Ligand fonksiyonlu polimer mikro küre yüzeylerine kendinden tohumlamalı elektrolizsiz kaplama yoluyla metal kaplanması
Self-seeded electroless metal plating on polymer microspheres with ligating surface groups
Yazar: KÜBRA YÜKSEL
Danışman: PROF. DR. OKAN SİRKECİOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Ana Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: Kimya = Chemistry

Özet:
Bu çalışmada, polimer mikro kürelerinin yüzeyinde oluşturulan metal şelatlarının indirgenmesiyle katalitik miktarda meydana gelen sıfır değerlikli metalin elektrolizsiz kaplama banyosundan metal kaplamada tohumlama merkezi olarak kullanılabileceğini ortaya koymuştur. Bu amaçla taşıyıcı polimer olarak çaprazbağlı glisidil metakrilat (GMA) mikroküreleri (210-420µm) kullanılmıştır. Bunların trietilen tetraamin (TETA) ile muamele edilmesiyle yüzeyi amin fonksiyonlu tanecikler elde edilmiştir. TETA foksiyon yoğunluğu yaklaşık 1 mmol g-1 olan küreciklerin Cu(II), Ni(II) ve Ag(I) iyonları içeren sulu çözeltilerle etkileştirilmesiyle yüzeylerinde metal şelatlar oluşturulmuştur.Bu şelatların yapısındaki metal iyonlarının hidrazin ve hipofosfit gibi indirgenlerle indirgenmesiyle mikroküre yüzeylerinde elementel metal meydana getirilmiştir. Bu metallerin elektrolizsiz banyo çözeltilerinden mikroküre yüzeylerine metal kaplanmasında tohumlama merkezi işlevini gördüğü kanıtlanmıştır.Literatürde bu tohumlama işlemi genellikle PdCl2 ve SnCl2 ile yapılmaktadır. Paladyumun pahalı olması nedeniyle bu yol elektronik baskı devrelerinin üretim maliyetlerini yükseltmektedir. Grubumuzca daha önce yapılan çalışmalarda, ?yüzey aktifleştirme? adıyla bilinen bu işlemin yerine elektrolizsiz kaplamanın yüzeyde oluşturulan az miktarda metalin tohumlama etkisiyle gerçekleştirilebileceği gösterilmiştir.Bu çalışmada ise, öncekilerden farklı olarak metal komplekslerinin indirgenmesiyle oluşan sıfır değerlikli (zerovalent) metalin tohumlama etkisiyle Cu(II), Ni(II) ve Ag(I)'ün elektrolizsiz banyolarında bu metallerin kaplanabileceği gösterilmiştir.Elde edilen polimer kürecikleri ve bunların metallenmiş türevleri FT-IR ve X-Ray elektron spektroskopisi (XPS) teknikleri ile karakterize edilmiştir.Özet olarak bu çalışma göstermiştir ki, TETA fonksiyonlu GMA mikroküreleri kendiliğinden tohumlamalı elektrolizsiz metal kaplama yoluyla bakır,nikel ve gümüş ile kolayca ve nispete kısa sürede kaplanabilmektedir.Buradaki çalışmada ise öncekilerden farklı olarak metal iyonlarının polimer yüzeyinde önceden meydana getirilen ve donor karakteri çok iyi olan ligandlarla kompleks oluşturması yolu seçilmiştir. Burada polimer mikro kürelerinin yüzeyinde oluşturulan kompleksin yapısında bulunan metalin indirgenmesinin mümkün olup olmadığı ve indirgenme başarılırsa bunun aynı metalin elektrolizsiz çözeltisinden çökeltmede tohumlama merkezleri olarak işlev görüp göremiyeceğinin incelenmesi amaçlanmıştır. Kısacası bu tez çalışmasının amacı polimer yüzeylerin metallerle şelat yapıcı ligandlar üzerinden elementel metal kaplanmasının başarılıp başarılamayacağının ortaya konulmasıdır. Bilindiği kadarıyla açık literatürde bu alanda yapılmış herhangi bir yayın bulunmamaktadır. Dolaysıyla bu çalışma literatürdeki bu eksikliği tamamlayacak ve açıklık getirecektir.

Abstract:
Electroless metal plating (EMP) is a versatile method for surface metallization of plastics and ceramics. Common electroless metal plating process involves surface metallization, surface activation by Pd(II) and SnCl2 solutions and electroless metal deposition steps. The surface modification step is of prime importance to attain good adhensionof the metal layer to the substrate surfaces. Numerous techniques such as ion assisted laser treatment, plasma modification, excimer UV laser and dielectric barrier discharge have been developed for modification of polymer surfaces. Beside thosehigh energy- irradiation methods, wet chemical methods such as nitration and sulfonation have been reported to be efficient in modification of relatively polar polymer surfaces.The deposition of zero-valent metals onto polymer surfaces has received much attention for its potential applications in prepearing light-weight mirrors, solar energy conventers and catalysts. Even though the polymer-assisted microdispersion of metal sols was performed half a century ago, the metallization of polymer surfaces is a relatively new area of research.In more recent methods, metal ions in aqueous solutions are seized by ligating groups such as amino, carboxyl, or quaternary amino groups on polymer surfaces. Thereafter, these ions are reduced by a suitable reducing agent suc as sodium hypophosphite or dimethylamino borane. Details of the preparation for the electroless plating of vinyl benzyl ammonium-based polymer beads were given by Warshawsky and Upson. In those methods, the deposited metals are mostly amorphous and nonuniform and so lack metallic luster. With this approach, metal-plated polymer particles thar are up to %10 noble metal have been obtained.Multimetalized layers on polymer surfaces have also been achieved subtractive and additive deposition techniques. In the subtractive deposition techniques, metal-coated polymers are immersed in a different metal-ion solution, and metals on the surfaces are replaced with another metal with less negative reduction potential. In the additive method, additional metal deposition occurs on premetalized surface by the catalytic effect of existing metal used together with a reducing agent.Coating of polymer surfaces is of interest in very various industries such as electronics, catalysts, textile and automotive industry. There appear few common methods of metal coatings on wood, selluloce and on polymer metarials. Physical vapor deposition, chemical vapor deposition, sputtering, microcontact printing and electroless plating have found extensive use for decorative or mechanical inforcement purposes. Altough such methods give satisfactory metal coatings generally these suffer from with adhesion to the surfaces.Among those methods the electroless plating method is attractive due to its relatively cheap processing. In classical way of the metal plating method surface of the substrate first, is subjected to pretreatment to create hydrophilicity. This is the first step of the process which is crucial to attain better adhesion with the metal coating layer. This can be carried out by chemical means or by plasma techniques in large scale industry processes. The latter is mostly prefered industrial processes due to its high speed. In the plasma modification the surface is modified to impart amino or hydroperoxy groups by ordinary or cold-plasma techniques this makes the surface hydrophilic enough to provide good adhesion.The second step, so called ? surface activation? involves PdCl2+ SnCl2 treatment which provides zerovalent palladium element in few miligrams persquare meter. This is essencial for the success of the electoless metal plating in the next step. The role of palladium is seeding of the metal deposition. İncreasing the palladium density gives high speed depositions, but its high cost makes its use in tiny quantities.The last step is the electroless plating in which the article to be plated is simply soaked into the electoless plating solution. Many electroless plating solutions are now avaliable commercially. Metallization with this solutions proceeds in satisfactory rates. By this way 1-5 µm metal thicknesses can be attained.The galvanic replacement method developed in recent years is closely related to the electroless metallization process. In this process a metal coating on the article surface is simply replaced with a more noble metal by treating with the metal ion solution.The difference is that, this process does not need the use of electoless metal plating solution. The driving of the process is the difference between reduction potentials of the two metal ions.The standart electroless plating process described above is already being used in industrial surface metallization process. Common drawbacks of this process is weak adhension to the surface and cost of the surface activation process.To overcome those drawbacks in our previous works we disclosed the use of the metal to be coated as seeding material. In those studies, the polymer surfaces modified with hydrazine or sulfonyl hydrazide gruoups were employed for generation of small quantities of copper metal from aqueous Cu(II) solution. The copper was demostrated to serve seeding points for copper plating from the electroless solution in the final step. This showed that the electroless plating can be achieved without using palladium element. Moreover it was shown that adhension to the metal layer is enhanced considerably.As an extension of those studies in present work we describe a self-seeded electroless metallization process, which involves chemical reduction of the metal chelate to give zerovalent metal on the substrate in tiny quantities. The zerovalent metals so generated were demonstrated to provide seeding effect for depositing much more metal from the electroless metal solution.For this propose epoxy functional polymer microspheres were prepeared by terpolymerization of glycdyl methacrylate (GMA)-methyl methacrylate (MMA)- ethylen glycoldimethacrylate (EGDMA) mixture (in 30/60/10 molar ratio) in aqueous suspension. The resulting microspheres were made amine functional by treating with triethylentetraamine (TETA) at 120 0C. The resulting material was used as macrochealting agent for complexing with Cu(II), Ni(II) and Ag(I) ions in aqueous solution. The microspheres bearing the coloured metal chelates on their surfaces were treated with strong reducing agents such as hydrazine and sodium hypophospite in water. It was observed that, copper and silver complexes are easliy reduced with hyrazine whereas, reduction of nickel is slow. Reduction of nickel was achieved by heating in a sodium hypophosphite solution. The reduction of metal ions can be followed visually by rapid change of the colours of the mixtures.It is important to note that, the fresh metal surfaces are very susceptible to air oxygen to give metal oxides. Therefore great care must be exercised to avoid air oxidation and the samples must be stored in tightly closed bottles.Both XPS and metal analyses indicated presences of 1,5- 2,04 mmol g-1 of metals. We have not pay attention to attain high metal contents in the step.In the last step, the microspheres containing above zerovalent metals were subjected to electroless plating for 4-6 h. The resulting products showed considerable mass increases implying succesful metallizations in each case. The overall mass increases of the microspheres were in 33,8-41.1 % . The simply process is simply depicted in the following scene. In the study we have used common electroless plating solutions given in the literature and not pay attention for the optimization of the metal thicknesses. However the results show satisfactory metallization in each case.Moreover, to inspect kinetics of the metallization, the microspheres with the copper seeds were treated with the electroless copper solution in different time intervals. The copper plating was monitored by mass increases of the samples. It was shown that, the copper deposition is fast at the beginning without using a special accelerating agent, but becomes slow with time.The copper plating-time plot showed leveling of the deposition at about two hours and remains almost constant beyond that. At this point, why the metal deposition stops after some time is a question mark at this moment. However it highly probably that the metalized surface loss the activity in seeding by oxidation or absorption of some charged ions.The overall results revealed that, the self-seeded metalization presented provides sucessful metalization with copper, nickel and silver by wet-chemical process. The metalized microspheres might be useful as catalyst in the reactions where zerovalent metals employed.