Search results “Syndiotactic wikipedia the free”
System Of A Down - Toxicity
System of a Down's official music video for 'Toxicity'. Click to listen to System of a Down on Spotify: http://smarturl.it/SystemSpotify?IQid=SystemToxicity As featured on Toxicity. Click to buy the track or album via iTunes: http://smarturl.it/SystemToxicity?IQid=SystemToxicity Google Play: http://smarturl.it/ToxicityGPlay?IQid=SystemToxicity Amazon: http://smarturl.it/ToxicityAmazon?IQid=SystemToxicity More from System of a Down Chop Suey!: https://youtu.be/CSvFpBOe8eY Aerials: https://youtu.be/L-iepu3EtyE B.Y.O.B: https://youtu.be/zUzd9KyIDrM More great Alternative videos here: http://smarturl.it/Alternative00?IQid=SystemToxicity Follow System of a Down Website: http://www.systemofadown.com/ Facebook: https://www.facebook.com/systemofadown Twitter: https://twitter.com/systemofadown Instagram: https://instagram.com/systemofadown/ Subscribe to System of a Down on YouTube: http://smarturl.it/SYODSub?IQid=SystemToxicity --------- Lyrics: Conversion, software version 7.0 Looking at life through the eyes of a tire hub Eating seeds as a pastime activity The toxicity of our city, of our city New, what do you own the world? How do you own disorder, disorder Now, somewhere between the sacred silence, sacred silence and sleep Somewhere between the sacred silence and sleep Disorder, disorder, disorder More wood for their fires, loud neighbours Flashlight reveries caught in the headlights of a truck Eating seeds as a pastime activity The toxicity of our city, of our city
Views: 268292595 systemofadownVEVO
Kalki - Varanasi (Official Music Video)
-- GET READY FOR A BIG TRIP -- A film by Basile Pierrat Varanasi is a project born out of an artistic encounter between Kalki, the DJ and techno/trance producer, and Basile Pierrat. The film was created on the base of a common vision: a project without concession, only answering to their own aesthetic and artistic vision. A music video that had therefore to be entirely realized without any label or agency. Basile Pierrat got a bit crazy and started this shooting with just a script, a camera and a one-way ticket to New Delhi as the only preparation. Completely alone, in the middle of this beautiful and insane country, a film to produce within a month: an unforgettable experience and a big challenge. GRAB YOUR COPY ON BEATPORT: http://bit.ly/Kalki-Varanasi-Beatport Subscribe: http://bit.ly/SubscribeKalki Listen to: http://bit.ly/KalkiMusic Follow Kalki: Facebook: http://www.facebook.com/KalkiMusic Soundcloud: http://soundcloud.com/KalkiMusic Twitter: http://twitter.com/KalkiMusic Official Website: http://Kalkimusic.com Kalki is a Dj & Producer of Progressive Trance.
Views: 4423973 Kalki
Counterion A counterion (pronounced as two words, i.e."counter" "ion", and sometimes written as two words) is the ion that accompanies an ionic species in order to maintain electric neutrality. =======Image-Copyright-Info======= Image is in public domain Author-Info: Ben Mills Image Source: https://en.wikipedia.org/wiki/File:Lithium-tetrakis(pentafluorophenyl)borate-2D-skeletal.png =======Image-Copyright-Info======== -Video is targeted to blind users Attribution: Article text available under CC-BY-SA image source in video https://www.youtube.com/watch?v=Z82pJObk41s
Views: 784 WikiAudio
What is GLASS TRANSITION? What does GLASS TRANSITION mean? GLASS TRANSITION meaning & explanation
What is GLASS TRANSITION? What does GLASS TRANSITION mean? GLASS TRANSITION meaning - GLASS TRANSITION definition - GLASS TRANSITION explanation. Source: Wikipedia.org article, adapted under https://creativecommons.org/licenses/by-sa/3.0/ license. The glass–liquid transition or glass transition for short is the reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased. An amorphous solid that exhibits a glass transition is called a glass. The reverse transition, achieved by supercooling a viscous liquid into the glass state, is called vitrification. The glass-transition temperature Tg of a material characterizes the range of temperatures over which this glass transition occurs. It is always lower than the melting temperature, Tm, of the crystalline state of the material, if one exists. Hard plastics like polystyrene and poly(methyl methacrylate) are used well below their glass transition temperatures, that is in their glassy state. Their Tg values are well above room temperature, both at around 100 °C (212 °F). Rubber elastomers like polyisoprene and polyisobutylene are used above their Tg, that is, in the rubbery state, where they are soft and flexible. Despite the change in the physical properties of a material through its glass transition, the transition is not considered a phase transition; rather it is a phenomenon extending over a range of temperature and defined by one of several conventions. Such conventions include a constant cooling rate (20 kelvins per minute (36 °F/min)) and a viscosity threshold of 1012 Pa·s, among others. Upon cooling or heating through this glass-transition range, the material also exhibits a smooth step in the thermal-expansion coefficient and in the specific heat, with the location of these effects again being dependent on the history of the material. The question of whether some phase transition underlies the glass transition is a matter of continuing research. The glass transition of a liquid to a solid-like state may occur with either cooling or compression. The transition comprises a smooth increase in the viscosity of a material by as much as 17 orders of magnitude without any pronounced change in material structure. The consequence of this dramatic increase is a glass exhibiting solid-like mechanical properties on the timescale of practical observation. This transition is in contrast to the freezing or crystallization transition, which is a first-order phase transition in the Ehrenfest classification and involves discontinuities in thermodynamic and dynamic properties such as volume, energy, and viscosity. In many materials that normally undergo a freezing transition, rapid cooling will avoid this phase transition and instead result in a glass transition at some lower temperature. Other materials, such as many polymers, lack a well defined crystalline state and easily form glasses, even upon very slow cooling or compression. The tendency for a material to form a glass while quenched is called glass forming ability. This ability depends on the composition of the material and can be predicted by the rigidity theory. Below the transition temperature range, the glassy structure does not relax in accordance with the cooling rate used. The expansion coefficient for the glassy state is roughly equivalent to that of the crystalline solid. If slower cooling rates are used, the increased time for structural relaxation (or intermolecular rearrangement) to occur may result in a higher density glass product. Similarly, by annealing (and thus allowing for slow structural relaxation) the glass structure in time approaches an equilibrium density corresponding to the supercooled liquid at this same temperature. Tg is located at the intersection between the cooling curve (volume versus temperature) for the glassy state and the supercooled liquid.
Views: 4806 The Audiopedia
वेजिटेबल बिरयानी (Vegetable Biryani) by Tarla Dalal
Vegetable Biryani,a most popular and common rice dish. Recipe link : http://www.tarladalal.com/Vegetable-Biryani-(-Chawal)-37251r Subscribe : http://goo.gl/omhUio Tarla Dalal App: http://www.tarladalal.com/free-recipe-app.aspx Facebook: http://www.facebook.com/pages/TarlaDalal/207464147348 YouTube Channel: http://www.youtube.com/user/TarlaDalalsKitchen/featured Pinterest: http://www.pinterest.com/tarladalal/ Google Plus: https://plus.google.com/107883620848727803776 Twitter: https://twitter.com/Tarla_Dalal Tarla Dalal Blogspot: http://tarladalal.blogspot.in/ Vegetable Biryani Vegetable biryani is the most popular and the most common rice dish that comes to one's mind when you think of indian cuisine. . . It is very tasty and definately worth a try ! Preparation Time: 15 minutes Cooking Time: 55 minutes Soakeing Time : 30 minutes Makes 6 servings Ingredients For The Rice 1 bayleaf (tejpatta) 25 mm (1") stick cinnamon (dalchini) 1 clove 1 cardamom (elaichi) 1 1/2 cups long grained rice ( basmati), soaked for 30 minutes and drained salt to taste For The Vegetable Gravy 1 1/2 cups boiled mixed vegetables (carrots , peas , cauliflower , french beans , potatoes) cut into cubes 1/4 cup paneer (cottage cheese) , cut into cubes 2 tbsp oil 1/2 tsp cumin seeds (jeera) 3/4 cup finely chopped onions 2 tsp ginger-green chilli paste 1/4 tsp turmeric powder (haldi) 2 tsp coriander (dhania) powder 1 tsp chilli powder 1/2 tsp garam masala 1 cup roughly chopped tomatoes salt to taste 1/4 cup milk a pinch of sugar Other Ingredients 1/4 cup curds (dahi) 1/4 cup finely chopped coriander (dhania) a few drops of edible saffron colour 2 tbsp ghee Method For the rice 1. Combine 4 1/2 cups of water, bayleaf, cinnamon, clove, cardamom, rice and salt in a deep non-stick pan and cover and cook on a medium flame for 10 minutes or till the rice is cooked. 2. Strain the rice using a strainer and keep aside. For the vegetable gravy 1. Heat the oil in a kadhai and add the cumin seeds. 2. When the seeds crackle, add the onions and sauté on a medium flame for 1 to 2 minutes or till the onions turn translucent. 3. Add the ginger-green chilli paste, turmeric powder, coriander powder, chilli powder and garam masala and sauté on a medium flame for a few seconds. 4. Add the tomatoes and 2 tbsp of water, mix well and cook on a medium flame for 4 to 5 minutes. 5. Add the mixed vegetables, paneer, salt and milk and cook on a medium flame for another 2 to 3 minutes, while stirring occasionally. 6. Add the sugar, mix well and cook on a medium flame for 1 more minute. How to proceed 1. Combine the curds, coriander and saffron colour in a bowl and mix well. 2. Add the prepared rice mixture and mix well. 3. Transfer 1/2 of the rice mixture in a handi and spread it evenly with the back of a spoon. 4. Add all the prepared vegetable gravy on it and spread it evenly. 5. Top it with the remaining 1/2 of the rice mixture and spread it evenly. 6. Pour the ghee evenly over it and cover it with a lid. 7. Place the handi on a non-stick tava (griddle) and cook on a slow flame for 25 to 30 minutes. 8. Serve hot.
Views: 1329174 Tarla Dalal
Mughal E Azam - Dilip Kumar - Madhubala - Prithviraj Kapoor - Full Movie In 15 Mins
Among the costliest movies of its time, Mughal E Azam is the first magnum opus of Indian cinema. A story of love and justice, the movie depicts the tussle between a shrewd Emperor and his love-struck son. Emperor Akbar (Prithviraj Kapoor) celebrates the return of his son, Crown Prince Salim (Dilip Kumar) with a lot of pomp and fervour. Akbar's happiness though is short-lived as Salim indulges in a public affair with Anarkali (Madhubala), a courtesan. Things come to such a pass that Crown Prince Salim rebels and declares war against his father. Will Akbar, The Great, go to the extent of sacrificing his son for the sake of honour? Your favorite Bollywood movies summed up in 15 minutes. Shemaroo Entertainment presents to you 15 Min Movie. Click here to see full list of 15 min movies, http://www. youtube. com/user/15minmovie/videos?view=0 SUBSCRIBE to http://www. YouTube. com/15MinMovie to stay updated on the latest Bollywood blockbusters now only in 15 MINUTES! Connect with us on :- Facebook, http://www. Facebook. com/Shemaroo. Entertainment. Ltd Twitter, http://Twitter. com/BollyFilmVideos Sign up for Free and get daily updates on New Videos, exclusive Web Shows, contests & much more http://youtube.shemaroo.com/default.aspx Send us your feedback and suggestions at : [email protected]
Views: 52642 Shemaroo Shorties
Ramayan Episode 61
Views: 2630161 Smruti Sahu
What is ADDITION POLYMER? What does ADDITION POLYMER mean? ADDITION POLYMER meaning & explanation
What is ADDITION POLYMER? What does ADDITION POLYMER mean? ADDITION POLYMER meaning - ADDITION POLYMER definition - ADDITION POLYMER explanation. Source: Wikipedia.org article, adapted under https://creativecommons.org/licenses/by-sa/3.0/ license. An addition polymer is a polymer which is formed by an addition reaction, where many monomers bond together via rearrangement of bonds without the loss of any atom or molecule under specific conditions of heat, pressure, and/or the presence of a catalyst. This is in contrast to a condensation polymer which is formed by a condensation reaction where a molecule, usually water, is lost during the formation. An addition polymer is formed by a reaction known as polyaddition or addition polymerization. This can occur in a variety of ways including free radical polymerization, cationic polymerization, anionic polymerization and coordination polymerization. Most of the common addition polymers are formed from unsaturated monomers (usually having a double bond). This includes polyethenes, polypropylene, PVC, Teflon, Buna rubbers, polyacrylates, polystyrene, and PCTFE. Addition polymers are also formed from monomers that have a closed ring. Through coordination polymerization, even saturated monomers can form addition polymers. When two or more types of monomer undergo addition polymerization, the polymer formed is known as an addition copolymer. Saran wrap, formed from polymerization of vinyl chloride and vinylidene chloride, is an addition copolymer. With exception of combustion, the backbone of addition polymers are generally chemically inert. This is due to the very strong C-C and C-H bonds and lack of polarisation within many addition polymers. For this reason they are non-biodegradable and hard to recycle. This is, again, in contrast to condensation polymers which are bio-degradable and can be recycled. Many exceptions to this rule are products of ring-opening polymerization, which tends to produce condensation-like polymers even though it is an additive process. For example, poly is chemically identical to polyethylene glycol except that it is formed by opening ethylene oxide rings rather than eliminating water from ethylene glycol. Nylon 6 was developed to thwart the patent on nylon 6,6, and while it does have a slightly different structure, its mechanical properties are remarkably similar to its condensation counterpart. One universal distinction between polymerization types is development of molecular weight by the different modes of propagation. Addition polymers form high molecular weight chains rapidly, with much monomer remaining. Since addition polymerization has rapidly growing chains and free monomer as its reactants, and condensation polymerization occurs in step-wise fashion between monomers, dimers, and other smaller growing chains, the effect of a polymer molecule's current size on a continuing reaction is profoundly different in these two cases. This has important effects on the distribution of molecular weights, or polydispersity, in the finished polymer. The first useful addition polymer was made by accident in 1933 by ICI chemists Reginald Gibson and Eric Fawcett. They were carrying out a series of experiments which involved reacting organic compounds under high temperatures and high pressures. They set up an experiment to react ethene with benzaldehyde in the hope of producing a ketone. They left the reaction vessel overnight, and the next morning they found a small amount of a white waxy solid. It was shown later that this solid was polyethylene.
Views: 907 The Audiopedia
Muqabla (Full Song) Ranjit Bawa-Binnu Dhillon-Bailaras--New Punjabi Songs 2017-Latest Punjabi Songs
Muqabla (Full Song) Ranjit Bawa-Binnu Dhillon-Bailaras-New Punjabi Songs 2017-Latest Punjabi Songs Song : Muqabla Singer : Ranjit Bawa MUSIC : Jatinder Shah LYRICS : Charan Likhari Mix & Master : Sameer Charegaonker YouTube Promotions By - KixTix Media P Ltd. Gaana : http://bit.ly/2ftbZEE Saavn : http://bit.ly/2xNab3m Wynk : http://wynk.in/u/101ZEDHj8LTn8j on Wynk Music I Tunes : http://apple.co/2wYeHYV Spotify : http://spoti.fi/2xHF0Gu Amazon : http://amzn.to/2yIQb04 Jio Music : http://bit.ly/2xCNJrH Idea : http://www.ideamusiclounge.com/mobileshare/?es=dHlwZT10cmFjayZpZD0zMDMxMDI4 Operator Codes :- Airtel Subscribers Direct Dial to 5432116366781 Set as Hello tune https://www.airtelhellotunes.in/single/index/vcode/009163600006781 Vodafone Subscribers for Caller Tune Direct Dial 5379834327 Idea Subscribers for Dialer Tone Direct Dial 567899834327 Aircel Subscribers SMS DT SPACE 6859030 to 53000 BSNL North Subscribers SMS BT SPACE 6859030 to 56700 BSNL South Subscribers SMS BT SPACE 9834327 to 56700 Published Year : 2017 Copyright : White Hill Music & Entertainment Private Limited F-545,1st Floor,Phase -8A Industrial Area,Mohali - 160059 Digitally Powered By : One Digital Entertainment Subscribe us on :- YouTube : http://bit.ly/WhiteHillProduction Facebook : https://www.facebook.com/whitehillproduction & https://www.facebook.com/whitehillmusic Twitter : https://twitter.com/whitehillproduc Instagram : https://www.instagram.com/whitehillmusic/ Website : https://www.whitehillproduction.com
Views: 4915643 White Hill Music
What Points Reham Khan Exposed About Imran Khan in Her Book
What Points Reham Khan Exposed About Imran Khan in Her Book
Views: 377487 Urdu World TV
cham cham he barsan ge
Views: 87504 Nabi Ahmad
ESP Painting & "Dreams"
A look inside our strange world.. Cobalt-60 After entering a living mammal (such as a human being), some of the 60 Co is excreted in feces. The remainder is taken up by tissues, mainly the liver, kidneys, and bones, where the prolonged exposure to gamma radiation can cause cancer. Over time, the absorbed cobalt is eliminated in urine Used for : As a tracer for cobalt in chemical reactions Sterilization of medical equipment. Radiation source for medical radiotherapy. Cobalt therapy, using beams of gamma rays from 60 Co teletherapy machines to treat cancer, has been widely used since the 1950s. Radiation source for industrial radiography. Radiation source for leveling devices and thickness gauges. Radiation source for pest insect sterilization. As a radiation source for food irradiation and blood irradiation. As a radiation source for laboratory mutagenesis use. As a radiation source for stereoregular polymerization reactions, for example in preparation of syndiotactic polymethyl methacrylate. https://en.wikipedia.org/wiki/Cobalt-60 Stolen cobalt-60 found in Mexico; thieves may be doomed December 5, 2013 https://www.washingtonpost.com/world/stolen-cobalt-60-found-in-mexico-curious-thieves-likely-doomed/2013/12/05/262ef990-5d66-11e3-8d24-31c016b976b2_story.html https://duckduckgo.com/?q=cobalt+60&t=h_&ia=web Mineral industry of Africa https://en.wikipedia.org/wiki/Mineral_industry_of_Africa Central African Mining and Exploration Company https://en.wikipedia.org/wiki/Central_African_Mining_and_Exploration_Company THE COBALT PIPELINE Tracing the path from deadly hand-dug mines in Congo to consumers’ phones and laptops https://www.washingtonpost.com/graphics/business/batteries/congo-cobalt-mining-for-lithium-ion-battery/ https://duckduckgo.com/?q=cobalt+60+in+africa&t=h_&ia=web 1,100-year-old Mayan ruins found in North Georgia http://www.rawstory.com/2011/12/1100-year-old-mayan-ruins-found-in-north-georgia/ Pyramids in Florida and Georgia Constructed by Mayans? http://www.mayainamerica.com/2012/01/pyramids-in-florida-and-georgia.html Kenimer Site https://en.wikipedia.org/wiki/Kenimer_Site https://duckduckgo.com/?q=pyramids+in+georgia&t=h_&ia=web https://www.google.com/search?q=Kenimer+Mound&oq=Kenimer+Mound&aqs=chrome..69i57&sourceid=chrome&ie=UTF-8 Georgia Guidestones https://en.wikipedia.org/wiki/Georgia_Guidestones Elbert County, Georgia https://en.wikipedia.org/wiki/Elbert_County,_Georgia
Views: 51 Rebecca Bradley
What does homopolymerization mean?
What does homopolymerization mean? A spoken definition of homopolymerization. Intro Sound: Typewriter - Tamskp Licensed under CC:BA 3.0 Outro Music: Groove Groove - Kevin MacLeod (incompetech.com) Licensed under CC:BA 3.0 Intro/Outro Photo: The best days are not planned - Marcus Hansson Licensed under CC-BY-2.0 Book Image: Open Book template PSD - DougitDesign Licensed under CC:BA 3.0 Text derived from: http://en.wiktionary.org/wiki/homopolymerization Text to Speech powered by TTS-API.COM
Entha Chitram Kada  Full Song|Dwaraka Movie Songs|Vijay Devarakonda, Pooja Jhaveri|MSR, Saikarthic
Watch & Enjoy Entha Chitram Full Song From Dwaraka Movie. Starring Vijay Devarakonda, Pooja Jhaveri & Prudhvi Raj, Music Composed By Sai Karthik, Directed by M.Srinivas Ravindra (MSR), Produced by Pradhyumna Chandrapati Under The Banner Of Legend Cinemas Private Limited. Movie Name: Dwaraka Banner: Legend Cinemas Private Limited Producer: Pradyumna Chandrapate Director: M.Srinivas Ravindra Music: Sai Karthik Casting: Vijay Devarakonda, Pooja Jhaveri Lyrics: Rahman Singer: Sameera Bharadwaj ----------------------------------------------------------------------------------------- Enjoy and stay connected with us!! ►Subscribe us on Youtube: http://bit.ly/adityamusic ►Like us: http://www.facebook.com/adityamusic ►Follow us: http://www.twitter.com/adityamusic ►Circle us: https://plus.google.com/+adityamusic SUBSCRIBE Aditya Music Channels for unlimited entertainment: ►For New Movies in HD: http://www.youtube.com/Adityamovies ►For Songs with Lyrics: https://www.youtube.com/AdityaMusicNM... ►For Devotional Songs: http://www.youtube.com/AdityaDevotional ►For Kids Educational: http://www.youtube.com/AdityaKids →"మా పాట మీ నోట" Telugu Lyrical Songs - http://bit.ly/1B2EcJG →Latest Tollywood Lyric Video Songs - http://bit.ly/1Km97mg →Ever Green Classics - https://goo.gl/1fZEDy →Popular Jukeboxes - https://goo.gl/LNvAIo →Telugu Songs with Lyrics - https://goo.gl/7ZmgWT © 2016 Aditya Music India Pvt. Ltd.
Views: 352456 Aditya Music
Views: 216038 Raj Aryaan
Pooja Pandey.नया साल का सबसे हिट गाना ।। HAPPY NEW YEAR.2018.New Bhojpuri Hit Songs.2018
इस वीडियो का Free MP3 Download करने के लिए हमारा Mobile APP MP3BAJAO Playstore से डाउनलोड करे या इस लिंक पर क्लिक करे :- https://goo.gl/CsZDkP ******** BHOJPURI VIDEO देखने के लिए हमारे चैनल को सब्सक्राइब करे :-https://goo.gl/7FNrFN ◄ Mp3 Download Link :- https://goo.gl/enuMDu Mobile App Download Link :- https://goo.gl/S5DKZH ◄ यदि आपको ए वीडियो पसंद आया तो कमेन्ट बॉक्स में अच्छे कमेन्ट जरूर दे और फेसबुक और व्हाट्सप पर भी अपने फ्रेंड के साथ शेयर करे आप के कमेन्ट से किसी कलाकार का अपमान न हो ऐसा कुछ न लिखे . ◄ आप भोजपुरी गाने की रिकॉर्डिंग के लिया हमरा डिजिटल स्टूडियो संजीवनी में फ़ोन कर सकते है हमारा नंबर यह है :-०११-22481764 sanjivanidigital, #sanjivanibhojpuri, sanjivanivideo, sanjivanistudio, ◄ संजीवनी स्टूडियो ,संजीवनी डिजिटल ,संजीवनी वीडियो,भोजपुरी हिट्स ४ u ये सब संजीवनी के अन्य चैनल है जिसे आप सब्सक्राइब कर सकते है ◄ आप हमारे फेसबुक और अन्य सोशल मीडिया से भी जुड़ सकते है नीचे दिए गए लिंक के क्लिक करके : FaceBook पर हमें लाइक करे :- https://goo.gl/0yY1uc Twitter पर हमें फॉलो करे :- https://goo.gl/V28Dac ◄ यदि आप bhojpuri songs, video bhojpuri, bhojpuri songs, video bhojpuri song, new bhojpuri, Bhojpuri Video Song, Bhojpuri Song, Item Song, Romantic Song, bhojpuri, Latest Bhojpuri Song, 2017, new BHOJPURI sONG, Bhojpuri New Song, 2017 के सबसे हिट भोजपुरी गाना पसंद करते है तो हमारे चैनल को सब्सक्राइब जरूर करे ◄ Album Detail यहा देखे :- एल्बम का नाम :- HAPPY NEW YEAR.2018 गायक का नाम :-Pooja Pandey कंपनी का नाम :- Sanjivani गीतकार का नाम :-Pooja Pandey संगीतकार का नाम :-Bala Ji
Views: 42886 Sanjivani Bhojpuri
Crystallization of polymers
Crystallization of polymers is a process associated with partial alignment of their molecular chains. These chains fold together and form ordered regions called lamellae, which compose larger spheroidal structures named spherulites. Polymers can crystallize upon cooling from the melt, mechanical stretching or solvent evaporation. Crystallization affects optical, mechanical, thermal and chemical properties of the polymer. The degree of crystallinity is estimated by different analytical methods and it typically ranges between 10 and 80%, thus crystallized polymers are often called 'semicrystalline'. The properties of semicrystalline polymers are determined not only by the degree of crystallinity, but also by the size and orientation of the molecular chains. Polymers are composed of long molecular chains which form irregular, entangled coils in the melt. Some polymers retain such a disordered structure upon freezing and thus convert into amorphous solids. In other polymers, the chains rearrange upon freezing and form partly ordered regions with a typical size of the order 1 micrometer. Although it would be energetically favorable for the polymer chains to align parallel, such alignment is hindered by the entanglement. Therefore, within the ordered regions, the polymer chains are both aligned and folded. Those regions are therefore neither crystalline nor amorphous and are classified as semicrystalline. Examples of semi-crystalline polymers are linear polyethylene, polyethylene terephthalate, polytetrafluoroethylene or isotactic polypropylene. Whether or not polymers can crystallize depends on their molecular structure – presence of straight chains with regularly spaced side groups facilitates crystallization. For example, crystallization occurs much easier in isotactic than in the atactic polypropylene form. Atactic polymers crystallize when the side groups are very small, as in polyvinyl and don't crystallize in case of large substituents like in rubber or silicones. Nucleation starts with small, nanometer-sized areas where as a result of heat motion some chains or their segments occur parallel. Those seeds can either dissociate, if thermal motion destroys the molecular order, or grow further, if the grain size exceeds a certain critical value. Apart from the thermal mechanism, nucleation is strongly affected by impurities, dyes, plasticizers, fillers and other additives in the polymer. This is also referred to as heterogeneous nucleation. This effect is poorly understood and irregular, so that the same additive can promote nucleation in one polymer, but not in another. Many of the good nucleating agents are metal salts of organic acids, which themselves are crystalline at the solidification temperature of the polymer solidification. Crystal growth is achieved by the further addition of folded polymer chain segments and only occurs for temperatures below the melting temperature Tm and above the glass transition temperature Tg. Higher temperatures destroy the molecular arrangement and below the glass transition temperature, the movement of molecular chains is frozen. Nevertheless, secondary crystallization can proceed even below Tg, in the time scale of months and years. This process affects mechanical properties of the polymers and decreases their volume because of a more compact packing of aligned polymer chains. The chains interact via various types of the van der Waals forces. The interaction strength depends on the distance between the parallel chain segments and it determines the mechanical and thermal properties of the polymer. Video Empire produces videos read aloud. Use the information in this video at your own risk. We cannot always guarantee accuracy. This video uses material from https://en.wikipedia.org/wiki/Crystallization_of_polymers, licensed with CC Attribution-ShareAlike 3.0. This video is licensed with CC Attribution-Share-Alike 3.0 https://creativecommons.org/licenses/by-sa/3.0/us/ In order to adapt this content it is required to comply with the license terms. Image licensing information is available via: https://en.wikipedia.org/wiki/Crystallization_of_polymers
Views: 2581 Video Empress