Latex parçacıklarından film oluşumu sürecinde parçacık ara yüzeylerinde kaynaşma ve polimer zincir difüzyonu
Başlık çevirisi mevcut değil.
- Tez No: 55535
- Danışmanlar: PROF.DR. ÖNDER PEKCAN
- Tez Türü: Doktora
- Konular: Fizik ve Fizik Mühendisliği, Physics and Physics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 91
Özet
ÖZET Bu çalışmada donor ve akseptör etiketli polimer zincirlerinden oluşan sert PMMA-PIB parçacıkları kullanılarak, mikron boyutlarında filmler yapıldı. Filmler farklı sıcaklık ve zaman aralıklarında tavlandılar. LS-50 Perkin Elmer kararlı durum spektrometresi kullanılarak, filmin tavlanma zamanına ve sıcaklığına bağlı olarak, donör ve akseptörün floresans emis yon şiddetleri ölçüldü. Filmin optiksel özelliklerinin tavlanma sıcaklık ve zamanına bağlı olarak değiştiği gözlendi. Bu değişimin donör ve ak septör emisyon şiddeti üzerindeki etkisini ortadan kaldırmak için bir optiksel düzeltme metodu geliştirildi. Bu optiksel düzeltme metodunun doğruluğunu görmek için, bilgisayarda floresans tekniğin simülasyonu yapıldı. Parçacık-parçacık ara yüzeyinde polimer zincir difüzyonu için bir model yapıldı. Difüzyon katsayılarım bulmadan polimer zincirlerinin aktivasyon enerjisini hesaplamak için yeni bir teknik geliştirildi. Farklı kalınlıklarda yapılan filmler için, kalınlığın polimer zinciri difüzyonuna etkisi incelendi ve difüzyon aktivasyon enerjisi hesaplandı. Tek bir film için, farklı sıcaklıklarda aynı zaman aralıklarında tavlamalar yapılarak, zincirlerin difüzyon aktivasyon enerjisi hesaplandı. Difüzyon deneyi seri sinde ise, tek bir film aynı sıcaklıkta farklı zaman aralıklarında tavlandı. Bu deney serisinde tavlanan filmler için zincir difüzyon katsayıları bulundu ve bunlardan yararlanılarak, Arrhenius ifadesinden polimer zincirinin difüzyon aktivasyon enerjisi hesaplandı. Burada hesaplanan aktivasyon enerjisi ile, bizim geliştirdiğimiz metod ile bulunan aktivasyon enerjilerinin birbirine yakın değerler olduğu görüldü.
Özet (Çeviri)
STUDYING HEALING AND INTERDIFFUSION DURING LATEX FILM FORMATION BY FLUORESCENCE TECHNIQUE SUMMARY“Polymer latex”is the term used to describe the polymers that are packed in discrete particles which must coalescence during drying and subsequent aging to form a protective polymer film. Dispersions in water are called lattices or emulsions, and those in aliphatic hydrocarbons are referred to as“non-aqueous”dispersions (NAD). NADs tend to aggregate or“flocculate”, readily in the absence of a stabilizer agent, due to the Van der Waals attraction forces between the particles. If a layer of a suitable polymer surrounding the particles is present, then a dispersion occurs in the shell surrounding the polymer and containing the“stabilizer”or“dispersant”. This shell is called the“stearic barrier”. In good solvents, dispersion stability occurs due to the repulsive force generated upon the contact of the stearic barrier of the latex- particles. The magnitude of the repulsive force depends critically on the distance separating the particle surfaces and on the quality of the solvent for the polymer serving as the stabilizer. If minimum film formation temperature (MFT) is around the room temperature, the polymer latex particles are called“soft latex particles”, and after the evaporation of the solvent, the latex particles become de formed. Film formation process of soft latex particles can be divided into several steps, which are depicted in cartoon form in Fig. 1. 2onOoOoo X) Fig. 1 Pictorial view of the formation of a film produced by vater evap oration from a dispersion of soft latex particles. vuAnother type of polymer latex particles is“hard polymer latex parti cles”. After the evaporation of solvent at the room temperature, the par ticles are not deformed, and minimum film formation temperature of the polymer latex is higher than the room temperature. Hard latex particles become deformed after annealing above its glass transition temperature. Then chain diffusion is detected between the particle-particle interface. PMMA glass transition temperature is about 110°C, and PMMA parti cles are hard latex. In this work, we have used poly(methyl methacrylate) (PMMA) parti cles prepared by non- aqueous dispersion (NAD) polymerization. These particles were labeled with appropriate donor (naphthalene, N), and ac ceptor (pyrene, P) chromophores. 1-3 pun particles which has two compo nents were used. The major part, PMMA, comprises 96% of the material, and the minor component, polyisobutylene (PIB), forms an interpenetrat ing network through the particle interior and is very soluble in certain hydrocarbon media. A thin layer of PIB covers the particle surface and provides colloidal stability in stearic stabilization. When two film samples prepared from these latex particles are brought into a contact at a temperature above the glass transition, the junction surface develops increasing mechanical strength until, at very long con tact times, the full fracture strength of the bulk polymer is reached. At this point the junction surface has, in all respects, become indistinguish able from any other surface that might be located within the bulk mate- rial,that is the junction has“healed”. During the healing process at the junction surface, the penetration of the chains in random directions leads to an increasing number of intersections of polymer chains. The molec ular interpenetration process is related to the self-diffusion in the bulk polymer, but the two are not identical. In a self-diffusion measurement, we see the polymer coils move over distances many times their mean di ameter (Fig. (2.a)), whereas healing is essentially completed in the time that takes a polymer molecule initially next to the junction surface to move halfway across it (Fig. (2.b)). (a) (bi Fig. 2 Self-diffusion (a), and healing (b) in polymer systems. The latex films were prepared as follows; the same weights of N- and P-labeled particles were dispersed with heptane in a test tube. After complete mixing, dispersion was dropped on a round window plate with vma diameter of 1.3 cm. Heptane was allowed to evaporate, and the window was placed on a solid surface with the accessory of Model LS-50 fluores cence spectrometer of Perkin-Elmer. All measurements were carried out in the front face position at room temperature. N-P film sample was excited at 286 nm, in order to maximize naphthalene absorbance. The film of latex particles was annealed above Tg of PMMA for various time and temperature intervals. The process of interparticle polymer diffusion has been studied by non- radiative energy transfer (DET), using the steady state fluorescence tech nique. Emission spectra of N and P are detected by exciting N at 286 nm before and after each annealing step. In Fig. 3 the solid line indicates the spectra before annealing, where the origin of P intensity is DET due to the radiative energy transfer between N-and P-labeled particles at the contact surfaces. From the point of view of DET, the changing of intensities are quite surprising. One would expect a decrease in Ijv(i) due to DET as Ip(t) is increased. This unexpected variations in !#(*) and Ip(t) are related to the changing of the optical properties of the film during annealing process. When only P was excited at 345 nm, its emission spectra are shown in Fig. (4). These spectra were used to observed the changes of the optical properties of the film during the annealing processes. We proposed photon diffusion theory to explain the changins in P intensity or in the optical properties of the film depending on annealing process. The collision probability, P{r), of a travelling photon with any scattering center in a film is given by, P(r) = 1 - exp(-r/ < r >) where r is the distance of a photon between each consecutive collision, and < r > is defined as the mean free path of a photon. In order to derive the relation for the fluorescence intensity of P, lop, we defined the probability of a photon encountering a pyrene molecule to be Pp(s) = 1 - exp(-sflp) Here, s presents the total distance that the photon travels in the film, and L is the mean distance that the photon travels in the film, before it finds a pyrene molecule. Monte Carlo simulations were carried out to calculate the number of scattered {Nsc) and emitted (Nop) photons from a film by employing photon diffusion theory. Healing of particle-particle junction was modeled by the variation in the mean free path (< r >) of a photon in a latex film at each annealing step. Scanning electron mi croscopy (SEM) was used to detect the disappearance of particle-particle boundaries, which then was related to the variation in transparency and the optical path, s, of a photon in a latex film. Pyrene emission intensity lop in experiment and Nop in simulation have the same character, both of them having a maximum. But these are not identical, because some parameters used in the simulation are not related to the optical prop erties of the films. For example, one of them, photon mean free path, < r >, determines the optical properties of the films and the fluorescence emission intensities. This shows that photon diffusion theory can be used IX800- 300 360 Wavelength (nm) 420 460 500 Figure 3 Emission spectra of naphthalene (N) and pyrene (P) when N-P film is excited at 286 nm before annealing (continous line) and after annealing at 100, 140, 160 °C for 30 min intervals. to model the optical properties of the annealed latex particles during film formation process.60 -\ CL O c CD c >- Wavelength (nm) Figure 4 Emission (Iop) and scattered (Jac) spectra of latex film after annealing at 100, 130, 170, 210 °C for 30 min intervals. When the film is exposed to 286 nm wavelength, the probability of a photon encountering a naphthalene molecule is Pn(sn) = 1 - exp(-Siv/Jjv) XIHere, s# represents the toted distance the photon travels in the film, and Jjv is the mean distance that the photon travels in the film, before it finds a naphthalene molecule. Rate equations for N and P are related to the photon encountering probabilities and the chain diffusion between the particles. N intensity- must be increased, as P intensity decreases upon DET, which depends on the chain diffusion between the particles. The number of the excited naphthalene molecules in the intermixed region is referred as N£, and the number of pyrene molecules is Pq. The number of excited naphthalene molecules, N*, and the number of excited pyrene molecules, P*, depend on the probability of a photon encountering a naphthalene molecule. If there is not any P around N approximately in the Foerster distance, N* may de-excite either radiatively by fluorescence emission with rate parameter kFM, or radiationlessly by internal quenching with rate param eter fcjjv- In the intermixed region, N* transfers its energy by dipole- dipole interaction to P with nonradiative energy transfer rate parameter ko.A- The rate equation for [N*] is thus d[N* = I0[N](l - t-»*1“) - kDA[NZ}[Po] - (kFN + kIN)[N* dt -kFN[N*}[P]{l-e-a^ln The film is exposed to the light intensity, Jo, to excite N. Pyrene and naphthalene concentration in the film is [P] and [N] respectively. The rate equation for pyrene is ^p = fciVP[iV0*][Po] - fcFiV[iV*][Pl(l - t”*'1*) -(kFp + kIP)[P*} Under photostationary state conditions, d[N*}/dt - d[P*]/dt = 0 and using these two rate equations one can obtain the following relation I0[N}{1 - e-3»'h») = (kFN + kIN)[N*) + (kFP + kIP)[P*} If P?j{sn) probability is fixed, the naphthalene and pyrene intensities will be independent of the optical properties of the film. Normalizing the full fluorescence spectra on the right hand side of the above equation corresponds to fixing Pn($n) at the left hand side of the above equation. In order to correct the N and P emissions, the full fluorescence emission spectra areas are normalized to 1000, after the area of the naphthalene and pyrene spectra are calculated separately, and corrected emission in tensities are obtained. Using the corrected pyrene emission intensities (I'P), PMMA back bone chain diffusion coefficients found for different annealing tempera- tureof the films. The diffusion coefficients changes between 4.34 x 10~14- 8.06 x 10-12cm2/sn within 170-210 °C. Using the diffusion coefficients, backbone diffusion activation energy is calculated and found to be 27.81 xukcal/mol. A new method is developed for calculating the PMMA back bone chain diffusion activation energy, without finding the diffusion co efficients, by using the corrected pyrene emission intensities. The crossing density of polymer chains at the particle-particle interface was found to depend linearly on (time)1/2. The activation energy for back- and-forth motion of a reptating polymer chain was measured and found to be 29 kcal/mol. The corresponding frequencies of a reptating chain were between 1.5 and 42 s-1 above Tg. Various latex films with different latex contents were used to measure the percentage of the critical occupation for reliable steady-state fluo rescence measurements. The diffusion activation energies in these latex films were calculated with the new method, and were found to be 26.38 kcal/mole, which was attributed to the backbone motion of the PMMA chains. Only pyrene is excited, and its fluorescence emission spectrum is de tected to examine the healing of the polymer molecules during the an nealing of the latex film above the glass transition temperature. The healing temperature, T#, and the healing time, th, axe measured when the pyrene fluorescence emission intensity becomes maximum. Healing activation energy is calculated, and is found to be 9.84 kcal/mole. xm
Benzer Tezler
- Organik ve su bazlı latekslerden film oluşumunun foton geçirme ve yansıtma teknikleri ile incelenmesi
Investigation of film formation from organic and water based latexes using photon transmission and reflection techniques
ERTAN ARDA
Doktora
Türkçe
2001
Fizik ve Fizik MühendisliğiTrakya ÜniversitesiFizik Ana Bilim Dalı
PROF. DR. HÜSEYİN DİRİM
- Film formation, morphological, optical and electrical percolation behaviors of PS/MWCNT and PS/GO nanocomposite films
PS/MWCNT and PS/GO nanokompozit filmlerinin film oluşum, morfolojik, optiksel ve elektriksel perkolasyon davranışları
BARIŞ DEMİRBAY
Yüksek Lisans
İngilizce
2017
Fizik ve Fizik Mühendisliğiİstanbul Teknik ÜniversitesiFizik Mühendisliği Ana Bilim Dalı
DOÇ. DR. ŞAZİYE UĞUR
- Sert latekslerden film oluşumunun faton soğurma yöntemi ile çalışılması
Başlık çevirisi yok
FİGEN KENEROĞLU
- Kararlı durum floresans tekniği kullanarak TiO2-polistiren lateks kompozitlerden film oluşumunun incelenmesi
Investigation of film formation from TiO2-polystyrene latex composite by using steady state flourescence technique
SELİN SUNAY
- Environmentally friendly components for energy storage devices
Enerji depolama cihazlarında çevre dostu bileşenlerin kullanımı
ELENA STOJANOVSKA
Doktora
İngilizce
2019
Bilim ve Teknolojiİstanbul Teknik ÜniversitesiPolimer Bilim ve Teknolojisi Ana Bilim Dalı
DOÇ. DR. ALİ KILIÇ