Solid State of matter,
Crystalline, Amorphous & Polymorphism Forms,
Classification of solid state of matter On the basis of Internal Structure,
PHYSICAL PHARMACEUTICS-I,
Habet,
B.Pharm,
R. VIJAYAKUMAR., M Pharm,
Research Scholar
department of Pharmaceutical Technology.
Anna university- BIT
Tiruchirappalli
III Semester.
UNIT-IV / Micromeritics
Preformulation Studies: Introduction to preformulation, goals and objectives, study of
physicochemical characteristics of drug substances.
a. Physical properties: Physical form (crystal & amorphous), particle size, shape, flow
properties, solubility profile (pKa, pH, partition coefficient), polymorphism.
b. Chemical Properties: Hydrolysis, oxidation, reduction, racemisation, polymerization
BCS classification of drugs & its significant
Application of preformulation considerations in the development of solid, liquid oral and
parenteral dosage forms and its impact on stability of dosage forms.
Solid State of matter,
Crystalline, Amorphous & Polymorphism Forms,
Classification of solid state of matter On the basis of Internal Structure,
PHYSICAL PHARMACEUTICS-I,
Habet,
B.Pharm,
R. VIJAYAKUMAR., M Pharm,
Research Scholar
department of Pharmaceutical Technology.
Anna university- BIT
Tiruchirappalli
III Semester.
UNIT-IV / Micromeritics
Preformulation Studies: Introduction to preformulation, goals and objectives, study of
physicochemical characteristics of drug substances.
a. Physical properties: Physical form (crystal & amorphous), particle size, shape, flow
properties, solubility profile (pKa, pH, partition coefficient), polymorphism.
b. Chemical Properties: Hydrolysis, oxidation, reduction, racemisation, polymerization
BCS classification of drugs & its significant
Application of preformulation considerations in the development of solid, liquid oral and
parenteral dosage forms and its impact on stability of dosage forms.
The following presentation is only for quick reference. I would advise you to read the theoretical aspects of the respective topic and then use this presentation for your last minute revision. I hope it helps you..!!
Mayur D. Chauhan
Definition
Application
Difference between molecular and Colloidal dispersion
Characteristics of dispersed phase
Classification of colloidal dispersion
Purification of colloidal dispersion
A pharmaceutical suspension is a coarse dispersion of insoluble solid particles in a liquid medium. ... However, it is difficult and also impractical to impose a sharp boundary between the suspensions and the dispersions having finer particles. Suspensions are an important class of pharmaceutical dosage forms
Dispersion system
suspensions
interfacial properties of suspensions
zeta potential
Sedimentation parameters
Settling in suspension
Formulation of suspension
Preparation of suspension
For more such informative content, go to https://scifitechify.blogspot.com/. Surface chemistry presentation will provide lots of valuable information about its day-to-day applications in real life. It explains concepts of adsorption, absorption, activation energy, Arrhenius equation, colloids, solutions, chemical processes etc.
It also elaborates on specific chemical reactions like peptisation reaction.
Introduction
Definition
Features desired in pharmaceutical suspension
Advantage/Disadvantages of pharmaceutical suspension
Flocculated and deflocculated suspension
Interfacial properties of suspending particles
Settling in suspensions
Effect of Brownian movement,
Sedimentation of flocculated particles,
Sedimentation parameters
Formulation of suspensions
Wetting of Particles,
Controlled flocculation,
Flocculation in structured vehicle
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Ve...kevinkariuki227
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
TEST BANK for Operations Management, 14th Edition by William J. Stevenson, Verified Chapters 1 - 19, Complete Newest Version.pdf
These lecture slides, by Dr Sidra Arshad, offer a quick overview of physiological basis of a normal electrocardiogram.
Learning objectives:
1. Define an electrocardiogram (ECG) and electrocardiography
2. Describe how dipoles generated by the heart produce the waveforms of the ECG
3. Describe the components of a normal electrocardiogram of a typical bipolar leads (limb II)
4. Differentiate between intervals and segments
5. Enlist some common indications for obtaining an ECG
Study Resources:
1. Chapter 11, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 9, Human Physiology - From Cells to Systems, Lauralee Sherwood, 9th edition
3. Chapter 29, Ganong’s Review of Medical Physiology, 26th edition
4. Electrocardiogram, StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK549803/
5. ECG in Medical Practice by ABM Abdullah, 4th edition
6. ECG Basics, http://www.nataliescasebook.com/tag/e-c-g-basics
Ethanol (CH3CH2OH), or beverage alcohol, is a two-carbon alcohol
that is rapidly distributed in the body and brain. Ethanol alters many
neurochemical systems and has rewarding and addictive properties. It
is the oldest recreational drug and likely contributes to more morbidity,
mortality, and public health costs than all illicit drugs combined. The
5th edition of the Diagnostic and Statistical Manual of Mental Disorders
(DSM-5) integrates alcohol abuse and alcohol dependence into a single
disorder called alcohol use disorder (AUD), with mild, moderate,
and severe subclassifications (American Psychiatric Association, 2013).
In the DSM-5, all types of substance abuse and dependence have been
combined into a single substance use disorder (SUD) on a continuum
from mild to severe. A diagnosis of AUD requires that at least two of
the 11 DSM-5 behaviors be present within a 12-month period (mild
AUD: 2–3 criteria; moderate AUD: 4–5 criteria; severe AUD: 6–11 criteria).
The four main behavioral effects of AUD are impaired control over
drinking, negative social consequences, risky use, and altered physiological
effects (tolerance, withdrawal). This chapter presents an overview
of the prevalence and harmful consequences of AUD in the U.S.,
the systemic nature of the disease, neurocircuitry and stages of AUD,
comorbidities, fetal alcohol spectrum disorders, genetic risk factors, and
pharmacotherapies for AUD.
New Drug Discovery and Development .....NEHA GUPTA
The "New Drug Discovery and Development" process involves the identification, design, testing, and manufacturing of novel pharmaceutical compounds with the aim of introducing new and improved treatments for various medical conditions. This comprehensive endeavor encompasses various stages, including target identification, preclinical studies, clinical trials, regulatory approval, and post-market surveillance. It involves multidisciplinary collaboration among scientists, researchers, clinicians, regulatory experts, and pharmaceutical companies to bring innovative therapies to market and address unmet medical needs.
Title: Sense of Taste
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the structure and function of taste buds.
Describe the relationship between the taste threshold and taste index of common substances.
Explain the chemical basis and signal transduction of taste perception for each type of primary taste sensation.
Recognize different abnormalities of taste perception and their causes.
Key Topics:
Significance of Taste Sensation:
Differentiation between pleasant and harmful food
Influence on behavior
Selection of food based on metabolic needs
Receptors of Taste:
Taste buds on the tongue
Influence of sense of smell, texture of food, and pain stimulation (e.g., by pepper)
Primary and Secondary Taste Sensations:
Primary taste sensations: Sweet, Sour, Salty, Bitter, Umami
Chemical basis and signal transduction mechanisms for each taste
Taste Threshold and Index:
Taste threshold values for Sweet (sucrose), Salty (NaCl), Sour (HCl), and Bitter (Quinine)
Taste index relationship: Inversely proportional to taste threshold
Taste Blindness:
Inability to taste certain substances, particularly thiourea compounds
Example: Phenylthiocarbamide
Structure and Function of Taste Buds:
Composition: Epithelial cells, Sustentacular/Supporting cells, Taste cells, Basal cells
Features: Taste pores, Taste hairs/microvilli, and Taste nerve fibers
Location of Taste Buds:
Found in papillae of the tongue (Fungiform, Circumvallate, Foliate)
Also present on the palate, tonsillar pillars, epiglottis, and proximal esophagus
Mechanism of Taste Stimulation:
Interaction of taste substances with receptors on microvilli
Signal transduction pathways for Umami, Sweet, Bitter, Sour, and Salty tastes
Taste Sensitivity and Adaptation:
Decrease in sensitivity with age
Rapid adaptation of taste sensation
Role of Saliva in Taste:
Dissolution of tastants to reach receptors
Washing away the stimulus
Taste Preferences and Aversions:
Mechanisms behind taste preference and aversion
Influence of receptors and neural pathways
Impact of Sensory Nerve Damage:
Degeneration of taste buds if the sensory nerve fiber is cut
Abnormalities of Taste Detection:
Conditions: Ageusia, Hypogeusia, Dysgeusia (parageusia)
Causes: Nerve damage, neurological disorders, infections, poor oral hygiene, adverse drug effects, deficiencies, aging, tobacco use, altered neurotransmitter levels
Neurotransmitters and Taste Threshold:
Effects of serotonin (5-HT) and norepinephrine (NE) on taste sensitivity
Supertasters:
25% of the population with heightened sensitivity to taste, especially bitterness
Increased number of fungiform papillae
Flu Vaccine Alert in Bangalore Karnatakaaddon Scans
As flu season approaches, health officials in Bangalore, Karnataka, are urging residents to get their flu vaccinations. The seasonal flu, while common, can lead to severe health complications, particularly for vulnerable populations such as young children, the elderly, and those with underlying health conditions.
Dr. Vidisha Kumari, a leading epidemiologist in Bangalore, emphasizes the importance of getting vaccinated. "The flu vaccine is our best defense against the influenza virus. It not only protects individuals but also helps prevent the spread of the virus in our communities," he says.
This year, the flu season is expected to coincide with a potential increase in other respiratory illnesses. The Karnataka Health Department has launched an awareness campaign highlighting the significance of flu vaccinations. They have set up multiple vaccination centers across Bangalore, making it convenient for residents to receive their shots.
To encourage widespread vaccination, the government is also collaborating with local schools, workplaces, and community centers to facilitate vaccination drives. Special attention is being given to ensuring that the vaccine is accessible to all, including marginalized communities who may have limited access to healthcare.
Residents are reminded that the flu vaccine is safe and effective. Common side effects are mild and may include soreness at the injection site, mild fever, or muscle aches. These side effects are generally short-lived and far less severe than the flu itself.
Healthcare providers are also stressing the importance of continuing COVID-19 precautions. Wearing masks, practicing good hand hygiene, and maintaining social distancing are still crucial, especially in crowded places.
Protect yourself and your loved ones by getting vaccinated. Together, we can help keep Bangalore healthy and safe this flu season. For more information on vaccination centers and schedules, residents can visit the Karnataka Health Department’s official website or follow their social media pages.
Stay informed, stay safe, and get your flu shot today!
ARTIFICIAL INTELLIGENCE IN HEALTHCARE.pdfAnujkumaranit
Artificial intelligence (AI) refers to the simulation of human intelligence processes by machines, especially computer systems. It encompasses tasks such as learning, reasoning, problem-solving, perception, and language understanding. AI technologies are revolutionizing various fields, from healthcare to finance, by enabling machines to perform tasks that typically require human intelligence.
Explore natural remedies for syphilis treatment in Singapore. Discover alternative therapies, herbal remedies, and lifestyle changes that may complement conventional treatments. Learn about holistic approaches to managing syphilis symptoms and supporting overall health.
New Directions in Targeted Therapeutic Approaches for Older Adults With Mantl...i3 Health
i3 Health is pleased to make the speaker slides from this activity available for use as a non-accredited self-study or teaching resource.
This slide deck presented by Dr. Kami Maddocks, Professor-Clinical in the Division of Hematology and
Associate Division Director for Ambulatory Operations
The Ohio State University Comprehensive Cancer Center, will provide insight into new directions in targeted therapeutic approaches for older adults with mantle cell lymphoma.
STATEMENT OF NEED
Mantle cell lymphoma (MCL) is a rare, aggressive B-cell non-Hodgkin lymphoma (NHL) accounting for 5% to 7% of all lymphomas. Its prognosis ranges from indolent disease that does not require treatment for years to very aggressive disease, which is associated with poor survival (Silkenstedt et al, 2021). Typically, MCL is diagnosed at advanced stage and in older patients who cannot tolerate intensive therapy (NCCN, 2022). Although recent advances have slightly increased remission rates, recurrence and relapse remain very common, leading to a median overall survival between 3 and 6 years (LLS, 2021). Though there are several effective options, progress is still needed towards establishing an accepted frontline approach for MCL (Castellino et al, 2022). Treatment selection and management of MCL are complicated by the heterogeneity of prognosis, advanced age and comorbidities of patients, and lack of an established standard approach for treatment, making it vital that clinicians be familiar with the latest research and advances in this area. In this activity chaired by Michael Wang, MD, Professor in the Department of Lymphoma & Myeloma at MD Anderson Cancer Center, expert faculty will discuss prognostic factors informing treatment, the promising results of recent trials in new therapeutic approaches, and the implications of treatment resistance in therapeutic selection for MCL.
Target Audience
Hematology/oncology fellows, attending faculty, and other health care professionals involved in the treatment of patients with mantle cell lymphoma (MCL).
Learning Objectives
1.) Identify clinical and biological prognostic factors that can guide treatment decision making for older adults with MCL
2.) Evaluate emerging data on targeted therapeutic approaches for treatment-naive and relapsed/refractory MCL and their applicability to older adults
3.) Assess mechanisms of resistance to targeted therapies for MCL and their implications for treatment selection
Knee anatomy and clinical tests 2024.pdfvimalpl1234
This includes all relevant anatomy and clinical tests compiled from standard textbooks, Campbell,netter etc..It is comprehensive and best suited for orthopaedicians and orthopaedic residents.
Title: Sense of Smell
Presenter: Dr. Faiza, Assistant Professor of Physiology
Qualifications:
MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology
ICMT, CHPE, DHPE (STMU)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)
Learning Objectives:
Describe the primary categories of smells and the concept of odor blindness.
Explain the structure and location of the olfactory membrane and mucosa, including the types and roles of cells involved in olfaction.
Describe the pathway and mechanisms of olfactory signal transmission from the olfactory receptors to the brain.
Illustrate the biochemical cascade triggered by odorant binding to olfactory receptors, including the role of G-proteins and second messengers in generating an action potential.
Identify different types of olfactory disorders such as anosmia, hyposmia, hyperosmia, and dysosmia, including their potential causes.
Key Topics:
Olfactory Genes:
3% of the human genome accounts for olfactory genes.
400 genes for odorant receptors.
Olfactory Membrane:
Located in the superior part of the nasal cavity.
Medially: Folds downward along the superior septum.
Laterally: Folds over the superior turbinate and upper surface of the middle turbinate.
Total surface area: 5-10 square centimeters.
Olfactory Mucosa:
Olfactory Cells: Bipolar nerve cells derived from the CNS (100 million), with 4-25 olfactory cilia per cell.
Sustentacular Cells: Produce mucus and maintain ionic and molecular environment.
Basal Cells: Replace worn-out olfactory cells with an average lifespan of 1-2 months.
Bowman’s Gland: Secretes mucus.
Stimulation of Olfactory Cells:
Odorant dissolves in mucus and attaches to receptors on olfactory cilia.
Involves a cascade effect through G-proteins and second messengers, leading to depolarization and action potential generation in the olfactory nerve.
Quality of a Good Odorant:
Small (3-20 Carbon atoms), volatile, water-soluble, and lipid-soluble.
Facilitated by odorant-binding proteins in mucus.
Membrane Potential and Action Potential:
Resting membrane potential: -55mV.
Action potential frequency in the olfactory nerve increases with odorant strength.
Adaptation Towards the Sense of Smell:
Rapid adaptation within the first second, with further slow adaptation.
Psychological adaptation greater than receptor adaptation, involving feedback inhibition from the central nervous system.
Primary Sensations of Smell:
Camphoraceous, Musky, Floral, Pepperminty, Ethereal, Pungent, Putrid.
Odor Detection Threshold:
Examples: Hydrogen sulfide (0.0005 ppm), Methyl-mercaptan (0.002 ppm).
Some toxic substances are odorless at lethal concentrations.
Characteristics of Smell:
Odor blindness for single substances due to lack of appropriate receptor protein.
Behavioral and emotional influences of smell.
Transmission of Olfactory Signals:
From olfactory cells to glomeruli in the olfactory bulb, involving lateral inhibition.
Primitive, less old, and new olfactory systems with different path
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Tom Selleck Health: A Comprehensive Look at the Iconic Actor’s Wellness Journeygreendigital
Tom Selleck, an enduring figure in Hollywood. has captivated audiences for decades with his rugged charm, iconic moustache. and memorable roles in television and film. From his breakout role as Thomas Magnum in Magnum P.I. to his current portrayal of Frank Reagan in Blue Bloods. Selleck's career has spanned over 50 years. But beyond his professional achievements. fans have often been curious about Tom Selleck Health. especially as he has aged in the public eye.
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Introduction
Many have been interested in Tom Selleck health. not only because of his enduring presence on screen but also because of the challenges. and lifestyle choices he has faced and made over the years. This article delves into the various aspects of Tom Selleck health. exploring his fitness regimen, diet, mental health. and the challenges he has encountered as he ages. We'll look at how he maintains his well-being. the health issues he has faced, and his approach to ageing .
Early Life and Career
Childhood and Athletic Beginnings
Tom Selleck was born on January 29, 1945, in Detroit, Michigan, and grew up in Sherman Oaks, California. From an early age, he was involved in sports, particularly basketball. which played a significant role in his physical development. His athletic pursuits continued into college. where he attended the University of Southern California (USC) on a basketball scholarship. This early involvement in sports laid a strong foundation for his physical health and disciplined lifestyle.
Transition to Acting
Selleck's transition from an athlete to an actor came with its physical demands. His first significant role in "Magnum P.I." required him to perform various stunts and maintain a fit appearance. This role, which he played from 1980 to 1988. necessitated a rigorous fitness routine to meet the show's demands. setting the stage for his long-term commitment to health and wellness.
Fitness Regimen
Workout Routine
Tom Selleck health and fitness regimen has evolved. adapting to his changing roles and age. During his "Magnum, P.I." days. Selleck's workouts were intense and focused on building and maintaining muscle mass. His routine included weightlifting, cardiovascular exercises. and specific training for the stunts he performed on the show.
Selleck adjusted his fitness routine as he aged to suit his body's needs. Today, his workouts focus on maintaining flexibility, strength, and cardiovascular health. He incorporates low-impact exercises such as swimming, walking, and light weightlifting. This balanced approach helps him stay fit without putting undue strain on his joints and muscles.
Importance of Flexibility and Mobility
In recent years, Selleck has emphasized the importance of flexibility and mobility in his fitness regimen. Understanding the natural decline in muscle mass and joint flexibility with age. he includes stretching and yoga in his routine. These practices help prevent injuries, improve posture, and maintain mobilit
2. Contents
• Introduction
• Characteristics of suspension
• Surface and interfacial phenomenon
• Particle interaction
• Electrical properties of interface
• DLVO theory
• Wetting
• Adsorption
• Instabilities and stability concept
• Formulation additives 2
3. What is a suspension?
• A pharmaceutical suspension is a coarse
dispersion in which insoluble solid
particles are dispersed in a liquid medium.
• The particles have a diameter for most
part greater than 0.1µm.
• A suspension is a system that generally
consists of two phases of matter, although
number of components can be higher.
3
4. Dispersed phase and dispersion
media
• Dispersed refers to the suspended particle
and dispersion media refers to the vehicle
or liquid in which the particles are
suspended.
4
5. Characteristics of suspensions.
• Suspension should have optimum physical, chemical, and
pharmacological properties.
• Other concerns are;
a. Particle size distribution.
b. Specific surface area
c. Inhibition of crystal growth.
d. Changes in polymeric form
e. Sedimentation rate.
f. Flocculation
g. Solid liquid interface
a. Wetting
b. Contact angle
c. adsorption 5
6. Particle shape and distribution
analysis.
• Particles can exist in various shapes and geometry. The
most common shapes are spheres, cylinders, rods,
needles, and various crystalline shapes.
• Shape can be the factor in understanding the packaging
of sediment and settling characteristics.
• The size as well as their shape can influence on the
prospects for reversible change.
• Attraction between two dispersed particles will be
affected by the surface characteristics of the particles.
• Particles have the ability to exert attractive forces across
large surface will most likely result in greater attraction
and adhesion.
6
7. Contd……
• The particle shape of the suspended particles
(suspensoids) may have an impact on the packing of
sediment (e.g., packing density and settling
characteristics), and thus product’s resuspendability and
stability.
• Packing density is defined as the weight to volume ratio
of the sediment at equilibrium.
• A wide particle size distribution often results in a high-
density suspension, whereas widely differing particle
shapes (e.g., plates, needles, filaments, and prisms)
often produce low density slurries. Symmetrical barrel-
shaped particles of calcium carbonate were found to
produce stable suspensions without caking upon
storage, while asymmetric needle-shaped particles
formed a tenacious sediment cake, which could not be
easily redispersed
7
8. Particle size
• Suspension having particle size greater than
1µm diameter are coarse suspension whereas
suspensions having particle size less than 1µm
are colloidal suspension.
• Determination of particle size
– Optical microscopy
– Sieving
– Sedimentation rate method
– Light energy diffraction.
– Laser holography
– Cascade impaction
– Coulter counter method.
8
9. Contd…..
• Certain types of dosage forms require specific size
ranges; for example, suspension aerosols delivering
drugs into the respiratory tract should contain particles in
the order of 0.5 to 5 mm and no particles larger than 10
mm.
• The particle size data can be presented by graphical and
digital methods. When the number or weight of particles
lying within a certain size range is plotted against the
size range or mean particle size, a bar graph (histogram)
or a frequency distribution curve is obtained
• Alternatively, the cumulative percentage over or under a
particular size can be plotted against the particle size.
This results in a typical sigmoidal curve called
cumulative frequency plot. From these data, the mean
particle size, standard deviation, and the extent of
polydispersity may be determined.
9
10. Settling of suspension
• One aspect of physical stability is concerned with keeping
the particles uniformly distributed throughout the
suspensions.
• where:
• g is the gravitational field strength (m/s2)
• R is the radius of the spherical particle (m)
• ρp is the mass density of the particles (kg/m3)
• ρm is the mass density of the fluid (kg/m3)
• μ is the dynamic viscosity (kg/m*s).
10
11. Methods to determine settling
• Andreason pipette method
• Photo sedimentation-transmittance of light
is measured
• Cahn sedimentation method
• Centrifugal method- for particle size less
than 5micrometer
11
12. • In a typical particle size analysis 3 factors
require calculation
1. Sedimentation time
2. Centrifugation time
3. Cumulative percent finer
12
13. Surface and interfacial
phenomenon
• One of the most obvious properties of a disperse system
is the vast interfacial area that exists between the
dispersed phase and the dispersion medium .
• When considering the surface and interfacial properties
of the dispersed particles, two factors must be taken into
account: the first relates to an increase in the surface
free energy as the particle size is reduced and the
specific surface increased;
• the second deals with the presence of an electrical
charge on the particle surface.
13
14. The interface
• An interface is defined as a boundary
between two phases. The solid-liquid and
the liquid-liquid interfaces are of primary
interest in suspensions and emulsions,
respectively.
• A large surface area of the dispersed
particles is associated with a high surface
free energy that renders the system
thermodynamically unstable.
14
15. • The surface free energy, ΔG, can be
calculated from the total surface area, ΔA,
as follows:
• ΔG =γsl ΔA or ΔG= γLL ΔA
• where γsl and γLL are the interfacial
tensions between the solid particles and
the liquid medium and the liquid and liquid
mediums, respectively.
15
16. • Very small dispersed particles are highly
energetic. To approach a stable state, they
tend to regroup themselves to reduce the
surface free energy of the system. An
equilibrium will be reached when ΔG =0.
This condition may be accomplished either
by a reduction of the interfacial tension or
by a decrease of the total surface area.
16
17. PARTICLE INTERACTION
• The interactions between similar particles,
dissimilar particles, and the dispersion medium
constitute a complex but essential part of
dispersion technology. Such interparticle
interactions include both attractive and repulsive
forces.
• These forces depend upon the nature, size, and
orientation of the species as well as on the
distance of separation between and among the
particles of the dispersed phase and the
dispersion medium, respectively.
17
18. Contd……
• As the particles approach one another,
both attractive and repulsive forces are
operative. If the attractive forces prevail,
agglomerates result, indicating an
instability in the system.
• If repulsive forces dominate, a
homogeneously dispersed or stable
dispersion remains.
18
20. Types of forces existing betweem
the particles
• Various types of attractive interactions are
operating:
I. dipole-dipole or Keesom orientation forces,
II. dipole-induced dipole or Debye induction
forces,
III. induced dipole-induced dipole or London
dispersion forces,
IV. electrostatic forces between charged particles.
V.Vander waal’s forces of attraction.
20
21. Contd ……..
• . The strongest forces are the electrostatic interactions
between charged particles. These forces, either
attractive or repulsive, are effective over a relatively long
range and dependent on the ionic charge and size of the
particle.
• Even though vander waals forces are relatively weak,
the van der Waals forces coupled with hydrogen bond
interactions are significant factors describing the
behavior of most nonionic compounds in liquids and
other dispersion media. These various types of attractive
interparticulate forces can lead to the instabilities of
disperse systems
21
22. Electrical properties of the
interfaces
• Most insoluble materials, either solids or liquids, develop
a surface charge when dispersed within an aqueous
medium. These surface charges of particles may arise
from several mechanisms.
• For example, the ionization of functional groups present
at the surface of the particle, such as carboxylic acid or
amine groups, can be involved.
• Furthermore, surface charges can be developed due to
the adsorption or desorption of protons.
• A variety of colloidal systems (e.g., polymers, metal
oxides) fall into this group. For example, the surface
hydroxyl groups of aluminum hydroxide gel
22
23. CONTD…….
• Surface charges can also be introduced by ionic
surfactants. For example, oil globules in an o/w emulsion
exhibit a surface charge if anionic or cationic surface-
active agents are used.
• The surfactant molecules are oriented at the oil-water
interface so that the charged hydrophilic groups are
directed toward the water phase. Ion deficiencies in the
crystal lattice or interior of the particles may also cause
surface charges.
• When a charged particle is dispersed within a dispersion
medium containing dissolved cations and anions, the
surface charges of the particle interact with the dissolved
ions in solution.
23
24. DLVO THEORY
• Derjaguin, Landau, Verwey, and Overbeek developed a
theory giving insight into the energy of interaction
between suspended particles. This theory is thus often
referred to as the DLVO theory.
• It relates the stability of a disperse system to the
electrolyte content in the continuous phase and provides
an insight into the factors responsible for controlling the
rate at which particles in disperse systems come into
contact or aggregate.
• The process of aggregation subsequently accelerates
particle sedimentation and affects redispersibility of the
disperse systems
24
25. Schematic form of the curve of total potential energy
(Vtotal) against distance of surface separation (H) for
interaction between two particles, with Vtotal= VA + VR.
25
26. CONTD…
• According to the DLVO theory, disperse systems
become unstable whenever their kinetic energy is
sufficient to overcome the primary maximum. Thus, the
instability of disperse systems increases when
decreasing the height of this energy barrier and when
increasing the kinetic energy of the particles.
• The reduction of the primary maximum can result from
the addition of substances, which
• (i) neutralize the surface particle charge or cause the
loss of the hydration layer;
• (ii) compress the electric double layer; and/or
• (iii) cause adsorbed species (e.g., surfactants) to desorb
from the particle surface.
26
27. CONTD….
• . The primary factor determining the thickness of the
electric double layer is the potential energy drop-off. The
potential gradient strongly depends on the concentration
and charge of any electrolyte present in the dispersion
medium. In water at room temperature, the thickness of
the electric double layer ranges from 1 to 1000 A˚ ,
depending on the concentration of ions in the bulk
phase. Increasing electrolyte concentrations lead to
compressed double layers (decreasing double layer
thicknesses). Thus, the particles can approach each
other more closely, and the attractive forces become
more important. The concentration of foreign electrolytes
required to cause flocculation decreases as the valence
of the coagulating ion increases. For example, less Al3+
ions are required to flocculate a suspension than Na+
ions. 27
28. WETTING
• The wetting process is a primary concern particularly in
the preparation of a liquid disperse system in which the
internal phase is a solid (suspension).
• A solid material to be suspended must first be separated
into single particles, and the particles must be
individually wetted by the dispersion medium to achieve
a homogeneous distribution of the internal phase.
• Upon wetting, the air at the solid surface is replaced by
the liquid medium. Obviously, the tendency of a solid to
be wetted by a liquid is primarily determined by the
interaction between the three phases.
28
29. CONTD…
• Experimentally, the degree of wetting of a powder can be
evaluated by observing the contact angle, θ, which is
defined by the boundaries of the solid surface and the
tangent to the curvature of the liquid drop.
• The contact angle results from an equilibrium involving
three interfacial tensions: those acting at the interfaces
liquid-gas, solid-liquid, and solid-gas. A contact angle of
00 indicates an extensive interaction between the solid
and the liquid phase.
• Thus, the solid is completely wetted by the liquid. Partial
wetting occurs when the contact angles are between 00
and 90 0.In contrast, contact angles greater than 900 are
classified as nonwetting situations in which the liquid
cannot spread over the solid surface spontaneously. If
the angle is close to 1800, the solid substance is called
“unwettable” by the liquid.
29
30. CONTD….
• Hydrophilic substances are readily wetted by water or
other polar liquids because of the good interfacial
interaction resulting in small contact angles (Fig. 2).
Once dispersed, they may significantly increase the
viscosity of the liquid system. On the other hand,
hydrophobic substances repel water but can easily be
wetted by nonpolar liquids. They usually do not alter the
viscosity of aqueous systems. In pharmaceutical dosage
forms, aqueous vehicles or hydroalcoholic mixtures are
often used. Thus, proper wetting of hydrophobic drugs is
a necessary first step when preparing suspensions.
30
31. • Hydrophobic materials are often extremely difficult to
disperse owing to poor wetting or presence of entrained
air pockets, minute quantities of grease, and other
contaminants. The powder may just float on the surface
of the liquid, despite its higher density. Fine powders are
particularly susceptible to this effect, and they may fail to
become wetted even when mechanically forced below
the surface of the suspending medium.
• To overcome this problem, to improve the wetting
characteristics of hydrophobic drug powders, often
anionic or nonionic surfactants are used. These
substances decrease the solid-liquid interfacial tension,
thus facilitating the wetting process. The mechanism of
surfactant action involves the preferential adsorption of
the hydrophobic part of the surfactant onto the
hydrophobic surface of the particle. The polar part of the
surfactant is directed toward the aqueous medium. 31
32. Adsorption
• Adsorption is the tendency of atoms, molecules, ions,
etc. to locate at a particular surface/ interface in a
concentration that is different from the concentrations in
the surrounding bulk media.
• Adsorption at the interface tends to increase with
increasing thermodynamic activity of the surfactant in
solution, until a complete monolayer is formed at the
interface, or until the active sites are saturated with
surfactant molecules.
• The adsorption of surfactants alters the properties at the
interface and promotes wetting of the dispersed phase in
suspensions. The reduction of the interfacial tension can
effectively decrease the resulting surface free energy
and hence the tendency for coalescence or aggregation.
Thus, the formation and stabilization of the disperse
systems can be significantly facilitated.
32
33. • The adsorption of ionic surfactants generally
increases the charge density on the surface of
the dispersed particles, thus improving the
stability of the dispersion.
• Protective colloids or polymeric materials can be
adsorbed onto the surface of the dispersed
phase. Polymer adsorption can be accomplished
simply by adding a solution of adsorbable
polymeric species into a slurry of the dispersed
particles
33
35. • The content uniformity and long-term stability of
a pharmaceutical product are required for a
consistent and accurate dosing.
• Aggregation of dispersed particles and resulting
instabilities such as flocculation, sedimentation
(in suspensions), or creaming and coalescence
(in emulsions) often represent major challenges
in formulating pharmaceutical disperse systems.
35
36. • An instability of a dispersion may result from the
tendency of the system to reduce its surface free energy,
ΔG.
• “Flocculation” is generally understood as a process in
which particles are allowed to come together and form
loosely bound clusters, having an open type of structure.
• Deflocculation is the opposite, that is, breakdown of
clusters into individual particles.
• Although disperse systems are thermodynamically
unstable, certain systems can remain “stable” over a
prolonged period of time. Thermodynamically driven
changes to a lower energy state may be reversible or
irreversible.
36
37. • A disperse system remains stable as long as the
repulsive forces are sufficiently strong to
outweigh the van der Waals and/or other
attractive forces. These repulsive forces are
generally acquired through one or more of the
following mechanisms: (i) electrostatic Disperse
Systems repulsion, which arises from the
presence of an ionic charge on the surface of
the dispersed particles and (ii) steric repulsion,
which arises from the presence of uncharged
molecules on the surface of the particles.
37
38. Stabilization by Electrostatic
Repulsion
• The electrostatic repulsive forces can
prevent the dispersed particles having
surface charges of the same sign from
approaching each other, thus stabilizing
the dispersion against interparticle
attraction or coagulation.
38
39. • In suspensions, the addition of ions that are adsorbed
onto the surface of the dispersed particles generally
creates strong repulsion forces between suspended
particles and stabilizes the system.
• In contrast, the addition of water-miscible solvents (e.g.,
alcohols, glycerin, or propylene glycol) to aqueous
dispersions can lower the dielectric constant of the
medium.
• This results in a reduction of the thickness of the electric
double layer and the magnitude of the potential energy
barrier. Thus, the addition of these solvents tends to
cause instability or makes the system more sensitive to
coagulation 39
40. Stabilization by Steric
Repulsion
• When a strongly hydrated hydrophilic polymer is
adsorbed onto the surface of a hydrophobic solid particle
surrounded by an aqueous medium, the affinity of the
polymer for water can exceed the attractive forces
between the suspended particles. For example, a
hydrophilic polymer such as gelatin can increase the
strength of the protective hydration layer formed around
the dispersed particles. Water-soluble polymers, whose
adsorption stabilizes dispersions and protects them
against coagulation, are also called “protective colloids.”
• Adsorption of nonionic polymers (e.g., gums or water-
soluble cellulosic derivatives) or surfactants (e.g.,
polysorbate 80) of sufficient chain length can create
steric hindrance between adjacent particles 40