Surface Active Agents Flashcards
What is interface
The boundary formed when two faces meet
The interface between a liquid/solid and a gas
Surface
Difference between surface tension and interfacial tension
Surface is between solid/liquid and gas
Interfacial is boundary for all states
Importance of interfacial phenomenon
- Adsorption of drugs onto solid adjuncts in dosage forms.
- Penetration of molecules through biological membranes (Absorption).
- Emulsion formation and stability.
- The dispersion of insoluble particles in liquid media to form suspensions.
The force per unit length that must be applied parallel to the surface so as to counterbalance the net inward pull,
Surface tension
For liquids, the surface free energy is numerically equal…?
to the surface tension
Interfacial tensions are less than surface tensions because
the adhesive forces between two liquid phases forming an interface are greater than when a liquid and a gas phase exist together.
if two liquids are completely miscible do interface or interfacial tension exists between them?
No
Surface/ interfacial free energy is…?
Surface or Interfacial Free Energy is the energy per unit area or work done to increase the surface by one unit of area.
What is the unit for surface tension
N/m or dynes/cm.
1 dyne/cm = 0.001 N/m
Unit of surface free energy
Joules/m2 or ergs /cm2.
What are the four methods of measuring ST
A. Simple methods
- Capillary rise
- Drop weight and drop count
B. Tensiometry
- Wilhelmy plate
- Ring detachment method (Du Nouy Tensiometer)
What affects the instrument used to measure surface or interfacial tension
- whether inter or surface tension is to measured
Accuracy
Size of sample
Why is θ zero in capillary tube method
because water completely wets capillary wall. For other liquids used in pharmacy θ is very small (θ nearly equals 0 == cos 0 = 1)
Formula for upward force
Surface tension x circumference
γ.2πr.Cos θ
γ2πr
Formula for downward force
Mass x acceleration due to gravity
m x g πr^2hρg
What is the surface tension at equilibrium using capillary tube
Upward movement = downward movement
γ2πr =πr^2hρg
γ =rhρg/2
Density of liquid in density bottle
(W3 – W1/W2 – W1) x density of water
W1 = weight of empty specific gravity bottle
W2 = weight of bottle with water
W3 = weight of bottle with liquid Density of liquid
What method is Stalagmometer or drop pipette used for
Drop Weight and Drop Count Method
Drop weight and drop count formula
W = γ2πr
Vρ = γ 2πr
This method is used to measure Surface and Interfacial tensions.It is convenient for rapid determination of small samples.
Ring Detachment Method (Du Noüy Ring)
Ring Detachment Method formula
F = γ 2π(r1+r2)
r1 is the same as r2, when correction factor is added
γ, Surface tension = Dial reading in dynes/2x ring circumference X correction factor
γ = F/4πr x correction factor
In Ring Detachment Method how are the liquids poured for interfacial tension determination
For interfacial tension the denser liquid is poured first into the vessel and the lighter one poured on top with the ring at the interface
How do sugar, in organic salts, alcohols and surfactants affect surface tension
Sugars: have little or no effect.
Inorganic salts: increase surface tension
Alcohols: prgressively decreases surface tension
Surfactants: decrease surface tension
How does temp affect surface tension
Surface tension is dependent on temperature. The general trend is that surface tension
decreases with the increase of temperature.
an adsorption process in which there is intimate contact of a liquid phase with a solid phase.
Wetting phenomena
Water wets clean glass but does not wet wax.
True/ False
True
Applications of string in pharmacy
•Preparation of suspensions and emulsions.
●In the process of granulation, powders are mixed with liquid binders.
●Film coating requires the wetting of liquids over the surface of tablets.
•Dissolution of tablets
What is contact angle
Contact angle is defined as angle between the liquid droplet and the surface over which it spreads
If the contact angle is lower than 90 or greater than 90 what does it mean
If the contact angle is lower than 90o, the solid is termed wettable.
If the contact angle is higher than 90o, the solid is non-wettable.
A contact angle equal to zero (0) indicates complete wettability
substances that absorb to surfaces or interfaces, causing a marked decrease in the surface tension
Surfactants
Are surfactants amphiphilic?
Yes
What are the two groups in a surfactant
hydrophobic group that has no affinity for aqueous solvents
a hydrophilic group that has an affinity for water.
A quantitative measure of wetting
Spreading co efficient
the energy difference between the solid substrate with the contacting gas and liquid phases.
Spreading coefficient,
If your spreading co efficient is less than zero what does it mean
Your liquid is not wettable
Formula for cohesive, adhesive and the spreadabilty of two liquids
cohesive forces
Wc = 2γL
adhesive forces)
Wa = γL + γS – γLS
γS = interfacial tension of sublayer
γLS = interfacial tension of solid/liquid interface
Spreading Coefficient (S) = Wa – Wc
When a thin layer of Liquid L1 is being spread over a second Liquid L2 as substrate
What is the spreadability formula
SL1/L2 = γL2 – (γL1L2 + γL1)
Adsorbed materials are divided into two groups
What are they
Those that form soluble monolayers and those that form insoluble films.
What forms monomolecular layers at interface of disperse and continuous phases
Surfactants
What forms multimolecular layers around droplets of the disperse phase
Hydrophilic colloids, (protective colloids)
What do hydrophilic colloids in emulsions do
Their primary function is to physically block coalescence via film formation( multimolecular layers)
Since they are generally high molecular weight, water soluble polymers, they increase the viscosity of the continuous phase and reduce the mobility of the dispersed particles.
How are surfactants classified
ionic (cationic, anionic, amphiphilic) or nonionic.
Egs of ionic surfactants
quaternary ammonium compound: ，such as Benzalkonium chloride and Benzalkonium bromide.
.amine salt: [RNH3+]X- ，[R2NH2+]X-
Notes: 1. toxic, used only as antiseptics; 2. incompatible with anionic surfactants and polyvalent anions ; 3. unstable at high pH
Egs of anionic surfactants
Salts of higher fatty acids (soaps) Sodium dodecyl sulfate (SDS), Sodium lauryl sulphate (SLS) (widely used to produce o/w emulsions). •Sodium glycocholate •Sodium taurocholate •Alkylbenzene sulfonates (detergents)
What are amphiphilic surfactants
Amphiphilic surfactants
•• This type of surfactant possesses both positively and negatively charged groups depending on the pH of the system. They are cationic at low pH and anionic at high pH.
Egs ;Lecithin
What ionic surfactant is less toxic
Amphiphilic
●Polyhydric alcohol: Tweens, Span
●Polyoxyethylene
●Pluronic (Poloxamer)
●Sucrose esters (SE)
Examples of nonionic surfactants
A non ionic surfactant Produced by the esterification of one or more of the hydroxyl groups of sorbitan with either lauric, palmitic or stearic acid.
Spans
What is the application of spans as surfactants
APPLICATION
:This range of surfactants exhibits lipophilic properties and tends to form w/o emulsions.
polyoxyethylene fatty acid esters eg. Polyoxyethylene 40 stearate is a water- soluble material often used with stearyl alcohol to give o/w emulsions.
Myrj surfactants
polyoxyethylene fatty ethers which are condensation products of polyethylene glycol and fatty alcohols, usually cetyl or cetostearyl,
Brijj surfactants
What is Poloxamer 188 (F68) used for
used as emulsifying agents for intravenous fat emulsions.
It comprises a very large group of compounds with Mw 1000- 14000, HLB value is 0.5~30;
Polyoxyethylene surfactants
What is critical Michelle concentration
CMC: Concentration of surfactants at which micelles are formed.
spherical structure with the hydrophobic ends inside the sphere with the hydrophilic ends on the outer surface of the sphere,
Micelle
What is HLB used for
surfactants contain both hydrophilic groups and lipophilic groups with one or the other being more predominant Hlb is used to find the ratio of these
It is a value between 0-40 defining the affinity of a surfactant for water or oil.
HLB value
What is the HLB for non-ionic surfactants
What does HLB< 10 mean and HLB > 10 mean
HLB value of non-ionic surfactants ranges from 0-20.
HLB numbers >10 have an affinity for water (hydrophilic)
and number <10 have an affinity of oil (lipophilic).
.
What is the HLB Value for
w/o emulsifier, o/w emulsifier, Detergent , Solubilizer , wetting agent, anti foaming agent
0 – 3
Antifoaming
4 – 6
w/o emulsifier
7 – 9
Wetting agent
8 – 18
o/w emulsifier
13 – 15
Detergent
10 - 18
Solubilizer
What is the formula for finding HLB value
HLB = 20 [1- (S/A)]
•Where
◦S = Saponification Number of ester.
◦A = Acid number of the fatty acid
What is the HLB value formula when sap value can’t be obtained
HLB = (E + P)/5
- where
- • E = % w/w of oxyethylene chains.
- • P = % w/w of polyhydric alcohol group in the molecules (glycerol, sorbitol).
What is the formula for HLB using Davies calculation( Table)
HLB = Σ(hydrophilic group No.) – Σ(lipophilic group No.) + 7
If the hydrophilic portion of the SAA molecule consists only of oxyethylene groups then ….what is the HLB formula
HLB= E/5
Medicinal application of SAA
- As antimicrobials
- • Quaternary ammonium compounds e.g. cetrimide and benzalkonium chloride have antibacterial properties and used as;
- • Disinfectants for instruments and skin, antibacterial creams, and throat lozenges.
- As expectorant; removal of mucus from the respiratory tract in case of bronchial asthma and bronchitis
- • The inhalation of SAA promote wetting and softening of the hardened mucus facilitating its removal.
- • 3. As cleansing agents; On human skin:
- • Repeated contact between the skin and certain detergent solutions may causes skin irritation and dry skin.
Pharmaceutical application of SAA
- As solubilizing agents;
•for poorly soluble drugs such as oil soluble vitamins, volatile oils, hormones,…
•e.g., Vitamine A is unpalatable if taken in form of fish liver oil but is palatable when administered in form of o/w emulsion or as solubilized system in water. Such solubilized systems are more resistant to oxidation than oily solution.
•2. As wetting agents
•Hydrophobic powder form aggregates and float on the surface of water. Surfactants (wetting agents) increase the affinity of hydrophobic powder for water by reducing the interfacial tension between the solid-liquid and facilitated the formation of uniform suspension of hydrophobic powder.
67
As flocculating agents
•In flocculated suspension
•• The individual particles are of mixed charges, thus attraction between them will tend to collect into flocs and flocculated suspension is produced. The flocculated particles settle rapidly but do not form hard cake.
•• Ionic SAA causes flocculation by neutralizing the charge on each particle.
•As emulsifying agents
• E.g., spans and tweens and natural occurring emulsifying agents as acacia and tragacanth. To form o/w or w/o emulsions.
• As additive in semi-solid preparation;
• To increase the capacity of ointment bases to take up aqueous liquids by addition of SAA.
• To enhance the release of drugs from ointments bases and so
enhance the drug absorption by the skin.
What is adsorption
process that occurs when molecules of a gas or liquid accumulates on the surface of a solid or liquid (adsorbent), forming a molecular or atomic film (adsorbate).
What is coverage
- a measure of the extent of adsorption of a species onto a surface.
Egs of absorbent and uses
Alumina (Aluminium oxide) (drying)
•Silica gel (Silicon dioxide) (drying)
•Zeolite molecular sieves (Aluminium silicate)
(gas & liquid separations, drying)
•Active carbon (gas & liquid separations, guard beds)
•Carbon molecular sieves (drying)
•Impregnated carbons (Cu-chlorides - CO separation)
•Clays (natural and pillared clays)
•Resins, polymers (biological, ions, large molecules)
What is the difference between the two types of adsorption
Physisorption and chemisorption according to
Bonding
Enthalpy
Nature
Surface specificity
Saturation
Bonding
P-WEAK, LONG RANGE
Van der Waals interactions (e.g. London dispersion, dipole-dipole)..
C-STRONG, SHORT RANGE
Chemical bonding involving orbital overlap and charge transfer.
Saturation
P-Multi-layer
C-Mono-layer
Nature
P-Reversible.
C-Mostly Irreversible
Surface specificity
P-No
C- Yes
Enthalpy
P-5-50 kJ mol-1
C- 40-800 kJ mol-1
Factors which affect absorption
Nature of adsorbate (gas) and adsorbent (solid): easily liquified gases are easily adsorbed to a greater extent (CO2 NH3, Cl2, SO2 ) than the elemental gases (H2, N2, O2, He). Porous and finely powdered solids adsorb more than non-porous.
•Surface area of the adsorbent.
- Pressure of the adsorbate gas.
- Temperature of the system
Pharmaceutical uses of absorption
Chromatographic techniques
- Removal of unwanted materials
- Use of activated charcoal in the removal of toxins or poisons from the body (orally)
- Use of adsorbents in haemodialysis to remove the products of dialysis from dialysing solution.
- Problems in formulations where drugs or other materials such as preservatives are adsorbed by containers.
- The adsorption of insulin onto intravenous administration sets.
