Supplementary Files
Online Resource 1
Online Resource 2
Title of the article : Selection of electroactive copolymers synthesized from 3-octylthiophene / biphenyl at low potentials as precursors for nanostructured thin film formation
Journal name : Journal of Materials Science
Author Names : Sophia Karamanou 1,** , Johannis Simitzis 1,*
Affiliations : National Technical University of Athens, School of Chemical Engineering, Department III, “Materials Science and Engineering”, Laboratory Unit “Advanced and Composite Materials", 9 Heroon Polytechniou str., Zografou Campus, 157 73 Athens, Greece
E-mail address : ,
Corresponding author : J. Simitzis
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Online Resource 1
It refers to the section 3.2 of the manuscript
AFM analysis of the polymers
From the values of the ratio R (Table 4), the shape of the particles can be estimated as follows. The image processing concerns the representation of the particles in the level (in two dimensions, 2D) and not in the space (in three dimensions, 3D). Generally, different approaches for the molecular size and shape of small molecules such as solvents have been proposed [42, 43]. A such method is based on the molecular surface area and the volume estimated from the van der Waals radii of the constituent atoms and the manner and geometry of their mutual bonding [42]. The ratio of the van der Waals surface area to the van der Waals volume, AvdW / VvdW is a measure of the shape of the molecules indicating : oblate (AvdW / VvdW ≤ 1.33), globular (1.33 ≤ AvdW / VvdW ≤ 1.40), or prolate (1.40 ≤ AvdW / VvdW). Very small molecules, such as water and chloroform have values of this ratio >1.75[42, 43]. This approach is very difficult to be applied for the macromolecules in the space and especially for the polymers of the present work.
On the other hand, based on the geometrical characteristics in the level, useful conclusions for the shape of the particles can be obtained. Thus, R=DmaxDmin = 1 refers to the circle in the level (which corresponds to sphere or globular in the space). A very great difference between Dmax and Dmin such as having the value of R = 10 presents a degenerated ellipse in the level (which corresponds to ellipsoids in the space). Consequently, the values of R could be ranged between 1 (= 1•100) and 10 (= 1•101), i.e. in one order of magnitude. By presenting the geometrical shape of different values of R in the level, it could be defined the value R = 1.50 as the limit between the circle (R = 1) and a typical ellipse (which is more pronounced for R = 1.80 or more). In a first approach for a corresponding representation in the space, the values below 1.50 resemble globular shape, the value R = 1.50 resembles oblate shape and the value R = 1.80 resembles prolate (oval) shape. The value of the particles R = 1.81 for the (P3OT)1.70/10 indicates a typical ellipse in the level or oval shape in the space. This shape is due to the long length of the macromolecules on one hand and to the spin coating process (removal of the solvent by the centrifugal force) applied to obtain the film on the other.
Furthermore, the thickness of the film was determined by AFM. The method is based on the carefully scratch a line into the film and then make AFM topographic image to measure the scratched depth by cover the unscratched areas on both sites. The thickness of the films of the homopolymer (P3OT)1.70/10 and copolymer (Copol)1.70/10 was : 150±50 nm. According to literature, there is not an “absolutely” definition for the thickness of thin films. As examples, the thickness of spin coating polymer films greater than 200 nm are characterized as thin films and lower than 200 nm thickness as ultrathin films [45]. However, other authors refer as thin film more greater thickness reaching also the micro-region as 3 μm thick [46]. Consequently, there is no doubt that the synthesized films in the present work are thin films.
The previously described characteristics of the polymers will be further compared with that of the literature, mainly for the homopolymer (P3OT) and not for the copolymer due to the lack of comparable data. Regioregular head-to-tail (RRHT) poly(3-alkylthiophene)s (PATs), especially (P3OT), commercial available, have been used as precursor in order to prepare one-dimensional aggregation (1D aggregates) by proper choice of solvent / non-solvent and suitable method obtaining rod-like structures with lengths up to 700 nm and diameters 3.5-5 nm [44]. Length of the particles varies from several nanometers to several hundred nanometers and can be adjusted by the solvent composition or concentration of PATs. Such well-defined organic semiconductor 1D particles can be used as building blocks for future nanoscale and molecular level electronic devices and optoelectronic devices such as polymer light-emitting diodes and solar cells [44].
Online Resource 2
It refers to the section 3.2 of the manuscript
Μethodology to estimate different parameters in molecular level, especially for the macromolecules in solution.
The molecular weight of the structural unit of copolymer mo is calculated from the equation : mo=(UBiph*moBiph+U3OcT*mo3OcT)2=190.67, e.g. 1 mol = 190.67 g, where: moBiph is the molecular weight of Biph structural unit, mo3OcT is the molecular weight of 3-OcT structural unit, U3Oct / UBiph = 1.18 / 1 : the ratio of the structural units of 3-octylthiophene per that derived from biphenyl into the macromolecule.
The molecular weights of the homopolymer and copolymer are referred to Fig.6 and they are expressed in various types. The viscosity average molecular weight MV, can be used instead of the weight-average molecular weight Mw, however the latter is broadly used in the literature. The density of the homopolymers and the copolymer (Table 5, Nr. 4) has been determined based on the values of the corresponding crystalline homopolymers [50]. Specifically, the value of density of the homopolymer (P3OT) is approximately 1.315 g mL-1, and it has been determined as the average of the density values for the orthorhombic and monoclinic homopolymer. The value of density of the homopolymer (PP) is 1.334 g mL-1 and corresponds to the monoclinic (PP) [35]. The value of density of the copolymer has been determined as the average of the corresponding homopolymers, taking into consideration that the ratio of the monomeric units is approx. 1/1. Concerning the results, the equivalent diameter of a viscosimetrically equivalent sphere for the homopolymer is 9.46 nm and for the copolymer is 8.48 nm (Scheme 1, b). The ratio of VcVD (Table 5, Nr 16) : volume Vc which is available in each molecule for a given concentration c, per volume VD of the hydrodynamic sphere of diameter Deff, is much greater than one, indicating that the polymers (homopolymer and copolymer) are as particles in the solution and not as a network (of secondary forces) [49]. Generally, the macromolecular solutions belong in the group of colloid solutions. Contrarily to the colloid particles of common dispersions, the polymers in solutions are as random chains containing solvent and therefore are characterized as molecular colloids [49].
Furthermore, the ratio of VeqηVchain (Table 5, Nr 19) : volume Veqη of one (ideal) random chain (equivalent sphere) per volume Vchain of one polymer chain is 21.4/1 for the homopolymer and 20.09/1 for the copolymer. This means that the volume of one random chain contains 95.32 mL of solvent in 100 mL of one polymer chain and solvent i.e. 95.32 % for the (P3OT), and 95.02 % for the (Copol). The critical concentration ccrit (Table 5, Nr 20) for the homopolymer and the copolymer is 6.09 and 6.5 [g/100 mL], respectively. The critical concentration concerns that concentration by just, the total amount of solvent is penetrated (enclosed) in the random chains, i.e. there is not free solvent [49]. Thus, the concentration of homo- and co-polymer in anisole of c = 0.1 [g L-1] or 0.01 [g/100 mL] used for the DLS and for the spin coating is much lower than the ccrit, which means that a great amount of solvent is free in the solutions used.
According to the comments previously described for Table 4, the particles of the polymers in the (solid) thin films have ellipsoid shape. These particles have been formed from the polymer solution in anisole after the spin coating. During the latter treatment, the solvent is continuously removed and the solution behaves like that of a poor solvent taking place association between the random chains and finally precipitates the solid polymer. The ellipsoid shape in the solid state indicates a similar shape (ellipsoid) as the random chains in the solution whereas the shape of the latter is equivalently represented by the hydrodynamic sphere according to the DLS. According to Table 5, Nr 12, the equivalent radius of a viscosimetrically equivalent sphere are 4.73 nm for the homopolymer and 4.24 nm for the copolymer. The ellipsoid shape of the random chains in the solution indicates that the long axis of the ellipsoid is much higher than the equivalent diameter of a viscosimetrically equivalent sphere (Scheme.1, b). It is noticed that these values are determined based on the (ideal) random chain, however by the real random chains the linear dimensions are increased taking into consideration intramolecular interactions, bond angles between atoms, conformation angles etc [47, 48]. Anyway, the radius of real random chains is generally in the order of 10 nm for most polymers (not biopolymers). Consequently, in Table 3, the radius of the random chains (i.e. separate random chains containing also solvent in the corresponding separate spheres) should be accepted between the range of 10 – 100 nm and especially at the low limit. The greater radius could be considered as aggregates between the random chains (i.e. random chains containing also solvent in the aggregated spheres), and the solution remains as particles solution. The homopolymer and copolymer contain high percentage of individual random chains.
By comparing the nanostructured shapes of the present polymers with that from literature [12, 51], they are ascertained some similarities with the nanorod shape of some other polymers. From an interfacial polymerization of 3,4-ethylenedioxythiophene (EDOT), the produced PEDOT contained nanocrystals in the shape of nanoneedles having approximately 15 nm wide and 50 nm long with pointed tips and consisted of multiple chains. PEDOT produced by interfacial polymerization technique consisted of short nanorod like structures with an average diameter of 30 nm [51]. Generally, each of the dimensions of nanorods ranges from 1–100 nm and the aspect ratios (length divided by width) are 3-5. Both solution of homopolymer (P3OT)1.70/10 and copolymer (Copol)1.70/10 in anisole, studied by DLS, exhibit high percentages by weight of particles in the nanometer region (below 100 nm), i.e. almost 100 % nanostructures for the homopolymer and 79.1 % (~4/5) nanostructures for the copolymer.
The thin films (solids) of all polymers formed by spin coating of the previous solution, generally exhibit nanostructures, having ellipsoid shapes (see above for AFM). Let as take as an example the homopolymer (P3OT)1.70/10, which is previously described as a typical ellipse in the level or having oval shape in the space based on the mean value (Dmax and Dmin) of the (solid) particles and their ratio R=DmaxDmin = 1.81. By selecting separate particles which contribute to this value of R, there are some of them having Dmin ≈ 100 nm and Dmax ≈ 350 nm and corresponding value of R = 3.5. Consequently, the aspect ratios (length divided by width) of these particles are between 3 and 5 and they can be characterized as rods, which approaches the nanorods (for typical nanorods each of the dimensions should be ranged from 1–100 nm). On the other hand, from Table 5, the equivalent diameter of a viscosimetrically equivalent sphere of the homopolymer (P3OT)1.70/10 is deq[η] = 9.46 nm. By calculating the volume of a such ellipsoid (one solid particle as an ellipsoid) and the volume of a typical nanorod (e.g. length Lnr = 100 nm and width Wnr = 30 nm having aspect ratio R = 3.33) and taking the volume of one (ideal) random chain (equivalent sphere) (see Table 5, Nr 13), then the ellipsoid contains approx. 10 times (11.66) more random chains than the typical nanorod. Furthermore, the additional aggregates of macromolecules from the polymer in solution to the solid polymer formed (after solvent removal) for the (P3OT)1.70/10 were calculated to be ~1.8 times more than those of (Copol)1.70/10. The calculation for each polymer is based on the volume of the (solid) ellipsoid (Table 4, dimensions : Dmin, Dmax, H), Vellipsoid, the volume of hydrodynamic sphere (Figure 8a and 8b, for Rh = 10 nm and Rh = 100 nm), Vsphere, and the ratio of Vellipsoid / Vsphere. The additional aggregates for (P3OT)1.70/10, solid, compared to those of (Copol)1.70/10 solid, are due to the correspondingly greater ellipsoid volume of the former (~1.8 times more than those of the copolymer).
Generally, for the production of nanofibers, nanorods etc. from the solution of the homopolymer (P3OT)1.70/10 (or from the corresponding copolymer), all parameters and conditions of the processes (kind of solvent, concentration, temperature, rate of solvent removal etc.) should be optimized in order to eliminate the aggregation between the random chains (macromolecules). Furthermore, small devices e.g. porous membrane (successfully applied for nanofibers formation [25]), resembling the spinneret for the formation of monofilaments from the solution of a proper polymer could be developed. All these aspects go beyond the scope of the present work.
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