas adsorbed per unit area of solid is measured by using adsorption isotherms. The graph plots between volume of gas adsorbed versus pressure are Known as “adsorption isotherms”. It adsorption is monomolecular ( single gas ), the adsorption isotherm is appears as following. PowerPoint Presentation: If adsorption is multi-molecular the adsorption isotherms appears as following: volume of gas adsorb - ed pressure FREUNDLICH ADSORPTION ISOTHERM: According to freundlich ‘x’ moles of gas is adsorbed on m grams of solid, then x/m is proportional to pressure x/m α p y=x/m=kp 1/n PowerPoint Presentation: The amount of gas adsorbed can be determined by plotting the graph between x/m Vs P. It gives a non-linear graph. x/m p Because of non-linear it converted into logarthmic where x/m=kp 1/n log x/m=logk+1/n log p logy=logk+1/n log p (where x/m=y) The graph plotted between log p Vs log x/m(log y) gives straight line and the slope is equal to 1/n the intercept is equal to k. PowerPoint Presentation: LANGMUIR ADSORPTION ISOTHERM: Langmuir derived an simple adsorption based on some assumptions. These assumptions are: The molecules or atoms of gas are adsorbed at active site of the solid ,and it is one molecule thick (monolayer). The adsorbed layer is uniform. There is no interaction between adjacent adsorbed molecules. Derivation: A fraction of active site occupied by gas molecule at pressure P is represented by θ , And the fraction of site is not occupied by molecules is represented by (1- θ ). PowerPoint Presentation: The rate of adsorption (r1) is proportional to unoccupied site and the pressure. r 1 =k 1 (1- θ )P The rate of evaporation of molecules is proportional to fraction of occupied site. r 2 =k 2 θ at equilibrium r 1 = r 2 k 1 (1- θ) p= k 2 θ k 1 p(1- θ )= k 2 θ k 1 p-k 1 p θ = k 2 θ k 1 p=k 2 θ +k 1 p θ By rearranging we obtain k 1 p/k 2 +k 1 p = ( k 1 /k 2 )p / 1+( k 1 /k 2 )p here k 1 /k 2 =b, and y/ y m = θ y= mass of gas adsorbed on solid, at pressure p y m = mass of gas adsorbed on 1 gram of solid where this equation rearranged as y/ y m = bp /1+bp y= bpy m /1+bp PowerPoint Presentation: Then plot the graph between p/y VS p, it gives straight line wih slope 1/ y m and intercept 1/ y m b 1/ y m p/y p TYPES OF ISOTHERMS : 1.Type1 : It represents increasing in adsorption mith increasing pressure. It is adsorption non porus solid where mono layer is formed . Languir-Freunlich isotherms are Eg : adsorption of nitrogen on charcoal PowerPoint Presentation: 2.TYPE-2: It is sigmoid in shape, it is adsorption on non- porus solid and forms multilayer. It is repressented by BET equation 1/ y m b P/y( p o -p)= 1/y m b+b+1/ y m p/ p o If monolayer is formed, this equation reduces to langmuir equation. The amount of adsorption is measured by plottin graph b/w p/y( p o -p) Vs p/ p o it gives straight line with slope b-1/ y m and intercept 1/ y m b . In BET equation the constant b is greater than “2” eg : adsorption of nitrogen ion iron. 1/ y m b b-1/ y m PowerPoint Presentation: 3. TYPE-3 : It is not commonly observed it is obtained, when the heat of 1 st layer is lees than that of next layer. In BET equation the constant b is less than 2. eg : adsorption of bromine on silica . 4.TYPR4: It repressents adsorption of gas on porous solids where multilayer is formed. eg:adsorption of benzene on silica gel. 5. TYPE5 : It is similar to 3 rd isotherm but adsorption is occurred on porous solid Eg : water vapour on charcoal at 180 o C. ADSORPTIN SOLID-LIQUID INTERFACE: A number of drugs such as dyes, alkaloids, fatty acids and inorganic acids are adsorbed on solid surface such as alumina and charcoal. At low concentration of solution this adsorption is similar to adsorption of gas. PowerPoint Presentation: So langmuir adsorption isotherm is slightly modified and explained adsorption pattern In this case vapour pressure is replaced with concentration of solute c/y=1/ y m b +c/ y m APPLICATIONS: Activated charcoal: It is used as an antidote in poisoning by sulphonamides , tolbutamide and other drugs It is also used in over dose of paracetamol , other dose of paracetamol causes liver damage, renal and death due to hepatotoxicity . Charcoal enhance the diffusion of drug from tissue of GI tract to GI contents, So it increase elimination of drug this process called as gastro intestinal dialysis. t is also used in purification of water. PowerPoint Presentation: WETTING: Wetting is an adsorption process in which an intimate contact of the solids with liquid phase is achieved IMPORTANCE: Intimate contact of solids or liquids with liquids is an initial step towards the preparation of suspensions and emulsions In case of granulation prior to tableting , the powders are mixed with a liquid binding agents The success of this process in part depends on the wetting and spreading of the liquid over the solid. Film coating requires the wetting and spreading of liquids over the tablet surface Dissolution of a tablet or a capsule necessitates the penetration of liquid into pores of the dosage forms PowerPoint Presentation: CONTACT ANGLE: Contact angle can be defined as an angle between the liquid droplet and surface which it spreads. Contact angle is used as an indicator to evaluate the efficiency of a wetting agent. These examples illustrate the importance of contact angle and surface tension of liquid. Surfactants are used to aid wetting of powders because they are capable of Lowering interfacial tension Lowering of contact angle between the solids and liquids Displacing the air and permit the intimate contact PowerPoint Presentation: The contact angles can taken up any values between 0 0 and 180 0 C as shown below θ < 90º indicates good wetting θ = 90º indicates partial wetting θ > 90º indicates non wetting A low contact angle indicates that adhesive forces between the liquid and solid and wetting occurs High contact angle indicates that the cohesive forces of the liquid   PowerPoint Presentation: The basic equation that applies to the wetting is Young equation, which is based on the free energy caused by an increase in the area of solid that is wetted by a liquid. ϒ S/A = ϒ S/L + ϒ L/A Cos θ Contact Angle of some drugs: Drugs Contact angle θ ( 0 ) Indomethacin 90 Tolbutamide 72 Nitro furantoin 69 Phenyl butazone 109 Chloramphenicol Palmitate ( α - form) 122 Ampicillin (trihydrate) 21 Lactose 30 PowerPoint Presentation: DRAVES TEST: A weighed amount of cotton is allowed to sink through a wetting solution in a 500ml measuring cylinder the time required for sinking is noted and compared. The lower the time it has taken, higher is efficiency . The spreading qualities are normally assessed by subjective evaluations. PowerPoint Presentation: CRYSTAL GROWTH MECHANISM: The size distribution of dispersed systems may increase during ageing, owning to three principal mechanisms: Ostwald ripening Polymorphic transformation Temperature cycling Ostwald ripening: The basics for ostwald ripening is found in an equation analogous to equation ( kelvin equation In P/P 0 = 2 ϒ V/ Rrp ) and it applies to the equilibrium solubility of small particles. It is important to distinguish between equilibrium solubility and the rate at which a substance dissolves. PowerPoint Presentation: Dissolution rate is affected by particle size since the surface area of the solid at the solvent increases with decrease in the particle size Equilibrium solubility at given temperature is affected by particle size, range near the colloidal dimension i.e , less than 5 microns Eg : Equilibrium solubility at 25 0 C at calcium sulphate with average particle size of 2 microns is 2.085gm/L when the average particle size is reduced to 0.3 microns, the equilibrium solubility is increases to 2.476gm/L. In practical sense the solution that is saturated with small particles supersaturated with respective large particles of the same substance This condition process causes crystal growth in a suspension as solute diffuses from the saturated layer. PowerPoint Presentation: The remaining saturated particles gets surrounded to the large particles. Precipitation on the surface of the large particles occurs as the saturated layer becomes super saturated with respect to the equilibrium solubility of the large particles The overall effect is an increase in particle size and decrease in the no of particles in suspension The final conclusion of this process is the formation of one large particle that represents thermodynamically stable state of a suspension. Polymorphic transformation: Polymorph exhibit different equilibrium solubilities for eg , four polymorphs of phenylbutazone were identified by X-ray diffraction, thermal analysis and infrared spectroscopy and were found to have different solubilities . The difference in the solubility of polymorphs therefore provides a driving force for crystal growth in suspension PowerPoint Presentation: EQULIBRIUM SOLUBILITY OF POLYMORPHS OF PHENYLBUTAZONE TEMPERATURE CYCLING: It may lead to crystal growth as solubility depends upon crystal growth, as solubility depends on temperature In most cases, solubility is directly related to temperature, so that a slight rise in temperature leads to an increased equilibrium solubility. A drop in temperature, however slight, results in a super saturated solution surrounding each particle Precipitation occurs to relieve the supersaturation and crystal growth occurs. Form Equilibrium solubility, mg/100ml 1 288.7 2 279.7 3 233.6 4 230.0 PowerPoint Presentation: REFERENCES : Leon Lachman ; The theory and practice of industrial pharmacy; Page No:116-117. www.ask.com www.google.com www.slideshare.com C.V.S Subramanyam ; A text book of Physical pharmacy; Pg No : 381- 384

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