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Crystalline And Amorphous Solids
 
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Follow us at: https://plus.google.com/+tutorvista/ Check us out at http://www.tutorvista.com/content/physics/physics-iii/solids-and-fluids/amorphous-solids.php Crystalline And Amorphous Solids Amorphous solids and crystalline solids if the size of the crystals is very small. Even amorphous materials have some short-range order at the atomic length scale due the nature of chemical bonding. Furthermore, in very small crystals a large fraction of the atoms are located at or near the surface of the crystal; relaxation of the surface and interfacial effects distort the atomic positions, decreasing the structural order. Even the most advanced structural characterization techniques, such as x-ray diffraction and transmission electron microscopy, have difficulty in distinguishing between amorphous and crystalline structures on these length scales.The transition from the liquid state to the glass, at a temperature below the equilibrium melting point of the material, is called the glass transition. The glass transition temperature, Tg, is the temperature at which an amorphous solid, such as glass or a polymer, becomes brittle on cooling, or soft on heating. More specifically, it defines a pseudo second order phase transition in which a supercooled melt yields, on cooling, a glassy structure and properties similar to those of crystalline materials e.g. of an isotropic solid material. Tg is usually applicable to wholly or partially amorphous solids such as common glasses and plastics (organic polymers). Below the glass transition temperature, Tg, amorphous solids are in a glassy state and most of their joining bonds are intact. In inorganic glasses, with increased temperature more and more joining bonds are broken by thermal fluctuations so that broken bonds (termed configurons) begin to form clusters. Above Tg these clusters become macroscopic large facilitating the flow of material. In organic polymers, secondary, non-covalent bonds between the polymer chains become weak above Tg. Above Tg glasses and organic polymers become soft and capable of plastic deformation without fracture. This behavior is one of the things which make most plastics useful . It is important to note that the glass transition temperature is a kinetic parameter, and thus parametrically depends on the melt cooling rate. Thus the slower the melt cooling rate, the lower Tg. In addition, Tg depends on the measurement conditions, which are not universally defined . The glass transition temperature is approximately the temperature at which the viscosity of the liquid exceeds a certain value (about 1012 Pa•s). The transition temperature depends on cooling rate, with the glass transition occurring at higher temperatures for faster cooling rates. The precise nature of the glass transition is the subject of ongoing research. While it is clear that the glass transition is not a first-order thermodynamic transition (such as melting), there is debate as to whether it is a higher-order transition such percolation type transformation , or merely a kinetic effect. The process of forming a crystalline structure from a fluid or from materials dissolved in the fluid is often referred to as crystallization. In the old example referenced by the root meaning of the word crystal, water being cooled undergoes a phase change from liquid to solid beginning with small ice crystals that grow until they fuse, forming a polycrystalline structure. The physical properties of the ice depend on the size and arrangement of the individual crystals, or grains, and the same may be said of metals solidifying from a molten state.Which crystal structure the fluid will form depends on the chemistry of the fluid, the conditions under which it is being solidified, and also on the ambient pressure. While the cooling process usually results in the generation of a crystalline material, under certain conditions, the fluid may be frozen in a noncrystalline state. In most cases, this involves cooling the fluid so rapidly that atoms cannot travel to their lattice sites before they lose mobility. A noncrystalline material, which has no long-range order, is called an amorphous, vitreous, or glassy material. Please like our facebook page http://www.facebook.com/tutorvista
Views: 100235 TutorVista
Polymerization
 
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In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many forms of polymerization and different systems exist to categorize them. This video is targeted to blind users. Attribution: Article text available under CC-BY-SA Creative Commons image source in video
Views: 240 Audiopedia
Explain Configuration and Conformation | Stereochemistry | Organic Chemistry
 
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Download our Android app at https://goo.gl/5JM1G2 Stereochemistry: It is a branch of chemistry which deals with the 3 dimensional arrangements of different atoms of a molecule with respect to each other in a space around it. Configuration of an organic molecule represents an exact 3D arrangement of all the atom in a molecule with respect to each other. e.g. consider a molecule of methane with molecular formula CH4. Its 2D and 3D configurations are Conformation: Conformation can be discussed only for those organic molecules which posses at least two carbon atom is directly attached with each other. e. G. Consider a molecule of ethane C2H6. It has been observed that the entire molecule of ethane can undergo different structural arrangements / changes just by single bond rotation. Different structural arrangement obtained as a result of free rotation around C -C single bond are treated as the conformation of that molecule, more over the relative study of stability of different conformation possible for same molecule is known as conformational analysis. For Details Visit http://cepekmedia.co.nf http://cepek.hol.es/ http://edmerls.66Ghz.com/ http://edmerls.tk/
Views: 11616 Cepek Media
Structures of polymers {Texas A&M: Intro to Materials}
 
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Tutorial video illustrating "polymeric" crystal structures and microstructures. How do polymer chains pack together to form crystal structures? What geometries do crystalline regions tend to form in polymers? Video lecture for Introduction to Materials Science & Engineering (MSEN 201/MEEN 222), Texas A&M University, College Station, TX. http://engineering.tamu.edu/materials
Views: 11422 Patrick Shamberger
Thermoplasts and Thermosets
 
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Thermoplasts and Thermosets
Effects of Glass transition temperature
 
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This lecture explains the concept of Glass transition temperature, experimental methods to determine it and discusses the factors which affect it.
Polymer Molecular Weight
 
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Calculates the number average and the weight average molecular weight from a polymer molecular weight distribution. Made by faculty at the University of Colorado Boulder Department of Chemical and Biological Engineering. Check out our Materials Science playlist at http://www.youtube.com/playlist?list=PLC9CE6BFBB0D003CD
Views: 72262 LearnChemE
Polymeric Structure
 
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This lecture explains about the molecular weight calculation in polymers, physical states of polymer, tacticity.
Branching (polymer chemistry) | Wikipedia audio article
 
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This is an audio version of the Wikipedia Article: https://en.wikipedia.org/wiki/Branching_(polymer_chemistry) 00:02:05 1 Special types of branched polymer 00:03:25 2 Branching in radical polymerization 00:05:37 3 Branching index Listening is a more natural way of learning, when compared to reading. Written language only began at around 3200 BC, but spoken language has existed long ago. Learning by listening is a great way to: - increases imagination and understanding - improves your listening skills - improves your own spoken accent - learn while on the move - reduce eye strain Now learn the vast amount of general knowledge available on Wikipedia through audio (audio article). You could even learn subconsciously by playing the audio while you are sleeping! If you are planning to listen a lot, you could try using a bone conduction headphone, or a standard speaker instead of an earphone. Listen on Google Assistant through Extra Audio: https://assistant.google.com/services/invoke/uid/0000001a130b3f91 Other Wikipedia audio articles at: https://www.youtube.com/results?search_query=wikipedia+tts Upload your own Wikipedia articles through: https://github.com/nodef/wikipedia-tts Speaking Rate: 0.9822041450093175 Voice name: en-AU-Wavenet-A "I cannot teach anybody anything, I can only make them think." - Socrates SUMMARY ======= In polymer chemistry, branching occurs by the replacement of a substituent, e.g., a hydrogen atom, on a monomer subunit, by another covalently bonded chain of that polymer; or, in the case of a graft copolymer, by a chain of another type. Branched polymers have more compact and symmetrical molecular conformations, and exhibit intra-heterogeneous dynamical behavior with respect to the unbranched polymers. In crosslinking rubber by vulcanization, short sulfur branches link polyisoprene chains (or a synthetic variant) into a multiply branched thermosetting elastomer. Rubber can also be so completely vulcanized that it becomes a rigid solid, so hard it can be used as the bit in a smoking pipe. Polycarbonate chains can be crosslinked to form the hardest, most impact-resistant thermosetting plastic, used in safety glasses.Branching may result from the formation of carbon-carbon or various other types of covalent bonds. Branching by ester and amide bonds is typically by a condensation reaction, producing one molecule of water (or HCl) for each bond formed. Polymers which are branched but not crosslinked are generally thermoplastic. Branching sometimes occurs spontaneously during synthesis of polymers; e.g., by free-radical polymerization of ethylene to form polyethylene. In fact, preventing branching to produce linear polyethylene requires special methods. Because of the way polyamides are formed, nylon would seem to be limited to unbranched, straight chains. But "star" branched nylon can be produced by the condensation of dicarboxylic acids with polyamines having three or more amino groups. Branching also occurs naturally during enzymatically-catalyzed polymerization of glucose to form polysaccharides such as glycogen (animals), and amylopectin, a form of starch (plants). The unbranched form of starch is called amylose. The ultimate in branching is a completely crosslinked network such as found in Bakelite, a phenol-formaldehyde thermoset resin.
Views: 21 wikipedia tts
Branching (chemistry) | Wikipedia audio article
 
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This is an audio version of the Wikipedia Article: https://en.wikipedia.org/wiki/Branching_(polymer_chemistry) 00:02:09 1 Special types of branched polymer 00:03:32 2 Branching in radical polymerization 00:05:49 3 Branching index Listening is a more natural way of learning, when compared to reading. Written language only began at around 3200 BC, but spoken language has existed long ago. Learning by listening is a great way to: - increases imagination and understanding - improves your listening skills - improves your own spoken accent - learn while on the move - reduce eye strain Now learn the vast amount of general knowledge available on Wikipedia through audio (audio article). You could even learn subconsciously by playing the audio while you are sleeping! If you are planning to listen a lot, you could try using a bone conduction headphone, or a standard speaker instead of an earphone. Listen on Google Assistant through Extra Audio: https://assistant.google.com/services/invoke/uid/0000001a130b3f91 Other Wikipedia audio articles at: https://www.youtube.com/results?search_query=wikipedia+tts Upload your own Wikipedia articles through: https://github.com/nodef/wikipedia-tts Speaking Rate: 0.96470202252444 Voice name: en-US-Wavenet-E "I cannot teach anybody anything, I can only make them think." - Socrates SUMMARY ======= In polymer chemistry, branching occurs by the replacement of a substituent, e.g., a hydrogen atom, on a monomer subunit, by another covalently bonded chain of that polymer; or, in the case of a graft copolymer, by a chain of another type. Branched polymers have more compact and symmetrical molecular conformations, and exhibit intra-heterogeneous dynamical behavior with respect to the unbranched polymers. In crosslinking rubber by vulcanization, short sulfur branches link polyisoprene chains (or a synthetic variant) into a multiply branched thermosetting elastomer. Rubber can also be so completely vulcanized that it becomes a rigid solid, so hard it can be used as the bit in a smoking pipe. Polycarbonate chains can be crosslinked to form the hardest, most impact-resistant thermosetting plastic, used in safety glasses.Branching may result from the formation of carbon-carbon or various other types of covalent bonds. Branching by ester and amide bonds is typically by a condensation reaction, producing one molecule of water (or HCl) for each bond formed. Polymers which are branched but not crosslinked are generally thermoplastic. Branching sometimes occurs spontaneously during synthesis of polymers; e.g., by free-radical polymerization of ethylene to form polyethylene. In fact, preventing branching to produce linear polyethylene requires special methods. Because of the way polyamides are formed, nylon would seem to be limited to unbranched, straight chains. But "star" branched nylon can be produced by the condensation of dicarboxylic acids with polyamines having three or more amino groups. Branching also occurs naturally during enzymatically-catalyzed polymerization of glucose to form polysaccharides such as glycogen (animals), and amylopectin, a form of starch (plants). The unbranched form of starch is called amylose. The ultimate in branching is a completely crosslinked network such as found in Bakelite, a phenol-formaldehyde thermoset resin.
Views: 3 wikipedia tts
Polymers: Introduction and Classification
 
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This lecture introduces to the basics of Polymers, their classifications and application over wide domains.
Lec 29 | MIT 3.091SC Introduction to Solid State Chemistry, Fall 2010
 
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Lecture 29: Polymers: Synthesis, Properties & Applications Instructor: Donald Sadoway View the complete course: http://ocw.mit.edu/3-091SCF10 License: Creative Commons BY-NC-SA More information at http://ocw.mit.edu/terms More courses at http://ocw.mit.edu
Views: 20702 MIT OpenCourseWare
Lecture - 11 Polymers (Contd.)
 
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Lecture Series on Materials Science by Prof.SK. Gupta, Department of Applied Mechanics ,IIT Delhi. For more details on NPTEL visit http://nptel.iitm.ac.in
Views: 22549 nptelhrd
Mobile camera Se kisi bhi language ka translate kaise kare
 
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दोस्तों आप सभी का बहुत-बहुत स्वागत है हमारी YouTube चैनल ऑनलाइन जॉब में इस वीडियो में हमें बताएंगे आप अपने मोबाइल कैमरे से किसी भी भाषा में ट्रांसलेट कैसे करें कोई भी भाषा हो उसका ट्रांसलेट आपके मोबाइल के कैमरे से हो जाएगा अगर आपके पास कोई बुक है उस पर कुछ भी लिखा हुआ है तो वह आपकी भाषा में उसका ट्रांसलेट कर देंगे अपने मोबाइल के कैमरे से स्कैन करके उस भाषा का ट्रांसलेट कर सकते हैं ट्रांसलेट एप्लीकेशन डाउनलोड करने के लिए इस लिंक को टच करें https://play.google.com/store/apps/details?id=com.google.android.apps.translate दोस्तों अगर अभी तक आपने हमारे चैनल को सब्सक्राइब नहीं किया है तो प्लीज जल्दी सब्सक्राइब कर लीजिए ताकि आप देख सके हमारी वीडियो सबसे पहले इस वीडियो को ज्यादा से ज्यादा शेयर करें अपने दोस्तों को Facebook पर Whatsapp पर ताकि सभी लोगों को यह जानकारी मिल सके आपने अपना कीमती समय दिया इसके लिए आपका बहुत-बहुत धन्यवाद दोस्तों आप हमारा वीडियो ऐसे ही देखते रहें और खुश रहें
Views: 58249 Online Job
15. Metals and Catalysis in Alkene Oxidation, Hydrogenation, Metathesis, and Polymerization
 
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Freshman Organic Chemistry II (CHEM 125B) Alkenes may be oxidized to diols by permanganate or by OsO4 catalysis. Metal catalysts provide orbitals that allow simultaneous formation of two bonds from metal to alkene or H2. Coupling such oxidative additions to reductive eliminations, provides a low-energy catalytic path for addition of H2 to an alkene. Such catalytic hydrogenation is often said to involve syn stereochemistry, but the primary literature shows that addition can be anti when allylic rearrangement occurs on the catalyst. Similar oxidative/reductive cycles operate in olefin metathesis and metal-catalyzed polymerization. Careful catalyst design allows control over polymer stereochemistry (tacticity). Polymerizations catalyzed by free-radicals or acids typically lack stereochemical control, but there are ways to control regiochemistry and chain length. Latex, a natural polymer, coagulates to form a rubber ball. 00:00 - Chapter 1. Alkene Dihydroxylation 04:28 - Chapter 2. Catalytic Hydrogenation of Alkenes: Oxidative Addition, Reductive Elimination 15:08 - Chapter 3. Catalytic Hydrogenation of Alkenes: Stereochemistry 25:50 - Chapter 4. Olefin Metathesis, Polymerization, and Tacticity 39:00 - Chapter 5. Radical Polymerization 43:16 - Chapter 6. Electrophilic Oligomerization and Polymerization and Rubber Complete course materials are available at the Open Yale Courses website: http://oyc.yale.edu This course was recorded in Spring 2011.
Views: 7591 YaleCourses
Introduction to Polymers
 
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Views: 1760 IIT Guwahati