 Welcome to this course on Interfacial Engineering under the NPTEL program. In this first lecture, I intend to provide a general introduction and look at some of the definitions, examples and challenges offered by interfacial engineering especially to chemical engineers. This picture is intended to make way for an unusual introduction to interfaces. What thoughts about interfaces could be provoked by observations of different things visible in this picture? We might think about water air interface as seen at the bottom over here where the pool of water is in contact with air or one might see the turbulent fall of water here which creates billions of droplets of different sizes some of which might actually remain suspended in air creating the mist or fog here. Presence of these ultra fine droplets suspended in air can lead to this spectacular rainbow through the optical phenomena of reflection and refraction. If we seek more interfaces visible here, there is an interesting pattern of rock here clearly indicating that when the rocks crystallize for the first time they created these interfaces. We are clearly visible strata of rocks so that there is an interface between solid and solid. Among the smaller scale structures we will have empty number of crystallites sharing interfaces with adjacent crystallites. One may even look at the interface between the soil and the soil and rock or between the roots of the plants here and the soil the droplets of water which might be present on the leaves here and so on. The point to note is we have myriad interfaces all around us. I would like you to consider this observation by Theodor von Karman who astutely stated that scientists study the world as it is. Engineers create the world that has never been both are equally important for the progress of mankind or if you look at the statement by Fung et al in their classic engineering text foundations of solid mechanics. We understand that engineering is quite different from science. Scientists try to understand nature. Engineers try to make things that do not exist in nature. They stress invention. To embody an invention the engineer must put his idea in concrete terms and design something that people can use. That something can be device, a gadget, a material, a method, a computing program an innovative experiment, a new solution to a problem or an improvement on what is existing. Since a design has to be concrete it must have its geometry, dimensions and characteristic numbers. Almost all engineers working on new designs find that they do not have all the needed information. Most often they are limited by insufficient scientific knowledge. Thus they study mathematics, physics, chemistry, biology and mechanics. Often they have to add to the sciences relevant to their profession. Thus engineering sciences are born. I would like to make a comment here that by virtue of their professional responsibility engineers are required to make things happen for some useful end. And as historically has been borne out the practical successful implementations have long preceded the complete understanding of the phenomena or even indirect observations made. One can look at the development of hydrostatics as a body of knowledge well before the fluid mechanics or fluid dynamics as we understand it today. The dams had to be built and engineers needed to understand what all factors need to be taken into account in building successful dams and so on. You could take this line of thought to practically all engineering inventions not just in chemical engineering or interfacial engineering which we would like to believe is a sub part of chemical engineering with multidisciplinary cross connections with all sciences and engineering. Here is an interesting observation about scientists and engineers making up less than 5 percent of the total population, but creating up to 50 percent of the GDP or as Kevin Ulmer Director of Exploratory Research, JNX Corporation writes. Protein engineering represents the first major step towards more general capability for molecular engineering which would allow us to structure matter atom by atom. The realization that all material is made up of molecules or atoms is probably the most valuable contribution of science and as Feynman puts it if we had to pass on a single message to the posterity should the current population of mankind were to disappear in a flash that would be the atomic nature of all materials. Richard Feynman believed that with this hypothesis atomic hypothesis all science could be rebuilt if required. Now we come to the interfacial engineering and focus on interface. Defining an interface like any other entity is stating precisely and sharply the concept about the reality. The interface however itself is not sharp. According to Professor H. Ted Davis of University of Minnesota, an interface is a zone a few nanometers thick lying between two coexisting phases. Clearly, interface is not a geometrical plane or Eli Osipo Director of Surface Chemistry Department of Foster Digital Incorporation define an interface as the region between two contacting phases generally two condensed phases. By condensed phase we should understand that we mean either a solid or liquid phase of a material. Once again there is a clear message here that interface is not a geometrical plane as one normally would tend to remember from textbook graphics. To get a little more comprehensive idea of interface we could go back to Micropedia of Encyclopedia Britannica where an interface is defined more elaborately as follows. Surface separating two phases of matter each of which may be solid, liquid or gaseous. An interface is not a geometrical surface but a thin layer that has properties differing from those of the bulk material on either side of the interface. A common interface is that between a body of water and the air which exhibits such properties as surface tension by which the interface acts somewhat like a stretched elastic memory. Chemical effects or processes that occur at interfaces include the evaporation of liquids, the action of detergents and chemical catalysts and the adsorption of gases on metals. When we think about the types of interfaces that we may come across basically five types of interfaces are feasible. A gas liquid interface or a gas solid interface, a liquid-liquid interface, a liquid-solid interface and solid-solid interface. Two gas phases could not possibly have a stable interface because intermingling of gases would naturally occur. It is here that I would like to put in perspective to close concepts colloids against interfaces. Broadly, colloids when we think of we tend to remember somehow very fine particles of solid suspended in a liquid, gold salts for example. But it is important to recognize that colloids have been more broadly defined as fluid bounded persistent structures sub-microscopically small in at least one dimension. In the face of this definition interfaces of types 1 and 3 that is gas-liquid and liquid-liquid interfaces truly qualify as colloids while those of types 2 and 4 gas-solid and liquid-solid interfaces do so only in a partial sense. Solid-solid interfaces clearly do not conform to the above definition and hence cannot be classified as colloids. Interface is a broader concept than colloid. You might consider this mnemonic interface is a bigger word, a bigger set than colloid counting just the letters. Here I cite some of the numbers which are somewhat older, representative of mid-90s. Social processes impact 23 percent of a 150 billion dollar US industry and interfacial engineering will contribute an increasingly larger percentage in the future. Rest of the world will be similarly affected. On the other hand from the pure point of view of pursuit of scientific and technological knowledge, surfaces, interfaces and microstructures are key to an improved understanding of many diverse branches of knowledge including electrochemistry, corrosion, processes of manufacture of micro circuits, colloids, surfactants, advanced ceramics and membranes. Digital science may be defined as the branch of knowledge concerned with the study of phenomena occurring at various types of interfaces encompassing their formation, modification and destruction as well as of the properties of stable or dynamic interfaces between different phases. It is difficult to define interfacial engineering, but here is an attempt interfacial engineering may be defined as the branch of applied knowledge concerned with the interfacial processes and having enhancement, separation or control of interface formation as its primary goals, establishment of its connections with the other engineering and scientific disciplines being the assimilative and augmentative objectives. I will show you a figure here which is an elementary sketch of the connections of interfacial engineering with various existing and identified disciplines of science and engineering. This is only indicative and you could add more connections with more disciplines in case you continue to think about interfacial engineering seriously over a longer time frame. As per chemical engineering, the first connections one immediately comes up with are between interfacial engineering and heat transfer, mass transfer without chemical reaction, process modeling, thermodynamics, kinetics, fluid and particle mechanics and rheology material science and engineering to name a few. This intricate role played by surface physics and chemistry and solid state physics and disciplines like optics and electromagnetism, disciplines like optics and electromagnetism not to forget of biochemical engineering. Many of the most important interfacial phenomena occur in living systems. Typical challenges posed by interfacial engineering specifically to the chemical engineers are enumerated as follows. First challenge may be to understand the mechanisms to formulate mathematical models and to use these models for process analysis, design and scale up of interfacial processes. The second challenge may be to develop molecular level structure property relations for guiding the production of materials with specified physical and chemical properties. We need to go right from the fundamentals to the desired properties in mass produced products. The third challenge may be to build up an improved understanding of the transformations occurring at phase boundaries, both elementary chemical and physical transformations which occur at phase boundaries. We may next look at examples of interfacial processes. The first one here is the use of immobilized animal cell cultures for production of desired chemicals. For example, specific antibodies or special purpose proteins or ethanol. Selection and preparation of solid materials and process analysis, design and scale up offer chemical engineers a variety of new and exciting challenges. The second example of an interfacial process is the use of sol-gel process to produce microstructured ceramic parts for replacement of bone and tooth. The interfacial issues may include drying, consolidation and shaping the initial colloidal dispersion of ceramic particles followed by surface treatment of the parts to assure biocompatibility. The third example could be the use of surfactants as bilayered vesicles for micro-encapsulation and sites as specific drug delivery, micro-encapsulation and site specific drug delivery and for conducting artificial photosynthesis. The fourth example is the use of micelles for separation of protein products from fermentation broth. The landfill disposal of garbage may also involve microbial reactions at interfaces between solids. Besides the reactions the movement of fluid through the soil may be driven by interfacial tension. These are other examples of interfacial processes. Towards the high end applications controlled processes to produce molecularly tailored, reliable, microstructured or nanostructured materials for high technology, electronic, computer and communication industries, crystal growth, thin film growth, thin film coatings, reduction of thin films on solids. For example by electron beam evaporation, molecular beam epitaxy, ion beam bombardment, ion beam bombardment sputtering, DC arc deposition, plasma spraying and CVD or chemical vapor deposition processes. Production of advanced ceramic materials such as optical fibers, alternatives to alloys in the form of thin films, micro and nanostructured materials etc could also constitute interfacial processes. Then processes involving coatings such as in photographic films like like SX70, various paper products, magnetic memory tapes and discs, optical discs, photoresist, conducting films, piezoelectric films, optical wave guides and membranes etc. We next look at some interesting examples of products of interfacial engineering. The first one is a common carbon paperless copying using latex of micro encapsulated ink drops. You have seen how by writing on a top sheet, the impression of your writing or image is transferred to a lower sheet without having a carbon paper in between. The underside of the top sheet is covered with micro encapsulated ink drops which burst and release the ink upon application of pressure on the top sheet. One could have pressure sensitive micro encapsulated adhesives. The third example given here is thin films for welding with a matchstick. Those of you who are fond of reading scientific American might have seen this example. Thin films were intended to provide a very lightweight and therefore economical welding application for such spatial purposes as for facilitating the needs of astronauts in a spaceship. Obviously, it is not possible to carry huge gas cylinders about the spaceships and therefore some thin films were prepared which could be specifically made by expensive techniques mass production might reduce the cost but by lighting these thin films two metallic parts could be welded quite as well as by conventional technique. Many of you are aware of electronic inks. These make use of very fine particles, spherical particles half of which are white and the other half black. By using electrical or magnetic fields, we could make the particles face the display side creating images. Large display boards may be possible using the electronic inks which could be used over and over again. Next slide here pollution preventing lithographic inks having had some personal research experience of over a decade and half little do most people know how polluting can be printing inks. Just to give you some numerical estimates over 131,000 tons of volatile organic compounds or VOCs are emitted in US alone from the printing industry. A comparable figure corresponding figure from European Union is about 187,000 tons per annum. Mind you these are volatile organic compounds which can create a lot of health problem for the workers on shop floor with conventional printing inks. It is hardly possible to be inside a printing shop for more than 10 minutes. The VOCs can cause multiple complications related to breathing and may even be contributing to the carcinogenic effects. But it is possible to develop printing inks on a totally different platform starting with vegetable oils so that the inks are comparable in performance to the conventional inks based on petroleum products. Conventional inks contain resins and solvents which are both based on petroleum products. Both the ink and the cleaning solutions which are generally mixtures of aliphatic and aromatic compounds contribute to emission of VOCs. The new ink is non-volatile. There are no VOCs in the ink and it can be washed essentially with water. So, there is no emission of VOCs from the cleaning solvent itself. During the use the ink gets cross linked in presence of light and air oxygen in air and becomes permanent of paper. This printing ink can be also removed during de-inking with much greater ease and will have other sustainable benefits. Then we think of a number of other examples solid foams which make most of the cushions that we use these days, bi-liquid foams or polyaphrones which are special liquid-liquid dispersions with microscopic polyhedral structure for the disperse phase unlike emulsions. Computer chips, photolithography and use of photoresist is a clever example of an interfacial engineering product. I mentioned micro-encapsulated products earlier. They could be for controlled release of drugs or potential new applications could be in the form of phase change materials for augmentation of heat transfer. Myriad other products like photocopying products like wet and dry toners, detergents, low VOC paints, self-cleaning glass panes and pollution abating road surface coatings or linings based on titanium dioxide. Disinfectants, insecticides, herbicides, variety of cosmetic and personal care products like moisturizers, space creams, shampoos, shaving creams, etc. Even contact lenses and all kinds of medicines. Specialized food products like milk products, ice creams, cheeses, yogurts and so on. Newer fuels like biodiesels, ethanol blended petrol, newer lubricants which are based on biodegradable formulations, fruit preservatives and polishes, flour and wood polishes, fabric whiteners and brightners, all kinds of adhesive and tapes like double sided tapes, cello tapes, correction fluids and tapes. Plastic products of all kinds like wrappers, packings, polyurethane foam, packaging materials, bags, PET bottles, etc. Glasses especially high quality high refractive index glasses, optical quality glasses, photochromatic glasses, suspended particle devices, tempered and float glasses. Other examples could be specialty ceramics like monoliths and zeolites. An impactful range of products based on Teflon which involve coatings and lubricants. Photocatalysts and photo electrochemical cells, etc. These may auger well for future hydrogen production technologies. Although current efficiencies of the photo catalysts and photo electrochemical cells is below the levels which would be economical. Lithium batteries and solar cells and important interventions like nucleating agents for artificial rains which would have great significance for hot and arid countries like ours. Besides achieving artificial rains one might also want to conserve water by cutting down evaporation losses from water bodies. It is even in that application we might have simple and economically viable interfacial engineering based solutions for conservation of water. So, obviously there will be important considerations like what we use for reducing evaporation must not be toxic in any sense to the aquatic flora and fauna and obviously there should be no deterioration and emission of harmful products from the surface layers which might be used for retarding water losses by evaporation. With this brief general introduction I conclude today's lecture and we will look at some more examples before we get down to focus on the properties of especially gas liquid interfaces in a fair amount of detail. My effort will be to clarify all the concepts basic concepts in a different way and also to remove many misconceptions which inevitably make their way into our normal education. Thank you.