Electromagnetic properties of DBSA-doped polyaniline

doctoral thesis

• Title: Electromagnetic properties of DBSA-doped polyaniline : from fundamentals towards application
• Title (croatian): Elektromagnetska svojstva polianilina dopiranog s DBSA : od temelja prema primjeni
• Author: Mirko Baćani
• Mentor: Dinko Babić (mentor)
• Committee member: Ivan Kokanović (predsjednik povjerenstva)
• Committee member: Dinko Babić (član povjerenstva)
• Committee member: Laszlo Forro (član povjerenstva)
• Committee member: Osor-Slaven Barišić (član povjerenstva)
• Committee member: Hrvoje Buljan (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2014-05-09, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

We have carried out a comparative experimental study of the dc electrical conductivity s and magnetic susceptibility χ of own-made polyaniline (PANI) pellets doped with dodecybenzenesulphonic acid (DBSA), a long molecule with surfactant properties. For all samples, we find that s at low temperatures (T) is governed by the variable-range hopping (VRH) in a homogeneously disordered three-dimensional (3D) system of coupled one-dimensional (1D) chains. Depending on the doping and the corresponding disorder level, the VRH exponents are either 1/2, 2/5, or 1/4. At higher T, in all samples, we find an exponent 1 that signifies nearest-neighbour hopping. All these exponents are predicted in a model by Fogler, Teber, and Shklovskii for the charge transport in quasi- 1D Anderson-Mott insulators, and conditions for their appearance depend on disorder and T. We identified the presence of a soft (Coulomb) gap in our samples, which signifies a long-range Coulomb interaction. Change from one exponent into another in σ(T) appears at a crossover temperature T* where there are also noticeable features in χ(T). This coupling of charge and spin is discussed in the spirit of kBT being the thermal energy which causes an enhancement of the density of delocalised (Pauli) spins at the expense of localised (Curie) spins as T rises above T*. Utilising the observed correlation between spin dynamics and electronic transport, we estimate the energy scales in the electronic structure of PANI–DBSA. Utilising a property that both PANI–DBSA and multiwall carbon nanotubes (MWCNT’s) are soluble in chloroform, we have produced bulk blends of these two materials, the achieved mass fraction of MWCNT’s being up to 40 %. This is as remarkable as the accompanying effective loss of the temperature dependence of s: it decreases by only 3 times from room temperature to 10 K, whereas this decrease for pure PANI–DBSA is by a factor of 10^6. Thus, our blends simultaneously offer a solution to the problem of applications of MWCNT’s in bulk form, as well as to that of poor conductivity of PANI–DBSA at low T. It is also possible to make thin films, both of PANI–DBSA and of the blends, on a commercial plastic substrate (FR4).

Abstract (croatian)

Provedeno je komparativno eksperimentalno istraživanje temperaturne (T) ovisnosti istosmjerne električne vodljivosti σ i magnetske susceptibilnosti χ na tabletama polianilina (PANI) dopiranog s dodecilbenzensulfonskom kiselinom (DBSA), koja je dugačka molekula sa surfaktantskim svojstvima. Niskotemperaturno ponašanje u svim uzorcima karakterizirano je skočnom vodljivošću promjenjivog dosega (VRH) u homogeno neuređenom trodimenzionalnom (3D) sustavu vezanih jednodimenzionalnih (1D) lanaca. Ovisno o dopiranju i pripadnom stupnju nereda u materijalu, VRH eksponenti su 1/2, 2/5 ili 1/4, dok je na višim T u svim uzorcima nađen eksponent 1, koji ukazuje na redukciju srednjeg dosega skokova na prve susjede. Svi ti eksponenti anticipirani su u teoriji Foglera, Tebera, i Shklovskiija za transport naboja u kvazi-1D Anderson-Mott izolatorima, a uvjeti za njihovo pojavljivanje ovise o neredu i T. Utvrdili smo prisustvo mekog (kulonskog) procijepa, što ukazuje na postojanje dugodosežne kulonske interakcije u našim uzorcima. Promjene s jednog eksponenta na drugi zbivaju se u σ(T) na temperaturama prijelaza T*, gdje su također zamjetne i promjene u χ(T) krivuljama, što ukazuje na vezanje naboja i spina. Diskutirano je kako kBT* ima ulogu termičke energije koja uzrokuje povećanje gustoće delokaliziranih (Paulijevih) spinova na račun lokaliziranih (Curiejevih) spinova pri porastu T iznad T*. Uočena korelacija između spinske dinamike i elektronskog transporta omogućila nam je procjenu energijskih skala u elektronskoj strukturi PANI–DBSA. Koristeći svojstvo topivosti u kloroformu, koje je zajedničko i PANI–DBSA polimeru i višezidnim ugljikovim nanocjevčicama (MWCNT), načinili smo volumne kompozite ta dva materijala. Postignut je značajan maseni udio MWCNT od do 40 %. Značajan je i prateći efektivni gubitak temperaturne ovisnosti s: smanji se svega 3 puta od sobne temperature do 10 K, dok je to smanjenje za čisti PANI–DBSA za faktor 10^6. Tako naši blendovi istovremeno nude rješenje problema primjene MWCNT u volumnom obliku, te problema loše vodljivosti PANI–DBSA na niskim T. Također je moguće raditi tanke filmove, i od PANI–DBSA i od blendova, na komercijalnom plastičnom supstratu (FR4).

• Keywords: plyaniline; electrical conductivity; HHopping transport; Coulomb gap; magnetic susceptibility; carbon nanotubes; blends
• Keywords (croatian): polianilin; električna vodljivost; skočna vodljivost; kulonski procijep; magnetska susceptibilnost; ugljikove nanocjevčice; kompoziti
• Language: english
• URN:NBN: urn:nbn:hr:217:107232
• Study programme: Title: Physics; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: 168 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-22 10:19:28