WAVE PARTICLE DUALITY

wave particle duality

What if I tell you, that you are a wave? Or that every single entity is a wave and a particle, and that too at the same time!! This is the statement of one of the most important principle of quantum mechanics, the wave particle duality. Quantum mechanics has wrapped away the old concept of wave and particles being entirely opposite entities, and incorporated them in such a way, that both of them are now actually one thing.

 HISTORY OF WAVE PARTICLE NATURE OF LIGHT

Humans have been trying to understand the nature of light from the very start of our existence. It was Greeks who first studied light in a scientifical way. Democritus stated that light is made up of subcomponents. Euclid gave the mechanism for certain phenomena of light. In 11th century , Arabic scientist Ibn al-Haytham wrote the first comprehensive Book of optics describing reflectionrefraction, and the operation of a pinhole lens via rays of light traveling from the point of emission to the eye.Isaac Newton championed the corpuscular nature of light . On the other hand Robert hook and Huygens developed the wave viewpoint of light .

Thomas young , through his famous double slit experiment, proved the wave nature of light. Maxwell developed his famous equation for light as an electromagnetic radiation.

Then , in 19th century , Max plank gave ideas of photons through experiments on black body radiation. Elbert Einstein took this idea to photoelectric effect and showed the particle like nature of light.

nature of light

THE DE BROGLIE’S HYPOTHESIS ON WAVE PARTICLE DUALITY

The scientifical world was spilt in two sides, one believing light to be wave and other believing it to be particles (photons). In 1924 , De Broglie proposed his hypothesis in his PHD thesis :

Electrons as well as all matter have both the wave and particle nature. The wavelength of wave associated with a particle is related to its momentum by the following relation:

λ = h/p = h/mv

where, λ is wavelength

h is planks constant, having value of 6.626176 x 10-34 joule-seconds.

m is mass of the object

v is the velocity  

According to this equation every object has a wavelength, but massive and slower (relative to speed of light) has wavelength so small that it is not observable.

de broglie hypothesis

Wavelength of a man

Suppose a 60 kg man is moving with a speed of 20 m/s. Then his wavelength would be:

Λ = (6.626176 x 10-34) / (60×20) = 5.52 × 10-37 m

This wavelength is too small to be observed. So, we don’t usually notice wave effects of massive objects.

Wavelength of an electron

 Now consider an electron of mass 9.1 × 10-31 kg moving with a speed of 5.93 × 106 m/s .The be Broglie wavelength comes out to be

Λ= = (6.626176 x 10-34) / (9.1 × 10-31 ×   5.93 × 106) = 1.22 × 10-10 m

This is in order of nanometer and can be observed.

wave particle nature of electron

EXPERIMENTAL EVIDENCE

In 1927 at Bell Labs, Clinton Davisson and Lester Germer fired slow-moving electrons at a crystalline nickel target. The angular dependence of the diffracted electron intensity was measured, and was determined to have the same diffraction pattern as those predicted by Bragg for x-rays. After this experiment , the de Broglie equation has been shown to apply to elementary particles, neutral atoms, and molecules as heavy as Buckyball’s .

A picture containing room experiment Description automatically generated

BOTTOM LINE

As confusing as it seems, quantum physics has helped us to see the reality in a completely different way. wave nature duality is yet another surprising idea that sort of defies our mind but understanding this idea will help us to gain a better knowledge of physics and ultimately a better knowledge of reality of the universe.  

Classification Of Polymers

There are many ways to classify polymers. Some of the classifications is specific to the use of the polymer, others deal with the synthesis of a polymer. These classifications are pertinent as this makes the study of polymers easier. Before classifying polymers, let’s classify materials.

We are done with the classification of materials, we will now select the section of the polymer from the realm of materials and classify them in different ways, to make it easy for different people to study it.

There are different criteria on which the polymers are classified. Some of them are:

  1. Intermolecular Interaction
  2. Skeletal Structure
  3. Type of mer involved
  4. Reaction mechanism 

Intermolecular Interaction

Based on intermolecular forces, polymers are divided into three; i.e.

  1. Thermoplastics
  2. Thermosets
  3. Elastomers

Thermoplastics are those polymers which soften and ultimately melt upon heating. These polymers show a rational behavior (as one may think) as common solids, i.e. their molecular motion increases as heat is added to them and after a certain amplitude of motion, the molecules are allowed to freely slide over each other (at melting point). The polymeric chains have stronger bonds and restricted motion at normal temperatures, when subjected to heat, the amplitude of the molecular motion increases resulting in lowering of intermolecular forces as a consequence of which polymer softens and ultimately melts.

Thermosets are those polymers which harden or cure upon heating. To explain this behaviour one needs to know about the term cross-linking. Cross-linking is the chemical bonding of two different chains of a polymer. In thermosets, as the polymer is heated, the kinetic energy of the chains increase and the potential sites in two different chains of the polymer reacts at this higher energy, forming new chemical bonds and thus hardens the polymer due to restricted movement of the polymeric chains.

Elastomers are polymers which are relatively flexible if compared to thermosets, and harder if compared to thermoplastics. They are three to ten times stretchable. They have lower cross-linking density, hence the flexible characteristic. These polymers have limited sites to crosslink hence the flexibility.

Skeletal Structure

Depending on the structure of the polymer, it is divided into three types:

  1. Straight Polymers
  2. Branched Polymers
  3. Network Polymers

Monomers react with each other in end to end fashion such that they form linear or straight chains of polymers. These monomers are known as straight polymers

When monomers react in a manner that branches are formed in the chains of the polymers, then those polymers are known as branched polymers.

When the monomers react to form a network, a 3-D structure, then those polymers are known as Network polymers.

Types of mer Involved

On the basis of monomer involved in the polymer, it is divided into three:

  1. Homopolymer
  2. Copolymer
  3. Blending Polymer

Homopolymers are those polymers which are formed by the same type of monomer. For example polyethylene. The entire polymer is made up of a single type of monomer i.e. ethylene.

Blending polymers are those polymers which are made of more than one type of monomers, but they are not chemically bonded. These kinds of polymers are used to enhance the strength of a polymeric membrane to withstand operating conditions.

Copolymers are those polymers which consist of more than one type of monomer, for example, polystyrene-butadiene rubber. Copolymers are further divided into four based on the arrangement of the monomeric units. The types are:

  1. Random Copolymer
  2. Alternate Copolymer
  3. Block Copolymer
  4. Graft Copolymer

In random copolymer, there is no order of arrangement of the attachment of two polymers, e.g. A-A-B-B-B-B-A-B-B-A-B-A-B-A-A-A

Alternate copolymers are those in which the order of the monomer alternates e.g.

A-B-A-B-A-B-A-B-A-B-A-B-A-B-A-B

Block copolymers are those in which one block of monomers join to other block of monomers e.g.

A-A-A-A-A-B-B-B-A-A-A-A-B-B-B-A-A-A-A-B-B-B

Graft copolymers are those in which the backbone chain is made of one type of monomer and side chain from another type of monomer.

Reaction Mechanism

Polymers are divided into two, based on the reaction mechanism, i.e.:

  1. Step Growth Polymer
  2. Chain Growth Polymer

In step-growth polymerization, the polymer grows in a stepwise fashion. A bifunctional monomer is required in step growth polymerization, e.g. formation of Nylon.

In chain growth polymerization, the polymer grows via a chain reaction mechanism where an initiator is needed to initiate the reaction, forming a free radical which would propagate the reaction to form chains of polymers, examples include polyethylene, polypropylene etc.

Introduction to Polymer Science

Polymer is a macro-molecule made up by reacting many smaller molecules known as monomers. The properties of a polymer is a function of primary and secondary bonding.   Most importantly, polymer science is a multidisciplinary subject, generally studied by chemists, chemical engineers and material engineers.

History Of Polymer Science

Humans have been using polymers long ago, in the form of natural polymers. The polymers in use were: silk, cotton, wood, wool, leather etc. In 1885, first polymer was synthesized, a semi-synthetic polymer known as nitrocellulose. Nitrocellulose was made flexible with the help of a plasticizer, called camphor. It was used to film movies. Later on, it was also used as varnish for furniture etc. 

The property that hindered its widespread use was its flammability due to the nitrate group. Afterwards, nitrate was replaced by acetate. Later on artificial silk was also synthesized which led to the production of rayon. 

The first purely synthetic polymer was synthesized in 1910, Bakelite, a densely crosslinked polymer formed by the reaction of phenol with formaldehyde. At that time, polymers were synthesized by hit and trial method and little was known about the relation between its chemical structure and its physical properties.

In 1920, Staudinger came up with the macromolecular hypothesis. This was the time when polymer science caught the attention of scientists. Carothers, a DuPoint Chemist, suggested that if the macromolecular hypothesis is true, then if a diacid is reacted with diols, with the reaction stoichiometry of one to one, then these molecules should react forming a long chain. Carothers discovered polyester, succeedingly synthesizing nylon and neoprene.

Primary Bonding

Primary  bonding is chemical bonding between atoms, which is a result of complete electron transfer, or  mutual transfer of electrons. There are three main types of primary bonding :

  1. Ionic 
  2. Covalent
  3. Metallic

Secondary Bonding

Secondary bonding is physical bonding between atoms or molecules. This plays a role in the physical properties of a polymer and other materials. Examples of secondary bonding are Van Der Waal forces, dipole-dipole interactions, hydrogen bonding, etc. 

Bulk Properties

When many molecules of the same type are joined, properties of large collection of molecules are measured, known as bulk properties. Bulk properties are a function of:

  • Molecular Properties
  • Collective Properties

Molecular Properties

These properties depend upon the molecular nature of materials such as chemical reactivity.Moreover, the reactivity further defines the type of polymer formed and the ease with which a polymer can be formed.

Collective Properties

These properties depend upon the interaction of molecules with each other in a material, for example crystal formation is a collective property. Furthermore, these properties will dictate the level of crystalline nature of a polymer.

Degree of polymerization

Degree of polymerization tells how many monomeric units have chemically reacted to form a certain polymer. Degree of polymerization is given by the formula :

Degree Of Polymerization =

(Molecular Weight of Polymer)/(Molecular weight of monomer)

What is Chemistry

Chemistry is the study of matter, its properties, changes in matter and the laws and principles governing it. Chemistry is everywhere around you and it is inevitable, even if you hate it. The air you breathe, the scents you smell, the food you eat, the drugs you take, even you yourself are a splendid example of chemistry. Chemistry studies matter on the macroscopic level and finds the reasons for its properties at the microscopic and submicroscopic levels. 

Chemistry helps to predict properties of matter, as a certain pattern is followed by properties the matter possesses. An example to support the previous line: When all the elements of the periodic table were not yet discovered and the periodic table was not yet invented, Mendeleev, a chemist, invented a periodic table based on atomic masses. He believed that the properties of the elements followed some periodic arrangement and thought that the gaps between the two elements are non-discovered elements. He predicted the properties of an element below Aluminum, which later on was discovered, Gallium, and had almost similar properties as he had predicted.

Preliminaries

Before we further talk about chemistry, we need to put forward some definitions:

Matter

Matter is anything that has mass and occupies space, e.g. air, water, human chair etc.

Property

Property is a characteristic of a substance based on which it is distinguished from other materials e.g. a metal and a non-metal can be distinguished by the property of conductivity(there are many other properties that distinguish metals from nonmetals, conductivity is cited as an example).

Elements

Element is a substance that is made up of the same atoms throughout e.g. oxygen is an element that is made from the same atoms having atomic number 8.

Atoms 

Atoms are infinitesimally small building blocks of elements. To have insight, hydrogen’s atomic radius is 0.529 * 10^-10 m, an average human hair is 5 * 10^-5 m thick and radius of hydrogen is almost a million times smaller than the thickness of a human hair.

Why Study Chemistry?

You may have encountered chemistry as a subject even if you are not a chemistry major. Every field is related to chemistry, be it Biology, Engineering, Medical, Geology, Pharmacology, etc. It is chemistry which helps pharmacists and pharmacologist to produce new drugs, synthesize artificial vitamins and many other supplements. It helps engineers better understand processes on the molecular level e.g. it helps chemical engineers understand processes and how to get maximum production from a certain reaction with particular resources.

In Biology or the Medical field, it helps the doctors or biologists to understand the interior reactions in a living organism, the interaction of the human body with external agents, etc. and to identify substances that are toxic and injurious to the health of a specific organism. It helps Geologists understand how formations form and how the composition of formation affects its structure. This is the reason Chemistry is termed as “The Central Science”.

Who are chemists and what do they do?

Chemists are those people who have a degree in chemistry major. They are employed in many places e.g. as a team member of the research and development team in a chemical industry producing new chemicals(as once Haber produced ammonia with BASF), in a pharmaceutical industry producing new life saving drugs, in an environmental regulatory authority, keeping a check on the carbon emissions in a particular area or may be they are given the job to analyze materials as a quality control  team member. In short, chemists:

  1. Produce new chemicals of some desired properties
  2. Measure properties of matter
  3. Develop mathematical equations to better understand matter at microscopic level as well as macroscopic level.

Classification of matter

Matter is classified based on

  1. Its physical state 
  2. Its composition. 

Physical State:

Matter is divided into four states of matter on the basis of its physical state i.e. Solid, Liquid, Gas, and Plasma. A gas has no fixed shape or volume and takes the shape of the container. It has the ability to compress and expand. A liquid has a fixed volume but no definite shape. It takes the shape of the container. Solid has a fixed shape as well as volume. Both liquids and gases do not compress to a significant level.

Composition:

Matter is divided into elements, compound, and mixture, based on composition. Before knowing these three, we need to know what is substance. Substance is matter whose properties do not change from sample to sample and has fixed composition. Element, as described earlier, is a substance made up of one kind of atoms. Compound, on the other hand, is a substance made up of the combination of different types of atoms such as water, which is made up of two atoms of hydrogen and a single oxygen atom. Mixture is a mix of different kinds of substances for example salt in water. This has no definitive properties and is a function of composition.