en>Rjwilmsi: /* References */Added 1 doi to a journal cite using AWB (10222)

2014-06-18T07:59:43Z

References: Added 1 doi to a journal cite using AWB (10222)

en>Helpful Pixie Bot: ISBNs (Build KE)

2012-05-11T05:40:23Z

ISBNs (Build KE)

New page

A '''high-refractive-index polymer''' (HRIP) is a [[polymer]] that has a [[refractive index]] greater than 1.50.<ref name=Liu>{{cite journal|author=Jin-gang Liu and Mitsuru Ueda|title=High refractive index polymer: fundamental and practical applications|journal=J. Mater. Chem.|year=2009|volume=19|pages=8907|doi=10.1039/B909690F|issue=47}}</ref>

Such materials are required for [[anti-reflective coating]] and photonic devices such as [[light emitting diode]]s (LEDs) and [[image sensor]]s.<ref name=Liu /><ref name=Yen>{{cite journal|author=Hung-Ju Yen and Guey-Sheng Liou|title=A facile approach towards optically isotropic, colorless, and thermoplastic polyimidothioethers with high refractive index|journal=J. Mater. Chem.|year=2010|volume=20|pages=4080|doi=10.1039/c000087f|issue=20}}</ref> The refractive index of a polymer is based on several factors which include [[polarizability]], chain flexibility, [[molecular geometry]] and the polymer backbone orientation.<ref>{{cite journal|author=Cheng Li, Zhuo Li, Jin-gang Liu, Xiao-juan Zhao, Hai-xia Yang and Shi-yong Yang|title=Synthesis and characterization of organo-soluble thioether-bridged polyphenylquinoxalines with ultra-high refractive indices and low birefringences|journal=Polymer|year=2010|volume=51|pages=3851|doi=10.1016/j.polymer.2010.06.035|issue=17}}</ref><ref>{{cite journal|author=Kwansoo Han, Woo-Hyuk Jang and Tae Hyung Rhee|title=Synthesis of fluorinated polyimides and their application to passive optical waveguides|journal=J. Appl. Polym. Sci.|year=2000|volume=77|pages=2172|doi=10.1002/1097-4628(20000906)77:10<2172::AID-APP10>3.0.CO;2-9|issue=10}}</ref>

As of 2004, the highest refractive index for a polymer was 1.76.<ref>Naoki Sadayori and Yuji Hotta "Polycarbodiimide having high index of refraction and production method thereof" [http://www.google.com/patents?vid=va2WAAAAEBAJ US patent 2004/0158021 A1] (2004)</ref> Substituents with high molar fractions or high-n [[nanoparticle]]s in a polymer matrix have been introduced to increase the refractive index in polymers.<ref name=Seto>{{cite journal|author=Ryota Seto, Takahiro Kojima, Katsumoto Hosokawa, Yasuhito Koyama, Gen-ichi Konishi and Toshikazu Takata|title=Synthesis and property of 9,9-spirobifluorene-containing aromatic polyesters as optical polymers with high refractive index and low birefringence|journal=Polymer|year=2010|volume=51|pages=4744|doi=10.1016/j.polymer.2010.08.032|issue=21}}</ref>

==Properties==
===Refractive index===

A typical polymer has a refractive index of 1.30–1.70, but a higher refractive index is often required for specific applications. The refractive index is related to the molar refractivity, structure and weight of the monomer. In general, high [[molar refractivity]] and low molar volumes increase the refractive index of the polymer.<ref name=Liu />

===Optical properties===
[[Optical dispersion]] is an important property of an HRIP. It is characterized by the [[Abbe number]]. A high refractive index material will generally have a small Abbe number, or a high optical dispersion.<ref name=Matsuda>{{cite journal|author=Tatsuhito Matsuda, Yasuaki Funae, Masahiro Yoshida, Tetsuya Yamamoto and Tsuguo Takaya|title=Optical material of high refractive index resin composed of sulfur-containing aromatic methacrylates|journal=J. Appl. Polym. Science|year=2000|volume=50|page=50|doi=10.1002/(SICI)1097-4628(20000404)76:1<50::AID-APP7>3.0.CO;2-X}}</ref> A low birefringence has been required along with a high refractive index for many applications. It can be achieved by using different [[functional groups]] in the initial [[monomer]] to make the HRIP. [[Aromaticity|Aromatic]] monomers both increase refractive index and decrease the [[optical anisotropy]] and thus the birefringence.<ref name=Seto>{{cite journal|author=Ryota Seto, Takahiro Kojima, Katsumoto Hosokawa, Yasuhito Koyama, Gen-ichi Konishi, Toshikazu Takata |journal=Polymer|year=2010|volume=51|pages=4744–4749|doi=10.1016/j.polymer.2010.08.032|title=Synthesis and property of 9,9′-spirobifluorene-containing aromatic polyesters as optical polymers with high refractive index and low birefringence|issue=21}}</ref>

[[File:Calcite.jpg|thumb|Example of birefringence]]

A high clarity (optical transparency) is also desired in a high refractive index polymer. The clarity is dependent on the refractive indexes of the polymer and of the initial monomer.<ref>{{cite journal|author=P. Nolan, M. Tillin and D. Coates|title=High on-state clarity polymer dispersed liquid crystal films |journal=Liquid Crystals|year=1993|volume=14|issue=2|pages=339|doi=10.1080/02678299308027648}}</ref>

===Thermal stability===
When looking at thermal stability, the typical variables measured include [[glass transition]], initial [[decomposition temperature]], degradation temperature and the [[melting]] temperature range.<ref name=Yen /> The thermal stability can be measured by [[thermogravimetric analysis]] and [[differential scanning calorimetry]]. [[Polyesters]] are considered thermally stable with a degradation temperature of 410 °C. The decomposition temperature changes depending on the substituent that is attached to the monomer used in the [[polymerization]] of the high refractive index polymer. Thus, longer [[alkyl]] substituents results in lower thermal stability.<ref name=Seto />

===Solubility===
Most applications favor polymers which are soluble in as many [[solvents]] as possible. Highly refractive [[polyesters]] and polyimides are soluble in common organic solvents such as [[dichloromethane]], [[methanol]], [[hexanes]], [[acetone]] and [[toluene]].<ref name=Yen /><ref name=Seto />

==Synthesis==

The synthesis route depends on the HRIP type. The Michael polyaddition is used for a polyimide because it can be carried out at room temperature and can used for [[step-growth polymerization]]. This synthesis was first succeeded with polyimidothiethers, resulting in optically transparent polymers with high refractive index.<ref name=Yen /> Polycondensation reactions are also common to make high refractive index polymers, such as polyesters.<ref name=Seto />

[[File:michael addition.png|thumb|550px|center|Example of a Michael polyaddition]]
[[File:Polycondensation.png|thumb|550px|center|Example of a polycondensation]]

==Types==
High refractive indices have been achieved either by introducing substituents with high molar refractions (intrinsic HRIPs) or by combining high-n nanoparticles with polymer matrixes (HRIP nanocomposites).

===Intrinsic HRIP===
[[File:PIs.png|thumb|360px|A sulfur-containing polyimide with high refractive index]]

[[Sulfur]]-containing substituents including linear [[thioether]] and [[sulfone]], cyclic [[thiophene]], thiadiazole and [[thianthrene]] are the most commonly used groups for increasing refractive index of a polymer.<ref>{{cite journal|author=Jin-gang Liu, Yasuhiro Nakamura, Yuji Shibasaki, Shinji Ando and Mitsuru Ueda|title=High refractive index polyimides derived from 2,7-Bis(4-aminophenylenesulfanyl)thianthrene and aromatic dianhydrides|journal=Macromolecules|year=2007|volume=40|pages=4614|doi=10.1021/ma070706e|bibcode = 2007MaMol..40.4614L|issue=13 }}</ref><ref>{{cite journal|author=Jin-Gang Liu, Yasuhiro Nakamura, Yuji Shibasaki, Shinji Ando and Mitsuru Ueda|title=Synthesis and characterization of highly refractive polyimides from 4,4′-thiobis[(p-phenylenesulfanyl)aniline] and various aromatic tetracarboxylic dianhydrides|journal=J. Polym. Sci., Part A: Polym. Chem.|year=2007|volume=45|pages=5606|doi=10.1002/pola.22308|bibcode = 2007JPoSA..45.5606L|issue=23 }}</ref><ref>{{cite journal|author=Nam-Ho You, Yasuo Suzuki, Daisuke Yorifuji, Shinji Ando and Mitsuru Ueda|title=Synthesis of high refractive index polyimides derived from 1,6-Bis(p-aminophenylsulfanyl)-3,4,8,9-tetrahydro-2,5,7,10-tetrathiaanthracene and aromatic dianhydrides|journal=Macromolecules|year=2008|volume=41|pages=6361|doi=10.1021/ma800982x|bibcode = 2008MaMol..41.6361Y|issue=17 }}</ref> Polymers with sulfur-rich thianthrene and tetrathiaanthrene moieties exhibit n values above 1.72, depending on the degree of molecular packing.

[[File:Wiki-halogen.png|thumb|160px|left|A halogen-containing polymethacrylate]]
[[Halogen]] elements, especially [[bromine]] and [[iodine]], were the earliest components used for developing HRIPs. In 1992, Gaudiana ''et al.'' reported a series of [[polymethylacrylate]] compounds containing lateral brominated and iodinated [[carbazole]] rings. They had refractive indices of 1.67–1.77 depending on the components and numbers of the halogen substituents.<ref>Russell A. Gaudiana, Richard A. Minns and Howard G. Rogers "High refractive index polymers" {{US patent|5132430}} (1992)</ref> However, recent applications of halogen elements in [[microelectronic]]s have been severely limited by the [[WEEE]] directive and [[RoHS]] legislation adopted by the [[European Union]] to reduce potential pollution of the environment.<ref>{{cite journal|author=Emma Goosey|title=Brominated flame retardants: their potential impacts and routes into the environment|journal=Circuit World|year=2006|volume=32|pages=32|doi=10.1108/03056120610683603|issue=4}}</ref>

[[File:Wiki-phosphonate.png|thumb|A polyphosphonate]]
[[Phosphorus]]-containing groups, such as [[phosphonate]]s and [[phosphazene]]s, often exhibit high molar refractivity and optical [[transmittance]] in the visible light region.<ref>{{cite journal|author=Michael Olshavsky and Harry R. Allcock|title=Polyphosphazenes with high refractive indices: Optical dispersion and molar refractivity|journal=Macromolecules|year=1997|volume=30|pages=4179|doi=10.1021/ma961628q|bibcode = 1997MaMol..30.4179O|issue=14 }}</ref><ref>{{cite journal|author=Toshiki Fushimi and Harry R. Allcock|title=Cyclotriphosphazenes with sulfur-containing side groups: refractive index and optical dispersion|journal=Dalton Trans.|year=2009|pages=2477|doi=10.1039/B819826H|issue=14}}</ref> Polyphosphonates have high refractive indices due to the [[phosphorus]] moiety even if they have chemical structures analogous to [[polycarbonates]].<ref>{{cite journal|author=H. K. Shobha, H. Johnson, M. Sankarapandian, Y. S. Kim, P. Rangarajan, D. G. Baird and J. E. McGrath|title=Synthesis of high refractive-index melt-stable aromatic polyphosphonates|journal=J. Polym. Sci., Part A: Polym. Chem.|year=2001|volume=39|pages=2904|doi=10.1002/pola.1270|bibcode = 2001JPoSA..39.2904S|issue=17 }}</ref> In addition, polyphosphonates exhibit good thermal stability and optical transparency; they are also suitable for [[casting]] into plastic lenses.

[[File:Wiki-organometallic2.png|thumb|150px|left|Organometallic HRIP]]
[[Organometallic]] components result in HRIPs with good [[film]] forming ability and relatively low optical dispersion. Polyferrocenylsilanes<ref>{{cite journal|author=Ian Manners|title=Polyferrocenylsilanes: metallopolymers for electronic and photonic applications|journal=J. Opt. Soc. Am. A|year=2002|volume=4|pages=S221|doi=10.1088/1464-4258/4/6/356|bibcode = 2002JOptA...4S.221M|issue=6 }}</ref> and polyferrocenes containing phosphorus spacers and [[phenyl]] side chains show unusually high n values (n=1.74 and n=1.72).<ref>{{cite journal|doi=10.1002/anie.200604420|title=Polyferrocenylsilane-Based Polymer Systems|year=2007|last1=Bellas|first1=Vasilios|last2=Rehahn|first2=Matthias|journal=Angewandte Chemie International Edition|volume=46|issue=27|pages=5082}}</ref> They might be good candidates for all-polymer photonic devices because of their intermediate optical dispersion between organic polymers and [[inorganic]] [[glass]]es.

===HRIP nanocomposite===
Hybrid techniques which combine an organic polymer matrix with highly refractive inorganic nanoparticles could result in high n values. The factors affecting the refractive index of a high-n nanocomposite include the characteristics of the polymer matrix, nanoparticles and
the hybrid technology between inorganic and organic components. The refractive index of a nanocomposite can be estimated as <math>{n_{comp}} = {\text{Φ}_p}{n_p} + {\text{Φ}_{org}}{n_{org}}</math>, where <math>{n_{comp}}</math>, <math>{n_p}</math> and <math>{n_{org}}</math> stand for the refractive indices of the nanocomposite, nanoparticle and organic matrix, respectively. <math>{\text{Φ}_p}</math> and <math>{\text{Φ}_{org}}</math> represent the volume fractions of the nanoparticles and organic matrix, respectively.<ref>{{cite journal|author=Lorenz Zimmermann, Martin Weibel, Walter Caseri, Ulrich W. Suter and Paul Walther|title=Polymer nanocomposites with "ultralow" refractive index|journal=Polym. Adv. Tech.|year=1993|volume=4|pages=1|doi=10.1002/pat.1993.220040101}}</ref> The nanoparticle load is also important in designing HRIP nanocomposites for optical applications, because excessive concentrations increase the optical loss and decrease the processability of the nanocomposites. The choice of nanoparticles is often influenced by their size and surface characteristics. In order to increase optical transparency and reduce [[Rayleigh scattering]] of the nanocomposite, the diameter of the nanoparticle should be below 25 nm.<ref>{{cite journal|author=H. Althues, J. Henle and S. Kaskel|title=Functional inorganic nanofillers for transparent polymers|journal=Chem. Soc. Rev.|year=2007|volume=9|pages=1454–65|doi=10.1002/chin.200749270|issue=49|pmid=17660878}}</ref> Direct mixing of nanoparticles with the polymer matrix often results in the undesirable aggregation of nanoparticles – this is avoided by modifying their surface. The most commonly used nanoparticles for HRIPs include TiO2 ([[anatase]], n=2.45; [[rutile]], n=2.70),<ref>{{cite journal|author=Akhmad Herman Yuwono, Binghai Liu, Junmin Xue, John Wang, Hendry Izaac Elim, Wei Ji, Ying Li and Timothy John White|title=Controlling the crystallinity and nonlinear optical properties of transparent TiO2–PMMA nanohybrids|journal=J. Mater. Chem.|year=2004|volume=14|pages=2978|doi=10.1039/b403530e|issue=20}}</ref> ZrO2 (n=2.10),<ref>{{cite journal|author=Naoaki Suzuki, Yasuo Tomita, Kentaroh Ohmori, Motohiko Hidaka and Katsumi Chikama|title=Highly transparent ZrO2 nanoparticle-dispersed acrylate photopolymers for volume holographic recording|journal=Opt. Express|year=2006|volume=14|pages=012712|doi=10.1364/OE.14.012712|bibcode = 2006OExpr..1412712S|issue=26 }}</ref> [[amorphous silicon]] (n=4.23), [[PbS]] (n=4.20)<ref>{{cite journal|author=Fotios Papadimitrakopoulos, Peter Wisniecki and Dorab E. Bhagwagar|title=Mechanically attrited silicon for high refractive index nanocomposites|journal=Chem. Mater.|year=1997|volume=9|pages=2928|doi=10.1021/cm970278z|issue=12}}</ref> and [[ZnS]] (n=2.36).<ref>{{cite journal|author=Changli Lü, Zhanchen Cui, Zuo Li, Bai Yang and Jiacong Shen|title=High refractive index thin films of ZnS/polythiourethane nanocomposites|journal=J. Mater. Chem.|year=2003|volume=13|pages=526|doi=10.1039/B208850A|issue=3}}</ref> Polyimides have high refractive indexes and thus are often used as the matrix for high-n nanoparticles. The resulting nanocomposites exhibit a tunable refractive index ranging from 1.57 to 1.99.<ref>{{cite journal|author=Chih-Ming Chang, Cheng-Liang Chang and Chao-Ching Chang|title=Synthesis and optical properties of soluble polyimide/titania hybrid thin films|journal=Macromol. Mater. Eng.|year=2006|volume=291|pages=1521|doi=10.1002/mame.200600244|issue=12}}</ref>
[[File:Wiki-nano.png|thumb|700px|center|High-n polyimide nanocomposite]]

==Applications==

[[File:Matrixw.jpg|thumb|A CMOS image sensor]]

===Image sensors===
A [[microlens]] array is a key component of optoelectronics, optical communications, [[CMOS]] [[image sensors]] and [[displays]]. Polymer-based microlenses are easier to make and are more flexible than conventional glass-based lenses. The resulting devices use less power, are smaller in size and are cheaper to produce.<ref name=Liu />

===Lithography===
Another application of HRIPs is in [[immersion lithography]]. It is a new technique for circuit manufacturing that uses both photoresists and high refractive index fluids. The photoresist needs to have an n value of greater than 1.90. It has been shown that non-aromatic, sulfur-containing HRIPs are the best materials for an optical photoresist system.<ref name=Liu />

===LEDs===
[[File:RBG-LED.jpg|thumb|LEDs of the 5mm diffused type]]
Light-emitting diodes (LEDs) are a common solid-state light source. High-brightness LEDs (HBLEDs) are often limited by the relatively low light extraction efficiency due to the mismatch of the refractive indices between the LED material ([[GaN]], n=2.5) and the organic encapsulant ([[epoxy]] or silicone, n=1.5). Higher light outputs can be achieved by using an HRIP as the encapsulant.<ref>{{cite journal|author=Frank W. Mont, Jong Kyu Kim, Martin F. Schubert, E. Fred Schubert and Richard W. Siegel|title=High-refractive-index TiO2-nanoparticle-loaded encapsulants for light-emitting diodes|journal=J. Appl. Phys.|year=2008|volume=103|pages=83120|doi=10.1063/1.2903484|bibcode = 2008JAP...103h3120M|issue=8 }}</ref>

==See also==
{{colbegin}}
*[[Refractive index]]
*[[Refractometer]]
*[[Abbe number]]
*[[Optoelectronics]]
*[[Polarizability]]
*[[Birefringence]]
*[[Lorentz-Lorenz equation]]
*[[Dispersion (optics)|Dispersion]]
*[[Optical anisotropy]]
*[[Nanocomposite]]
*[[Image sensor]]
*[[Immersion lithography]]
*[[Organic light emitting diode]] (OLED)
{{colend}}

==References==
{{reflist|30em}}

==Further reading==
*{{cite book|author=Ralf B. Wehrspohn, Heinz-Siegfried Kitzerow and Kurt Busch|title=Nanophotonic Materials|year=2008|publisher=Wiley-VCH Inc.|location=Germany|isbn=978-3-527-40858-0}}

[[Category:Optics]]
[[Category:Polymers| ]]

V-statistic - Revision history

en>Rjwilmsi: /* References */Added 1 doi to a journal cite using AWB (10222)

en>Helpful Pixie Bot: ISBNs (Build KE)